Bio


Dr. Mercola is Professor of Medicine and Professor in the Stanford Cardiovascular Institute. He completed postdoctoral training at the Dana-Farber Cancer Institute and Harvard Medical School, was on the faculty in the Department of Cell Biology at Harvard Medical School for 12 years, and later at the Sanford-Burnham-Prebys Institute and Department of Bioengineering at the University of California, San Diego before relocating to Stanford in 2015.

Prof. Mercola is known for identifying many of the factors that are responsible for inducing and forming the heart, including the discovery that Wnt inhibition is a critical step in cardiogenesis that provided the conceptual basis and reagents for the large-scale production of cardiovascular tissues from pluripotent stem cells. He has collaborated with medicinal chemists, optical engineers and software developers to pioneer the use of patient iPSC-cardiomyocytes for disease modeling, safety pharmacology and drug development. His academic research is focused on developing and using quantitative high throughput assays of patient-specific cardiomyocyte function to discover druggable targets for preserving contractile function in heart failure and promoting regeneration following ischemic injury. He co-established drug screening and assay development at the Conrad Prebys Drug Discovery Center (San Diego), which operated as one of 4 large screening centers of the US National Institutes of Health (NIH) Molecular Libraries screening initiative and continues as one of the largest academic drug screening centers.

Prof. Mercola received an NIH MERIT award for his work on heart formation, and authored over 130 papers. He holds numerous patents, including describing the invention of the first engineered dominant negative protein and small molecules for stem cell and cancer applications. He serves on multiple editorial and advisory boards, including Vala Sciences,, Regencor, The Ted Rogers Centre for Heart Research and the Human Biomolecular Research Institute. His laboratory is funded by the National Institutes of Health (NIH), California Institute for Regenerative Medicine, the PLN Foundation and the Fondation Leducq.

Academic Appointments


2020-21 Courses


Stanford Advisees


All Publications


  • CRISPR/Cas9-based targeting of fluorescent reporters to human iPSCs to isolate atrial and ventricular-specific cardiomyocytes. Scientific reports Chirikian, O., Goodyer, W. R., Dzilic, E., Serpooshan, V., Buikema, J. W., McKeithan, W., Wu, H., Li, G., Lee, S., Merk, M., Galdos, F., Beck, A., Ribeiro, A. J., Paige, S., Mercola, M., Wu, J. C., Pruitt, B. L., Wu, S. M. 2021; 11 (1): 3026

    Abstract

    Generating cardiomyocytes (CMs) from human induced pluripotent stem cells (hiPSCs) has represented a significant advance in our ability to model cardiac disease. Current differentiation protocols, however, have limited use due to their production of heterogenous cell populations, primarily consisting of ventricular-like CMs. Here we describe the creation of two chamber-specific reporter hiPSC lines by site-directed genomic integration using CRISPR-Cas9 technology. In the MYL2-tdTomato reporter, the red fluorescent tdTomato was inserted upstream of the 3' untranslated region of the Myosin Light Chain 2 (MYL2) gene in order faithfully label hiPSC-derived ventricular-like CMs while avoiding disruption of endogenous gene expression. Similarly, in the SLN-CFP reporter, Cyan Fluorescent Protein (CFP) was integrated downstream of the coding region of the atrial-specific gene, Sarcolipin (SLN). Purification of tdTomato+ and CFP+ CMs using flow cytometry coupled with transcriptional and functional characterization validated these genetic tools for their use in the isolation of bona fide ventricular-like and atrial-like CMs, respectively. Finally, we successfully generated a double reporter system allowing for the isolation of both ventricular and atrial CM subtypes within a single hiPSC line. These tools provide a platform for chamber-specific hiPSC-derived CM purification and analysis in the context of atrial- or ventricular-specific disease and therapeutic opportunities.

    View details for DOI 10.1038/s41598-021-81860-x

    View details for PubMedID 33542270

  • Small-molecule probe reveals a kinase cascade that links stress signaling to TCF/LEF and Wnt responsiveness. Cell chemical biology Cheng, J., Tsuda, M., Okolotowicz, K., Dwyer, M., Bushway, P. J., Colas, A. R., Lancman, J. J., Schade, D., Perea-Gil, I., Bruyneel, A. A., Lee, J., Vadgama, N., Quach, J., McKeithan, W. L., Biechele, T. L., Wu, J. C., Moon, R. T., Si Dong, P. D., Karakikes, I., Cashman, J. R., Mercola, M. 2021

    Abstract

    Wnt signaling plays a central role in tissue maintenance and cancer. Wnt activates downstream genes through β-catenin, which interacts with TCF/LEF transcription factors. A major question is how this signaling is coordinated relative to tissue organization and renewal. We used a recently described class of small molecules that binds tubulin to reveal a molecular cascade linking stress signaling through ATM, HIPK2, and p53 to the regulation of TCF/LEF transcriptional activity. These data suggest a mechanism by which mitotic and genotoxic stress can indirectly modulate Wnt responsiveness to exert coherent control over cell shape and renewal. These findings have implications for understanding tissue morphogenesis and small-molecule anticancer therapeutics.

    View details for DOI 10.1016/j.chembiol.2021.01.001

    View details for PubMedID 33503403

  • Patient-Specific Induced Pluripotent Stem Cells Implicate Intrinsic Impaired Contractility in Hypoplastic Left Heart Syndrome. Circulation Paige, S. L., Galdos, F. X., Lee, S., Chin, E. T., Ranjbarvaziri, S., Feyen, D. A., Darsha, A. K., Xu, S., Ryan, J. A., Beck, A. L., Qureshi, M. Y., Miao, Y., Gu, M., Bernstein, D., Nelson, T. J., Mercola, M., Rabinovitch, M., Ashley, E. A., Parikh, V. N., Wu, S. M. 2020; 142 (16): 1605–8

    View details for DOI 10.1161/CIRCULATIONAHA.119.045317

    View details for PubMedID 33074758

  • Hyperglycemia Acutely Increases Cytosolic Reactive Oxygen Species via O-linked GlcNAcylation and CaMKII Activation in Mouse Ventricular Myocytes. Circulation research Lu, S., Liao, Z., Lu, X., Katschinski, D. M., Mercola, M., Chen, J., Heller Brown, J., Molkentin, J. D., Bossuyt, J., Bers, D. M. 2020

    Abstract

    Rationale: Diabetes mellitus (DM) is a complex, multisystem disease, affecting large populations worldwide. Chronic CaMKII activation may occur in DM and be arrhythmogenic. Diabetic hyperglycemia was shown to activate CaMKII by (1) O-linked attachment of N-acetylglucosamine (O-GlcNAc) at S280 leading to arrhythmia and (2) a reactive-oxygen species (ROS) mediated oxidation of CaMKII, that can increase post-infarction mortality. Objective: To test whether high extracellular [glucose] (Hi-Glu) promotes ventricular myocyte ROS generation and the role played by CaMKII. Methods and Results: We tested how extracellular Hi-Glu influences ROS production in adult ventricular myocytes, using H2DCFDA and genetically targeted Grx-roGFP2 redox sensors. Hi-Glu (30 mmol/L) significantly increased the rate of ROS generation, an effect prevented in myocytes pretreated with CaMKII inhibitor KN-93 or from either global or cardiac specific CaMKIIdelta knockout mice. CaMKII knockout or inhibition also prevented Hi-Glu induced sarcoplasmic reticulum (SR) Ca2+ release events (Ca2+ sparks). Thus, CaMKII activation is required for Hi-Glu induced ROS generation and SR Ca leak in cardiomyocytes. To test the involvement of O-GlcNAc-CaMKII pathway, we inhibited GlcNAcylation removal by Thiamet G (Thm-G), which mimicked the Hi-Glu-induced ROS production. Conversely, inhibition of GlcNAcylation (OSMI-1) prevented ROS induction in response to either Hi-Glu or Thm-G. Moreover, in a CRSPR-based knock-in mouse in which the functional GlcNAcylation site on CaMKIIdelta was ablated (S280A) neither Hi-Glu nor Thm-G induced myocyte ROS generation. So CaMKIIdelta-S280 is required for the Hi-Glu-induced (and GlcNAc-dependent) ROS production. To identify the ROS source(s), we used different inhibitors of NOX2 (Gp91ds-tat peptide), NOX4 (GKT137831), mitochondrial ROS (Mito-Tempo) and NOS pathway inhibitors (L-NAME, L-NIO and L-NPA). Only NOX2 inhibition or KO prevented Hi-Glu/Thm-G induced ROS generation. Conclusions: Diabetic hyperglycemia induces acute cardiac myocyte ROS production by NOX2 that requires O-GlcNAcylation of CaMKIIdelta at S280. This novel ROS induction may exacerbate pathological consequences of diabetic hyperglycemia.

    View details for DOI 10.1161/CIRCRESAHA.119.316288

    View details for PubMedID 32134364

  • iPSC Modeling of RBM20-Deficient DCM Identifies Upregulation of RBM20 as a Therapeutic Strategy. Cell reports Briganti, F., Sun, H., Wei, W., Wu, J., Zhu, C., Liss, M., Karakikes, I., Rego, S., Cipriano, A., Snyder, M., Meder, B., Xu, Z., Millat, G., Gotthardt, M., Mercola, M., Steinmetz, L. M. 2020; 32 (10): 108117

    Abstract

    Recent advances in induced pluripotent stem cell (iPSC) technology and directed differentiation of iPSCs into cardiomyocytes (iPSC-CMs) make it possible to model genetic heart disease in vitro. We apply CRISPR/Cas9 genome editing technology to introduce three RBM20 mutations in iPSCs and differentiate them into iPSC-CMs to establish an in vitro model of RBM20 mutant dilated cardiomyopathy (DCM). In iPSC-CMs harboring a known causal RBM20 variant, the splicing of RBM20 target genes, calcium handling, and contractility are impaired consistent with the disease manifestation in patients. A variant (Pro633Leu) identified by exome sequencing of patient genomes displays the same disease phenotypes, thus establishing this variant as disease causing. We find that all-trans retinoic acid upregulates RBM20 expression and reverts the splicing, calcium handling, and contractility defects in iPSC-CMs with different causal RBM20 mutations. These results suggest that pharmacological upregulation of RBM20 expression is a promising therapeutic strategy for DCM patients with a heterozygous mutation in RBM20.

    View details for DOI 10.1016/j.celrep.2020.108117

    View details for PubMedID 32905764

  • Metabolic Maturation Media Improve Physiological Function of Human iPSC-Derived Cardiomyocytes. Cell reports Feyen, D. A., McKeithan, W. L., Bruyneel, A. A., Spiering, S., Hörmann, L., Ulmer, B., Zhang, H., Briganti, F., Schweizer, M., Hegyi, B., Liao, Z., Pölönen, R. P., Ginsburg, K. S., Lam, C. K., Serrano, R., Wahlquist, C., Kreymerman, A., Vu, M., Amatya, P. L., Behrens, C. S., Ranjbarvaziri, S., Maas, R. G., Greenhaw, M., Bernstein, D., Wu, J. C., Bers, D. M., Eschenhagen, T., Metallo, C. M., Mercola, M. 2020; 32 (3): 107925

    Abstract

    Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) have enormous potential for the study of human cardiac disorders. However, their physiological immaturity severely limits their utility as a model system and their adoption for drug discovery. Here, we describe maturation media designed to provide oxidative substrates adapted to the metabolic needs of human iPSC (hiPSC)-CMs. Compared with conventionally cultured hiPSC-CMs, metabolically matured hiPSC-CMs contract with greater force and show an increased reliance on cardiac sodium (Na+) channels and sarcoplasmic reticulum calcium (Ca2+) cycling. The media enhance the function, long-term survival, and sarcomere structures in engineered heart tissues. Use of the maturation media made it possible to reliably model two genetic cardiac diseases: long QT syndrome type 3 due to a mutation in the cardiac Na+ channel SCN5A and dilated cardiomyopathy due to a mutation in the RNA splicing factor RBM20. The maturation media should increase the fidelity of hiPSC-CMs as disease models.

    View details for DOI 10.1016/j.celrep.2020.107925

    View details for PubMedID 32697997

  • Reengineering an Antiarrhythmic Drug Using Patient hiPSC Cardiomyocytes to Improve Therapeutic Potential and Reduce Toxicity. Cell stem cell McKeithan, W. L., Feyen, D. A., Bruyneel, A. A., Okolotowicz, K. J., Ryan, D. A., Sampson, K. J., Potet, F., Savchenko, A., Gómez-Galeno, J., Vu, M., Serrano, R., George, A. L., Kass, R. S., Cashman, J. R., Mercola, M. 2020

    Abstract

    Modeling cardiac disorders with human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes is a new paradigm for preclinical testing of candidate therapeutics. However, disease-relevant physiological assays can be complex, and the use of hiPSC-cardiomyocyte models of congenital disease phenotypes for guiding large-scale screening and medicinal chemistry have not been shown. We report chemical refinement of the antiarrhythmic drug mexiletine via high-throughput screening of hiPSC-CMs derived from patients with the cardiac rhythm disorder long QT syndrome 3 (LQT3) carrying SCN5A sodium channel variants. Using iterative cycles of medicinal chemistry synthesis and testing, we identified drug analogs with increased potency and selectivity for inhibiting late sodium current across a panel of 7 LQT3 sodium channel variants and suppressing arrhythmic activity across multiple genetic and pharmacological hiPSC-CM models of LQT3 with diverse backgrounds. These mexiletine analogs can be exploited as mechanistic probes and for clinical development.

    View details for DOI 10.1016/j.stem.2020.08.003

    View details for PubMedID 32931730

  • A Novel Recessive Mutation in SPEG Causes Early Onset Dilated Cardiomyopathy. PLoS genetics Levitas, A., Muhammad, E., Zhang, Y., Perea Gil, I., Serrano, R., Diaz, N., Arafat, M., Gavidia, A. A., Kapiloff, M. S., Mercola, M., Etzion, Y., Parvari, R., Karakikes, I. 2020; 16 (9): e1009000

    Abstract

    Dilated cardiomyopathy (DCM) is a common cause of heart failure and sudden cardiac death. It has been estimated that up to half of DCM cases are hereditary. Mutations in more than 50 genes, primarily autosomal dominant, have been reported. Although rare, recessive mutations are thought to contribute considerably to DCM, especially in young children. Here we identified a novel recessive mutation in the striated muscle enriched protein kinase (SPEG, p. E1680K) gene in a family with nonsyndromic, early onset DCM. To ascertain the pathogenicity of this mutation, we generated SPEG E1680K homozygous mutant human induced pluripotent stem cell derived cardiomyocytes (iPSC-CMs) using CRISPR/Cas9-mediated genome editing. Functional studies in mutant iPSC-CMs showed aberrant calcium homeostasis, impaired contractility, and sarcomeric disorganization, recapitulating the hallmarks of DCM. By combining genetic analysis with human iPSCs, genome editing, and functional assays, we identified SPEG E1680K as a novel mutation associated with early onset DCM and provide evidence for its pathogenicity in vitro. Our study provides a conceptual paradigm for establishing genotype-phenotype associations in DCM with autosomal recessive inheritance.

    View details for DOI 10.1371/journal.pgen.1009000

    View details for PubMedID 32925938

  • Sacubitril/Valsartan Improves Cardiac Function and Decreases Myocardial Fibrosis Via Downregulation of Exosomal miR-181a in a Rodent Chronic Myocardial Infarction Model. Journal of the American Heart Association Vaskova, E., Ikeda, G., Tada, Y., Wahlquist, C., Mercola, M., Yang, P. C. 2020: e015640

    Abstract

    Background Exosomes are small extracellular vesicles that function as intercellular messengers and effectors. Exosomal cargo contains regulatory small molecules, including miRNAs, mRNAs, lncRNAs, and small peptides that can be modulated by different pathological stimuli to the cells. One of the main mechanisms of action of drug therapy may be the altered production and/or content of the exosomes. Methods and Results We studied the effects on exosome production and content by neprilysin inhibitor/angiotensin receptor blockers, sacubitril/valsartan and valsartan alone, using human-induced pluripotent stem cell-derived cardiomyocytes under normoxic and hypoxic injury model in vitro, and assessed for physiologic correlation using an ischemic myocardial injury rodent model in vivo. We demonstrated that the treatment with sacubitril/valsartan and valsartan alone resulted in the increased production of exosomes by induced pluripotent stem cell-derived cardiomyocytes in vitro in both conditions as well as in the rat plasma in vivo. Next-generation sequencing of these exosomes exhibited downregulation of the expression of rno-miR-181a in the sacubitril/valsartan treatment group. In vivo studies employing chronic rodent myocardial injury model demonstrated that miR-181a antagomir has a beneficial effect on cardiac function. Subsequently, immunohistochemical and molecular studies suggested that the downregulation of miR-181a resulted in the attenuation of myocardial fibrosis and hypertrophy, restoring the injured rodent heart after myocardial infarction. Conclusions We demonstrate that an additional mechanism of action of the pleiotropic effects of sacubitril/valsartan may be mediated by the modulation of the miRNA expression level in the exosome payload.

    View details for DOI 10.1161/JAHA.119.015640

    View details for PubMedID 32538237

  • Small-Molecule Modulation of TDP-43 Recruitment to Stress Granules Prevents Persistent TDP-43 Accumulation in ALS/FTD NEURON Fang, M. Y., Markmiller, S., Vu, A. Q., Javaherian, A., Dowdle, W. E., Jolivet, P., Bushway, P. J., Castello, N. A., Baral, A., Chan, M. Y., Linsley, J. W., Linsley, D., Mercola, M., Finkbeiner, S., Lecuyer, E., Lewcock, J. W., Yeo, G. W. 2019; 103 (5): 802-+

    Abstract

    Stress granules (SGs) form during cellular stress and are implicated in neurodegenerative diseases such as amyotrophic lateral sclerosis and frontotemporal dementia (ALS/FTD). To yield insights into the role of SGs in pathophysiology, we performed a high-content screen to identify small molecules that alter SG properties in proliferative cells and human iPSC-derived motor neurons (iPS-MNs). One major class of active molecules contained extended planar aromatic moieties, suggesting a potential to intercalate in nucleic acids. Accordingly, we show that several hit compounds can prevent the RNA-dependent recruitment of the ALS-associated RNA-binding proteins (RBPs) TDP-43, FUS, and HNRNPA2B1 into SGs. We further demonstrate that transient SG formation contributes to persistent accumulation of TDP-43 into cytoplasmic puncta and that our hit compounds can reduce this accumulation in iPS-MNs from ALS patients. We propose that compounds with planar moieties represent a promising starting point to develop small-molecule therapeutics for treating ALS/FTD.

    View details for DOI 10.1016/j.neuron.2019.05.048

    View details for Web of Science ID 000484400200009

    View details for PubMedID 31272829

    View details for PubMedCentralID PMC6728177

  • Identification of a potent inhibitor of notch signaling Galeno, J., Hurtado, C., Cashman, J., Mercola, M., Cheng, J., Yardimci, C. AMER CHEMICAL SOC. 2019
  • Integrated analysis of transcriptional regulation in PLN R14del cardiomyopathy Pei, J., Harakalova, M., Nagyova, E., Gho, J. H., Sepehrkhouy, S., van Dinter, J., van Mil, A., Buijsrogge, M. P., de Jonge, N., Huibers, M. M., Nieuwenhuis, E. S., den Ruijter, H. M., Pasterkamp, G., Doevendans, P. A., Hajjar, R., Mercola, M., Sluijter, J. G., de Weger, R. A., Cheng, C., Vink, A., Mokry, M., Asselbergs, F. W. NATURE PUBLISHING GROUP. 2019: 790–91
  • Stars in the Night Sky: iPSC-Cardiomyocytes Return the Patient Context to Drug Screening CELL STEM CELL Hnatiuk, A., Mercola, M. 2019; 24 (4): 506–7
  • A Premature Termination Codon Mutation in MYBPC3 Causes Hypertrophic Cardiomyopathy via Chronic Activation of Nonsense-Mediated Decay CIRCULATION Seeger, T., Shrestha, R., Lam, C., Chen, C., McKeithan, W. L., Lau, E., Wnorowski, A., McMullen, G., Greenhaw, M., Lee, J., Oikonomopoulos, A., Lee, S., Yang, H., Mercola, M., Wheeler, M., Ashley, E. A., Yang, F., Karakikes, I., Wu, J. C. 2019; 139 (6): 799–811
  • AlleleProfileR: A versatile tool to identify and profile sequence variants in edited genomes. PloS one Bruyneel, A. A., Colas, A. R., Karakikes, I., Mercola, M. 2019; 14 (12): e0226694

    Abstract

    Gene editing strategies, such as zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and clustered regularly interspaced short palindromic repeat/Cas9 (CRISPR/Cas9), are revolutionizing biology. However, quantitative and sensitive detection of targeted mutations are required to evaluate and quantify the genome editing outcomes. Here we present AlleleProfileR, a new analysis tool, written in a combination of R and C++, with the ability to batch process the sequence analysis of large and complex genome editing experiments, including the recently developed base editing technologies.

    View details for DOI 10.1371/journal.pone.0226694

    View details for PubMedID 31877162

  • Disruption of NOTCH signaling by a small molecule inhibitor of the transcription factor RBPJ. Scientific reports Hurtado, C., Safarova, A., Smith, M., Chung, R., Bruyneel, A. A., Gomez-Galeno, J., Oswald, F., Larson, C. J., Cashman, J. R., Ruiz-Lozano, P., Janiak, P., Suzuki, T., Mercola, M. 2019; 9 (1): 10811

    Abstract

    NOTCH plays a pivotal role during normal development and in congenital disorders and cancer. γ-secretase inhibitors are commonly used to probe NOTCH function, but also block processing of numerous other proteins. We discovered a new class of small molecule inhibitor that disrupts the interaction between NOTCH and RBPJ, which is the main transcriptional effector of NOTCH signaling. RBPJ Inhibitor-1 (RIN1) also blocked the functional interaction of RBPJ with SHARP, a scaffold protein that forms a transcriptional repressor complex with RBPJ in the absence of NOTCH signaling. RIN1 induced changes in gene expression that resembled siRNA silencing of RBPJ rather than inhibition at the level of NOTCH itself. Consistent with disruption of NOTCH signaling, RIN1 inhibited the proliferation of hematologic cancer cell lines and promoted skeletal muscle differentiation from C2C12 myoblasts. Thus, RIN1 inhibits RBPJ in its repressing and activating contexts, and can be exploited for chemical biology and therapeutic applications.

    View details for DOI 10.1038/s41598-019-46948-5

    View details for PubMedID 31346210

  • Crataegus Extract WS1442 Stimulates Cardiomyogenesis and Angiogenesis From Stem Cells: A Possible New Pharmacology for Hawthorn? Frontiers in pharmacology Halver, J., Wenzel, K., Sendker, J., Carrillo Garcia, C., Erdelmeier, C. A., Willems, E., Mercola, M., Symma, N., Konemann, S., Koch, E., Hensel, A., Schade, D. 2019; 10: 1357

    Abstract

    Extracts from the leaves and flowers of Crataegus spp. (i.e., hawthorn species) have been traditionally used with documented preclinical and clinical activities in cardiovascular medicine. Based on reported positive effects on heart muscle after ischemic injury and the overall cardioprotective profile, the present study addressed potential contributions of Crataegus extracts to cardiopoietic differentiation from stem cells. The quantified Crataegus extract WS1442 stimulated cardiomyogenesis from murine and human embryonic stem cells (ESCs). Mechanistically, this effect was found to be induced by promoting differentiation of cardiovascular progenitor cell populations but not by proliferation. Bioassay-guided fractionation, phytochemical and analytical profiling suggested high-molecular weight ingredients as the active principle with at least part of the activity due to oligomeric procyanidines (OPCs) with a degree of polymerization between 3 and 6 (DP3-6). Transcriptome profiling in mESCs suggested two main, plausible mechanisms: These were early, stress-associated cellular events along with the modulation of distinct developmental pathways, including the upregulation of brain-derived neurotrophic factor (BDNF) and retinoic acid as well as the inhibition of transforming growth factor beta/bone morphogenetic protein (TGFbeta/BMP) and fibroblast growth factor (FGF) signaling. In addition, WS1442 stimulated angiogenesis ex vivo in Sca-1+ progenitor cells from adult mice hearts. These in vitro data provide evidence for a differentiation promoting activity of WS1442 on distinct cardiovascular stem/progenitor cells that could be valuable for therapeutic heart regeneration after myocardial infarction. However, the in vivo relevance of this new pharmacological activity of Crataegus spp. remains to be investigated and active ingredients from bioactive fractions will have to be further characterized.

    View details for DOI 10.3389/fphar.2019.01357

    View details for PubMedID 31849643

  • High-Throughput Phenotypic Screening Using Induced Pluripotent Stem Cell Derived Cardiomyocytes Identifies Compounds That Rescue Genetic Dilated Cardiomyopathy Perea-Gil, I., Prado, M., Bruyneel, A. A., McKeithan, W. L., Feyen, D. A., Nair, P., Mercola, M., Karakikes, I. LIPPINCOTT WILLIAMS & WILKINS. 2018: E72
  • Mechanosensitive miR-376c Modulates Arrhythmia Susceptibility Via Regulation Of KCNJ2 In hiPSC-derived Cardiomyocytes Wahlquist, C. A., Rojas-Munoz, A., Brunyeel, A. A., Greenhaw, M., Chung, R., Vu, M., Karakikes, I., Mercola, M. LIPPINCOTT WILLIAMS & WILKINS. 2018: E79
  • Use of human induced pluripotent stem cell-derived cardiomyocytes to assess drug cardiotoxicity NATURE PROTOCOLS Sharma, A., McKeithan, W. L., Serrano, R., Kitani, T., Burridge, P. W., del Alamo, J. C., Mercola, M., Wu, J. C. 2018; 13 (12): 3018–41
  • Use of human induced pluripotent stem cell-derived cardiomyocytes to assess drug cardiotoxicity. Nature protocols Sharma, A., McKeithan, W. L., Serrano, R., Kitani, T., Burridge, P. W., Del Alamo, J. C., Mercola, M., Wu, J. C. 2018

    Abstract

    Cardiotoxicity has historically been a major cause of drug removal from the pharmaceutical market. Several chemotherapeutic compounds have been noted for their propensities to induce dangerous cardiac-specific side effects such as arrhythmias or cardiomyocyte apoptosis. However, improved preclinical screening methodologies have enabled cardiotoxic compounds to be identified earlier in the drug development pipeline. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) can be used to screen for drug-induced alterations in cardiac cellular contractility, electrophysiology, and viability. We previously established a novel 'cardiac safety index' (CSI) as a metric that can evaluate potential cardiotoxic drugs via high-throughput screening of hiPSC-CMs. This metric quantitatively examines drug-induced alterations in CM function, using several in vitro readouts, and normalizes the resulting toxicity values to the in vivo maximum drug blood plasma concentration seen in preclinical or clinical pharmacokinetic models. In this ~1-month-long protocol, we describe how to differentiate hiPSCs into hiPSC-CMs and subsequently implement contractility and cytotoxicity assays that can evaluate drug-induced cardiotoxicity in hiPSC-CMs. We also describe how to carry out the calculations needed to generate the CSI metric from these quantitative toxicity measurements.

    View details for PubMedID 30413796

  • High-Throughput Physiological Assay for Force and Stiffness Quantification in IPS Derived Cardiomyocytes Serrano, R., McKeithan, W. L., Mercola, M., del Alamo, J. C. LIPPINCOTT WILLIAMS & WILKINS. 2018
  • Exosomal miR-106a-363 Cluster Repairs the Injured Myocardium Jung, J., Tada, Y., Wahlquist, C., Bornstadt, D., Santoso, M., Woo, J., Mercola, M., Yang, P. LIPPINCOTT WILLIAMS & WILKINS. 2018
  • b-Annulated 1,4-dihydropyridines as Notch inhibitors BIOORGANIC & MEDICINAL CHEMISTRY LETTERS Gomez-Galeno, J. E., Hurtado, C., Cheng, J., Yardimci, C., Mercola, M., Cashman, J. R. 2018; 28 (20): 3363–67

    Abstract

    The Notch signaling pathway is involved in cell proliferation and differentiation, and has been recognized as an active pathway in regenerating tissue and cancerous cells. Notch signaling inhibition is considered a viable approach to the treatment of a variety of conditions including colorectal cancer, pancreatic cancer, breast cancer and metastatic melanoma. The discovery that the b-annulated dihydropyridine FLI-06 (1) is an inhibitor of the Notch pathway with an EC50 ≈ 2.5 μM prompted us to screen a library of related analogs. After structure activity studies were conducted, racemic compound 7 was identified with an EC50 = 0.36 μM. Synthesis of individual enantiomers provided (+)-7 enantiomer with an EC50 = 0.13 μM, or about 20-fold the potency of 1.

    View details for PubMedID 30201292

  • A Premature Termination Codon Mutation in MYBPC3 Causes Hypertrophic Cardiomyopathy via Chronic Activation of Nonsense-Mediated Decay. Circulation Seeger, T., Shrestha, R., Lam, C. K., Chen, C., McKeithan, W. L., Lau, E., Wnorowski, A., McMullen, G., Greenhaw, M., Lee, J., Oikonomopoulos, A., Lee, S., Yang, H., Mercola, M., Wheeler, M., Ashley, E. A., Yang, F., Karakikes, I., Wu, J. C. 2018

    Abstract

    BACKGROUND: Hypertrophic cardiomyopathy (HCM) is frequently caused by mutations in myosin binding protein C3 ( MYBPC3) resulting in a premature termination codon (PTC). The underlying mechanisms of how PTC mutations in MYBPC3 lead to the onset and progression of HCM are poorly understood. This study's aim was to investigate the molecular mechanisms underlying the pathogenesis of HCM associated with MYBPC3 PTC mutations by utilizing human isogenic induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs).METHODS: Isogenic iPSC lines were generated from patients harboring MYBPC3 PTC mutations (p.R943x; p.R1073P_Fsx4) using genome editing and then differentiated into cardiomyocytes. Comprehensive phenotypical and transcriptome analyses were performed.RESULTS: We observed aberrant calcium handling properties with prolonged decay kinetics and elevated diastolic calcium levels in HCM iPSC-CMs compared to isogenic controls without structural abnormalities or contractile dysfunction. The mRNA expression levels of MYBPC3 were significantly reduced in mutant iPSC-CMs, but the protein levels were comparable among isogenic iPSC-CMs, suggesting that haploinsufficiency of MYBPC3 does not contribute to the pathogenesis of HCM in vitro. Furthermore, truncated MYBPC3 peptides were not detected. At the molecular level, the nonsense-mediated decay (NMD) pathway was activated, and a set of genes involved in major cardiac signaling pathways was dysregulated in HCM iPSC-CMs, indicating an HCM gene signature in vitro. Specific inhibition of the NMD pathway in mutant iPSC-CMs resulted in reversal of the molecular phenotype and normalization of calcium handling abnormalities.CONCLUSIONS: iPSC-CMs carrying MYBPC3 PTC mutations displayed aberrant calcium signaling and molecular dysregulations in the absence of significant haploinsufficiency of MYBPC3 protein. Here we provided the first evidence of the direct connection between the chronically activated NMD pathway and HCM disease development.

    View details for PubMedID 30586709

  • Will iPSC-cardiomyocytes revolutionize the discovery of drugs for heart disease? CURRENT OPINION IN PHARMACOLOGY Bruyneel, A. N., McKeithan, W. L., Feyen, D. M., Mercola, M. 2018; 42: 55–61
  • A Novel Inhibitor Targets Both Wnt Signaling and ATM/p53 in Colorectal Cancer CANCER RESEARCH Cheng, J., Dwyer, M., Okolotowicz, K. J., Mercola, M., Cashman, J. R. 2018; 78 (17): 5072–83

    Abstract

    For 2017, the estimated lifetime risk of developing colorectal cancer was 1 in 22. Even though preventative colonoscopy screening and standard-of-care surgery, radiation, and chemotherapy have decreased the death rate from colorectal cancer, new therapies are needed for metastatic colorectal cancer. Here, we developed a novel small molecule, compound 2, that inhibited proliferation and viability of human colorectal cancer cells (HCT-116, DLD-1, SW480, and 10.1). Compound 2 inhibited cell migration, invasion, and epithelial-mesenchymal transition processes and potently increased cell apoptosis in human colorectal cancer cells. Compound 2 also modulated mitotic stress signaling, leading to both inhibition of Wnt responsiveness and stabilization and activation of p53 to cause cell-cycle arrest. In mouse xenografts, treatment with compound 2 (20 mg/kg/day, i.p.) induced cell death and inhibited tumor growth more than four-fold compared with vehicle at day 34. Neither acute cytotoxicity nor toxicity in animals (up to 1,000 mg/kg, i.p.) were observed for compound 2 To our knowledge, compound 2 is the first reported potent small molecule that inhibits Wnt/β-catenin signaling, activates p53 signaling regardless of p53 mutation status, and binds microtubules without detectable toxicity. Thus, compound 2 offers a novel mechanism of action and a new strategy to treat colorectal cancer.Significance: These findings identify a potent small molecule that may be therapeutically useful for colon cancer that works by inhibiting Wnt/β-catenin signaling, activating p53, and binding microtubules without detectable toxicity. Cancer Res; 78(17); 5072-83. ©2018 AACR.

    View details for PubMedID 30032112

  • Novel tertiary sulfonamides as potent anti-cancer agents BIOORGANIC & MEDICINAL CHEMISTRY Okolotowicz, K. J., Dwyer, M., Ryan, D., Cheng, J., Cashman, E. A., Moore, S., Mercola, M., Cashman, J. R. 2018; 26 (15): 4441–51

    Abstract

    For adult women in the United States, breast cancer is the most prevalent form of cancer. Compounds that target dysregulated signal transduction can be efficacious anti-cancer therapies. A prominent signaling pathway frequently dysregulated in breast cancer cells is the Wingless-related integration site (Wnt) pathway. The purpose of the work was to optimize a "hit" from a screening campaign. 76,000 compounds were tested in a Wnt transcription assay and revealed potent and reproducible "hit," compound 1. Medicinal chemistry optimization of 1 led to more potent and drug-like molecules, 19, 24 and 25 (i.e., Wnt pathway IC50 values = 11, 18 and 7 nM, respectively). The principal results showed compounds 19, 24 and 25 were potent anti-proliferative agents in breast cancer cell lines, MCF-7 (i.e., IC50 values = 10, 7 and 4 nM, respectively) and MDA-MB 231 (i.e., IC50 values = 13, 13 and 16 nM, respectively). Compound 19 synergized anti-proliferation with chemotherapeutic Doxorubicin in vitro. A major conclusion was that compound 19 enhanced anti-proliferation of Doxorubicin in vitro and in a xenograft animal model of breast cancer.

    View details for PubMedID 30075999

  • Will iPSC-cardiomyocytes revolutionize the discovery of drugs for heart disease? Current opinion in pharmacology Bruyneel, A. A., McKeithan, W. L., Feyen, D. A., Mercola, M. 2018; 42: 55–61

    Abstract

    Cardiovascular disease remains the largest single cause of mortality in the Western world, despite significant advances in clinical management over the years. Unfortunately, the development of new cardiovascular medicines is stagnating and can in part be attributed to the difficulty of screening for novel therapeutic strategies due to a lack of suitable models. The advent of human induced pluripotent stem cells and the ability to make limitless numbers of cardiomyocytes could revolutionize heart disease modeling and drug discovery. This review summarizes the state of the art in the field, describes the strengths and weaknesses of the technology, and applications where the model system would be most appropriate.

    View details for PubMedID 30081259

  • Using iPSC Models to Probe Regulation of Cardiac Ion Channel Function CURRENT CARDIOLOGY REPORTS Bruyneel, A. N., McKeithan, W. L., Feyen, D. M., Mercola, M. 2018; 20 (7): 57

    Abstract

    Cardiovascular disease is the leading contributor to mortality and morbidity. Many deaths of heart failure patients can be attributed to sudden cardiac death due primarily to ventricular arrhythmia. Currently, most anti-arrhythmics modulate ion channel conductivity or β-adrenergic signaling, but these drugs have limited efficacy for some indications, and can potentially be proarrhythmic.Recent studies have shown that mutations in proteins other than cardiac ion channels may confer susceptibility to congenital as well as acquired arrhythmias. Additionally, ion channels themselves are subject to regulation at the levels of channel expression, trafficking and post-translational modification; thus, research into the regulation of ion channels may elucidate disease mechanisms and potential therapeutic targets for future drug development. This review summarizes the current knowledge of the molecular mechanisms of arrhythmia susceptibility and discusses technological advances such as induced pluripotent stem cell-derived cardiomyocytes, gene editing, functional genomics, and physiological screening platforms that provide a new paradigm for discovery of new therapeutic targets to treat congenital and acquired diseases of the heart rhythm.

    View details for PubMedID 29802473

  • INHIBITING MIR-25 THROUGH TOUGH DECOY GENE THERAPY IMPROVES CALCIUM HANDLING AND ABROGATES CARDIAC DYSFUNCTION IN AGED MDX/UTRN KO MICE Kepreotis, S., Jeong, D., Mercola, M., Hajjar, R. J. WILEY. 2018: 5
  • EXOSOMAL MIR-106A-363 CLUSTER FROM THE HYPOXIC HUMAN IPSC-DERIVED CARDIOMYOCYTES RESTORE THE ISCHEMIC MYOCARDIUM Jung, J., Tada, Y., Bornstaedt, D., Wahlquist, C., Mercola, M., Woo, Y., Yang, P. ELSEVIER SCIENCE INC. 2018: 14
  • High-Throughput Functional Screening Assay of Force and Stiffness in IPSC Derived Cardiomyocytes Serrano, R., McKeithan, W., Mercola, M., del Alamo, J. CELL PRESS. 2018: 312A
  • Id genes are essential for early heart formation GENES & DEVELOPMENT Cunningham, T. J., Yu, M. S., McKeithan, W. L., Spiering, S., Carrette, F., Huang, C., Bushway, P. J., Tierney, M., Albini, S., Giacca, M., Mano, M., Puri, P., Sacco, A., Ruiz-Lozano, P., Riou, J., Umbhauer, M., Duester, G., Mercola, M., Colas, A. R. 2017; 31 (13): 1325–38

    Abstract

    Deciphering the fundamental mechanisms controlling cardiac specification is critical for our understanding of how heart formation is initiated during embryonic development and for applying stem cell biology to regenerative medicine and disease modeling. Using systematic and unbiased functional screening approaches, we discovered that the Id family of helix-loop-helix proteins is both necessary and sufficient to direct cardiac mesoderm formation in frog embryos and human embryonic stem cells. Mechanistically, Id proteins specify cardiac cell fate by repressing two inhibitors of cardiogenic mesoderm formation-Tcf3 and Foxa2-and activating inducers Evx1, Grrp1, and Mesp1. Most importantly, CRISPR/Cas9-mediated ablation of the entire Id (Id1-4) family in mouse embryos leads to failure of anterior cardiac progenitor specification and the development of heartless embryos. Thus, Id proteins play a central and evolutionarily conserved role during heart formation and provide a novel means to efficiently produce cardiovascular progenitors for regenerative medicine and drug discovery applications.

    View details for PubMedID 28794185

    View details for PubMedCentralID PMC5580654

  • The CSRP2BP histone acetyltransferase drives smooth muscle gene expression NUCLEIC ACIDS RESEARCH Ma, Y., Li, Q., Li, A., Wei, Y., Long, P., Jiang, X., Sun, F., Weiskirchen, R., Wu, B., Liang, C., Groetzinger, J., Wei, Y., Yu, W., Mercola, M., Huang, Y., Wang, J., Yu, Y., Schwartz, R. J. 2017; 45 (6): 3046–58

    Abstract

    The expression of nearly all smooth muscle genes are controlled by serum response factor binding sites in their promoter regions. However, SRF alone is not sufficient for regulating smooth muscle cell development. It associates with other cardiovascular specific cofactors to regulate smooth muscle gene expression. Previously, we showed that the transcription co-factor CRP2 was a regulator of smooth muscle gene expression. Here, we report that CSRP2BP, a coactivator for CRP2, is a histone acetyltransferase and a driver of smooth muscle gene expression. CSRP2BP directly interacted with SRF, CRP2 and myocardin. CSRP2BP synergistically activated smooth muscle gene promoters in an SRF-dependent manner. A combination of SRF, GATA6 and CRP2 required CSRP2BP for robust smooth muscle gene promoter activity. Knock-down of Csrp2bp in smooth muscle cells resulted in reduced smooth muscle gene expression. We conclude that the CSRP2BP histone acetyltransferase is a coactivator for CRP2 that works synergistically with SRF and myocardin to regulate smooth muscle gene expression.

    View details for DOI 10.1093/nar/gkw1227

    View details for Web of Science ID 000398376200020

    View details for PubMedID 27940555

    View details for PubMedCentralID PMC5389687

  • High-throughput screening of tyrosine kinase inhibitor cardiotoxicity with human induced pluripotent stem cells. Science translational medicine Sharma, A., Burridge, P. W., McKeithan, W. L., Serrano, R., Shukla, P., Sayed, N., Churko, J. M., Kitani, T., Wu, H., Holmström, A., Matsa, E., Zhang, Y., Kumar, A., Fan, A. C., Del Álamo, J. C., Wu, S. M., Moslehi, J. J., Mercola, M., Wu, J. C. 2017; 9 (377)

    Abstract

    Tyrosine kinase inhibitors (TKIs), despite their efficacy as anticancer therapeutics, are associated with cardiovascular side effects ranging from induced arrhythmias to heart failure. We used human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), generated from 11 healthy individuals and 2 patients receiving cancer treatment, to screen U.S. Food and Drug Administration-approved TKIs for cardiotoxicities by measuring alterations in cardiomyocyte viability, contractility, electrophysiology, calcium handling, and signaling. With these data, we generated a "cardiac safety index" to reflect the cardiotoxicities of existing TKIs. TKIs with low cardiac safety indices exhibit cardiotoxicity in patients. We also derived endothelial cells (hiPSC-ECs) and cardiac fibroblasts (hiPSC-CFs) to examine cell type-specific cardiotoxicities. Using high-throughput screening, we determined that vascular endothelial growth factor receptor 2 (VEGFR2)/platelet-derived growth factor receptor (PDGFR)-inhibiting TKIs caused cardiotoxicity in hiPSC-CMs, hiPSC-ECs, and hiPSC-CFs. With phosphoprotein analysis, we determined that VEGFR2/PDGFR-inhibiting TKIs led to a compensatory increase in cardioprotective insulin and insulin-like growth factor (IGF) signaling in hiPSC-CMs. Up-regulating cardioprotective signaling with exogenous insulin or IGF1 improved hiPSC-CM viability during cotreatment with cardiotoxic VEGFR2/PDGFR-inhibiting TKIs. Thus, hiPSC-CMs can be used to screen for cardiovascular toxicities associated with anticancer TKIs, and the results correlate with clinical phenotypes. This approach provides unexpected insights, as illustrated by our finding that toxicity can be alleviated via cardioprotective insulin/IGF signaling.

    View details for DOI 10.1126/scitranslmed.aaf2584

    View details for PubMedID 28202772

  • Bringing new dimensions to drug discovery screening: impact of cellular stimulation technologies. Drug discovery today Molokanova, E., Mercola, M., Savchenko, A. 2017

    Abstract

    The current mandate for the drug discovery industry is to develop more efficient drugs faster while reducing the costs associated with their development. Incorporation of cell stimulation technologies during screening assays is expected to revolutionize the discovery of novel drugs as well as safety pharmacology. In this review, we highlight 'classical' and emerging cell stimulation technologies that provide the ability to evaluate the effects of drug candidates on cells in different functional states to assess clinically relevant phenotypes.

    View details for DOI 10.1016/j.drudis.2017.01.015

    View details for PubMedID 28179145

  • miR-25 Tough Decoy Enhances Cardiac Function in Heart Failure. Molecular therapy : the journal of the American Society of Gene Therapy Jeong, D., Yoo, J., Lee, P., Kepreotis, S. V., Lee, A., Wahlquist, C., Brown, B. D., Kho, C., Mercola, M., Hajjar, R. J. 2017

    Abstract

    MicroRNAs are promising therapeutic targets, because their inhibition has the potential to normalize gene expression in diseased states. Recently, our group found that miR-25 is a key SERCA2a regulating microRNA, and we showed that multiple injections of antagomirs against miR-25 enhance cardiac contractility and function through SERCA2a restoration in a murine heart failure model. However, for clinical application, a more stable suppressor of miR-25 would be desirable. Tough Decoy (TuD) inhibitors are emerging as a highly effective method for microRNA inhibition due to their resistance to endonucleolytic degradation, high miRNA binding affinity, and efficient delivery. We generated a miR-25 TuD inhibitor and subcloned it into a cardiotropic AAV9 vector to evaluate its efficacy. The AAV9 TuD showed selective inhibition of miR-25 in vitro cardiomyoblast culture. In vivo, AAV9-miR-25 TuD delivered to the murine pressure-overload heart failure model selectively decreased expression of miR-25, increased levels of SERCA2a protein, and ameliorated cardiac dysfunction and fibrosis. Our data indicate that miR-25 TuD is an effective long-term suppressor of miR-25 and a promising therapeutic candidate to treat heart failure.

    View details for PubMedID 29273502

  • Id genes are essential for early heart formation Genes & Dev. Cunningham, T. J., Yu, M. S., McKeithan, W. L., Spiering, S., Carrette, F., Huang, C., Bushway, P. J., Tierney, M., Albini, S., Giacca, M., Mano, M., Puri, P., Sacco, A., Riou, J., Umbhauer, M., Duester, G., Mercola, M., Colas, A. R. 2017; 31: 1325-1338

    View details for DOI 10.1101/gad.300400.117v1

  • An Automated Platform for Assessment of Congenital and Drug-Induced Arrhythmia with hiPSC-Derived Cardiomyocytes. Frontiers in physiology McKeithan, W. L., Savchenko, A., Yu, M. S., Cerignoli, F., Bruyneel, A. A., Price, J. H., Colas, A. R., Miller, E. W., Cashman, J. R., Mercola, M. 2017; 8: 766

    Abstract

    The ability to produce unlimited numbers of human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) harboring disease and patient-specific gene variants creates a new paradigm for modeling congenital heart diseases (CHDs) and predicting proarrhythmic liabilities of drug candidates. However, a major roadblock to implementing hiPSC-CM technology in drug discovery is that conventional methods for monitoring action potential (AP) kinetics and arrhythmia phenotypes in vitro have been too costly or technically challenging to execute in high throughput. Herein, we describe the first large-scale, fully automated and statistically robust analysis of AP kinetics and drug-induced proarrhythmia in hiPSC-CMs. The platform combines the optical recording of a small molecule fluorescent voltage sensing probe (VoltageFluor2.1.Cl), an automated high throughput microscope and automated image analysis to rapidly generate physiological measurements of cardiomyocytes (CMs). The technique can be readily adapted on any high content imager to study hiPSC-CM physiology and predict the proarrhythmic effects of drug candidates.

    View details for PubMedID 29075196

    View details for PubMedCentralID PMC5641590

  • miR-322/-503 cluster is expressed in the earliest cardiac progenitor cells and drives cardiomyocyte specification PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Shen, X., Soibam, B., Benham, A., Xu, X., Chopra, M., Peng, X., Yu, W., Bao, W., Liang, R., Azares, A., Liu, P., Gunaratne, P. H., Mercola, M., Cooney, A. J., Schwartz, R. J., Liu, Y. 2016; 113 (34): 9551-9556

    Abstract

    Understanding the mechanisms of early cardiac fate determination may lead to better approaches in promoting heart regeneration. We used a mesoderm posterior 1 (Mesp1)-Cre/Rosa26-EYFP reporter system to identify microRNAs (miRNAs) enriched in early cardiac progenitor cells. Most of these miRNA genes bear MESP1-binding sites and active histone signatures. In a calcium transient-based screening assay, we identified miRNAs that may promote the cardiomyocyte program. An X-chromosome miRNA cluster, miR-322/-503, is the most enriched in the Mesp1 lineage and is the most potent in the screening assay. It is specifically expressed in the looping heart. Ectopic miR-322/-503 mimicking the endogenous temporal patterns specifically drives a cardiomyocyte program while inhibiting neural lineages, likely by targeting the RNA-binding protein CUG-binding protein Elav-like family member 1 (Celf1). Thus, early miRNAs in lineage-committed cells may play powerful roles in cell-fate determination by cross-suppressing other lineages. miRNAs identified in this study, especially miR-322/-503, are potent regulators of early cardiac fate.

    View details for DOI 10.1073/pnas.1608256113

    View details for PubMedID 27512039

  • The All-Chemical Approach: A Solution for Converting Fibroblasts Into Myocytes. Circulation research Liu, Y., Mercola, M., Schwartz, R. J. 2016; 119 (4): 505-507

    View details for DOI 10.1161/CIRCRESAHA.116.309146

    View details for PubMedID 27492839

    View details for PubMedCentralID PMC4987128

  • Extracellular vesicles as effective substitutes for cell therapy for chronic heart failure Kervadec, A., Bellamy, V., El Harane, N., Smit, N., Meijborg, V., Nematalla, H., Perier, M. C., Renault, M. P., Colas, A., Hagege, A., Colonel, R., Mercola, M., Silvestre, J. S., Menasche, P., Renault, N. OXFORD UNIV PRESS. 2016: 397
  • High throughput physiological screening of iPSC-derived cardiomyocytes for drug development BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH del Alamo, J. C., Lemons, D., Serrano, R., Savchenko, A., Cerignoli, F., Bodmer, R., Mercola, M. 2016; 1863 (7): 1717-1727

    Abstract

    Cardiac drug discovery is hampered by the reliance on non-human animal and cellular models with inadequate throughput and physiological fidelity to accurately identify new targets and test novel therapeutic strategies. Similarly, adverse drug effects on the heart are challenging to model, contributing to costly failure of drugs during development and even after market launch. Human induced pluripotent stem cell derived cardiac tissue represents a potentially powerful means to model aspects of heart physiology relevant to disease and adverse drug effects, providing both the human context and throughput needed to improve the efficiency of drug development. Here we review emerging technologies for high throughput measurements of cardiomyocyte physiology, and comment on the promises and challenges of using iPSC-derived cardiomyocytes to model disease and introduce the human context into early stages of drug discovery. This article is part of a Special Issue entitled: Cardiomyocyte biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel.

    View details for DOI 10.1016/j.bbamcr.2016.03.003

    View details for Web of Science ID 000378360400004

    View details for PubMedID 26952934

    View details for PubMedCentralID PMC4885786

  • Notch-independent RBPJ controls angiogenesis in the adult heart NATURE COMMUNICATIONS Diaz-Trelles, R., Scimia, M. C., Bushway, P., Tran, D., Monosov, A., Monosov, E., Peterson, K., Rentschler, S., Cabrales, P., Ruiz-Lozano, P., Mercola, M. 2016; 7

    Abstract

    Increasing angiogenesis has long been considered a therapeutic target for improving heart function after injury such as acute myocardial infarction. However, gene, protein and cell therapies to increase microvascularization have not been successful, most likely because the studies failed to achieve regulated and concerted expression of pro-angiogenic and angiostatic factors needed to produce functional microvasculature. Here, we report that the transcription factor RBPJ is a homoeostatic repressor of multiple pro-angiogenic and angiostatic factor genes in cardiomyocytes. RBPJ controls angiogenic factor gene expression independently of Notch by antagonizing the activity of hypoxia-inducible factors (HIFs). In contrast to previous strategies, the cardiomyocyte-specific deletion of Rbpj increased microvascularization of the heart without adversely affecting cardiac structure or function even into old age. Furthermore, the loss of RBPJ in cardiomyocytes increased hypoxia tolerance, improved heart function and decreased pathological remodelling after myocardial infarction, suggesting that inhibiting RBPJ might be therapeutic for ischaemic injury.

    View details for DOI 10.1038/ncomms12088

    View details for Web of Science ID 000379113200001

    View details for PubMedID 27357444

    View details for PubMedCentralID PMC4931341

  • Inhibition of Tumor Growth in an Orthotopic Model of Invasive Pancreatic Cancer: A Novel Molecular Pathway Inhibitor Cheng, J., Okolotowicz, K., Lowy, A. M., Mercola, M., Cashman, J. FEDERATION AMER SOC EXP BIOL. 2016
  • Metallic Nanoislands on Graphene as Highly Sensitive Transducers of Mechanical, Biological, and Optical Signals NANO LETTERS Zaretski, A. V., Root, S. E., Savchenko, A., Molokanova, E., Printz, A. D., Jibril, L., Arya, G., Mercola, M., Lipomi, D. J. 2016; 16 (2): 1375-1380

    Abstract

    This article describes an effect based on the wetting transparency of graphene; the morphology of a metallic film (≤20 nm) when deposited on graphene by evaporation depends strongly on the identity of the substrate supporting the graphene. This control permits the formation of a range of geometries, such as tightly packed nanospheres, nanocrystals, and island-like formations with controllable gaps down to 3 nm. These graphene-supported structures can be transferred to any surface and function as ultrasensitive mechanical signal transducers with high sensitivity and range (at least 4 orders of magnitude of strain) for applications in structural health monitoring, electronic skin, measurement of the contractions of cardiomyocytes, and substrates for surface-enhanced Raman scattering (SERS, including on the tips of optical fibers). These composite films can thus be treated as a platform technology for multimodal sensing. Moreover, they are low profile, mechanically robust, semitransparent and have the potential for reproducible manufacturing over large areas.

    View details for DOI 10.1021/acs.nanolett.5b04821

    View details for Web of Science ID 000370215200081

    View details for PubMedID 26765039

    View details for PubMedCentralID PMC4751512

  • A molecular pathway inhibitor that inhibits tumor growth in an orthotopic model of invasive pancreatic cancer Cashman, J., Okolotowicz, K., Cheng, J., Lowy, A. M., Mercola, M. TAYLOR & FRANCIS LTD. 2016: 57–58
  • DISEASE IN A DISH: PATIENT-SPECIFIC hiPSC-DERIVED CARDIOMYOCYTES TO STUDY LONG QT INTERVAL AND hERG CHANNEL TOXICITY Ryan, D. A., Okolotowicz, K. J., McKeithan, W. L., Savtchenko, A., Kass, R. S., Mercola, M., Cashman, J. R. TAYLOR & FRANCIS LTD. 2015: 100
  • Epicardial FSTL1 reconstitution regenerates the adult mammalian heart. Nature Wei, K., Serpooshan, V., Hurtado, C., Diez-Cuñado, M., Zhao, M., Maruyama, S., Zhu, W., Fajardo, G., Noseda, M., Nakamura, K., Tian, X., Liu, Q., Wang, A., Matsuura, Y., Bushway, P., Cai, W., Savchenko, A., Mahmoudi, M., Schneider, M. D., van den Hoff, M. J., Butte, M. J., Yang, P. C., Walsh, K., Zhou, B., Bernstein, D., Mercola, M., Ruiz-Lozano, P. 2015; 525 (7570): 479-485

    Abstract

    The elucidation of factors that activate the regeneration of the adult mammalian heart is of major scientific and therapeutic importance. Here we found that epicardial cells contain a potent cardiogenic activity identified as follistatin-like 1 (Fstl1). Epicardial Fstl1 declines following myocardial infarction and is replaced by myocardial expression. Myocardial Fstl1 does not promote regeneration, either basally or upon transgenic overexpression. Application of the human Fstl1 protein (FSTL1) via an epicardial patch stimulates cell cycle entry and division of pre-existing cardiomyocytes, improving cardiac function and survival in mouse and swine models of myocardial infarction. The data suggest that the loss of epicardial FSTL1 is a maladaptive response to injury, and that its restoration would be an effective way to reverse myocardial death and remodelling following myocardial infarction in humans.

    View details for DOI 10.1038/nature15372

    View details for PubMedID 26375005

  • Retinoic Acid Activity in Undifferentiated Neural Progenitors Is Sufficient to Fulfill Its Role in Restricting Fgf8 Expression for Somitogenesis PLOS ONE Cunningham, T. J., Brade, T., Sandell, L. L., Lewandoski, M., Trainor, P. A., Colas, A., Mercola, M., Duester, G. 2015; 10 (9)

    Abstract

    Bipotent axial stem cells residing in the caudal epiblast during late gastrulation generate neuroectodermal and presomitic mesodermal progeny that coordinate somitogenesis with neural tube formation, but the mechanism that controls these two fates is not fully understood. Retinoic acid (RA) restricts the anterior extent of caudal fibroblast growth factor 8 (Fgf8) expression in both mesoderm and neural plate to control somitogenesis and neurogenesis, however it remains unclear where RA acts to control the spatial expression of caudal Fgf8. Here, we found that mouse Raldh2-/- embryos, lacking RA synthesis and displaying a consistent small somite defect, exhibited abnormal expression of key markers of axial stem cell progeny, with decreased Sox2+ and Sox1+ neuroectodermal progeny and increased Tbx6+ presomitic mesodermal progeny. The Raldh2-/- small somite defect was rescued by treatment with an FGF receptor antagonist. Rdh10 mutants, with a less severe RA synthesis defect, were found to exhibit a small somite defect and anterior expansion of caudal Fgf8 expression only for somites 1-6, with normal somite size and Fgf8 expression thereafter. Rdh10 mutants were found to lack RA activity during the early phase when somites are small, but at the 6-somite stage RA activity was detected in neural plate although not in presomitic mesoderm. Expression of a dominant-negative RA receptor in mesoderm eliminated RA activity in presomitic mesoderm but did not affect somitogenesis. Thus, RA activity in the neural plate is sufficient to prevent anterior expansion of caudal Fgf8 expression associated with a small somite defect. Our studies provide evidence that RA restriction of Fgf8 expression in undifferentiated neural progenitors stimulates neurogenesis while also restricting the anterior extent of the mesodermal Fgf8 mRNA gradient that controls somite size, providing new insight into the mechanism that coordinates somitogenesis with neurogenesis.

    View details for DOI 10.1371/journal.pone.0137894

    View details for Web of Science ID 000361601100172

    View details for PubMedID 26368825

    View details for PubMedCentralID PMC4569375

  • 1,5-Disubstituted benzimidazoles that direct cardiomyocyte differentiation from mouse embryonic stem cells BIOORGANIC & MEDICINAL CHEMISTRY Okolotowicz, K. J., Bushway, P., Lanier, M., Gilley, C., Mercola, M., Cashman, J. R. 2015; 23 (17): 5282-5292

    Abstract

    Cardiomyopathy is the leading cause of death worldwide. Despite progress in medical treatments, heart transplantation is one of the only current options for those with infarcted heart muscle. Stem cell differentiation technology may afford cell-based therapeutics that may lead to the generation of new, healthy heart muscle cells from undifferentiated stem cells. Our approach is to use small molecules to stimulate stem cell differentiation. Herein, we describe a novel class of 1,5-disubstituted benzimidazoles that induce differentiation of stem cells into cardiac cells. We report on the evaluation in vitro for cardiomyocyte differentiation and describe structure-activity relationship results that led to molecules with drug-like properties. The results of this study show the promise of small molecules to direct stem cell lineage commitment, to probe signaling pathways and to develop compounds for the stimulation of stem cells to repair damaged heart tissue.

    View details for DOI 10.1016/j.bmc.2015.07.073

    View details for Web of Science ID 000360349900004

    View details for PubMedID 26278027

    View details for PubMedCentralID PMC4766108

  • Developmental origin of age-related coronary artery disease. Cardiovascular research Wei, K., Díaz-Trelles, R., Liu, Q., Diez-Cuñado, M., Scimia, M., Cai, W., Sawada, J., Komatsu, M., Boyle, J. J., Zhou, B., Ruiz-Lozano, P., Mercola, M. 2015; 107 (2): 287-294

    Abstract

    Age and injury cause structural and functional changes in coronary artery smooth muscle cells (caSMCs) that influence the pathogenesis of coronary artery disease. Although paracrine signalling is widely believed to drive phenotypic changes in caSMCs, here we show that developmental origin within the fetal epicardium can have a profound effect as well.Fluorescent dye and transgene pulse-labelling techniques in mice revealed that the majority of caSMCs are derived from Wt1(+), Gata5-Cre(+) cells that migrate before E12.5, whereas a minority of cells are derived from a later-emigrating, Wt1(+), Gata5-Cre(-) population. We functionally evaluated the influence of early emigrating cells on coronary artery development and disease by Gata5-Cre excision of Rbpj, which prevents their contribution to coronary artery smooth muscle cells. Ablation of the Gata5-Cre(+) population resulted in coronary arteries consisting solely of Gata5-Cre(-) caSMCs. These coronary arteries appeared normal into early adulthood; however, by 5-8 months of age, they became progressively fibrotic, lost the adventitial outer elastin layer, were dysfunctional and leaky, and animals showed early mortality.Taken together, these data reveal heterogeneity in the fetal epicardium that is linked to coronary artery integrity, and that distortion of the coronaries epicardial origin predisposes to adult onset disease.

    View details for DOI 10.1093/cvr/cvv167

    View details for PubMedID 26054850

  • Stereoselective synthesis of mexiletine and structural analogs with chiral tert-butanesulfinamide TETRAHEDRON LETTERS Ryan, D. A., Okolotowicz, K. J., Mercola, M., Cashman, J. R. 2015; 56 (28): 4195–99
  • Cholesterol-derived glucocorticoids control early fate specification in embryonic stem cells STEM CELL RESEARCH Cabral-Teixeira, J., Martinez-Fernandez, A., Cai, W., Terzic, A., Mercola, M., Willems, E. 2015; 15 (1): 88-95

    Abstract

    Aside from its role in cell membrane integrity, cholesterol is a key component in steroid hormone production. The vital functions of steroid hormones such as estrogen, testosterone, glucocorticoids (Gcrts) and mineralocorticoids (Mnrts) in perinatal and adult life are well understood; however, their role during early embryonic development remains largely unexplored. Here we show that siRNA-mediated perturbation of steroid hormone production during mesoderm formation has important consequences on cardiac differentiation in mouse embryonic stem cells (mESC). Both Gcrts and Mnrts are capable of driving cardiac differentiation in mESC. Interestingly, the Gcrt receptor is widely expressed during gastrulation in the mouse, and is exclusively localized in the nuclei-and thus active-in visceral endoderm cells, suggesting that it functions much earlier than previously anticipated. We therefore studied Gcrt signaling in mESC as a model of the gastrulating embryo, and found that Gcrt signaling regulates expression of the transcription factor Hnf4a and the secreted Nodal and BMP inhibitor Cer1 in the early visceral endoderm. RNAi-mediated knockdown of Gcrt function blocked cardiomyocyte differentiation, with limited effects on other cardiovascular cell types including vascular endothelial cells and smooth muscle. Furthermore, the cardiogenic effect of Gcrts required Hnf4a and paracrine Cer1. These results establish a novel function for cholesterol-derived steroid hormones and identify Gcrt signaling in visceral endoderm cells as a regulator of Cer1 and cardiac fate.

    View details for DOI 10.1016/j.scr.2015.04.010

    View details for Web of Science ID 000359994400009

    View details for PubMedID 26024790

    View details for PubMedCentralID PMC4516691

  • Cyclic stretch of embryonic cardiomyocytes increases proliferation, growth, and expression while repressing Tgf-beta signaling JOURNAL OF MOLECULAR AND CELLULAR CARDIOLOGY Banerjee, I., Carrion, K., Serrano, R., Dyo, J., Sasik, R., Lund, S., Willems, E., Aceves, S., Meili, R., Mercola, M., Chen, J., Zambon, A., Hardiman, G., Doherty, T. A., Lange, S., del Alamo, J. C., Nigam, V. 2015; 79: 133-144

    Abstract

    Perturbed biomechanical stimuli are thought to be critical for the pathogenesis of a number of congenital heart defects, including Hypoplastic Left Heart Syndrome (HLHS). While embryonic cardiomyocytes experience biomechanical stretch every heart beat, their molecular responses to biomechanical stimuli during heart development are poorly understood. We hypothesized that biomechanical stimuli activate specific signaling pathways that impact proliferation, gene expression and myocyte contraction. The objective of this study was to expose embryonic mouse cardiomyocytes (EMCM) to cyclic stretch and examine key molecular and phenotypic responses. Analysis of RNA-Sequencing data demonstrated that gene ontology groups associated with myofibril and cardiac development were significantly modulated. Stretch increased EMCM proliferation, size, cardiac gene expression, and myofibril protein levels. Stretch also repressed several components belonging to the Transforming Growth Factor-β (Tgf-β) signaling pathway. EMCMs undergoing cyclic stretch had decreased Tgf-β expression, protein levels, and signaling. Furthermore, treatment of EMCMs with a Tgf-β inhibitor resulted in increased EMCM size. Functionally, Tgf-β signaling repressed EMCM proliferation and contractile function, as assayed via dynamic monolayer force microscopy (DMFM). Taken together, these data support the hypothesis that biomechanical stimuli play a vital role in normal cardiac development and for cardiac pathology, including HLHS.

    View details for DOI 10.1016/j.yjmcc.2014.11.003

    View details for Web of Science ID 000353525800014

    View details for PubMedID 25446186

    View details for PubMedCentralID PMC4302020

  • High content screening for modulators of cardiac differentiation in human pluripotent stem cells. Methods in molecular biology (Clifton, N.J.) Spiering, S., Davidovics, H., Bushway, P. J., Mercola, M., Willems, E. 2015; 1263: 43-61

    Abstract

    Chemical genomics has the unique potential to expose novel mechanisms of complex cellular biology through screening of small molecules in in vitro assays of a biological phenotype of interest, followed by target identification. In the case of disease-specific assays, the cellular proteins identified might constitute novel drug targets, and the small molecules themselves might be developed as drug leads. In cardiovascular biology, a chemical genomics approach to study the formation of cardiomyocyte, vascular endothelial, and smooth muscle lineages might contribute to therapeutic regeneration. Here, we describe methods used to develop high content screening assays implementing multipotent cardiovascular progenitors derived from human pluripotent stem cells and have identified novel compounds that direct cardiac differentiation.

    View details for DOI 10.1007/978-1-4939-2269-7_4

    View details for PubMedID 25618335

    View details for PubMedCentralID PMC4766105

  • Cyclic stretch of Embryonic Cardiomyocytes Increases Proliferation, Growth, and Expression While Repressing Tgf-[beta] Signaling Banerjee, I., Carrion, K., Serrano, R., Dyo, J., Lund, S., Willems, E., Aceves, S., Meili, R., Mercola, M., Chen, J., Zambon, A., Zambon, A., Hardiman, G., Doherty, T. A., del Alamo, J. C., Nigam, V. LIPPINCOTT WILLIAMS & WILKINS. 2014
  • Inhibition of miR-25 improves cardiac contractility in the failing heart NATURE Wahlquist, C., Jeong, D., Rojas-Munoz, A., Kho, C., Lee, A., Mitsuyama, S., Van Mil, A., Park, W. J., Sluijter, J. P., Doevendans, P. A., Hajjar, R. J., Mercola, M. 2014; 508 (7497): 531-?

    Abstract

    Heart failure is characterized by a debilitating decline in cardiac function, and recent clinical trial results indicate that improving the contractility of heart muscle cells by boosting intracellular calcium handling might be an effective therapy. MicroRNAs (miRNAs) are dysregulated in heart failure but whether they control contractility or constitute therapeutic targets remains speculative. Using high-throughput functional screening of the human microRNAome, here we identify miRNAs that suppress intracellular calcium handling in heart muscle by interacting with messenger RNA encoding the sarcoplasmic reticulum calcium uptake pump SERCA2a (also known as ATP2A2). Of 875 miRNAs tested, miR-25 potently delayed calcium uptake kinetics in cardiomyocytes in vitro and was upregulated in heart failure, both in mice and humans. Whereas adeno-associated virus 9 (AAV9)-mediated overexpression of miR-25 in vivo resulted in a significant loss of contractile function, injection of an antisense oligonucleotide (antagomiR) against miR-25 markedly halted established heart failure in a mouse model, improving cardiac function and survival relative to a control antagomiR oligonucleotide. These data reveal that increased expression of endogenous miR-25 contributes to declining cardiac function during heart failure and suggest that it might be targeted therapeutically to restore function.

    View details for DOI 10.1038/nature13073

    View details for Web of Science ID 000334741600038

    View details for PubMedID 24670661

    View details for PubMedCentralID PMC4131725

  • HDAC-regulated myomiRs control BAF60 variant exchange and direct the functional phenotype of fibro-adipogenic progenitors in dystrophic muscles GENES & DEVELOPMENT Saccone, V., Consalvi, S., Giordani, L., Mozzetta, C., Barozzi, I., Sandona, M., Ryan, T., Rojas-Munoz, A., Madaro, L., Fasanaro, P., Borsellino, G., De Bardi, M., Frige, G., Termanini, A., Sun, X., Rossant, J., Bruneau, B. G., Mercola, M., Minucci, S., Puri, P. L. 2014; 28 (8): 841-857

    Abstract

    Fibro-adipogenic progenitors (FAPs) are important components of the skeletal muscle regenerative environment. Whether FAPs support muscle regeneration or promote fibro-adipogenic degeneration is emerging as a key determinant in the pathogenesis of muscular diseases, including Duchenne muscular dystrophy (DMD). However, the molecular mechanism that controls FAP lineage commitment and activity is currently unknown. We show here that an HDAC-myomiR-BAF60 variant network regulates the fate of FAPs in dystrophic muscles of mdx mice. Combinatorial analysis of gene expression microarray, genome-wide chromatin remodeling by nuclease accessibility (NA) combined with next-generation sequencing (NA-seq), small RNA sequencing (RNA-seq), and microRNA (miR) high-throughput screening (HTS) against SWI/SNF BAF60 variants revealed that HDAC inhibitors (HDACis) derepress a "latent" myogenic program in FAPs from dystrophic muscles at early stages of disease. Specifically, HDAC inhibition induces two core components of the myogenic transcriptional machinery, MYOD and BAF60C, and up-regulates the myogenic miRs (myomiRs) (miR-1.2, miR-133, and miR-206), which target the alternative BAF60 variants BAF60A and BAF60B, ultimately directing promyogenic differentiation while suppressing the fibro-adipogenic phenotype. In contrast, FAPs from late stage dystrophic muscles are resistant to HDACi-induced chromatin remodeling at myogenic loci and fail to activate the promyogenic phenotype. These results reveal a previously unappreciated disease stage-specific bipotency of mesenchimal cells within the regenerative environment of dystrophic muscles. Resolution of such bipotency by epigenetic intervention with HDACis provides a molecular rationale for the in situ reprogramming of target cells to promote therapeutic regeneration of dystrophic muscles.

    View details for DOI 10.1101/gad.234468.113

    View details for Web of Science ID 000334585400005

    View details for PubMedID 24682306

    View details for PubMedCentralID PMC4003277

  • Reprogramming the Cardiac Field CIRCULATION RESEARCH Willems, E., Mercola, M. 2014; 114 (3): 409-411

    View details for DOI 10.1161/CIRCRESAHA.113.302946

    View details for Web of Science ID 000335586800005

    View details for PubMedID 24481840

    View details for PubMedCentralID PMC4046860

  • Multiparametric One-Color Assays for Functional Assessment of Cardiomyocytes Savtchenko, A., Ruidiaz, M., Miller, E. W., McKeithan, W., Heynen-Genel, S., Mercola, M. CELL PRESS. 2014: 720A
  • Technical Variations in Low-Input RNA-seq Methodologies SCIENTIFIC REPORTS Bhargava, V., Head, S. R., Ordoukhanian, P., Mercola, M., Subramaniam, S. 2014; 4

    Abstract

    Recent advances in RNA-seq methodologies from limiting amounts of mRNA have facilitated the characterization of rare cell-types in various biological systems. So far, however, technical variations in these methods have not been adequately characterized, vis-à-vis sensitivity, starting with reduced levels of mRNA. Here, we generated sequencing libraries from limiting amounts of mRNA using three amplification-based methods, viz. Smart-seq, DP-seq and CEL-seq, and demonstrated significant technical variations in these libraries. Reduction in mRNA levels led to inefficient amplification of the majority of low to moderately expressed transcripts. Furthermore, noise in primer hybridization and/or enzyme incorporation was magnified during the amplification step resulting in significant distortions in fold changes of the transcripts. Consequently, the majority of the differentially expressed transcripts identified were either high-expressed and/or exhibited high fold changes. High technical variations ultimately masked subtle biological differences mandating the development of improved amplification-based strategies for quantitative transcriptomics from limiting amounts of mRNA.

    View details for DOI 10.1038/srep03678

    View details for Web of Science ID 000329846100007

    View details for PubMedID 24419370

    View details for PubMedCentralID PMC3890974

  • A POTENT MOLECULAR PATHWAY INHIBITOR THAT INHIBITS CANCER CELL PROLIFERATION Cashman, J., Okolotowicz, K., Dwyer, M., Chen, S., Mercola, M. INFORMA HEALTHCARE. 2014: 103
  • Coordinate Nodal and BMP inhibition directs Baf60c-dependent cardiomyocyte commitment GENES & DEVELOPMENT Cai, W., Albini, S., Wei, K., Willems, E., Guzzo, R. M., Tsuda, M., Giordani, L., Spiering, S., Kurian, L., Yeo, G. W., Puri, P. L., Mercola, M. 2013; 27 (21): 2332-2344

    Abstract

    A critical but molecularly uncharacterized step in heart formation and regeneration is the process that commits progenitor cells to differentiate into cardiomyocytes. Here, we show that the endoderm-derived dual Nodal/bone morphogenetic protein (BMP) antagonist Cerberus-1 (Cer1) in embryonic stem cell cultures orchestrates two signaling pathways that direct the SWI/SNF chromatin remodeling complex to cardiomyogenic loci in multipotent (KDR/Flk1+) progenitors, activating lineage-specific transcription. Transient inhibition of Nodal by Cer1 induces Brahma-associated factor 60c (Baf60c), one of three Baf60 variants (a, b, and c) that are mutually exclusively assembled into SWI/SNF. Blocking Nodal and BMP also induces lineage-specific transcription factors Gata4 and Tbx5, which interact with Baf60c. siRNA to Cer1, Baf60c, or the catalytic SWI/SNF subunit Brg1 prevented the developmental opening of chromatin surrounding the Nkx2.5 early cardiac enhancer and cardiomyocyte differentiation. Overexpression of Baf60c fully rescued these deficits, positioning Baf60c and SWI/SNF function downstream from Cer1. Thus, antagonism of Nodal and BMP coordinates induction of the myogenic Baf60c variant and interacting transcription factors to program the developmental opening of cardiomyocyte-specific loci in chromatin. This is the first demonstration that cues from the progenitor cell environment direct the subunit variant composition of SWI/SNF to remodel the transcriptional landscape for lineage-specific differentiation.

    View details for DOI 10.1101/gad.225144.113

    View details for Web of Science ID 000326921900005

    View details for PubMedID 24186978

    View details for PubMedCentralID PMC3828519

  • Jumonji and Cardiac Fate CIRCULATION RESEARCH Willems, E., Mercola, M. 2013; 113 (7): 837-839

    View details for DOI 10.1161/CIRCRESAHA.113.302202

    View details for Web of Science ID 000329479600004

    View details for PubMedID 24030015

    View details for PubMedCentralID PMC3974910

  • Simultaneous recording of action potentials and calcium transients from stem cell-derived cardiomyocytes: Applications for cardiotoxicity testing Whittaker, R., Cerignoli, F., Ingermanson, R., Towart, R., Gallacher, D. J., Mercola, M., Price, J. ELSEVIER SCIENCE INC. 2013: E47
  • Quantitative Transcriptomics using Designed Primer-based Amplification SCIENTIFIC REPORTS Bhargava, V., Ko, P., Willems, E., Mercola, M., Subramaniam, S. 2013; 3

    Abstract

    We developed a novel Designed Primer-based RNA-sequencing strategy (DP-seq) that uses a defined set of heptamer primers to amplify the majority of expressed transcripts from limiting amounts of mRNA, while preserving their relative abundance. Our strategy reproducibly yielded high levels of amplification from as low as 50 picograms of mRNA while offering a dynamic range of over five orders of magnitude in RNA concentrations. We also demonstrated the potential of DP-seq to selectively suppress the amplification of the highly expressing ribosomal transcripts by more than 70% in our sequencing library. Using lineage segregation in embryonic stem cell cultures as a model of early mammalian embryogenesis, DP-seq revealed novel sets of low abundant transcripts, some corresponding to the identity of cellular progeny before they arise, reflecting the specification of cell fate prior to actual germ layer segregation.

    View details for DOI 10.1038/srep01740

    View details for Web of Science ID 000318145200001

    View details for PubMedID 23624976

    View details for PubMedCentralID PMC3638165

  • Induced Pluripotent Stem Cells in Cardiovascular Drug Discovery CIRCULATION RESEARCH Mercola, M., Colas, A., Willems, E. 2013; 112 (3): 534-548

    Abstract

    The unexpected discovery that somatic cells can be reprogrammed to a pluripotent state yielding induced pluripotent stem cells has made it possible to produce cardiovascular cells exhibiting inherited traits and disorders. Use of these cells in high throughput analyses should broaden our insight into fundamental disease mechanisms and provide many benefits for patients, including new therapeutics and individually tailored therapies. Here we review recent progress in generating induced pluripotent stem cell-based models of cardiovascular disease and their multiple applications in drug development.

    View details for DOI 10.1161/CIRCRESAHA.111.250266

    View details for Web of Science ID 000314356700021

    View details for PubMedID 23371902

    View details for PubMedCentralID PMC3706265

  • Developing microRNA screening as a functional genomics tool for disease research. Frontiers in physiology Lemons, D., Maurya, M. R., Subramaniam, S., Mercola, M. 2013; 4: 223-?

    Abstract

    Originally discovered as regulators of developmental timing in C. elegans, microRNAs (miRNAs) have emerged as modulators of nearly every cellular process, from normal development to pathogenesis. With the advent of whole genome libraries of miRNA mimics suitable for high throughput screening, it is possible to comprehensively evaluate the function of each member of the miRNAome in cell-based assays. Since the relatively few microRNAs in the genome are thought to directly regulate a large portion of the proteome, miRNAome screening, coupled with the identification of the regulated proteins, might be a powerful new approach to gaining insight into complex biological processes.

    View details for DOI 10.3389/fphys.2013.00223

    View details for PubMedID 23986717

    View details for PubMedCentralID PMC3753477

  • CARDIOVASCULAR BIOLOGY A boost for heart regeneration NATURE Mercola, M. 2012; 492 (7429): 360-362

    View details for Web of Science ID 000312488200039

    View details for PubMedID 23222522

  • BAF60 A, B, and Cs of muscle determination and renewal GENES & DEVELOPMENT Puri, P. L., Mercola, M. 2012; 26 (24): 2673-2683

    Abstract

    Developmental biologists have defined many of the diffusible and transcription factors that control muscle differentiation, yet we still have only rudimentary knowledge of the mechanisms that dictate whether a myogenic progenitor cell forms muscle versus alternate lineages, including those that can be pathological in a state of disease or degeneration. Clues about the molecular basis for lineage determination in muscle progenitors are only now emerging from studies of chromatin modifications that avail myogenic genes for transcription, together with analysis of the composition and activities of the chromatin-modifying complexes themselves. Here we review recent progress on muscle determination and explore a unifying theme that environmental cues from the stem or progenitor niche control the selection of specific subunit variants of the switch/sucrose nonfermentable (SWI/SNF) chromatin-modifying complex, creating a combinatorial code that dictates whether cells adopt myogenic versus nonmyogenic cell fates. A key component of the code appears to be the mutually exclusive usage of the a, b, and c variants of the 60-kD structural subunit BAF60 (BRG1/BRM-associated factor 60), of which BAF60c is essential to activate both skeletal and cardiac muscle programs. Since chromatin remodeling governs myogenic fate, the combinatorial assembly of the SWI/SNF complex might be targeted to develop drugs aimed at the therapeutic reduction of compensatory fibrosis and fatty deposition in chronic muscular disorders.

    View details for DOI 10.1101/gad.207415.112

    View details for Web of Science ID 000312775700002

    View details for PubMedID 23222103

    View details for PubMedCentralID PMC3533072

  • Whole-genome microRNA screening identifies let-7 and mir-18 as regulators of germ layer formation during early embryogenesis GENES & DEVELOPMENT Colas, A. R., McKeithan, W. L., Cunningham, T. J., Bushway, P. J., Garmire, L. X., Duester, G., Subramaniam, S., Mercola, M. 2012; 26 (23): 2567-2579

    Abstract

    Tight control over the segregation of endoderm, mesoderm, and ectoderm is essential for normal embryonic development of all species, yet how neighboring embryonic blastomeres can contribute to different germ layers has never been fully explained. We postulated that microRNAs, which fine-tune many biological processes, might modulate the response of embryonic blastomeres to growth factors and other signals that govern germ layer fate. A systematic screen of a whole-genome microRNA library revealed that the let-7 and miR-18 families increase mesoderm at the expense of endoderm in mouse embryonic stem cells. Both families are expressed in ectoderm and mesoderm, but not endoderm, as these tissues become distinct during mouse and frog embryogenesis. Blocking let-7 function in vivo dramatically affected cell fate, diverting presumptive mesoderm and ectoderm into endoderm. siRNA knockdown of computationally predicted targets followed by mutational analyses revealed that let-7 and miR-18 down-regulate Acvr1b and Smad2, respectively, to attenuate Nodal responsiveness and bias blastomeres to ectoderm and mesoderm fates. These findings suggest a crucial role for the let-7 and miR-18 families in germ layer specification and reveal a remarkable conservation of function from amphibians to mammals.

    View details for DOI 10.1101/gad.200758.112

    View details for Web of Science ID 000311944000002

    View details for PubMedID 23152446

    View details for PubMedCentralID PMC3521625

  • Synthesis and SAR of b-Annulated 1,4-Dihydropyridines Define Cardiomyogenic Compounds as Novel Inhibitors of TGF beta Signaling JOURNAL OF MEDICINAL CHEMISTRY Schade, D., Lanier, M., Willems, E., Okolotowicz, K., Bushway, P., Wahlquist, C., Gilley, C., Mercola, M., Cashman, J. R. 2012; 55 (22): 9946-9957

    Abstract

    A medium-throughput murine embryonic stem cell (mESC)-based high-content screening of 17000 small molecules for cardiogenesis led to the identification of a b-annulated 1,4-dihydropyridine (1,4-DHP) that inhibited transforming growth factor β (TGFβ)/Smad signaling by clearing the type II TGFβ receptor from the cell surface. Because this is an unprecedented mechanism of action, we explored the series' structure-activity relationship (SAR) based on TGFβ inhibition, and evaluated SAR aspects for cell-surface clearance of TGFβ receptor II (TGFBR2) and for biological activity in mESCs. We determined a pharmacophore and generated 1,4-DHPs with IC(50)s for TGFβ inhibition in the nanomolar range (e.g., compound 28, 170 nM). Stereochemical consequences of a chiral center at the 4-position was evaluated, revealing 10- to 15-fold more potent TGFβ inhibition for the (+)- than the (-) enantiomer. This stereopreference was not observed for the low level inhibition against Activin A signaling and was reversed for effects on calcium handling in HL-1 cells.

    View details for DOI 10.1021/jm301144g

    View details for Web of Science ID 000311461500045

    View details for PubMedID 23130626

    View details for PubMedCentralID PMC3518459

  • High throughput measurement of Ca2+ dynamics for drug risk assessment in human stem cell-derived cardiomyocytes by kinetic image cytometry JOURNAL OF PHARMACOLOGICAL AND TOXICOLOGICAL METHODS Cerignoli, F., Charlot, D., Whittaker, R., Ingermanson, R., Gehalot, P., Savchenko, A., Gallacher, D. J., Towart, R., Price, J. H., McDonough, P. M., Mercola, M. 2012; 66 (3): 246-256

    Abstract

    Current methods to measure physiological properties of cardiomyocytes and predict fatal arrhythmias that can cause sudden death, such as Torsade de Pointes, lack either the automation and throughput needed for early-stage drug discovery and/or have poor predictive value. To increase throughput and predictive power of in vitro assays, we developed kinetic imaging cytometry (KIC) for automated cell-by-cell analyses via intracellular fluorescence Ca²⁺ indicators. The KIC instrument simultaneously records and analyzes intracellular calcium concentration [Ca²⁺](i) at 30-ms resolution from hundreds of individual cells/well of 96-well plates in seconds, providing kinetic details not previously possible with well averaging technologies such as plate readers. Analyses of human embryonic stem cell and induced pluripotent stem cell-derived cardiomyocytes revealed effects of known cardiotoxic and arrhythmogenic drugs on kinetic parameters of Ca²⁺ dynamics, suggesting that KIC will aid in the assessment of cardiotoxic risk and in the elucidation of pathogenic mechanisms of heart disease associated with drugs treatment and/or genetic background.

    View details for DOI 10.1016/j.vascn.2012.08.167

    View details for Web of Science ID 000311489100006

    View details for PubMedID 22926323

    View details for PubMedCentralID PMC3667588

  • TGF beta-Dependent Epithelial-to-Mesenchymal Transition Is Required to Generate Cardiospheres from Human Adult Heart Biopsies STEM CELLS AND DEVELOPMENT Forte, E., Miraldi, F., Chimenti, I., Angelini, F., Zeuner, A., Giacomello, A., Mercola, M., Messina, E. 2012; 21 (17): 3081-3090

    Abstract

    Autologous cardiac progenitor cells (CPCs) isolated as cardiospheres (CSps) represent a promising candidate for cardiac regenerative therapy. A better understanding of the origin and mechanisms underlying human CSps formation and maturation is undoubtedly required to enhance their cardiomyogenic potential. Epithelial-to-mesenchymal transition (EMT) is a key morphogenetic process that is implicated in the acquisition of stem cell-like properties in different adult tissues, and it is activated in the epicardium after ischemic injury to the heart. We investigated whether EMT is involved in the formation and differentiation of human CSps, revealing that an up-regulation of the expression of EMT-related genes accompanies CSps formation that is relative to primary explant-derived cells and CSp-derived cells grown in a monolayer. EMT and CSps formation is enhanced in the presence of transforming growth factor β1 (TGFβ1) and drastically blocked by the type I TGFβ-receptor inhibitor SB431452, indicating that TGFβ-dependent EMT is essential for the formation of these niche-like 3D-multicellular clusters. Since TGFβ is activated in the myocardium in response to injury, our data suggest that CSps formation mimics an adaptive mechanism that could potentially be enhanced to increase in vivo or ex vivo regenerative potential of adult CPCs.

    View details for DOI 10.1089/scd.2012.0277

    View details for Web of Science ID 000310840500002

    View details for PubMedID 22765842

    View details for PubMedCentralID PMC4146498

  • Serum-free generation of multipotent mesoderm (Kdr+) progenitor cells in mouse embryonic stem cells for functional genomics screening. Current protocols in stem cell biology McKeithan, W. L., Colas, A. R., Bushway, P. J., Ray, S., Mercola, M. 2012; Chapter 1: Unit 1F 13-?

    Abstract

    This unit describes a robust protocol for producing multipotent Kdr-expressing mesoderm progenitor cells in serum-free conditions, and for functional genomics screening using these cells. Kdr-positive cells are able to differentiate into a wide array of mesodermal derivatives, including vascular endothelial cells, cardiomyocytes, hematopoietic progenitors, and smooth muscle cells. The efficient generation of such progenitor cells is of particular interest because it permits subsequent steps in cardiovascular development to be analyzed in detail, including deciphering the mechanisms that direct differentiation. In addition, the oligonucleotide transfection protocol used to functionally screen siRNA and miRNA libraries is a powerful tool to reveal networks of genes, signaling proteins, and miRNAs that control the diversification of cardiovascular lineages from multipotent progenitors. Technical limitations, troubleshooting, and potential applications of these methods are discussed.

    View details for DOI 10.1002/9780470151808.sc01f13s23

    View details for PubMedID 23154934

    View details for PubMedCentralID PMC3562707

  • Identification of a specific reprogramming-associated epigenetic signature in human induced pluripotent stem cells PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Ruiz, S., Diep, D., Gore, A., Panopoulos, A. D., Montserrat, N., Plongthongkum, N., Kumar, S., Fung, H., Giorgetti, A., Bilic, J., Batchelder, E. M., Zaehres, H., Kan, N. G., Schoeler, H. R., Mercola, M., Zhang, K., Izpisua Belmonte, J. C. 2012; 109 (40): 16196-16201

    Abstract

    Generation of human induced pluripotent stem cells (hiPSCs) by the expression of specific transcription factors depends on successful epigenetic reprogramming to a pluripotent state. Although hiPSCs and human embryonic stem cells (hESCs) display a similar epigenome, recent reports demonstrated the persistence of specific epigenetic marks from the somatic cell type of origin and aberrant methylation patterns in hiPSCs. However, it remains unknown whether the use of different somatic cell sources, encompassing variable levels of selection pressure during reprogramming, influences the level of epigenetic aberrations in hiPSCs. In this work, we characterized the epigenomic integrity of 17 hiPSC lines derived from six different cell types with varied reprogramming efficiencies. We demonstrate that epigenetic aberrations are a general feature of the hiPSC state and are independent of the somatic cell source. Interestingly, we observe that the reprogramming efficiency of somatic cell lines inversely correlates with the amount of methylation change needed to acquire pluripotency. Additionally, we determine that both shared and line-specific epigenetic aberrations in hiPSCs can directly translate into changes in gene expression in both the pluripotent and differentiated states. Significantly, our analysis of different hiPSC lines from multiple cell types of origin allow us to identify a reprogramming-specific epigenetic signature comprised of nine aberrantly methylated genes that is able to segregate hESC and hiPSC lines regardless of the somatic cell source or differentiation state.

    View details for DOI 10.1073/pnas.1202352109

    View details for Web of Science ID 000309611400053

    View details for PubMedID 22991473

    View details for PubMedCentralID PMC3479609

  • A Nodal-to-TGF beta Cascade Exerts Biphasic Control Over Cardiopoiesis CIRCULATION RESEARCH Cai, W., Guzzo, R. M., Wei, K., Willems, E., Davidovics, H., Mercola, M. 2012; 111 (7): 876-?

    Abstract

    The transforming growth factor-β (TGFβ) family member Nodal promotes cardiogenesis, but the mechanism is unclear despite the relevance of TGFβ family proteins for myocardial remodeling and regeneration.To determine the function(s) of TGFβ family members during stem cell cardiogenesis.Murine embryonic stem cells were engineered with a constitutively active human type I Nodal receptor (caACVR1b) to mimic activation by Nodal and found to secrete a paracrine signal that promotes cardiogenesis. Transcriptome and gain- and loss-of-function studies identified the factor as TGFβ2. Both Nodal and TGFβ induced early cardiogenic progenitors in embryonic stem cell cultures at day 0 to 2 of differentiation. However, Nodal expression declines by day 4 due to feedback inhibition, whereas TGFβ persists. At later stages (days 4-6), TGFβ suppresses the formation of cardiomyocytes from multipotent Kdr(+) progenitors while promoting the differentiation of vascular smooth muscle and endothelial cells.Nodal induces TGFβ, and both stimulate the formation of multipotent cardiovascular Kdr(+) progenitors. TGFβ, however, becomes uniquely responsible for controlling subsequent lineage segregation by stimulating vascular smooth muscle and endothelial lineages and simultaneously blocking cardiomyocyte differentiation.

    View details for DOI 10.1161/CIRCRESAHA.112.270272

    View details for Web of Science ID 000308868800014

    View details for PubMedID 22872153

    View details for PubMedCentralID PMC3766357

  • Image-based automatic calcium transient analysis for early cardiotoxicity testing in hiPSC-derived cardiomyocytes Mercola, M., Cerignoli, F., Whittaker, R., McDonough, P., Ingermanson, R., Towart, R., Gallacher, D. J., Price, J. ELSEVIER SCIENCE INC. 2012: 170
  • APJ acts as a dual receptor in cardiac hypertrophy NATURE Scimia, M. C., Hurtado, C., Ray, S., Metzler, S., Wei, K., Wang, J., Woods, C. E., Purcell, N. H., Catalucci, D., Akasaka, T., Bueno, O. F., Vlasuk, G. P., Kaliman, P., Bodmer, R., Smith, L. H., Ashley, E., Mercola, M., Brown, J. H., Ruiz-Lozano, P. 2012; 488 (7411): 394-398

    Abstract

    Cardiac hypertrophy is initiated as an adaptive response to sustained overload but progresses pathologically as heart failure ensues. Here we report that genetic loss of APJ, a G-protein-coupled receptor, confers resistance to chronic pressure overload by markedly reducing myocardial hypertrophy and heart failure. In contrast, mice lacking apelin (the endogenous APJ ligand) remain sensitive, suggesting an apelin-independent function of APJ. Freshly isolated APJ-null cardiomyocytes exhibit an attenuated response to stretch, indicating that APJ is a mechanosensor. Activation of APJ by stretch increases cardiomyocyte cell size and induces molecular markers of hypertrophy. Whereas apelin stimulates APJ to activate Gαi and elicits a protective response, stretch signals in an APJ-dependent, G-protein-independent fashion to induce hypertrophy. Stretch-mediated hypertrophy is prevented by knockdown of β-arrestins or by pharmacological doses of apelin acting through Gαi. Taken together, our data indicate that APJ is a bifunctional receptor for both mechanical stretch and the endogenous peptide apelin. By sensing the balance between these stimuli, APJ occupies a pivotal point linking sustained overload to cardiomyocyte hypertrophy.

    View details for DOI 10.1038/nature11263

    View details for Web of Science ID 000307501000045

    View details for PubMedID 22810587

    View details for PubMedCentralID PMC3422434

  • Transcription factors ETS2 and MESP1 transdifferentiate human dermal fibroblasts into cardiac progenitors PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Islas, J. F., Liu, Y., Weng, K., Robertson, M. J., Zhang, S., Prejusa, A., Harger, J., Tikhomirova, D., Chopra, M., Iyer, D., Mercola, M., Oshima, R. G., Willerson, J. T., Potaman, V. N., Schwartz, R. J. 2012; 109 (32): 13016-13021

    Abstract

    Unique insights for the reprograming of cell lineages have come from embryonic development in the ascidian Ciona, which is dependent upon the transcription factors Ci-ets1/2 and Ci-mesp to generate cardiac progenitors. We tested the idea that mammalian v-ets erythroblastosis virus E26 oncogene homolog 2 (ETS2) and mesoderm posterior (MESP) homolog may be used to convert human dermal fibroblasts into cardiac progenitors. Here we show that murine ETS2 has a critical role in directing cardiac progenitors during cardiopoiesis in embryonic stem cells. We then use lentivirus-mediated forced expression of human ETS2 to convert normal human dermal fibroblasts into replicative cells expressing the cardiac mesoderm marker KDR(+). However, although neither ETS2 nor the purported cardiac master regulator MESP1 can by themselves generate cardiac progenitors de novo from fibroblasts, forced coexpression of ETS2 and MESP1 or cell treatment with purified proteins reprograms fibroblasts into cardiac progenitors, as shown by the de novo appearance of core cardiac transcription factors, Ca(2+) transients, and sarcomeres. Our data indicate that ETS2 and MESP1 play important roles in a genetic network that governs cardiopoiesis.

    View details for DOI 10.1073/pnas.1120299109

    View details for Web of Science ID 000307551700041

    View details for PubMedID 22826236

    View details for PubMedCentralID PMC3420197

  • Small Molecule-Mediated TGF-beta Type II Receptor Degradation Promotes Cardiomyogenesis in Embryonic Stem Cells CELL STEM CELL Willems, E., Cabral-Teixeira, J., Schade, D., Cai, W., ReeveS, P., Bushway, P. J., Lanier, M., Walsh, C., Kirchhausen, T., Izpisua Belmonte, J. C., Cashman, J., Mercola, M. 2012; 11 (2): 242-252

    Abstract

    The cellular signals controlling the formation of cardiomyocytes, vascular smooth muscle, and endothelial cells from stem cell-derived mesoderm are poorly understood. To identify these signals, a mouse embryonic stem cell (ESC)-based differentiation assay was screened against a small molecule library resulting in a 1,4-dihydropyridine inducer of type II TGF-β receptor (TGFBR2) degradation-1 (ITD-1). ITD analogs enhanced proteasomal degradation of TGFBR2, effectively clearing the receptor from the cell surface and selectively inhibiting intracellular signaling (IC(50) ~0.4-0.8 μM). ITD-1 was used to evaluate TGF-β involvement in mesoderm formation and cardiopoietic differentiation, which occur sequentially during early development, revealing an essential role in both processes in ESC cultures. ITD-1 selectively enhanced the differentiation of uncommitted mesoderm to cardiomyocytes, but not to vascular smooth muscle and endothelial cells. ITD-1 is a highly selective TGF-β inhibitor and reveals an unexpected role for TGF-β signaling in controlling cardiomyocyte differentiation from multipotent cardiovascular precursors.

    View details for DOI 10.1016/j.stem.2012.04.025

    View details for Web of Science ID 000307432600014

    View details for PubMedID 22862949

    View details for PubMedCentralID PMC3419596

  • A Novel TGFb Selective Inhibitor Drives Cardiogenesis in Embryonic Stem Cells Willems, E., Teixeira, J., Schade, D., Lanier, M., Bushway, P., Cashman, J., Mercola, M. LIPPINCOTT WILLIAMS & WILKINS. 2012
  • RBPJ Controls the Angiogenic Response of Mouse Adult Cardiomyocytes Trelles, R., Scimia, M., Lozano, P., Mercola, M. LIPPINCOTT WILLIAMS & WILKINS. 2012
  • HNF4 alpha Antagonists Discovered by a High-Throughput Screen for Modulators of the Human Insulin Promoter CHEMISTRY & BIOLOGY Kiselyuk, A., Lee, S., Farber-Katz, S., Zhang, M., Athavankar, S., Cohen, T., Pinkerton, A. B., Ye, M., Bushway, P., Richardson, A. D., Hostetler, H. A., Rodriguez-Lee, M., Huang, L., Spangler, B., Smith, L., Higginbotham, J., Cashman, J., Freeze, H., Itkin-Ansari, P., Dawson, M. I., Schroeder, F., Cang, Y., Mercola, M., Levine, F. 2012; 19 (7): 806-818

    Abstract

    Hepatocyte nuclear factor (HNF)4α is a central regulator of gene expression in cell types that play a critical role in metabolic homeostasis, including hepatocytes, enterocytes, and pancreatic β cells. Although fatty acids were found to occupy the HNF4α ligand-binding pocket and were proposed to act as ligands, there is controversy about both the nature of HNF4α ligands as well as the physiological role of the binding. Here, we report the discovery of potent synthetic HNF4α antagonists through a high-throughput screen for effectors of the human insulin promoter. These molecules bound to HNF4α with high affinity and modulated the expression of known HNF4α target genes. Notably, they were found to be selectively cytotoxic to cancer cell lines in vitro and in vivo, although in vivo potency was limited by suboptimal pharmacokinetic properties. The discovery of bioactive modulators for HNF4α raises the possibility that diseases involving HNF4α, such as diabetes and cancer, might be amenable to pharmacologic intervention by modulation of HNF4α activity.

    View details for DOI 10.1016/j.chembiol.2012.05.014

    View details for Web of Science ID 000307261100007

    View details for PubMedID 22840769

    View details for PubMedCentralID PMC3447631

  • Meeting review: cardiomyocyte regeneration and protection, La Jolla, California, June 2011. Mercola, M., Doevendans, P. 2012: 100–105

    View details for DOI 10.1007/s12265-011-9323-x

    View details for PubMedID 22057688

  • Wnt Inhibition Correlates with Human Embryonic Stem Cell Cardiomyogenesis: A Structure-Activity Relationship Study Based on Inhibitors for the Wnt Response JOURNAL OF MEDICINAL CHEMISTRY Lanier, M., Schade, D., Willems, E., Tsuda, M., Spiering, S., Kalisiak, J., Mercola, M., Cashman, J. R. 2012; 55 (2): 697-708

    Abstract

    Human embryonic stem cell-based high-content screening of 550 known signal transduction modulators showed that one "lead" (1, a recently described inhibitor of the proteolytic degradation of Axin) stimulated cardiomyogenesis. Because Axin controls canonical Wnt signaling, we conducted an investigation to determine whether the cardiogenic activity of 1 is Wnt-dependent, and we developed a structure-activity relationship to optimize the cardiogenic properties of 1. We prepared analogues with a range of potencies (low nanomolar to inactive) for Wnt/β-catenin inhibition and for cardiogenic induction. Both functional activities correlated positively (r(2) = 0.72). The optimal compounds induced cardiogenesis 1.5-fold greater than 1 at 30-fold lower concentrations. In contrast, no correlation was observed for cardiogenesis and modulation of transforming growth factor β (TGFβ)/Smad signaling that prominently influences cardiogenesis. Taken together, these data show that Wnt signaling inhibition is essential for cardiogenic activity and that the pathway can be targeted for the design of druglike cardiogenic molecules.

    View details for DOI 10.1021/jm2010223

    View details for Web of Science ID 000299453300013

    View details for PubMedID 22191557

    View details for PubMedCentralID PMC3335202

  • Laser-Based Propagation of Human iPS and ES Cells Generates Reproducible Cultures with Enhanced Differentiation Potential STEM CELLS INTERNATIONAL Elliott, K., Peterson, C., Soundararajan, A., Kan, N., Nelson, B., Spiering, S., Mercola, M., Bright, G. R. 2012; 2012: 926463

    Abstract

    Proper maintenance of stem cells is essential for successful utilization of ESCs/iPSCs as tools in developmental and drug discovery studies and in regenerative medicine. Standardization is critical for all future applications of stem cells and necessary to fully understand their potential. This study reports a novel approach for the efficient, consistent expansion of human ESCs and iPSCs using laser sectioning, instead of mechanical devices or enzymes, to divide cultures into defined size clumps for propagation. Laser-mediated propagation maintained the pluripotency, quality, and genetic stability of ESCs/iPSCs and led to enhanced differentiation potential. This approach removes the variability associated with ESC/iPSC propagation, significantly reduces the expertise, labor, and time associated with manual passaging techniques and provides the basis for scalable delivery of standardized ESC/iPSC lines. Adoption of standardized protocols would allow researchers to understand the role of genetics, environment, and/or procedural effects on stem cells and would ensure reproducible production of stem cell cultures for use in clinical/therapeutic applications.

    View details for DOI 10.1155/2012/926463

    View details for Web of Science ID 000323785300001

    View details for PubMedID 22701128

    View details for PubMedCentralID PMC3369526

  • SMALL MOLECULE-MEDIATED TGF β TYPE II RECEPTOR DEGRADATION PROMOTES CARDIOMYOGENESIS IN EMBRYONIC STEM CELLS Cashman, J., Willems, E., Teixeira, J. C., Schade, D., Reeves, P., Bushway, P. J., Lanier, M., Cai, W., Walsh, C., Izpisua-Belmonte, J., Mercola, M. INFORMA HEALTHCARE. 2012: 65–66
  • Fine-Tuning of Drp1/Fis1 Availability by AKAP121/Siah2 Regulates Mitochondrial Adaptation to Hypoxia MOLECULAR CELL Kim, H., Scimia, M. C., Wilkinson, D., Trelles, R. D., Wood, M. R., Bowtell, D., Dillin, A., Mercola, M., Ronai, Z. A. 2011; 44 (4): 532-544

    Abstract

    Defining the mechanisms underlying the control of mitochondrial fusion and fission is critical to understanding cellular adaptation to diverse physiological conditions. Here we demonstrate that hypoxia induces fission of mitochondrial membranes, dependent on availability of the mitochondrial scaffolding protein AKAP121. AKAP121 controls mitochondria dynamics through PKA-dependent inhibitory phosphorylation of Drp1 and PKA-independent inhibition of Drp1-Fis1 interaction. Reduced availability of AKAP121 by the ubiquitin ligase Siah2 relieves Drp1 inhibition by PKA and increases its interaction with Fis1, resulting in mitochondrial fission. High AKAP121 levels, seen in cells lacking Siah2, attenuate fission and reduce apoptosis of cardiomyocytes under simulated ischemia. Infarct size and degree of cell death were reduced in Siah2(-/-) mice subjected to myocardial infarction. Inhibition of Siah2 or Drp1 in hatching C. elegans reduces their life span. Through modulating Fis1/Drp1 complex availability, our studies identify Siah2 as a key regulator of hypoxia-induced mitochondrial fission and its physiological significance in ischemic injury and nematode life span.

    View details for DOI 10.1016/j.molcel.2011.08.045

    View details for Web of Science ID 000297387800006

    View details for PubMedID 22099302

    View details for PubMedCentralID PMC3360955

  • Cardiomyocytes from stem cells: Towards "Disease in a dish" Cashman, J. R., Lanier, M., Schade, D., Willems, E., Tsuda, M., Mercola, M. INFORMA HEALTHCARE. 2011: 81
  • Small-Molecule Inhibitors of the Wnt Pathway Potently Promote Cardiomyocytes From Human Embryonic Stem Cell-Derived Mesoderm CIRCULATION RESEARCH Willems, E., Spiering, S., Davidovics, H., Lanier, M., Xia, Z., Dawson, M., Cashman, J., Mercola, M. 2011; 109 (4): 360-364

    Abstract

    Human embryonic stem cells can form cardiomyocytes when cultured under differentiation conditions. Although the initiating step of mesoderm formation is well characterized, the subsequent steps that promote for cardiac lineages are poorly understood and limit the yield of cardiomyocytes.Our aim was to develop a human embryonic stem cell-based high-content screening assay to discover small molecules that drive cardiogenic differentiation after mesoderm is established to improve our understanding of the biology involved. Screening of libraries of small-molecule pathway modulators was predicted to provide insight into the cellular proteins and signaling pathways that control stem cell cardiogenesis.Approximately 550 known pathway modulators were screened in a high-content screening assay, with hits being called out by the appearance of a red fluorescent protein driven by the promoter of the cardiac-specific MYH6 gene. One potent small molecule was identified that inhibits transduction of the canonical Wnt response within the cell, which demonstrated that Wnt inhibition alone was sufficient to generate cardiomyocytes from human embryonic stem cell-derived mesoderm cells. Transcriptional profiling of inhibitor-treated compared with vehicle-treated samples further indicated that inhibition of Wnt does not induce other mesoderm lineages. Notably, several other Wnt inhibitors were very efficient in inducing cardiogenesis, including a molecule that prevents Wnts from being secreted by the cell, which confirmed that Wnt inhibition was the relevant biological activity.Pharmacological inhibition of Wnt signaling is sufficient to drive human mesoderm cells to form cardiomyocytes; this could yield novel tools for the benefit of pharmaceutical and clinical applications.

    View details for DOI 10.1161/CIRCRESAHA.111.249540

    View details for Web of Science ID 000293504100004

    View details for PubMedID 21737789

    View details for PubMedCentralID PMC3327303

  • A Chemical Biology Approach to Myocardial Regeneration JOURNAL OF CARDIOVASCULAR TRANSLATIONAL RESEARCH Willems, E., Lanier, M., Forte, E., Lo, F., Cashman, J., Mercola, M. 2011; 4 (3): 340–50

    Abstract

    Heart failure is one of the major causes of death in the Western world because cardiac muscle loss is largely irreversible and can lead to a relentless decline in cardiac function. Novel therapies are needed since the only therapy to effectively replace lost myocytes today is transplantation of the entire heart. The advent of embryonic and induced pluripotent stem cell (ESC/iPSC) technologies offers the unprecedented possibility of devising cell replacement therapies for numerous degenerative disorders. Not only are ESCs and iPSCs a plausible source of cardiomyocytes in vitro for transplantation, they are also useful tools to elucidate the biology of stem cells that reside in the adult heart and define signaling molecules that might enhance the limited regenerative capability of the adult human heart. Here, we review the extracellular factors that control stem cell cardiomyogenesis and describe new approaches that combine embryology with stem cell biology to discover drug-like small molecules that stimulate cardiogenesis and potentially contribute to the development of pharmaceutical strategies for heart muscle regeneration.

    View details for DOI 10.1007/s12265-011-9270-6

    View details for Web of Science ID 000290809800011

    View details for PubMedID 21424858

    View details for PubMedCentralID PMC3327297

  • Cardiac muscle regeneration: lessons from development GENES & DEVELOPMENT Mercola, M., Ruiz-Lozano, P., Schneider, M. D. 2011; 25 (4): 299-309

    Abstract

    The adult human heart is an ideal target for regenerative intervention since it does not functionally restore itself after injury yet has a modest regenerative capacity that could be enhanced by innovative therapies. Adult cardiac cells with regenerative potential share gene expression signatures with early fetal progenitors that give rise to multiple cardiac cell types, suggesting that the evolutionarily conserved regulatory networks that drive embryonic heart development might also control aspects of regeneration. Here we discuss commonalities of development and regeneration, and the application of the rich developmental biology heritage to achieve therapeutic regeneration of the human heart.

    View details for DOI 10.1101/gad.2018411

    View details for Web of Science ID 000287365000003

    View details for PubMedID 21325131

    View details for PubMedCentralID PMC3042154

  • What Your Heart Doth Know CELL STEM CELL Willems, E., Mercola, M. 2011; 8 (2): 124-126

    Abstract

    Combining embryological insight with careful analysis of early stage cardiomyocyte differentiation, Kattman et al. (2011) in this issue of Cell Stem Cell have defined minimal culture conditions to efficiently produce cardiomyocytes from hESCs and hiPSCs. The lessons learned are applicable to the derivation of other organotypic cell types.

    View details for DOI 10.1016/j.stem.2011.01.003

    View details for Web of Science ID 000287633400003

    View details for PubMedID 21295266

    View details for PubMedCentralID PMC3057384

  • Phenothiazine Neuroleptics Signal to the Human Insulin Promoter as Revealed by a Novel High-Throughput Screen JOURNAL OF BIOMOLECULAR SCREENING Kiselyuk, A., Farber-Katz, S., Cohen, T., Lee, S., Geron, I., Azimi, B., Heynen-Genel, S., Singer, O., Price, J., Mercola, M., Itkin-Ansari, P., Levine, F. 2010; 15 (6): 663-670

    Abstract

    A number of diabetogenic stimuli interact to influence insulin promoter activity, making it an attractive target for both mechanistic studies and therapeutic interventions. High-throughput screening (HTS) for insulin promoter modulators has the potential to reveal novel inputs into the control of that central element of the pancreatic beta-cell. A cell line from human islets in which the expression of insulin and other beta-cell-restricted genes are modulated by an inducible form of the bHLH transcription factor E47 was developed. This cell line, T6PNE, was adapted for HTS by transduction with a vector expressing green fluorescent protein under the control of the human insulin promoter. The resulting cell line was screened against a library of known drugs for those that increase insulin promoter activity. Members of the phenothiazine class of neuroleptics increased insulin gene expression upon short-term exposure. Chronic treatment, however, resulted in suppression of insulin promoter activity, consistent with the effect of phenothiazines observed clinically to induce diabetes in chronically treated patients. In addition to providing insights into previously unrecognized targets and mechanisms of action of phenothiazines, the novel cell line described here provides a broadly applicable platform for mining new molecular drug targets and central regulators of beta-cell differentiated function.

    View details for DOI 10.1177/1087057110372257

    View details for Web of Science ID 000279950400006

    View details for PubMedID 20547533

    View details for PubMedCentralID PMC3374493

  • Alternative splicing regulates mouse embryonic stem cell pluripotency and differentiation PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Salomonis, N., Schlieve, C. R., Pereira, L., Wahlquist, C., Colas, A., Zambon, A. C., Vranizan, K., Spindler, M. J., Pico, A. R., Cline, M. S., Clark, T. A., Williams, A., Blume, J. E., Samal, E., Mercola, M., Merrill, B. J., Conklin, B. R. 2010; 107 (23): 10514-10519

    Abstract

    Two major goals of regenerative medicine are to reproducibly transform adult somatic cells into a pluripotent state and to control their differentiation into specific cell fates. Progress toward these goals would be greatly helped by obtaining a complete picture of the RNA isoforms produced by these cells due to alternative splicing (AS) and alternative promoter selection (APS). To investigate the roles of AS and APS, reciprocal exon-exon junctions were interrogated on a genome-wide scale in differentiating mouse embryonic stem (ES) cells with a prototype Affymetrix microarray. Using a recently released open-source software package named AltAnalyze, we identified 144 genes for 170 putative isoform variants, the majority (67%) of which were predicted to alter protein sequence and domain composition. Verified alternative exons were largely associated with pathways of Wnt signaling and cell-cycle control, and most were conserved between mouse and human. To examine the functional impact of AS, we characterized isoforms for two genes. As predicted by AltAnalyze, we found that alternative isoforms of the gene Serca2 were targeted by distinct microRNAs (miRNA-200b, miRNA-214), suggesting a critical role for AS in cardiac development. Analysis of the Wnt transcription factor Tcf3, using selective knockdown of an ES cell-enriched and characterized isoform, revealed several distinct targets for transcriptional repression (Stmn2, Ccnd2, Atf3, Klf4, Nodal, and Jun) as well as distinct differentiation outcomes in ES cells. The findings herein illustrate a critical role for AS in the specification of ES cells with differentiation, and highlight the utility of global functional analyses of AS.

    View details for DOI 10.1073/pnas.0912260107

    View details for Web of Science ID 000278549300035

    View details for PubMedID 20498046

    View details for PubMedCentralID PMC2890851

  • Non-Cardiomyocytes Influence the Electrophysiological Maturation of Human Embryonic Stem Cell-Derived Cardiomyocytes During Differentiation STEM CELLS AND DEVELOPMENT Kim, C., Majdi, M., Xia, P., Wei, K. A., Talantova, M., Spiering, S., Nelson, B., Mercola, M., Chen, H. V. 2010; 19 (6): 783-795

    Abstract

    Various types of cardiomyocytes undergo changes in automaticity and electrical properties during fetal heart development. Human embryonic stem cell-derived cardiomyocytes (hESC-CMs), like fetal cardiomyocytes, are electrophysiologically immature and exhibit automaticity. We used hESC-CMs to investigate developmental changes in mechanisms of automaticity and to determine whether electrophysiological maturation is driven by an intrinsic developmental clock and/or is regulated by interactions with non-cardiomyocytes in embryoid bodies (EBs). We isolated pure populations of hESC-CMs from EBs by lentivirus-engineered Puromycin resistance at various stages of differentiation. Using pharmacological agents, calcium (Ca(2+)) imaging, and intracellular recording techniques, we found that intracellular Ca(2+)-cycling mechanisms developed early and contributed to dominant automaticity throughout hESC-CM differentiation. Sarcolemmal ion channels evolved later upon further differentiation within EBs and played an increasing role in controlling automaticity and electrophysiological properties of hESC-CMs. In contrast to the development of intracellular Ca(2+)-handling proteins, ion channel development and electrophysiological maturation of hESC-CMs did not occur when hESC-CMs were isolated from EBs early and maintained in culture without further interaction with non-cardiomyocytes. Adding back non-cardiomyocytes to early-isolated hESC-CMs rescued the arrest of electrophysiological maturation, indicating that non-cardiomyocytes in EBs drive electrophysiological maturation of early hESC-CMs. Non-cardiomyocytes in EBs contain most cell types present in the embryonic heart that are known to influence early cardiac development. Our study is the first to demonstrate that non-cardiomyocytes influence electrophysiological maturation of early hESC-CMs in cultures. Defining the nature of these extrinsic signals will aid in the directed maturation of immature hESC-CMs to mitigate arrhythmogenic risks of cell-based therapies.

    View details for DOI 10.1089/scd.2009.0349

    View details for Web of Science ID 000279033900004

    View details for PubMedID 20001453

    View details for PubMedCentralID PMC3135229

  • Hybrid Median Filter Background Estimator for Correcting Distortions in Microtiter Plate Data ASSAY AND DRUG DEVELOPMENT TECHNOLOGIES Bushway, P. J., Azimi, B., Heynen-Genel, S., Price, J. H., Mercola, M. 2010; 8 (2): 238-250

    Abstract

    Microtiter plate (MTP) assays often exhibit distortions, such as caused by edge-dependent drying and robotic fluid handling variation. Distortions vary by assay system but can have both systematic patterns (predictable from plate to plate) and random (sporadic and unpredictable) components. Random errors can be especially difficult to resolve by assay optimization alone, and postassay algorithms reported to date have smoothing effects that often blunt hits. We implemented a 5 x 5 bidirectional hybrid median filter (HMF) as a local background estimator to scale each data point to the MTP global background median and compared it with a recently described Discrete Fourier Transform (DFT) technique for correcting errors on computationally and experimentally generated MTP datasets. Experimental data were generated from a 384-well format fluorescent bioassay using cells engineered to express eGFP and DsRED. MTP arrays were produced with and without control treatments used to simulate hits in random wells. The HMF demonstrated the greatest improvements in MTP coefficients of variation and dynamic range (defined by the ratio of average hit amplitude to standard deviation, SD) for all synthetic and experimental MTPs examined. After HMF application to a MTP of eGFP signal from mouse insulinoma (MIN6) cells obtained by a plate-reader, the assay coefficient of variation (CV) decreased from 8.0% in the raw dataset to 5.1% and the hit amplitudes were reduced by only 1% while the DFT method increased the CV by 36.0% and reduced the hit amplitude by 21%. Thus, our results show that the bidirectional HMF provides superior corrections of MTP data distortions while at the same time preserving hit amplitudes and improving dynamic range. The software to perform hybrid median filter MTP corrections is available at http://bccg.burnham.org/HTS/HMF_Download_Page.aspx, password is pbushway.

    View details for DOI 10.1089/adt.2009.0242

    View details for Web of Science ID 000277283900010

    View details for PubMedID 20230301

    View details for PubMedCentralID PMC3096555

  • DMSO-Free Cryopreservation of Dissociated Human Embryonic Stem Cells Katkov, I. I., Nelson, B., Mercola, M., Snyder, E. Y., Arav, A. MEDIMOND S R L. 2010: 57–61
  • Cardiac myocyte force development during differentiation and maturation Jacot, J. G., Kita-Matsuo, H., Wei, K. A., Chen, H., Omens, J. H., Mercola, M., McCulloch, A. D., Beyar, R., Landesberg, A. WILEY-BLACKWELL. 2010: 121–27

    Abstract

    The maturation of cardiac myocytes during the immediate prenatal period coincides with changes in the mechanical properties of the extracellular matrix. We investigated the effects of extracellular stiffness on cardiomyocyte maturation in neonatal rat ventricular myocytes grown on collagen-coated gels. Cells on 10-kPa substrates developed aligned sarcomeres, while cells on stiffer substrates had unaligned sarcomeres and stress fibers. Cells generated greater mechanical force on gels with stiffness similar to that of the native myocardium than on stiffer or softer substrates. To investigate the differentiation of myocyte progenitors, we used clonal expansion of engineered human embryonic stem cells. Puromycin-selected cardiomyocytes exhibited a gene expression profile similar to that of adult human cardiomyocytes and generated force and action potentials consistent with normal fetal cardiomyocytes. These results suggest that extracellular stiffness significantly affects maturation and differentiation of immature ventricular myocytes.

    View details for DOI 10.1111/j.1749-6632.2009.05091.x

    View details for Web of Science ID 000277731600016

    View details for PubMedID 20201894

    View details for PubMedCentralID PMC2920416

  • Electrophysiological Challenges of Cell-Based Myocardial Repair CIRCULATION Chen, H. V., Kim, C., Mercola, M. 2009; 120 (24): 2496-2508
  • Alternative Splicing in the Differentiation of Human Embryonic Stem Cells into Cardiac Precursors PLOS COMPUTATIONAL BIOLOGY Salomonis, N., Nelson, B., Vranizan, K., Pico, A. R., Hanspers, K., Kuchinsky, A., Ta, L., Mercola, M., Conklin, B. R. 2009; 5 (11): e1000553

    Abstract

    The role of alternative splicing in self-renewal, pluripotency and tissue lineage specification of human embryonic stem cells (hESCs) is largely unknown. To better define these regulatory cues, we modified the H9 hESC line to allow selection of pluripotent hESCs by neomycin resistance and cardiac progenitors by puromycin resistance. Exon-level microarray expression data from undifferentiated hESCs and cardiac and neural precursors were used to identify splice isoforms with cardiac-restricted or common cardiac/neural differentiation expression patterns. Splice events for these groups corresponded to the pathways of cytoskeletal remodeling, RNA splicing, muscle specification, and cell cycle checkpoint control as well as genes with serine/threonine kinase and helicase activity. Using a new program named AltAnalyze (http://www.AltAnalyze.org), we identified novel changes in protein domain and microRNA binding site architecture that were predicted to affect protein function and expression. These included an enrichment of splice isoforms that oppose cell-cycle arrest in hESCs and that promote calcium signaling and cardiac development in cardiac precursors. By combining genome-wide predictions of alternative splicing with new functional annotations, our data suggest potential mechanisms that may influence lineage commitment and hESC maintenance at the level of specific splice isoforms and microRNA regulation.

    View details for DOI 10.1371/journal.pcbi.1000553

    View details for Web of Science ID 000274228500001

    View details for PubMedID 19893621

    View details for PubMedCentralID PMC2764345

  • RBPJK, a Notch Downstream Transcription Factor, Regulates Paracrine Adult Cardiomyocyte Stress Response Trelles, R., Tran, D., Scimia, M., Monosov, A., Monosov, E., Mercola, M. LIPPINCOTT WILLIAMS & WILKINS. 2009: E53
  • APJ Receptor Activity in the Pressure Overload Model Scimia, M. C., Ling, Z., Asaka, T., Bodmer, R., Mercola, M., Ruiz-Lozano, P. LIPPINCOTT WILLIAMS & WILKINS. 2009: E31
  • APJ Receptor Activity Can be Independent by Its Ligand Apelin Scimia, M., Ling, Z., Bodmer, R., Mercola, M., Ruiz-Lozano, P. CHURCHILL LIVINGSTONE INC MEDICAL PUBLISHERS. 2009: S2
  • Natural and Synthetic Regulators of Embryonic Stem Cell Cardiogenesis PEDIATRIC CARDIOLOGY Willems, E., Bushway, P. J., Mercola, M. 2009; 30 (5): 635-642

    Abstract

    Debilitating cardiomyocyte loss underlies the progression to heart failure. Although there have been significant advances in treatment, current therapies are intended to improve or preserve heart function rather than regenerate lost myocardium. A major hurdle in implementing a cell-based regenerative therapy is the inefficient differentiation of cardiomyocytes from either endogenous or exogenous stem cell sources. Moreover, cardiomyocytes that develop in human embryonic stem cell (hESC) or human-induced pluripotent stem cell (hIPSC) cultures are comparatively immature, even after prolonged culture, and differences in their calcium handling, ion channel, and force generation properties relative to adult cardiomyocytes raise concerns of improper integration and function after transplantation. Thus, the discovery of natural and novel small molecule synthetic regulators of differentiation and maturation would accelerate the development of stem-cell-based myocardial therapies. Here, we document recent advances in defining natural signaling pathways that direct the multistep cardiomyogenic differentiation program and the development of small molecules that might be used to enhance differentiation as well as the potential characteristics of lead candidates for pharmaceutical stimulation of endogenous myocardial replacement.

    View details for DOI 10.1007/s00246-009-9409-2

    View details for Web of Science ID 000267033500009

    View details for PubMedID 19319460

    View details for PubMedCentralID PMC3478151

  • Lentiviral Vectors and Protocols for Creation of Stable hESC Lines for Fluorescent Tracking and Drug Resistance Selection of Cardiomyocytes PLOS ONE Kita-Matsuo, H., Barcova, M., Prigozhina, N., Salomonis, N., Wei, K., Jacot, J. G., Nelson, B., Spiering, S., Haverslag, R., Kim, C., Talantova, M., Bajpai, R., Calzolari, D., Terskikh, A., McCulloch, A. D., Price, J. H., Conklin, B. R., Chen, H. S., Mercola, M. 2009; 4 (4)

    Abstract

    Developmental, physiological and tissue engineering studies critical to the development of successful myocardial regeneration therapies require new ways to effectively visualize and isolate large numbers of fluorescently labeled, functional cardiomyocytes.Here we describe methods for the clonal expansion of engineered hESCs and make available a suite of lentiviral vectors for that combine Blasticidin, Neomycin and Puromycin resistance based drug selection of pure populations of stem cells and cardiomyocytes with ubiquitous or lineage-specific promoters that direct expression of fluorescent proteins to visualize and track cardiomyocytes and their progenitors. The phospho-glycerate kinase (PGK) promoter was used to ubiquitously direct expression of histone-2B fused eGFP and mCherry proteins to the nucleus to monitor DNA content and enable tracking of cell migration and lineage. Vectors with T/Brachyury and alpha-myosin heavy chain (alphaMHC) promoters targeted fluorescent or drug-resistance proteins to early mesoderm and cardiomyocytes. The drug selection protocol yielded 96% pure cardiomyocytes that could be cultured for over 4 months. Puromycin-selected cardiomyocytes exhibited a gene expression profile similar to that of adult human cardiomyocytes and generated force and action potentials consistent with normal fetal cardiomyocytes, documenting these parameters in hESC-derived cardiomyocytes and validating that the selected cells retained normal differentiation and function.The protocols, vectors and gene expression data comprise tools to enhance cardiomyocyte production for large-scale applications.

    View details for DOI 10.1371/journal.pone.0005046

    View details for Web of Science ID 000265505700004

    View details for PubMedID 19352491

    View details for PubMedCentralID PMC2662416

  • Discovering potent molecules with human embryonic stem cells to treat heart disease Gilley, C. B., Lanier, M., Okolotowicz, K., Wu, T., Ding, J., Bushway, P., Teixeira, J., Willems, E., Tsuda, M., Colas, A., Xia, Z., Mercola, M., Dawson, M., Cashman, J. AMER CHEMICAL SOC. 2009
  • Deletion of Shp2 Tyrosine Phosphatase in Muscle Leads to Dilated Cardiomyopathy, Insulin Resistance, and Premature Death MOLECULAR AND CELLULAR BIOLOGY Princen, F., Bard, E., Sheikh, F., Zhang, S. S., Wang, J., Zago, W. M., Wu, D., Trelles, R. D., Bailly-Maitre, B., Kahn, C. R., Chen, Y., Reed, J. C., Tong, G. G., Mercola, M., Chen, J., Feng, G. 2009; 29 (2): 378-388

    Abstract

    The intracellular signaling mechanisms underlying the pathogenesis of cardiac diseases are not fully understood. We report here that selective deletion of Shp2, an SH2-containing cytoplasmic tyrosine phosphatase, in striated muscle results in severe dilated cardiomyopathy in mice, leading to heart failure and premature mortality. Development of cardiomyopathy in this mouse model is coupled with insulin resistance, glucose intolerance, and impaired glucose uptake in striated muscle cells. Shp2 deficiency leads to upregulation of leukemia inhibitory factor-stimulated phosphatidylinositol 3-kinase/Akt, Erk5, and Stat3 pathways in cardiomyocytes. Insulin resistance and impaired glucose uptake in Shp2-deficient mice are at least in part due to impaired protein kinase C-zeta/lambda and AMP-kinase activities in striated muscle. Thus, we have generated a mouse line modeling human patients suffering from cardiomyopathy and insulin resistance. This study reinforces a concept that a compound disease with multiple cardiovascular and metabolic disturbances can be caused by a defect in a single molecule such as Shp2, which modulates multiple signaling pathways initiated by cytokines and hormones.

    View details for DOI 10.1128/MCB.01661-08

    View details for Web of Science ID 000262045800007

    View details for PubMedID 19001090

    View details for PubMedCentralID PMC2612510

  • A novel activity of the Dickkopf-1 amino terminal domain promotes axial and heart development independently of canonical Wnt inhibition DEVELOPMENTAL BIOLOGY Korol, O., Gupta, R. W., Mercola, M. 2008; 324 (1): 131-138

    Abstract

    The secreted Dickkopf-1 (Dkk1) protein mediates numerous cell fate decisions and morphogenetic processes. Its carboxyl terminal cysteine-rich region (termed C1) binds LRP5/6 and inhibits canonical Wnt signaling. Paradoxically, the isolated C1 domain of Dkk1 as well as Wnt antagonists that act by sequestering Wnts, such as Frz-B, WIF-1 and Crescent, are poor mimics of the inductive and patterning activities of Dkk1 critical for heart and axial development. To understand the basis for the unique properties of Dkk1, we investigated the function of its amino terminal cysteine-rich region (N1). N1 does not bind LRP or Kremen nor inhibit Wnt signaling and has had no known function. We show that it can synergize with BMP antagonism to induce prechordal and axial mesoderm when expressed as an independent protein in Xenopus embryos. Moreover, we show that it can function in trans to complement the activity of C1 protein to mediate two embryologic functions of Dkk1: induction of chordal and prechordal mesoderm and specification of heart tissue from non-cardiogenic mesoderm. Remarkably, N1 also synergizes with WIF-1 and Crescent, indicating that N1 signals independently of C1 and its interactions with LRP. Since cleavage of Dkk1 is not detected, these results define N1 as a novel signaling domain within the intact protein that is responsible for the potent effects of Dkk1 on the induction and patterning of the body axis and heart. We conclude that this new activity is also likely to synergize with canonical Wnt inhibitory in the numerous developmental and disease processes that involve Dkk1.

    View details for DOI 10.1016/j.ydbio.2008.09.012

    View details for Web of Science ID 000261837200013

    View details for PubMedID 18840423

    View details for PubMedCentralID PMC3038239

  • Contrasting Expression of Keratins in Mouse and Human Embryonic Stem Cells PLOS ONE Maurer, J., Nelson, B., Cecena, G., Bajpai, R., Mercola, M., Terskikh, A., Oshima, R. G. 2008; 3 (10)

    Abstract

    RNA expression data reveals that human embryonic stem (hES) cells differ from mouse ES (mES) cells in the expression of RNAs for keratin intermediate filament proteins. These differences were confirmed at the cellular and protein level and may reflect a fundamental difference in the epithelial nature of embryonic stem cells derived from mouse and human blastocysts. Mouse ES cells express very low levels of the simple epithelial keratins K8, K18 and K19. By contrast hES cells express moderate levels of the RNAs for these intermediate filament proteins as do mouse stem cells derived from the mouse epiblast. Expression of K8 and K18 RNAs are correlated with increased c-Jun RNA expression in both mouse and human ES cell cultures. However, decreasing K8 and K18 expression associated with differentiation to neuronal progenitor cells is correlated with increasing expression of the Snai2 (Slug) transcriptional repression and not decreased Jun expression. Increasing K7 expression is correlated with increased CDX2 and decreased Oct4 RNA expression associated with the formation of trophoblast derivatives by hES cells. Our study supports the view that hES cells are more similar to mouse epiblast cells than mouse ES cells and is consistent with the epithelial nature of hES cells. Keratin intermediate filament expression in hES cells may modulate sensitivity to death receptor mediated apoptosis and stress.

    View details for DOI 10.1371/journal.pone.0003451

    View details for Web of Science ID 000265125600010

    View details for PubMedID 18941637

    View details for PubMedCentralID PMC2565505

  • Notch activates cell cycle reentry and progression in quiescent cardiomyocytes JOURNAL OF CELL BIOLOGY Campa, V. M., Gutierrez-Lanza, R., Cerignoli, F., Diaz-Trelles, R., Nelson, B., Tsuji, T., Barcova, M., Jiang, W., Mercola, M. 2008; 183 (1): 129-141

    Abstract

    The inability of heart muscle to regenerate by replication of existing cardiomyocytes has engendered considerable interest in identifying developmental or other stimuli capable of sustaining the proliferative capacity of immature cardiomyocytes or stimulating division of postmitotic cardiomyocytes. Here, we demonstrate that reactivation of Notch signaling causes embryonic stem cell-derived and neonatal ventricular cardiomyocytes to enter the cell cycle. The proliferative response of neonatal ventricular cardiomyocytes declines as they mature, such that late activation of Notch triggers the DNA damage checkpoint and G2/M interphase arrest. Notch induces recombination signal-binding protein 1 for Jkappa (RBP-Jkappa)-dependent expression of cyclin D1 but, unlike other inducers, also shifts its subcellular distribution from the cytosol to the nucleus. Nuclear localization of cyclin D1 is independent of RBP-Jkappa. Thus, the influence of Notch on nucleocytoplasmic localization of cyclin D1 is an unanticipated property of the Notch intracellular domain that is likely to regulate the cell cycle in multiple contexts, including tumorigenesis as well as cardiogenesis.

    View details for DOI 10.1083/jcb.200806104

    View details for Web of Science ID 000259985000013

    View details for PubMedID 18838555

    View details for PubMedCentralID PMC2557048

  • A comparative analysis of standard microtiter plate reading versus imaging in cellular assays ASSAY AND DRUG DEVELOPMENT TECHNOLOGIES Bushway, P. J., Mercola, M., Price, J. H. 2008; 6 (4): 557–67

    Abstract

    We evaluated the performance of two plate readers (the Beckman Coulter [Fullerton, CA] DTX and the PerkinElmer [Wellesley, MA] EnVision) and a plate imager (the General Electric [Fairfield, CT] IN Cell 1000 Analyzer) in a primary fluorescent cellular screen of 10,000 Molecular Libraries Screening Center Network library compounds for up- and down-regulation of vascular cell adhesion molecule (VCAM)-1, which has been shown to be up-regulated in atherothrombotic vascular disease and is a general indicator of chronic inflammatory disease. Prior to screening, imaging of a twofold, six-step titration of fluorescent cells in a 384-well test plate showed greater consistency, sensitivity, and dynamic range of signal detection curves throughout the detection range, as compared to the plate readers. With the same 384-well test plate, the detection limits for fluorescent protein-labeled cells on the DTX and EnVision instruments were 2,250 and 560 fluorescent cells per well, respectively, as compared to 280 on the IN Cell 1000. During VCAM screening, sensitivity was critical for detection of antagonists, which reduced brightness of the primary immunofluorescence readout; inhibitor controls yielded Z' values of 0.41 and 0.16 for the IN Cell 1000 and EnVision instruments, respectively. The best 1% of small molecule inhibitors from all platforms were visually confirmed using images from the IN Cell 1000. The EnVision and DTX plate readers mutually identified approximately 57% and 21%, respectively, of the VCAM-1 inhibitors visually confirmed in the IN Cell best 1% of inhibitors. Furthermore, the plate reader hits were largely exclusive, with only 6% agreement across all platforms (three hits out of 47). Taken together, the imager outperformed the plate readers at hit detection in this bimodal assay because of superior sensitivity and had the advantage of speeding hit confirmation during post-acquisition analysis.

    View details for DOI 10.1089/adt.2008.139

    View details for Web of Science ID 000259642400007

    View details for PubMedID 18795873

    View details for PubMedCentralID PMC2956680

  • Natural and small molecule regulators of cardiogenesis Mercola, M. FEDERATION AMER SOC EXP BIOL. 2008
  • Natural and small molecule regulators of stem cell cardiomyocyte differentiation Mercola, M. ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD. 2008: 435
  • Signaling Pathways in Embryonic Heart Induction CARDIOVASCULAR DEVELOPMENT Guzzo, R. M., Foley, A. C., Ibarra, Y. M., Mercola, M., Bodmer, R. 2008; 18: 117–51
  • Automated calcium measurements in live cardiomyocytes Charlot, D., Campa, V., Azimi, B., Mercola, M., Ingermanson, R., McDonough, P. M., Price, J. H., IEEE IEEE. 2008: 316-+
  • Targeting Nanoparticle Probes to Differentiating Stem Cells Cabral-Teixeira, J., Talsky, K., Zhang, L., Maurer, J., Tsuda, M., Chao, Y. S., Prigozhina, N., Price, J., Snyder, E., Mercola, M., Ruoslahti, E., West, M. D., Larocca, D., Laudon, M., Romanowicz, B. CRC PRESS-TAYLOR & FRANCIS GROUP. 2008: 430-+
  • Chemical probes of neural stem cell self-renewal NATURE CHEMICAL BIOLOGY Mercola, M. 2007; 3 (5): 246-247

    View details for DOI 10.1038/nchembio0507-246

    View details for Web of Science ID 000245851100005

    View details for PubMedID 17438546

  • Multiple functions of Cerberus cooperate to induce heart downstream of Nodal DEVELOPMENTAL BIOLOGY Foley, A. C., Korol, O., Timmer, A. M., Mercola, M. 2007; 303 (1): 57-65

    Abstract

    The TGFbeta family member Nodal has been implicated in heart induction through misexpression of a dominant negative version of the type I Nodal receptor (Alk4) and targeted deletion of the co-receptor Cripto in murine ESCs and mouse embryos; however, whether Nodal acts directly or indirectly to induce heart tissue or interacts with other signaling molecules or pathways remained unclear. Here we present Xenopus embryological studies demonstrating an unforeseen role for the DAN family protein Cerberus within presumptive foregut endoderm as essential for differentiation of cardiac mesoderm in response to Nodal. Ectopic activation of Nodal signaling in non-cardiogenic ventroposterior mesendoderm, either by misexpression of the Nodal homologue XNr1 together with Cripto or by a constitutively active Alk4 (caAlk4), induced both cardiac markers and Cerberus. Mosaic lineage tracing studies revealed that Nodal/Cripto and caAlk4 induced cardiac markers cell non-autonomously, thus supporting the idea that Cerberus or another diffusible factor is an essential mediator of Nodal-induced cardiogenesis. Cerberus alone was found sufficient to initiate cardiogenesis at a distance from its site of synthesis. Conversely, morpholino-mediated specific knockdown of Cerberus reduced both endogenous cardiomyogenesis and ectopic heart induction resulting from misactivation of Nodal/Cripto signaling. Since the specific knockdown of Cerberus did not abrogate heart induction by the Wnt antagonist Dkk1, Nodal/Cripto and Wnt antagonists appear to initiate cardiogenesis through distinct pathways. This idea was further supported by the combinatorial effect of morpholino-medicated knockdown of Cerberus and Hex, which is required for Dkk1-induced cardiogenesis, and the differential roles of essential downstream effectors: Nodal pathway activation did not induce the transcriptional repressor Hex while Dkk-1 did not induce Cerberus. These studies demonstrated that cardiogenesis in mesoderm depends on Nodal-mediated induction of Cerberus in underlying endoderm, and that this pathway functions in a pathway parallel to cardiogenesis initiated through the induction of Hex by Wnt antagonists. Both pathways operate in endoderm to initiate cardiogenesis in overlying mesoderm.

    View details for DOI 10.1016/j.ydbio.2006.10.033

    View details for Web of Science ID 000244542800005

    View details for PubMedID 17123501

    View details for PubMedCentralID PMC1855199

  • Cardiac Development of Human Embryonic Stem Cells HUMAN STEM CELL MANUAL: A LABORATORY GUIDE Barcova, M., Campa, V. M., Mercola, M., Loring, J. F., Wesselschmidt, R. L., Schwartz, P. H. 2007: 227–37
  • Toward automated analyses of migration and differentiation in cultured human embryonic stem cells Prigozhina, N. L., Russo, J. A., Pekurovsky, A., Kita-Matsuo, H., Clancy, J. W., Mercola, M., Price, J. H., IEEE IEEE. 2007: 1104–7
  • Developmental patterning of the cardiac atrioventricular canal by Notch and Hairy-related transcription factors DEVELOPMENT Rutenberg, J. B., Fischer, A., Jia, H., Gessler, M., Zhong, T. P., Mercola, M. 2006; 133 (21): 4381-4390

    Abstract

    Mutations in Notch2, Jagged1 or homologs of the Hairy-related transcriptional repressor Hey2 cause congenital malformations involving the non-chamber atrioventricular canal (AVC) and inner curvature (IC) regions of the heart, but the underlying mechanisms have not been investigated. By manipulating signaling directly within the developing chick heart, we demonstrated that Notch2, Hey1 and Hey2 initiate a signaling cascade that delimits the non-chamber AVC and IC regions. Specifically, misactivation of Notch2 signaling, or misexpression of either Hey1 or Hey2, repressed Bmp2. Because Jagged (also known as Serrate in non-mammalian species) ligands were found to be present in prospective chamber myocardium, these data support the model that Notch2 and Hey proteins cause the progressive restriction of Bmp2 expression to within the developing AVC and IC, where it is essential for differentiation. Misactivation or inhibition of Notch2 specifically induced or inhibited Hey1, respectively, but these manipulations did not affect Hey2, implicating Hey1 as the direct mediator of Notch2. Bmp2 within the developing AVC and IC has been shown to induce Tbx2, and we found that Tbx2 misexpression inhibited the expression of both Hey1 and Hey2. Tbx2, therefore, is envisaged to constitute a feedback loop that sharpens the border with the developing AVC and IC by delimiting Hey gene expression to within prospective chamber regions. Analysis of the loss-of-function phenotype in mouse embryos homozygous for targeted disruption of Hey2 revealed an expanded AVC domain of Bmp2. Similarly, zebrafish gridlock (Hey2 homolog) mutant embryos showed ectopic expression of Bmp4, which normally marks AVC myocardium in this species. Thus, Hey pathway regulation of cardiac Bmp appears to be an evolutionarily conserved mechanism to delimit AVC and IC fate, and provides a potential mechanistic explanation for cardiac malformations caused by mutations in Serrate/Jagged1 and Notch signaling components.

    View details for DOI 10.1242/dev.02607

    View details for Web of Science ID 000241217400023

    View details for PubMedID 17021042

    View details for PubMedCentralID PMC3619037

  • Cryopreservation by slow cooling with DMSO diminished production of Oct-4 pluripotency marker in human embryonic stem cells CRYOBIOLOGY Katkov, I. I., Kim, M. S., Bajpai, R., Altman, Y. S., Mercola, M., Loring, J. F., Terskikh, A. V., Snyder, E. Y., Levine, F. 2006; 53 (2): 194-205

    Abstract

    We tested a "standard" cryopreservation protocol (slow cooling with 10% DMSO) on the human embryonic stem cell (hESC) line H9 containing an Oct-4 (POU5F1) promoter-driven, enhanced green fluorescent protein (EGFP) reporter to monitor maintenance of pluripotency. Cells were cooled to -80 degrees C in cryovials and then transferred to a -80 degrees C freezer. Cells were held at -80 degrees C for 3 days ("short-term storage") or 3 months ("long-term storage"). Vials were thawed in a +36 degrees C water bath and cells were cultured for 3, 7, or 14 days. Propidium iodide (PI) was used to assess cell viability by flow cytometry. Control cells were passaged on the same day that the frozen cells were thawed. The majority of cells in control hESC cultures were Oct-4 positive and almost 99% of EGFP+ cells were alive as determined by exclusion of PI. In contrast, the frozen cells, even after 3 days of culture, contained only 50% live cells, and only 10% were EGFP-positive. After 7 days in culture, the proportion of dead cells decreased and there was an increase in the Oct-4-positive population but microscopic examination revealed large patches of EGFP-negative cells within clusters of colonies even after 14 days of culturing. After 3 months of storage at -80 degrees C the deleterious effect of freezing was even more pronounced: the samples regained a quantifiable number of EGFP-positive cells only after 7 days of culturing following thawing. It is concluded that new protocols and media are required for freezing hESC and safe storage at -80 degrees C as well as studies of the mechanisms of stress-related events associated with cell cryopreservation.

    View details for DOI 10.1016/j.cryobiol.2006.05.005

    View details for Web of Science ID 000241145300005

    View details for PubMedID 16839540

  • Beta-cell differentiation from nonendocrine epithelial cells of the adult human pancreas NATURE MEDICINE Hao, E., Tyrberg, B., Itkin-Ansari, P., Lakey, J. R., Geron, I., Monosov, E. Z., Barcova, M., Mercola, M., Levine, F. 2006; 12 (3): 310-316

    Abstract

    The nature and even existence of adult pancreatic endocrine stem or progenitor cells is a subject of controversy in the field of beta-cell replacement for diabetes. One place to search for such cells is in the nonendocrine fraction of cells that remain after islet isolation, which consist of a mixture of epithelia and mesenchyme. Culture in G418 resulted in elimination of the mesenchymal cells, leaving a highly purified population of nonendocrine pancreatic epithelial cells (NEPECs). To evaluate their differentiation potential, NEPECs were heritably marked and transplanted under the kidney capsule of immunodeficient mice. When cotransplanted with fetal pancreatic cells, NEPECs were capable of endocrine differentiation. We found no evidence of beta-cell replication or cell fusion that could have explained the appearance of insulin positive cells from a source other than NEPECs. Nonendocrine-to-endocrine differentiation of NEPECs supports the existence of endocrine stem or progenitor cells within the epithelial compartment of the adult human pancreas.

    View details for DOI 10.1038/nm1367

    View details for Web of Science ID 000235802900030

    View details for PubMedID 16491084

  • Dkk1 coordinates cell migration with inhibition of beta-catenin signaling. Gupta, R. W., Mercola, M. KARGER. 2006
  • Characterization of miRNA Expression in the Differentiation of Human Embryonic Stem Cells into Cardiomyocytes Nelson, B., Landers, M., Barcova, M., Perera, R., Adams, C., Mercola, M. AMER SOC CELL BIOLOGY. 2006
  • High-throughput screening for modulators of stem cell differentiation MEASURING BIOLOGICAL RESPONSES WITH AUTOMATED MICROSCOPY Bushway, P. J., Mercola, M., Inglese, J. 2006; 414: 300–316

    Abstract

    Realizing the potential of stem cell biology requires the modulation of self-renewal and differentiation, both of which are incompletely understood. This chapter describes methods for the design, development, and implementation of cell-based screens of small molecules, genes and expressed proteins for modulation of stem and progenitor cell fate. These include the engineering of embryonic and other stem cells with gene promoter-reporter protein constructs and their application in automated screening. We discuss considerations of promoter reporter selection, assay development and implementation, and image acquisition, analysis, and data handling. Such black-box screens are useful for the identification of probes of developmental processes and should provide tools that will identify druggable targets for biochemical assays.

    View details for DOI 10.1016/S0076-6879(06)14017-3

    View details for Web of Science ID 000243221500017

    View details for PubMedID 17110199

  • Embryonic heart induction Foley, A. C., Gupta, R. W., Guzzo, R. M., Korol, O., Mercola, M., Sideman, S., Beyar, R., Landesberg, A. BLACKWELL PUBLISHING. 2006: 85–96

    Abstract

    We have characterized two signaling pathways that induce heart tissue during embryonic development. The first is initiated by the Wnt antagonist Dickkopf1 (Dkk1) and involves the homeodomain transcription factor Hex. Other Wnt antagonists are less effective and the potency of Dkk1 might be due to synergy between Wnt antagonizing and another, novel activity emanating from its amino terminal cysteine-rich domain. The second signal is initiated by Nodal and its co-receptor Cripto. Importantly, both the Dkk1/Wnt antagonism and Nodal pathways act on the endoderm that underlies the future heart to control secretion of diffusible factors that induce cardiogenesis in adjacent mesoderm. In this article, we summarize data that Dkk1 induces cardiogenic differentiation cell non-autonomously through the action of the homeodomain transcription factor Hex. We also discuss recent data showing that Nodal also acts indirectly through stimulation of the secreted protein Cerberus, which is a member of the differential-screening selected aberrant in neuroblastoma (DAN) family of secreted proteins. Finally, we present the model that signaling from Dkk1 regulates novel activities, in addition to Wnt antagonism, which are essential for progression beyond initiation of cardiogenesis to control later stages of cardiomyocyte differentiation and myocardial tissue organization.

    View details for DOI 10.1196/annals.1380.008

    View details for Web of Science ID 000244100900008

    View details for PubMedID 17132777

  • Natural and small molecule inducers of cardiogenesis Mercola, M., Foley, A. C., Teixeira, J. C., Bushway, P. J., Ibarra, Y., Wei, Z., Kozikowski, A. P., Duester, G., Dawson, M. ELSEVIER SCIENCE BV. 2005: S12
  • Zebrafish narrowminded disrupts the transcription factor prdm1 and is required for neural crest and sensory neuron specification DEVELOPMENTAL BIOLOGY Hernandez-Lagunas, L., Choi, I. F., Kaji, T., Simpson, P., Hershey, C., Zhou, Y., Zon, L., Mercola, M., Artinger, K. B. 2005; 278 (2): 347–57

    Abstract

    Specification of both neural crest cells and Rohon-Beard (RB) sensory neurons involves a complex series of interactions between the neural and non-neural ectoderm. The molecular mechanisms directing this process are not well understood. The zebrafish narrowminded (nrd) mutation is unique, since it is one of two mutations in which defects are observed in both cell populations: it leads to a complete absence of RB neurons and a reduction in neural crest cells and their derivatives. Here, we show that nrd is a mutation in prdm1, a SET/zinc-finger domain transcription factor. A Morpholino-mediated depletion of prdm1 phenocopies the nrd mutation, and conversely overexpression of prdm1 mRNA rescues the nrd RB sensory neuron and neural crest phenotype. prdm1 is expressed at the border of the neural plate within the domain where neural crest cells and RB sensory neurons form. Analysis of prdm1 function by overexpression indicates that prdm1 functions to promote the cell fate specification of both neural crest cells and RB sensory neurons, most likely as a downstream effector of the BMP signaling pathway.

    View details for DOI 10.1016/j.ydbio.2004.11.014

    View details for Web of Science ID 000226970000008

    View details for PubMedID 15680355

    View details for PubMedCentralID PMC4028833

  • Heart induction by Wnt antagonists depends on the homeodomain transcription factor Hex GENES & DEVELOPMENT Foley, A. C., Mercola, M. 2005; 19 (3): 387-396

    Abstract

    Inhibition of canonical Wnt/beta-catenin signaling by Dickkopf-1 (Dkk-1) or Crescent initiates cardiogenesis in vertebrate embryos. However, nearly nothing is known about the downstream effectors of these secreted Wnt antagonists or the mechanism by which they activate heart formation. Here we show that Wnt antagonists in Xenopus stimulate cardiogenesis non-cell-autonomously, up to several cells away from those in which canonical Wnt/beta-catenin signaling is blocked, indicative of an indirect role in heart induction. A screen for downstream mediators revealed that Dkk-1 and other inhibitors of the canonical Wnt pathway induce the homeodomain transcription factor Hex, which is normally expressed in endoderm underlying the presumptive cardiac mesoderm in amphibian, bird, and mammalian embryos. Loss of Hex function blocks both endogenous heart development and ectopic heart induction by Dkk-1. As with the canonical Wnt pathway antagonists, ectopic Hex induces expression of cardiac markers non-cell-autonomously. Thus, to initiate cardiogenesis, Wnt antagonists act on endoderm to up-regulate Hex, which, in turn, controls production of a diffusible heart-inducing factor. This novel function for Hex suggests an etiology for the cardiac malformations in Hex mutant mice and will make possible the isolation of factors that induce heart directly in the mesoderm.

    View details for DOI 10.1101/gad.1279405

    View details for Web of Science ID 000226800100010

    View details for PubMedID 15687261

    View details for PubMedCentralID PMC546516

  • Isoxazolyl-serine-based agonists of peroxisome proliferator-activated receptor: Design, synthesis, and effects on cardiomyocyte differentiation JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wei, Z. L., Petukhov, P. A., Bizik, F., Teixeira, J. C., Mercola, M., Volpe, E. A., Glazer, R. I., Willson, T. M., Kozikowski, A. P. 2004; 126 (51): 16714–15

    Abstract

    The peroxisome proliferator-activated receptors (PPARs) are important molecular targets for the development of drugs for the treatment of human metabolic diseases, inflammation, and cancer. They are known to be activated by a variety of structurally diverse compounds. Using a structure-based drug design approach, we designed and synthesized a series of novel isoxazolyl-serine-based PPAR ligands possessing moderate affinities. Some of the new PPAR ligands were able to stimulate cardiomyocyte differentiation from murine ES cells. Ligand 1a was the most active one tested at concentrations between 1.25 to 20 muM between days 2-6, coinciding with the period when mesodermal cells can be recruited to become cardiomyocytes. Notably, the known PPARalpha, gamma, and delta agonists tested, e.g., fenofibrate, rosiglitazone, and GW501516, were inactive in this assay.

    View details for DOI 10.1021/ja046386l

    View details for Web of Science ID 000225910400015

    View details for PubMedID 15612696

  • No pancreatic endocrine stem cells? NEW ENGLAND JOURNAL OF MEDICINE Levine, F., Mercola, M. 2004; 351 (10): 1024-1026

    View details for Web of Science ID 000223637400015

    View details for PubMedID 15342812

  • Heart induction: Embryology to cardiomyocyte regeneration TRENDS IN CARDIOVASCULAR MEDICINE Foley, A., Mercola, M. 2004; 14 (3): 121–25

    Abstract

    Developmental biologists have uncovered many of the signaling proteins that are required to recruit early embryonic cells to the myocardial lineage. A detailed understanding of their function should provide insights into the difficult task of inducing embryonic stem cells to develop cardiomyocyte precursors for cell-based therapies. These proteins may also prove to be useful to stimulate progenitor cells to differentiate into cardiomyocytes within the damaged heart.

    View details for DOI 10.1016/j.tcm.2004.01.003

    View details for Web of Science ID 000221535500007

    View details for PubMedID 15121161

  • Left-right asymmetry: Nodal points JOURNAL OF CELL SCIENCE Mercola, M. 2003; 116 (16): 3251–57

    Abstract

    The striking left-right asymmetry of visceral organs is known to depend on left- and right-side-specific cascades of gene expression during early embryogenesis. Now, developmental biologists are characterizing the earliest steps in asymmetry determination that dictate the sidedness of asymmetric gene expression. The proteins and structures involved control fascinating physiological processes, such as extracellular fluid flow and membrane voltage potential and yet little is known about how their activities are coordinated to control laterality. By analogy with intercellular signalling in certain epithelial and endothelial cells, however, it is reasonable to speculate that at least three of these players, monocilia, gap junction communication and the Ca2+ channel polycystin-2, participate in a signalling pathway that propagates left-right cues through multicellular fields.

    View details for DOI 10.1242/jcs.00668

    View details for Web of Science ID 000187394800001

    View details for PubMedID 12857784

  • Dkk1 induces heart by stimulating a diffusible intermediary factor Foley, A., Mercola, M. ACADEMIC PRESS INC ELSEVIER SCIENCE. 2003: 488
  • Dix proteins position the neural plate border and determine adjacent cell fates DEVELOPMENT Woda, J. M., Pastagia, J., Mercola, M., Artinger, K. B. 2003; 130 (2): 331–42

    Abstract

    The lateral border of the neural plate is a major source of signals that induce primary neurons, neural crest cells and cranial placodes as well as provide patterning cues to mesodermal structures such as somites and heart. Whereas secreted BMP, FGF and Wnt proteins influence the differentiation of neural and non-neural ectoderm, we show here that members of the Dlx family of transcription factors position the border between neural and non-neural ectoderm and are required for the specification of adjacent cell fates. Inhibition of endogenous Dlx activity in Xenopus embryos with an EnR-Dlx homeodomain fusion protein expands the neural plate into non-neural ectoderm tissue whereas ectopic activation of Dlx target genes inhibits neural plate differentiation. Importantly, the stereotypic pattern of border cell fates in the adjacent ectoderm is re-established only under conditions where the expanded neural plate abuts Dlx-positive non-neural ectoderm. Experiments in which presumptive neural plate was grafted to ventral ectoderm reiterate induction of neural crest and placodal lineages and also demonstrate that Dlx activity is required in non-neural ectoderm for the production of signals needed for induction of these cells. We propose that Dlx proteins regulate intercellular signaling across the interface between neural and non-neural ectoderm that is critical for inducing and patterning adjacent cell fates.

    View details for DOI 10.1242/dev.00212

    View details for Web of Science ID 000180733900009

    View details for PubMedID 12466200

    View details for PubMedCentralID PMC4018238

  • Isolation and characterization of Xenopus Hey-1: A downstream mediator of Notch signaling DEVELOPMENTAL DYNAMICS Rones, M. S., Woda, J., Mercola, M., McLaughlin, K. A. 2002; 225 (4): 554–60

    Abstract

    Regulation of Notch signaling likely occurs, at least in part, at the level of basic helix-loop-helix (bHLH) transcription factors that function downstream of Suppressor of Hairless (Su(H)) in the Notch pathway. To begin to characterize modulation of Notch signaling during organogenesis, we examined the bHLH transcription factor, XHey-1 (hairy related-1) in early Xenopus laevis embryos. XHey-1 is expressed in numerous tissues during early development including the somites, head, embryonic kidneys, and heart. Importantly, the expression of XHey-1 was significantly altered in response to perturbation of Notch signaling by means of inducible constructs that served to either activate or suppress Notch signaling through Su(H) in a temporally controlled manner.

    View details for DOI 10.1002/dvdy.10192

    View details for Web of Science ID 000179635700018

    View details for PubMedID 12454931

  • Asymmetries in H+/K+-ATPase and cell membrane potentials comprise a very early step in left-right patterning CELL Levin, M., Thorlin, T., Robinson, K. R., Nogi, T., Mercola, M. 2002; 111 (1): 77-89

    Abstract

    A pharmacological screen identified the H+ and K+ ATPase transporter as obligatory for normal orientation of the left-right body axis in Xenopus. Maternal H+/K+-ATPase mRNA is symmetrically expressed in the 1-cell Xenopus embryo but becomes localized during the first two cell divisions, demonstrating that asymmetry is generated within two hours postfertilization. Although H+/K+-ATPase subunit mRNAs are symmetrically localized in chick embryos, an endogenous H+/K+-ATPase-dependent difference in membrane voltage potential exists between the left and right sides of the primitive streak. In both species, pharmacologic or genetic perturbation of endogenous H+/K+-ATPase randomized the sided pattern of asymmetrically expressed genes and induced organ heterotaxia. Thus, LR asymmetry determination depends on a very early differential ion flux created by H+/K+-ATPase activity.

    View details for Web of Science ID 000178461900010

    View details for PubMedID 12372302

  • REST mRNA expression in normal and regenerating avian auditory epithelium HEARING RESEARCH Roberson, D. W., Alosi, J. A., Mercola, M., Cotanche, D. A. 2002; 172 (1-2): 62–72

    Abstract

    Hair cells (HCs) and supporting cells (SCs) in the auditory epithelium initially arise from a sheet of undifferentiated cells. Although much has been learned about the initial steps leading to the fate determination of HCs and SCs, respectively, little is known about what molecular events 'finalize' cell fate determination. We investigated the role of repressor element-1 (RE-1) silencing transcription factor (REST), whose inactivation is known to be a requirement for a cell to assume a neuronal identity. Here we show by in situ hybridization (ISH) that SCs express REST messenger RNA (mRNA) but sensory HCs lack detectable expression. Using a more sensitive reverse transcription-polymerase chain reaction assay, however, we detected the presence of a neuron-specific splice variant in the epithelium, suggesting that HCs express REST mRNA at levels too low to be detectable by ISH. In regenerating auditory epithelium, we found that REST mRNA was expressed and upregulated in all remaining cells in the damaged region of the epithelium, consistent with its expression pattern during development prior to neurogenesis. Surprisingly, REST mRNA was also upregulated in SCs in the apical, undamaged region of the epithelium, and readily detectable by ISH in the HCs in this region. This finding suggests that the grossly undamaged region of the epithelium is in fact biochemically altered towards a 'less developed' state. Our results indicate that REST inactivation is an important step in finalizing HC fate in the chick inner ear.

    View details for DOI 10.1016/S0378-5955(02)00512-9

    View details for Web of Science ID 000178608200007

    View details for PubMedID 12361867

  • Wnt antagonism and the initiation of embryonic cardiogenesis Mercola, M. FEDERATION AMER SOC EXP BIOL. 2002: A1087
  • Dlx proteins are required for development of neural crest derived craniofacial cartilages. Pastagia, J., Woda, J., Artinger, K. B., Mercola, M. INT AMER ASSOC DENTAL RESEARCHI A D R/A A D R. 2002: A502
  • The biology of becoming: Cell fate decisions during embryonic kidney development. McLaughlin, K. A., Rones, M. S., Mercola, M. ACADEMIC PRESS INC. 2001: 205
  • A role for Dlx3 in neural plate border formation. Woda, J. M., Pastagia, J., Artinger, K. B., Mercola, M. ACADEMIC PRESS INC. 2001: 216–17
  • Wnt antagonism initiates cardiogenesis in Xenopus laevis GENES & DEVELOPMENT Schneider, V. A., Mercola, M. 2001; 15 (3): 304–15

    Abstract

    Heart induction in Xenopus occurs in paired regions of the dorsoanterior mesoderm in response to signals from the Spemann organizer and underlying dorsoanterior endoderm. These tissues together are sufficient to induce heart formation in noncardiogenic ventral marginal zone mesoderm. Similarly, in avians the underlying definitive endoderm induces cardiogenesis in precardiac mesoderm. Heart-inducing factors in amphibians are not known, and although certain BMPs and FGFs can mimic aspects of cardiogenesis in avians, neither can induce the full range of activities elicited by the inducing tissues. Here we report that the Wnt antagonists Dkk-1 and Crescent can induce heart formation in explants of ventral marginal zone mesoderm. Other Wnt antagonists, including the frizzled domain-containing proteins Frzb and Szl, lacked this activity. Unlike Wnt antagonism, inhibition of BMP signaling did not promote cardiogenesis. Ectopic expression of GSK3beta, which inhibits beta-catenin-mediated Wnt signaling, also induced cardiogenesis in ventral mesoderm. Analysis of Wnt proteins expressed during gastrulation revealed that Wnt3A and Wnt8, but not Wnt5A or Wnt11, inhibited endogenous heart induction. These results indicate that diffusion of Dkk-1 and Crescent from the organizer initiate cardiogenesis in adjacent mesoderm by establishing a zone of low Wnt3A and Wnt8 activity.

    View details for DOI 10.1101/gad.855601

    View details for Web of Science ID 000166875800006

    View details for PubMedID 11159911

    View details for PubMedCentralID PMC312618

  • TGF-beta superfamily signaling and left-right asymmetry. Science's STKE : signal transduction knowledge environment Whitman, M., Mercola, M. 2001; 2001 (64): re1

    Abstract

    Despite an outwardly bilaterally symmetrical appearance, most internal organs of vertebrates display considerable left-right (LR) asymmetry in their anatomy and physiology. The orientation of LR asymmetry with respect to the dorsoventral and anteroposterior body axes is invariant such that fewer than 1 in 10,000 individuals exhibit organ reversals. The stereotypic orientation of LR asymmetry is ensured by distinct left- and right-side signal transduction pathways that are initiated by divergent members of the transforming growth factor-beta (TGF-beta) superfamily of secreted proteins. During early embryogenesis, the TGF-beta-like protein Nodal (or a Nodal-related ortholog) is expressed by the left lateral plate mesoderm and provides essential LR cues to the developing organs. In chick embryos at least, bone morphogenetic protein (BMP) signaling is active on the right side of the embryo and must be inhibited on the left in order for Nodal to be expressed. Thus, at a key point in the determination of LR asymmetry, left-sided signaling is mediated by the transcription factors Smad2 and Smad3 (regulated by Nodal), whereas signaling on the right depends on Smad1 and Smad5 (which are regulated by BMP). This review summarizes the considerable progress that has been made in recent years in understanding the complex network of feedback and feedforward circuitry that regulates both the left- and right-sided pathways. Also discussed is the problem of how signal transduction mediated by the Smad proteins can pattern LR asymmetry without interfering with coincident dorsoventral patterning, which relies on the same Smad proteins.

    View details for DOI 10.1126/stke.2001.64.re1

    View details for PubMedID 11752633

  • Left-right asymmetry determination in vertebrates ANNUAL REVIEW OF CELL AND DEVELOPMENTAL BIOLOGY Mercola, M., Levin, M. 2001; 17: 779–805

    Abstract

    A distinctive and essential feature of the vertebrate body is a pronounced left-right asymmetry of internal organs and the central nervous system. Remarkably, the direction of left-right asymmetry is consistent among all normal individuals in a species and, for many organs, is also conserved across species, despite the normal health of individuals with mirror-image anatomy. The mechanisms that determine stereotypic left-right asymmetry have fascinated biologists for over a century. Only recently, however, has our understanding of the left-right patterning been pushed forward by links to specific genes and proteins. Here we examine the molecular biology of the three principal steps in left-right determination: breaking bilateral symmetry, propagation and reinforcement of pattern, and the translation of pattern into asymmetric organ morphogenesis.

    View details for DOI 10.1146/annurev.cellbio.17.1.779

    View details for Web of Science ID 000172448800023

    View details for PubMedID 11687504

  • Notch regulates cell fate in the developing pronephros DEVELOPMENTAL BIOLOGY McLaughlin, K. A., Rones, M. S., Mercola, M. 2000; 227 (2): 567–80

    Abstract

    The mechanisms that regulate cell fate within the pronephros are poorly understood but are important for the subsequent development of the urogenital system and show many similarities to nephrogenesis in the definitive kidney. Dynamic expression of Notch-1, Serrate-1, and Delta-1 in the developing Xenopus pronephros suggests a role for this pathway in cell fate segregation. Misactivation of Notch signaling using conditionally active forms of either Notch-1 or RBP-J/Su(H) proteins prevented normal duct formation and the proper expression of genetic markers of duct cell differentiation. Inhibition of endogenous Notch signaling elicited the opposite effect. Taken together with the mRNA expression patterns, these data suggest that endogenous Notch signaling functions to inhibit duct differentiation in the dorsoanterior region of the anlage where cells are normally fated to form tubules. In addition, elevated Notch signaling in the pronephric anlage both perturbed the characteristic pattern of the differentiated tubule network and increased the expression of early markers of pronephric precursor cells, Pax-2 and Wilms' tumor suppressor gene (Wt-1). We propose that Notch signaling plays a previously unrecognized role in the early selection of duct and tubule cell fates as well as functioning subsequently to control tubule cell patterning and development.

    View details for DOI 10.1006/dbio.2000.9913

    View details for Web of Science ID 000165363000024

    View details for PubMedID 11071775

  • Expression of connexin 30 in Xenopus embryos and its involvement in hatching gland function DEVELOPMENTAL DYNAMICS Levin, M., Mercola, M. 2000; 219 (1): 96–101

    Abstract

    Connexins are a family of proteins that assemble to form gap junction channels. Cell-cell communication through gap junctions mediates many important events in embryogenesis, including limb patterning, lens physiology, neuronal function, left-right asymmetry, and secretion from gland tissue. We studied the expression of connexin 30 (Cx30) in the Xenopus embryo and find that it is expressed in the developing hatching gland and pronephros. To determine whether its expression plays a functional role in the activity of the hatching gland, we exposed pre-hatching embryos to drugs that block gap junctional communication. This resulted in a continuation of normal growth and development but specifically abolished hatching. The treatment did not affect Cx30 or Xenopus hatching enzyme transcription, suggesting a post-transcriptional effect on Cx30 gap junctions. We conclude that junctional communication, possibly mediated by Cx30, is involved in secretion of hatching enzyme in Xenopus.

    View details for DOI 10.1002/1097-0177(200009)219:1<96::AID-DVDY1034>3.0.CO;2-0

    View details for Web of Science ID 000089062600012

    View details for PubMedID 10974676

  • Serrate and Notch specify cell fates in the heart field by suppressing cardiomyogenesis DEVELOPMENT Rones, M. S., McLaughlin, K. A., Raffin, M., Mercola, M. 2000; 127 (17): 3865–76

    Abstract

    Notch signaling mediates numerous developmental cell fate decisions in organisms ranging from flies to humans, resulting in the generation of multiple cell types from equipotential precursors. In this paper, we present evidence that activation of Notch by its ligand Serrate apportions myogenic and non-myogenic cell fates within the early Xenopus heart field. The crescent-shaped field of heart mesoderm is specified initially as cardiomyogenic. While the ventral region of the field forms the myocardial tube, the dorsolateral portions lose myogenic potency and form the dorsal mesocardium and pericardial roof (Raffin, M., Leong, L. M., Rones, M. S., Sparrow, D., Mohun, T. and Mercola, M. (2000) Dev. Biol., 218, 326-340). The local interactions that establish or maintain the distinct myocardial and non-myocardial domains have never been described. Here we show that Xenopus Notch1 (Xotch) and Serrate1 are expressed in overlapping patterns in the early heart field. Conditional activation or inhibition of the Notch pathway with inducible dominant negative or active forms of the RBP-J/Suppressor of Hairless [Su(H)] transcription factor indicated that activation of Notch feeds back on Serrate1 gene expression to localize transcripts more dorsolaterally than those of Notch1, with overlap in the region of the developing mesocardium. Moreover, Notch pathway activation decreased myocardial gene expression and increased expression of a marker of the mesocardium and pericardial roof, whereas inhibition of Notch signaling had the opposite effect. Activation or inhibition of Notch also regulated contribution of individual cells to the myocardium. Importantly, expression of Nkx2. 5 and Gata4 remained largely unaffected, indicating that Notch signaling functions downstream of heart field specification. We conclude that Notch signaling through Su(H) suppresses cardiomyogenesis and that this activity is essential for the correct specification of myocardial and non-myocardial cell fates.

    View details for Web of Science ID 000089430700021

    View details for PubMedID 10934030

  • Patterning the pronephros: A role for notch signaling in kidney organogenesis McLaughlin, K. A., Rones, M. S., Mercola, M. ACADEMIC PRESS INC. 2000: 251
  • Gap junction-mediated transfer of left-right patterning signals. Levin, M., Mercola, M. FEDERATION AMER SOC EXP BIOL. 2000: A541
  • Subdivision of the cardiac Nkx2.5 expression domain into myogenic and nonmyogenic compartments DEVELOPMENTAL BIOLOGY Raffin, M., Leong, L. M., Rones, M. S., Sparrow, D., Mohun, T., Mercola, M. 2000; 218 (2): 326–40

    Abstract

    Nkx2.5 is expressed in the cardiogenic mesoderm of avian, mouse, and amphibian embryos. To understand how various cardiac fates within this domain are apportioned, we fate mapped the mesodermal XNkx2.5 domain of neural tube stage Xenopus embryos. The lateral portions of the XNkx2.5 expression domain in the neural tube stage embryo (stage 22) form the dorsal mesocardium and roof of the pericardial cavity while the intervening ventral region closes to form the myocardial tube. XNkx2.5 expression is maintained throughout the period of heart tube morphogenesis and differentiation of myocardial, mesocardial, and pericardial tissues. A series of microsurgical experiments showed that myocardial differentiation in the lateral portion of the field is suppressed during normal development by signals from the prospective myocardium and by tissues located more dorsally in the embryo, in particular the neural tube. These signals combine to block myogenesis downstream of XNkx2.5 and at or above the level of contractile protein gene expression. We propose that the entire XNkx2.5/heart field is transiently specified as cardiomyogenic. Suppression of this program redirects lateral cells to adopt dorsal mesocardial and dorsal pericardial fates and subdivides the field into distinct myogenic and nonmyogenic compartments.

    View details for DOI 10.1006/dbio.1999.9579

    View details for Web of Science ID 000085517000018

    View details for PubMedID 10656773

  • Gap junction-mediated transfer of left-right patterning signals in the early chick blastoderm is upstream of Shh asymmetry in the node DEVELOPMENT Levin, M., Mercola, M. 1999; 126 (21): 4703–14

    Abstract

    Invariant patterning of left-right asymmetry during embryogenesis depends upon a cascade of inductive and repressive interactions between asymmetrically expressed genes. Different cascades of asymmetric genes distinguish the left and right sides of the embryo and are maintained by a midline barrier. As such, the left and right sides of an embryo can be viewed as distinct and autonomous fields. Here we describe a series of experiments that indicate that the initiation of these programs requires communication between the two sides of the blastoderm. When deprived of either the left or the right lateral halves of the blastoderm, embryos are incapable of patterning normal left-right gene expression at Hensen's node. Not only are both flanks required, suggesting that there is no single signaling source for LR pattern, but the blastoderm must be intact. These results are consistent with our previously proposed model in which the orientation of LR asymmetry in the frog, Xenopus laevis, depends on large-scale partitioning of LR determinants through intercellular gap junction channels (M. Levin and M. Mercola (1998) Developmental Biology 203, 90-105). Here we evaluate whether gap junctional communication is required for the LR asymmetry in the chick, where it is possible to order early events relative to the well-characterized left and right hierarchies of gene expression. Treatment of cultured chick embryos with lindane, which diminishes gap junctional communication, frequently unbiased normal LR asymmetry of Shh and Nodal gene expression, causing the normally left-sided program to be recapitulated symmetrically on the right side of the embryo. A survey of early expression of connexin mRNAs revealed that Cx43 is present throughout the blastoderm at Hamburger-Hamilton stage 2-3, prior to known asymmetric gene expression. Application of antisense oligodeoxynucleotides or blocking antibody to cultured embryos also resulted in bilateral expression of Shh and Nodal transcripts. Importantly, the node and primitive streak at these stages lack Cx43 mRNA. This result, together with the requirement for an intact blastoderm, suggests that the path of communication through gap junction channels circumvents the node and streak. We propose that left-right information is transferred unidirectionally throughout the epiblast by gap junction channels in order to pattern left-sided Shh expression at Hensen's node.

    View details for Web of Science ID 000083881600003

    View details for PubMedID 10518488

  • Gap junction-mediated transfer of left-right patterning signals Levin, M., Mercola, M. AMER SOC CELL BIOLOGY. 1999: 7A
  • Cerberus regulates left-right asymmetry of the embryonic head and heart CURRENT BIOLOGY Zhu, L., Marvin, M. J., Gardiner, A., Lassar, A. B., Mercola, M., Stern, C. D., Levin, M. 1999; 9 (17): 931–38

    Abstract

    Most of the molecules known to regulate left-right asymmetry in vertebrate embryos are expressed on the left side of the future trunk region of the embryo. Members of the protein family comprising Cerberus and the putative tumour suppressor Dan have not before been implicated in left-right asymmetry. In Xenopus, these proteins have been shown to antagonise members of the transforming growth factor beta (TGF-beta) and Wnt families of signalling proteins.Chick Cerberus (cCer) was found to be expressed in the left head mesenchyme and in the left flank of the embryo. Expression on the left side of the head was controlled by Sonic hedgehog (Shh) acting through the TGF-beta family member Nodal; in the flank, cCer was also regulated by Shh, but independently of Nodal. Surprisingly, although no known targets of Cerberus are expressed asymmetrically on the right side of the embryo at these stages, misexpression of cCer on this side of the embryo led to upregulation of the transcription factor Pitx2 and reversal of the direction of heart and head turning, apparently as independent events. Consistent with the possibility that cCer may be acting on bilaterally expressed TGF-beta family members such as the bone morphogenetic proteins (BMPs), this result was mimicked by right-sided misexpression of the BMP antagonist, Noggin.Our findings suggest that cCer maintains a delicate balance of different TGF-beta family members involved in laterality decisions, and reveal the existence of partially overlapping molecular pathways regulating left-right asymmetry in the head and trunk of the embryo.

    View details for DOI 10.1016/S0960-9822(99)80419-9

    View details for Web of Science ID 000082518200017

    View details for PubMedID 10508582

  • Zebrafish narrowminded suggests a genetic link between formation of neural crest and primary sensory neurons DEVELOPMENT Artinger, K. B., Chitnis, A. B., Mercola, M., Driever, W. 1999; 126 (18): 3969–79

    Abstract

    In the developing vertebrate nervous system, both neural crest and sensory neurons form at the boundary between non-neural ectoderm and the neural plate. From an in situ hybridization based expression analysis screen, we have identified a novel zebrafish mutation, narrowminded (nrd), which reduces the number of early neural crest cells and eliminates Rohon-Beard (RB) sensory neurons. Mosaic analysis has shown that the mutation acts cell autonomously suggesting that nrd is involved in either the reception or interpretation of signals at the lateral neural plate boundary. Characterization of the mutant phenotype indicates that nrd is required for a primary wave of neural crest cell formation during which progenitors generate both RB sensory neurons and neural crest cells. Moreover, the early deficit in neural crest cells in nrd homozygotes is compensated later in development. Thus, we propose that a later wave can compensate for the loss of early neural crest cells but, interestingly, not the RB sensory neurons. We discuss the implications of these findings for the possibility that RB sensory neurons and neural crest cells share a common evolutionary origin.

    View details for Web of Science ID 000082965700001

    View details for PubMedID 10457007

    View details for PubMedCentralID PMC4059008

  • Spatially distinct head and heart inducers within the Xenopus organizer region CURRENT BIOLOGY Schneider, V. A., Mercola, M. 1999; 9 (15): 800–809

    Abstract

    The mouse anterior visceral endoderm, an extraembryonic tissue, expresses several genes essential for normal development of structures rostral to the anterior limit of the notochord and has been termed the head organizer. This tissue also has heart-inducing activity and expresses mCer1 which, like its Xenopus homolog cerberus, can induce markers of cardiac specification and anterior neural tissue when ectopically expressed. We investigated the relationship between head and heart induction in Xenopus embryos, which lack extraembryonic tissues.We found three regions of gene expression in the Xenopus organizer: deep endoderm, which expressed cerberus; prechordal mesoderm, which showed overlapping but non-identical expression of genes characteristic of the murine head organizer, such as XHex and XANF-1; and leading-edge dorsoanterior endoderm, which expressed both cerberus and a subset of the genes expressed by the prechordal mesoderm. Microsurgical ablation of the cerberus-expressing endoderm decreased the incidence of heart, but not head, formation. Removal of prechordal mesoderm, in contrast, caused deficits of anterior head structures. Finally, although misexpression of cerberus induced ectopic heads, it was unable to induce genes thought to participate in head induction.In Xenopus, the cerberus-expressing endoderm is required for heart, but not head, inducing activity. Therefore, this tissue is not the topological equivalent of the murine anterior visceral endoderm. We propose that, in Xenopus, cerberus is redundant to other bone morphogenetic protein (BMP) and Wnt antagonists located in prechordal mesoderm for head induction, but may be necessary for heart induction.

    View details for DOI 10.1016/S0960-9822(99)80363-7

    View details for Web of Science ID 000081850800020

    View details for PubMedID 10469564

  • Spatially distinct head and heart inducers in the Xenopus organiser Schneider, V. A., Mercola, M. ACADEMIC PRESS INC. 1999: 230
  • Zebrafish narrowminded is involved in the specification of neural crest and primary sensory neurons Artinger, K. B., Chitnis, A. B., Driever, W., Mercola, M. ACADEMIC PRESS INC. 1999: 200
  • The role of notch signaling during cardiogenesis Rones, M. S., Mercola, M. ACADEMIC PRESS INC. 1999: 211
  • Embryological basis for cardiac left-right asymmetry SEMINARS IN CELL & DEVELOPMENTAL BIOLOGY Mercola, M. 1999; 10 (1): 109–16

    Abstract

    Asymmetric heart tube looping and chamber morphogenesis is a complex process that is just beginning to be understood at the genetic level. Rightward looping is the first embryological manifestation of consistently oriented, left-right asymmetric development of nearly all visceral organs. Intuitively, invariant anatomical asymmetry must derive from a novel mechanism capable of integrating dorsoventral and anteroposterior information. The details of this process are emerging for several vertebrates and reveal that overall left-right asymmetry, once polarized with respect to dorsoventral and anteroposterior axes, unfolds through distinct left- and right-sided programs of gene expression. These, in turn, regulate expression of cardiac and chamber-specific genes which guide heart morphogenesis and differentiation.

    View details for DOI 10.1006/scdb.1998.0280

    View details for Web of Science ID 000079926500014

    View details for PubMedID 10355035

  • Gap junctions are involved in the early generation of left-right asymmetry DEVELOPMENTAL BIOLOGY Levin, M., Mercola, M. 1998; 203 (1): 90–105

    Abstract

    Invariant left-right asymmetry of the visceral organs is a fundamental feature of vertebrate embryogenesis. While a cascade of asymmetrically expressed genes has been described, the embryonic mechanism that orients the left-right axis relative to the dorsoventral and anteroposterior axes (a prerequisite for asymmetric gene expression) is unknown. We propose that this process involves dorsoventral differences in cell-cell communication through gap junctions composed of connexin proteins. Global modulation of gap junctional states in Xenopus embryos by pharmacological agents specifically induced heterotaxia involving mirror-image reversals of heart, gut, and gall bladder. Greatest sensitivity was observed between st. 5 and st. 12, well before the onset of organogenesis. Moreover, heterotaxia was also induced following microinjection of dominant negative and wild-type connexin mRNAs to modify the endogenous dorsoventral difference in junctional communication. Heterotaxia was induced by either blocking gap junction communication (GJC) dorsally or by introducing communication ventrally (but not the reverse). Both connexin misexpression and exposure to GJC-modifying drugs altered expression of the normally left-sided gene XNR-1, demonstrating that GJC functions upstream of XNR-1 in the pathway that patterns left-right asymmetry. Finally, lineage analysis to follow the progeny of microinjected cells indicated that they generally do not contribute the asymmetric organs. Together with the early sensitivity window, this suggests that GJC functions as part of a fundamental, early aspect of left-right patterning. In addition, we show that a potential regulatory mutation in Connexin43 is sufficient to cause heterotaxia. Despite uncertainty about the prevalence of the serine364 to proline substitution reported in human patients with laterality defects, the mutant protein is both a mild hypomorph and a potent antimorph as determined by the effect of its expression on left-right patterning. Taken together, our data suggest that endogenous dorsoventral differences in GJC within the early embryo are needed to consistently orient left-right asymmetry.

    View details for DOI 10.1006/dbio.1998.9024

    View details for Web of Science ID 000076869400008

    View details for PubMedID 9806775

  • PDGF mediates cardiac microvascular communication JOURNAL OF CLINICAL INVESTIGATION Edelberg, J. M., Aird, W. C., Wu, W., Rayburn, H., Mamuya, W. S., Mercola, M., Rosenberg, R. D. 1998; 102 (4): 837–43

    Abstract

    The diversity of cellular and tissue functions within organs requires that local communication circuits control distinct populations of cells. Recently, we reported that cardiac myocytes regulate the expression of both von Willebrand factor (vWF) and a transgene with elements of the vWF promoter in a subpopulation of cardiac microvascular endothelial cells (J. Cell Biol. 138:1117). The present study explores this communication. Histological examination of the cardiac microvasculature revealed colocalization of the vWF transgene with the PDGF alpha-receptor. Transcript analysis demonstrated that in vitro cardiac microvascular endothelial cells constitutively express PDGF-A, but not B. Cardiac myocytes induced endothelial expression of PDGF-B, resulting in PDGF-AB. Protein measurement and transcript analysis revealed that PDGF-AB, but not PDGF-AA, induced endothelial expression of vWF and its transgene. Antibody neutralization of PDGF-AB blocked the myocyte-mediated induction. Immunostaining demonstrated that vWF induction is confined to PDGF alpha-receptor-positive endothelial cells. Similar experiments revealed that the PDGF-AB/alpha-receptor communication also induces expression of vascular endothelial growth factor and Flk-1, critical components of angiogenesis. The existence of this communication pathway was confirmed in vivo. Injection of PDGF-AB neutralizing antibody into the amniotic fluid surrounding murine embryos extinguished expression of the transgene. In summary, these studies suggest that environmental induction of PDGF-AB/alpha-receptor interaction is central to the regulation of cardiac microvascular endothelial cell hemostatic and angiogenic activity.

    View details for DOI 10.1172/JCI3058

    View details for Web of Science ID 000075556500023

    View details for PubMedID 9710453

    View details for PubMedCentralID PMC508947

  • PDGF: Signaling pathways involved in cellular migration and cell death McLaughlin, K. A., Symes, K., Mercola, M. L. ACADEMIC PRESS INC. 1998: 224
  • Gap junctions are involved in early determination of left-right asymmetry Levin, M., Mercola, M. ACADEMIC PRESS INC. 1998: 160
  • Restriction of the heart field Rones, M. S., Raffin, M. J., Mercola, M. ACADEMIC PRESS INC. 1998: 205
  • The compulsion of chirality: toward an understanding of left-right asymmetry GENES & DEVELOPMENT Levin, M., Mercola, M. 1998; 12 (6): 763–69

    View details for DOI 10.1101/gad.12.6.763

    View details for Web of Science ID 000072770300001

    View details for PubMedID 9512510

  • Small-molecule control of insulin and PDGF receptor signaling and the role of membrane attachment CURRENT BIOLOGY Yang, J. X., Symes, K., Mercola, M., Schreiber, S. L. 1998; 8 (1): 11–18

    Abstract

    Receptor tyrosine kinases (RTKs) regulate the proliferation, differentiation and metabolism of cells, and play key roles in tissue repair, tumorigenesis and development. To facilitate the study of RTKs, we have made conditional alleles that encode monomeric forms of the normally heterotetrameric insulin receptor and monomeric platelet-derived growth factor (PDGF) beta receptors fused to the FK506-binding protein 12 (FKBP12). The chimeric receptors can be induced to undergo dimerization or oligomerization by a small synthetic molecule called FK1012, and the consequences were studied in cells and embryonic tissues.When equipped with an amino-terminal plasma membrane localization sequence and expressed in HEK293 cells, these chimeric receptors could signal to downstream targets as indicated by the FK1012-dependent activation of p70 S6 kinase (p70(S6k)) and mitogen-activated protein (MAP) kinase. In Xenopus embryos, the engineered PDGF receptor protein induced the formation of mesoderm from animal-pole explants in an FK1012-dependent manner. A cytosolic variant of the protein underwent efficient transphosphorylation, yet failed to activate appreciably either p70(S6k) or MAP kinase following treatment with FK1012. These results provide evidence of a requirement for membrane localization of RTKs, consistent with current models of RTK signaling.We have developed an approach using the small molecule FK1012 to conditionally activate chimeric proteins containing FKBP fused to the insulin receptor or to the PDGF beta receptor. Using this system, we were able to induce mesoderm formation in Xenopus animal-cap tissue and to demonstrate that membrane localization is required for RTK signaling in transfected cells. This system should allow the further dissection of RTK-mediated pathways.

    View details for DOI 10.1016/S0960-9822(98)70015-6

    View details for Web of Science ID 000071331700012

    View details for PubMedID 9427627

  • Evolutionary conservation of mechanisms upstream of asymmetric nodal expression: Reconciling chick and Xenopus DEVELOPMENTAL GENETICS Levin, M., Mercola, M. 1998; 23 (3): 185–93

    Abstract

    Recent experiments have suggested a pathway of genes that regulate left-right asymmetry in vertebrate embryogenesis. The most downstream member of this cascade is nodal (XNR-1 in frogs), which is expressed in the left-side lateral mesoderm. Previous work in the chick [Levin, 1998] suggests that an inductive interaction by Shh (Sonic hedgehog) present at the midline was needed for the left-sided expression of nodal, which by default would not be expressed. Interestingly, it has been reported [Lohr et al., 1997] that in Xenopus, right-side mesoderm that is explanted at st. 15 and allowed to develop in culture, goes on to express nodal, suggesting that lateral mesoderm expresses this gene by default and that a repression of nodal by the midline is needed to achieve asymmetry. Such a contradiction raises interesting questions about the degree of conservation of the mechanisms upstream of nodal asymmetry and, in general, about the differences in the LR pathway among species. Thus we examined this issue directly. We show that in the chick, as in the frog, explanted mesoderm from both sides does, indeed, go on to express nodal, including both the medial and lateral expression domains. Ectopic nodal expression in the medial domain on the right side is not sufficient to induce an ectopic lateral domain. We also show that explanted lateral tissue regenerates node/notochord structures exhibiting Shh expression. Furthermore, we show that Xenopus explants done at st. 15 also regenerate notochord by the stage at which XNR-1 would be expressed. Thus explants are not isolated from the influence of the midline. In contrast to the midline repressor model previously suggested [Lohr et al., 1997] to explain the presence of nodal expression in explants, we propose that the expression is due to induction by signals secreted by regenerating node and notochord tissue (Shh in the chick). Thus our results are consistent with Shh being necessary for nodal induction in both species, and we provide an explanation for both sets of data in terms of a single conserved mechanism upstream of nodal expression.

    View details for DOI 10.1002/(SICI)1520-6408(1998)23:3<185::AID-DVG4>3.3.CO;2-T

    View details for Web of Science ID 000077186000004

    View details for PubMedID 9842713

  • Organizer induction determines left-right asymmetry in Xenopus DEVELOPMENTAL BIOLOGY Nascone, N., Mercola, M. 1997; 189 (1): 68–78

    Abstract

    Vertebrates appear bilaterally symmetrical but have considerable left-right (LR) asymmetry in the anatomy and placement of internal organs such as the heart. Although a number of asymmetrically expressed genes are known to affect LR patterning, both the initial source of asymmetry and the mechanism that correctly orients the LR axis remain controversial. In this study, we show that the induction of dorsal organizing centers in the embryo can orient LR asymmetry. Ectopic organizing centers were induced by microinjection of mRNA encoding a variety of body axis duplicating proteins, including members of the Wnt signal transduction pathway. The ectopic and primary body axes form side-by-side conjoined twins, with the secondary axis developing as either the left or right sibling. In all cases, correct LR asymmetry was observed in the left twin, regardless of whether it was derived from the primary axis or induced de novo by injection of Xwnt-8, beta-catenin, or Siamois mRNA. In contrast, the right twin was generally unbiased, regardless of the origin of the left body axis, as seen in many instances of experimentally induced and spontaneous conjoined twins. An unanticipated exception was that right twins induced by beta-catenin and Siamois, two downstream effectors of Wnt signaling, exhibited predominately normal heart looping, even when they formed the right twin. Taken together, these results indicate that LR asymmetry is locally oriented as a consequence of Wnt signaling through beta-catenin and Siamois. We discuss the possibility that signals upstream of beta-catenin and Siamois might be required in order for a right sibling to be randomized.

    View details for DOI 10.1006/dbio.1997.8635

    View details for Web of Science ID A1997XV82400007

    View details for PubMedID 9281338

  • Organizer induction determines left-right asymmetry Mercola, M., Nascone, N. ACADEMIC PRESS INC JNL-COMP SUBSCRIPTIONS. 1997: S55
  • Spina bifida occulta in Homozygous Patch mouse embryos DEVELOPMENTAL DYNAMICS Payne, J., Shibasaki, F., Mercola, M. 1997; 209 (1): 105–16

    Abstract

    In normal embryos, mRNA encoding platelet-derived growth factor A (PDGF A) and the platelet-derived growth factor receptor alpha (PDGFR alpha) are found within and adjacent to the site of vertebral development, the sclerotome. These patterns of expression are consistent with PDGF action on the developing sclerotome and dermis. Homozygous Patch (Ph) mutant mouse embryos lack the receptor gene (Pdgfra) due to an extensive deletion at that locus. Consistent with the spatial pattern of Pdgfra expression, striking deformities are found in the spine and ribcage of Ph/Ph embryos. In particular, we show that late-gestation Ph/Ph embryos have occult spina bifida involving the entire spinal column. We have analyzed the progression of the axial defects in homozygous Patch embryos in detail. By late gestation it appears that the components of the vertebrae are present, yet the neural arches of the spine are misshapen. We propose that PDGF A is required for proper positioning of the neural arch condensation at all axial levels. Furthermore, since the neural tube appears to close normally, we suggest that spina bifida in the Ph homozygote is caused primarily by a somitic mesoderm abnormality rather than a neural tube defect.

    View details for Web of Science ID A1997WW89500010

    View details for PubMedID 9142500

  • Distribution and functions of platelet-derived growth factors and their receptors during embryogenesis INTERNATIONAL REVIEW OF CYTOLOGY - A SURVEY OF CELL BIOLOGY, VOL 172 Ataliotis, P., Mercola, M., Jeon, K. W. 1997; 172: 95–127

    Abstract

    Platelet-derived growth factors (PDGFs) are soluble proteins that mediate intercellular signaling via receptor tyrosine kinases. The patterns of PDGF and PDGF receptor expression during embryogenesis are complex and dynamic and suggest that signaling can be autocrine or paracrine, depending on the particular tissue and the stage of development. Mesenchymal cells throughout the embryo and within some developing organs produce PDGF receptors, whereas their ligands are often produced by adjacent epithelial or endothelial cells. Disruption of PDGF signaling in the embryo leads to morphogenetic defects and embryonic or perinatal lethality. Tissues that are particularly susceptible to the absence of PDGF signaling are migrating mesoderm cells during gastrulation, nonneuronal neural crest cell derivatives, and kidney mesangial cells. These tissues share the common feature of undergoing epithelial-mesenchymal transitions. We review current knowledge of the distribution of PDGF ligands and receptors and discuss how this distribution may relate to several roles for PDGF during embryogenesis, particularly the regulation of mesenchymal cell behavior.

    View details for DOI 10.1016/S0074-7696(08)62359-1

    View details for Web of Science ID A1997BH57K00003

    View details for PubMedID 9102395

  • Endoderm and cardiogenesis - New insights TRENDS IN CARDIOVASCULAR MEDICINE Nascone, N., Mercola, M. 1996; 6 (7): 211–16

    Abstract

    Classic studies of vertebrate heart development have implicated the endoderm in an inductive role, based on its ability to induce rhythmic beating in explants of presumptive heart mesoderm. Recent experiments, aided by the use of heart-specific molecular markers, have defined discrete phases of cardiogenesis that depend on endodermal signals for functional contractility. In addition, the ability of the endoderm to generate a beating heart from tissues fated to form other cell types suggests that endoderm may also be involved in the initial specification of the early heart field.

    View details for DOI 10.1016/S1050-1738(96)00086-2

    View details for Web of Science ID A1996VQ75300002

    View details for PubMedID 21232299

  • Embryonic mesoderm cells spread in response to platelet-derived growth factor and signaling by phosphatidylinositol 3-kinase PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Symes, K., Mercola, M. 1996; 93 (18): 9641–44

    Abstract

    Abnormal mesoderm movement, leading to defects in axial organization, is observed in mouse and Xenopus laevis embryos deprived of platelet-derived growth factor (PDGF) AA signaling. However, neither the cellular response to PDGF nor the signaling pathways involved are understood. Herein we describe an in vitro assay to examine the direct effect of PDGF AA on aggregates of Xenopus embryonic mesoderm cells. We find that PDGF AA stimulates aggregates to spread on fibronectin. This behavior is similar to that of migrating mesoderm cells in vivo that spread and form lamellipodia and filipodia on contact with fibronectin-rich extracellular matrix. We go on to show two lines of evidence that implicate phosphatidylinositol 3-kinase (PI3K) as an important component of PDGF-induced mesoderm cell spreading. (i) The fungal metabolite wortmannin, which inhibits signaling by PI3K, blocks mesoderm spreading in response to PDGF AA. (ii) Activation of a series of receptors with specific tyrosine-to-phenylalanine mutations revealed PDGF-induced spreading of mesoderm cells depends on PI3K but not on other signaling molecules that interact with PDGF receptors including phospholipase C gamma, Ras GTPase-activating protein, and phosphotyrosine phosphatase SHPTP2. These results indicate that a PDGF signal, medicated by PI3K, can facilitate embryonic mesoderm cell spreading on fibronectin. We propose that PDGF, produced by the ectoderm, influences the adhesive properties of the adjacent mesoderm cells during gastrulation.

    View details for DOI 10.1073/pnas.93.18.9641

    View details for Web of Science ID A1996VF61400059

    View details for PubMedID 8790383

    View details for PubMedCentralID PMC38481

  • The role of the organizer in Xenopus left-right asymmetry Nascone, N., Mercola, M. ACADEMIC PRESS INC JNL-COMP SUBSCRIPTIONS. 1996: C10
  • Cloning and expression of Xenopus CCT gamma, a chaperonin subunit developmentally regulated in neural-derived and myogenic lineages DEVELOPMENTAL DYNAMICS Dunn, M. K., Mercola, M. 1996; 205 (4): 387–94

    Abstract

    The chaperonin containing TCP-1 (CCT) is a eukaryotic cytoplasmic chaperonin, consisting of multiple distinct subunits in a double-toroid structure. In vitro, the CCT has been shown to assist in the folding of tubulin and actin into active conformations through an ATP-dependent mechanism. The function and distribution of these proteins in vivo are also not known. In this report, we show that the expression of two CCT subunits (alpha and gamma) are developmentally regulated in neural-derived and myogenic lineages. While expression in the central nervous system and muscle is consistent with a role in tubulin and actin conformation, we also detect robust expression in the developing cranial neural crest. Enrichment in the neural crest may represent the presence of a novel substrate for the CCT. We have also cloned the complete cDNA for the Xenopus ortholog of CCT gamma, which has 87% amino acid identity with the mouse protein. This remarkable evolutionary conservation suggests a conserved function for this protein among vertebrates, and possibly among all eukaryotes.

    View details for Web of Science ID A1996UC04700003

    View details for PubMedID 8901050

  • PDGF SIGNALING IS REQUIRED FOR GASTRULATION OF XENOPUS-LAEVIS DEVELOPMENT ATALIOTIS, P., SYMES, K., CHOU, M. M., HO, L., MERCOLA, M. 1995; 121 (9): 3099–3110

    Abstract

    During Xenopus gastrulation, platelet-derived growth factor (PDGF) receptor-alpha is expressed in involuting marginal zone cells which migrate over ectodermal cells expressing PDGF-A. To investigate the role of PDGF signalling during this process, we have generated a novel point mutant of PDGF receptor-alpha analogous to the W37 mutation of c-kit. This molecule is a specific, potent, dominant inhibitor of PDGF signalling in vivo. Injection of RNA encoding this protein into Xenopus embryos prevents closure of the blastopore, leads to abnormal gastrulation and a loss of anterior structures. Convergent extension is not inhibited in these embryos, but rather, involuting mesodermal cells fail to adhere to the overlying ectoderm. PDGF may therefore be required for mesodermal cell-substratum interaction.

    View details for Web of Science ID A1995RV11900037

    View details for PubMedID 7555734

  • CYCLOPAMINE, A STEROIDAL ALKALOID, DISRUPTS DEVELOPMENT OF CRANIAL NEURAL CREST CELLS IN XENOPUS DEVELOPMENTAL DYNAMICS DUNN, M. K., MERCOLA, M., MOORE, D. D. 1995; 202 (3): 255–70

    Abstract

    Cyclopamine is a steroidal alkaloid which causes limb and craniofacial defects in many vertebrate species. We have used Xenopus laevis as a model system to characterize the defects caused by cyclopamine at the cellular level. The most dramatic consequence of cyclopamine treatment in the Xenopus embryo is a defect in formation of craniofacial cartilage. Much of this cartilage is absent in treated animals. As in avian and mammalian species, Xenopus craniofacial cartilage is derived primarily from cells of the cranial neural crest. Grafting experiments show that development of the cartilaginous derivatives of the cranial neural crest is impaired after cyclopamine treatment, and this is at least partially due to a direct effect on presumptive crest cells. A culture system was used to determine the cellular response to the drug. Cyclopamine did not block the initial emigration of cells from a neural plate explant. However, cell death is seen in treated cultures after 4 days. Trunk neural crest cells and transformed cell lines are resistant to cyclopamine. We therefore conclude that cyclopamine specifically causes death of cranial neural crest cells and that lethality is likely to account for the teratogenic effects of this compound.

    View details for DOI 10.1002/aja.1002020305

    View details for Web of Science ID A1995QN66000004

    View details for PubMedID 7780175

  • AN INDUCTIVE ROLE FOR THE ENDODERM IN XENOPUS CARDIOGENESIS DEVELOPMENT NASCONE, N., MERCOLA, M. 1995; 121 (2): 515–23

    Abstract

    Heart induction in Xenopus has been thought to be dependent primarily on the interaction of the heart primordia with the Spemann organizer. We demonstrate, however, that signals derived from the deep dorsoanterior endoderm during early gastrulation are also essential for heart formation. The presence of deep endoderm dramatically enhances heart formation in explants of heart primordia, both in the presence and absence of organizer. Likewise, extirpation of the entire endoderm can decrease the frequency of heart formation in embryos that retain organizer activity. Finally, we show that the combined presence of both endoderm and organizer is necessary and sufficient to induce heart in ventral mesoderm explants that would not otherwise form heart tissue. Xenopus heart induction, therefore, may be a multistep process requiring separate dorsalization and cardiogenic signalling events. This is the first demonstration of a heart-inducing role for the endoderm in Xenopus, indicating that the mechanism of heart formation may be similar in most vertebrates.

    View details for Web of Science ID A1995QK89600022

    View details for PubMedID 7768189

  • LOCALIZATION OF PDGF-A AND PDGFR-ALPHA MESSENGER-RNA IN XENOPUS EMBRYOS SUGGESTS SIGNALING FROM NEURAL ECTODERM AND PHARYNGEAL ENDODERM TO NEURAL CREST CELLS MECHANISMS OF DEVELOPMENT HO, L., SYMES, K., YORDAN, C., GUDAS, L. J., MERCOLA, M. 1994; 48 (3): 165–74

    Abstract

    In situ hybridization analysis of Xenopus laevis embryos reveals that mRNA encoding the platelet-derived growth factor alpha receptor (PDGFR alpha) is expressed in cephalic neural crest masses prior to migration from the future neural tube and during their migration into the visceral arches. The analysis of fluorescently labeled neural crest tissue transplanted to unlabeled host embryos demonstrates that neural crest cells are the only detectable source of PDGFR alpha mRNA within visceral arches. Transcripts encoding PDGF A are present in neural ectoderm, otic vesicle and pharyngeal endoderm. Their location suggests that PDGF A provides a signal, first from the neural epithelium and later from the otic vesicle and pharyngeal endoderm, to cephalic neural crest cells during their migration in the arch region.

    View details for DOI 10.1016/0925-4773(94)90057-4

    View details for Web of Science ID A1994QC45700003

    View details for PubMedID 7893600

  • MORPHOLOGICAL DIFFERENCES IN XENOPUS EMBRYONIC MESODERMAL CELLS ARE SPECIFIED AS AN EARLY RESPONSE TO DISTINCT THRESHOLD CONCENTRATIONS OF ACTIVIN DEVELOPMENT SYMES, K., YORDAN, C., MERCOLA, M. 1994; 120 (8): 2339–46

    Abstract

    The involution of presumptive mesoderm that occurs during amphibian gastrulation is a complex process requiring the coordinated action of a diverse range of cells. We show that cells with distinct morphologies, resembling each of those normally found in the involuting tissue of the Xenopus embryo, are induced in dispersed animal pole cells by different doses of the potent mesoderm-inducing factor activin. Each cell type is induced within a restricted dose range of activin concentrations, the boundaries of which are well demarcated shortly after activin treatment. In contrast, Brachyury and goosecoid, two genes thought to pattern the presumptive mesoderm, and the gene encoding platelet-derived growth factor receptor alpha, which is expressed in the mesoderm of gastrula stage embryos, are induced by broad, overlapping ranges of high activin concentrations at such early times. Similarly, the response of the gene encoding platelet-derived growth factor A, which is expressed normally in ectoderm of gastrula stage embryos, diminishes gradually as the activin concentration increases. Dose windows for the expression of these four genes narrow and become distinct from one another in cell aggregates after several hours in culture, suggesting that activin prompts a dynamic program of gene expression in induced mesoderm.

    View details for Web of Science ID A1994PA81400025

    View details for PubMedID 7925034

  • XENOPUS-LAEVIS CELLULAR RETINOIC ACID-BINDING PROTEIN - TEMPORAL AND SPATIAL EXPRESSION PATTERN DURING EARLY EMBRYOGENESIS MECHANISMS OF DEVELOPMENT HO, L., MERCOLA, M., GUDAS, L. J. 1994; 47 (1): 53–64

    Abstract

    There is increasing evidence that retinoic acid (RA) has a role in establishing normal axial patterns during Xenopus laevis embryo-genesis. Several types of retinoid binding proteins are thought to mediate the effects of RA. We report the isolation of a cDNA, named xCRABP-b, which encodes a X. laevis cellular retinoic acid-binding protein (xCRABP). This cDNA hybridises to a transcript in gastrular stage embryos of approximately 3 kb, much larger than those CRABP transcripts expressed in mice. The expression of the xCRABP mRNA is generally restricted to tissues which are sensitive to the teratogenic effects of excess RA. It is likely, that during normal X. laevis embryogenesis, concentrations of RA in RA-responsive cells are modulated by the xCRABP gene product.

    View details for DOI 10.1016/0925-4773(94)90095-7

    View details for Web of Science ID A1994PF47300005

    View details for PubMedID 7947321

  • THE XENOPUS PLATELET-DERIVED GROWTH-FACTOR ALPHA-RECEPTOR - CDNA CLONING AND DEMONSTRATION THAT MESODERM INDUCTION ESTABLISHES THE LINEAGE-SPECIFIC PATTERN OF LIGAND AND RECEPTOR GENE-EXPRESSION DEVELOPMENTAL GENETICS JONES, S. D., HO, L., SMITH, J. C., YORDAN, C., STILES, C. D., MERCOLA, M. 1993; 14 (3): 185–93

    Abstract

    We have cloned the Xenopus PDGF alpha receptor cDNA and have used this clone, along with cDNA encoding PDGF A, to examine their expression pattern in Xenopus embryos and to determine the factors responsible for lineage specificity. Recombinant Xenopus alpha receptor expressed in COS cells exhibits PDGF-A-dependent tyrosine kinase activity. We find that receptor mRNA is present in cultured marginal zone tissue explants and in animal cap tissue induced to form mesoderm either by grafting to vegetal tissue or by treatment with recombinant activin A. In contrast, PDGF A mRNA is expressed in cultured, untreated animal cap tissue and is suppressed by mesoderm induction. These results suggest that ectodermally produced PDGF A may act on the mesoderm during gastrulation and that mesoderm induction establishes the tissue pattern of ligand and receptor expression.

    View details for DOI 10.1002/dvg.1020140305

    View details for Web of Science ID A1993LM47600004

    View details for PubMedID 8358864

  • EXPRESSION OF MOUSE PDGF-A AND PDGF ALPHA-RECEPTOR GENES DURING PREIMPLANTATION AND POSTIMPLANTATION DEVELOPMENT - EVIDENCE FOR A DEVELOPMENTAL SHIFT FROM AN AUTOCRINE TO A PARACRINE MODE OF ACTION MECHANISMS OF DEVELOPMENT PALMIERI, S. L., PAYNE, J., STILES, C. D., BIGGERS, J. D., MERCOLA, M. 1992; 39 (3): 181–91

    Abstract

    We examined the expression of platelet-derived growth factor (PDGF)-A and the PDGF alpha-receptor in pre-implantation and early post-implantation mouse embryos. At two-cell and blastocyst stages, all cells express mRNA and protein for both ligand and receptor. In contrast, early post-implantation embryos express PDGF-A chain mRNA in both embryonic ectoderm and in the ectoderm lining the ectoplacental cavity, while mRNA for PDGF alpha-receptor is localized to the mesoderm layers of both embryonic and extra-embryonic membranes. At days 3.5 and 7.5, receptors are demonstrably functional in response to exogenous PDGF-AA. We propose that chronic autostimulation of PDGF alpha-receptors occurs in pre-implantation embryos, whereas, following implantation, early mesoderm development is dependent on stimulation by ectodermally produced PDGF-A.

    View details for DOI 10.1016/0925-4773(92)90045-L

    View details for Web of Science ID A1992KG00100006

    View details for PubMedID 1292572

  • RAPID, COMPLETE AND REVERSIBLE TRANSFORMATION BY V-SIS PRECEDES IRREVERSIBLE TRANSFORMATION ONCOGENE MERCOLA, D., CARPENTER, P. M., GROVERBARDWICK, A., MERCOLA, M. 1992; 7 (9): 1793–1803

    Abstract

    v-sis is the oncogene of simian sarcoma virus, but whether tumor growth is maintained by v-sis expression alone or requires additional changes is unknown. To distinguish these possibilities we studied a model of reversible transformation including tumorigenicity using NIH3T3 cells bearing a metallothionein promoter-v-sis construction. Cells subcultured from 10 out of 18 tumors from athymic mice, all less than 0.1 g and less than or equal to 21 days in age, reverted to a normal phenotype but exhibited transformation upon addition of zinc as judged by morphology, growth rate, saturation density and anchorage independence of growth. Thus, activation of v-sis alone is sufficient for initiation and early autocrine-based growth of tumors. However, the cells from the remaining and predominantly larger, 0.5 +/- 0.7 g, tumors did not revert and exhibited zinc-independent transformation as judged by the same criteria. Southern analysis and examination of the regulation of v-sis product expression in cells derived from these tumors showed no change in zinc-dependent and reversible regulation of v-sis sequences. These results suggest that subsequent tumor growth strongly favors acquisition of additional irreversible change(s) in the tumor cell genome at high frequency (44%). Thus an early event of a multistep process stimulated by v-sis-dependent transformation best accounts for the sum of results.

    View details for Web of Science ID A1992JJ37600016

    View details for PubMedID 1501889

  • THE REGULATION OF PDGF AND PDGF RECEPTOR EXPRESSION IN F9 TERATOCARCINOMA CELLS WANG, C., MERCOLA, M., STILES, C. D. WILEY. 1991: A1623
  • PLATELET-DERIVED GROWTH-FACTOR RECEPTOR ALPHA-SUBUNIT GENE (PDGFRA) IS DELETED IN THE MOUSE PATCH (PH) MUTATION PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA STEPHENSON, D. A., MERCOLA, M., ANDERSON, E., WANG, C. Y., STILES, C. D., BOWENPOPE, D. F., CHAPMAN, V. M. 1991; 88 (1): 6–10

    Abstract

    Platelet-derived growth factor receptors are composed of two subunits (alpha and beta) that associate with one another to form three functionally active dimeric receptor species. The two subunits are encoded by separate loci in humans and other species. In this study, we used conventional interspecific backcross mapping and an analysis of a deletional mutation to establish close linkage between the alpha-subunit gene (Pdgfra) and the dominant spotting (W) locus on mouse chromosome 5. Further, by analyzing the restriction fragment length polymorphisms in interspecific F1 hybrids, we were able to demonstrate that the closely associated patch (Ph) locus carries a deletion in Pdgfra. This observation was confirmed by both DNA and RNA analysis of 10.5-day fetuses produced from crosses between Ph heterozygotes. Out of 16 fetuses analyzed, Pdgfra genomic sequences were absent and no mRNA for the receptor was detected in 6 fetuses that were developmentally abnormal (the presumptive Ph homozygotes). We also determined that the deletion associated with the Ph mutation does not extend into the coding sequences of the adjacent Kit gene, by analysis of the genomic DNA from both the interspecific F1 hybrids and the presumptive Ph homozygotes. The absence of Pdgfra genomic sequences and the lack of detectable message associated with the Ph mutation should make this mutant a valuable asset for understanding the role of the receptor alpha subunit during mammalian development.

    View details for DOI 10.1073/pnas.88.1.6

    View details for Web of Science ID A1991EQ54400002

    View details for PubMedID 1846043

    View details for PubMedCentralID PMC50736

  • Reversible transformation by v-sis: a model cell line for analysis of transformation by antisense methods. Antisense research and development Carpenter, P. M., Mercola, M., Mercola, D. 1991; 1 (3): 289–95

    Abstract

    Cellular homologs of v-sis are implicated in numerous human tumor types (Eva et al., 1982; Betsholtz et al., 1984; Johnson et al., 1985; Bronzert et al., 1987; Igarashi et al., 1987; Nister et al., 1988a,b; Versnel et al., 1988; Matsui et al., 1989), but whether tumor growth is maintained by sis expression alone or requires additional changes is unknown. To distinguish these possibilities, we studied reversible transformation of NIH-3T3 cells bearing an inducible v-sis construction. Cells subcultured from 10 of 18 tumors, all less than 0.1 gram and less than or equal to 21 days in age, reverted to a normal phenotype by four criteria, but again exhibited transformation upon induction. Thus, activation of the v-sis autocrine loop alone is sufficient for initiation of tumors. Cells from the remaining and larger, 0.5 +/- 0.7 gram, tumors did not revert by any criteria. This suggests that subsequent tumor growth is maintained by acquisition of irreversible change(s) that occurs at high frequency in vivo.

    View details for PubMedID 1821651

  • DOMINANT-NEGATIVE MUTANTS OF A PLATELET-DERIVED GROWTH-FACTOR GENE GENES & DEVELOPMENT MERCOLA, M., DEININGER, P. L., SHAMAH, S. M., PORTER, J., WANG, C. Y., STILES, C. D. 1990; 4 (12B): 2333–41

    Abstract

    Using site-directed mutagenesis of a PDGF-A cDNA clone, we identify two domains that are required to generate stable, mitogenically active PDGF-AA homodimers. Alteration of the tetra-basic amino acid sequence (Arg84-Arg-Lys-Arg to Arg-Ser-Asn-Gly) results in the formation of stable pro-PDGF-A homodimers that lack mitogenic activity. Substitution of serine for Cys129 destabilizes PDGF-A subunits within the cell. Genes incorporating either the processing lesion or the cysteine substitution suppress wild-type PDGF-A gene expression in a trans-dominant fashion. Suppression occurs because the mutant PDGF subunits dimerize with wild-type subunits to form inactive or unstable heterodimers. Suppression is exerted across phylogenetic boundaries; thus, the mouse PDGF-A chain mutants inhibit the activity of the wild-type Xenopus PDGF-A. The cysteine mutant gene suppresses expression of PDGF-B (c-sis), as well as PDGF-A. The processing mutant gene, however, suppresses only PDGF-A. Dominant-negative mutations of PDGF and other growth factors which, like PDGF, function as dimers may prove useful for creating animals models of growth factor deficiency disease states and for revealing the function of growth factors during early embryonic development.

    View details for DOI 10.1101/gad.4.12b.2333

    View details for Web of Science ID A1990EQ62400010

    View details for PubMedID 2279701

  • SELECTIVE EXPRESSION OF PDGF-A AND ITS RECEPTOR DURING EARLY MOUSE EMBRYOGENESIS DEVELOPMENTAL BIOLOGY MERCOLA, M., WANG, C. Y., KELLY, J., BROWNLEE, C., JACKSONGRUSBY, L., STILES, C., BOWENPOPE, D. 1990; 138 (1): 114–22

    Abstract

    Murine homologs of the PDGF A, PDGF B, and PDGF receptor alpha subunit genes were cloned. These were used, together with a mouse PDGF receptor beta subunit cDNA clone, to monitor gene expression in early postimplantation mouse embryos and in F9 embryonal carcinoma cells. RNAse protection analysis shows that PDGF A chain, but not B chain, mRNA is expressed in 6.5- to 8.5-day embryonic and extraembryonic tissues. Both alpha and beta receptor subunit mRNAs are expressed in early embryos, however, alpha subunit mRNA appears earlier and is more abundant than beta subunit mRNA. Undifferentiated F9 embryonal carcinoma stem cells express abundant levels of A chain, but not B chain, mRNA. Neither of the PDGF receptor genes is expressed in stem cells. Treatment with retinoic acid stimulates expression of both PDGF receptor genes. As in postimplantation mouse embryos, alpha receptor subunit mRNA appears earlier and is substantially more abundant than beta subunit mRNA. Collectively, these data demonstrate that the genes encoding the two chains of PDGF and their receptors are regulated independently during development and suggest that the two systems have some nonoverlapping functions in vivo. PDGF A, but not PDGF B, may be particularly important in modulating early events in mouse embryonic development.

    View details for DOI 10.1016/0012-1606(90)90181-H

    View details for Web of Science ID A1990CT46800011

    View details for PubMedID 2155144

  • PLATELET-DERIVED GROWTH FACTOR-A CHAIN IS MATERNALLY ENCODED IN XENOPUS EMBRYOS SCIENCE MERCOLA, M., MELTON, D. A., STILES, C. D. 1988; 241 (4870): 1223–25

    Abstract

    Transcription of zygotic genes does not occur in early Xenopus embryos until the mid-blastula transition, 6 to 7 hours after fertilization. Before this time, development is directed by maternal proteins and messenger RNAs stored within the egg. Two different forms of the A chain of platelet-derived growth factor (PDGF) are shown here to be encoded by maternal messenger RNAs. The two forms closely resemble human PDGF; however, the long form contains a hydrophobic region near the carboxyl terminus. The presence of PDGF messenger RNA in the embryo supports the idea that endogenous growth factors act at the earliest stages of embryogenesis.

    View details for DOI 10.1126/science.3413486

    View details for Web of Science ID A1988P902100040

    View details for PubMedID 3413486

  • GROWTH-FACTOR SUPERFAMILIES AND MAMMALIAN EMBRYOGENESIS DEVELOPMENT MERCOLA, M., STILES, C. D. 1988; 102 (3): 451–60

    Abstract

    With the availability of amino acid and nucleotide sequence information has come the realization that growth factors can be clustered in to superfamilies. Several of these superfamilies contain molecules that were not initially identified because of growth-promoting activities; rather they were discovered through their ability to regulate other processes. Certain members of these superfamilies are present during early mammalian embryogenesis. However, until recently, it has been difficult to manipulate the developing mammalian embryo to observe directly the effects of inappropriate, excessive, or reduced expression of these molecules. Despite this limitation, at least some of these molecules have been implicated in the control of differentiation and morphogenesis, two actions unpredicted from the cell biology of most of the growth factors. Moreover, these actions are reflected in nonmammalian species where homologues of the mammalian growth factors control crucial steps in the choice of developmental fate. This review describes five growth factor superfamilies and the role these molecules may have in controlling proliferation, differentiation, and morphogenesis during mammalian development.

    View details for Web of Science ID A1988M701500001

    View details for PubMedID 3053123

  • STRONG TRANSCRIPTIONAL ACTIVATION OF TRANSLOCATED C-MYC GENES OCCURS WITHOUT A STRONG NEARBY ENHANCER OR PROMOTER NUCLEIC ACIDS RESEARCH KAKKIS, E., MERCOLA, M., CALAME, K. 1988; 16 (1): 77–96

    Abstract

    We have studied the transcriptional activation of translocated c-myc genes in murine plasmacytomas in which the translocation juncture occurs within the first intron of c-myc and juxtaposes c-myc with the immunoglobulin C alpha gene segment. It has been widely suggested that a novel transcriptional enhancer element located near the C alpha gene segment might activate the translocated c-myc gene. We have carried out an extensive search for such an element and find no significant transcriptional enhancer activity in a 22 kb region encompassing the translocation junction, C alpha gene segment and regions 3' of C alpha. We also find that the cryptic promoter region of the translocated c-myc gene is a very weak promoter of transcription. Despite this evidence against the presence of strong transcriptional regulatory elements, the translocated c-myc gene locus is transcribed at high rates that are 25-greater than 100% of that measured for the highly active immunoglobulin genes in murine plasmacytomas. These data suggest the presence of a novel type of strong activator of transcription in the murine heavy chain locus.

    View details for DOI 10.1093/nar/16.1.77

    View details for Web of Science ID A1988L683300006

    View details for PubMedID 2829126

    View details for PubMedCentralID PMC334614

  • DIFFERENTIAL COLONY HYBRIDIZATION - MOLECULAR-CLONING FROM A ZERO DATA-BASE METHODS IN ENZYMOLOGY COCHRAN, B. H., ZUMSTEIN, P., ZULLO, J., ROLLINS, B., MERCOLA, M., STILES, C. D. 1987; 147: 64–85

    View details for Web of Science ID A1987M168100006

    View details for PubMedID 2444861

  • IMMUNOGLOBULIN HEAVY-CHAIN ENHANCER REQUIRES ONE OR MORE TISSUE-SPECIFIC FACTORS SCIENCE MERCOLA, M., GOVERMAN, J., MIRELL, C., CALAME, K. 1985; 227 (4684): 266–70

    Abstract

    Enhancer sequences are regulatory regions that greatly increase transcription of certain eukaryotic genes. An immunoglobulin heavy-chain variable gene segment is moved from a region lacking enhancer activity to a position adjacent to the known heavy-chain enhancer early in B-cell maturation. In lymphoid cells, the heavy-chain and SV40 enhancers bind a common factor essential for enhancer function. In contrast, fibroblast cells contain a functionally distinct factor that is used by the SV40 but not by the heavy-chain enhancer. The existence of different factors in these cells may explain the previously described lymphoid cell specificity of the heavy-chain enhancer.

    View details for DOI 10.1126/science.3917575

    View details for Web of Science ID A1985TZ25700010

    View details for PubMedID 3917575

  • TRANSCRIPTIONAL ENHANCER ELEMENTS IN THE MOUSE IMMUNOGLOBULIN HEAVY-CHAIN LOCUS SCIENCE MERCOLA, M., WANG, X. F., OLSEN, J., CALAME, K. 1983; 221 (4611): 663–65

    Abstract

    Two regions in the immunoglobulin heavy chain locus were tested for their ability to enhance transcription of the SV40 early promoter. A portion of the intervening sequence between the heavy chain joining region (Jh) and the constant region of the mu chain (Cmu) can enhance transcription when it is cloned either 5' or 3' to the SV40 early promoter. The region between C alpha and the alpha switch site, which occurs 5' to the translocated c-myc oncogene in many murine plasmacytomas, does not show transcriptional enhancer activity in this assay.

    View details for DOI 10.1126/science.6306772

    View details for Web of Science ID A1983RB26000030

    View details for PubMedID 6306772