- Metabolic Bone Disease
- Diabetes and Metabolism
Assistant Professor, Medicine - Endocrinology, Gerontology, & Metabolism
Member, Child Health Research Institute
Member, Stanford Cancer Institute
Honors & Awards
Cancer Grant Recipient, The Mary Kay Foundation (2013)
NIH Director's New Innovator Award, NIH (2011)
Clinical Scientist Program Instructor Development Award, Harvard Stem Cell Institute (2009)
Claflin Distinguished Scholar Award, Massachusetts General Hospital (2009)
John Haddad Young Investigator Award, Advances in Mineral Metabolism (2008)
Merck Senior Fellow Award, The Endocrine Society (2007)
Young Investigator Award, American Society for Bone and Mineral Research Annual Meeting (2006)
Endocrine Scholars Award, The Endocrine Society (2006)
Alpha Omega Alpha, Duke University School of Medicine (1997)
Phi Beta Kappa, Stanford University (1993)
Marsden Memorial Award in Chemistry, Stanford University (1993)
Boards, Advisory Committees, Professional Organizations
Member, The Endocrine Society (2003 - Present)
Ex Officio, Council, The Endocrine Society (2006 - 2010)
Co-Chair, Trainee & Career Development Core Committee, The Endocrine Society (2007 - 2010)
Member, The American Society for Bone and Mineral Research (2005 - Present)
Membership Enhancement Committee, The American Society for Bone and Mineral Research (2013 - Present)
Board of Directors, Advances in Mineral Metabolism (2013 - Present)
Board Certification: Endocrinology, Diabetes and Metabolism, American Board of Internal Medicine (2006)
Fellowship:Massachusetts General Hospital (2006) MA
Board Certification: Internal Medicine, American Board of Internal Medicine (2004)
Residency:Brigham and Women's Hospital Harvard Medical School (2003) MA
Medical Education:Duke University School of Medicine (2001) NC
MD/PhD, Duke University (2001)
Current Research and Scholarly Interests
Osteoporosis, a disease of fragile bones resulting in fractures, will strike 50% of women and 25% of men. As a physician scientist, my laboratory is studying stem cells in the skeleton and bone marrow to develop novel regenerative approaches to increase bone quality and strength. We are also interested in how the skeleton supports hematopoiesis, and how diseases and medications that impact bone may affect blood cell production and cancer metastasis. For more detailed descriptions of ongoing research projects in the lab, visit our website at joywulab.stanford.edu.
Independent Studies (10)
- Directed Reading in Immunology
IMMUNOL 299 (Win, Spr)
- Directed Reading in Medicine
MED 299 (Aut)
- Early Clinical Experience in Immunology
IMMUNOL 280 (Win, Spr)
- Early Clinical Experience in Medicine
MED 280 (Win)
- Graduate Research
IMMUNOL 399 (Aut, Win, Spr, Sum)
- Graduate Research
MED 399 (Aut)
- Medical Scholars Research
MED 370 (Aut)
- Teaching in Immunology
IMMUNOL 290 (Win, Spr)
- Undergraduate Research
IMMUNOL 199 (Aut, Win, Spr)
- Undergraduate Research
MED 199 (Aut)
- Directed Reading in Immunology
Graduate and Fellowship Programs
Wnts produced by Osterix-expressing osteolineage cells regulate their proliferation and differentiation
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2014; 111 (49): E5262-E5271
Wnt signaling is a critical regulator of bone development, but the identity and role of the Wnt-producing cells are still unclear. We addressed these questions through in situ hybridization, lineage tracing, and genetic experiments. First, we surveyed the expression of all 19 Wnt genes and Wnt target gene Axin2 in the neonatal mouse bone by in situ hybridization, and demonstrated-to our knowledge for the first time-that Osterix-expressing cells coexpress Wnt and Axin2. To track the behavior and cell fate of Axin2-expressing osteolineage cells, we performed lineage tracing and showed that they sustain bone formation over the long term. Finally, to examine the role of Wnts produced by Osterix-expressing cells, we inhibited Wnt secretion in vivo, and observed inappropriate differentiation, impaired proliferation, and diminished Wnt signaling response. Therefore, Osterix-expressing cells produce their own Wnts that in turn induce Wnt signaling response, thereby regulating their proliferation and differentiation.
View details for DOI 10.1073/pnas.1420463111
View details for Web of Science ID 000345921500004
View details for PubMedID 25422448
- Loss of G(s)alpha Early in the Osteoblast Lineage Favors Adipogenic Differentiation of Mesenchymal Progenitors and Committed Osteoblast Precursors JOURNAL OF BONE AND MINERAL RESEARCH 2014; 29 (11): 2414-2426
Teriparatide ( PTH1-34) Treatment Increases Peripheral Hematopoietic Stem Cells in Postmenopausal Women
JOURNAL OF BONE AND MINERAL RESEARCH
2014; 29 (6): 1380-1386
Cells of the osteoblast lineage play an important role in regulating the hematopoietic stem cell (HSC) niche and early B cell development in animal models, perhaps via parathyroid hormone (PTH) dependent mechanisms. There are few human clinical studies investigating this phenomenon. We studied the impact of long-term daily teriparatide (PTH 1-34) treatment on cells of the hematopoietic lineage in postmenopausal women. Twenty-three postmenopausal women at high risk of fracture received teriparatide 20 mcg SC daily for 24 months as part of a prospective longitudinal trial. Whole blood measurements were obtained at baseline, 3, 6, 12, and 18 months. Flow cytometry was performed to identify hematopoietic subpopulations, including HSCs (CD34 + /CD45(moderate); ISHAGE protocol) and early transitional B cells (CD19 + , CD27-, IgD + , CD24[hi], CD38[hi]), CD38[hi]). Serial measurements of spine and hip bone mineral density as well as serum P1NP, osteocalcin, and CTX were also performed. The average age of study subjects was 64 ± 5. We found that teriparatide treatment led to an early increase in circulating HSC number of 40% ± 14% (p = 0.004) by month 3, which persisted to month 18 before returning to near baseline by 24 months. There were no significant changes in transitional B cells or total B cells over the course of the study period. In addition, there were no differences in complete blood count profiles as quantified by standard automated flow cytometry. Interestingly, the peak increase in HSC number was inversely associated with increases in bone markers and spine BMD. Daily teriparatide treatment for osteoporosis increases circulating HSCs by 3 to 6 months in postmenopausal women. This may represent a proliferation of marrow HSCs or increased peripheral HSC mobilization. This clinical study establishes the importance of PTH in the regulation of the HSC niche within humans. © 2014 American Society for Bone and Mineral Research.
View details for DOI 10.1002/jbmr.2171
View details for Web of Science ID 000336001500010
View details for PubMedID 24420643
Differential regulation of myeloid leukemias by the bone marrow microenvironment.
2013; 19 (11): 1513-1517
Like their normal hematopoietic stem cell counterparts, leukemia stem cells (LSCs) in chronic myelogenous leukemia (CML) and acute myeloid leukemia (AML) are presumed to reside in specific niches in the bone marrow microenvironment (BMM) and may be the cause of relapse following chemotherapy. Targeting the niche is a new strategy to eliminate persistent and drug-resistant LSCs. CD44 (refs. 3,4) and interleukin-6 (ref. 5) have been implicated previously in the LSC niche. Transforming growth factor-β1 (TGF-β1) is released during bone remodeling and plays a part in maintenance of CML LSCs, but a role for TGF-β1 from the BMM has not been defined. Here, we show that alteration of the BMM by osteoblastic cell-specific activation of the parathyroid hormone (PTH) receptor attenuates BCR-ABL1 oncogene-induced CML-like myeloproliferative neoplasia (MPN) but enhances MLL-AF9 oncogene-induced AML in mouse transplantation models, possibly through opposing effects of increased TGF-β1 on the respective LSCs. PTH treatment caused a 15-fold decrease in LSCs in wild-type mice with CML-like MPN and reduced engraftment of immune-deficient mice with primary human CML cells. These results demonstrate that LSC niches in CML and AML are distinct and suggest that modulation of the BMM by PTH may be a feasible strategy to reduce LSCs, a prerequisite for the cure of CML.
View details for DOI 10.1038/nm.3364
View details for PubMedID 24162813
Myelopoiesis is regulated by osteocytes through Gsa-dependent signaling.
2013; 121 (6): 930-939
Hematopoietic progenitors are regulated in their respective niches by cells of the bone marrow microenvironment. The bone marrow microenvironment is composed of a variety of cell types, and the relative contribution of each of these cells for hematopoietic lineage maintenance has remained largely unclear. Osteocytes, the most abundant yet least understood cells in bone, are thought to initiate adaptive bone remodeling responses via osteoblasts and osteoclasts. Here we report that these cells regulate hematopoiesis, constraining myelopoiesis through a Gs?-mediated mechanism that affects G-CSF production. Mice lacking Gs? in osteocytes showed a dramatic increase in myeloid cells in bone marrow, spleen, and peripheral blood. This hematopoietic phenomenon was neither intrinsic to the hematopoietic cells nor dependent on osteoblasts but was a consequence of an altered bone marrow microenvironment imposed by Gs? deficiency in osteocytes. Conditioned media from osteocyte-enriched bone explants significantly increased myeloid colony formation in vitro, which was blocked by G-CSF–neutralizing antibody, indicating a critical role of osteocyte-derived G-CSF in the myeloid expansion.
View details for DOI 10.1182/blood-2012-06-437160
View details for PubMedID 23160461
G(s)alpha enhances commitment of mesenchymal progenitors to the osteoblast lineage but restrains osteoblast differentiation in mice
JOURNAL OF CLINICAL INVESTIGATION
2011; 121 (9): 3492-3504
The heterotrimeric G protein subunit Gs? stimulates cAMP-dependent signaling downstream of G protein-coupled receptors. In this study, we set out to determine the role of Gs? signaling in cells of the early osteoblast lineage in vivo by conditionally deleting Gs? from osterix-expressing cells. This led to severe osteoporosis with fractures at birth, a phenotype that was found to be the consequence of impaired bone formation rather than increased resorption. Osteoblast number was markedly decreased and osteogenic differentiation was accelerated, resulting in the formation of woven bone. Rapid differentiation of mature osteoblasts into matrix-embedded osteocytes likely contributed to depletion of the osteoblast pool. In addition, the number of committed osteoblast progenitors was diminished in both bone marrow stromal cells (BMSCs) and calvarial cells of mutant mice. In the absence of Gs?, expression of sclerostin and dickkopf1 (Dkk1), inhibitors of canonical Wnt signaling, was markedly increased; this was accompanied by reduced Wnt signaling in the osteoblast lineage. In summary, we have shown that Gs? regulates bone formation by at least two distinct mechanisms: facilitating the commitment of mesenchymal progenitors to the osteoblast lineage in association with enhanced Wnt signaling; and restraining the differentiation of committed osteoblasts to enable production of bone of optimal mass, quality, and strength.
View details for DOI 10.1172/JCI46406
View details for Web of Science ID 000294753700017
View details for PubMedID 21804192
- Role of the Osteoblast Lineage in the Bone Marrow Hematopoietic Niches JOURNAL OF BONE AND MINERAL RESEARCH 2009; 24 (5): 759-764
Osteoblastic regulation of B lymphopoiesis is mediated by G(s)alpha-dependent signaling pathways
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2008; 105 (44): 16976-16981
Osteoblasts play an increasingly recognized role in supporting hematopoietic development and recently have been implicated in the regulation of B lymphopoiesis. Here we demonstrate that the heterotrimeric G protein alpha subunit G(s)alpha is required in cells of the osteoblast lineage for normal postnatal B lymphocyte production. Deletion of G(s)alpha early in the osteoblast lineage results in a 59% decrease in the percentage of B cell precursors in the bone marrow. Analysis of peripheral blood from mutant mice revealed a 67% decrease in the number of circulating B lymphocytes by 10 days of age. Strikingly, other mature hematopoietic lineages are not decreased significantly. Mice lacking G(s)alpha in cells of the osteoblast lineage exhibit a reduction in pro-B and pre-B cells. Furthermore, interleukin (IL)-7 expression is attenuated in G(s)alpha-deficient osteoblasts, and exogenous IL-7 is able to restore B cell precursor populations in the bone marrow of mutant mice. Finally, the defect in B lymphopoiesis can be rescued by transplantation into a WT microenvironment. These findings confirm that osteoblasts are an important component of the B lymphocyte niche and demonstrate in vivo that G(s)alpha-dependent signaling pathways in cells of the osteoblast lineage extrinsically regulate bone marrow B lymphopoiesis, at least partially in an IL-7-dependent manner.
View details for DOI 10.1073/pnas.0802898105
View details for Web of Science ID 000260913800034
View details for PubMedID 18957542
Activation of the Wnt/Planar Cell Polarity Pathway Is Required for Pericyte Recruitment during Pulmonary Angiogenesis
AMERICAN JOURNAL OF PATHOLOGY
2015; 185 (1): 69-84
Pericytes are perivascular cells localized to capillaries that promote vessel maturation, and their absence can contribute to vessel loss. Whether impaired endothelial-pericyte interaction contributes to small vessel loss in pulmonary arterial hypertension (PAH) is unclear. Using 3G5-specific, immunoglobulin G-coated magnetic beads, we isolated pericytes from the lungs of healthy subjects and PAH patients, followed by lineage validation. PAH pericytes seeded with healthy pulmonary microvascular endothelial cells failed to associate with endothelial tubes, resulting in smaller vascular networks compared to those with healthy pericytes. After the demonstration of abnormal polarization toward endothelium via live-imaging and wound-healing studies, we screened PAH pericytes for abnormalities in the Wnt/planar cell polarity (PCP) pathway, which has been shown to regulate cell motility and polarity in the pulmonary vasculature. PAH pericytes had reduced expression of frizzled 7 (Fzd7) and cdc42, genes crucial for Wnt/PCP activation. With simultaneous knockdown of Fzd7 and cdc42 in healthy pericytes in vitro and in a murine model of angiogenesis, motility and polarization toward pulmonary microvascular endothelial cells were reduced, whereas with restoration of both genes in PAH pericytes, endothelial-pericyte association was improved, with larger vascular networks. These studies suggest that the motility and polarity of pericytes during pulmonary angiogenesis are regulated by Wnt/PCP activation, which can be targeted to prevent vessel loss in PAH.
View details for DOI 10.1016/j.ajpath.2014.09.013
View details for Web of Science ID 000346887200008
RARγ is a negative regulator of osteoclastogenesis.
The Journal of steroid biochemistry and molecular biology
2015; 150: 46-53
Vitamin A is known to influence post-natal bone content, with excess intake being associated with reduced bone mineral density and increased fracture risk. Despite this, the roles retinoids play in regulating osteoclastogenesis, particularly in vivo, remain unresolved. This study therefore aimed to determine the effect of loss of retinoic acid receptors (RAR)α or RARγ on bone mass (analyzed by histomorphometry and dual-energy X-ray absorptiometry) and osteoclastogenesis in mice in vivo. RARγ null mice had significantly less trabecular bone at 8 weeks of age compared to wildtype littermates. In contrast, no change in trabecular bone mass was detected in RARα null mice at this age. Further histomorphometric analysis revealed a significantly greater osteoclast surface in bones from 8-week-old RARγ null male mice. This in vivo effect was cell lineage autonomous, and was associated with increased osteoclastogenesis in vitro from hematopoietic cells obtained from 8-week-old RARγ null male mice. The use of highly selective agonists in RANKL-induced osteoclast differentiation of wild type mouse whole bone marrow cells and RAW264.7 cells in vitro showed a stronger inhibitory effect of RARγ than RARα agonists, suggesting that RARγ is a more potent inhibitor of osteoclastogenesis. Furthermore, NFAT activation was also more strongly inhibited by RARγ than RARα agonists. While RARα and RARγ antagonists did not significantly affect osteoclast numbers in vitro, larger osteoclasts were observed in cultures stimulated with the antagonists, suggesting increased osteoclast fusion. Further investigation into the effect of retinoids in vivo revealed that oral administration of 5mg/kg/day ATRA for 10 days protected against bone loss induced by granulocyte colony-stimulating factor (G-CSF) by inhibiting the pro-osteoclastogenic action of G-CSF. Collectively, our data indicates a physiological role for RARγ as a negative regulator of osteoclastogenesis in vivo and in vitro, and reveals distinct influences of RARα and RARγ in bone structure regulation.
View details for DOI 10.1016/j.jsbmb.2015.03.005
View details for PubMedID 25800721
The PTH-G alpha(s)-Protein Kinase A Cascade Controls alpha NAC Localization To Regulate Bone Mass
MOLECULAR AND CELLULAR BIOLOGY
2014; 34 (9): 1622-1633
The binding of PTH to its receptor induces Gαs-dependent cAMP accumulation to turn on effector kinases, including protein kinase A (PKA). The phenotype of mice with osteoblasts specifically deficient for Gαs is mimicked by a mutation leading to cytoplasmic retention of the transcriptional coregulator αNAC, suggesting that Gαs and αNAC form part of a common genetic pathway. We show that treatment of osteoblasts with PTH(1-34) or the PKA-selective activator 6Bnz-cAMP lead to translocation of αNAC to the nucleus. αNAC was phosphorylated by PKA at serine 99 in vitro. Phospho-S99-αNAC accumulated in osteoblasts exposed to PTH(1-34) or 6Bnz-cAMP but not in treated cells expressing dominant negative PKA. Nuclear accumulation was abrogated by an S99A mutation but enhanced by a phosphomimetic residue (S99D). ChIP analysis showed that PTH(1-34) or 6Bnz-cAMP treatment leads to accumulation of αNAC at the Osteocalcin (Ocn) promoter. Altered gene dosage for Gαs and αNAC in compound heterozygous mice results in reduced bone mass, increased numbers of osteocytes, and enhanced expression of Sost. Our results show that αNAC is a substrate of PKA following PTH signaling. This enhances αNAC translocation to the nucleus and leads to its accumulation at target promoters to regulate transcription and affect bone mass.
View details for DOI 10.1128/MCB.01434-13
View details for Web of Science ID 000334316300007
View details for PubMedID 24550008
Mesenchymal progenitors and the osteoblast lineage in bone marrow hematopoietic niches.
Current osteoporosis reports
2014; 12 (1): 22-32
The bone marrow cavity is essential for the proper development of the hematopoietic system. In the last few decades, it has become clear that mesenchymal stem/progenitor cells as well as cells of the osteoblast lineage, besides maintaining bone homeostasis, are also fundamental regulators of bone marrow hematopoiesis. Several studies have demonstrated the direct involvement of mesenchymal and osteoblast lineage cells in the maintenance and regulation of supportive microenvironments necessary for quiescence, self-renewal and differentiation of hematopoietic stem cells. In addition, specific niches have also been identified within the bone marrow for maturing hematopoietic cells. Here we will review recent findings that have highlighted the roles of mesenchymal progenitors and cells of the osteoblast lineage in regulating distinct stages of hematopoiesis.
View details for DOI 10.1007/s11914-014-0190-7
View details for PubMedID 24477415
Interactions Between B Lymphocytes and the Osteoblast Lineage in Bone Marrow
CALCIFIED TISSUE INTERNATIONAL
2013; 93 (3): 261-268
The regulatory effects of the immune system on the skeleton during homeostasis and activation have been appreciated for years. In the past decade it has become evident that bone tissue can also regulate immune cell development. In the bone marrow, the differentiation of hematopoietic progenitors requires specific microenvironments, called "niches," provided by various subsets of stromal cells, many of which are of mesenchymal origin. Among these stromal cell populations, cells of the osteoblast lineage serve a supportive function in the maintenance of normal hematopoiesis, and B lymphopoiesis in particular. Within the osteoblast lineage, distinct differentiation stages exert differential regulatory effects on hematopoietic development. In this review we will highlight the critical role of osteoblast progenitors in the perivascular B lymphocyte niche.
View details for DOI 10.1007/s00223-013-9753-3
View details for Web of Science ID 000323233500009
View details for PubMedID 23839529
Potent constitutive cyclic AMP-generating activity of XL alpha s implicates this imprinted GNAS product in the pathogenesis of McCune-Albright Syndrome and fibrous dysplasia of bone
2011; 48 (2): 312-320
Patients with McCune-Albright syndrome (MAS), characterized primarily by hyperpigmented skin lesions, precocious puberty, and fibrous dyslasia of bone, carry postzygotic heterozygous mutations of GNAS causing constitutive cAMP signaling. GNAS encodes the ?-subunit of the stimulatory G protein (Gs?), as well as a large variant (XL?s) derived from the paternal allele. The mutations causing MAS affect both GNAS products, but whether XL?s, like Gs?, can be involved in the pathogenesis remains unknown. Here, we investigated biopsy samples from four previously reported and eight new patients with MAS. Activating mutations of GNAS (Arg201 with respect to the amino acid sequence of Gs?) were present in all the previously reported and five of the new cases. The mutation was detected within the paternally expressed XL?s transcript in five and the maternally expressed NESP55 transcript in four cases. Tissues carrying paternal mutations appeared to have higher XL?s mRNA levels than maternal mutations. The human XL?s mutant analogous to Gs?-R201H (XL?s-R543H) showed markedly higher basal cAMP accumulation than wild-type XL?s in transfected cells. Wild-type XL?s demonstrated higher basal and isoproterenol-induced cAMP signaling than Gs? and co-purified with G?1?2 in transduced cells. XL?s mRNA was measurable in mouse calvarial cells, with its level being significantly higher in undifferentiated cells than those expressing preosteoblastic markers osterix and alkaline phosphatase. XL?s mRNA was also expressed in murine bone marrow stromal cells and preosteoblastic MC3T3-E1 cells. Our findings are consistent with the possibility that constitutive XL?s activity adds to the molecular pathogenesis of MAS and fibrous dysplasia of bone.
View details for DOI 10.1016/j.bone.2010.09.032
View details for Web of Science ID 000286543700019
View details for PubMedID 20887824
Spermatogenesis and the regulation of Ca2+-calmodulin-dependent protein kinase IV localization are not dependent on calspermin
MOLECULAR AND CELLULAR BIOLOGY
2001; 21 (17): 6066-6070
Calspermin and Ca(2+)-calmodulin-dependent protein kinase IV (CaMKIV) are two proteins encoded by the Camk4 gene. CaMKIV is found in multiple tissues, including brain, thymus, and testis, while calspermin is restricted to the testis. In the mouse testis, both proteins are expressed within elongating spermatids. We have recently shown that deletion of CaMKIV has no effect on calspermin expression but does impair spermiogenesis by disrupting the exchange of sperm basic nuclear proteins. The function of calspermin within the testis is unclear, although it has been speculated to play a role in binding and sequestering calmodulin during the development of the germ cell. To investigate the contribution of calspermin to spermatogenesis, we have used Cre/lox technology to specifically delete calspermin, while leaving kinase expression intact. We unexpectedly found that calspermin is not required for male fertility. We further demonstrate that CaMKIV expression and localization are unaffected by the absence of calspermin and that calspermin does not colocalize to the nuclear matrix with CaMKIV.
View details for Web of Science ID 000170349900034
View details for PubMedID 11486043
Female fertility is reduced in mice lacking Ca2+ calmodulin-dependent protein kinase IV
2000; 141 (12): 4777-4783
Ca2+/calmodulin-dependent protein kinase IV (CaMKIV) is a serine/threonine protein kinase with limited tissue distribution. CaMKIV is highly expressed in the testis, where it is found in transcriptionally inactive elongating spermatids. We have recently generated mice deficient in CaMKIV. In the absence of CaMKIV, the exchange of sperm nuclear basic proteins in male spermatids is impaired, resulting in male infertility secondary to defective spermiogenesis. The involvement of CaMKIV in female fertility has not been addressed. Here we report that female fertility is markedly reduced in CaMKIV-deficient mice due to impaired follicular development and ovulation. CaMKIV is expressed in the ovary, where it is localized in granulosa cells. We further find that in cultured granulosa cells, CaMKIV expression and subcellular localization are hormonally regulated. As granulosa cells differentiate, CaMKIV levels decrease and the kinase translocates from the nucleus into the cytoplasm. Our results demonstrate a critical role for CaMKIV in female reproduction and point to a potential function in granulosa cell differentiation.
View details for Web of Science ID 000165360900056
View details for PubMedID 11108293
Spermiogenesis and exchange of basic nuclear proteins are impaired in male germ cells lacking Camk4
2000; 25 (4): 448-452
Ca2+/calmodulin-dependent protein kinase IV (Camk4; also known as CaMKIV), a multifunctional serine/threonine protein kinase with limited tissue distribution, has been implicated in transcriptional regulation in lymphocytes, neurons and male germ cells. In the mouse testis, however, Camk4 is expressed in spermatids and associated with chromatin and nuclear matrix. Elongating spermatids are not transcriptionally active, raising the possibility that Camk4 has a novel function in male germ cells. To investigate the role of Camk4 in spermatogenesis, we have generated mice with a targeted deletion of the gene Camk4. Male Camk4-/- mice are infertile with impairment of spermiogenesis in late elongating spermatids. The sequential deposition of sperm basic nuclear proteins on chromatin is disrupted, with a specific loss of protamine-2 and prolonged retention of transition protein-2 (Tnp2) in step-15 spermatids. Protamine-2 is phosphorylated by Camk4 in vitro, implicating a connection between Camk4 signalling and the exchange of basic nuclear proteins in mammalian male germ cells. Defects in protamine-2 have been identified in sperm of infertile men, suggesting that our results may have clinical implications for the understanding of human male infertility.
View details for Web of Science ID 000088615000024
View details for PubMedID 10932193
Ca2+/calmodulin-dependent protein kinase IV is expressed in spermatids and targeted to chromatin and the nuclear matrix
JOURNAL OF BIOLOGICAL CHEMISTRY
2000; 275 (11): 7994-7999
Ca(2+)/calmodulin-dependent protein kinase IV and calspermin are two proteins encoded by the Camk4 gene. Both are highly expressed in the testis, where in situ hybridization studies in rat testes have demonstrated that CaMKIV mRNA is localized to pachytene spermatocytes, while calspermin mRNA is restricted to spermatids. We have examined the expression patterns of both CaMKIV and calspermin in mouse testis and unexpectedly find that CaMKIV is expressed in spermatogonia and spermatids but excluded from spermatocytes, while calspermin is found only in spermatids. CaMKIV and calspermin expression in the testis are stage-dependent and appear to be coordinately regulated. In germ cells, we find that CaMKIV is associated with the chromatin. We further demonstrate that a fraction of CaMKIV in spermatids is hyperphosphorylated and specifically localized to the nuclear matrix. These novel findings may implicate CaMKIV in chromatin remodeling during nuclear condensation of spermatids.
View details for Web of Science ID 000085913300078
View details for PubMedID 10713118
Books and Book Chapters
- Development of the skeleton Osteoporosis, 4th Edition Academic Press. 2013
- The role of bone cells in establishing the hematopoietic stem cell niche Osteoimmunology: Interactions of the Immune and Skeletal Systems 2011: 81-99