Dr. Moritz Mall is a research scientist in the laboratory of Prof. Marius Wernig at the Institute of Stem Cell Biology and Regenerative Medicine at Stanford University. After studying biochemistry and molecular biology at the LMU in Munich and the ETH in Zurich he received his Ph.D. from the EMBL in Heidelberg for his mechanistic studies on mitotic cell division. Dr. Mall’s current research focus is on the mechanisms of cell fate determination during reprogramming, development and disease.
Honors & Awards
Trainee Professional Development Award, Society for Neuroscience (2016)
DFG Postdoctoral Fellowship, German Research Foundation (2014-2016)
EMBL International PhD programme fellowship, European Molecular Biology Laboratory (2007-2011)
Education & Certifications
PhD, EMBL Heidelberg & ETH Zurich, Cell Biology (2011)
MSc, ETH Zurich, Biochemistry & Molecular Biology (2007)
Vordiplom, LMU Munich, Biology & Human Genetics (2004)
Myt1l safeguards neuronal identity by actively repressing many non-neuronal fates.
2017; 544 (7649): 245–49
Normal differentiation and induced reprogramming require the activation of target cell programs and silencing of donor cell programs. In reprogramming, the same factors are often used to reprogram many different donor cell types. As most developmental repressors, such as RE1-silencing transcription factor (REST) and Groucho (also known as TLE), are considered lineage-specific repressors, it remains unclear how identical combinations of transcription factors can silence so many different donor programs. Distinct lineage repressors would have to be induced in different donor cell types. Here, by studying the reprogramming of mouse fibroblasts to neurons, we found that the pan neuron-specific transcription factor Myt1-like (Myt1l) exerts its pro-neuronal function by direct repression of many different somatic lineage programs except the neuronal program. The repressive function of Myt1l is mediated via recruitment of a complex containing Sin3b by binding to a previously uncharacterized N-terminal domain. In agreement with its repressive function, the genomic binding sites of Myt1l are similar in neurons and fibroblasts and are preferentially in an open chromatin configuration. The Notch signalling pathway is repressed by Myt1l through silencing of several members, including Hes1. Acute knockdown of Myt1l in the developing mouse brain mimicked a Notch gain-of-function phenotype, suggesting that Myt1l allows newborn neurons to escape Notch activation during normal development. Depletion of Myt1l in primary postmitotic neurons de-repressed non-neuronal programs and impaired neuronal gene expression and function, indicating that many somatic lineage programs are actively and persistently repressed by Myt1l to maintain neuronal identity. It is now tempting to speculate that similar 'many-but-one' lineage repressors exist for other cell fates; such repressors, in combination with lineage-specific activators, would be prime candidates for use in reprogramming additional cell types.
View details for DOI 10.1038/nature21722
View details for PubMedID 28379941
The novel tool of cell reprogramming for applications in molecular medicine.
Journal of molecular medicine (Berlin, Germany)
Recent discoveries in the field of stem cell biology have enabled scientists to "reprogram" cells from one type to another. For example, it is now possible to place adult skin or blood cells in a dish and convert them into neurons, liver, or heart cells. It is also possible to literally "rejuvenate" adult cells by reprogramming them into embryonic-like stem cells, which in turn can be differentiated into every tissue and cell type of the human body. Our ability to reprogram cell types has four main implications for medicine: (1) scientists can now take skin or blood cells from patients and convert them to other cells to study disease processes. This disease modeling approach has the advantage over animal models because it is directly based on human patient cells. (2) Reprogramming could also be used as a "clinical trial in a dish" to evaluate the general efficacy and safety of newly developed drugs on human patient cells before they would be tested in animal models or people. (3) In addition, many drugs have deleterious side effects like heart arrhythmias in only a small and unpredictable subpopulation of patients. Reprogramming could facilitate precision medicine by testing the safety of already approved drugs first on reprogrammed patient cells in a personalized manner prior to administration. For example, drugs known to sometimes cause arrhythmias could be first tested on reprogrammed heart cells from individual patients. (4) Finally, reprogramming allows the generation of new tissues that could be grafted therapeutically to regenerate lost or damaged cells.
View details for DOI 10.1007/s00109-017-1550-4
View details for PubMedID 28597071
Generation of pure GABAergic neurons by transcription factor programming.
2017; 14 (6): 621–28
Approaches to differentiating pluripotent stem cells (PSCs) into neurons currently face two major challenges-(i) generated cells are immature, with limited functional properties; and (ii) cultures exhibit heterogeneous neuronal subtypes and maturation stages. Using lineage-determining transcription factors, we previously developed a single-step method to generate glutamatergic neurons from human PSCs. Here, we show that transient expression of the transcription factors Ascl1 and Dlx2 (AD) induces the generation of exclusively GABAergic neurons from human PSCs with a high degree of synaptic maturation. These AD-induced neuronal (iN) cells represent largely nonoverlapping populations of GABAergic neurons that express various subtype-specific markers. We further used AD-iN cells to establish that human collybistin, the loss of gene function of which causes severe encephalopathy, is required for inhibitory synaptic function. The generation of defined populations of functionally mature human GABAergic neurons represents an important step toward enabling the study of diseases affecting inhibitory synaptic transmission.
View details for DOI 10.1038/nmeth.4291
View details for PubMedID 28504679
Partial Reprogramming of Pluripotent Stem Cell-Derived Cardiomyocytes into Neurons.
2017; 7: 44840
Direct reprogramming of somatic cells has been demonstrated, however, it is unknown whether electrophysiologically-active somatic cells derived from separate germ layers can be interconverted. We demonstrate that partial direct reprogramming of mesoderm-derived cardiomyocytes into neurons is feasible, generating cells exhibiting structural and electrophysiological properties of both cardiomyocytes and neurons. Human and mouse pluripotent stem cell-derived CMs (PSC-CMs) were transduced with the neurogenic transcription factors Brn2, Ascl1, Myt1l and NeuroD. We found that CMs adopted neuronal morphologies as early as day 3 post-transduction while still retaining a CM gene expression profile. At week 1 post-transduction, we found that reprogrammed CMs expressed neuronal markers such as Tuj1, Map2, and NCAM. At week 3 post-transduction, mature neuronal markers such as vGlut and synapsin were observed. With single-cell qPCR, we temporally examined CM gene expression and observed increased expression of neuronal markers Dcx, Map2, and Tubb3. Patch-clamp analysis confirmed the neuron-like electrophysiological profile of reprogrammed CMs. This study demonstrates that PSC-CMs are amenable to partial neuronal conversion, yielding a population of cells exhibiting features of both neurons and CMs.
View details for DOI 10.1038/srep44840
View details for PubMedID 28327614
Dissecting direct reprogramming from fibroblast to neuron using single-cell RNA-seq
2016; 534 (7607): 391-?
Direct lineage reprogramming represents a remarkable conversion of cellular and transcriptome states. However, the intermediate stages through which individual cells progress during reprogramming are largely undefined. Here we use single-cell RNA sequencing at multiple time points to dissect direct reprogramming from mouse embryonic fibroblasts to induced neuronal cells. By deconstructing heterogeneity at each time point and ordering cells by transcriptome similarity, we find that the molecular reprogramming path is remarkably continuous. Overexpression of the proneural pioneer factor Ascl1 results in a well-defined initialization, causing cells to exit the cell cycle and re-focus gene expression through distinct neural transcription factors. The initial transcriptional response is relatively homogeneous among fibroblasts, suggesting that the early steps are not limiting for productive reprogramming. Instead, the later emergence of a competing myogenic program and variable transgene dynamics over time appear to be the major efficiency limits of direct reprogramming. Moreover, a transcriptional state, distinct from donor and target cell programs, is transiently induced in cells undergoing productive reprogramming. Our data provide a high-resolution approach for understanding transcriptome states during lineage differentiation.
View details for DOI 10.1038/nature18323
View details for Web of Science ID 000377856800037
View details for PubMedID 27281220
View details for PubMedCentralID PMC4928860
The primate-specific noncoding RNA HPAT5 regulates pluripotency during human preimplantation development and nuclear reprogramming.
2016; 48 (1): 44-52
Long intergenic noncoding RNAs (lincRNAs) are derived from thousands of loci in mammalian genomes and are frequently enriched in transposable elements (TEs). Although families of TE-derived lincRNAs have recently been implicated in the regulation of pluripotency, little is known of the specific functions of individual family members. Here we characterize three new individual TE-derived human lincRNAs, human pluripotency-associated transcripts 2, 3 and 5 (HPAT2, HPAT3 and HPAT5). Loss-of-function experiments indicate that HPAT2, HPAT3 and HPAT5 function in preimplantation embryo development to modulate the acquisition of pluripotency and the formation of the inner cell mass. CRISPR-mediated disruption of the genes for these lincRNAs in pluripotent stem cells, followed by whole-transcriptome analysis, identifies HPAT5 as a key component of the pluripotency network. Protein binding and reporter-based assays further demonstrate that HPAT5 interacts with the let-7 microRNA family. Our results indicate that unique individual members of large primate-specific lincRNA families modulate gene expression during development and differentiation to reinforce cell fate.
View details for DOI 10.1038/ng.3449
View details for PubMedID 26595768
Generation of induced neuronal cells by the single reprogramming factor ASCL1.
Stem cell reports
2014; 3 (2): 282-296
Direct conversion of nonneural cells to functional neurons holds great promise for neurological disease modeling and regenerative medicine. We previously reported rapid reprogramming of mouse embryonic fibroblasts (MEFs) into mature induced neuronal (iN) cells by forced expression of three transcription factors: ASCL1, MYT1L, and BRN2. Here, we show that ASCL1 alone is sufficient to generate functional iN cells from mouse and human fibroblasts and embryonic stem cells, indicating that ASCL1 is the key driver of iN cell reprogramming in different cell contexts and that the role of MYT1L and BRN2 is primarily to enhance the neuronal maturation process. ASCL1-induced single-factor neurons (1F-iN) expressed mature neuronal markers, exhibited typical passive and active intrinsic membrane properties, and formed functional pre- and postsynaptic structures. Surprisingly, ASCL1-induced iN cells were predominantly excitatory, demonstrating that ASCL1 is permissive but alone not deterministic for the inhibitory neuronal lineage.
View details for DOI 10.1016/j.stemcr.2014.05.020
View details for PubMedID 25254342
View details for PubMedCentralID PMC4176533
Mitotic lamin disassembly is triggered by lipid-mediated signaling.
journal of cell biology
2012; 198 (6): 981-990
Disassembly of the nuclear lamina is a key step during open mitosis in higher eukaryotes. The activity of several kinases, including CDK1 (cyclin-dependent kinase 1) and protein kinase C (PKC), has been shown to trigger mitotic lamin disassembly, yet their precise contributions are unclear. In this study, we develop a quantitative imaging assay to study mitotic lamin B1 disassembly in living cells. We find that CDK1 and PKC act in concert to mediate phosphorylation-dependent lamin B1 disassembly during mitosis. Using ribonucleic acid interference (RNAi), we showed that diacylglycerol (DAG)-dependent PKCs triggered rate-limiting steps of lamin disassembly. RNAi-mediated depletion or chemical inhibition of lipins, enzymes that produce DAG, delayed lamin disassembly to a similar extent as does PKC inhibition/depletion. Furthermore, the delay of lamin B1 disassembly after lipin depletion could be rescued by the addition of DAG. These findings suggest that lipins activate a PKC-dependent pathway during mitotic lamin disassembly and provide evidence for a lipid-mediated mitotic signaling event.
View details for DOI 10.1083/jcb.201205103
View details for PubMedID 22986494
Coordination of Kinase and Phosphatase Activities by Lem4 Enables Nuclear Envelope Reassembly during Mitosis
2012; 150 (1): 122-135
Mitosis in metazoa requires nuclear envelope (NE) disassembly and reassembly. NE disassembly is driven by multiple phosphorylation events. Mitotic phosphorylation of the protein BAF reduces its affinity for chromatin and the LEM family of inner nuclear membrane proteins; loss of this BAF-mediated chromatin-NE link contributes to NE disassembly. BAF must reassociate with chromatin and LEM proteins at mitotic exit to reform the NE; however, how its dephosphorylation is regulated is unknown. Here, we show that the C. elegans protein LEM-4L and its human ortholog Lem4 (also called ANKLE2) are both required for BAF dephosphorylation. They act in part by inhibiting BAF's mitotic kinase, VRK-1, in vivo and in vitro. In addition, Lem4/LEM-4L interacts with PP2A and is required for it to dephosphorylate BAF during mitotic exit. By coordinating VRK-1- and PP2A-mediated signaling on BAF, Lem4/LEM-4L controls postmitotic NE formation in a function conserved from worms to humans.
View details for DOI 10.1016/j.cell.2012.04.043
View details for Web of Science ID 000306115000012
View details for PubMedID 22770216
RET rearrangements in post-Chernobyl papillary thyroid carcinomas with a short latency analysed by interphase FISH
BRITISH JOURNAL OF CANCER
2006; 94 (10): 1472-1477
Tissue samples from 13 post-Chernobyl childhood thyroid tumours that occurred within a short period of time (4-8 years) after the Chernobyl accident have been investigated by interphase FISH analysis for rearrangements of RET. In all, 77% of cases showed RET/PTC rearrangements and a distinct intratumoural genetic heterogeneity. The data were compared to findings on 32 post-Chernobyl PTCs that occurred after a longer period of time (9-12 years) after the accident. In none of the cases from either group were 100% of cells positive for RET rearrangement. In addition, the pattern of RET-positive cells was different in the two groups (short vs longer latency). A significant clustering of aberrant cells could be detected in the long-latency subgroup, whereas the aberrant cells were more homogeneously distributed among the short-latency tumours. The findings suggest that oligoclonal tumour development occurs in post-Chernobyl PTCs. This pattern of different clones within the tumour appears to become more discrete in cases with longer latencies, suggesting either outgrowth of individual clones or development of later subclones with time.
View details for DOI 10.1038/sj.bjc.6603109
View details for Web of Science ID 000237648200018
View details for PubMedID 16641909
The conserved transmembrane nucleoporin NDC1 is required for nuclear pore complex assembly in vertebrate cells
2006; 22 (1): 93-103
Nuclear pore complexes (NPCs) are large proteinaceous channels embedded in the nuclear envelope (NE), through which exchange of molecules between the nucleus and cytosol occurs. Biogenesis of NPCs is complex and poorly understood. In particular, almost nothing is known about how NPCs are anchored in the NE. Here, we characterize vertebrate NDC1--a transmembrane nucleoporin conserved between yeast and metazoans. We show by RNA interference (RNAi) and biochemical depletion that NDC1 plays an important role in NPC and NE assembly in vivo and in vitro. RNAi experiments suggest a functional link between NDC1 and the soluble nucleoporins Nup93, Nup53, and Nup205. Importantly, NDC1 interacts with Nup53 in vitro. This suggests that NDC1 function involves forming a link between the NE membrane and soluble nucleoporins, thereby anchoring the NPC in the membrane.
View details for DOI 10.1016/j.molcel.2006.02.015
View details for Web of Science ID 000236897700010
View details for PubMedID 16600873