Project description:The earliest skeletal muscle progenitor cells (SMPCs) derived from human pluripotent stem cells (hPSCs) are often identified by factors expressed by a diverse number of progenitors. An early transcriptional checkpoint that defines myogenic commitment could improve hPSC differentiation to skeletal muscle. Analysis of several myogenic factors in human embryos and early hPSC differentiations found SIX1+PAX3+ co-expression was most indictive of myogenesis. Using dCas9-KRAB hPSCs, we demonstrate that early inhibition of SIX1 alone significantly decreased PAX3 expression, reduced PAX7+ SMPCs, and myotubes later in differentiation. Emergence of SIX1+PAX3+ precursors can be improved by manipulating seeding density, monitoring metabolic secretion and altering the concentration of CHIR99021. These modifications resulted in the co-emergence of hPSC-derived sclerotome, cardiac and neural crest that we hypothesized enhanced hPSC myogenic differentiation. Inhibition of non-myogenic lineages modulated PAX3 independent of SIX1. To better understand SIX1 expression, we compared directed differentiations to fetal progenitors and adult satellite cells by RNA-seq. Although SIX1 continued to be expressed across human development, SIX1 co-factor expression was dependent on developmental timing. We provide a resource to enable efficient derivation of skeletal muscle from hPSCs.
Project description:To better characterize the transcriptomic profile of hPSC-derived SMPCS, we performed a comparative analysis on the gene signature of FACS-enriched human embryonic (week 9-10), fetal (week 16-20), and hPSC SMPCs and adult SCs using bulk RNA seq.
Project description:The transcriptional mechanisms driving lineage specification during development are still largely unknown as the interplay of multiple transcription factors makes it difficult to dissect these molecular events. Using a cell-based differentiation platform to probe transcription function, we investigated the role of the key paraxial mesoderm and skeletal myogenic commitment factors, Msgn1, Tbx6, Foxc1, Pax3, Paraxis, Meox1, Six1 and Myf5, in paraxial mesoderm and skeletal myogenesis. From this study, we define a genetic hierarchy, with Pax3 emerging as the gatekeeper between the presomitic mesoderm and the myogenic lineage. By assaying chromatin accessibility, genomic binding and transcription profiling in mesodermal cells from mouse and human Pax3-induced embryonic stem cells and Pax3-null E9.5 mouse embryos, we identified conserved Pax3 functions in the activation of the skeletal myogenic lineage through modulation of Hedgehog, Notch, and BMP signaling pathways. In addition, we demonstrate that Pax3 molecular function involves chromatin remodeling of its bound elements through an increase in chromatin accessibility and cooperation with Six4 and Tead2 factors. Together, our data provide the first integrated analysis of Pax3 function, demonstrating its ability to remodel chromatin in mesodermal cells from developing embryos and proving a mechanistic footing for the transcriptional hierarchy driving myogenesis.
Project description:The fusion transcription factor PAX3-FOXO1 drives oncogenesis in a subset of rhabdomyosarcomas, however the mechanisms by which it remodels chromatin are unknown. We find PAX3-FOXO1 reprograms the cis-regulatory landscape by inducing super enhancers (SEs), in collaboration with master transcription factors MYOG, MYOD and MYCN. This myogenic SE circuitry is consistent across cell lines and primary tumors. Deregulation of PAX3-FOXO1 itself occurs by translocation-induced chromatin loops bringing the PAX3 promoter under the control of FOXO1 enhancers. Protein targets induced by, or bound to, PAX3-FOXO1 occupied SEs, were selectively sensitive to small molecule inhibition. PAX3-FOXO1 co-binds BRD4 at SEs, and BET bromodomains are required for PAX3-FOXO1-dependent transcription and cancer cell growth.
Project description:The fusion transcription factor PAX3-FOXO1 drives oncogenesis in a subset of rhabdomyosarcomas, however the mechanisms by which it remodels chromatin are unknown. We find PAX3-FOXO1 reprograms the cis-regulatory landscape by inducing super enhancers (SEs), in collaboration with master transcription factors MYOG, MYOD and MYCN. This myogenic SE circuitry is consistent across cell lines and primary tumors. Deregulation of PAX3-FOXO1 itself occurs by translocation-induced chromatin loops bringing the PAX3 promoter under the control of FOXO1 enhancers. Protein targets induced by, or bound to, PAX3-FOXO1 occupied SEs, were selectively sensitive to small molecule inhibition. PAX3-FOXO1 co-binds BRD4 at SEs, and BET bromodomains are required for PAX3-FOXO1-dependent transcription and cancer cell growth.
Project description:The skeletal myogenic lineage in developing embryos is specified within the somites and requires members of the Paired box (Pax) family of transcription factors. In particular, Pax3 is the first member of this family expressed in the central region of the dermomyotome and it is necessary for specification, migration and survival of the myogenic progenitors that will form the muscles of the limbs, diaphragm and tongue. To investigate Pax3 molecular functions in the developing mesoderm, we generated doxycycline-inducible mouse embryonic stem (ES) cells expressing untagged and HaFlag-tagged-Pax3. These cell lines were used to unbiasedly identify its interacting partners by tandem affinity purification followed by mass spectrometry.
Project description:Genetic and shRNA-mediated inhibition of SIX1 expression in RMS cells induces myogenic differentiation and impedes RMS tumor growth. To elucidate the mechanism by which SIX1 loss activates a differentiation program, we performed SIX1, MYOD1, and H3K27ac ChIPseq in two SIX1 knockdown SMS-CTR cell lines and one control SMS-CTR cell line to profile changes in transcriptional activity and myogenic transcription factor binding in fusion-negative Rhabdomyosarcoma.
Project description:Fusion-positive rhabdomyosarcoma (FP-RMS) driven by the expression of the PAX3-FOXO1 (P3F) fusion oncoprotein is an aggressive subtype of pediatric rhabdomyosarcoma. FP-RMS histologically resembles developing muscle yet occurs throughout the body in areas devoid of skeletal muscle highlighting that FP-RMS is not derived from an exclusively myogenic cell of origin. Here we demonstrate that P3F reprograms mouse and human endothelial progenitors to FP-RMS. We show that P3F expression in aP2-Cre expressing cells reprograms endothelial progenitors to functional myogenic stem cells capable of regenerating injured muscle fibers. Further, we describe a FP-RMS mouse model driven by P3F expression and Cdkn2a loss in endothelial cells. Additionally, we show that P3F expression in TP53-null human iPSCs blocks endothelial-directed differentiation and guides cells to become myogenic cells that form FP-RMS tumors in immunocompromised mice. Together these findings demonstrate that FP-RMS can originate from aberrant development of non-myogenic cells driven by P3F.
Project description:Fusion-positive rhabdomyosarcoma (FP-RMS) driven by the expression of the PAX3-FOXO1 (P3F) fusion oncoprotein is an aggressive subtype of pediatric rhabdomyosarcoma. FP-RMS histologically resembles developing muscle yet occurs throughout the body in areas devoid of skeletal muscle highlighting that FP-RMS is not derived from an exclusively myogenic cell of origin. Here we demonstrate that P3F reprograms mouse and human endothelial progenitors to FP-RMS. We show that P3F expression in aP2-Cre expressing cells reprograms endothelial progenitors to functional myogenic stem cells capable of regenerating injured muscle fibers. Further, we describe a FP-RMS mouse model driven by P3F expression and Cdkn2a loss in endothelial cells. Additionally, we show that P3F expression in TP53-null human iPSCs blocks endothelial-directed differentiation and guides cells to become myogenic cells that form FP-RMS tumors in immunocompromised mice. Together these findings demonstrate that FP-RMS can originate from aberrant development of non-myogenic cells driven by P3F.
Project description:Fusion-positive rhabdomyosarcoma (FP-RMS) driven by the expression of the PAX3-FOXO1 (P3F) fusion oncoprotein is an aggressive subtype of pediatric rhabdomyosarcoma. FP-RMS histologically resembles developing muscle yet occurs throughout the body in areas devoid of skeletal muscle highlighting that FP-RMS is not derived from an exclusively myogenic cell of origin. Here we demonstrate that P3F reprograms mouse and human endothelial progenitors to FP-RMS. We show that P3F expression in aP2-Cre expressing cells reprograms endothelial progenitors to functional myogenic stem cells capable of regenerating injured muscle fibers. Further, we describe a novel FP-RMS mouse model driven by P3F expression and CDKN2A loss in endothelial cells. Additionally, we show that P3F expression in p53 null human iPSCs blocks endothelial directed differentiation and guides cells to become myogenic cells that form FP-RMS tumors in immunocompromised mice. Together these findings demonstrate that FP-RMS can originate from aberrant development of non-myogenic cells driven by P3F.