Project description:Direct lineage reprogramming provides a unique system to study cell fate transitions and unearth molecular mechanisms that safeguard cellular identity. We previously reported on direct conversion of mouse fibroblasts into induced myogenic progenitor cells (iMPCs) by means of transient MyoD overexpression in concert with small molecules treatment. Here we employed integrative multi-omic assays to delineate the molecular landscape of fibroblast reprogramming into iMPCs in comparison to transdifferentiation into myogenic cells solely by MyoD overexpression. Utilizing bulk RNA-sequencing and mass spectrometry we characterized molecular regulators and pathways that endow a myogenic stem cell identity on fibroblasts only in the presence of small molecule treatment. We further demonstrate that iMPC reprogramming is a stepwise process, commencing with the appearance of myofibers and committed myogenic progenitors prior to the formation of satellite cell-like myogenic progenitors that express a suite of stem cell markers including Pax7, Dek, Myf5, Sox8, and Dmrt2. To directly compare iMPCs to satellite cell-derived primary myoblasts, we employed a fluorescent Pax7-GFP reporter to purify Pax7+ cells from the heterogenous iMPC cultures and assess their equivalency to FACS-purified Pax7-GFP+ myoblasts. We demonstrate that Pax7+ iMPCs share molecular attributes with myoblasts, however also express genes and signaling pathways that are indicative of activated satellite cells including Carm1, Dlk1, Lgr5, Fos, Dek, Calcr and Pitx3. We further establish that iMPC formation and maintenance is dependent on the Notch pathway, as small molecule inhibition of Notch abrogates iMPC formation and derails stable iMPC cultures via depletion of Pax7 expressing cells. Lastly, using single cell RNA-sequencing we determine the cell populations that comprise iMPCs in addition to reconstructing the differentiation trajectory present in these heterogenous cultures. We demonstrate that a highly proliferative activated satellite cell-like population differentiates into committed myoblasts and myocytes that further give rise to myofibers that express mature muscle markers, thus capturing a dynamic differentiation program in vitro. Collectively, this study charts a molecular blueprint for reprogramming fibroblasts into myogenic stem and progenitor cells and further establishes the fidelity of stable iMPC cultures in capturing skeletal muscle regeneration in vitro for disease modeling and basic research applications.
Project description:Direct lineage reprogramming provides a unique system to study cell fate transitions and unearth molecular mechanisms that safeguard cellular identity. We previously reported on direct conversion of mouse fibroblasts into induced myogenic progenitor cells (iMPCs) by means of transient MyoD overexpression in concert with small molecules treatment. Here we employed integrative multi-omic assays to delineate the molecular landscape of fibroblast reprogramming into iMPCs in comparison to transdifferentiation into myogenic cells solely by MyoD overexpression. Utilizing bulk RNA-sequencing and mass spectrometry we characterized molecular regulators and pathways that endow a myogenic stem cell identity on fibroblasts only in the presence of small molecule treatment. We further demonstrate that iMPC reprogramming is a stepwise process, commencing with the appearance of myofibers and committed myogenic progenitors prior to the formation of satellite cell-like myogenic progenitors that express a suite of stem cell markers including Pax7, Dek, Myf5, Sox8, and Dmrt2. To directly compare iMPCs to satellite cell-derived primary myoblasts, we employed a fluorescent Pax7-GFP reporter to purify Pax7+ cells from the heterogenous iMPC cultures and assess their equivalency to FACS-purified Pax7-GFP+ myoblasts. We demonstrate that Pax7+ iMPCs share molecular attributes with myoblasts, however also express genes and signaling pathways that are indicative of activated satellite cells including Carm1, Dlk1, Lgr5, Fos, Dek, Calcr and Pitx3. We further establish that iMPC formation and maintenance is dependent on the Notch pathway, as small molecule inhibition of Notch abrogates iMPC formation and derails stable iMPC cultures via depletion of Pax7 expressing cells. Lastly, using single cell RNA-sequencing we determine the cell populations that comprise iMPCs in addition to reconstructing the differentiation trajectory present in these heterogenous cultures. We demonstrate that a highly proliferative activated satellite cell-like population differentiates into committed myoblasts and myocytes that further give rise to myofibers that express mature muscle markers, thus capturing a dynamic differentiation program in vitro. Collectively, this study charts a molecular blueprint for reprogramming fibroblasts into myogenic stem and progenitor cells and further establishes the fidelity of stable iMPC cultures in capturing skeletal muscle regeneration in vitro for disease modeling and basic research applications.
Project description:Direct lineage reprogramming provides a unique system to study cell fate transitions and unearth molecular mechanisms that safeguard cellular identity. We previously reported on direct conversion of mouse fibroblasts into induced myogenic progenitor cells (iMPCs) by means of transient MyoD overexpression in concert with small molecules treatment. Here we employed integrative multi-omic assays to delineate the molecular landscape of fibroblast reprogramming into iMPCs in comparison to transdifferentiation into myogenic cells solely by MyoD overexpression. Utilizing bulk RNA-sequencing and mass spectrometry we characterized molecular regulators and pathways that endow a myogenic stem cell identity on fibroblasts only in the presence of small molecule treatment. We further demonstrate that iMPC reprogramming is a stepwise process, commencing with the appearance of myofibers and committed myogenic progenitors prior to the formation of satellite cell-like myogenic progenitors that express a suite of stem cell markers including Pax7, Dek, Myf5, Sox8, and Dmrt2. To directly compare iMPCs to satellite cell-derived primary myoblasts, we employed a fluorescent Pax7-GFP reporter to purify Pax7+ cells from the heterogenous iMPC cultures and assess their equivalency to FACS-purified Pax7-GFP+ myoblasts. We demonstrate that Pax7+ iMPCs share molecular attributes with myoblasts, however also express genes and signaling pathways that are indicative of activated satellite cells including Carm1, Dlk1, Lgr5, Fos, Dek, Calcr and Pitx3. We further establish that iMPC formation and maintenance is dependent on the Notch pathway, as small molecule inhibition of Notch abrogates iMPC formation and derails stable iMPC cultures via depletion of Pax7 expressing cells. Lastly, using single cell RNA-sequencing we determine the cell populations that comprise iMPCs in addition to reconstructing the differentiation trajectory present in these heterogenous cultures. We demonstrate that a highly proliferative activated satellite cell-like population differentiates into committed myoblasts and myocytes that further give rise to myofibers that express mature muscle markers, thus capturing a dynamic differentiation program in vitro. Collectively, this study charts a molecular blueprint for reprogramming fibroblasts into myogenic stem and progenitor cells and further establishes the fidelity of stable iMPC cultures in capturing skeletal muscle regeneration in vitro for disease modeling and basic research applications.
Project description:Direct lineage reprogramming provides a unique system to study cell fate transitions and unearth molecular mechanisms that safeguard cellular identity. We previously reported on direct conversion of mouse fibroblasts into induced myogenic progenitor cells (iMPCs) by transient MyoD overexpression in concert with small molecules treatment. Here we employed integrative multi-omic approaches to delineate the molecular landscape of fibroblast reprogramming into iMPCs in comparison to transdifferentiation into myogenic cells solely by MyoD overexpression. Utilizing bulk RNA-sequencing and mass spectrometry, we uncovered molecular regulators and pathways that endow a myogenic stem cell identity on fibroblasts only in the presence of small molecule treatment. In addition, we demonstrate that Pax7+ cells in iMPCs share molecular attributes with myoblasts, however in addition express unique genes, proteins and pathways that are indicative of a more activated satellite cell-like state in vitro. Collectively, this study charts a molecular blueprint for reprogramming fibroblasts into muscle stem and progenitor cells and further establishes the fidelity of stable iMPC cultures in capturing skeletal muscle regeneration in vitro for disease modeling and basic research applications.
Project description:Engineered CRISPR/Cas9-based transcriptional activators can potently and specifically activate endogenous fate-determining genes to direct differentiation of pluripotent stem cells. Here, we demonstrate that endogenous activation of the PAX7 transcription factor results in stable epigenetic remodeling and directly reprograms human pluripotent stem cells into skeletal myoblast progenitor cells. Compared to the exogenous overexpression of PAX7 cDNA, we find that endogenous activation results in the generation of more proliferative myogenic progenitors that can maintain PAX7 expression over multiple passages in serum-free conditions while preserving the capacity for terminal myogenic differentiation. Transplantation of human myogenic progenitors derived from endogenous activation of PAX7 into immunodeficient mice resulted in a greater number of human dystrophin+ myofibers compared to exogenous PAX7 overexpression. RNA-seq analysis also revealed transcriptome-wide differences between myogenic progenitors generated via CRISPR-based endogenous activation of PAX7 and exogenous PAX7 cDNA overexpression. These studies demonstrate the utility of CRISPR/Cas9-based transcriptional activators for progenitor cell specification and their potential for regenerative medicine.
Project description:MicroRNAs (miRNAs) are important in the regulation of many biological processes such as growth and development. To evaluate the role of miRNAs in skeletal muscle regeneration, global miRNA expression was measured during muscle cell growth and differentiation. Primary cultures of murine myogenic progenitor cells (MPC) were studied for miRNA expression using quantitative PCR-array. During MPC differentiation or proliferation, 139 or 16 miRNAs, respectively, exhibited significant >2-fold changes. Cluster analysis revealed 5 distinct miRNA expression patterns at different stages of differentiation. Fourteen miRNAs exhibiting >10-fold change during differentiation included miR-1, 10b, 96, 98, 133a, 139-5p, 330, 335-3p, 339-5p, 344, 486, 499, 504, and 598. Ten of these miRNAs were located in introns of protein coding genes, such as miR-499 located in the myosin heavy chain isoform Myh7b. In silico analysis of possible miRNA-mRNA interactions indicated that many of these miRNAs targeted mRNA critically involved in muscle differentiation. Interestingly, several miRNAs targeted different sites in a given mRNA, suggesting coordinated expression of multiple miRNAs to ensure the regulation of essential genes. These results identify differentially expressed miRNAs that could represent new regulatory elements in MPC proliferation and differentiation. Myogenic progenitor cell (MPC) growth and differentiation are key elements duing muscle regeneration. Using defined culture conditions to promote proliferation or differentiation, we profiled miRNA expression in primary cultures of murine MPC.