Induced muscle progenitor cells [ATAC-seq]

The generation of myotubes from fibroblasts upon forced MyoD expression is a classic example of factor-induced reprogramming in mammals. We recently discovered that additional modulation of signaling pathways with small molecules facilitates reprogramming to more primitive induced muscle progenitor cells (iMPCs). However, the mechanisms by which a single transcription factor drives differentiated cells into distinct developmental states remain unknown. We therefore dissected the transcriptional and epigenetic dynamics of fibroblasts undergoing MyoD-dependent reprogramming to either myotubes or iMPCs using a novel MyoD transgenic model. To this end, we performed ATAC sequencing for Pax7-nGFP positive iMPCs/satellite cells, cells undergoing dedifferentiation (i.e. Dox+FRG) or transdifferentiation (i.e. Dox) and cells overexpressing a wild type MyoD or a mutant MyoD (i.e. MN) in the presence of FRG. Our analyses elucidate the role of MyoD in myogenic reprogramming and derive general principles by which transcription factors and signaling pathways cooperate to rewire cell identity. Our results may also inform on potential therapeutic applications of direct reprogramming. ATAC-seq was performed for 14 samples in duplicate.