Dissecting mechanisms by which MyoD and small molecules convert fibroblasts to muscle progenitor cells

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 single cell RNA sequencing for Pax7-nGFP positive iMPCs/satellite cells and cells undergoing dedifferentiation (i.e. Dox+FRG) or transdifferentiation (i.e. Dox) 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. single cell RNA-seq was performed for 10 samples