A robust and practical myogenic cell system to explore cellular and genomic features of muscle differentiation [RNA-Seq]
The ability to recapitulate muscle differentiation in vitro has proven invaluable to investigate mechanisms of myogenesis, muscle cell function and muscle diseases. However, obtaining myoblasts from patients with neuromuscular diseases poses ethical and procedural challenges which limit investigations of molecular mechanisms of muscle pathophysiology. Alternative myogenic models have been developed, such as the derivation of myogenic cells from skin fibroblasts through activation of an endogenous myogenic program triggered by exogenous expression of murine Myod. In the context of this RNA-seq dataset, we compare the transcriptome of myo-converted human fibroblasts and isogenic in vitro differentiated myoblasts. We show that myogenic induction of fibroblasts elicits genome-wide transcriptomic changes indicative of strong myogenic commitment and differentiation, including marked upregulation of genes implicated in cell cycle exit and in several myogenic pathways. Yet, we find that myotubes are further along myogenic commitment than myo-converted fibroblasts under the conditions tested. Extension of myo-conversion to 7 days does not significantly enhance myogenic commitment, from a gene expression standpoint. This suggests that myo-converted fibroblasts and myotubes retain some cell type specificity of gene expression profiles. Although these myogenic cell types are not identical, our results nonetheless favor a view of myo-converted fibroblasts as a robust and practical model to investigate cellular and genomic properties of cells from patients with muscle pathologies. Overall design: We tested two myogenic differentiation cellular models. To this end, we differentiated immortalized myoblasts (MB) into  myotubes  for 5 days (MT) in 3 indpendent differentiation replicates, and compared the transcriptome of undifferentiated (untreated) myoblasts with that of myotubes. We also elicited a myogenic conversion of immortalized fibroblasts ('NI') for 5 days ('DOX') or 7 days ('McF_D07') in 3 independent replicates (Rep1-3), and compared the transcriptome of unconverted (untreated) fibroblasts and myo-converted fibroblasts. We also compared the transcriptome of day-5 or day-7 myo-converted fibroblasts with that of myotubes.