Fig. 1

Myoblastic differentiation. During the early stages, satellite cells are activated, they proliferate and express MyoD, initiating transcription of muscle-specific genes required for early differentiation. As myogenesis proceeds, some activated satellite cells return to quiescence and renew the satellite cell reserve population, whereas others exit the cell cycle to undergo further differentiation. Those post-mitotic myocytes show a shift in gene expression that allows their fusion to form multinucleated myotubes capable of undergoing terminal differentiation. During these phases, EZH2 expression decreases dramatically coupled with a decrease in lysine 27 methylation of histone H3. Conversely, methylation of lysine 4 of histone H3 increases, allowing RNA polymerase access to muscle-specific genes