Figure 1: A large fraction of myotube-specific enhancer that is bound by MyoD, becomes bound by MyoD already in the proliferative stage.
Myotube-specific enhancers become active exclusively after muscle differentiation as manifested by the presence of p300, PolII, H3K4me1 and H3K27ac. Clustering of myotube-specific enhancers that are bound by MyoD before or after muscle differentiation indicates that the majority (~72%) of these condition-specific enhancers becomes bound by MyoD already in the proliferative stage and prior to the point in which they turn active, suggesting that throughout the myoblastic stage these myotube-specific enhancers could be co-bound by MyoD and another placeholder that negates the activity of MyoD and preserves these enhancers as inactive/poised. MB, myoblasts; MT, myotubes.