Figure 8.

Schematic representation of the function of Shh during limb muscle development. In normal conditions, Shh patterns limb muscles non-cell-autonomously along the AP axis through the lateral plate-derived limb mesenchyme (1) such that when Hh activity is removed in the nonmuscle limb mesenchyme by Prx1-Cre recombinase AP patterning of the limb muscles is affected. Meanwhile, cell-autonomous function of Hh signaling is required to maintain cell survival in the dermomyotome (2), promote the formation of slow muscle fibers (3), initiate Myf5 and MyoD expression in a timely manner, and regulate directional migration of the distal myocytes by maintaining Net1 expression (4). Thus, in the absence of Hh activity in the muscle progenitor cells, there is increased apoptosis in the dermomyotome, decreased slow muscle fibers, and loss of distal muscles.