Practice question

Limb musculature derives from somitic dermomyotome that delaminates and migrates into lateral plate mesoderm-derived bud. Regulation of specification, delamination, and maintenance of migratory muscle precursors depends on transcription factor Pax3 acting downstream of c-Met, Lbx1, and SF-HGF signaling, activating myogenic determination genes MyoD and Myf5. Pitx1 determines hindlimb identity, Sox9 drives cartilage, FGF10 initiates bud. Pax3 mutant Splotch mice lack all limb muscles while skeletal elements develop normally, confirming Pax3 as selective master regulator of appendicular myogenesis and precursor survival and migration.