Head muscle development

Vertebrate movement depends on trunk skeletal muscles, which are derived from the segmented paraxial mesoderm known as somites (Christ and Ordahl 1995). During embryogenesis, muscle precursor cells proliferate extensively prior to their differentiation and fusion into muscle fibers containing multiple nuclei. Skeletal muscle was the first tissue in which a determination gene for cell fate, MyoD, was identified in vertebrates (Weintraub et al. 1991). Molecular and technical advances in the last two decades have resulted in a detailed understanding of the embryology of this tissue, and its genetic regulation by key transcription factors, including the paired/homeobox genes Pax3 and Pax7, and the myogenic regulatory genes Myf5, MyoD, Mrf4, and Myogenin (MRFs: myogenic regulatory factors (Kassar-Duchossoy et al. 2004)). These genes are crucial for regulating muscle cell fate, as shown by genetic loss-of-function analyses. Because many transcription factors that regulate the fate of muscle progenitors have been identified, skeletal muscle tissue constitutes an ideal model for the study of organogenesis and regeneration (Tajbakhsh 2005). Questions related to the inductive processes and the molecular events underpinning embryonic myogenesis are currently under intensive study worldwide. Answers to these questions may provide basic insights into developmental biology, as well as to the growing field of regenerative medicine as myogenesis in adult muscle stem cells recapitulates that of the embryo.