THE MYOD FAMILY OF TRANSCRIPTION FACTORS AND SKELETAL MYOGENESIS

Gene targeting has allowed the dissection of complex biological proces ses at the genetic level. Our understanding of the nuances of skeletal muscle development has been greatly increased by the analysis of mice carrying targeted null mutations in the Myf-5, MyoD and myogenin gene s, encoding members of the myogenic regulatory factor (MRF) family. Th ese experiments have elucidated the hierarchical relationships existin g between the MRFs, and established that functional redundancy is a fe ature of the MRF regulatory network. Either MyoD or Myf-5 is sufficien t for the formation or survival of skeletal myoblasts. Myogenin acts l ater in development and plays an essential in vivo role in the termina l differentiation of myotubes.