Regulation of muscle cell growth and differentiation by the myod family of helix-loop-helix proteins

This chapter focuses on the mechanisms that control proliferation and differentiation in the myogenic lineage and on the role of the recently identified skeletal muscle regulatory gene family in mediating these events. The prototype of this family of myogenic regulatory factors is MyoD that has the potential to activate the skeletal muscle phenotype in a variety of cell types, and represents a focal point for positive and negative control of myogenesis. The skeletal muscle cell system provides a powerful model for exploring the mechanistic basis for the antagonism between cell growth and differentiation. The recent identification of the MyoD family of musclespecific transcription factors offers opportunities to dissect at the molecular level of the mechanisms through which defined cell typespecific transcription factors can activate an entire differentiation program, as well as to unravel the mechanisms through which the growth factor and oncogenic signals can disrupt cellular differentiation. Because the mechanisms for the growth factor signaling and induction of cell proliferation are conserved in diverse cell types, it is tempting to speculate that the molecular mechanisms responsible for the antagonism between cell proliferation and differentiation in muscle cells are also operative in other cell types. However, resolution of this question must await the identification of the regulatory factors that specify cell fate in other lineages.