MOLECULAR EVOLUTION OF THE MYOD FAMILY OF TRANSCRIPTION FACTORS

Myogenesis in skeletal muscle is a cascade of developmental events whose initiation involves the MyoD family of transcription factors. Evolutionary analyses of amino acid sequences of this family of transcriptional activators suggest that the vertebrate genes MyoD1, myf-5, Myog (myogenin), and myf-6 were derived by gene duplications from a single ancestral gene. A common genetic origin predicts some functional redundancy between MyoD1 and myf-5 and between Myog and myf-6. Experimental studies have suggested that these pairs of genes can substitute for each other during myogenesis. Separate analyses of the conserved basic helix-loop-helix and nonconserved flanking elements yield similar branching sequences but show evolutionary change in the basic helix-loop helix region has occurred at a much slower rate.