3 ZEBRAFISH MEF2 GENES DELINEATE SOMITIC AND CARDIAC-MUSCLE DEVELOPMENT IN WILD-TYPE AND MUTANT EMBRYOS

The zebrafish is an important experimental system for vertebrate embry ology, and is well suited to the molecular analysis of muscle developm ent. Transcription factors, such as the MEF2s, regulate skeletal and c ardiac muscle-specific genes during development. We report the identif ication of three zebrafish MEF2 genes which, like their mammalian coun terparts, encode factors that function as DNA-binding transcriptional activators of muscle specific promoters. The pattern of MEF2 expressio n in zebrafish defines discrete cell populations in the developing som ites and heart and has mechanistic implications for developmental regu lation of the MEF2 genes, when compared with other species. Alteration of MEF2 expression in two mutants affecting somitogenesis provides in sight into the control of muscle formation in the embryo.