HES6 acts as a transcriptional repressor in myoblasts and can induce the myogenic differentiation program

ES6 is a novel member of the family of basic helix-loop-helix mammalian hom ologues of Drosophila Hairy and Enhancer of split. We have analyzed the bio chemical and functional roles of HES6 in myoblasts. HES6 interacted with th e corepressor transducin-like Enhancer of split 1 in yeast and mammalian ce lls through its WRPW COOH-terminal motif. HES6 repressed transcription from an N box-containing template and also when tethered to DNA through the GAL 4 DNA binding domain. On N box-containing promoters, HES6 cooperated with H ES1 to achieve maximal repression. An HES6-VP16 activation domain fusion pr otein activated the N box-containing reporter, confirming that HES6 bound t he N box in muscle cells. The expression of HES6 was induced when myoblasts fused to become differentiated myotubes. Constitutive expression of HES6 i n myoblasts. inhibited expression of MyoR, a repressor of myogenesis, and i nduced differentiation, as evidenced by fusion into myotubes and expression of the muscle marker myosin heavy chain. Reciprocally, blocking endogenous HES6 function by using a WRPW-deleted dominant negative HES6 mutant led to increased expression of MyoR and completely blocked the muscle development program. Our results show that HES6 is an important regulator of myogenesi s and suggest that MyoR is a target for HES6-dependent transcriptional repr ession.