The initial somitic phase of Myf5 expression requires neither Shh signaling nor Gli regulation.

Myf5, the skeletal muscle determination gene, is first expressed in the dorso-medial aspect of the somite under the control of an element we have called the early epaxial enhancer. It has subsequently been reported that this enhancer is a direct target of Shh signaling mediated by Gli transcription factors (Gustafsson et al. 2002). We here demonstrate that activation of Myf5 expression depends on neither Shh function nor an intact Gli binding site, although the Gli site is necessary for continuation of expression. We suggest that the discrepancy is due to the existence of specific interactions between the enhancer and the Myf5 promoter.