MyoD stimulates Delta‐1 transcription and triggers Notch signaling in the Xenopus gastrula

The Notch signaling cascade is involved in many developmental decisions, a paradigm of which has been the selection between epidermal and neural cell fates in both invertebrates and vertebrates. Notch has also been implicated as a regulator of myogenesis, although its precise function there has remained controversial. Here we show that the muscle‐determining factor MyoD is a direct, positive regulator of the Notch ligand Delta‐1 in prospective myoblasts of the pre‐involuted mesoderm in Xenopus gastrulae. Injection of a dominant MyoD repressor variant ablates mesodermal Delta‐1 expression in vivo . Furthermore, MyoD‐dependent Delta‐1 induction is sufficient to activate transcription from promoters of E(spl)‐related genes in a Notch‐dependent manner. These results indicate that a hallmark of neural cell fate determination, i.e. the feedback loop between differentiation promoting basic helix–loop–helix proteins and the Notch regulatory circuitry, is conserved in myogenesis, supporting a direct involvement of Notch in muscle determination.