Expression of myf-5, a key component of myogenic regulatory genes, expands into the ventral marginal zone during Xenopus gastrulation after the dorsal activation takes place. Little is known about how this dynamic expression pattern occurs. Here, we provide evidences to suggest that Activin/Nodal signals participate in the regulation of ventral expression of Xmyf-5 in gastrula embryos. Two Smad binding elements (SBEs) within the Xenopus myf-5 promoter can specifically interact with Smad4 protein. Furthermore, we demonstrate that the two SBEs are both indispensable for conferring responsiveness to Activin/Nodal signals and to ventral expression of myf-5 in Xenopus gastrula embryos. (C) 2003 Elsevier Inc. All rights reserved.