Antagonizing the Spemann organizer: role of the homeobox gene Xvent‐1

We have identified a novel homeobox gene, Xvent‐1, that is differentially expressed in the ventral marginal zone of the early Xenopus gastrula. Evidence is presented from mRNA microinjection experiments for a role for this gene in dorsoventral patterning of mesoderm. First, Xvent‐1 is induced by BMP‐4, a gene known to be a key regulator of ventral mesoderm development. Second, Xvent‐1 and the organizer‐specific gene goosecoid are able to interact, directly or indirectly, in a cross‐regulatory loop suppressing each other's expression, consistent with their mutually exclusive expression in the marginal zone. Third, microinjection of Xvent‐1 mRNA ventralizes dorsal mesoderm. The results suggest that Xvent‐1 functions in a ventral signaling pathway that maintains the ventral mesodermal state and antagonizes the Spemann organizer.