REQUIREMENT FOR XVENT-1 AND XVENT-2 GENE-FUNCTION IN DORSOVENTRAL PATTERNING OF XENOPUS MESODERM

Xvent-1 and Xvent-2 are members of a novel homeobox subfamily that hav e been implicated in dorsoventral patterning in Xenopus mesoderm and a re thought to function in BMP signalling. Here we investigate the requ irement for Xvent function by employing two dominant-negative strategi es. Loss of Xvent function dorsalizes ventral mesoderm, induces second ary embryonic axes and directly neuralizes ectoderm, We further find t hat (1) Xvents act as transcriptional repressors, (2) Xvents function in an additive fashion and (3) a surprising number of genes are able t o rescue dominant-negative Xvent phenotypes including Bmp-4, Smad-1 an d wild-type Xvents and Xhox3, but not Xwnt-8. The results show that Xv ent-1 and Xvent-2 are essential for ventral mesoderm formation and for preventing neural differentiation. A model is suggested to explain ho w Bmp-4 positional information is converted into distinct cellular res ponses.