The Xvent-2 homeobox gene is part of the BMP-4 signalling pathway controling dorsoventral patterning of Xenopus mesoderm

We describe a novel Xenopus homeobox gene, Xvent-2, which together with the previously identified homeobox gene Xvent-1, defines a novel class of homeobox genes. vent genes are related by sequence homology, expression pattern and gain-of-function phenotype. Evidence is presented for a role of Xvent-2 in the BMP-4 pathway involved in dorsoventral patterning of mesoderm. (1) Xvent-2 is expressed in regions that also express BMP-4. (2) Xvent-2 and BMP-4 interact in a positive feedback loop. (3) Xvent-2 ventralizes dorsal mesoderm in a dose-dependent manner resulting in phenoytpes ranging from microcephaly to Bauchstück pieces, as does BMP-4. (4) Like BMP-4 and gsc, Xvent-2 and gsc are able to interact in a crossregulatory loop to suppress each other. (5) Microinjection of Xvent-2 mRNA can rescue dorsalization by a dominant-negative BMP-4 receptor. The results suggest that Xvent-2 functions in the BMP-4 signalling pathway that antagonizes the Spemann organizer.