REGULATION OF DORSAL-VENTRAL PATTERNING - THE VENTRALIZING EFFECTS OFTHE NOVEL XENOPUS HOMEOBOX GENE VOX

The formation of the dorsal-ventral axis in Xenopus laevis is elicited by a signaling cascade on the dorsal side of the embryo initiated by cortical rotation. These early developmental events impart an initial axial polarity to the embryo. By the time gastrulation occurs, the emb ryo has established opposing dorsal and ventral regulatory regions. Th rough a dynamic process, the embryo acquires a definitive pattern that reflects the distribution of future cell fates. Here we present a nov el homeobox gene, Vox, whose expression reflects this dynamic process. Vox is first expressed throughout the embryo and subsequently elimina ted from the notochord and neural plate. Ectopic expression of Vox dem onstrates that the normal function of this gene may be to suppress dor sal genes such as Xnot and chordin, and induce ventral and paraxial ge nes such as Bmp-4 and MyoD. Ectopic expression of BMP-4 ventralizes em bryos and positively regulates the expression of Vox, suggesting that these genes are components of a reciprocal regulatory network.