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 embryo has established opposing dorsal and ventral regulatory regions. Through a dynamic process, the embryo acquires a definitive pattern that reflects the distribution of future cell fates. Here we present a novel homeobox gene, Vox, whose expression reflects this dynamic process. Vox is first expressed throughout the embryo and subsequently eliminated from the notochord and neural plate. Ectopic expression of Vox demonstrates that the normal function of this gene may be to suppress dorsal genes such as Xnot and chordin, and induce ventral and paraxial genes such as Bmp-4 and MyoD. Ectopic expression of BMP-4 ventralizes embryos and positively regulates the expression of Vox, suggesting that these genes are components of a reciprocal regulatory network.

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