THE ROLE OF GSC AND BMP-4 IN DORSAL-VENTRAL PATTERNING OF THE MARGINAL ZONE IN XENOPUS - A LOSS-OF-FUNCTION STUDY USING ANTISENSE RNA

The dorsal-specific homeobox gene goosecoid (gsc) and the bone morphogenetic protein 4 gene (BMP-4) are expressed in complementary regions of the Xenopus gastrula, Injection of gsc mRNA dorsalizes ventral mesodermal tissue and can induce axis formation in normal and UV-ventralized embryos, On the other hand, BMP-Q mRNA injection, which has a strong ventralizing effect on whole embryos, has been implicated in ventralization by UV, and can rescue tail structures in embryos dorsalized by LiCl, The above-mentioned putative roles for BMP-I and gsc are based on gain-of-function experiments, In order to determine the in vivo role of these two genes in the patterning of the Xenopus mesoderm during gastrulation, partial loss-of-function experiments were performed using antisense RNA injections, Using marker genes that are expressed early in gastrulation, we show that antisense gsc RNA has a ventralizing effect on embryos, whereas antisense BMP-I RNA dorsalizes mesodermal tissue, These loss-of-function studies also show a requirement for gsc and BMP-4 in the dorsalization induced by LiCl and in the ventralization generated by UV irradiation, respectively, Thus, both gain- and loss-of-function results for gsc and BMP-I support the view that these two genes are necessary components of the dorsal and ventral patterning pathways in Xenopus embryos.