DORSALIZING AND NEURALIZING PROPERTIES OF XDSH, A MATERNALLY EXPRESSED XENOPUS HOMOLOG OF DISHEVELLED

Signaling factors of the Wnt proto-oncogene family are implicated in d orsal axis formation during vertebrate development, but the molecular mechanism of this process is not known. Studies in Drosophila have ind icated that the dishevelled gene product is required for wingless (Wnt 1 homolog) signal transduction. We demonstrate that injection of mRNA encoding a Xenopus homolog of dishevelled (Xdsh) into prospective vent ral mesodermal cells triggers a complete dorsal axis formation in Xeno pus embryos. Lineage tracing experiments show that cells derived from the injected blastomere contribute to anterior and dorsal structures o f the induced axis. In contrast to its effect on mesoderm, overexpress ion of Xdsh mRNA in prospective ectodermal cells triggers anterior neu ral tissue differentiation. These studies suggest that Wnt signal tran sduction pathway is conserved between Drosophila and vertebrates and p oint to a role for maternal Xdsh product in dorsal axis formation and in neural induction.