FRIZZLED-8 IS EXPRESSED IN THE SPEMANN ORGANIZER AND PLAYS A ROLE IN EARLY MORPHOGENESIS

Wnts are secreted signaling molecules implicated in a large number of developmental processes. Frizzled proteins have been identified as lik ely receptors for Wnt ligands in vertebrates and invertebrates, but a functional role for vertebrate frizzleds has not yet been defined. To assess the endogenous role of frizzled proteins during vertebrate deve lopment, we have identified and characterized a Xenopus frizzled gene (xfz8). It is highly expressed in the deep cells of the Spemann organi zer prior to dorsal lip formation and in the early involuting marginal zone. Ectopic expression of xfz8 in ventral cells leads to complete s econdary axis formation and can synergize with Xwnt-8 while an inhibit ory form of xfz8 (Nxfz8) blocks axis duplication by Xwnt-8, consistent with a role for xfz8 in Wnt signal transduction. Expression of Nxfz8 in dorsal cells has profound effects on morphogenesis during gastrulat ion and neurulation that result in dramatic shortening of the anterior -posterior axis. Our results suggest a role for xfz8 in morphogenesis during the gastrula stage of embryogenesis.