BETA-CATENIN HAS WNT-LIKE ACTIVITY AND MIMICS THE NIEUWKOOP SIGNALINGCENTER IN XENOPUS DORSAL-VENTRAL PATTERNING

beta-Catenin is a protein known to associate with the cytoplasmic doma ins of members of the cadherin family of cell adhesion molecules. Rece ntly, Funayama et al. (Funayama et al. (1995). J. Cell Biol. 128, 959- 968.) demonstrated that overexpression of beta-catenin causes the form ation of a secondary axis in Xenopus laevis embryos. In order to under stand the role of beta-catenin in axis formation, we examined its biol ogical activity in further detail, beta-Catenin is effective at induci ng a secondary axis when overexpressed in the vegetal ventral region o f early cleavage stage (4-32 cell) embryos. beta-Catenin may act as pa rt of the Nieuwkoop center because cells overexpressing beta-catenin d o not contribute directly to axial structures. Overexpression of beta- catenin can specify de novo axis formation, as shown by its ability to rescue UV-ventralized embryos. Overexpression of beta-catenin alone i s not sufficient to cause elongation of animal caps or to induce mesod ermal markers in animal caps. In these assays, overexpression of beta- catenin behaves like ectopic expression of certain members of the Wnt gene family. Like Wnts, overexpression of beta-catenin was also found to increase gap junctional communication in cells of the ventral anima l cap. Overexpression of beta-catenin causes a small increase in the r ate of aggregation of Xenopus blastomeres. Overexpression of C-cadheri n causes a more dramatic increase in the rate of aggregation of Xenopu s blastomeres, but does not enhance gap junction communication or indu ce axis duplication; hence, rye argue that increased adhesion is not s ufficient to account for beta-catenin's ability to regulate patterning or gap junction communication. We propose a signaling role for beta-c atenin during axis formation in Xenopus. (C) 1995 Academic Press, Inc.