OVEREXPRESSION OF CADHERINS AND UNDEREXPRESSION OF BETA-CATENIN INHIBIT DORSAL MESODERM INDUCTION IN EARLY XENOPUS EMBRYOS

The cadherin-catenin complex has an important role in cell-cell adhesi on and may also function in signaling pathways. We report that overexp ression of three cadherin types in Xenopus embryos causes them to deve lop with reduced dorsal axial structures. The same phenotype is produc ed in embryos that have been depleted of maternal beta-catenin protein by an antisense oligodeoxynucleotide complementary to beta-catenin mR NA. They show an inhibition in the expression of dorsal mesodermal mar kers MyoD and goosecoid, but not of ventral and general mesodermal mar kers. They lack notochords, somites, and neural tubes and are defectiv e in dorsal mesodermal signaling in Nieuwkoop assays. The phenotype ca n be rescued by the injection of beta-catenin mRNA and not by the inje ction of Xwnt-8 mRNA. These results show that beta-catenin has an impo rtant role in dorsal mesoderm induction. They directly demonstrate the activity of a maternal mRNA in axis specification.