Induction of a secondary body axis in Xenopus by antibodies to β-catenin

We have obtained evidence that a known intracellular component of the cadherin cell-cell adhesion machinery, β-catenin, contributes to the development of the body axis in the frog Xenopus laevis. Vertebrate β-catenin is homologus to the Drosophila segment polarity gene product armadillo, and to vertebrate plakoglobin (McCrea, P. D., C. W. Turck, and B. Gumbiner. 1991. Science (Wash. DC). 254: J 1359-1361.). β-Catenin was found present in all Xenopus embryonic stages examined, and associated with C-cadherin, the major cadherin present in early Xenopus embryos. To test β-catenin's function, affinity purified Fab fragments were injected into ventral blastomeres of developing four-cell Xenopus embryos. A dramatic phenotype, the duplication of the dorsoanterior embryonic axis, was observed. Furthermore, Fab injections were capable of rescuing dorsal features in UV-ventralized embryos. Similar phenotypes have been observed in misexpression studies of the Wnt and other gene products, suggesting that β-catenin participates in a signaling pathway which specifies embryonic patterning.