CHANGES IN THE PATTERN OF ADHERENS JUNCTION-ASSOCIATED BETA-CATENIN ACCOMPANY MORPHOGENESIS IN THE SEA-URCHIN EMBRYO

beta-Catenin was originally identified biochemically as a protein that binds E-cadherin in cultured cells and that interaction was later sho wn to be essential for cadherin function. Independently, armadillo, th e beta-catenin homolog in Drosophila melanogaster, was identified as a segment polarity gene necessary for the transduction of wingless (Wnt ) signals during embryonic and larval development. Recently, several i nvestigations have also shown that beta-catenin plays a critical role in axial patterning of early Xenopus, zebrafish, and mouse embryos. In these systems, the localization of beta-catenin to the plasma membran e, cytosol, and nucleus is predictive of its role in cell adhesion and signaling. In order to examine the potential role of beta-catenin in regulating cell adhesion during embryogenesis, we cloned beta-catenin in the sea urchin Lytechinus variegatus and characterized its subcellu lar distribution in cells undergoing morphogenetic movements. Indicati ve of a role in the establishment and maintenance of cell adhesion, be ta-catenin is associated with lateral cell-cell contacts and accumulat es at adherens junctions from cleavage stages onward. At gastrulation, changes in junctional beta-catenin localization accompany several mor phogenetic events. The epithelial-mesenchymal conversion that characte rizes the ingression of both primary and secondary mesenchyme cells co incides with a rapid and dramatic loss of adherens junction-associated beta-catenin. In addition, epithelial cells in the archenteron displa y a significant decrease in adherens junction-associated beta-catenin levels as they undergo convergent-extension movements. These data are consistent with a role for beta-catenin in regulating cell adhesion an d adherens junction function during gastrulation in the sea urchin emb ryo. (C) 1997 Academic Press.