THE ROLES OF MATERNAL ALPHA-CATENIN AND PLAKOGLOBIN IN THE EARLY XENOPUS EMBRYO

Catenins (alpha-, beta- and gamma- or plakoglobin) are cytoplasmic cad herin-associated proteins. Studies on cultured cells have suggested th at both alpha-catenin and plakoglobin are important for the adhesive f unction of cadherins. alpha-catenin binds to both beta-catenin and pla koglobin and may link the cadherin/catenin complex to actin filaments. Separate domains of plakoglobin bind to cadherin and alpha-catenin, s uggesting it mag act as a bridge between these molecules. However, pla koglobin may have other activities: it is expressed in both desmosomal junctions in association with desmogleins and the cytoplasm in conjun ction with APC, and previous work suggests it mag act in a dorsal sign alling pathway when overexpressed in Xenopus embryos. Here, we have st udied the roles of alpha-catenin and plakoglobin directly, by depletin g the maternal mRNAs coding for each of them in developing Xenopus emb ryos. We find that depletion of maternal alpha-catenin causes the loss of intercellular adhesion at the blastula stage, similar to that repo rted previously for EP cadherin. Depletion of plakoglobin results in a partial loss of adhesion, and a loss of embryonic shape, but does not affect dorsal signalling.