CATENINS IN XENOPUS EMBRYOGENESIS AND THEIR RELATION TO THE CADHERIN-MEDIATED CELL-CELL ADHESION SYSTEM

In the course of an analysis of cell-cell adhesion in the Xenopus embr yo, antibodies directed against alpha- and beta-catenin were applied t o investigate their relation to the cadherins occurring early in this system. The results demonstrate that alpha- and beta-catenin are provi ded maternally and increase in amount throughout embryogenesis. Immuno precipitations indicate that both of the catenins are complexed to U-c adherin in the early phase of embryogenesis and to F-cadherin, when it appears during gastrulation. An excess of alpha-catenin occurs in fre e form in the early embryo, whereas all of the beta-catenin seems to b e complexed to cadherin. Synthesis of the two components throughout ea rly embryogenesis and their binding to newly synthesized cadherins wer e demonstrated by metabolic labelling. The spatial distribution of alp ha-catenin was analysed by immunohistology. During cleavage alpha-cate nin is deposited evenly along the plasma membranes within the embryo, while the cell peripheries at the surface of the embryo remain devoid of alpha-catenin. At later stages, the pattern of alpha-catenin distri bution becomes more complex. Quantitative differences in the intensity of staining along the plasma membranes in the different regions of th e embryo can be distinguished. Particularly the appearance of E-cadher in in the gastrula ectoderm is accompanied by conspicous depositions o f alpha-catenin along the respective plasma membranes in this layer. A ll cells in the later embryo, apart from the neural crest cells, carry alpha-catenin on their plasma membranes indicating the universal char acter of cadherin-mediated cell-cell adhesion in the Xenopus embryo.