Résumé
β-catenin is a cytoplasmic protein associated with cadherin adhesion molecules and has been implicated in axis formation in Xenopus (McCrea, P. D., Brieher, W. M. and Gumbiner, B. M. (1993) J. Cell Biol. 127, 477-484). We have studied its distribution in Xenopus embryos by immuno-fluorescence on frozen sections. Consistent with its function in cell-cell adhesion, β-catenin is present in every cell. However, high levels are expressed in certain regions and different tissues of the embryo. No simple correlation appears to exist between the levels of β-catenin with the expected strength of adhesion. High levels of β-catenin were found in regions undergoing active morphogenetic movements, such as the marginal zone of blastulae and gastrulae. This suggests that high expression of β-catenin could be involved in dynamic adhesion events. Surprisingly, β-catenin also accumulates on plasma membranes that probably do not establish direct or strong contacts with other cells. In particular, high amounts of β-catenin are found transiently at boundaries between tissue anlagen and at the intersomitic boundaries. This unexpected pattern of β-catenin expression raises the possibility that this molecule participates in developmental processes, perhaps independently of its classical role in cell-cell adhesion.