LACK OF BETA-CATENIN AFFECTS MOUSE DEVELOPMENT AT GASTRULATION

Molecular analysis of the cadherin-catenin complex elucidated the cent ral role of beta-catenin in this adhesion complex, as it binds to the cytoplasmic domain of E-cadherin and to alpha-catenin, beta-catenin ma y also function in signalling pathways, given its homology to the gene product of the Drosophila segment polarity gene armadillo, which is k nown to be involved in the wingless signalling cascade. To study the f unction of beta-catenin during mouse development, gene knock-out exper iments were performed in embryonic stem cells and transgenic mice were generated, beta-catenin null-mutant embryos formed blastocysts, impla nted and developed into egg-cylinder-stage embryos, At day 7 post coit um, the development of the embryonic ectoderm was affected in mutant e mbryos. Cells detached from the ectodermal cell layer and were dispers ed into the proamniotic cavity, No mesoderm formation was observed in mutant embryos. The development of extraembryonic structures appeared less dramatically or not at all affected. Our results demonstrate that , although beta-catenin is expressed rather ubiquitously, it is specif ically required in the ectodermal cell layer.