Cell-junctional and cytoskeletal organization in mouse blastocysts lacking E-cadherin.

Trophectoderm epithelium formation, the first visible differentiation process during mouse embryonic development, is affected in embryos lacking the cell adhesion molecule E-cadherin. Here we analyze the developmental potential of such E-cadherin-negative embryos, focusing on the organization of cell junctions and the cytoskeleton. To do this we used antibodies directed against alpha-, beta-, or gamma-(plakoglobin)-catenin and junctional and cytoskeletal proteins including ZO-1 and occludin (tight junctions), desmoglein1 (desmosomes), connexin43 (gap junctions), and EndoA (cytokeratin intermediate filaments). Membrane localization of alpha- and beta-catenin, and ZO-1, as well as cortical actin filament organization were abnormal in E-cadherin-negative embryos, and the expression levels of alpha- and beta-catenin were dramatically reduced, all suggesting a regulatory role for E-cadherin in forming the cadherin-catenin complex. In contrast, the membrane localization of plakoglobin, occludin, desmoglein1, connexin43, and cytokeratin filaments appeared unaltered. The unusual morphogenesis in E-cadherin-negative embryos apparently reflects defects in the molecular architecture of a supermolecular assembly involving zonulae adherens, tight junctions, and cortical actin filament organization, although the individual structures still appeared normal in electron microscopical analysis.