Cadherin-Catenin Complexes During Zebrafish Oogenesis: Heterotypic Junctions

During vertebrate oogenesis, the germ cells and associated so-matic cells remain connected by a variety of adhering junctional complexes. However, the molecular composition of these cellular structures is largely unknown. To identify the proteins forming the heterotypic adherens junctions between oocytes and follicle cells in the zebrafish (Danio rerio), the cDNAs encoding aE-catenin and plakoglobin were isolated. Using these cDNAs, in combina-tion with the previously isolated b-catenin cDNA, and antibodies specific for a- and b-catenin, plakoglobin, and N- and E-cadherin, we found differences in catenin and plakoglobin gene expression during oogenesis. The immunolocalization of these plaque pro-teins, as well as of cadherins, in the ovarian follicle indicated an enrichment of a- and b-catenin and of E-cadherin-like protein(s) in the oocyte cortex, notably at sites of oocyte-follicle cell con-tacts, suggesting the presence of hitherto unknown heterotypic adherens junctions between these cells. By contrast, plakoglobin and N-cadherin localization was restricted to cell-cell contacts in the follicle cell layer. During oocyte maturation, mRNAs for aE-and b-catenin and plakoglobin accumulated, and all three plaque-forming proteins were stored in unfertilized eggs, either in com-plexed forms with cadherins or as free cytoplasmic pools. These findings suggest possible roles of these junctional proteins during early embryogenesis