A two-tiered mechanism for stabilization and immobilization of E-cadherin

Epithelial tissues maintain a robust architecture which is important for their barrier function, but they are also remodelled through the reorganization of cell - cell contacts. Tissue stability requires intercellular adhesion mediated by E- cadherin, in particular its trans- association in homophilic complexes supported by actin filaments through beta- and alpha- catenin. How alpha- catenin dynamic interactions between E- cadherin/ beta- catenin and cortical actin control both stability and remodelling of adhesion is unclear. Here we focus on Drosophila homophilic E- cadherin complexes rather than total E- cadherin, including diffusing 'free' E- cadherin, because these complexes are a better proxy for adhesion. We find that E- cadherin complexes partition in very stable microdomains ( that is, bona fide adhesive foci which are more stable than remodelling contacts). Furthermore, we find that stability and mobility of these microdomains depend on two actin populations: small, stable actin patches concentrate at homophilic E- cadherin clusters, whereas a rapidly turning over, contractile network constrains their lateral movement by a tethering mechanism. alpha- Catenin controls epithelial architecture mainly through regulation of the mobility of homophilic clusters and it is largely dispensable for their stability. Uncoupling stability and mobility of E- cadherin complexes suggests that stable epithelia may remodel through the regulated mobility of very stable adhesive foci.