Interdigitated dynamic actin protrusions maintain stable cadherin adhesion

Cadherins build stable, cohesive sheets of cells using paradoxically weak bonds. Actin is thought to convert weak binding into strong adhesion either by transmitting myosin dependent pulling forces to adhesive junctions or by clustering cadherins in the plane of the membrane. Here, however, we show that continuous actin polymerization stabilizes cadherin adhesion by directly driving membrane protrusions, not by promoting contractility or cadherin clustering. Lateral membranes of epithelial cells are continuously pushed against each another by protrusions. Micrometer sized cadherin puncta, long thought to be clusters of cadherins, turn out to be patches of microspikes interlocked by cadherin homophilic bonds to hold neighboring cells together. When actin polymerization is blocked, protrusions cease, puncta disappear, and lateral membranes detach from one another. In contrast, inhibiting myosin II contractility has no effect on adhesion. One Sentence SummaryStronger together: membrane interdigitations keep cells attached.