Jack of all trades: functional modularity in the adherens junction

Adherens junctions, broadly defined as attachment sites in which cadherin adhesion receptors connect the actin cytoskeletons of neighboring animal cells, are multi-tasking by nature. In addition to mediating cell-cell adhesion and providing the tissue with mechanical continuity and barrier function, they maintain polarity, are sites of mechanosensing and signaling, and they regulate actomyosin dynamics and can thus generate forces to drive morphogenesis. Here we propose that the key to performing such diverse tasks is the integration within the cadherin adhesome of functional modules that evolved independently to perform other duties within the cell, and we discuss three such functional modules: force transmission, actin dynamics regulation, and contractile force generation. We compare each module to a more ancient cellular structure with similar function, identify shared components, and speculate on how the module was integrated into the cadherin adhesome.