Actin-Delimited Adhesion-Independent Clustering of E-Cadherin Forms the Nanoscale Building Blocks of Adherens Junctions

E-cadherin is the major adhesion receptor in epithelial adherens junctions, which connect cells to form tissues and are essential for morphogenesis and homeostasis. The mechanism by which E-cadherin monomers cluster and become organized in adherens junctions remains poorly understood. Here, using superresolution microscopy techniques in combination with structure-informed functional mutations, we found that loosely organized clusters of approximately five E-cadherin molecules that form independently of cis or trans interactions, and that are delimited by the cortical F-actin meshwork, are the precursors of trans-ligated adhesive clusters that make up the adherens junction. The density of E-cadherin clusters was wide ranged, and notably, we could detect densities consistent with the crystal lattice structure at the core of adhesive clusters, which were dependent on extracellular domain interactions. Thus, our results elucidate the nanoscale architecture of adherens junctions, as well as the molecular mechanisms driving its assembly.