Membrane-tethered cadherin substrates reveal actin architecture at adherens junctions

Adherens junctions (AJs) are E-cadherin-based adhesions at cell-cell contacts that connect the actin cytoskeleton of epithelial cells. Formation and maturation of these junctions is important in development, e.g. for the generation of epithelial tissues, and loss of adherens junctions is linked to metastasis in cancer. It is well established that AJ formation is a mechano-sensitive process involving cis and trans clustering of E-cadherin and the mechanotransducive activation of α-catenin that connects E-cadherin with the actin cytoskeleton. However, how mobility of E-cadherin in the cell membrane and their local density influences actin polymerisation is less well understood, due to limitations in controlling physical properties of cell membranes and performing high-resolution microscopy in model organisms or cell-monolayers. Here we place MCF7 cells labelled with fluorescent actin, E-cadherin and α-catenin, on fluid supported lipid bilayers (SLB) containing the extracellular domain of E-cadherin, as a biomimetic system enabling super-resolution microscopy of AJs. We found that MCF7 cells were able to attach and spread on these substrates, recruiting E-cadherin and α-catenin to form AJs that can mature and are mobile. Interestingly, we found that depending on E-cadherin mobility within the SLB, distinct types of actin architecture emerge. Low mobility substrates support formin-based linear actin polymerisation while high mobility substrates support Arp2/3-based branched actin network polymerisation. These polymerising actin structures are spatially confined to regions of low E-cadherin density suggesting they play a role in AJ repair. Following how these actin structures at the cell-SLB interface evolve over time indicates regions of both linear and branched actin being present at mature cell-cell contacts.