Membrane-tethered cadherin substrates reveal actin architecture at adherens junctions

Adherens junctions (AJ) are E-cadherin-based adhesions at cell-cell contacts that connect the actin cytoskeleton of epithelial cells. The 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 is a mechano-sensitive process involving the clustering of E-cadherins within the plasma membrane of cells and across adjacent cells, and the mechanical activation of α-catenins that connect E-cadherins with the actin cytoskeleton. However, how membrane mobility of E-cadherins and their organisation in time and space influence this process is less well understood, partly due to limitations to control the physical properties of cell membranes and perform high resolution 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 containing the extracellular domain of cadherin as a biomimetic system to enable super resolution TIRF-SIM imaging of AJ. 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 the mobility of E-cadherin within the SLB, distinct types of actin architecture emerge over time. Low mobility substrates support formin-based linear polymerisation while high mobility substrates support Arp2/3 -based branched actin polymerisation. These regions are spatially delimited within the cell and can change over time, giving rise to a mature state containing regions of both branched and linear actin.