We studied the growth of asymmetric cellular contacts : adherens junctions and focal contacts. We showed, by imaging, micromanipulation and cellular assembly modification experiments, that adherens junctions between two apparently identical cells exhibit a symmetry breaking due to different roles of actin cytoskeleton for both cells in contact : the “donor” cell polymerizes actin which leads to cell membranes contact; as a response, the “receiving” cell assembles acto-myosin bundles which promotes local force application on the junctions and a consequent increase of their length. Growth curves of adherens junctions when cell contractility is increased using controlled nocodazole concentrations have been measured. Fits of experimental growth curves allowed a determination of the contractile forces applied by the “receiving” cell. We were thus able to obtain for the first time the force-extension diagram for adherens junctions by a non-invasive method. The biological approaches used to name the key cytoskeletal players and the physical approaches used to fit growth laws have both shown that intercellular contacts exhibits local reinforcement in a manner similar to focal contact reinforcement. We have finally observed by TIRFM internal dynamics of growing focal contacts using different labelled proteins (fibronectin, integrin, vinculin, actin) in order to propose a mechanosensing mechanism.
