A new approach to measure forces at junction vertices in an epithelium

The mechanical properties of cell-cell junctions are critical for the stability of an epithelium. Cell-cell junction ablation experiments are classically used as a readout for junctional mechanics. However, without the knowledge of the viscoelastic properties of the microenvironment of the ablated junction, tensile junctional forces cannot be measured. Here we combine laser ablation with intracellular microrheology and develop a model to measure tensile forces exerted on cell-cell junctions. We show that the overexpression of the proto-oncogene atypical Protein Kinase C iota (aPKCi) in a single cell within a normal epithelium induces a gradient of junctional tension with neighbouring cells. Our method allows us to demonstrate that junctions contacting the aPKCi-overexpressing cell display a mechanical asymmetry which correlates with the levels of E-cadherin and P-MLC2. Measuring intracellular viscoelasticity is crucial for accurate measurements of cell-cell junction mechanics in the context of development or cancer research. TeaserWe combine cytoplasmic and junctional mechanics to detect asymmetry in forces exerted on cell-cell junctions.