Generating active T1 transitions through mechanochemical feedback

Convergence-extension in embryos is controlled by chemical and mechanical signalling. A key cellular process is the exchange of neighbours via T1 transitions. We propose and analyse a model with positive feedback between recruitment of myosin motors and mechanical tension in cell junctions. The model produces active T1 events, which act to elongate the tissue perpendicular to external pulling. Using an idealized tissue patch comprising several active cells embedded in a matrix of passive hexagonal cells we identified an optimal range of pulling forces to trigger an active T1 event. We show that pulling also generates tension chains in a realistic patch made entirely of active cells of random shapes, and leads to convergence-extension over a range of parameters. Our findings show that active intercalations can generate stress that activates T1 events in neighbouring cells resulting in tension dependent tissue re-organisation, in qualitative agreement with experiments on gastrulation in chick embryos.