Active junctions as a pathway to stress generation in morphogenesis

During gastrulation, and other development stages like germ band extension, epithelial cell sheets spontaneously organise to exert contractile mechanical forces, resulting in convergence-extension flow. Current models assume different types of chemical signalling based pre-patterning of the junctions, leading to both tension and flow. Here we present a model of self-amplifying contractile cell sheets that posits a myosin-dependent junction contractility with a tension-dependent feedback loop. This active mechanics model leads to the spontaneous formation of tension chains with both isotropic characteristics and directionality in the presence of an applied stress. We discuss the necessary and sufficient ingredients for the local mechanics to generate chains, and then focus on the flow that results from the activated junctions. We find that disordered flow arises spontaneously, and characterize the conditions for convergence-extension flow using small active cell groups embedded in a passive matrix.