Tension remodeling controls topological transitions in confluent tissues

Tissue fluidity, mediated by the exchange of cellular neighbors, is critical for large-scale cellular rearrangements during tissue morphogenesis, repair, and collective cell migration. Cellular neighbor exchange events rely on the instability of four-fold vertices that are formed when intercellular junctions shrink to a single point during contraction, followed by the junctions resolving in the orthogonal direction. However, in vivo experimental data show that four-fold vertices can remain stable for long times, raising the question of how cellular tensions are remodeled to ensure the stability of higher-order vertices and their eventual splitting into tricellular vertices. Existing vertex-based models of confluent tissues with constant and uniform tension are unable to account for the observed phenomena. We, therefore, present a new dynamic vertex model of epithelial tissues, where the tension in the intercellular junction is remodeled depending on the magnitude and direction of the local strain. The model demonstrates that tension increase upon contraction and reduction upon extension can induce the stability of higher-order vertices. Furthermore, asymmetric rates of tension remodeling in response to contraction and extension can result in vertex instability and fluid tissues.