Tricellular junctions: a hot corner of epithelial biology.

As the result of an intricate interplay between mechanical and biochemical cues, coordinated cell dynamics are at the basis of tissue development, homeostasis and repair. Numerous studies have addressed the interplay between these two inputs and their impact on cellular dynamics. These studies largely focus on bicellular junctions (BCJs). Recent works have illuminated that tricellular junctions (TCJs), the junctions where three cells contact, play important roles in epithelial tissues beyond their well-known structural function in preserving epithelial barrier integrity. Indeed, TJCs have recently been implicated in the regulation of collective cell migration, division orientation, cell proliferation and cell mechanical properties. More generally, the TCJ distribution aligns with the cell shape and mechanical stress orientation within the tissue, while their number encapsulates the packing topology. Importantly, known regulators of growth signalling and of cell mechanical properties are also localized at TCJs. Therefore, TCJs emerge as spatial sites to sense and integrate biochemical and mechanical inputs to guide epithelial tissue dynamics.