Supracellular Actin Network Remodeling During the Jamming Transition in Pseudostratified Epithelia

The tight regulation of the transition between stationary and migratory states is crucial to the proper functioning of epithelial cells during both homeostasis and pathological processes. The study of phase transitions in tissues provides insight into the underlying mechanisms of cellular movement. Recently, several biological tissues have been found to undergo jamming transitions, analogous to those previously described in soft matter particle physics. Human bronchial epithelial cells (HBECs) are a key model system for studying the biological jamming transition, having been shown to transition between a fluid-like unjammed state in which the cellular collective freely remodels, and a solid-like jammed state where motion is arrested. Previous cell culture work found that as basal stem cells differentiate to form a mature epithelium, the cellular collective slows, the shapes of individual cells became more rounded and less variable, as predicted by vertex models, and the tissue undergoes a jamming transition. However, the differentiating HBEC layer exhibits a complex, pseudostratified architecture which has not been accounted for in the models or analysis of collective behavior. Here, through the combination of live imaging and immunohistochemistry, we show that a multicellular dynamical change in HBECs is accompanied by supracellular structural changes in the actin cytoskeleton. As cells jam, the apical actin network percolates across the cell layer, leading to a rigidity transition. These findings provide preliminary evidence of a percolation transition in pseudostratified epithelia by characterizing the connection between multicellular dynamics and structural changes.