Glassy dynamics in active epithelia emerge from an interplay of mechanochemical feedback and crowding.

Glassy dynamics in epithelial tissues remain a subject of debate, as theory predicts its emergence only at unrealistically low cellular activity, yet experimental studies have shown glassy dynamics at physiologically active conditions. In this study, we address this paradox by integrating experimental observations in epithelial monolayers with an active vertex model. We demonstrate that while crowding is essential, it is not sufficient for glassy dynamics to emerge. A mechanochemical feedback loop (MCFL-I), mediated by cell shape changes through the contractile actomyosin network is required to drive glass transition in dense epithelial tissues. Such mechanochemical feedback is captured experimentally via a crosstalk between actin-based cell clustering and dynamic heterogeneity, as well as via force induced actin reorganisation in epithelial cells. Incorporating MCFL into the vertex model reveals contrasting results from those previously predicted by theories- we show that the MCFL can counteract cell division-induced fluidisation and enable glassy dynamics to emerge through active cell-to-cell communication. Furthermore, our analysis reveals the existence of collective mechanochemical oscillations that arise from the crosstalk of MCFL-I with oscillatory MCFL-II, capturing ERK mediated cell shape changes. Together, we demonstrate that an interplay between crowding and active mechanochemical feedback enables the emergence of glass-like traits and collective biochemical oscillations in epithelial tissues with active cell-to-cell contacts.