Fig. 7.

Active edges as a source of stress in epithelial tissue. (A) Schematic of vertex model with junction tension fluctuations. A fluctuating additional tension is applied between junctions i and j. The fluctuations can be either contractile or extensile and have a characteristic persistence time $\tau$ (see SI Appendix for values of all simulation parameters used). Snapshots of cellular configuration at phi = 100% and 20% are also shown, respectively (${\tau }^R=1$). (B) Plot of cell speed versus the fraction of active edges in simulated vertex models with fluctuating edge tension (${\tau }^R=1$). Different curves represent different values of the target shape parameter $p_0$. (C) Images of MDCK monolayers with cell cycle information extracted from pip-FUCCI biosensor. Images from the individual biosensor channels are segmented and overlaid in pseudocolors green (PIP–Venus) and purple (Geminin–mCherry). Presence of only green indicates G1/G0 phase, only purple indicates S phase, and both markers indicates G2/M phase. (D) Plot of cell speed against fraction of cells in G1/G0 phase of the cell cycle. Error bars represent the SD between 30 fields of view. (E) Plot of cell speed versus shape parameter from simulations. Curves represent different values of ${\tau }^R$ (dashed, dotted lines) and the target shape parameter $p_0$ (color scale). (F) Schematic phase diagram of epithelial arrest, in which edge thickness represents the magnitude of tension on an edge and arrows represent cell displacements. In addition to fluid and jammed phases which occur at different cell shapes, monolayers can arrest at high average cell shape parameter, indicating a low fluctuation regime. In this low fluctuation regime, the magnitudes of active fluctuations are too small to produce large cell displacements and frequent neighbor rearrangements.