Figure 3.

Group plithotaxis: global alignment of stress and velocity drive intercellular coordination. (a) Motion clusters (left, red regions) derived from the velocity field (left inset, a magnified region from the main panel); stress clusters (right, blue regions) derived from the stress ellipse (right inset, a magnified region from the main panel). Scale bar = 100 μm. (b–d) Motion- and stress-coordinated clusters are interlinked. (b) Time course of probabilities for a cell to belong to either a motion cluster (red), or a stress cluster (light blue), or both (intersection, yellow). (c) Correlation between P(motion) and P(stress) for all time points (Pearson correlation: N = 96, R = 0.4, p < 0.00005). (d) Expected versus observed probability of the intersection between motion and stress clusters. Assuming that these clusters are spatially independent, the expected probability would be P(motion) ^∗P(stress). The observed probability is higher by 40% on average than the expected probability. (e) Comparison of cell dynamics inside and outside clusters. Distributions of ratios between properties of cells that participate in coordinated clusters (inside) and those that do not (outside). Distributions were generated from pooled ratios of averages over space and time (n > 5500; Fig. S4). (f) Proposed model, see text for discussion. (g) Stress coordination spatially precedes motion coordination. Motion clusters (red, solid line marks boundaries) and stress clusters (blue, dashed line marks boundaries) at three time points. Motion and stress clusters are spatially interlinked (magenta). Motion clusters are closer to the monolayer edge than stress clusters, implying that stress coordination precedes motion coordination. Over time, cells deeper in the monolayer first participate in stress clusters and later in motion clusters (Movie S1). Scale bar = 100 μm.