Figure 1. Extrusion correlates with singularities in cell orientation (+1/2 defects) in the epithelia.

a, (left) Schematics of confluent monolayer and extruding cell (grey: cell body, blue: nucleus, orange: apoptotic extruding cell). (middle) Side view confocal image of confluent MDCK monolayer and extruding cell (green - actin, blue - nucleus). (right) Corresponding images of activation of caspase-3 signal (red). b, Phase-contrast images showing monolayer dynamics before extrusion (yellow arrowhead) at t = 0 min, overlaid with velocity field vectors. Length of vectors is proportional to their magnitude. c, d, Corresponding images overlaid with red lines (represented as black lines in panel below) showing average local orientation of cells. The group of cells moving toward the extrusion forms comet-like configuration (blue dot: comet core, arrow: comet tail-to-head direction). e, Experimental and schematic images of +1/2 defect (top – comet configuration) and -1/2 defect (bottom – triangle configuration). Red lines denote average cell orientations, blue dot and arrow represent defect core and tail-to-head direction of +1/2 defect. Green triangle represents -1/2 defect core. f, (left) Schematic: determination of correlation between +1/2 defects and extrusions: distance, r_e of each extrusion to its closest +1/2 defect in the preceding frame is measured, and the number of these defects per unit area as function of r_e is normalized (right). See Methods. n = 50 (MDCK, WT) extrusions from 4 independent movies in 3 independent experiments, n = 61 (MDCK, mytomycin-c treatment) extrusions from 3 independent movies in 2 independent experiments, n = 85 (MCF10A) extrusions in 2 independent movies, n = 79 (HaCaT) extrusions in 2 independent movies. Scale bars, 10 μm.