Cells undergo apical constriction in the developing neuroepithelium. (A) Schematic indicates the embryonic stage and the red box shows the imaging location in the caudal neural plate. Computational segmentation (right panel) of the Lifeact-EGFP signal (left panel) in live imaging of the neuroepithelium identifies cells undergoing apical constriction. (B) Time series of an apically constricting cell (blue cell in segmented image in A). (C) The ratio of Lifeact-EGFP intensity at the apical cortex relative to the cell junctions increases as the apical cell area shrinks. Graphs show mean (colored line) ± SEM (shading) for the normalized Lifeact-EGFP intensity and apical cell area over time in three embryos. (D) Heatmap of apical area change over time in cells undergoing apical constriction and non-constricting cells. Example from 1 embryo, n = 7 constricting cells and 47 non-constricting cells. Cells are aligned by the maximal observed area. (E) Constricting cells have a higher variance of apical area change than non-constricting cells, n = 14 constricting cells and 62 non-constricting cells from 2 embryos. *** P < 0.001 (two-sided Mann-Whitney test). (F) Rate of area change during expansion and contraction phases of constricting cells, n = 19 cells from three embryos. Area change is faster during contraction phases. **P < 0.01 (bilateral Mann-Whitney test). Violin plots show mean and first and third quartiles.