Figure 3. Wound edge intercalation preserves cell shape.

a, Maximum intensity projection images of a wound in a sqh^AX3; sqh-GFP, Ecad-tdTomato wing disc before (left) and immediately after (right) wound closure (scale bar = 3µm). b, Quantification of wound edge cell polygon number before ablation, immediately after ablation and immediately after wound closure. The distribution of polygon number is significantly shifted left after ablation (Kolmogorov-Smirnov Test, D=0.2892, p=0.0019) but is restored upon closure (Kolmogorov-Smirnov Test, D=0.07583, p=0.9692). c, Colour coding of the first three rows away from the wound edge (first row blue, second row orange, third row yellow) for time points immediately after wounding (0.25 mins) and soon after the onset of wound edge intercalation (33 mins). Image is an adaptive projection of Ecad-GFP overlaid by skeletonised cell outlines. Scale bar = 5µm. d, Quantification of the percentage change in mean cell elongation for the first three rows of cells (colour coding as in c) over time for 5 WT wounds. Moving average curves (±4 time points) are shown. The transition between fast and slow closure phases is marked by a dotted line (18.37 mins). e, Percentage change in mean elongation of first row cells for three time windows; 0-10 mins (wound recoil), 10-140 mins (early wound closure), 140 mins – close (late wound closure). Data is pooled from the data set in d. Cells were significantly elongated during the recoil phase (Wilcoxon Signed Rank Test, p<0.0001). Cells were significantly more elongated during early wound closure than during late wound closure (Kolomogorov-Smirnov Test, D=0.5703, p<0.0001). Error bars = SD. f, h, Skeletonised cell outlines of cells starting at the wound edge (wound shaded in grey) at three time points in a (f) single WT wing disc (scale bar = 3µm) and a (h) single WT stage 13 embryo (scale bar = 5µm). g, Quantification of intercalation rates in rows of cells away from the wound for WT wing discs (black) and vertex model simulations with high (dark blue) and low (light blue) purse string strength. The intercalation rate in simulations is significantly higher in the first row of cells with a high purse string strength (Kolomogorov-Smirnov Test, D=0.6667, p=0.0097). i, Quantification of the percentage of cells remaining close to the wound’s centre after closure, as a measure of intercalation. A significantly higher percentage of cells remain close to the wound centre in embryos (n=3) compared to wing discs (n=5) (unpaired t-test with Welch’s correction, t=5.466, df=2.103, p=0.0285).