Rab11DN injection results in increased frequency of apical re-expansion during apical constriction. (A and B) Example cell area change and constriction rate over time in GST and Rab11DN injected embryos. Yellow shaded area, constriction phase; white area, stabilization phase; red shaded area, apical re-expansion. Vertical lines in B: peak of constriction rate. (C) Rab11DN injection does not affect the frequency of cell constriction pulses. Pulse interval was calculated as the interval between neighboring constriction peaks. The central mark indicates the median, and the bottom and top edges of the box indicate the 25th and 75th percentiles, respectively. The whiskers extend to the most extreme data points not considered outliers. Two-sample, two-tailed unpaired t test was used for statistical comparison. n.s., P > 0.05. (D and E) Rab11DN injected embryos exhibited increased frequency of apical re-expansion events. (D) Heatmap showing constriction rate of individual cell over ∼200 s window during mid-apical constriction phase in GST and Rab11DN injected embryos. The positive constriction rate indicates apical re-expansion. N = 21 cells from two GST-injected embryos. N = 26 cells from two Rab11DN-injected embryos. Red boxes correspond to the examples shown in E. Asterisks in E: gaps resulted from myosin break event. Scale bars, 2 μm. (F) Apical AJ is pulled inward (red arrows) when myosin break (yellow asterisks) occurs in the adjacent cell. Scale bar, 2 μm. (G) Quantification of myosin break orientation in GST- and Rab11DN-injected embryos. Dataset from Fig. 9 (late injection) was used for this analysis. (H) Schematics of proposed actomyosin-dependent feedback mechanism.