Apical constriction of NBs is achieved by cycles of strong contractions followed by short and weak expansions. (A) Single profile of apical membrane area loss during ingression. (B and C) Rate of apical area change in an NB (B) and a NIC (C) normalized to the apical area size at each time point. Positive rates are expansions, negative rates are contractions, and time 0 depicts the onset of ingression. (D) Relative area change (area(t) − area(t − 1 min)/area(t)) during contractions and expansions in NBs and NICs. Onset to end minus 10 min was considered early ingression, and the last 10 min was considered late ingression. n = 123–328 contractions/expansions per condition. From left to right: ****, P = 2.4 × 10−9; 5.3 × 10−7; 9.6 × 10−12; 4.7 × 10−17; and 2.4 × 10−27; **, P = 0.005; ns (not significant), P = 0.97 and 0.33 (KS test). n = 19 NBs and 19 NICs (seven embryos). (E) Durations of contractions and expansions in seconds. Median values: 51.5, 39.4, and 28.8 s for contractions and 23.1, 14.2, and 32.2 s for expansions. From left to right: ****, P = 3.6 × 10−6; 6.6 × 10−12; and 1.7 × 10−10; **, P = 0.003; ns, P = 0.11 and 0.75 (KS test). Bars are IQRs. n values are as in D. (F) Fraction of time NBs and NICs spend contracting and expanding their apical membranes. From left to right: ****, P = 1.2 × 10−9; 1.4 × 10−11; and 1.1 × 10−11; ns, P = 0.155 (KS test). n values are as in D. (G) Mean period of apical oscillations in NBs and NICs; 183.6 ± 48.9 s for NBs and 161.7 ± 58.9 s for NICs. P = 0.25 (KS test). Data presented are means ± SEM. n values are as in D.
