Planar-polarized myosin distribution correlates with planar disassembly of NB cell contacts. (A) Stills of a time-lapse video of an NB (asterisk) labeled with Sqh::GFP (myosin, green) and GAP43::mCherry (cell membrane, red). Myosin is enriched at AP junctions (arrowheads). Time point 20 min corresponds to a 2.5-µm2 apical area in NBs. Bar, 5 µm. P, posterior, A, anterior, D, dorsal, V, ventral. (B) Ratios between myosin intensity at AP (75–90°) and DV (0–15°) edges in NBs (n = 13 cells, seven embryos; data presented are means ± SEM) and in ectoderm cells during ingression. Time points are as in A. (C) Kymographs of myosin (Sqh::GFP) during the last 15 min of AP and DV edge disassembly in NBs. DV edges show more discontinuous myosin distribution than AP edges. Time intervals, 15 s. (D) Myosin levels (IQRs) in AP junctions (n = 12) and DV junctions (n = 11) in NBs versus DV junctions in NICs (n = 10). From left to right: ****, P = 2.5 × 10−173; 2.8 × 10−219; and P = 2.7 × 10−13 (KS test). (E) Correlation coefficients between AP/DV edge length and junctional myosin levels during ingression. Median correlation coefficient for AP edges was R = −0.54 and for DV edges was R = −0.39. Bars are IQRs. n = 20 junctions per condition, nine embryos. (F) AP and DV NB edge length during ingression. t = 0 min, onset of ingression. Speed of AP and DV edge contraction in NBs (means ± SD): −0.72 ± 0.3 µm/min and −0.33 ± 0.1 µm/min, respectively. P = 5 × 10−5 (two-tailed t test). Speed of DV edge length in NICs: 0.05 ± 0.06 µm/min. n = 11 junctions per condition, two embryos. (G–I) Representative plots of junctional myosin levels and AP or DV edge length in an NB and NIC. a.u., arbitrary units.
