Cyst regulates actomyosin dynamics at AJs. (A) Z-projections taken from live stage-8 embryos expressing myosin::GFP (Sqh::GFP) in a control (n = 3) or cyst RNAi (n = 3) background. The ventral ectoderm is shown with the arrowhead pointing to the ventral midline. The cyst RNAi embryo shows a reduction of myosin::GFP. Scale bar, 10 µm. (B) Stills of time-lapse videos (Videos 5 and 6) showing myosin::GFP in a control embryo (maternal expression of mCherry RNAi) and in a cyst-depleted embryo (maternal expression of cyst RNAi in a Df(cysts)/+ mother). Time is minutes after the onset of germband extension. In the control, multicellular myosin II cables form at the anterior-posterior cell–cell contacts during axis elongation. Junctional myosin levels and multicellular cables are reduced in cyst-depleted embryos. Scale bar, 10 µm. (C) Stills of time-lapse videos (Videos 7 and 8) showing myosin::GFP expression in a control embryo (H2O injected) and in a crb dsRNA–injected embryo. Time is minutes after the onset of germband extension. Junctional myosin levels are reduced, and medial myosin levels gradually become enhanced in the crb-depleted embryo. (D) Quantification of junctional and medial myosin levels in control and cyst-depleted embryos at the time points indicated in B. Bars indicate mean ± SEM. Three embryos per condition; n values indicate number of cell edges analyzed for junctional myosin and number of apical surface areas analyzed for medial myosin. For junctional myosin, from left to right: ****, P = 4.2 × 10−4, 5.9 × 10−5, 3.10−16, 4.2 × 10−21, and 3.4 × 10−16 (Kolmogorov–Smirnov test); for medial myosin, from left to right: ns, P = 0.19, P = 0.59, and P = 0.99; **, P = 6 × 10−2 (Kolmogorov–Smirnov test). (E) Quantification of junctional and medial myosin levels in control and crb RNAi embryos at the time points indicated in C. Bars indicate mean ± SEM. Three to five embryos per condition; n values indicate number of cell edges analyzed for junctional myosin and number of apical surface areas analyzed for medial myosin. For junctional myosin, from left to right: ****, P = 6.5 × 10−53, 5.5 × 10−72, 2.5 × 10−60, 7.2 × 10−66, and 3.0 × 10−62 (Kolmogorov–Smirnov test); for medial myosin, from left to right: ****, P = 1.10−6 and 8.8 × 10−8; **, 2 × 10−3 and 10−3; ****, P = 2.7 × 10−9 (Kolmogorov–Smirnov test).
