Myosin distribution and Rho1 activity in embryos expressing α-Cat M region deletions. (A) Representative images of ectoderm during germband extension of α-Cat-RNAi α-CatX embryos. Myosin cables are highlighted with orange lines in the right duplicate images. (B) Series of stills from a live α-Cat-RNAi α-Cat-ΔM23 embryo showing gaps forming at vertical edges (arrowheads) with accumulations of myosin at gap perimeters. (C) Stills from live α-Cat-RNAi α-CatX embryos expressing the Rho1 activity probe, Ani-RBD::GFP. Note accumulation of Ani-RBD::GFP in gap areas (arrowheads). (D) Series of stills from a live α-Cat-RNAi α-Cat-ΔM23 embryo showing enrichment of Ani-RBD::GFP at a gap between cells (arrowheads). Cell contacts first split and subsequently Ani-RBD signal increases. (E) Quantification of total myosin (cytoplasmic and junctional) and junctional myosin as a fraction of total myosin in α-Cat-RNAi α-CatX embryos. (F) Quantification of Ani-RBD::GFP signal at cortices of cells which are not in contact with a gap (intact). At right, mean FI of Ani-RBD::GFP signal at the perimeter (with no subtraction of cytoplasmic FI) of cells with intact junctions is compared to the perimeter of gaps (for Ani-RBD at gaps, significance determined by Mann-Whitney two-tailed test). For E and F, significance is determined by Kruskal–Wallis test with Dunn’s multiple comparisons test (**** = P < 0.0001, ** = P < 0.01). n = pooled number of cells (c) from number of embryos (e). Bold line, median; dotted lines, interquartile ranges. Scale bar in A–D, 10 μm. Schematics above plots describe measurement used in this and following figures (see Fig. S5 for legend).