Reducing NMY-2 levels prevents large ruptures and ring regressions in cyk-1(RNAi) rings. (A) Images of ABa rings in embryos co-expressing LifeAct::GFP and NMY-2::mCherry. Two different stages of ring constriction are shown for each condition. (B) Individual ring closure profiles in ABa/p cells. (C) Ring constriction rate (mean ±95% CI) in ABa/p cells. n is the number of contractile rings analyzed (n = 27 in control, n = 11 in nmy-2(RNAi), n = 21 in cyk-1(RNAi) and n = 18 in cyk-1(RNAi);nmy-2(RNAi)). Statistical significance was determined using unpaired one-way ANOVA followed by Bonferroni’s multiple comparison test. ****P < 0.0001; **P < 0.01; ns, not significant, P ≥ 0.05. (D) Instantaneous ring perimeter change (10-s interval) versus ring perimeter of ABa/p rings throughout constriction. 11 contractile rings were analyzed per condition. (E) Images of constricting ABa rings in embryos expressing GFP::ANI-1. cyk-1(RNAi);nmy-2(RNAi) induces small discontinuities in the ring (arrowheads). Blue region is shown at different time points at higher magnification. Numbers correspond to time in seconds. Scale bars in A and E, 5 µm.