Reducing NMY-2 levels suppresses the large ruptures and regressions of cyk-1(RNAi) rings induced by SMA-1 loss. (A) Time between each consecutive rupture in cyk-1(RNAi);sma-1(ru18) rings (n = 60 events). (B) Individual ring closure profiles in ABa/p cells. (C) Instantaneous ring perimeter change (10 s interval) versus ring perimeter in ABa/p cells throughout constriction. 11 contractile rings were analyzed per condition. (D) Ring constriction rate (mean ±95% CI). n is the number of contractile rings analyzed (n = 27 in control, n = 21 in cyk-1(RNAi), n = 18 in cyk-1(RNAi);nmy-2(RNAi), n = 17 in cyk-1(RNAi);nmy-2(RNAi);sma-1(ru18), and n = 35 in cyk-1(RNAi);sma-1(ru18)). Statistical significance was determined using unpaired one-way ANOVA followed by Bonferroni’s multiple comparison test. ****P < 0.0001; ns, not significant, P ≥ 0.05. Conditions in D and E are colored as in B and C. (E) Gap size of ruptures or discontinuities observed in 11 rings for each condition, measured as illustrated in the schematic in Fig. 7 D. (F and F′) Images from a time-lapse series of constricting ABa rings expressing NMY-2::GFP and an mCherry-tagged plasma membrane probe (mCH::PH, F); and in (F′) a zoomed view of two examples of discontinuities in cyk-1(RNAi);nmy-2(RNAi);sma-1(ru18) rings (arrowheads); see Video 9. Numbers correspond to time in seconds. Scale bar in F, 5 µm; and in F′, 2 µm.