ABa/p rings without PLST-1 constrict at a normal rate, contain normal levels of F-actin and myosin, and have a more rounded shape than controls. (A) Time interval (mean ±95% CI) between nuclear envelope breakdown (NEBD) and constriction initiation (ring perimeter of 60 µm), and between initiation and final stages of constriction (ring perimeter of 10 µm) in ABa/p cells. Seven cells were analyzed per condition. (B) Ring constriction rate (mean ±95% CI) in ABa/p cells. n is the number of contractile rings analyzed (n = 27 in control and n = 26 in plst-1(prt86)). (C) Mean fluorescence intensity of LifeAct::GFP (±95% CI) in the peripheral arc of ABa rings. n is the number of contractile rings analyzed (n = 6 in control, n = 6 in plst-1(prt89), n = 12 in cyk-1(RNAi), and n = 12 in cyk-1(RNAi);plst-1(prt89)). (D) Images of ABp rings co-labeled with LifeAct::GFP and NMY-2::mCherry. Two different stages of ring constriction are shown. (E) Images of ABa rings with a perimeter of ∼40 µm. Illustrations show the shape of the rings as determined by manual tracing. (F) Curvature and curvature standard deviation (mean ±95% CI) of ABa rings determined as illustrated in (F′). n is the number of contractile rings analyzed (n = 10 in control, n = 12 in plst-1(prt89), n = 8 in sma-1(ru18), n = 9 in nmy-2(RNAi), and n = 10 in mlc-4(RNAi)). (F′) Examples of individual profiles of point curvature along the ring perimeter. Colors as in F. Statistical significance was determined using a two-tailed, unpaired Student’s t test in A and B or using unpaired one-way ANOVA followed by Bonferroni’s multiple comparison test in C and F. ****P < 0.0001; ns, not significant, P ≥ 0.05. Scale bars in D and E, 5 µm.