Aurora B^AIR-2 has a role in contractile ring constriction that is independent of its roles in meiotic and mitotic chromosome segregation, MKLP1^ZEN-4 targeting to the midzone, and midzone microtubule bundling. (A and B) Mean furrow diameter is plotted versus time. Embryos were removed from the mean when the furrow began to regress in that embryo. The asterisks indicate the point when fewer than two embryos still had ingressing furrows. The control curve is the same in A and B. (C) The mean maximum extent of ingression expressed as a percentage of initial diameter (left) and the mean rate of diameter decrease over the time interval 80–140 s after constriction onset (right) are shown for the indicated conditions. The asterisks indicate that mean values for zen-4(RNAi);air-2(or207ts) are significantly different (two-tailed t test, P < 0.05) from zen-4(RNAi). All imaging for A–C was done using the postmeiotic upshift conditions outlined in Fig. 2 A. Error bars are SEM. (D) Single-plane confocal images from time-lapse sequences of control (n > 20), spd-1(RNAi) (n = 17), zen-4(RNAi) (n = 4), and zen-4 & spd-1(RNAi) (n = 4) embryos expressing GFP:AIR-2. Bar, 5 µm.