The septins are required for timely cytoplasmic isolation and for midbody release. (A) Graph plotting the mean initial slope of the NID versus time in seconds after furrow initiation for control and septin^unc-59(RNAi) embryos. Error bars are the 90% confidence interval; mean n = 10 slope measurements per time point. (B and C, top) Central plane confocal images of control and septin^unc-59(RNAi) embryos expressing a fluorescently tagged plasma membrane probe and the midbody markers mCherry-Mklp1^ZEN-4 (B; n = 11 embryos) or GFP–CYK-7 (C; n = 11 embryos). Times are relative to anaphase of the second division. Released fragments marked with the plasma membrane probe are indicated (white arrowheads). Arrows point to the midbody/midbody ring from the first division, which is released in control embryos (green arrows) and fails to be released in septin^unc-59(RNAi) embryos (yellow arrows). Asterisks mark the tip of the ingressing furrow from the second embryonic division. (bottom) Graphs plotting the times when the mCherry-Mklp1^ZEN-4–marked midbodies or GFP–CYK-7–marked midbody rings were released. In cases in which the midbody/midbody ring was not released, the data point refers to the endpoint of the time-lapse sequence. (D) The central region of confocal images of control (n = 11) and septin^unc-59(RNAi) (n = 10) embryos expressing the mCherry-tagged plasma membrane probe and GFP–Aurora B^AIR-2. (E) Confocal images of septin^unc-59(RNAi) (n = 6 embryos) embryos expressing GFP–ESCRT-I^MVB-12. Times in D and E are relative to anaphase of the second division. Dashed yellow lines mark the cell boundaries. Bars, 5 µm.