The septins and ESCRT machinery function at different stages of abscission. (A, left) The central region of confocal images of control, septin^unc-59(RNAi), and ESCRT-I^tsg-101(RNAi) (>10 embryos for each condition) embryos expressing a GFP-tagged plasma membrane probe at different time points after furrow initiation. (right) Differential interference contrast (DIC) images of control, septin^unc-59(RNAi), or ESCRT-I^tsg-101(RNAi) embryos at the two-cell stage. The region in the yellow boxes is shown at higher magnification in the images to the right. (B) Central plane confocal images of four-cell stage control, septin^unc-59(RNAi), and ESCRT-I^tsg-101(RNAi) embryos expressing a fluorescently tagged plasma membrane probe along with the midbody marker mCherry-MKLP1^ZEN-4 (top; n = 21 control, 12 septin^unc-59(RNAi), and 16 ESCRT-I^tsg-101(RNAi) embryos) or the midbody ring marker GFP–CYK-7 (bottom; n = 19 control, 12 septin^unc-59(RNAi), and 6 ESCRT-I^tsg-101(RNAi) embryos). The midbody is released into the posterior cell in control embryos, protrudes from cell–cell boundary in septin^unc-59(RNAi) embryos, and is enclosed within a plasma membrane–bound compartment embedded in the cell–cell boundary in ESCRT-I^tsg-101(RNAi) embryos. White boxes on the low magnification images mark the location of the region shown at higher magnification in the adjacent images. Bars, 5 µm.