SEPT9 mediates midbody abscission. (A–C) HeLa cells were transfected with siRNA, and randomly selected cells were followed through division by time-lapse microscopy. The time (in hours:minutes) since the beginning of DNA segregation is shown. Black arrows point to intact midbodies, whereas white arrows denote abscission. Bars, 32 µm. (A) Division of HeLa cells after treatment with control siRNA. (B) SEPT11 KD causes defects early in cytokinesis. (C) SEPT9 KD causes defects in midbody abscission. See Videos 1–5 for complete movies. (D and E) Quantification of the effect of SEPT9 KD on midbody abscission in HeLa (D) and ARPE-19 cells (E). The time from DNA segregation to midbody abscission was determined, and the cumulative percentage of cells that were abscised is plotted as a function of time. For D, n = 45 cells for control KD and n = 30 cells for SEPT9 KD; for E, n = 34 cells for control KD and n = 25 cells for SEPT9 KD.