PLK1-independent furrow ingression requires centralspindlin. (A) Western blot of samples derived from HeLa cells transfected with either siLuc or siRACGAP1. The Western blot was probed with an anti-RACGAP1 antibody. α-Tubulin is shown as loading control. (B) HeLa cells were transfected with siLuc or siMKLP1 and processed for IF (right). The percentage of cells with detectable MKLP1 in anaphase was scored and used as a measure for knock-down efficiency (left). The number of cells that were scored per condition is indicated (n). One representative experiment out of two is shown. ****, P < 0.0001; χ2 test for comparison of the indicated conditions. (C and D) HeLa cells transfected with the indicated siRNAs were imaged live. PLK1 was inhibited by addition of BI2536 (100 nM) before anaphase onset (PLK1 inh.). PLK1 was inhibited by addition of BI2536 (100 nM) before anaphase onset. The number of cells showing complete furrow ingression, full-furrow ingression followed by furrow regression, visible but minimal furrow ingression, or no furrow ingression was scored. The number of cells analyzed per condition is indicated (n). One representative experiment out of two is shown. ****, P < 0.0001; ***, P < 0.001; χ2 test for comparison of the indicated conditions; ns, not significant. (E) DIC stills of HeLa cells transfected with the indicated siRNAs with or without addition of BI2536 (100 nM) before anaphase onset. Bars: 10 µm. Stills of more time frames are shown in Fig. S1 D.