Purvalanol A–induced mitotic exit from monopolar mitosis. (A) Summary of morphological changes after exit from monopolar arrest. Monopolar HeLa cells were fixed either before (a) or 5–30 min after (b–h) purvalanol A addition. Images are arranged to simulate a time course. Note the initial recruitment of RhoA to the cortex is approximately symmetric (b) but rapidly becomes asymmetrical (c–e). Similar stages in bipolar mitosis (i) and cytokinesis (j–n) are shown for comparison. (B) Phase-contrast time-lapse sequence that illustrates morphological changes of the cortex (video 1). The temperature in time-lapse experiments was 27°C, which slows down the sequence of morphological changes but does not otherwise alter them. Typical cytokinesis blebs occurred on one side of the cell (red arrows). On the opposite side, a protrusion gradually expanded and a furrow (green arrows) developed between it and the cell body. (C) Distribution of microtubules and cytokinesis proteins using spinning disc confocal microscopy. Note the highly polarized microtubules and cytokinetic cortical proteins at the cap. All microtubule-associated cytokinesis proteins, except Aurora B, are concentrated at microtubules tips. Aurora B localizes at the gap region between the cortex and microtubules. Bars, 5 μm.