Mitotic abnormalities in video-recorded importin-β–overexpressing HeLa cells. (A) A mitotic HeLa cell transfected with vector and H2B-GFP construct to visualize chromosomes (Video 1). (B) A tripolar mitosis transfected with importin-β 1−876 and H2B-GFP; chromosomes segregate into three unequal masses (Video 2). (C) An importin-β–transfected cell in which chromosomes align at the equator (68 min), then lose alignment (278 min), then reach alignment again (322 min), lose it (352 min), and eventually align stably (382 min) before segregation (Video 3). (D) An importin-β–transfected mitosis displaying unstable positioning of the spindle axis (double-arrowed red line). The spindle undergoes extensive rotation (30- to 76-min panels) before the onset of segregation (Video 4). All images were taken under an inverted microscope (Ti Eclipse, Nikon; DIC frames every 2 min, fluorescence frames every 20–30 min). Bars, 10 µm.