Top2α inhibition correlates with impaired localization of phosphorylated INCENP-S91 and Aurora B to the midbody ring in cytokinesis with spontaneous chromatin bridges. (A–F) Localization and mean intensity of ATM or phosphorylated Chk2-T68 (pChk2) at the bridge DNA next to the midbody in BE cells with chromatin bridges, in the absence (control) or presence of Top2α siRNA. (G–L) Localization and mean intensity of phosphorylated INCENP-S91 (pINCENP) or Aurora B (AurB) at the midbody ring. Mean ± SD from n cells. Values in control were set to 1. ***, P < 0.001 (Student’s t test). (M–P) Localization and mean intensity of Mre11 at the bridge DNA next to the midbody in BE cells expressing siRNA-resistant (R) WT, Y805F, or AEEA GFP:Top2^R proteins, or GFP-only, in the absence or presence of Top2α siRNA. Mean ± SD from n cells. Values in GFP were set to 1. ***, P < 0.001 (ANOVA and Student’s t test). Broken chromatin bridges are indicated by dotted arrows. Arrowheads indicate DNA knots. Midbodies (boxed areas) were reexported and are shown at higher magnification. Numbers below/next to each bar indicate n. Scale bars, 5 μm.