Top2-inhibition correlates with chromatin bridge breakage in cytokinesis. (A) Telophase BE cells with chromatin bridges. (B) Frequency of broken DNA bridges in untreated (control) cells or cells transfected with Top2α siRNA. (C) Fluorescence and phase-contrast live-cell imaging of HeLa cells expressing LAP2b:RFP. Cells were untreated (control) or treated with Top2-inhibitor ICRF-193 immediately before filming. Time is from the detection of the intercellular canals that contain LAP2b:RFP bridges. (D) Times to intercellular canal breakage in cells from C. (E) HeLa LAP2b:RFP cells exhibiting LAP2b:RFP bridges were analyzed by fluorescence microscopy of fixed samples. (F) Frequency of broken LAP2b:RFP bridges from E. (G) Percentage of broken DNA bridges in BE cells transfected with GFP or GFP:Vps4-K173Q in the absence or presence of Top2α siRNA. Mean ± SD from three independent experiments (n > 120). (H) Localization of Mre11 and Top2α on DNA knots. (I–Q) Localization and mean intensity of Mre11, Rad50, or Nbs1 at the bridge DNA next to the midbody in BE cells with chromatin bridges. Mean ± SD from n cells. Values in control were set to 1. ***, P < 0.001 (Student’s t test). Intact DNA bridges or intercellular canals are indicated by solid arrows; broken DNA bridges or canals 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.