Chk2 inhibition correlates with chromatin breakage in cytokinesis. (A) Telophase BE cells with chromatin bridges. (B) Frequency of cells with broken DNA bridges. BE cells were transfected and treated with 10 µM Chk2 inhibitor II (inhII), or 10 µM AZ3146 for 4 h. (C and D) Example of a chromatin bridge that is positive for γ-H2AX staining (open arrowhead) and frequency of γ-H2AX–positive chromatin bridges. Values represent mean ± SD from three independent experiments (n > 150). (E and F) Fluorescence (t = 0 min) and phase-contrast live-cell imaging of HeLa cells expressing LAP2b:RFP. Cells were untreated (control) or treated with 10 µM Chk2 inhibitor II immediately before filming. Time is from the detection of the intercellular canals containing LAP2b:RFP bridges. Intact intercellular canals are indicated by solid arrows, and broken canals are indicated by dotted arrows. Related to Video 6 and Video 7. (G) HeLa LAP2b:RFP cells exhibiting LAP2b:RFP bridges were analyzed by fluorescence microscopy of fixed samples. (H) Frequency of broken LAP2b:RFP bridges from G. (I) Percentage of broken DNA bridges in BE cells transfected with GFP or GFP:Vps4-K173Q. Values represent mean ± SD from three independent experiments (n > 150). (J–N) Localization and mean intensity of phosphorylated INCENP-Ser91 (pINCENP-Ser91) or total INCENP at the midbody in BE cells with chromatin bridges. Values represent mean ± SD from n cells. Values in control were set to 1. ***, P < 0.001 (ANOVA and Student’s t test). Broken chromatin or LAP2b:RFP bridges are indicated by dotted arrows. Insets show 1.6× magnification of the midbodies. S, serine. Scale bars, 5 µm.