Aurora B depletion impairs ATM activation at late midbodies. (A and B) Localization and mean intensity of phosphorylated INCENP-Ser91 (pINCENP-Ser91) at the midbody center after treatment of BE cells with 10 µM KU-55933 in cytokinesis. (C) Frequency of midbody stage BE cells. Values represent mean ± SD from three independent experiments (n > 900). (D) Model for the role of ATM and Chk2 in abscission delay in normally segregating cells. Dashed arrow indicates feedback loop. p, phosphorylation. (E) Mre11 does not localize to late midbodies. As a positive control, Mre11 forms DNA foci after treatment of BE cells with 1 mM hydroxyurea (HU) for 4 h. (F, G, and J–M) Localization and mean intensity of phospho-ATM-Ser1981 (pATM-Ser1981), phospho-Chk2-Thr68 (pChk2-Thr68), or ATM at the midbody center in BE cells. Values represent mean ± SD, from n cells. Values in control were set to 1. ***, P < 0.001 (ANOVA and Student’s t test). Tubulin values indicate midbody thickness. Insets show 1.6× magnification of the midbodies. Scale bars, 5 µm. (H and I) Western blot analysis of total Mre11, actin, Aurora B (AurB), and tubulin. T, threonine.