Aurora B is mislocalized and aberrantly active in midbody-stage cells depleted of Nup153. (A and B) siRNA-treated cells were stained for Aurora B (A) and pAurora B (B). Note that Aurora B (and pAurora B) mislocalizes in cytoplasmic foci upon Nup153 depletion. Insets show normal Aurora B localization in interphase cells. (C and D) Localization of Aurora B (C) and the spindle checkpoint protein Mad1 (D) during prometaphase (left) and metaphase (right). CREST antiserum was used to indicate centromeres. (E) Detection of pAurora B and CRIK illustrates that mislocalized pAurora B foci are neither ectopic nor residual midbodies (arrowheads). Insets show a cell with what is likely a residual midbody. (F) Cells stained for pAurora B and INCENP. Brackets indicate midbody-stage cells. Bars: (A, B, E, and F) 10 µm; (C and D) 5 µm.