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Fig. 4. Triple labeling of Ptk1 cells with autoimmune antibody to detect centromeres (A, D, G, J, M, and P), with antibody to topoisomerase II{alpha} (B, E, H, K, N, and Q) and with the DNA stain DAPI (C, F, I, L, O, and R). Many interphase cells exhibit low or undetectable expression of topoisomerase II{alpha} (A–C). Cells in late G2 phase as evidenced by double centromere spots invariably show strong expression of topoisomerase II{alpha} (D–F). Prophase cells showed diffuse labeling of the chromosome arms with anti-topoisomerase II{alpha} and a concentration at the centromeres (arrows; G–I). During prometaphase, topoisomerase II{alpha} was concentrated at the centromeres (arrows) and along the central axis of the chromosome arms (arrowhead; J–L). Metaphase cells showed strong labeling of centromeres (arrows) and chromosome arms (M–O). At late anaphase, the topoisomerase II{alpha} was no longer highly concentrated at centromeres but was present on chromosome arms (P–R). Bar, 5 µm.