ΔCDK-RB-induced dispersion is not dependent on the expression of DNDP1, but it requires HDAC activity and topoisomerase activity. WT and ΔCDK-RB RPE cells were treated as indicated, and the FISH signal in chromosome 7 α-satellite region was analyzed. Representative FISH signals together with skeleton dot images are shown. The percentage of foci in each category is indicated. (A and B) Cells expressing DNDP1. DNDP1 did not alter dispersion induced by ΔCDK-RB. All quantitation is from two independent biological replicates, set up and performed on different days. (C and D) Cells treated with TSA for 72 h. Note that TSA treatment prevented the significant increase in dispersed foci and mean dot length seen in ΔCDK-RB cells. (E and F) Cells treated with TOPIIβ or control siRNAs (CTRL Si) for 72 h. TOPIIβ knockdown reduced the dispersion induced by ΔCDK-RB. Numbers of foci quantified for each sample (n) are as follows (in the order they appear on the bar graphs): B, n = 89, 59, 58, 45; D, n = 105, 75, 62, 89; F, n = 103, 66, 76, 68. Error bars are SEM. Nonparametric two-tailed Mann–Whitney U test was performed for pairs of samples indicated in B, D, and F (left panels), and asterisks denote P values. For B, D, and F (right panels), asterisks denote P values from nonparametric two-tailed multiple t tests (without correction for multiple comparisons). ns, P > 0.05; *, P ≤ 0.05; **, P ≤ 0.01; ***, P ≤ 0.001; ****, P ≤ 0.0001. Scale bar (including insets) = 2 µm. Dashed lines indicate the cutoffs for defining the categories compact, diffused, and dispersed for chromosome 7 α-satellite.