Figure 6.—

Disruption of Top2 perturbs homolog pairing. (A–C) dsRNA directed against Top2 reduces pairing at 28B1 in Kc₁₆₇ cells as illustrated by nuclei imaged with DAPI and FISH (A), a pairing profile (B), and a percentile plot (C). dsRNA directed against Top1 has little effect. B shows the results (±SD) of experiments using three distinct dsRNAs targeting Top2 and two distinct dsRNAs targeting Top1, as well as two control experiments run without dsRNA. The percentile plot combines data described in B. (D and E) ICRF-193 (10 μm) reduces pairing at 28B1 (D) and 16E1 (E) in Kc₁₆₇ cells. Camptothecin (4 μm) and m-amsacrine (5 μm) are less perturbing. Control nuclei were from cells treated with DMSO. Data represent two trials. (F and G) Pairing is more disrupted at 28B1 (F; P < 0.0001) than it is at 16E1 (G; P = 0.003) by ICRF-193 in clone 8 cells. Little disruption was observed when cells were treated with camptothecin (4 μm), m-amsacrine (5 μm), or DMSO (control). The data are from two independent experiments, one in which cells were treated with drugs for 24 hr and the other in which cells were treated for 30 hr. For each time point, nuclei imaged with FISH targeting 28B1 or 16E1 were from the same culture. N, number of nuclei from both time points combined. (Insets in D and F) Mitotic indexes correspond to one of the two independent trials shown.