FIGURE 8.

Long-term expression of Top2Δ20 in Top2-depleted cells triggers the accumulation of a population with doubled DNA content. On day 29 of CuSO₄ induction, the cell cycle profiles of S2 cells transfected with the indicated constructs were recorded. Top2-depleted cells rescued by Top2Δ20 showed a peak representing high DNA content, whereas cells rescued by Top2(WT) or Top2(2SA) showed no significant difference from untransfected cells. The arrow marks the cell population with polyploidy. Among 32 Top2-depleted cells rescued by Top2Δ20, observed by karyotype analysis, 18 cells contained more than 20 chromosomes, whereas only 14 cells appeared to have 12 long chromosomes as in untransfected cells. The elevated population of cells with more than 20 chromosomes observed in karyotype analysis was also concordant with the appearance of a population of cells with higher DNA content from flow cytometry.