Fig. 2.

Topo II is not required for the structural integrity of mitotic chromosomes. Shown are representative images following the expansion and refolding assay. Stages (1)–(3) represent the first cycle of expansion and refolding, and (4) is the refolded status after cycle 2. Stage (1) colcemid-arrested metaphase before treatment; stage (2) first round expansion in the low salt + EDTA TEEN buffer; stage (3) first round contraction in the low salt + Mg²⁺ RSB buffer; stage (4) appearance after a second round of expansion and contraction. Topo II-depleted chromosomes (both α-only depleted/120 hours dox, and α- plus β-depleted/120 hours dox + 72 hours siRNA) recover their normal starting morphology, which is a slightly thinner and more ribbon-like appearance than that displayed by the control chromosomes (Carpenter and Porter, 2004). All images are shown at the same magnification, with some regions enlarged for clarity. Scale bar, 10 μm.