Figure 2.

Immunostaining of centromeric histone variant Cna1p (red). (a) Wild-type (WT). In round, early meiotic MICs of untreated wild type, centromeres are grouped together in a small region (a1). As MIC elongation begins, this grouping is lost (a2 and a3), but centromeres reassemble again at one tip of the MIC while elongation proceeds (a4 and a5). (b) In the spo11Δ mutant, centromere rearrangement arrests at the dispersed stage, but UV treatment restores not only MIC elongation but also wild-type internal organization, as suggested by the clustering of centromeres (c1 and c2). Kinase inhibitors caffeine (d) and wortmannin (e) prevent both centromere clustering and MIC elongation. Also in the presence of the MT inhibitor nocodazole, centromere clustering fails (f). The MT inhibitor benomyl permits centromere clustering in most MICs although MIC elongation does not take place (g). Note that in elongating MICs (of WT and spo11Δ + UV), where centromeres are not yet completely clustered, there is always at least one Cna1p dot at the very tip. This suggests that the pushing of centromeres away from the telomeric pole of the MIC mediates its stretching. Bar, 10 μm.