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. 2005 Jul 18;170(2):213–223. doi: 10.1083/jcb.200501042

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Copyright © 2005, The Rockefeller University Press

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Figure 1. — Meiotic telomere dynamics and exit from the bouquet stage require functional cohesin. (A) Projections of trajectories (red threads) of tracked Rap1-GFP telomere spots from a time-lapse image series displayed over an image frame of the respective nucleus. Vegetative telomere clusters (veg.) displaying locally accumulated trajectory projections as a result of constrained motility range. Leptotene telomeres (L) move across the nuclear periphery, which leads to a web of trajectories around the nucleus. Bouquet nucleus (B) with trajectories confined to a limited sector of the nuclear periphery, indicative of telomere clustering. Pachytene nucleus (P) with trajectories around the nucleus, consistent with unconstrained, peripheral telomere movements around the nucleus. Bar, 1 μm. (B) Cumulative plot displaying the velocities of single telomere signals derived from movements of tracked GFP-Rap1 signals in an image series captured every 0.5 s during 7 min. Each trajectory represents a traceable telomere signal through an image series (focal plane fixed at nuclear equator). The trajectories are ranked according to speed. It is evident that in the wild type, vegetative telomere movements are slower than leptotene/bouquet movements, whereas pachytene telomere movements are the most rapid ones. In rec8Δ cells, vegetative telomere velocities match those of wild type, whereas telomere velocities in bouquet-like rec8Δ meiocytes are variable. (C) Analysis of bouquet frequencies by telomere FISH to meiotic time courses. The wild-type frequency of nuclei with a single telomere cluster reaches a maximum after 210 min in sporulation medium (SPM). Wild-type time courses were shorter because meiotic divisions appeared after 270 min and rendered FISH patterns difficult to interpret. rec8Δ and rec8Δ spo11Δ nuclei maintain a telomere cluster up to meiosis I division (compare C with E). Telomere cluster frequency drops after 420 min in rec8Δ spo11Δ meiosis when meiotic divisions become abundant (E). Meiotic expression of the mitotic cohesin SCC1 (P_rec8-SCC1) restores bouquet-stage exit in a rec8Δ background, leading to low frequencies of nuclei with a single telomere cluster. Reduction of meiotic CDC5 expression by SCC1 promoter control in REC8 meiosis (P_scc1-CDC5) does not increase telomere clustering. A delay in bouquet formation is evident in red1Δ, P_rec8-SCC1, and P_scc1-CDC5 meiosis. (D) Development of FACS profiles in wild-type (WT), rec8Δ, and rec8Δ spo11Δ sporulation indicates that all strains pass through S-phase. G1/2, cell-cycle stage gap1/2. (E) Timing of meiotic divisions in wild-type, rec8Δ, and rec8Δ spo11Δ strains derived by scoring bi- and tetranucleate cells (100–200 per time point). Divisions were significantly delayed in rec8Δ meiosis and occurred at a maximum of 20% (even in longer time courses; not depicted), whereas the spo11Δ mutation eliminated the DSB-dependent prophase I arrest.