CELL CYCLE-DEPENDENT SPECIFIC POSITIONING AND CLUSTERING OF CENTROMERES AND TELOMERES IN FISSION YEAST

Fluorescence in situ hybridization (FISH) shows that fission yeast cen tromeres and telomeres make up specific spatial arrangements in the nu cleus. Their positioning and clustering are cell cycle regulated. In G 2, centromeres cluster adjacent to the spindle pole body (SPB), while in mitosis, their association with each other and with the SPB is disr upted. Similarly, telomeres cluster at the nuclear periphery in G2 and their associations are disrupted in mitosis. Mitotic centromeres inte ract with the spindle. They remain undivided until the spindle reaches a critical length, then separate and move towards the poles. This dem onstrated, for the first time, that anaphase A occurs in fission yeast . The mode of anaphase A and B is similar to that of higher eukaryotes . In nda3 and cut7 mutants defective in tubulin or a kinesin-related m otor, cells are blocked in early stages of mitosis due to the absence of the spindle, and centromeres dissociate but remain close to the SPB , whereas in a metaphase-arrested nuc2 mutant, they reside at the midd le of the spindle. FISH is therefore a powerful tool for analyzing mit otic chromosome movement and disjunction using various mutants. Surpri singly, in top2 defective in DNA topoisomerase II, while most chromati d DNAs remain undivided, sister centromeres are separated. Significanc e of this finding is discussed. In contrast, most chromatid DNAs are s eparated but telomeric DNAs are not in cut1 mutant. In cut1, the depen dence of SPB duplication on the completion of mitosis is abolished. In crm1 mutant cells defective in higher-order chromosome organization, the interphase arrangements of centromeres and telomeres are disrupted .