DYNAMICS OF CENTROMERES DURING METAPHASE-ANAPHASE TRANSITION IN FISSION YEAST - DIS1 IS IMPLICATED IN FORCE BALANCE IN METAPHASE BIPOLAR SPINDLE

In higher eukaryotic cells, the spindle forms along with chromosome co ndensation in mitotic prophase. In metaphase, chromosomes are aligned on the spindle with sister kinetochores facing toward the opposite pol es. In anaphase A, sister chromatids separate from each other without spindle extension, whereas spindle elongation takes place during anaph ase B. We have critically examined whether such mitotic stages also oc cur in a lower eukaryote, Schizosaccharomyces pombe. Using the green f luorescent protein tagging technique, early mitotic to late anaphase e vents were observed in living fission yeast cells. S. pombe has three phases in spindle dynamics, spindle formation (phase 1), constant spin dle length (phase 2), and spindle extension (phase 3). Sister centrome re separation (anaphase A) rapidly occurred at the end of phase 2. The centromere showed dynamic movements throughout phase 2 as it moved ba ck and forth and was transiently split in two before its separation, s uggesting that the centromere was positioned in a bioriented manner to ward the poles at metaphase. Microtubule-associating Dis1 was required for the occurrence of constant spindle length and centromere movement in phase 2. Normal transition from phase 2 to 3 needed DNA topoisomer ase IT and Cut1 but not Cut14. The duration of each phase was highly d ependent on temperature.