Sister kinetochores are mechanically fused during meiosis I in yeast

Biologists have wondered for decades how replicated sister chromatids, which normally separate during mitotic cell division, instead comigrate during the first meiotic division, meiosis I. This process segregates chromosomal homologs and is needed to produce haploid gametes after the second, more mitosis-like, meiotic division. One hypothesis for sister chromatid comigration suggests that meiosis I–specific factors directly cross-link the sister kinetochores that attach each sister chromatid to dynamic microtubule tips. Yeast possesses a putative kinetochore cross-linker, known as monopolin, but monopolin's precise role during meiosis I is unknown. Sarangapani et al. isolated functional meiotic kinetochores from yeast cells. They reconstituted kinetochore activity in vitro and found that monopolin causes kinetochore fusion and underlies the sister chromatid comigration seen in meiosis I. Science , this issue p. [248][1] [1]: /lookup/doi/10.1126/science.1256729