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Sister kinetochores are mechanically fused during meiosis I in yeast

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Science  10 Oct 2014:
Vol. 346, Issue 6206, pp. 248-251
DOI: 10.1126/science.1256729

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Abstract

Production of healthy gametes requires a reductional meiosis I division in which replicated sister chromatids comigrate, rather than separate as in mitosis or meiosis II. Fusion of sister kinetochores during meiosis I may underlie sister chromatid comigration in diverse organisms, but direct evidence for such fusion has been lacking. We used laser trapping and quantitative fluorescence microscopy to study native kinetochore particles isolated from yeast. Meiosis I kinetochores formed stronger attachments and carried more microtubule-binding elements than kinetochores isolated from cells in mitosis or meiosis II. The meiosis I–specific monopolin complex was both necessary and sufficient to drive these modifications. Thus, kinetochore fusion directs sister chromatid comigration, a conserved feature of meiosis that is fundamental to Mendelian inheritance.

Monopolin masterfully manages meiosis

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.

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