Modifying sister chromatid cohesion for meiosis.

Meiosis produces haploid gametes from diploid cells in two stages that in many ways resemble mitosis. However, the regulatory mechanisms governing kinetochore orientation and cohesion at the first meiotic division are different from those at mitosis: sister kinetochores are pulled forwards from the same spindle pole at metaphase, and centromeric cohesion is protected throughout anaphase. Consequently, homologous chromosomes, rather than sister chromatids, segregate to the opposite sides of a cell. The residual cohesion around centromeres plays an essential role at the second meiotic division, when spindle microtubules from opposite poles attach to sister chromatids. Recent studies have identified novel meiosis-specific kinetochore proteins, such as monopolin and shugoshin, and indicate that specific modifications in sister chromatid cohesion lie at the heart of the regulation of meiotic chromosome segregation.