Yan et al. describe how a Drosophila protein works with the cohesin complex to hold sister chromatids together during meiosis, ensuring their faithful segregation into sperm.
Just as in mitosis, the cohesin complex keeps sister chromatids together until they separate in the second of meiosis’ two divisions. In addition, sister chromatid cohesion helps homologous chromosomes pair up and divide in the first meiotic division. But the function of cohesins in Drosophila meiosis is largely unknown because mutations in the proteins are lethal, and flies lack a homologue of the meiosis-specific cohesin Rec8.
Yan et al. investigated a previously uncharacterized protein called SOLO (sisters on the loose), and found that it colocalized with the cohesin subunit SMC1 on meiotic centromeres in spermatocytes. SMC1 was mislocalized in the absence of SOLO, resulting in a loss of cohesion between the centromeres of sister chromatids. This caused chromosomes to missegregate in both rounds of meiotic division.
Although SOLO has no homology to cohesin proteins, it may be an integral component of the complex in flies, says senior author Bruce McKee. Alternatively, it may be a closely associated accessory protein. The team now plans to take a biochemical approach to studying how SOLO stabilizes the cohesin complex on meiotic centromeres. The researchers are also studying the function of SOLO in Drosophila oocytes, where cohesins are thought to have an additional role in joining homologous chromosomes together to facilitate meiotic recombination.