Description
We characterized STAG3 as a meiotic specific cohesin subunit, which is involved in control of arm chromatid cohesion but is not present during meiosis II. In addition, we localized Rad21, previously considered as mitotic specific cohesin, in meiotic cohesin complexes in mouse spermatocytes. In summary, our previous studies on chromosome segregation contributed to identify and characterize meiosis-specific cohesins in mammals and to show that in mammalian meiosis function different cohesin complexes during distinct meiotic stages. In the last two years, we have studied, in collaboration with other groups, the localization/function of cohesins in different animal models, such as the avian lampbrush chromosomes and the segregation of sexual chromosomes in marsupials. In grasshoppers, which have been considered as a gorgeous model for meiotic studies, we have described the sequential loading of several cohesin subunits onto meiotic chromosomes during the first meiotic prophase and the contribution of these proteins to the synaptonemal complex formation. Regulation of chromosome cohesion during the cell cycle, in both somatic and germinal cells, shows important differences in terms of localization on arms or centromeres. Since the cohesin complexes on arms are released during prophase in mitosis and during meiosis I, whereas centromeric cohesion remains until metaphase/anaphase in mitosis and until meiosis II, there must be a mechanism that protects the centromeric cohesin complexes from phosphorylation in the case of somatic cells and from the action of separase during the first meiotic division. A family of centromeric proteins denominated "shugoshins" (from Japanese, guardian of the spirit) was recently characterized in yeast as essential for the maintenance of centromeric cohesion in mitosis and meiosis. These proteins, Sgo1 and Sgo2, are orthologues of a centromeric protein, previously characterized in Drosophila, MeiS-332. Its protective function of centromeric cohesin complexes has been studied in yeast, and new functions have been suggested for these proteins in centromere dynamics during chromosome segregation. Nevertheless, the biological role/s of its mammalian orthologues in meiosis remains to be described.
Immunolocalization of cohesin subunits (green) and synaptonemal complex proteins SCP1 (fuchsia) and SCP3 (red) in human spermatocytes. CREST (anticentromere antibody, blue). AE (synaptonemal complex axial elements). CE (synaptonemal complex central element). CA (cohesin axis).
We are working on the composition and biological role of different meiotic cohesin complexes in mammals. We are also studying the contribution of Pds5 proteins to control of sister chromatid cohesion during meiotic divisions in mouse spermatocytes and, in collaboration with other national groups, the biological function/s of shugoshins Sgo1 and Sgo2 on the regulation of cohesin complex removal from chromosomes.
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