Involvement of the cohesin Rad21 and SCP3 in monopolar attachment of sister kinetochores during mouse meiosis I

Abstract

SCP3 is a meiosis-specific structural protein appearing at axial elements and lateral elements of the synaptonemal complex. We have analysed the behaviour of SCP3 and the cohesin subunit Rad21 in mouse spermatocytes by means of a squashing technique. Our results demonstrate that both proteins colocalize and are partially released from chromosome arms during late prophase I stages, although they persist at the interchromatid domain of metaphase I bivalents. Thus, Rad21 cannot be considered a `mitotic'-specific variant, but coexists with Rec8. During late prophase I SCP3 and Rad21 accumulate at centromeres, and together with the chromosomal passenger proteins INCENP and aurora-B kinase, show a complex `double cornet'-like distribution at the inner domain of metaphase I centromeres beneath the associated sister kinetochores. We have observed that Rad21 and SCP3 are displaced from centromeres during telophase I when sister kinetochores separate, and are not present at metaphase II centromeres. Thus, we hypothesise that Rad21, and the superimposed SCP3 and SCP2, are involved in the monopolar attachment of sister kinetochores during meiosis I, and are not responsible for the maintenance of sister-chromatid centromere cohesion during meiosis II as previously suggested.

Sex chromosomes, synapsis, and cohesins: a complex affair

“…2j-l). This is in agreement with the previous reports indicating that RAD21 colocalizes throughout meiosis with SYCP3 (Parra et al 2004).…”

“…In the last years, an increasing number of proteins have been shown to be either associated or adjacent to the AEs. The first group corresponds to the cohesin complex that includes: SMC1α (Eijpe et al 2000), SMC1β (Revenkova et al 2001), SMC3 (Eijpe et al 2000), REC8 (Eijpe et al 2003;Lee et al 2003), STAG3 (Prieto et al 2001), and RAD21 (Parra et al 2004;Xu et al 2004). Three of these proteins, namely SMC1β, STAG3, and REC8, are exclusively synthesized during meiosis, whereas SMC1α, SMC3, and RAD21 are present in both somatic and meiotic cells.…”

“…As mentioned, REC8 is a meiosis-specific cohesin subunit, which has been proposed to replace RAD21 during this cell division. However, RAD21 is actually expressed during meiosis (Prieto et al 2002) and moreover, it seems to interact with the SYCP2 and SYCP3 components of the AEs (Parra et al 2004). Consequently, besides its role in sister chromatid cohesion during meiosis, RAD21 may play additional roles in the structural organization of sex chromosomes, and also of the autosomes, that are different from those played by REC8.…”

Proteins Involved in Meiotic Recombination: A Role in Male Infertility?

“…However, other studies (also in the mouse), have shown that RAD21 associates with the lateral elements of the SC and has a temporal and spatial distribution similar to SMC3 and SMC1B, changing localization from along the entire chromatid arms to the centromeres at metaphase I, where it remains until anaphase II [Xu et al 2004;Firooznia et al 2005]. In further contrast, RAD21 was shown in another study to disassociate from the centromeres at anaphase I with no localization in meiosis II in mouse spermatocytes [Parra et al 2004]. Testes specific RNAi would be a useful tool in better establishing the role of RAD21 in meiotic cells.…”

“…RNAi knockdown of Rad21 in Drosophila D3 cells, results in loss of sister chromatid cohesion and longer than normal spindle fibers at metaphase of mitosis [Goshima et al 2005]. Although the cells being investigated are mitotic, given the localization of RAD21 to the centromeres in late prophase I of meiosis [Parra et al 2004], a similar response might be seen in meiotic cells.…”