Eukaryotic sister chromatids remain connected from the time of synthesis until they are separated in anaphase. This cohesion depends on a complex of proteins known as cohesins. In vertebrates, unlike in yeast, the cohesins dissociate from chromosome arms earlier in M phase, during prophase. Small amounts of cohesin remain near the centromere until metaphase, with complete removal at the beginning of anaphase.Sequence analysis predicted that RAD21 is a 631-amino acid phosphoprotein that is 96% and 25% identical to the mouse and yeast homologs, respectively, and that they are most conserved at the N and C termini. These proteins all have 2 nuclear localization signals and an acidic stretch consistent with a chromatin-binding role. Northern blot analysis revealed ubiquitous expression of a 3.1-kb transcript in mouse tissues, with highest expression in testis and thymus
NCBI Summary:
The protein encoded by this gene is highly similar to the gene product of Schizosaccharomyces pombe rad21, a gene involved in the repair of DNA double-strand breaks, as well as in chromatid cohesion during mitosis. This protein is a nuclear phospho-protein, which becomes hyperphosphorylated in cell cycle M phase. The highly regulated association of this protein with mitotic chromatin specifically at the centromere region suggests its role in sister chromatid cohesion in mitotic cells. [provided by RefSeq]
General function
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Cellular localization
Nuclear
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Ovarian function
Antral follicle growth, Oogenesis, Oocyte growth
Comment
Rec8-containing cohesin maintains bivalents without turnover during the growing phase of mouse oocytes. Tachibana-Konwalski K et al. During female meiosis, bivalent chromosomes are thought to be held together from birth until ovulation by sister chromatid cohesion mediated by cohesin complexes whose ring structure depends on kleisin subunits, either Rec8 or Scc1. Because cohesion is established at DNA replication in the embryo, its maintenance for such a long time may require cohesin turnover. To address whether Rec8- or Scc1-containing cohesin holds bivalents together and whether it turns over, we created mice whose kleisin subunits can be cleaved by TEV protease. We show by microinjection experiments and confocal live-cell imaging that Rec8 cleavage triggers chiasmata resolution during meiosis I and sister centromere disjunction during meiosis II, while Scc1 cleavage triggers sister chromatid disjunction in the first embryonic mitosis, demonstrating a dramatic transition from Rec8- to Scc1-containing cohesin at fertilization. Crucially, activation of an ectopic Rec8 transgene during the growing phase of Rec8(TEV)(/TEV) oocytes does not prevent TEV-mediated bivalent destruction, implying little or no cohesin turnover for =2 wk during oocyte growth. We suggest that the inability of oocytes to regenerate cohesion may contribute to age-related meiosis I errors.
Expression regulated by
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Ovarian localization
Oocyte, Cumulus, Granulosa, Theca, Luteal cells, Small luteal cells, Large luteal cells, Stromal cells, Surface epithelium
Comment
Lee J, et al reported the Analyses of mRNA Expression Patterns of Cohesin Subunits Rad21 and Rec8 in Mice and Germ Cell-Specific Expression of rec8 mRNA in Both Male and Female Mice.
A multisubunit protein complex called cohesin is required for the cohesion between sister chromatids in both mitosis and meiosis in yeast. Northern blot and reverse transcription-polymerase chain reaction (RT-PCR) analyses revealed that, in contrast to the ubiquitous expression of rad21 mRNA in all of the organs examined, rec8 was expressed only in the gonads. In the testis, rad21 mRNA was expressed in somatic cells and spermatogonia but not in spermatocytes, and conversely, rec8 mRNA was expressed in spermatocytes but not in spermatogonia or somatic cells. Spermatids expressed rad21 and rec8 mRNAs simultaneously. In the ovary, rad21 mRNA was detected in all of the ovarian cells including germ cells and somatic cells, whereas rec8 mRNA was detected only in oocytes. Unlike the widespread expression of rad21 gene, therefore, the gene expression of rec8 is strictly confined to spermatocytes and spermatids in male mouse and oocytes in female mouse. The restricted expression pattern of rec8 mRNA implies its essential role in meiosis in both sexes of mammals, as has been reported in yeast.
Follicle stages
Primordial, Primary, Secondary, Antral, Preovulatory, Corpus luteum
Comment
Metastasis-Associated Protein 3 (MTA3) Regulates G2/M Progression in Proliferating Mouse Granulosa Cells. Kwintkiewicz J et al. Metastasis associated protein 3 (MTA3) is a constituent of the Mi-2/nucleosome remodeling and deacetylase (NuRD) complex that regulates gene expression by altering chromatin structure and can facilitate cohesin loading onto DNA. The biological function of MTA3 within the NuRD complex is unknown. Here we show that MTA3 was expressed highly in granulosa cell nuclei of all ovarian follicle stages and at lower levels in corpora lutea. We tested the hypothesis that MTA3-NuRD complex function is required for granulosa cell proliferation. In the ovary, MTA3 interacted with NuRD proteins CHD4 and HDAC1 and the core cohesin complex protein RAD21. In cultured mouse primary granulosa cells, depletion of endogenous MTA3 using RNA interference slowed cell proliferation; this effect was rescued by co-expression of exogenous MTA3. Slowing of cell proliferation correlated with a significant decrease in cyclin B1 and cyclin B2 expression. Granulosa cell populations lacking MTA3 contained a significantly higher percentage of cells in G2/M phase and a lower percentage in S phase as compared to control cells. Furthermore, MTA3 depletion slowed entry into M phase as indicated by reduced phosphorylation of histone H3 at serine 10. These findings provide the first evidence that MTA3 interacts with NuRD and cohesin complex proteins in the ovary in vivo and regulates G2/M progression in proliferating granulosa cells.