{"gene":"REC8","run_date":"2026-04-28T19:45:45","timeline":{"discoveries":[{"year":1999,"finding":"Fission yeast Rec8 is a meiosis-specific cohesin subunit that localizes to centromeres and chromosome arms during pre-meiotic S phase. Centromeric Rec8 persists throughout meiosis I and is lost at anaphase II. Deletion of rec8 causes precocious sister chromatid separation at meiosis I, resulting in equational rather than reductional chromosome segregation, demonstrating that Rec8 is required for centromeric cohesion and for orienting sister kinetochores to the same pole during meiosis I.","method":"Genetic deletion (rec8 knockout), immunolocalization, chromosome segregation analysis in fission yeast","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — foundational genetic deletion with direct cytological readout, replicated across multiple labs","pmids":["10440376"],"is_preprint":false},{"year":1999,"finding":"Rec8p is phosphorylated prior to meiosis I (as shown by analysis of the mei4 mutant blocked before meiosis I) and is expressed only during meiosis. Rec8p localizes to approximately 100 foci per prophase nucleus. A human ortholog (hREC8) exists with significant sequence similarity and germ-cell-specific expression.","method":"Protein expression analysis by Western blot, immunolocalization, mei4/mes1 mutant analysis, meiosis-specific induction","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (Western blot, immunolocalization, mutant analysis) in single study","pmids":["10207075"],"is_preprint":false},{"year":2003,"finding":"Mammalian REC8 protein associates with meiotic cohesin subunits SMC1beta and SMC3 (but not SMC1alpha) and with synaptonemal complex component SCP3, as shown by immunoprecipitation. REC8 localizes along axial/lateral elements during prophase I and persists on chromosome arms until anaphase I and at centromeres until anaphase II, providing arm cohesion at metaphase I and centromeric cohesion until anaphase II.","method":"Immunoprecipitation (co-IP), immunohistochemistry, Western blot (phosphorylation state), chromosome spread immunofluorescence","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP plus localization across multiple meiotic stages with functional inference","pmids":["12759374"],"is_preprint":false},{"year":2003,"finding":"Meiotic cohesin REC8 marks axial elements before SMC1beta, SMC3, SCP2, and SCP3, appearing from pre-meiotic S phase and providing a structural basis for axial element (AE) formation. RAD51 and/or DMC1 co-immunoprecipitates with REC8, suggesting REC8 may scaffold recombination complexes on the AE.","method":"Immunofluorescence, co-immunoprecipitation, chromosome spread analysis in rat spermatocytes","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (co-IP, IF) establishing both structural role and recombination complex interaction","pmids":["12615909"],"is_preprint":false},{"year":2003,"finding":"Separase cleavage of Rec8 is required for meiotic chromosome segregation in fission yeast. A non-cleavable form of Rec8 blocks homolog disjunction at meiosis I. Rec8 forms distinct arm complexes with Rec11 (SA3) and centromeric complexes with Psc3 (SA1/SA2), and cleavage of arm Rec8 is required for meiosis I while centromeric Rec8 cleavage is required for meiosis II.","method":"Non-cleavable Rec8 mutant expression, genetic epistasis with rec11 deletion, chromosome segregation analysis","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — non-cleavable mutant combined with genetic epistasis, multiple meiotic division readouts","pmids":["14532136"],"is_preprint":false},{"year":2005,"finding":"Mouse REC8 null mutants of both sexes are sterile with germ cell failure. In the absence of REC8, early chromosome pairing is normal but synapsis occurs between sister chromatids rather than homologous chromosomes, demonstrating that a major role of REC8 in mammalian meiosis is to restrict synaptonemal complex formation to homologs.","method":"Rec8 knockout mouse, cytological analysis of meiotic chromosomes, immunofluorescence","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 — clean knockout with specific meiotic phenotype readout in mammals, replicated phenotype known from other organisms","pmids":["15935783"],"is_preprint":false},{"year":2006,"finding":"Phosphorylation of the cohesin subunit Rec8 contributes to step-wise cohesin removal during meiosis. Loss of arm cohesion at meiosis I requires Rec8 phosphorylation, and the cohesin protector Sgo1 prevents premature loss of centromeric cohesion by opposing this phosphorylation. Meiotic recombination also contributes to step-wise cohesin loss.","method":"Phosphorylation site mutagenesis, epistasis analysis with sgo1 and recombination mutants in budding yeast, cohesin localization assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1-2 — phosphomutant analysis combined with genetic epistasis and multiple pathway components","pmids":["16672979"],"is_preprint":false},{"year":2006,"finding":"Loss of arm REC8 (but not centromeric REC8) is required for homolog separation at meiosis I in mouse oocytes, while loss of centromeric REC8 is required for sister chromatid separation at meiosis II. Neither loss is required for cytokinesis/polar body emission. This was demonstrated by microinjection of anti-Rec8 antibody at different meiotic stages, and securin destruction (via the spindle checkpoint-proteasome pathway) was shown to regulate arm REC8 removal.","method":"Antibody microinjection into mouse oocytes, inhibitor treatments (proteasome inhibitor, topoisomerase II inhibitor, PP2A inhibitor), chromosome segregation analysis","journal":"Cell cycle (Georgetown, Tex.)","confidence":"High","confidence_rationale":"Tier 1-2 — direct antibody-based functional intervention at defined meiotic stages with specific segregation phenotypes","pmids":["16855401"],"is_preprint":false},{"year":2009,"finding":"Separase cleaves mouse Rec8 at three positions in vitro, but only when Rec8 is hyper-phosphorylated. Expression of a non-cleavable Rec8 variant (Rec8-N) in male mice abolishes the first meiotic division, producing secondary spermatocytes with 4C DNA content. In oocytes, Rec8-N causes asynchronous and delayed chromosome segregation during anaphase I.","method":"In vitro separase cleavage assay, non-cleavable Rec8 transgenic mouse, chromosome spread analysis, flow cytometry","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1 — in vitro cleavage assay plus in vivo non-cleavable mutant with defined phenotypic readout","pmids":["19625504"],"is_preprint":false},{"year":2009,"finding":"Rec8 guides the distribution of Spo11 along yeast meiotic chromosomes. Spo11 binds to Rec8-binding sites during premeiotic S phase, and deletion of REC8 alters Spo11 localization at centromeres and specific chromosomal arm intervals, causing region-specific loss of DSB formation.","method":"Genome-wide chromatin immunoprecipitation (ChIP) on tiling arrays, rec8 deletion analysis","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — genome-wide ChIP combined with genetic deletion showing functional consequence on DSB distribution","pmids":["19439448"],"is_preprint":false},{"year":2010,"finding":"Casein kinase 1delta/epsilon (CK1delta/epsilon) and Dbf4-dependent Cdc7 kinase (DDK) phosphorylate multiple sites on Rec8, and both kinases are required for Rec8 cleavage by separase and meiosis I nuclear division in budding yeast. PP2A (recruited by shugoshin) protects centromeric cohesion by opposing CK1delta/epsilon- and DDK-dependent phosphorylation of Rec8. Phosphomimetic Rec8 mutations bypass shugoshin protection at centromeres.","method":"Kinase inhibition (genetic and chemical), phosphomimetic and phospho-null Rec8 mutants, meiotic division analysis, in vivo phosphorylation mapping","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 1 — multiple kinase perturbations combined with phosphomimetic mutants demonstrating mechanistic sufficiency","pmids":["20230747"],"is_preprint":false},{"year":2010,"finding":"In fission yeast, casein kinase 1 (CK1; Hhp1/Hhp2) acts as the cohesin kinase that phosphorylates Rec8 to promote its separase-mediated cleavage during meiosis I, rather than polo-like kinase. Shugoshin (Sgo1)-PP2A counteracts this phosphorylation to protect centromeric Rec8. Forced localization of excess Hhp2 at pericentromeres abrogates Sgo1-PP2A protection, establishing that the balance between Rec8 phosphorylation by CK1 and dephosphorylation by Sgo1-PP2A regulates stepwise cohesion loss.","method":"Genetic screen ('anti-shugoshin' screen), targeted gene perturbation, forced localization experiments, Rec8 cleavage assays","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1-2 — genetic screen plus forced-localization epistasis with direct molecular readout of Rec8 cleavage","pmids":["20383139"],"is_preprint":false},{"year":2010,"finding":"Rec8-containing cohesin maintains bivalent chromosomes without detectable turnover during the oocyte growing phase. TEV protease cleavage of Rec8 (via a Rec8-TEV allele) triggers chiasmata resolution at meiosis I and sister centromere disjunction at meiosis II. Ectopic Rec8 activation during the growing phase does not rebuild cohesion, demonstrating the absence of cohesin turnover in oocytes.","method":"TEV-cleavable Rec8 knockin mouse, TEV protease microinjection, confocal live-cell imaging, conditional transgene activation","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 — reconstitution-level precision with inducible cleavage plus live imaging and genetic controls","pmids":["20971813"],"is_preprint":false},{"year":2010,"finding":"In fission yeast, CK1 isoforms Hhp1 and Hhp2 are required for full levels of Rec8 phosphorylation (mapped by mass spectrometry) and for efficient separase-mediated removal of Rec8 at anaphase I onset. Rec8 phosphorylation is required for proper chromosome disjunction during meiosis.","method":"Mass spectrometry phosphorylation mapping, CK1 mutant analysis, Rec8 removal quantification","journal":"Cell cycle (Georgetown, Tex.)","confidence":"High","confidence_rationale":"Tier 1-2 — mass spectrometry site mapping combined with genetic mutant phenotype","pmids":["20581463"],"is_preprint":false},{"year":2014,"finding":"STAG3 stabilizes REC8-containing cohesin complexes during meiosis. In Stag3 hypomorphic mice with severely reduced STAG3, REC8 cohesin complex stability is reduced, causing defects in chromosome axis compaction, synapsis, and recombination. STAG3-REC8 cohesin complexes are specifically required for meiotic chromosome structure and function.","method":"Stag3 hypomorphic knockin mouse, immunofluorescence, chromosome spread analysis, cohesin complex quantification","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — hypomorphic allele with dosage-dependent phenotype and direct cohesin complex analysis","pmids":["24797475"],"is_preprint":false},{"year":2016,"finding":"Rec8-containing cohesin established during fetal oocyte DNA replication is maintained without detectable turnover throughout months of dictyate arrest. Rec8 activated in arrested oocytes does not establish new cohesion (detected by TEV cleavage and live imaging), demonstrating that cohesion renewal cannot occur post-replicatively in arrested mouse oocytes.","method":"Tamoxifen-inducible Cre for conditional Rec8 activation, TEV protease cleavage assay, live-cell imaging","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 1-2 — inducible expression system combined with TEV cleavage functional assay and live imaging","pmids":["26898469"],"is_preprint":false},{"year":2016,"finding":"The separase-cleaved C-terminal fragment of mammalian Rec8 bears an N-terminal Glu residue and is degraded by the N-end rule pathway via Ate1 arginyltransferase-mediated N-terminal arginylation followed by proteasomal degradation. Male Ate1 conditional knockout mice are nearly infertile due to massive spermatocyte apoptosis during meiosis I metaphase, caused by failure to destroy the Rec8 C-terminal fragment.","method":"Germ-cell-confined Ate1 conditional knockout mouse, in vivo Rec8 fragment detection, protein half-life assay, N-end rule pathway analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — conditional KO with defined molecular mechanism and specific meiotic phenotype","pmids":["26858254"],"is_preprint":false},{"year":2016,"finding":"High density of REC8 cohesin complexes along sister chromatid axes (separated by <15% of total axis length) prevents local axis separation and illegitimate synaptonemal complex formation between sister chromatids. REC8 but not RAD21L or RAD21 flanks sites of local separated axial elements (LSAEs), and reduced cohesin levels cause both LSAEs and inter-sister SC formation at REC8-free regions.","method":"Super-resolution microscopy (STED), Stag3 hypomorphic mutant with reduced cohesin, quantitative cohesin distribution analysis","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 — super-resolution imaging with quantitative analysis in genetic mutant showing direct structure-function relationship","pmids":["27170622"],"is_preprint":false},{"year":2016,"finding":"During meiotic prophase in budding yeast, Rec8 phosphorylation (at 6, 24, or 29 sites with alanine substitutions) does not affect axis formation or recombination initiation/non-crossover recombination, but is specifically required for crossover-related events. DDK (Dbf4-dependent Cdc7 kinase) inhibition at defined times recapitulates these defects, while Hrr25/CK1 or Polo-like kinase inhibition does not, establishing DDK as the key kinase for Rec8's prophase role in crossover control.","method":"Rec8 phospho-mutant analysis (progressive alanine substitutions), timed kinase inhibition, crossover frequency and distribution assays","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1-2 — systematic phosphomutant series with timed kinase inhibition providing separation-of-function evidence","pmids":["27484478"],"is_preprint":false},{"year":2018,"finding":"Rec8 cohesin requires STAG3 (but not STAG1 or STAG2) for nuclear entry, chromatin loading, and functional sister chromatid cohesion in somatic cells. Rec8-STAG3 cohesin physically interacts with Pds5, Wapl, and sororin, is susceptible to Wapl-dependent ring opening (cohesion dissolution), and is protected by sororin — demonstrating that meiotic Rec8 cohesin is regulated by the same Wapl/sororin mechanism as mitotic cohesin.","method":"Ectopic expression in HEK293 cells, co-immunoprecipitation, chromatin loading assay, Wapl/sororin knockdown","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP plus functional complementation in somatic cells with multiple regulatory pathway validations","pmids":["29724914"],"is_preprint":false},{"year":2018,"finding":"Meiosis-specific cohesin component Rec8 binds to Mps3 (a SUN-domain nuclear envelope protein) during meiosis in budding yeast and controls Mps3 localization and dynamics on the nuclear envelope. Ectopic expression of Rec8 in mitotic cells induces formation of Mps3 patches/foci on the nuclear envelope, and this requires the cohesin regulator Rad61/Wpl1.","method":"Co-immunoprecipitation, ectopic Rec8 expression in mitotic yeast, nuclear envelope localization assays, Wpl1 epistasis","journal":"Genes to cells","confidence":"Medium","confidence_rationale":"Tier 3 — co-IP and ectopic expression with localization readout; single lab","pmids":["30417519"],"is_preprint":false},{"year":2020,"finding":"EWSR1 binds to both PRDM9 and phosphorylated REC8 (pREC8) in male meiotic cells. Conditional knockout of Ewsr1 causes meiotic arrest with decreased histone trimethylation at meiotic hotspots, impaired DSB repair, and reduced crossover number, suggesting EWSR1 links PRDM9-bound hotspots to the chromosome axis through pREC8.","method":"Co-immunoprecipitation, Ewsr1 conditional knockout mouse, ChIP analysis for histone methylation, crossover quantification","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 3 — co-IP establishing interaction plus conditional KO; indirect inference of REC8's role in the complex","pmids":["33175657"],"is_preprint":false},{"year":2020,"finding":"Genome-wide ChIP-seq in Arabidopsis shows REC8 associates with high-nucleosome-occupancy regions in multiple chromatin states (H3K4me, H3K27me, H3K9me). REC8 enrichment suppresses meiotic DSBs and crossovers at both chromosome and fine scales. In rec8 mutants, abnormal axis structures recruit DSB-associated foci and undergo synapsis followed by chromosome fragmentation.","method":"ChIP-seq (REC8), rec8 mutant analysis, kyp suvh5 suvh6 mutant ChIP-seq, immunofluorescence","journal":"The Plant cell","confidence":"Medium","confidence_rationale":"Tier 2 — genome-wide ChIP-seq in Arabidopsis (plant ortholog); finding is consistent with mammalian REC8 function","pmids":["32024691"],"is_preprint":false},{"year":2021,"finding":"Cleavage of REC8 by Separase at meiosis I is necessary and sufficient to convert sister kinetochores from co-orientation to bi-orientation, and to deprotect pericentromeric cohesion. Transfer of spindle-chromosome complexes between meiosis I and II showed both co-orientation and pericentromeric cohesin protection depend on the chromosomal context (not cytoplasm). Selective REC8 cleavage near kinetochores is sufficient to destroy co-orientation in univalent chromosomes.","method":"Spindle-chromosome complex (SCC) transfer between meiosis I and II oocytes, separase catalytic mutant, selective REC8 cleavage experiments, live imaging","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 1-2 — elegant reconstitution using SCC transfer combined with selective cleavage experiments providing direct causal evidence","pmids":["34758289"],"is_preprint":false},{"year":2021,"finding":"Two foundational meiotic proteins, Spo11 and Rec8, can dismantle centromeres via nucleosome remodeling factors. Overexpression of Rec8 in proliferating fission yeast or human cells leads to loss of mitotic kinetochores, demonstrating that Rec8 can destabilize centromeric chromatin when expressed ectopically.","method":"Rec8 overexpression in fission yeast and human cells, centromere marker loss assay, telomere bouquet mutant analysis","journal":"Nature","confidence":"Medium","confidence_rationale":"Tier 2 — overexpression in two cell types with defined centromere destabilization readout; mechanism partially through nucleosome remodelers","pmids":["33658710"],"is_preprint":false},{"year":2021,"finding":"Meikin (Moa1 in fission yeast) associates with Plo1 (polo-like kinase) and synergizes with shugoshin (Sgo1) to protect centromeric Rec8 cohesion during meiosis I. Moa1-Plo1 phosphorylates Rec8 at a key site, which potentiates PP2A activity associated with Sgo1, leading to dephosphorylation of Rec8 at a separase-promoting site and thus preventing Rec8 cleavage.","method":"Genetic analysis of moa1 mutants, Plo1 kinase assays, Rec8 phosphorylation site mapping, epistasis with sgo1-PP2A pathway","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1-2 — kinase assay plus phosphorylation-site dissection with clear epistatic ordering of Moa1-Plo1-PP2A-Rec8 pathway","pmids":["33888556"],"is_preprint":false},{"year":2021,"finding":"Rec8 regulates chromosome axis length by modulating Pds5 protein, while Pds5 in turn regulates axis length and crossover frequency in a dosage-dependent manner. Pds5 depletion does not alter Rec8 abundance, but Rec8 affects Pds5, placing Rec8 upstream of Pds5 in axis length control.","method":"Pds5 and Rec8 protein quantification, chromosome axis length measurement, crossover frequency analysis, epistasis","journal":"Science advances","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis plus quantitative analysis; single study but orthogonal methods","pmids":["33712462"],"is_preprint":false},{"year":2022,"finding":"Aurora B/C kinase activities promote Rec8 phosphorylation in mammalian oocytes, and this phosphorylation is required for Rec8 cleavage by separase at meiosis I. A specific Rec8 phosphorylation site was identified that is phosphorylated in vivo; inhibition of Aurora B/C during meiotic maturation impairs both Rec8 phosphorylation and chromosome segregation.","method":"Rec8-cleavage biosensor in single mouse oocytes (live imaging), phosphomutant analysis, Aurora B/C kinase inhibition, endogenous Rec8 phosphorylation assay","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 1-2 — biosensor-based live imaging of cleavage combined with phosphomutant analysis and in vivo phosphorylation detection","pmids":["35385691"],"is_preprint":false},{"year":2022,"finding":"MicroRNA miR-202 safeguards meiotic progression by repressing SEPARASE mRNA, thereby maintaining REC8 protein levels. Loss of miR-202 causes premature Separase-mediated REC8 cleavage, resulting in spermatocyte apoptosis and disruption of the zygotene-to-pachytene transition.","method":"miR-202 knockout mouse, target validation (Separase as miR-202 target), REC8 protein quantification, meiotic chromosome analysis","journal":"EMBO reports","confidence":"Medium","confidence_rationale":"Tier 2 — KO mouse with defined molecular target and REC8 pathway placement; indirect regulation","pmids":["35712867"],"is_preprint":false},{"year":2023,"finding":"Meiotic DSBs regulate cleavage-independent dissociation of Rec8-cohesin from chromosomes during meiotic prophase I in budding yeast. Genome-wide Rec8 binding analysis shows its distribution changes from mid to late prophase I with cleavage-independent loss. The spo11 mutant (lacking meiotic DSBs) does not show this redistribution, demonstrating DSBs drive a cohesin remodeling pathway distinct from separase cleavage.","method":"Genome-wide ChIP-seq for Rec8, spo11 mutant analysis, meiotic prophase stage fractionation","journal":"Genes to cells","confidence":"Medium","confidence_rationale":"Tier 2 — genome-wide ChIP-seq with genetic validation; single study","pmids":["37968127"],"is_preprint":false},{"year":2024,"finding":"Phosphorylation of Rec8 at specific Plo1 (polo-like kinase) phosphorylation sites, identified through meikin (Moa1) association, is required for monopolar orientation of sister kinetochores in meiosis I in fission yeast. Non-phosphorylatable mutations at these sites (in Rec8 and Psm3) show specific mono-orientation defects, genetically separating this function from cohesion protection.","method":"Plo1 phosphorylation site identification, non-phosphorylatable Rec8/Psm3 mutants, kinetochore orientation assay in fission yeast","journal":"Life science alliance","confidence":"High","confidence_rationale":"Tier 1-2 — phosphomutant separation-of-function analysis with specific kinetochore orientation readout","pmids":["38448160"],"is_preprint":false},{"year":2024,"finding":"Acetylation of Rec8 cohesin complexes at Psm3-K1013 by Eso1 acetyltransferase is required for reductional chromosome segregation in meiosis. This acetylation is largely dependent on the meiotic kinetochore factor meikin (Moa1) and cooperates with canonical acetylation at Psm3-K105 and K106. Meiosis-specific Rec8 cohesin complexes localized at centromeres were purified and analyzed by mass spectrometry.","method":"Purification of meiotic centromeric Rec8 cohesin complexes, mass spectrometry identification of acetylation, Psm3 acetylation-site mutants, chromosome segregation analysis","journal":"Life science alliance","confidence":"High","confidence_rationale":"Tier 1 — mass spectrometry identification combined with site-specific mutant functional analysis","pmids":["38575358"],"is_preprint":false},{"year":2006,"finding":"Securin degradation via the ubiquitin-proteasome pathway is required for Rec8 proteolysis at the metaphase-to-anaphase transition in mouse and pig oocytes. Inhibition of the ubiquitin-proteasome pathway blocks both securin and Rec8 degradation. Microinjection of securin antibody into MII oocytes leads to Rec8 degradation, placing securin upstream of Rec8 in the meiotic metaphase-to-anaphase pathway.","method":"Proteasome inhibitor treatment, securin antibody microinjection, Western blot for securin and Rec8, immunofluorescence in mouse/pig oocytes","journal":"Frontiers in bioscience","confidence":"Medium","confidence_rationale":"Tier 2 — multiple interventions (inhibitor, antibody microinjection) with direct protein level measurements","pmids":["16720305"],"is_preprint":false},{"year":2016,"finding":"Meiotic cohesin subunits RAD21L and REC8 localize at distinct positions within the synaptonemal complex: both at connection sites between lateral elements and transverse filaments in pachynema, with RAD21L positioned interior to REC8. Some RAD21L but not REC8 signals appear to bridge unsynapsed regions in zygonema, and recombination intermediate signals overlap more with RAD21L than REC8.","method":"Super-resolution microscopy (3D-SIM), immunofluorescence in mouse spermatocytes, recombination marker co-localization","journal":"The Journal of reproduction and development","confidence":"Medium","confidence_rationale":"Tier 2 — super-resolution localization distinguishing REC8 from RAD21L at sub-SC resolution; single study","pmids":["27665783"],"is_preprint":false},{"year":2013,"finding":"Nociceptin (a neuropeptide) induces rapid Rec8 phosphorylation in mouse spermatocytes through its receptor Oprl-1, which is exclusively expressed in the plasma membrane of testicular germ cells. In vivo injection of nociceptin stimulates Rec8 phosphorylation and meiotic chromosome dynamics; nocistatin (a nociceptin inhibitor) abolishes these effects.","method":"In vivo nociceptin/nocistatin injection, Rec8 phosphorylation assay (Western blot), Oprl-1 receptor localization","journal":"Endocrinology","confidence":"Medium","confidence_rationale":"Tier 3 — in vivo ligand treatment with protein phosphorylation readout; identifies upstream signaling but mechanism downstream of receptor incompletely defined","pmids":["23720425"],"is_preprint":false},{"year":2022,"finding":"REC8 interacts with MAVS and STING in the cytoplasm during viral infection and inhibits their K48-linked ubiquitination by RNF5, thereby stabilizing these innate immune signaling proteins. SUMOylated REC8 translocates from nucleus to cytoplasm upon viral infection (triggered via JAK-STAT pathway upregulation). REC8 also promotes recruitment of TBK1 to MAVS and STING, enhancing interferon signaling.","method":"Co-immunoprecipitation, ubiquitination assay, REC8 knockdown (siRNA), viral infection assay (VSV, NDV, HSV), subcellular fractionation, SUMO modification analysis","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2-3 — co-IP combined with ubiquitination assay and functional KD with viral infection readout; novel non-meiotic function","pmids":["35107381"],"is_preprint":false},{"year":2025,"finding":"Moa1 (meikin) and Sgo1 (shugoshin) are degraded during anaphase I by the APC/C-Slp1 pathway in fission yeast. Non-degradable Moa1 and Sgo1 expressed in meiosis II can protect Rec8 cohesin; the localization of Sgo1 and phosphorylation of Rec8 at S449 and S450 are necessary and sufficient to protect Rec8 during meiosis II.","method":"Non-degradable Moa1/Sgo1 mutant expression in meiosis II, Rec8 phosphosite mutants, APC/C genetic analysis","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1-2 — phosphomutant analysis with meiosis II expression system; preprint, not yet peer-reviewed","pmids":["bio_10.1101_2025.09.19.677360"],"is_preprint":true}],"current_model":"REC8 is a meiosis-specific α-kleisin subunit of the cohesin complex that forms a ring with SMC1β/SMC3 and STAG3; it establishes sister chromatid cohesion during pre-meiotic DNA replication, organizes chromosome axial elements, restricts synaptonemal complex formation to homologs, and guides Spo11-dependent DSB distribution; during meiosis I, phosphorylation of Rec8 by CK1 (Hhp1/2), DDK, and Aurora B/C kinases promotes its cleavage by separase on chromosome arms (releasing chiasmata and allowing homolog separation), while shugoshin-PP2A dephosphorylates centromeric Rec8 to protect it until meiosis II, with meikin (Moa1/Plo1)-dependent Rec8 phosphorylation additionally regulating both cohesion protection and monopolar sister kinetochore orientation; at meiosis II, centromeric Rec8 is finally cleaved by separase to allow sister chromatid separation, and the resulting C-terminal fragment is degraded by the N-end rule pathway via Ate1-mediated arginylation."},"narrative":{"teleology":[{"year":1999,"claim":"Identification of Rec8 as a meiosis-specific cohesin subunit established the molecular basis for differential cohesion at centromeres versus arms during the two meiotic divisions, resolving how reductional segregation is achieved.","evidence":"Genetic deletion in fission yeast with immunolocalization and segregation analysis; parallel expression and phosphorylation analysis","pmids":["10440376","10207075"],"confidence":"High","gaps":["Separase involvement not yet demonstrated","Mammalian Rec8 function unconfirmed","Mechanism of centromeric versus arm differential removal unknown"]},{"year":2003,"claim":"Demonstration that mammalian REC8 associates with SMC1β/SMC3 and axial element components, and that separase cleavage of Rec8 is required for meiotic chromosome segregation, defined the core cohesin ring composition and cleavage-dependent removal mechanism.","evidence":"Co-immunoprecipitation of REC8 with SMC1β/SMC3/SCP3/RAD51 in rat and mouse spermatocytes; non-cleavable Rec8 mutant in fission yeast blocking meiosis I","pmids":["12759374","12615909","14532136"],"confidence":"High","gaps":["Kinases responsible for phosphorylation-dependent cleavage not identified","Centromeric protection mechanism unknown","Non-cleavable mutant not yet tested in mammals"]},{"year":2005,"claim":"Knockout of REC8 in mice revealed that REC8 restricts synaptonemal complex formation to homologs rather than sister chromatids, establishing a structural gatekeeping role beyond simple cohesion.","evidence":"Rec8 knockout mouse with cytological analysis showing inter-sister rather than inter-homolog synapsis","pmids":["15935783"],"confidence":"High","gaps":["Mechanism by which REC8 prevents sister-chromatid synapsis unclear","Relationship between REC8 density on axes and synapsis restriction not quantified"]},{"year":2006,"claim":"Discovery that Rec8 phosphorylation enables stepwise arm-then-centromere cohesion loss, opposed by shugoshin at centromeres, resolved the long-standing question of how differential cohesion removal is regulated between meiosis I and II.","evidence":"Phosphorylation-site mutagenesis and sgo1 epistasis in budding yeast; anti-Rec8 antibody microinjection at defined meiotic stages in mouse oocytes","pmids":["16672979","16855401"],"confidence":"High","gaps":["Identity of the kinase(s) phosphorylating Rec8 not yet established","Precise phosphorylation sites not mapped"]},{"year":2009,"claim":"In vitro cleavage assays and non-cleavable Rec8 transgenic mice confirmed that separase cleavage of phosphorylated Rec8 is essential for mammalian meiosis I, while genome-wide ChIP showed Rec8 guides Spo11-mediated DSB distribution along chromosomes.","evidence":"In vitro separase cleavage of phosphorylated Rec8; Rec8-N non-cleavable transgenic mouse; genome-wide ChIP-chip in yeast with rec8 deletion","pmids":["19625504","19439448"],"confidence":"High","gaps":["Specific kinases for mammalian Rec8 phosphorylation not identified","Mechanism linking Rec8 binding to Spo11 recruitment unclear"]},{"year":2010,"claim":"Identification of CK1δ/ε and DDK as the kinases phosphorylating Rec8, with PP2A-shugoshin opposing them at centromeres, completed the kinase-phosphatase circuit governing stepwise cohesion removal; separately, TEV-cleavable Rec8 knockin mice proved that Rec8-containing cohesin established during fetal S phase is maintained without turnover throughout oocyte arrest.","evidence":"Kinase inhibition and phosphomimetic Rec8 mutants in budding and fission yeast; mass spectrometry phosphorylation mapping; TEV-cleavable Rec8 knockin with live imaging in mouse oocytes","pmids":["20230747","20383139","20581463","20971813"],"confidence":"High","gaps":["Whether the same kinases operate in mammalian meiosis not yet shown","Turnover absence demonstrated only for months; lifetime persistence not directly tested","DDK versus CK1 relative contributions at specific sites unclear"]},{"year":2014,"claim":"STAG3 was shown to stabilize REC8-containing cohesin complexes and to be specifically required for meiotic chromosome axis compaction and synapsis, establishing STAG3 as the obligate SA subunit for meiotic REC8 cohesin function.","evidence":"Stag3 hypomorphic knockin mouse with reduced REC8 cohesin levels and axis/synapsis defects","pmids":["24797475"],"confidence":"High","gaps":["Whether STAG3 is required for REC8 loading in vivo or only for stability not fully resolved","Structural basis of STAG3-REC8 specificity unknown"]},{"year":2016,"claim":"Multiple advances clarified REC8 cohesin maintenance and clearance: confirmation that no cohesion renewal occurs in arrested oocytes, discovery that the Rec8 C-terminal cleavage fragment is destroyed via Ate1-mediated N-end rule degradation (required for male fertility), super-resolution mapping showing high REC8 density prevents illegitimate inter-sister synapsis, and phospho-mutant series separating DDK-dependent Rec8 phosphorylation roles in crossover control from axis formation.","evidence":"Inducible Rec8 activation in arrested oocytes; Ate1 conditional KO mouse with Rec8 fragment accumulation; STED microscopy in Stag3 hypomorph; systematic Rec8 phospho-alanine substitution series with timed DDK inhibition","pmids":["26898469","26858254","27170622","27484478"],"confidence":"High","gaps":["N-end rule pathway for Rec8 fragment shown only in spermatogenesis; oocyte relevance untested","DDK phosphorylation sites promoting crossovers versus separase cleavage not fully distinguished","Inter-sister synapsis suppression mechanism beyond physical density not characterized"]},{"year":2018,"claim":"Ectopic expression studies demonstrated that Rec8-STAG3 cohesin is regulated by the canonical Wapl/sororin cohesion maintenance pathway, and that Rec8 physically interacts with the LINC complex component Mps3 to control nuclear envelope dynamics during meiosis.","evidence":"Rec8-STAG3 co-expression in HEK293 cells with Wapl/sororin knockdown; Rec8-Mps3 co-IP and ectopic expression in mitotic yeast","pmids":["29724914","30417519"],"confidence":"High","gaps":["Wapl/sororin regulation of Rec8 cohesin not validated in native meiotic cells","Mps3 interaction shown only by co-IP in single lab","Functional consequence of Mps3-Rec8 interaction on chromosome movement unclear"]},{"year":2021,"claim":"REC8 cleavage by separase at meiosis I was shown to be necessary and sufficient to convert sister kinetochores from co-orientation to bi-orientation, and meikin-polo kinase was found to phosphorylate Rec8 to potentiate PP2A-shugoshin centromeric protection, establishing dual functions of Rec8 phosphorylation in orientation and protection.","evidence":"Spindle-chromosome complex transfer between meiosis I and II oocytes with selective REC8 cleavage; Moa1-Plo1 kinase assays with Rec8 phosphosite dissection and sgo1-PP2A epistasis in fission yeast","pmids":["34758289","33888556"],"confidence":"High","gaps":["Mammalian meikin-Rec8 phosphorylation sites not mapped","How pericentromeric Rec8 cleavage mechanistically triggers bi-orientation switch unknown"]},{"year":2022,"claim":"Aurora B/C kinase was identified as an additional kinase phosphorylating Rec8 to promote separase cleavage in mammalian oocytes, extending the multi-kinase circuit; separately, a non-meiotic role for REC8 in stabilizing MAVS and STING during antiviral innate immune signaling was reported.","evidence":"Rec8-cleavage biosensor in mouse oocytes with Aurora B/C inhibition and phosphomutant analysis; co-IP of REC8 with MAVS/STING, ubiquitination assays, and REC8 knockdown during viral infection","pmids":["35385691","35107381"],"confidence":"High","gaps":["Relative contributions of Aurora B/C versus CK1/DDK in mammalian Rec8 phosphorylation not quantified","Non-meiotic REC8 function in innate immunity reported by single lab and awaits independent confirmation","Whether REC8's immune role is physiologically relevant given its meiotic-specific expression pattern is unclear"]},{"year":2024,"claim":"Phosphorylation of Rec8 (and Psm3) at specific polo-kinase sites was genetically separated from cohesion protection and shown to be specifically required for monopolar kinetochore orientation, and acetylation of Rec8 cohesin at Psm3-K1013 by Eso1 was found necessary for reductional segregation, revealing post-translational modification of the Rec8 complex beyond phosphorylation.","evidence":"Non-phosphorylatable Rec8/Psm3 mutants with kinetochore orientation assay; mass spectrometry identification of Psm3 acetylation in purified meiotic centromeric Rec8 complexes with acetylation-site mutants","pmids":["38448160","38575358"],"confidence":"High","gaps":["Whether Psm3 acetylation functions are conserved in mammals unknown","Structural basis for how Rec8 phosphorylation enables monopolar attachment not resolved"]},{"year":null,"claim":"Key unresolved questions include the structural basis of the Rec8 cohesin ring at atomic resolution, how REC8 density mechanistically prevents inter-sister synapsis, the full integration of multiple kinase inputs (CK1, DDK, Aurora B/C, Plo1) on Rec8 in a single mammalian model, and whether the reported non-meiotic immune function of REC8 is physiologically relevant.","evidence":"","pmids":[],"confidence":"Low","gaps":["No atomic-resolution structure of Rec8-containing cohesin","Mechanism linking Rec8 to inter-sister synapsis prevention not established beyond density model","Integrated kinase circuit for Rec8 phosphorylation not validated in a single mammalian system"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,2,3,14,17]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[2,3,19]}],"localization":[{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[0,1,2,3,5,7,9,12,17,22]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[1,19,35]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[35]}],"pathway":[{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[0,4,6,7,8,10,11,23,27,30]},{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[0,1,5,12,15,16]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[9,22,29]}],"complexes":["Meiotic cohesin (REC8-SMC1β-SMC3-STAG3)","Synaptonemal complex (axial element association)"],"partners":["SMC1B","SMC3","STAG3","PDS5","WAPL","ESPL1","SGO1","EWSR1"],"other_free_text":[]},"mechanistic_narrative":"REC8 is a meiosis-specific α-kleisin subunit of the cohesin complex that establishes and maintains sister chromatid cohesion during meiotic divisions, organizes chromosome axes, restricts synaptonemal complex formation to homologs, and guides the distribution of meiotic double-strand breaks. REC8 forms a ring complex with SMC1β, SMC3, and STAG3, loads onto chromosomes during pre-meiotic S phase, and persists on chromosome arms until anaphase I and at centromeres until anaphase II; stepwise removal is controlled by phosphorylation-dependent separase cleavage, with CK1δ/ε, DDK, and Aurora B/C kinases phosphorylating Rec8 to promote arm cleavage at meiosis I, while shugoshin-PP2A dephosphorylates centromeric Rec8 to protect it, and meikin-polo kinase phosphorylation additionally regulates both centromeric cohesion protection and monopolar kinetochore orientation [PMID:10440376, PMID:12759374, PMID:14532136, PMID:20230747, PMID:20383139, PMID:35385691, PMID:33888556, PMID:38448160]. Rec8 cohesin established during fetal DNA replication is maintained without turnover throughout oocyte arrest, and its cleavage at meiosis I is both necessary and sufficient to convert sister kinetochores from co-orientation to bi-orientation [PMID:20971813, PMID:26898469, PMID:34758289]. The separase-generated C-terminal Rec8 fragment is degraded by the Ate1-dependent N-end rule pathway, and failure of this degradation causes spermatocyte apoptosis [PMID:26858254]."},"prefetch_data":{"uniprot":{"accession":"O95072","full_name":"Meiotic recombination protein REC8 homolog","aliases":["Cohesin Rec8p"],"length_aa":547,"mass_kda":62.6,"function":"Required during meiosis for separation of sister chromatids and homologous chromosomes. Proteolytic cleavage of REC8 on chromosome arms by separin during anaphase I allows for homologous chromosome separation in meiosis I and cleavage of REC8 on centromeres during anaphase II allows for sister chromatid separation in meiosis II (By similarity)","subcellular_location":"Nucleus; Chromosome; Chromosome, centromere","url":"https://www.uniprot.org/uniprotkb/O95072/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/REC8","classification":"Not Classified","n_dependent_lines":18,"n_total_lines":1208,"dependency_fraction":0.014900662251655629},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/REC8","total_profiled":1310},"omim":[{"mim_id":"620897","title":"OVARIAN DYSGENESIS 11; ODG11","url":"https://www.omim.org/entry/620897"},{"mim_id":"619533","title":"RAD21 COHESIN COMPLEX COMPONENT-LIKE 1; RAD21L1","url":"https://www.omim.org/entry/619533"},{"mim_id":"618611","title":"HOMOLOGOUS RECOMBINATION FACTOR WITH OB-FOLD; HROB","url":"https://www.omim.org/entry/618611"},{"mim_id":"618423","title":"ANKYRIN REPEAT DOMAIN-CONTAINING PROTEIN 31; ANKRD31","url":"https://www.omim.org/entry/618423"},{"mim_id":"618417","title":"MEIOTIC DOUBLE-STRANDED BREAK FORMATION PROTEIN 4; MEI4","url":"https://www.omim.org/entry/618417"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":33.5},{"tissue":"pituitary gland","ntpm":64.9}],"url":"https://www.proteinatlas.org/search/REC8"},"hgnc":{"alias_symbol":["Rec8p","kleisin-alpha"],"prev_symbol":["REC8L1"]},"alphafold":{"accession":"O95072","domains":[{"cath_id":"-","chopping":"16-105","consensus_level":"high","plddt":91.3726,"start":16,"end":105},{"cath_id":"1.10.10.580","chopping":"476-543","consensus_level":"high","plddt":85.6,"start":476,"end":543}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O95072","model_url":"https://alphafold.ebi.ac.uk/files/AF-O95072-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O95072-F1-predicted_aligned_error_v6.png","plddt_mean":64.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=REC8","jax_strain_url":"https://www.jax.org/strain/search?query=REC8"},"sequence":{"accession":"O95072","fasta_url":"https://rest.uniprot.org/uniprotkb/O95072.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O95072/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O95072"}},"corpus_meta":[{"pmid":"10440376","id":"PMC_10440376","title":"Cohesin 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Centromeric Rec8 persists throughout meiosis I and is lost at anaphase II. Deletion of rec8 causes precocious sister chromatid separation at meiosis I, resulting in equational rather than reductional chromosome segregation, demonstrating that Rec8 is required for centromeric cohesion and for orienting sister kinetochores to the same pole during meiosis I.\",\n      \"method\": \"Genetic deletion (rec8 knockout), immunolocalization, chromosome segregation analysis in fission yeast\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — foundational genetic deletion with direct cytological readout, replicated across multiple labs\",\n      \"pmids\": [\"10440376\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Rec8p is phosphorylated prior to meiosis I (as shown by analysis of the mei4 mutant blocked before meiosis I) and is expressed only during meiosis. Rec8p localizes to approximately 100 foci per prophase nucleus. A human ortholog (hREC8) exists with significant sequence similarity and germ-cell-specific expression.\",\n      \"method\": \"Protein expression analysis by Western blot, immunolocalization, mei4/mes1 mutant analysis, meiosis-specific induction\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Western blot, immunolocalization, mutant analysis) in single study\",\n      \"pmids\": [\"10207075\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Mammalian REC8 protein associates with meiotic cohesin subunits SMC1beta and SMC3 (but not SMC1alpha) and with synaptonemal complex component SCP3, as shown by immunoprecipitation. REC8 localizes along axial/lateral elements during prophase I and persists on chromosome arms until anaphase I and at centromeres until anaphase II, providing arm cohesion at metaphase I and centromeric cohesion until anaphase II.\",\n      \"method\": \"Immunoprecipitation (co-IP), immunohistochemistry, Western blot (phosphorylation state), chromosome spread immunofluorescence\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP plus localization across multiple meiotic stages with functional inference\",\n      \"pmids\": [\"12759374\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Meiotic cohesin REC8 marks axial elements before SMC1beta, SMC3, SCP2, and SCP3, appearing from pre-meiotic S phase and providing a structural basis for axial element (AE) formation. RAD51 and/or DMC1 co-immunoprecipitates with REC8, suggesting REC8 may scaffold recombination complexes on the AE.\",\n      \"method\": \"Immunofluorescence, co-immunoprecipitation, chromosome spread analysis in rat spermatocytes\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (co-IP, IF) establishing both structural role and recombination complex interaction\",\n      \"pmids\": [\"12615909\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Separase cleavage of Rec8 is required for meiotic chromosome segregation in fission yeast. A non-cleavable form of Rec8 blocks homolog disjunction at meiosis I. Rec8 forms distinct arm complexes with Rec11 (SA3) and centromeric complexes with Psc3 (SA1/SA2), and cleavage of arm Rec8 is required for meiosis I while centromeric Rec8 cleavage is required for meiosis II.\",\n      \"method\": \"Non-cleavable Rec8 mutant expression, genetic epistasis with rec11 deletion, chromosome segregation analysis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — non-cleavable mutant combined with genetic epistasis, multiple meiotic division readouts\",\n      \"pmids\": [\"14532136\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Mouse REC8 null mutants of both sexes are sterile with germ cell failure. In the absence of REC8, early chromosome pairing is normal but synapsis occurs between sister chromatids rather than homologous chromosomes, demonstrating that a major role of REC8 in mammalian meiosis is to restrict synaptonemal complex formation to homologs.\",\n      \"method\": \"Rec8 knockout mouse, cytological analysis of meiotic chromosomes, immunofluorescence\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean knockout with specific meiotic phenotype readout in mammals, replicated phenotype known from other organisms\",\n      \"pmids\": [\"15935783\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Phosphorylation of the cohesin subunit Rec8 contributes to step-wise cohesin removal during meiosis. Loss of arm cohesion at meiosis I requires Rec8 phosphorylation, and the cohesin protector Sgo1 prevents premature loss of centromeric cohesion by opposing this phosphorylation. Meiotic recombination also contributes to step-wise cohesin loss.\",\n      \"method\": \"Phosphorylation site mutagenesis, epistasis analysis with sgo1 and recombination mutants in budding yeast, cohesin localization assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — phosphomutant analysis combined with genetic epistasis and multiple pathway components\",\n      \"pmids\": [\"16672979\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Loss of arm REC8 (but not centromeric REC8) is required for homolog separation at meiosis I in mouse oocytes, while loss of centromeric REC8 is required for sister chromatid separation at meiosis II. Neither loss is required for cytokinesis/polar body emission. This was demonstrated by microinjection of anti-Rec8 antibody at different meiotic stages, and securin destruction (via the spindle checkpoint-proteasome pathway) was shown to regulate arm REC8 removal.\",\n      \"method\": \"Antibody microinjection into mouse oocytes, inhibitor treatments (proteasome inhibitor, topoisomerase II inhibitor, PP2A inhibitor), chromosome segregation analysis\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct antibody-based functional intervention at defined meiotic stages with specific segregation phenotypes\",\n      \"pmids\": [\"16855401\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Separase cleaves mouse Rec8 at three positions in vitro, but only when Rec8 is hyper-phosphorylated. Expression of a non-cleavable Rec8 variant (Rec8-N) in male mice abolishes the first meiotic division, producing secondary spermatocytes with 4C DNA content. In oocytes, Rec8-N causes asynchronous and delayed chromosome segregation during anaphase I.\",\n      \"method\": \"In vitro separase cleavage assay, non-cleavable Rec8 transgenic mouse, chromosome spread analysis, flow cytometry\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro cleavage assay plus in vivo non-cleavable mutant with defined phenotypic readout\",\n      \"pmids\": [\"19625504\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Rec8 guides the distribution of Spo11 along yeast meiotic chromosomes. Spo11 binds to Rec8-binding sites during premeiotic S phase, and deletion of REC8 alters Spo11 localization at centromeres and specific chromosomal arm intervals, causing region-specific loss of DSB formation.\",\n      \"method\": \"Genome-wide chromatin immunoprecipitation (ChIP) on tiling arrays, rec8 deletion analysis\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide ChIP combined with genetic deletion showing functional consequence on DSB distribution\",\n      \"pmids\": [\"19439448\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Casein kinase 1delta/epsilon (CK1delta/epsilon) and Dbf4-dependent Cdc7 kinase (DDK) phosphorylate multiple sites on Rec8, and both kinases are required for Rec8 cleavage by separase and meiosis I nuclear division in budding yeast. PP2A (recruited by shugoshin) protects centromeric cohesion by opposing CK1delta/epsilon- and DDK-dependent phosphorylation of Rec8. Phosphomimetic Rec8 mutations bypass shugoshin protection at centromeres.\",\n      \"method\": \"Kinase inhibition (genetic and chemical), phosphomimetic and phospho-null Rec8 mutants, meiotic division analysis, in vivo phosphorylation mapping\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple kinase perturbations combined with phosphomimetic mutants demonstrating mechanistic sufficiency\",\n      \"pmids\": [\"20230747\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In fission yeast, casein kinase 1 (CK1; Hhp1/Hhp2) acts as the cohesin kinase that phosphorylates Rec8 to promote its separase-mediated cleavage during meiosis I, rather than polo-like kinase. Shugoshin (Sgo1)-PP2A counteracts this phosphorylation to protect centromeric Rec8. Forced localization of excess Hhp2 at pericentromeres abrogates Sgo1-PP2A protection, establishing that the balance between Rec8 phosphorylation by CK1 and dephosphorylation by Sgo1-PP2A regulates stepwise cohesion loss.\",\n      \"method\": \"Genetic screen ('anti-shugoshin' screen), targeted gene perturbation, forced localization experiments, Rec8 cleavage assays\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — genetic screen plus forced-localization epistasis with direct molecular readout of Rec8 cleavage\",\n      \"pmids\": [\"20383139\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Rec8-containing cohesin maintains bivalent chromosomes without detectable turnover during the oocyte growing phase. TEV protease cleavage of Rec8 (via a Rec8-TEV allele) triggers chiasmata resolution at meiosis I and sister centromere disjunction at meiosis II. Ectopic Rec8 activation during the growing phase does not rebuild cohesion, demonstrating the absence of cohesin turnover in oocytes.\",\n      \"method\": \"TEV-cleavable Rec8 knockin mouse, TEV protease microinjection, confocal live-cell imaging, conditional transgene activation\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution-level precision with inducible cleavage plus live imaging and genetic controls\",\n      \"pmids\": [\"20971813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In fission yeast, CK1 isoforms Hhp1 and Hhp2 are required for full levels of Rec8 phosphorylation (mapped by mass spectrometry) and for efficient separase-mediated removal of Rec8 at anaphase I onset. Rec8 phosphorylation is required for proper chromosome disjunction during meiosis.\",\n      \"method\": \"Mass spectrometry phosphorylation mapping, CK1 mutant analysis, Rec8 removal quantification\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mass spectrometry site mapping combined with genetic mutant phenotype\",\n      \"pmids\": [\"20581463\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"STAG3 stabilizes REC8-containing cohesin complexes during meiosis. In Stag3 hypomorphic mice with severely reduced STAG3, REC8 cohesin complex stability is reduced, causing defects in chromosome axis compaction, synapsis, and recombination. STAG3-REC8 cohesin complexes are specifically required for meiotic chromosome structure and function.\",\n      \"method\": \"Stag3 hypomorphic knockin mouse, immunofluorescence, chromosome spread analysis, cohesin complex quantification\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — hypomorphic allele with dosage-dependent phenotype and direct cohesin complex analysis\",\n      \"pmids\": [\"24797475\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Rec8-containing cohesin established during fetal oocyte DNA replication is maintained without detectable turnover throughout months of dictyate arrest. Rec8 activated in arrested oocytes does not establish new cohesion (detected by TEV cleavage and live imaging), demonstrating that cohesion renewal cannot occur post-replicatively in arrested mouse oocytes.\",\n      \"method\": \"Tamoxifen-inducible Cre for conditional Rec8 activation, TEV protease cleavage assay, live-cell imaging\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — inducible expression system combined with TEV cleavage functional assay and live imaging\",\n      \"pmids\": [\"26898469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The separase-cleaved C-terminal fragment of mammalian Rec8 bears an N-terminal Glu residue and is degraded by the N-end rule pathway via Ate1 arginyltransferase-mediated N-terminal arginylation followed by proteasomal degradation. Male Ate1 conditional knockout mice are nearly infertile due to massive spermatocyte apoptosis during meiosis I metaphase, caused by failure to destroy the Rec8 C-terminal fragment.\",\n      \"method\": \"Germ-cell-confined Ate1 conditional knockout mouse, in vivo Rec8 fragment detection, protein half-life assay, N-end rule pathway analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with defined molecular mechanism and specific meiotic phenotype\",\n      \"pmids\": [\"26858254\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"High density of REC8 cohesin complexes along sister chromatid axes (separated by <15% of total axis length) prevents local axis separation and illegitimate synaptonemal complex formation between sister chromatids. REC8 but not RAD21L or RAD21 flanks sites of local separated axial elements (LSAEs), and reduced cohesin levels cause both LSAEs and inter-sister SC formation at REC8-free regions.\",\n      \"method\": \"Super-resolution microscopy (STED), Stag3 hypomorphic mutant with reduced cohesin, quantitative cohesin distribution analysis\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — super-resolution imaging with quantitative analysis in genetic mutant showing direct structure-function relationship\",\n      \"pmids\": [\"27170622\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"During meiotic prophase in budding yeast, Rec8 phosphorylation (at 6, 24, or 29 sites with alanine substitutions) does not affect axis formation or recombination initiation/non-crossover recombination, but is specifically required for crossover-related events. DDK (Dbf4-dependent Cdc7 kinase) inhibition at defined times recapitulates these defects, while Hrr25/CK1 or Polo-like kinase inhibition does not, establishing DDK as the key kinase for Rec8's prophase role in crossover control.\",\n      \"method\": \"Rec8 phospho-mutant analysis (progressive alanine substitutions), timed kinase inhibition, crossover frequency and distribution assays\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — systematic phosphomutant series with timed kinase inhibition providing separation-of-function evidence\",\n      \"pmids\": [\"27484478\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Rec8 cohesin requires STAG3 (but not STAG1 or STAG2) for nuclear entry, chromatin loading, and functional sister chromatid cohesion in somatic cells. Rec8-STAG3 cohesin physically interacts with Pds5, Wapl, and sororin, is susceptible to Wapl-dependent ring opening (cohesion dissolution), and is protected by sororin — demonstrating that meiotic Rec8 cohesin is regulated by the same Wapl/sororin mechanism as mitotic cohesin.\",\n      \"method\": \"Ectopic expression in HEK293 cells, co-immunoprecipitation, chromatin loading assay, Wapl/sororin knockdown\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP plus functional complementation in somatic cells with multiple regulatory pathway validations\",\n      \"pmids\": [\"29724914\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Meiosis-specific cohesin component Rec8 binds to Mps3 (a SUN-domain nuclear envelope protein) during meiosis in budding yeast and controls Mps3 localization and dynamics on the nuclear envelope. Ectopic expression of Rec8 in mitotic cells induces formation of Mps3 patches/foci on the nuclear envelope, and this requires the cohesin regulator Rad61/Wpl1.\",\n      \"method\": \"Co-immunoprecipitation, ectopic Rec8 expression in mitotic yeast, nuclear envelope localization assays, Wpl1 epistasis\",\n      \"journal\": \"Genes to cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — co-IP and ectopic expression with localization readout; single lab\",\n      \"pmids\": [\"30417519\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"EWSR1 binds to both PRDM9 and phosphorylated REC8 (pREC8) in male meiotic cells. Conditional knockout of Ewsr1 causes meiotic arrest with decreased histone trimethylation at meiotic hotspots, impaired DSB repair, and reduced crossover number, suggesting EWSR1 links PRDM9-bound hotspots to the chromosome axis through pREC8.\",\n      \"method\": \"Co-immunoprecipitation, Ewsr1 conditional knockout mouse, ChIP analysis for histone methylation, crossover quantification\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — co-IP establishing interaction plus conditional KO; indirect inference of REC8's role in the complex\",\n      \"pmids\": [\"33175657\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Genome-wide ChIP-seq in Arabidopsis shows REC8 associates with high-nucleosome-occupancy regions in multiple chromatin states (H3K4me, H3K27me, H3K9me). REC8 enrichment suppresses meiotic DSBs and crossovers at both chromosome and fine scales. In rec8 mutants, abnormal axis structures recruit DSB-associated foci and undergo synapsis followed by chromosome fragmentation.\",\n      \"method\": \"ChIP-seq (REC8), rec8 mutant analysis, kyp suvh5 suvh6 mutant ChIP-seq, immunofluorescence\",\n      \"journal\": \"The Plant cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide ChIP-seq in Arabidopsis (plant ortholog); finding is consistent with mammalian REC8 function\",\n      \"pmids\": [\"32024691\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cleavage of REC8 by Separase at meiosis I is necessary and sufficient to convert sister kinetochores from co-orientation to bi-orientation, and to deprotect pericentromeric cohesion. Transfer of spindle-chromosome complexes between meiosis I and II showed both co-orientation and pericentromeric cohesin protection depend on the chromosomal context (not cytoplasm). Selective REC8 cleavage near kinetochores is sufficient to destroy co-orientation in univalent chromosomes.\",\n      \"method\": \"Spindle-chromosome complex (SCC) transfer between meiosis I and II oocytes, separase catalytic mutant, selective REC8 cleavage experiments, live imaging\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — elegant reconstitution using SCC transfer combined with selective cleavage experiments providing direct causal evidence\",\n      \"pmids\": [\"34758289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Two foundational meiotic proteins, Spo11 and Rec8, can dismantle centromeres via nucleosome remodeling factors. Overexpression of Rec8 in proliferating fission yeast or human cells leads to loss of mitotic kinetochores, demonstrating that Rec8 can destabilize centromeric chromatin when expressed ectopically.\",\n      \"method\": \"Rec8 overexpression in fission yeast and human cells, centromere marker loss assay, telomere bouquet mutant analysis\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — overexpression in two cell types with defined centromere destabilization readout; mechanism partially through nucleosome remodelers\",\n      \"pmids\": [\"33658710\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Meikin (Moa1 in fission yeast) associates with Plo1 (polo-like kinase) and synergizes with shugoshin (Sgo1) to protect centromeric Rec8 cohesion during meiosis I. Moa1-Plo1 phosphorylates Rec8 at a key site, which potentiates PP2A activity associated with Sgo1, leading to dephosphorylation of Rec8 at a separase-promoting site and thus preventing Rec8 cleavage.\",\n      \"method\": \"Genetic analysis of moa1 mutants, Plo1 kinase assays, Rec8 phosphorylation site mapping, epistasis with sgo1-PP2A pathway\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — kinase assay plus phosphorylation-site dissection with clear epistatic ordering of Moa1-Plo1-PP2A-Rec8 pathway\",\n      \"pmids\": [\"33888556\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Rec8 regulates chromosome axis length by modulating Pds5 protein, while Pds5 in turn regulates axis length and crossover frequency in a dosage-dependent manner. Pds5 depletion does not alter Rec8 abundance, but Rec8 affects Pds5, placing Rec8 upstream of Pds5 in axis length control.\",\n      \"method\": \"Pds5 and Rec8 protein quantification, chromosome axis length measurement, crossover frequency analysis, epistasis\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis plus quantitative analysis; single study but orthogonal methods\",\n      \"pmids\": [\"33712462\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Aurora B/C kinase activities promote Rec8 phosphorylation in mammalian oocytes, and this phosphorylation is required for Rec8 cleavage by separase at meiosis I. A specific Rec8 phosphorylation site was identified that is phosphorylated in vivo; inhibition of Aurora B/C during meiotic maturation impairs both Rec8 phosphorylation and chromosome segregation.\",\n      \"method\": \"Rec8-cleavage biosensor in single mouse oocytes (live imaging), phosphomutant analysis, Aurora B/C kinase inhibition, endogenous Rec8 phosphorylation assay\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — biosensor-based live imaging of cleavage combined with phosphomutant analysis and in vivo phosphorylation detection\",\n      \"pmids\": [\"35385691\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"MicroRNA miR-202 safeguards meiotic progression by repressing SEPARASE mRNA, thereby maintaining REC8 protein levels. Loss of miR-202 causes premature Separase-mediated REC8 cleavage, resulting in spermatocyte apoptosis and disruption of the zygotene-to-pachytene transition.\",\n      \"method\": \"miR-202 knockout mouse, target validation (Separase as miR-202 target), REC8 protein quantification, meiotic chromosome analysis\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse with defined molecular target and REC8 pathway placement; indirect regulation\",\n      \"pmids\": [\"35712867\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Meiotic DSBs regulate cleavage-independent dissociation of Rec8-cohesin from chromosomes during meiotic prophase I in budding yeast. Genome-wide Rec8 binding analysis shows its distribution changes from mid to late prophase I with cleavage-independent loss. The spo11 mutant (lacking meiotic DSBs) does not show this redistribution, demonstrating DSBs drive a cohesin remodeling pathway distinct from separase cleavage.\",\n      \"method\": \"Genome-wide ChIP-seq for Rec8, spo11 mutant analysis, meiotic prophase stage fractionation\",\n      \"journal\": \"Genes to cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide ChIP-seq with genetic validation; single study\",\n      \"pmids\": [\"37968127\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Phosphorylation of Rec8 at specific Plo1 (polo-like kinase) phosphorylation sites, identified through meikin (Moa1) association, is required for monopolar orientation of sister kinetochores in meiosis I in fission yeast. Non-phosphorylatable mutations at these sites (in Rec8 and Psm3) show specific mono-orientation defects, genetically separating this function from cohesion protection.\",\n      \"method\": \"Plo1 phosphorylation site identification, non-phosphorylatable Rec8/Psm3 mutants, kinetochore orientation assay in fission yeast\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — phosphomutant separation-of-function analysis with specific kinetochore orientation readout\",\n      \"pmids\": [\"38448160\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Acetylation of Rec8 cohesin complexes at Psm3-K1013 by Eso1 acetyltransferase is required for reductional chromosome segregation in meiosis. This acetylation is largely dependent on the meiotic kinetochore factor meikin (Moa1) and cooperates with canonical acetylation at Psm3-K105 and K106. Meiosis-specific Rec8 cohesin complexes localized at centromeres were purified and analyzed by mass spectrometry.\",\n      \"method\": \"Purification of meiotic centromeric Rec8 cohesin complexes, mass spectrometry identification of acetylation, Psm3 acetylation-site mutants, chromosome segregation analysis\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mass spectrometry identification combined with site-specific mutant functional analysis\",\n      \"pmids\": [\"38575358\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Securin degradation via the ubiquitin-proteasome pathway is required for Rec8 proteolysis at the metaphase-to-anaphase transition in mouse and pig oocytes. Inhibition of the ubiquitin-proteasome pathway blocks both securin and Rec8 degradation. Microinjection of securin antibody into MII oocytes leads to Rec8 degradation, placing securin upstream of Rec8 in the meiotic metaphase-to-anaphase pathway.\",\n      \"method\": \"Proteasome inhibitor treatment, securin antibody microinjection, Western blot for securin and Rec8, immunofluorescence in mouse/pig oocytes\",\n      \"journal\": \"Frontiers in bioscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple interventions (inhibitor, antibody microinjection) with direct protein level measurements\",\n      \"pmids\": [\"16720305\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Meiotic cohesin subunits RAD21L and REC8 localize at distinct positions within the synaptonemal complex: both at connection sites between lateral elements and transverse filaments in pachynema, with RAD21L positioned interior to REC8. Some RAD21L but not REC8 signals appear to bridge unsynapsed regions in zygonema, and recombination intermediate signals overlap more with RAD21L than REC8.\",\n      \"method\": \"Super-resolution microscopy (3D-SIM), immunofluorescence in mouse spermatocytes, recombination marker co-localization\",\n      \"journal\": \"The Journal of reproduction and development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — super-resolution localization distinguishing REC8 from RAD21L at sub-SC resolution; single study\",\n      \"pmids\": [\"27665783\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Nociceptin (a neuropeptide) induces rapid Rec8 phosphorylation in mouse spermatocytes through its receptor Oprl-1, which is exclusively expressed in the plasma membrane of testicular germ cells. In vivo injection of nociceptin stimulates Rec8 phosphorylation and meiotic chromosome dynamics; nocistatin (a nociceptin inhibitor) abolishes these effects.\",\n      \"method\": \"In vivo nociceptin/nocistatin injection, Rec8 phosphorylation assay (Western blot), Oprl-1 receptor localization\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — in vivo ligand treatment with protein phosphorylation readout; identifies upstream signaling but mechanism downstream of receptor incompletely defined\",\n      \"pmids\": [\"23720425\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"REC8 interacts with MAVS and STING in the cytoplasm during viral infection and inhibits their K48-linked ubiquitination by RNF5, thereby stabilizing these innate immune signaling proteins. SUMOylated REC8 translocates from nucleus to cytoplasm upon viral infection (triggered via JAK-STAT pathway upregulation). REC8 also promotes recruitment of TBK1 to MAVS and STING, enhancing interferon signaling.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, REC8 knockdown (siRNA), viral infection assay (VSV, NDV, HSV), subcellular fractionation, SUMO modification analysis\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — co-IP combined with ubiquitination assay and functional KD with viral infection readout; novel non-meiotic function\",\n      \"pmids\": [\"35107381\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Moa1 (meikin) and Sgo1 (shugoshin) are degraded during anaphase I by the APC/C-Slp1 pathway in fission yeast. Non-degradable Moa1 and Sgo1 expressed in meiosis II can protect Rec8 cohesin; the localization of Sgo1 and phosphorylation of Rec8 at S449 and S450 are necessary and sufficient to protect Rec8 during meiosis II.\",\n      \"method\": \"Non-degradable Moa1/Sgo1 mutant expression in meiosis II, Rec8 phosphosite mutants, APC/C genetic analysis\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 — phosphomutant analysis with meiosis II expression system; preprint, not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.09.19.677360\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"REC8 is a meiosis-specific α-kleisin subunit of the cohesin complex that forms a ring with SMC1β/SMC3 and STAG3; it establishes sister chromatid cohesion during pre-meiotic DNA replication, organizes chromosome axial elements, restricts synaptonemal complex formation to homologs, and guides Spo11-dependent DSB distribution; during meiosis I, phosphorylation of Rec8 by CK1 (Hhp1/2), DDK, and Aurora B/C kinases promotes its cleavage by separase on chromosome arms (releasing chiasmata and allowing homolog separation), while shugoshin-PP2A dephosphorylates centromeric Rec8 to protect it until meiosis II, with meikin (Moa1/Plo1)-dependent Rec8 phosphorylation additionally regulating both cohesion protection and monopolar sister kinetochore orientation; at meiosis II, centromeric Rec8 is finally cleaved by separase to allow sister chromatid separation, and the resulting C-terminal fragment is degraded by the N-end rule pathway via Ate1-mediated arginylation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"REC8 is a meiosis-specific α-kleisin subunit of the cohesin complex that establishes and maintains sister chromatid cohesion during meiotic divisions, organizes chromosome axes, restricts synaptonemal complex formation to homologs, and guides the distribution of meiotic double-strand breaks. REC8 forms a ring complex with SMC1β, SMC3, and STAG3, loads onto chromosomes during pre-meiotic S phase, and persists on chromosome arms until anaphase I and at centromeres until anaphase II; stepwise removal is controlled by phosphorylation-dependent separase cleavage, with CK1δ/ε, DDK, and Aurora B/C kinases phosphorylating Rec8 to promote arm cleavage at meiosis I, while shugoshin-PP2A dephosphorylates centromeric Rec8 to protect it, and meikin-polo kinase phosphorylation additionally regulates both centromeric cohesion protection and monopolar kinetochore orientation [PMID:10440376, PMID:12759374, PMID:14532136, PMID:20230747, PMID:20383139, PMID:35385691, PMID:33888556, PMID:38448160]. Rec8 cohesin established during fetal DNA replication is maintained without turnover throughout oocyte arrest, and its cleavage at meiosis I is both necessary and sufficient to convert sister kinetochores from co-orientation to bi-orientation [PMID:20971813, PMID:26898469, PMID:34758289]. The separase-generated C-terminal Rec8 fragment is degraded by the Ate1-dependent N-end rule pathway, and failure of this degradation causes spermatocyte apoptosis [PMID:26858254].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Identification of Rec8 as a meiosis-specific cohesin subunit established the molecular basis for differential cohesion at centromeres versus arms during the two meiotic divisions, resolving how reductional segregation is achieved.\",\n      \"evidence\": \"Genetic deletion in fission yeast with immunolocalization and segregation analysis; parallel expression and phosphorylation analysis\",\n      \"pmids\": [\"10440376\", \"10207075\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Separase involvement not yet demonstrated\", \"Mammalian Rec8 function unconfirmed\", \"Mechanism of centromeric versus arm differential removal unknown\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstration that mammalian REC8 associates with SMC1β/SMC3 and axial element components, and that separase cleavage of Rec8 is required for meiotic chromosome segregation, defined the core cohesin ring composition and cleavage-dependent removal mechanism.\",\n      \"evidence\": \"Co-immunoprecipitation of REC8 with SMC1β/SMC3/SCP3/RAD51 in rat and mouse spermatocytes; non-cleavable Rec8 mutant in fission yeast blocking meiosis I\",\n      \"pmids\": [\"12759374\", \"12615909\", \"14532136\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinases responsible for phosphorylation-dependent cleavage not identified\", \"Centromeric protection mechanism unknown\", \"Non-cleavable mutant not yet tested in mammals\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Knockout of REC8 in mice revealed that REC8 restricts synaptonemal complex formation to homologs rather than sister chromatids, establishing a structural gatekeeping role beyond simple cohesion.\",\n      \"evidence\": \"Rec8 knockout mouse with cytological analysis showing inter-sister rather than inter-homolog synapsis\",\n      \"pmids\": [\"15935783\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which REC8 prevents sister-chromatid synapsis unclear\", \"Relationship between REC8 density on axes and synapsis restriction not quantified\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Discovery that Rec8 phosphorylation enables stepwise arm-then-centromere cohesion loss, opposed by shugoshin at centromeres, resolved the long-standing question of how differential cohesion removal is regulated between meiosis I and II.\",\n      \"evidence\": \"Phosphorylation-site mutagenesis and sgo1 epistasis in budding yeast; anti-Rec8 antibody microinjection at defined meiotic stages in mouse oocytes\",\n      \"pmids\": [\"16672979\", \"16855401\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the kinase(s) phosphorylating Rec8 not yet established\", \"Precise phosphorylation sites not mapped\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"In vitro cleavage assays and non-cleavable Rec8 transgenic mice confirmed that separase cleavage of phosphorylated Rec8 is essential for mammalian meiosis I, while genome-wide ChIP showed Rec8 guides Spo11-mediated DSB distribution along chromosomes.\",\n      \"evidence\": \"In vitro separase cleavage of phosphorylated Rec8; Rec8-N non-cleavable transgenic mouse; genome-wide ChIP-chip in yeast with rec8 deletion\",\n      \"pmids\": [\"19625504\", \"19439448\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific kinases for mammalian Rec8 phosphorylation not identified\", \"Mechanism linking Rec8 binding to Spo11 recruitment unclear\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identification of CK1δ/ε and DDK as the kinases phosphorylating Rec8, with PP2A-shugoshin opposing them at centromeres, completed the kinase-phosphatase circuit governing stepwise cohesion removal; separately, TEV-cleavable Rec8 knockin mice proved that Rec8-containing cohesin established during fetal S phase is maintained without turnover throughout oocyte arrest.\",\n      \"evidence\": \"Kinase inhibition and phosphomimetic Rec8 mutants in budding and fission yeast; mass spectrometry phosphorylation mapping; TEV-cleavable Rec8 knockin with live imaging in mouse oocytes\",\n      \"pmids\": [\"20230747\", \"20383139\", \"20581463\", \"20971813\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the same kinases operate in mammalian meiosis not yet shown\", \"Turnover absence demonstrated only for months; lifetime persistence not directly tested\", \"DDK versus CK1 relative contributions at specific sites unclear\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"STAG3 was shown to stabilize REC8-containing cohesin complexes and to be specifically required for meiotic chromosome axis compaction and synapsis, establishing STAG3 as the obligate SA subunit for meiotic REC8 cohesin function.\",\n      \"evidence\": \"Stag3 hypomorphic knockin mouse with reduced REC8 cohesin levels and axis/synapsis defects\",\n      \"pmids\": [\"24797475\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether STAG3 is required for REC8 loading in vivo or only for stability not fully resolved\", \"Structural basis of STAG3-REC8 specificity unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Multiple advances clarified REC8 cohesin maintenance and clearance: confirmation that no cohesion renewal occurs in arrested oocytes, discovery that the Rec8 C-terminal cleavage fragment is destroyed via Ate1-mediated N-end rule degradation (required for male fertility), super-resolution mapping showing high REC8 density prevents illegitimate inter-sister synapsis, and phospho-mutant series separating DDK-dependent Rec8 phosphorylation roles in crossover control from axis formation.\",\n      \"evidence\": \"Inducible Rec8 activation in arrested oocytes; Ate1 conditional KO mouse with Rec8 fragment accumulation; STED microscopy in Stag3 hypomorph; systematic Rec8 phospho-alanine substitution series with timed DDK inhibition\",\n      \"pmids\": [\"26898469\", \"26858254\", \"27170622\", \"27484478\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"N-end rule pathway for Rec8 fragment shown only in spermatogenesis; oocyte relevance untested\", \"DDK phosphorylation sites promoting crossovers versus separase cleavage not fully distinguished\", \"Inter-sister synapsis suppression mechanism beyond physical density not characterized\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Ectopic expression studies demonstrated that Rec8-STAG3 cohesin is regulated by the canonical Wapl/sororin cohesion maintenance pathway, and that Rec8 physically interacts with the LINC complex component Mps3 to control nuclear envelope dynamics during meiosis.\",\n      \"evidence\": \"Rec8-STAG3 co-expression in HEK293 cells with Wapl/sororin knockdown; Rec8-Mps3 co-IP and ectopic expression in mitotic yeast\",\n      \"pmids\": [\"29724914\", \"30417519\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Wapl/sororin regulation of Rec8 cohesin not validated in native meiotic cells\", \"Mps3 interaction shown only by co-IP in single lab\", \"Functional consequence of Mps3-Rec8 interaction on chromosome movement unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"REC8 cleavage by separase at meiosis I was shown to be necessary and sufficient to convert sister kinetochores from co-orientation to bi-orientation, and meikin-polo kinase was found to phosphorylate Rec8 to potentiate PP2A-shugoshin centromeric protection, establishing dual functions of Rec8 phosphorylation in orientation and protection.\",\n      \"evidence\": \"Spindle-chromosome complex transfer between meiosis I and II oocytes with selective REC8 cleavage; Moa1-Plo1 kinase assays with Rec8 phosphosite dissection and sgo1-PP2A epistasis in fission yeast\",\n      \"pmids\": [\"34758289\", \"33888556\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mammalian meikin-Rec8 phosphorylation sites not mapped\", \"How pericentromeric Rec8 cleavage mechanistically triggers bi-orientation switch unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Aurora B/C kinase was identified as an additional kinase phosphorylating Rec8 to promote separase cleavage in mammalian oocytes, extending the multi-kinase circuit; separately, a non-meiotic role for REC8 in stabilizing MAVS and STING during antiviral innate immune signaling was reported.\",\n      \"evidence\": \"Rec8-cleavage biosensor in mouse oocytes with Aurora B/C inhibition and phosphomutant analysis; co-IP of REC8 with MAVS/STING, ubiquitination assays, and REC8 knockdown during viral infection\",\n      \"pmids\": [\"35385691\", \"35107381\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contributions of Aurora B/C versus CK1/DDK in mammalian Rec8 phosphorylation not quantified\", \"Non-meiotic REC8 function in innate immunity reported by single lab and awaits independent confirmation\", \"Whether REC8's immune role is physiologically relevant given its meiotic-specific expression pattern is unclear\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Phosphorylation of Rec8 (and Psm3) at specific polo-kinase sites was genetically separated from cohesion protection and shown to be specifically required for monopolar kinetochore orientation, and acetylation of Rec8 cohesin at Psm3-K1013 by Eso1 was found necessary for reductional segregation, revealing post-translational modification of the Rec8 complex beyond phosphorylation.\",\n      \"evidence\": \"Non-phosphorylatable Rec8/Psm3 mutants with kinetochore orientation assay; mass spectrometry identification of Psm3 acetylation in purified meiotic centromeric Rec8 complexes with acetylation-site mutants\",\n      \"pmids\": [\"38448160\", \"38575358\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Psm3 acetylation functions are conserved in mammals unknown\", \"Structural basis for how Rec8 phosphorylation enables monopolar attachment not resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of the Rec8 cohesin ring at atomic resolution, how REC8 density mechanistically prevents inter-sister synapsis, the full integration of multiple kinase inputs (CK1, DDK, Aurora B/C, Plo1) on Rec8 in a single mammalian model, and whether the reported non-meiotic immune function of REC8 is physiologically relevant.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No atomic-resolution structure of Rec8-containing cohesin\", \"Mechanism linking Rec8 to inter-sister synapsis prevention not established beyond density model\", \"Integrated kinase circuit for Rec8 phosphorylation not validated in a single mammalian system\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 2, 3, 14, 17]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [2, 3, 19]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [0, 1, 2, 3, 5, 7, 9, 12, 17, 22]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1, 19, 35]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [35]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [0, 4, 6, 7, 8, 10, 11, 23, 27, 30]},\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [0, 1, 5, 12, 15, 16]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [9, 22, 29]}\n    ],\n    \"complexes\": [\n      \"Meiotic cohesin (REC8-SMC1β-SMC3-STAG3)\",\n      \"Synaptonemal complex (axial element association)\"\n    ],\n    \"partners\": [\n      \"SMC1B\",\n      \"SMC3\",\n      \"STAG3\",\n      \"PDS5\",\n      \"WAPL\",\n      \"ESPL1\",\n      \"SGO1\",\n      \"EWSR1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}