{"gene":"REC8","run_date":"2026-06-10T06:43:36","timeline":{"discoveries":[{"year":1999,"finding":"Fission yeast Rec8 is a meiosis-specific cohesin that localizes to centromeres and chromosome arms during pre-meiotic S phase. Centromeric Rec8 persists through meiosis I and is lost at anaphase II. Deletion of rec8 causes premature sister chromatid separation at meiosis I, resulting in equational rather than reductional chromosome segregation, demonstrating that Rec8 maintains sister-chromatid cohesion and orients kinetochores for co-segregation of sisters at meiosis I.","method":"Gene deletion, cytological analysis, in situ hybridization, immunolocalization in fission yeast","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with defined chromosome segregation phenotype, replicated across multiple subsequent studies in other organisms","pmids":["10440376"],"is_preprint":false},{"year":1995,"finding":"The S. pombe rec8 gene product is required for linear element (axial core) formation, meiotic chromosome pairing, and sister chromatid cohesion. The rec8-110 mutant shows aberrant linear elements, shortened meiotic prophase, impaired homolog pairing, and precocious sister chromatid separation at meiosis I.","method":"Genetic analysis of rec8-110 mutant, cytology, in situ hybridization in S. pombe","journal":"Genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (genetics, cytology, in situ hybridization), replicated by subsequent studies","pmids":["8536990"],"is_preprint":false},{"year":1999,"finding":"Fission yeast Rec8p is expressed exclusively during meiosis and localizes to ~100 foci per prophase nucleus. Rec8p exists in an unphosphorylated form early in meiotic prophase and becomes phosphorylated prior to meiosis I (demonstrated using the mei4 mutant blocked before meiosis I). Rec8p persists beyond meiosis I (demonstrated using mes1 mutant blocked before meiosis II). A human ortholog (hREC8) maps to chromosome 14 and is expressed in germ line cells.","method":"Western blotting, immunolocalization, analysis of meiotic mutants (mei4, mes1) in S. pombe; cloning of human REC8","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — protein-level evidence with phosphorylation analysis, genetic tools, and cross-species conservation established","pmids":["10207075"],"is_preprint":false},{"year":2000,"finding":"Budding yeast Rec8p modulates meiotic S-phase progression: deletion of REC8 increases S-phase length (~10% in wild-type background; ~30% in spo11Δ background), demonstrating that Rec8p is a key coordinator of meiotic interhomolog and intersister interactions that feeds back on DNA replication progression.","method":"Genetic deletion analysis, S-phase length measurement in budding yeast","journal":"Genes & development","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean genetic deletion with quantitative S-phase measurements, single lab","pmids":["10691741"],"is_preprint":false},{"year":2003,"finding":"In rat meiocytes, REC8 appears before premeiotic S phase and forms axial element-like structures (REC8-AEs) before other cohesin subunits (SMC1beta, SMC3) or axial element proteins (SCP2, SCP3) are incorporated, suggesting REC8 provides the initial scaffold for axial element assembly. REC8 persists along chromosome arms until anaphase I and near centromeres until anaphase II, while SMC1beta, SMC3, SCP2, and SCP3 disappear from arms at metaphase I. RAD51 and/or DMC1 co-immunoprecipitates with REC8, suggesting REC8 also provides a basis for recombination complex assembly.","method":"Immunofluorescence, co-immunoprecipitation, temporal analysis of protein incorporation into axial elements in rat spermatocytes","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP, detailed immunofluorescence staging, multiple proteins analyzed, independent of S. pombe work","pmids":["12615909"],"is_preprint":false},{"year":2003,"finding":"Mammalian REC8 associates with SMC1beta and SMC3 (but not SMC1alpha) and with synaptonemal complex component SCP3, forming a meiosis-specific cohesin complex. REC8 is selectively lost from chromosome arms at the metaphase I-to-anaphase I transition while persisting at centromeres until anaphase II, providing a molecular basis for the stepwise loss of cohesion in mammalian meiosis.","method":"Immunoprecipitation, immunohistochemistry, Western blotting in mouse testis","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — co-IP demonstrating complex composition, immunolocalization across meiotic stages, replicated by other labs","pmids":["12759374"],"is_preprint":false},{"year":2003,"finding":"Separase activation and resultant Rec8 cleavage are required for meiotic chromosome segregation in fission yeast. A non-cleavable form of Rec8 blocks homolog disjunction at meiosis I. Rec8 forms distinct complexes along chromosome arms (with Rec11/SA3) versus centromeres (with Psc3/SA1-SA2), and cleavage of arm Rec8 is required for homolog segregation at meiosis I while centromeric Rec8 cleavage is required for sister segregation at meiosis II.","method":"Non-cleavable Rec8 mutant expression, genetic depletion of Rec11, chromosome segregation analysis in S. pombe","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis of cleavage sites combined with genetic epistasis, replicated by subsequent studies in multiple organisms","pmids":["14532136"],"is_preprint":false},{"year":2005,"finding":"Mouse REC8 knockout (both sexes) causes sterility due to germ cell failure. In the absence of REC8, early chromosome pairing appears normal but synapsis occurs between sister chromatids rather than homologs, demonstrating that a major role of REC8 in mammalian meiosis is to restrict synaptonemal complex formation to between homologous chromosomes.","method":"Rec8 knockout mouse, cytological analysis of meiotic chromosomes in both sexes","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — complete KO with defined cellular phenotype (inter-sister synapsis), replicated in multiple studies","pmids":["15935783"],"is_preprint":false},{"year":2006,"finding":"In budding yeast, phosphorylation of the cohesin subunit Rec8 contributes to the stepwise removal of cohesin during meiosis. Both Sgo1 (cohesin protector) and meiotic recombination cooperate with Rec8 phosphorylation to establish the meiotic chromosome segregation pattern.","method":"Phosphomutant Rec8 analysis, genetic manipulation of Sgo1 and recombination pathways, chromosome spreading in S. cerevisiae","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — phosphomutant analysis with multiple orthogonal genetic approaches, published in Nature","pmids":["16672979"],"is_preprint":false},{"year":2006,"finding":"In mouse oocytes, loss of arm REC8 (armRec8) is required for homolog separation at meiosis I, while loss of centromeric REC8 (cenRec8) is required for sister chromatid separation at meiosis II. Microinjection of anti-Rec8 antibody into metaphase I oocytes inhibits homolog separation but not polar body emission. Neither loss is required for spindle elongation or cytokinesis.","method":"Microinjection of anti-Rec8 antibody into mouse oocytes, immunofluorescence, pharmacological inhibitors","journal":"Cell cycle (Georgetown, Tex.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — antibody microinjection with functional readout, single lab with multiple conditions tested","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) causes sterility in male mice with failure of the first meiotic division, demonstrating that Rec8 cleavage by separase is required for chiasma resolution in mammalian meiosis.","method":"In vitro cleavage assay with hyper-phosphorylated Rec8, transgenic non-cleavable Rec8 mouse, chromosome spreads, DNA content analysis","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution of separase cleavage combined with in vivo non-cleavable mutant analysis","pmids":["19625504"],"is_preprint":false},{"year":2009,"finding":"In budding yeast, Spo11 initially accumulates around centromeres during premeiotic S phase, then redistributes to chromosome arms where a substantial fraction co-localizes with Rec8 binding sites. Deletion of REC8 alters the distribution of Spo11 at centromeres and specific chromosomal arm intervals, demonstrating that Rec8 prearranges the distribution of Spo11 along meiotic chromosomes to regulate DSB formation.","method":"ChIP with high-density tiling arrays (genome-wide Spo11 and Rec8 localization), REC8 deletion analysis in S. cerevisiae","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genome-wide ChIP analysis with genetic deletion, single lab","pmids":["19439448"],"is_preprint":false},{"year":2010,"finding":"Multiple phosphorylation sites within Rec8 and two kinases — casein kinase 1δ/ε (CK1δ/ε) and Dbf4-dependent Cdc7 kinase (DDK) — are required for Rec8 cleavage by separase and meiosis I nuclear division in budding yeast. Rec8 with phosphomimetic mutations is no longer protected from separase at centromeres even when kinases are inhibited. PP2A protects centromeric cohesion by opposing CK1δ/ε- and DDK-dependent phosphorylation of Rec8.","method":"Phosphomutant and phosphomimetic Rec8 analysis, kinase inhibition, kinase deletion, meiotic division assays in S. cerevisiae","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple phosphomutants, two different kinases identified, phosphomimetic rescue experiments, mechanistically rigorous","pmids":["20230747"],"is_preprint":false},{"year":2010,"finding":"In fission yeast, casein kinase 1 (CK1) ortholog Hhp2 (not Polo-like kinase as previously thought) acts as the cohesin kinase that promotes Rec8 cleavage during meiosis. Forced pericentromeric localization of excess Hhp2 abrogates Sgo1-PP2A protection of centromeric Rec8. The balance between Rec8 phosphorylation by CK1 and dephosphorylation by Sgo1-PP2A regulates the stepwise loss of chromosomal cohesion.","method":"Genetic screen for anti-shugoshin factors, forced localization of CK1, phosphorylation analysis, meiotic chromosome segregation assays in S. pombe","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic screen plus multiple orthogonal functional experiments, establishes kinase identity, published in Nature Cell Biology","pmids":["20383139"],"is_preprint":false},{"year":2010,"finding":"Casein kinase 1 (CK1) δ/ε isoforms Hhp1 and Hhp2 are required for full levels of Rec8 phosphorylation and efficient removal of Rec8 at anaphase I onset in fission yeast. Rec8 phosphorylation sites were mapped by mass spectrometry; phosphorylation is required for proper chromosome disjunction.","method":"Mass spectrometry phosphorylation site mapping, CK1 mutant analysis, Rec8 phosphorylation quantification in S. pombe","journal":"Cell cycle (Georgetown, Tex.)","confidence":"High","confidence_rationale":"Tier 1 / Strong — mass spectrometry site identification plus genetic validation, corroborates Ishiguro et al. 2010 findings","pmids":["20581463"],"is_preprint":false},{"year":2010,"finding":"Rec8-containing cohesin (dependent on kleisin subunit Rec8) holds bivalent chromosomes together in mouse oocytes from birth until ovulation. TEV protease cleavage of Rec8 (but not Scc1) triggers chiasmata resolution during meiosis I and sister centromere disjunction during meiosis II. There is a dramatic transition from Rec8- to Scc1-containing cohesin at fertilization. Cohesin does not turn over during ≥2 weeks of oocyte growth.","method":"TEV-cleavable Rec8 and Scc1 knock-in mice, microinjection of TEV protease into oocytes, confocal live-cell imaging, ectopic Rec8 transgene activation","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution-level genetic engineering with live imaging, multiple orthogonal experiments in a single rigorous study","pmids":["20971813"],"is_preprint":false},{"year":2014,"finding":"STAG3 stabilizes REC8 cohesin complexes during meiosis. In hypomorphic Stag3 mice with severely reduced STAG3, REC8 cohesin levels are reduced and meiocytes display chromosome axis compaction defects, aberrant synapsis, and impaired recombination. STAG3-REC8 cohesin complexes have a critical role in meiotic chromosome structure and function.","method":"Hypomorphic Stag3 mouse model, immunofluorescence, analysis of cohesin subunit dosage and meiotic phenotypes","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo hypomorphic allele with defined molecular phenotype (REC8 destabilization), multiple cellular readouts","pmids":["24797475"],"is_preprint":false},{"year":2016,"finding":"Cohesin established by Rec8 in fetal mouse oocytes is maintained without detectable turnover in oocytes arrested for months (dictyate stage). Rec8 activated during DNA replication in fetal oocytes establishes cohesion, but Rec8 activated in already-arrested oocytes does not establish new cohesion despite cohesin synthesis, demonstrating that cohesion establishment requires ongoing DNA replication.","method":"Tamoxifen-inducible Cre activation of Rec8 transgene in fetal vs. arrested oocytes, TEV cleavage assay, live-cell imaging","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 1 / Strong — inducible genetic system with TEV cleavage readout and live imaging, multiple time points tested","pmids":["26898469"],"is_preprint":false},{"year":2016,"finding":"High density of REC8 cohesin complexes along chromosome axes is required to constrain sister chromatid axes and prevent illegitimate inter-sister synaptonemal complex formation. Using super-resolution microscopy, REC8 foci are separated by <15% of total axis length in wild-type meiocytes; reduced cohesin levels lead to local axial separation and ectopic SC formation specifically at REC8-free sites.","method":"Super-resolution microscopy (STED/SIM) in hypomorphic Stag3 mouse meiocytes with reduced REC8 levels","journal":"EMBO reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — super-resolution imaging with quantitative analysis, single lab","pmids":["27170622"],"is_preprint":false},{"year":2016,"finding":"During meiotic prophase, Rec8 phosphorylation by Dbf4-dependent Cdc7 kinase (DDK) promotes crossover-specific events independently of cohesin cleavage. Rec8 phospho-mutants (with 6, 24, or 29 alanine substitutions) show normal axis formation and recombination initiation but defective crossover formation, with severity proportional to number of substitutions. Inhibition of DDK (but not Hrr25/CK1 or Cdc5/PLK) during prophase recapitulates rec8 phospho-mutant phenotypes.","method":"Rec8 phospho-alanine mutants, timed kinase inhibition, crossover and non-crossover recombination analysis in S. cerevisiae","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — phosphomutant series with separation-of-function analysis, single lab","pmids":["27484478"],"is_preprint":false},{"year":2016,"finding":"RAD21L and REC8 meiotic cohesin subunits occupy distinct positions within the synaptonemal complex as determined by 3D-SIM super-resolution microscopy: both localize at connection sites between lateral elements and transverse filaments of pachynema, with RAD21L positioned interior to REC8 sites. RAD21L (but not REC8) forms bridges between unsynapsed axial elements at zygonema and shows greater overlap with recombination intermediates.","method":"3D-SIM super-resolution microscopy of spermatocyte synaptonemal complexes","journal":"The Journal of reproduction and development","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — super-resolution structural localization, single lab","pmids":["27665783"],"is_preprint":false},{"year":2016,"finding":"The separase-cleaved C-terminal fragment of mammalian Rec8 bears N-terminal Glu, which is arginylated by Ate1 R-transferase and then degraded by the N-end rule pathway. Male germ cell-specific Ate1 knockout mice are nearly infertile due to massive apoptotic death of spermatocytes at metaphase I, caused by failure to destroy the C-terminal Rec8 fragment.","method":"Germ cell-specific Ate1 knockout mouse, biochemical analysis of Rec8 fragments, in vivo protein stability assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — conditional KO combined with biochemical mechanism identification (N-end rule arginylation of Rec8 cleavage product)","pmids":["26858254"],"is_preprint":false},{"year":2018,"finding":"When expressed in somatic (Hek293) cells, Rec8 has no affinity for Stag1 or Stag2 and remains cytoplasmic, but co-expression of Stag3 is sufficient for Rec8 to enter the nucleus, load onto chromatin, and replace Scc1 for sister chromatid cohesion. Rec8-Stag3 cohesin physically interacts with Pds5, Wapl, and sororin, and is susceptible to Wapl-dependent ring opening and sororin-mediated protection.","method":"Ectopic expression in Hek293 cells, chromatin fractionation, co-immunoprecipitation, sister chromatid cohesion assays","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (localization, chromatin loading, co-IP, functional rescue), identifies Stag3 as required partner","pmids":["29724914"],"is_preprint":false},{"year":2018,"finding":"Meiosis-specific cohesin component Rec8 binds to Mps3 SUN domain 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, requiring the cohesin regulator Rad61/Wpl1 (WAPL).","method":"Co-immunoprecipitation, ectopic Rec8 expression in mitotic yeast, fluorescence microscopy of nuclear envelope localization in S. cerevisiae","journal":"Genes to cells : devoted to molecular & cellular mechanisms","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP combined with ectopic expression and localization experiments, 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 before meiosis onset causes meiotic arrest with decreased H3K4/K36 trimethylation at hotspots, impaired DSB repair, and reduced crossover number, suggesting EWSR1 links PRDM9-bound hotspots to the chromosome axis through pREC8.","method":"Co-immunoprecipitation of EWSR1 with PRDM9 and pREC8, conditional Ewsr1 knockout mouse, ChIP-seq for histone methylation","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP establishing protein interactions plus conditional KO, single lab","pmids":["33175657"],"is_preprint":false},{"year":2021,"finding":"Cleavage of pericentromeric REC8 by Separase at meiosis I is necessary not only for converting sister kinetochores from co-orientation to bi-orientation at meiosis II but also for deprotection of pericentromeric cohesion. Selective cleavage of REC8 in the vicinity of kinetochores in univalent chromosomes is sufficient to destroy co-orientation. This was demonstrated by transferring spindle-chromosome complexes between meiosis I and II in mouse oocytes.","method":"Spindle-chromosome complex transfers between meiosis I and II oocytes, TEV cleavage of REC8, live imaging in mouse oocytes","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution-level experiment (SCC transfers) combined with site-specific TEV cleavage and live imaging","pmids":["34758289"],"is_preprint":false},{"year":2021,"finding":"Overexpression of Rec8 (or Spo11) in proliferating fission yeast and human cells leads to the loss of mitotic kinetochores, demonstrating that Rec8 can dismantle centromeric chromatin. Specific nucleosome remodeling factors mediate centromere dismantlement by Rec8. This centromere dismantlement is normally observable only in mutants lacking the telomere bouquet.","method":"Overexpression of Rec8 in fission yeast and human cells, kinetochore loss assays, identification of mediating nucleosome remodeling factors","journal":"Nature","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain-of-function overexpression in two cell types, single lab but published in Nature with functional mechanistic follow-up","pmids":["33658710"],"is_preprint":false},{"year":2021,"finding":"Meikin (Moa1 in fission yeast) associates with Plo1 kinase and phosphorylates Rec8, with a key phosphorylation site required for cohesion protection. The phosphorylation of Rec8 by Moa1-Plo1 potentiates PP2A activity associated with Sgo1, leading to dephosphorylation of Rec8 at another site, thereby preventing separase cleavage of centromeric Rec8.","method":"Genetic analysis, phosphorylation site mapping, epistasis between moa1, plo1, sgo1 and rec8 phospho-mutants in S. pombe","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 / Strong — identification of specific phosphorylation sites with phosphomutant analysis and genetic epistasis, mechanistic pathway established","pmids":["33888556"],"is_preprint":false},{"year":2022,"finding":"Aurora B/C kinase activities promote REC8 phosphorylation and cleavage in mammalian oocytes. Through phosphomutant analysis using a separase biosensor in live mouse oocytes, specific phosphorylation sites in Rec8 that promote its cleavage were identified. Inhibition of Aurora B/C during meiotic maturation impairs endogenous Rec8 phosphorylation and chromosome segregation.","method":"Fluorescent biosensor for Rec8 cleavage, microinjection into mouse oocytes, phosphomutant analysis, Aurora B/C inhibitor treatment, live imaging","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 1 / Strong — biosensor reconstitution in live cells combined with phosphomutant analysis and kinase inhibition, identifies Aurora B/C as the relevant mammalian kinase","pmids":["35385691"],"is_preprint":false},{"year":2022,"finding":"MicroRNA-202 (miR-202) represses Separase mRNA, thereby upregulating REC8 protein levels. Loss of miR-202 results in premature SEPARASE-mediated REC8 cleavage, spermatocyte apoptosis, and disrupted meiotic prophase I (synapsis and crossover defects, inter-sister chromatid synapses). Separase mRNA is a direct target of miR-202.","method":"miR-202 knockout mice, luciferase reporter assays demonstrating Separase as direct miR-202 target, immunofluorescence of REC8 and synapsis markers","journal":"EMBO reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse phenotype with direct target validation, single lab; mechanism is indirect (through Separase regulation)","pmids":["35712867"],"is_preprint":false},{"year":2023,"finding":"Cleavage-independent dissociation of Rec8 cohesin from chromosomes occurs during meiotic prophase I in response to DSBs. Genome-wide Rec8 binding profiles change from mid- to late-prophase I, and the ratio of Rec8 dissociation per chromosome correlates with meiotic DSB density. In the spo11 mutant deficient in DSB formation, Rec8 distribution does not change in late prophase I, demonstrating a DSB-dependent regulatory pathway for global Rec8-cohesin binding.","method":"Genome-wide ChIP-seq of Rec8 at mid- and late-prophase I, spo11 mutant analysis in S. cerevisiae","journal":"Genes to cells : devoted to molecular & cellular mechanisms","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genome-wide ChIP with genetic validation using spo11 mutant, single lab","pmids":["37968127"],"is_preprint":false},{"year":2024,"finding":"Plo1 (polo-like kinase) associated with meikin (Moa1) phosphorylates Rec8 at specific sites to regulate sister kinetochore mono-orientation at meiosis I. Non-phosphorylatable mutations at these Plo1 phosphorylation sites in Rec8 (and Psm3) cause specific mono-orientation defects without affecting cohesion protection, enabling genetic dissection of these two meikin functions.","method":"Identification of Plo1 phosphorylation sites in Rec8 and Psm3, non-phosphorylatable mutant analysis, kinetochore orientation assays in S. pombe","journal":"Life science alliance","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — phosphomutant analysis with specific functional readout, single lab","pmids":["38448160"],"is_preprint":false},{"year":2024,"finding":"Acetyltransferase Eso1 acetylates meiosis-specific Rec8 cohesin complexes at a new site, Psm3-K1013, which is largely dependent on the meiotic kinetochore factor meikin (Moa1). This acetylation cooperates with canonical Psm3-K105/K106 acetylation and plays a crucial role in establishing reductional chromosome segregation in meiosis.","method":"Purification of centromeric Rec8 cohesin complexes from meiotic cells, mass spectrometry identification of acetylation site, genetic analysis of Psm3-K1013 mutants in S. pombe","journal":"Life science alliance","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — biochemical purification with MS identification plus genetic validation, single lab","pmids":["38575358"],"is_preprint":false},{"year":2022,"finding":"In S. pombe, Sgo1 and Moa1 are degraded during anaphase I by the APC/C-Slp1 pathway. Non-degradable Sgo1 and Moa1 expressed in meiosis II can protect Rec8 cohesin. Sgo1 localization and phosphorylation of Rec8 at S449 and S450 are necessary and sufficient events for protecting Rec8 cohesin, with absence of either event leading to Rec8 deprotection at meiosis II.","method":"Non-degradable Sgo1/Moa1 mutant expression in meiosis II, phosphomutant analysis of Rec8 S449/S450, live imaging in S. pombe","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — phosphomutant and non-degradable protein analysis with functional readout, preprint not yet peer-reviewed","pmids":[],"is_preprint":true},{"year":2025,"finding":"REC8-cohesin preferentially localizes to open promoter regions of genes involved in spermatogonial differentiation and meiosis at early meiosis (preleptonema to zygonema). REC8-cohesin genomic distribution is altered by BEND2 knockout. REC8 interacts with mitotic cyclin CCNA2. These findings demonstrate that REC8-cohesin participates in chromatin reorganization and transcription regulation at the mitosis-to-meiosis transition.","method":"ChIP-seq for REC8, BEND2 KO mice, co-immunoprecipitation of REC8 with CCNA2, RNA-seq","journal":"Genomics, proteomics & bioinformatics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genome-wide ChIP combined with KO and co-IP, single lab","pmids":["41476252"],"is_preprint":false},{"year":2022,"finding":"REC8 interacts with MAVS and STING in the cytoplasm and inhibits their K48-linked ubiquitination triggered by RNF5, stabilizing these innate immune signaling proteins. SUMOylated REC8 translocates from nucleus to cytoplasm during viral infection and promotes recruitment of TBK1 to MAVS and STING. Knockdown of REC8 impairs innate immune responses against VSV, NDV, and HSV.","method":"Co-immunoprecipitation of REC8 with MAVS and STING, ubiquitination assays, REC8 knockdown with viral infection assays, REC8 SUMOylation and localization analysis","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple co-IPs with functional validation by knockdown, single lab, non-meiotic context","pmids":["35107381"],"is_preprint":false}],"current_model":"REC8 is the meiosis-specific α-kleisin subunit of the cohesin complex that forms a ring with SMC1β/SMC3 and STAG3 to mediate sister chromatid cohesion; it provides the structural scaffold for axial/lateral element assembly, restricts synaptonemal complex formation to between homologs, guides Spo11-mediated DSB distribution, and must be sequentially cleaved by separase — first on chromosome arms (triggered by CK1δ/ε- and DDK-dependent phosphorylation, including Aurora B/C in mammals) to resolve chiasmata at meiosis I, then at centromeres at meiosis II — while centromeric REC8 is protected during meiosis I by shugoshin-PP2A acting against these kinases, a mechanism reinforced by meikin-Plo1–dependent phosphorylation at Rec8-S450 that potentiates PP2A dephosphorylation at a second site; cohesin established during fetal DNA replication is maintained without turnover through prolonged oocyte arrest, and the separase-generated C-terminal Rec8 fragment is rapidly degraded via N-terminal arginylation by Ate1 and the N-end rule pathway."},"narrative":{"mechanistic_narrative":"REC8 is the meiosis-specific α-kleisin subunit of cohesin that mediates sister-chromatid cohesion and organizes the meiotic chromosome axis, and whose regulated cleavage drives the two-step chromosome segregation of meiosis [PMID:10440376, PMID:12759374, PMID:14532136]. Loss of REC8 causes premature sister separation and equational rather than reductional segregation at meiosis I, establishing its core role in maintaining cohesion and orienting sister kinetochores for co-segregation [PMID:10440376]. In mammals, REC8 assembles with SMC1β, SMC3 and the stromalin STAG3 into a meiosis-specific cohesin; STAG3 stabilizes REC8 and is necessary and sufficient to license REC8 chromatin loading and cohesion activity, even ectopically in somatic cells where REC8-STAG3 engages PDS5, WAPL and sororin [PMID:12759374, PMID:24797475, PMID:29724914]. REC8 is laid down before other cohesin and axial-element proteins to scaffold axial/lateral element assembly, and a high density of REC8 along sister axes restricts synaptonemal complex formation to between homologs rather than between sisters [PMID:12615909, PMID:15935783, PMID:27170622]; it further patterns Spo11-dependent DSB distribution and supports crossover formation [PMID:19439448, PMID:27484478]. Stepwise cohesion loss is controlled by phosphoregulation: casein kinase 1 (CK1δ/ε) and DDK phosphorylate REC8 to license separase cleavage, first on chromosome arms to resolve chiasmata at meiosis I and later at centromeres at meiosis II [PMID:14532136, PMID:19625504, PMID:20230747, PMID:20581463], while centromeric REC8 is protected by shugoshin-PP2A opposing these kinases, a protection potentiated by meikin-Polo kinase phosphorylation of REC8 at S450/S449 [PMID:20383139, PMID:33888556]. In mammalian oocytes Aurora B/C phosphorylates REC8 to promote its cleavage, and cohesin established during fetal DNA replication persists without turnover through prolonged dictyate arrest [PMID:20971813, PMID:26898469, PMID:35385691]. The separase-generated C-terminal REC8 fragment is destroyed via N-terminal arginylation by Ate1 and the N-end rule pathway, a step required for spermatocyte survival [PMID:26858254]. Beyond meiosis, REC8 has been implicated in cytoplasmic stabilization of MAVS/STING innate immune signaling [PMID:35107381].","teleology":[{"year":1995,"claim":"Established that the rec8 gene product is required for the integrated meiotic program—axial core formation, homolog pairing, and sister cohesion—defining it as a central organizer rather than a single-task factor.","evidence":"Genetic and cytological analysis of the rec8-110 mutant in fission yeast","pmids":["8536990"],"confidence":"High","gaps":["Molecular identity of Rec8 as a cohesin subunit not yet defined","No protein-level or biochemical characterization"]},{"year":1999,"claim":"Defined Rec8 as a meiosis-specific cohesin whose persistence at centromeres through meiosis I and loss at anaphase II underlies reductional segregation, answering how sisters co-segregate at MI.","evidence":"Gene deletion, immunolocalization and in situ hybridization in fission yeast; cloning of human REC8","pmids":["10440376","10207075"],"confidence":"High","gaps":["Mechanism of differential arm vs. centromere cohesion loss unknown","Phosphorylation function not yet linked to cleavage"]},{"year":2000,"claim":"Showed Rec8 feeds back on meiotic S-phase progression, linking cohesion establishment to replication timing.","evidence":"REC8 deletion and S-phase length measurement in budding yeast","pmids":["10691741"],"confidence":"Medium","gaps":["Molecular basis of S-phase coordination unresolved","Single genetic background"]},{"year":2003,"claim":"Established the mammalian REC8 cohesin composition (SMC1β/SMC3, with SCP3 association) and demonstrated that REC8 is incorporated first to scaffold axial element assembly and is lost stepwise from arms then centromeres.","evidence":"Immunoprecipitation, immunofluorescence staging and co-IP in rat and mouse meiocytes","pmids":["12615909","12759374"],"confidence":"High","gaps":["STAG3 not yet identified as the meiotic stromalin partner","Functional consequence of RAD51/DMC1 co-IP unestablished"]},{"year":2003,"claim":"Demonstrated that separase cleavage of Rec8 is required for segregation, with distinct arm vs. centromere complexes resolved at MI vs MII—the molecular basis of two-step segregation.","evidence":"Non-cleavable Rec8 mutant and Rec11 depletion in fission yeast","pmids":["14532136"],"confidence":"High","gaps":["Kinases licensing cleavage not yet identified","Protection mechanism at centromeres undefined"]},{"year":2005,"claim":"Defined a major mammalian REC8 function as restricting synapsis to homologs, since its loss causes inter-sister synapsis and sterility.","evidence":"Rec8 knockout mouse cytology in both sexes","pmids":["15935783"],"confidence":"High","gaps":["Quantitative axis-density requirement not addressed","Recombination/DSB phenotype not detailed"]},{"year":2006,"claim":"Showed Rec8 phosphorylation cooperates with shugoshin and recombination to set the stepwise cohesion-removal pattern, and confirmed in oocytes that arm vs. centromeric Rec8 loss drives MI vs MII separation.","evidence":"Phosphomutant analysis with Sgo1/recombination genetics in budding yeast; anti-Rec8 antibody microinjection in mouse oocytes","pmids":["16672979","16855401"],"confidence":"High","gaps":["Specific kinases not yet pinned down","Antibody microinjection lacks site resolution"]},{"year":2009,"claim":"Reconstituted that separase cleaves Rec8 only when hyper-phosphorylated and showed cleavage is required in vivo for chiasma resolution, coupling phosphoregulation directly to cleavage.","evidence":"In vitro cleavage assay and non-cleavable Rec8 transgenic mice; ChIP tiling of Spo11/Rec8 in budding yeast","pmids":["19625504","19439448"],"confidence":"High","gaps":["Identity of the relevant in vivo kinase(s) still open","Mechanism of Rec8-directed Spo11 prearrangement unresolved"]},{"year":2010,"claim":"Identified CK1δ/ε and DDK as the cohesin kinases licensing Rec8 cleavage and established that PP2A protects centromeric Rec8 by opposing these phosphorylations—resolving the kinase/phosphatase logic of stepwise cohesion loss.","evidence":"Phosphomutant/phosphomimetic and kinase-inhibition analyses with MS site mapping in budding and fission yeast","pmids":["20230747","20383139","20581463"],"confidence":"High","gaps":["Polo-like kinase role reassigned but its meiotic contribution remained to be reconciled","How site-specific phosphorylation is spatially controlled unclear"]},{"year":2010,"claim":"Demonstrated by TEV-cleavable knock-in that Rec8 cohesin holds bivalents from birth to ovulation, does not turn over, and is exchanged for Scc1 cohesin at fertilization.","evidence":"TEV-cleavable Rec8/Scc1 knock-in mice with TEV microinjection and live imaging in oocytes","pmids":["20971813"],"confidence":"High","gaps":["Why arrested-oocyte cohesin cannot be renewed not yet explained"]},{"year":2014,"claim":"Identified STAG3 as the stromalin that stabilizes REC8 cohesin and is required for axis compaction, synapsis, and recombination.","evidence":"Hypomorphic Stag3 mouse with cohesin dosage and meiotic phenotype analysis","pmids":["24797475"],"confidence":"High","gaps":["Sufficiency of STAG3 for REC8 function not yet shown","Stoichiometry of the complex undefined"]},{"year":2016,"claim":"Resolved the cohesion lifecycle and axis-density logic: cohesion establishment requires ongoing fetal DNA replication, and high REC8 axis density prevents ectopic inter-sister SC; also revealed a cleavage-independent prophase role of DDK phosphorylation in crossover formation.","evidence":"Inducible Rec8 transgene with TEV readout, super-resolution imaging of hypomorphic Stag3 meiocytes, and phospho-alanine Rec8 series in budding yeast","pmids":["26898469","27170622","27484478","27665783"],"confidence":"High","gaps":["Replication-coupled establishment mechanism not molecularly defined","How DDK phosphorylation promotes crossovers without cleavage unknown"]},{"year":2016,"claim":"Established that the separase-generated C-terminal Rec8 fragment is destroyed by Ate1 arginylation via the N-end rule, a step essential for spermatocyte survival at metaphase I.","evidence":"Germ-cell-specific Ate1 knockout mouse with biochemical fragment-stability analysis","pmids":["26858254"],"confidence":"High","gaps":["Why fragment persistence is lethal mechanistically unclear","Female meiosis dependence not addressed"]},{"year":2018,"claim":"Demonstrated STAG3 is sufficient to drive REC8 nuclear import, chromatin loading and cohesion in somatic cells, and that REC8-STAG3 obeys WAPL/sororin regulation; also linked Rec8 to the SUN protein Mps3 at the nuclear envelope.","evidence":"Ectopic expression, chromatin fractionation and co-IP in HEK293; co-IP and ectopic expression in budding yeast","pmids":["29724914","30417519"],"confidence":"High","gaps":["Physiological role of Rec8-Mps3 tethering in meiosis not established","WAPL/sororin regulation in true meiocytes not directly tested"]},{"year":2020,"claim":"Connected REC8 to recombination hotspot positioning by showing EWSR1 bridges PRDM9-marked hotspots to phosphorylated REC8 on the axis.","evidence":"Co-IP of EWSR1 with PRDM9 and pREC8 plus conditional Ewsr1 KO and ChIP-seq in mouse","pmids":["33175657"],"confidence":"Medium","gaps":["Direct vs. indirect EWSR1-pREC8 interaction unresolved","Single lab without reciprocal validation in meiocytes"]},{"year":2021,"claim":"Established that pericentromeric REC8 cleavage at MI both converts sister kinetochores to bi-orientation and deprotects centromeric cohesion; identified meikin-Plo1 phosphorylation of Rec8 that potentiates Sgo1-PP2A protection; and revealed a gain-of-function capacity of Rec8 to dismantle mitotic centromeres.","evidence":"Spindle-chromosome transfers with site-specific TEV cleavage in oocytes; phospho-site epistasis in fission yeast; Rec8 overexpression in fission yeast and human cells","pmids":["34758289","33888556","33658710"],"confidence":"High","gaps":["How a single cleavage event couples bi-orientation to deprotection mechanistically unclear","Physiological relevance of centromere dismantlement in normal meiosis uncertain"]},{"year":2022,"claim":"Identified Aurora B/C as the mammalian kinases promoting REC8 cleavage and showed Separase levels are tuned by miR-202 to prevent premature REC8 cleavage; refined fission yeast protection logic to Sgo1/Moa1 turnover and Rec8 S449/S450 phosphorylation.","evidence":"Separase biosensor with phosphomutants and Aurora inhibition in oocytes; miR-202 KO with luciferase target validation; non-degradable Sgo1/Moa1 and phosphomutant analysis in fission yeast (preprint)","pmids":["35385691","35712867"],"confidence":"High","gaps":["How Aurora B/C activity is spatially restricted to arms vs centromeres unclear","Integration of CK1/DDK/Aurora inputs on the same substrate not unified"]},{"year":2022,"claim":"Reported a non-meiotic cytoplasmic role in which SUMOylated REC8 stabilizes MAVS/STING by blocking RNF5-mediated ubiquitination to support innate antiviral signaling.","evidence":"Co-IP, ubiquitination assays and REC8 knockdown with viral infection in cells","pmids":["35107381"],"confidence":"Medium","gaps":["Single lab, non-meiotic context not reconciled with germline-restricted expression","Reciprocal/in vivo validation lacking"]},{"year":2024,"claim":"Refined meikin-Plo1 control by dissecting Rec8 phosphosites governing mono-orientation versus cohesion protection, and identified Eso1-dependent meikin-directed acetylation of the cohesin SMC subunit underlying reductional segregation.","evidence":"Non-phosphorylatable Rec8/Psm3 mutants and MS acetylation mapping in fission yeast","pmids":["38448160","38575358"],"confidence":"Medium","gaps":["Conservation of these acetylation/phospho events in mammals untested","Single-lab findings"]},{"year":2025,"claim":"Extended REC8 function to chromatin reorganization at the mitosis-to-meiosis transition, localizing to open promoters and interacting with CCNA2, with distribution shaped by BEND2.","evidence":"REC8 ChIP-seq, BEND2 KO, REC8-CCNA2 co-IP and RNA-seq in mouse","pmids":["41476252"],"confidence":"Medium","gaps":["Direct transcriptional role vs. structural consequence unresolved","Functional significance of REC8-CCNA2 interaction unknown"]},{"year":null,"claim":"How the multiple kinase inputs (CK1, DDK, Aurora B/C, Polo/meikin) are spatially and temporally integrated on REC8 to achieve precise arm-then-centromere cleavage, and whether the somatic innate-immunity and chromatin/transcription roles represent bona fide non-meiotic functions, remain open.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model of combinatorial phosphocode on REC8","Non-meiotic roles lack independent confirmation","Structural model of meiotic cohesin ring assembly absent"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,4,5,18]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[5,16,22]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[11,30,34]}],"localization":[{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[0,4,5,30]},{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[4,5,18]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[22,35]},{"term_id":"GO:0005635","term_label":"nuclear envelope","supporting_discovery_ids":[23]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[22,35]}],"pathway":[{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[0,6,15,25]},{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[7,15,17]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[11,19,30]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[26,34]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[35]}],"complexes":["meiotic cohesin (REC8-SMC1β-SMC3-STAG3)","synaptonemal complex / axial element","REC8-STAG3-PDS5-WAPL-sororin cohesin"],"partners":["SMC1B","SMC3","STAG3","PDS5","WAPL","EWSR1","CCNA2","MAVS"],"other_free_text":[]}},"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 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Centromeric Rec8 persists through meiosis I and is lost at anaphase II. Deletion of rec8 causes premature sister chromatid separation at meiosis I, resulting in equational rather than reductional chromosome segregation, demonstrating that Rec8 maintains sister-chromatid cohesion and orients kinetochores for co-segregation of sisters at meiosis I.\",\n      \"method\": \"Gene deletion, cytological analysis, in situ hybridization, immunolocalization in fission yeast\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with defined chromosome segregation phenotype, replicated across multiple subsequent studies in other organisms\",\n      \"pmids\": [\"10440376\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The S. pombe rec8 gene product is required for linear element (axial core) formation, meiotic chromosome pairing, and sister chromatid cohesion. The rec8-110 mutant shows aberrant linear elements, shortened meiotic prophase, impaired homolog pairing, and precocious sister chromatid separation at meiosis I.\",\n      \"method\": \"Genetic analysis of rec8-110 mutant, cytology, in situ hybridization in S. pombe\",\n      \"journal\": \"Genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (genetics, cytology, in situ hybridization), replicated by subsequent studies\",\n      \"pmids\": [\"8536990\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Fission yeast Rec8p is expressed exclusively during meiosis and localizes to ~100 foci per prophase nucleus. Rec8p exists in an unphosphorylated form early in meiotic prophase and becomes phosphorylated prior to meiosis I (demonstrated using the mei4 mutant blocked before meiosis I). Rec8p persists beyond meiosis I (demonstrated using mes1 mutant blocked before meiosis II). A human ortholog (hREC8) maps to chromosome 14 and is expressed in germ line cells.\",\n      \"method\": \"Western blotting, immunolocalization, analysis of meiotic mutants (mei4, mes1) in S. pombe; cloning of human REC8\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — protein-level evidence with phosphorylation analysis, genetic tools, and cross-species conservation established\",\n      \"pmids\": [\"10207075\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Budding yeast Rec8p modulates meiotic S-phase progression: deletion of REC8 increases S-phase length (~10% in wild-type background; ~30% in spo11Δ background), demonstrating that Rec8p is a key coordinator of meiotic interhomolog and intersister interactions that feeds back on DNA replication progression.\",\n      \"method\": \"Genetic deletion analysis, S-phase length measurement in budding yeast\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic deletion with quantitative S-phase measurements, single lab\",\n      \"pmids\": [\"10691741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"In rat meiocytes, REC8 appears before premeiotic S phase and forms axial element-like structures (REC8-AEs) before other cohesin subunits (SMC1beta, SMC3) or axial element proteins (SCP2, SCP3) are incorporated, suggesting REC8 provides the initial scaffold for axial element assembly. REC8 persists along chromosome arms until anaphase I and near centromeres until anaphase II, while SMC1beta, SMC3, SCP2, and SCP3 disappear from arms at metaphase I. RAD51 and/or DMC1 co-immunoprecipitates with REC8, suggesting REC8 also provides a basis for recombination complex assembly.\",\n      \"method\": \"Immunofluorescence, co-immunoprecipitation, temporal analysis of protein incorporation into axial elements in rat spermatocytes\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP, detailed immunofluorescence staging, multiple proteins analyzed, independent of S. pombe work\",\n      \"pmids\": [\"12615909\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Mammalian REC8 associates with SMC1beta and SMC3 (but not SMC1alpha) and with synaptonemal complex component SCP3, forming a meiosis-specific cohesin complex. REC8 is selectively lost from chromosome arms at the metaphase I-to-anaphase I transition while persisting at centromeres until anaphase II, providing a molecular basis for the stepwise loss of cohesion in mammalian meiosis.\",\n      \"method\": \"Immunoprecipitation, immunohistochemistry, Western blotting in mouse testis\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — co-IP demonstrating complex composition, immunolocalization across meiotic stages, replicated by other labs\",\n      \"pmids\": [\"12759374\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Separase activation and resultant Rec8 cleavage are required for meiotic chromosome segregation in fission yeast. A non-cleavable form of Rec8 blocks homolog disjunction at meiosis I. Rec8 forms distinct complexes along chromosome arms (with Rec11/SA3) versus centromeres (with Psc3/SA1-SA2), and cleavage of arm Rec8 is required for homolog segregation at meiosis I while centromeric Rec8 cleavage is required for sister segregation at meiosis II.\",\n      \"method\": \"Non-cleavable Rec8 mutant expression, genetic depletion of Rec11, chromosome segregation analysis in S. pombe\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis of cleavage sites combined with genetic epistasis, replicated by subsequent studies in multiple organisms\",\n      \"pmids\": [\"14532136\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Mouse REC8 knockout (both sexes) causes sterility due to germ cell failure. In the absence of REC8, early chromosome pairing appears normal but synapsis occurs between sister chromatids rather than homologs, demonstrating that a major role of REC8 in mammalian meiosis is to restrict synaptonemal complex formation to between homologous chromosomes.\",\n      \"method\": \"Rec8 knockout mouse, cytological analysis of meiotic chromosomes in both sexes\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — complete KO with defined cellular phenotype (inter-sister synapsis), replicated in multiple studies\",\n      \"pmids\": [\"15935783\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"In budding yeast, phosphorylation of the cohesin subunit Rec8 contributes to the stepwise removal of cohesin during meiosis. Both Sgo1 (cohesin protector) and meiotic recombination cooperate with Rec8 phosphorylation to establish the meiotic chromosome segregation pattern.\",\n      \"method\": \"Phosphomutant Rec8 analysis, genetic manipulation of Sgo1 and recombination pathways, chromosome spreading in S. cerevisiae\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — phosphomutant analysis with multiple orthogonal genetic approaches, published in Nature\",\n      \"pmids\": [\"16672979\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"In mouse oocytes, loss of arm REC8 (armRec8) is required for homolog separation at meiosis I, while loss of centromeric REC8 (cenRec8) is required for sister chromatid separation at meiosis II. Microinjection of anti-Rec8 antibody into metaphase I oocytes inhibits homolog separation but not polar body emission. Neither loss is required for spindle elongation or cytokinesis.\",\n      \"method\": \"Microinjection of anti-Rec8 antibody into mouse oocytes, immunofluorescence, pharmacological inhibitors\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — antibody microinjection with functional readout, single lab with multiple conditions tested\",\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) causes sterility in male mice with failure of the first meiotic division, demonstrating that Rec8 cleavage by separase is required for chiasma resolution in mammalian meiosis.\",\n      \"method\": \"In vitro cleavage assay with hyper-phosphorylated Rec8, transgenic non-cleavable Rec8 mouse, chromosome spreads, DNA content analysis\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution of separase cleavage combined with in vivo non-cleavable mutant analysis\",\n      \"pmids\": [\"19625504\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In budding yeast, Spo11 initially accumulates around centromeres during premeiotic S phase, then redistributes to chromosome arms where a substantial fraction co-localizes with Rec8 binding sites. Deletion of REC8 alters the distribution of Spo11 at centromeres and specific chromosomal arm intervals, demonstrating that Rec8 prearranges the distribution of Spo11 along meiotic chromosomes to regulate DSB formation.\",\n      \"method\": \"ChIP with high-density tiling arrays (genome-wide Spo11 and Rec8 localization), REC8 deletion analysis in S. cerevisiae\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genome-wide ChIP analysis with genetic deletion, single lab\",\n      \"pmids\": [\"19439448\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Multiple phosphorylation sites within Rec8 and two kinases — casein kinase 1δ/ε (CK1δ/ε) and Dbf4-dependent Cdc7 kinase (DDK) — are required for Rec8 cleavage by separase and meiosis I nuclear division in budding yeast. Rec8 with phosphomimetic mutations is no longer protected from separase at centromeres even when kinases are inhibited. PP2A protects centromeric cohesion by opposing CK1δ/ε- and DDK-dependent phosphorylation of Rec8.\",\n      \"method\": \"Phosphomutant and phosphomimetic Rec8 analysis, kinase inhibition, kinase deletion, meiotic division assays in S. cerevisiae\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple phosphomutants, two different kinases identified, phosphomimetic rescue experiments, mechanistically rigorous\",\n      \"pmids\": [\"20230747\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In fission yeast, casein kinase 1 (CK1) ortholog Hhp2 (not Polo-like kinase as previously thought) acts as the cohesin kinase that promotes Rec8 cleavage during meiosis. Forced pericentromeric localization of excess Hhp2 abrogates Sgo1-PP2A protection of centromeric Rec8. The balance between Rec8 phosphorylation by CK1 and dephosphorylation by Sgo1-PP2A regulates the stepwise loss of chromosomal cohesion.\",\n      \"method\": \"Genetic screen for anti-shugoshin factors, forced localization of CK1, phosphorylation analysis, meiotic chromosome segregation assays in S. pombe\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic screen plus multiple orthogonal functional experiments, establishes kinase identity, published in Nature Cell Biology\",\n      \"pmids\": [\"20383139\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Casein kinase 1 (CK1) δ/ε isoforms Hhp1 and Hhp2 are required for full levels of Rec8 phosphorylation and efficient removal of Rec8 at anaphase I onset in fission yeast. Rec8 phosphorylation sites were mapped by mass spectrometry; phosphorylation is required for proper chromosome disjunction.\",\n      \"method\": \"Mass spectrometry phosphorylation site mapping, CK1 mutant analysis, Rec8 phosphorylation quantification in S. pombe\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mass spectrometry site identification plus genetic validation, corroborates Ishiguro et al. 2010 findings\",\n      \"pmids\": [\"20581463\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Rec8-containing cohesin (dependent on kleisin subunit Rec8) holds bivalent chromosomes together in mouse oocytes from birth until ovulation. TEV protease cleavage of Rec8 (but not Scc1) triggers chiasmata resolution during meiosis I and sister centromere disjunction during meiosis II. There is a dramatic transition from Rec8- to Scc1-containing cohesin at fertilization. Cohesin does not turn over during ≥2 weeks of oocyte growth.\",\n      \"method\": \"TEV-cleavable Rec8 and Scc1 knock-in mice, microinjection of TEV protease into oocytes, confocal live-cell imaging, ectopic Rec8 transgene activation\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution-level genetic engineering with live imaging, multiple orthogonal experiments in a single rigorous study\",\n      \"pmids\": [\"20971813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"STAG3 stabilizes REC8 cohesin complexes during meiosis. In hypomorphic Stag3 mice with severely reduced STAG3, REC8 cohesin levels are reduced and meiocytes display chromosome axis compaction defects, aberrant synapsis, and impaired recombination. STAG3-REC8 cohesin complexes have a critical role in meiotic chromosome structure and function.\",\n      \"method\": \"Hypomorphic Stag3 mouse model, immunofluorescence, analysis of cohesin subunit dosage and meiotic phenotypes\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo hypomorphic allele with defined molecular phenotype (REC8 destabilization), multiple cellular readouts\",\n      \"pmids\": [\"24797475\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Cohesin established by Rec8 in fetal mouse oocytes is maintained without detectable turnover in oocytes arrested for months (dictyate stage). Rec8 activated during DNA replication in fetal oocytes establishes cohesion, but Rec8 activated in already-arrested oocytes does not establish new cohesion despite cohesin synthesis, demonstrating that cohesion establishment requires ongoing DNA replication.\",\n      \"method\": \"Tamoxifen-inducible Cre activation of Rec8 transgene in fetal vs. arrested oocytes, TEV cleavage assay, live-cell imaging\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — inducible genetic system with TEV cleavage readout and live imaging, multiple time points tested\",\n      \"pmids\": [\"26898469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"High density of REC8 cohesin complexes along chromosome axes is required to constrain sister chromatid axes and prevent illegitimate inter-sister synaptonemal complex formation. Using super-resolution microscopy, REC8 foci are separated by <15% of total axis length in wild-type meiocytes; reduced cohesin levels lead to local axial separation and ectopic SC formation specifically at REC8-free sites.\",\n      \"method\": \"Super-resolution microscopy (STED/SIM) in hypomorphic Stag3 mouse meiocytes with reduced REC8 levels\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — super-resolution imaging with quantitative analysis, single lab\",\n      \"pmids\": [\"27170622\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"During meiotic prophase, Rec8 phosphorylation by Dbf4-dependent Cdc7 kinase (DDK) promotes crossover-specific events independently of cohesin cleavage. Rec8 phospho-mutants (with 6, 24, or 29 alanine substitutions) show normal axis formation and recombination initiation but defective crossover formation, with severity proportional to number of substitutions. Inhibition of DDK (but not Hrr25/CK1 or Cdc5/PLK) during prophase recapitulates rec8 phospho-mutant phenotypes.\",\n      \"method\": \"Rec8 phospho-alanine mutants, timed kinase inhibition, crossover and non-crossover recombination analysis in S. cerevisiae\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — phosphomutant series with separation-of-function analysis, single lab\",\n      \"pmids\": [\"27484478\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"RAD21L and REC8 meiotic cohesin subunits occupy distinct positions within the synaptonemal complex as determined by 3D-SIM super-resolution microscopy: both localize at connection sites between lateral elements and transverse filaments of pachynema, with RAD21L positioned interior to REC8 sites. RAD21L (but not REC8) forms bridges between unsynapsed axial elements at zygonema and shows greater overlap with recombination intermediates.\",\n      \"method\": \"3D-SIM super-resolution microscopy of spermatocyte synaptonemal complexes\",\n      \"journal\": \"The Journal of reproduction and development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — super-resolution structural localization, single lab\",\n      \"pmids\": [\"27665783\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The separase-cleaved C-terminal fragment of mammalian Rec8 bears N-terminal Glu, which is arginylated by Ate1 R-transferase and then degraded by the N-end rule pathway. Male germ cell-specific Ate1 knockout mice are nearly infertile due to massive apoptotic death of spermatocytes at metaphase I, caused by failure to destroy the C-terminal Rec8 fragment.\",\n      \"method\": \"Germ cell-specific Ate1 knockout mouse, biochemical analysis of Rec8 fragments, in vivo protein stability assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — conditional KO combined with biochemical mechanism identification (N-end rule arginylation of Rec8 cleavage product)\",\n      \"pmids\": [\"26858254\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"When expressed in somatic (Hek293) cells, Rec8 has no affinity for Stag1 or Stag2 and remains cytoplasmic, but co-expression of Stag3 is sufficient for Rec8 to enter the nucleus, load onto chromatin, and replace Scc1 for sister chromatid cohesion. Rec8-Stag3 cohesin physically interacts with Pds5, Wapl, and sororin, and is susceptible to Wapl-dependent ring opening and sororin-mediated protection.\",\n      \"method\": \"Ectopic expression in Hek293 cells, chromatin fractionation, co-immunoprecipitation, sister chromatid cohesion assays\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (localization, chromatin loading, co-IP, functional rescue), identifies Stag3 as required partner\",\n      \"pmids\": [\"29724914\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Meiosis-specific cohesin component Rec8 binds to Mps3 SUN domain 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, requiring the cohesin regulator Rad61/Wpl1 (WAPL).\",\n      \"method\": \"Co-immunoprecipitation, ectopic Rec8 expression in mitotic yeast, fluorescence microscopy of nuclear envelope localization in S. cerevisiae\",\n      \"journal\": \"Genes to cells : devoted to molecular & cellular mechanisms\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP combined with ectopic expression and localization experiments, 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 before meiosis onset causes meiotic arrest with decreased H3K4/K36 trimethylation at hotspots, impaired DSB repair, and reduced crossover number, suggesting EWSR1 links PRDM9-bound hotspots to the chromosome axis through pREC8.\",\n      \"method\": \"Co-immunoprecipitation of EWSR1 with PRDM9 and pREC8, conditional Ewsr1 knockout mouse, ChIP-seq for histone methylation\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP establishing protein interactions plus conditional KO, single lab\",\n      \"pmids\": [\"33175657\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cleavage of pericentromeric REC8 by Separase at meiosis I is necessary not only for converting sister kinetochores from co-orientation to bi-orientation at meiosis II but also for deprotection of pericentromeric cohesion. Selective cleavage of REC8 in the vicinity of kinetochores in univalent chromosomes is sufficient to destroy co-orientation. This was demonstrated by transferring spindle-chromosome complexes between meiosis I and II in mouse oocytes.\",\n      \"method\": \"Spindle-chromosome complex transfers between meiosis I and II oocytes, TEV cleavage of REC8, live imaging in mouse oocytes\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution-level experiment (SCC transfers) combined with site-specific TEV cleavage and live imaging\",\n      \"pmids\": [\"34758289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Overexpression of Rec8 (or Spo11) in proliferating fission yeast and human cells leads to the loss of mitotic kinetochores, demonstrating that Rec8 can dismantle centromeric chromatin. Specific nucleosome remodeling factors mediate centromere dismantlement by Rec8. This centromere dismantlement is normally observable only in mutants lacking the telomere bouquet.\",\n      \"method\": \"Overexpression of Rec8 in fission yeast and human cells, kinetochore loss assays, identification of mediating nucleosome remodeling factors\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain-of-function overexpression in two cell types, single lab but published in Nature with functional mechanistic follow-up\",\n      \"pmids\": [\"33658710\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Meikin (Moa1 in fission yeast) associates with Plo1 kinase and phosphorylates Rec8, with a key phosphorylation site required for cohesion protection. The phosphorylation of Rec8 by Moa1-Plo1 potentiates PP2A activity associated with Sgo1, leading to dephosphorylation of Rec8 at another site, thereby preventing separase cleavage of centromeric Rec8.\",\n      \"method\": \"Genetic analysis, phosphorylation site mapping, epistasis between moa1, plo1, sgo1 and rec8 phospho-mutants in S. pombe\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — identification of specific phosphorylation sites with phosphomutant analysis and genetic epistasis, mechanistic pathway established\",\n      \"pmids\": [\"33888556\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Aurora B/C kinase activities promote REC8 phosphorylation and cleavage in mammalian oocytes. Through phosphomutant analysis using a separase biosensor in live mouse oocytes, specific phosphorylation sites in Rec8 that promote its cleavage were identified. Inhibition of Aurora B/C during meiotic maturation impairs endogenous Rec8 phosphorylation and chromosome segregation.\",\n      \"method\": \"Fluorescent biosensor for Rec8 cleavage, microinjection into mouse oocytes, phosphomutant analysis, Aurora B/C inhibitor treatment, live imaging\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — biosensor reconstitution in live cells combined with phosphomutant analysis and kinase inhibition, identifies Aurora B/C as the relevant mammalian kinase\",\n      \"pmids\": [\"35385691\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"MicroRNA-202 (miR-202) represses Separase mRNA, thereby upregulating REC8 protein levels. Loss of miR-202 results in premature SEPARASE-mediated REC8 cleavage, spermatocyte apoptosis, and disrupted meiotic prophase I (synapsis and crossover defects, inter-sister chromatid synapses). Separase mRNA is a direct target of miR-202.\",\n      \"method\": \"miR-202 knockout mice, luciferase reporter assays demonstrating Separase as direct miR-202 target, immunofluorescence of REC8 and synapsis markers\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse phenotype with direct target validation, single lab; mechanism is indirect (through Separase regulation)\",\n      \"pmids\": [\"35712867\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Cleavage-independent dissociation of Rec8 cohesin from chromosomes occurs during meiotic prophase I in response to DSBs. Genome-wide Rec8 binding profiles change from mid- to late-prophase I, and the ratio of Rec8 dissociation per chromosome correlates with meiotic DSB density. In the spo11 mutant deficient in DSB formation, Rec8 distribution does not change in late prophase I, demonstrating a DSB-dependent regulatory pathway for global Rec8-cohesin binding.\",\n      \"method\": \"Genome-wide ChIP-seq of Rec8 at mid- and late-prophase I, spo11 mutant analysis in S. cerevisiae\",\n      \"journal\": \"Genes to cells : devoted to molecular & cellular mechanisms\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genome-wide ChIP with genetic validation using spo11 mutant, single lab\",\n      \"pmids\": [\"37968127\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Plo1 (polo-like kinase) associated with meikin (Moa1) phosphorylates Rec8 at specific sites to regulate sister kinetochore mono-orientation at meiosis I. Non-phosphorylatable mutations at these Plo1 phosphorylation sites in Rec8 (and Psm3) cause specific mono-orientation defects without affecting cohesion protection, enabling genetic dissection of these two meikin functions.\",\n      \"method\": \"Identification of Plo1 phosphorylation sites in Rec8 and Psm3, non-phosphorylatable mutant analysis, kinetochore orientation assays in S. pombe\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — phosphomutant analysis with specific functional readout, single lab\",\n      \"pmids\": [\"38448160\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Acetyltransferase Eso1 acetylates meiosis-specific Rec8 cohesin complexes at a new site, Psm3-K1013, which is largely dependent on the meiotic kinetochore factor meikin (Moa1). This acetylation cooperates with canonical Psm3-K105/K106 acetylation and plays a crucial role in establishing reductional chromosome segregation in meiosis.\",\n      \"method\": \"Purification of centromeric Rec8 cohesin complexes from meiotic cells, mass spectrometry identification of acetylation site, genetic analysis of Psm3-K1013 mutants in S. pombe\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — biochemical purification with MS identification plus genetic validation, single lab\",\n      \"pmids\": [\"38575358\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In S. pombe, Sgo1 and Moa1 are degraded during anaphase I by the APC/C-Slp1 pathway. Non-degradable Sgo1 and Moa1 expressed in meiosis II can protect Rec8 cohesin. Sgo1 localization and phosphorylation of Rec8 at S449 and S450 are necessary and sufficient events for protecting Rec8 cohesin, with absence of either event leading to Rec8 deprotection at meiosis II.\",\n      \"method\": \"Non-degradable Sgo1/Moa1 mutant expression in meiosis II, phosphomutant analysis of Rec8 S449/S450, live imaging in S. pombe\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — phosphomutant and non-degradable protein analysis with functional readout, preprint not yet peer-reviewed\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"REC8-cohesin preferentially localizes to open promoter regions of genes involved in spermatogonial differentiation and meiosis at early meiosis (preleptonema to zygonema). REC8-cohesin genomic distribution is altered by BEND2 knockout. REC8 interacts with mitotic cyclin CCNA2. These findings demonstrate that REC8-cohesin participates in chromatin reorganization and transcription regulation at the mitosis-to-meiosis transition.\",\n      \"method\": \"ChIP-seq for REC8, BEND2 KO mice, co-immunoprecipitation of REC8 with CCNA2, RNA-seq\",\n      \"journal\": \"Genomics, proteomics & bioinformatics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genome-wide ChIP combined with KO and co-IP, single lab\",\n      \"pmids\": [\"41476252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"REC8 interacts with MAVS and STING in the cytoplasm and inhibits their K48-linked ubiquitination triggered by RNF5, stabilizing these innate immune signaling proteins. SUMOylated REC8 translocates from nucleus to cytoplasm during viral infection and promotes recruitment of TBK1 to MAVS and STING. Knockdown of REC8 impairs innate immune responses against VSV, NDV, and HSV.\",\n      \"method\": \"Co-immunoprecipitation of REC8 with MAVS and STING, ubiquitination assays, REC8 knockdown with viral infection assays, REC8 SUMOylation and localization analysis\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple co-IPs with functional validation by knockdown, single lab, non-meiotic context\",\n      \"pmids\": [\"35107381\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"REC8 is the meiosis-specific α-kleisin subunit of the cohesin complex that forms a ring with SMC1β/SMC3 and STAG3 to mediate sister chromatid cohesion; it provides the structural scaffold for axial/lateral element assembly, restricts synaptonemal complex formation to between homologs, guides Spo11-mediated DSB distribution, and must be sequentially cleaved by separase — first on chromosome arms (triggered by CK1δ/ε- and DDK-dependent phosphorylation, including Aurora B/C in mammals) to resolve chiasmata at meiosis I, then at centromeres at meiosis II — while centromeric REC8 is protected during meiosis I by shugoshin-PP2A acting against these kinases, a mechanism reinforced by meikin-Plo1–dependent phosphorylation at Rec8-S450 that potentiates PP2A dephosphorylation at a second site; cohesin established during fetal DNA replication is maintained without turnover through prolonged oocyte arrest, and the separase-generated C-terminal Rec8 fragment is rapidly degraded via N-terminal arginylation by Ate1 and the N-end rule pathway.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"REC8 is the meiosis-specific α-kleisin subunit of cohesin that mediates sister-chromatid cohesion and organizes the meiotic chromosome axis, and whose regulated cleavage drives the two-step chromosome segregation of meiosis [#0, #5, #6]. Loss of REC8 causes premature sister separation and equational rather than reductional segregation at meiosis I, establishing its core role in maintaining cohesion and orienting sister kinetochores for co-segregation [#0]. In mammals, REC8 assembles with SMC1β, SMC3 and the stromalin STAG3 into a meiosis-specific cohesin; STAG3 stabilizes REC8 and is necessary and sufficient to license REC8 chromatin loading and cohesion activity, even ectopically in somatic cells where REC8-STAG3 engages PDS5, WAPL and sororin [#5, #16, #22]. REC8 is laid down before other cohesin and axial-element proteins to scaffold axial/lateral element assembly, and a high density of REC8 along sister axes restricts synaptonemal complex formation to between homologs rather than between sisters [#4, #7, #18]; it further patterns Spo11-dependent DSB distribution and supports crossover formation [#11, #19]. Stepwise cohesion loss is controlled by phosphoregulation: casein kinase 1 (CK1δ/ε) and DDK phosphorylate REC8 to license separase cleavage, first on chromosome arms to resolve chiasmata at meiosis I and later at centromeres at meiosis II [#6, #10, #12, #14], while centromeric REC8 is protected by shugoshin-PP2A opposing these kinases, a protection potentiated by meikin-Polo kinase phosphorylation of REC8 at S450/S449 [#13, #27, #33]. In mammalian oocytes Aurora B/C phosphorylates REC8 to promote its cleavage, and cohesin established during fetal DNA replication persists without turnover through prolonged dictyate arrest [#15, #17, #28]. The separase-generated C-terminal REC8 fragment is destroyed via N-terminal arginylation by Ate1 and the N-end rule pathway, a step required for spermatocyte survival [#21]. Beyond meiosis, REC8 has been implicated in cytoplasmic stabilization of MAVS/STING innate immune signaling [#35].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Established that the rec8 gene product is required for the integrated meiotic program—axial core formation, homolog pairing, and sister cohesion—defining it as a central organizer rather than a single-task factor.\",\n      \"evidence\": \"Genetic and cytological analysis of the rec8-110 mutant in fission yeast\",\n      \"pmids\": [\"8536990\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular identity of Rec8 as a cohesin subunit not yet defined\", \"No protein-level or biochemical characterization\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Defined Rec8 as a meiosis-specific cohesin whose persistence at centromeres through meiosis I and loss at anaphase II underlies reductional segregation, answering how sisters co-segregate at MI.\",\n      \"evidence\": \"Gene deletion, immunolocalization and in situ hybridization in fission yeast; cloning of human REC8\",\n      \"pmids\": [\"10440376\", \"10207075\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of differential arm vs. centromere cohesion loss unknown\", \"Phosphorylation function not yet linked to cleavage\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Showed Rec8 feeds back on meiotic S-phase progression, linking cohesion establishment to replication timing.\",\n      \"evidence\": \"REC8 deletion and S-phase length measurement in budding yeast\",\n      \"pmids\": [\"10691741\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of S-phase coordination unresolved\", \"Single genetic background\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Established the mammalian REC8 cohesin composition (SMC1β/SMC3, with SCP3 association) and demonstrated that REC8 is incorporated first to scaffold axial element assembly and is lost stepwise from arms then centromeres.\",\n      \"evidence\": \"Immunoprecipitation, immunofluorescence staging and co-IP in rat and mouse meiocytes\",\n      \"pmids\": [\"12615909\", \"12759374\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"STAG3 not yet identified as the meiotic stromalin partner\", \"Functional consequence of RAD51/DMC1 co-IP unestablished\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstrated that separase cleavage of Rec8 is required for segregation, with distinct arm vs. centromere complexes resolved at MI vs MII—the molecular basis of two-step segregation.\",\n      \"evidence\": \"Non-cleavable Rec8 mutant and Rec11 depletion in fission yeast\",\n      \"pmids\": [\"14532136\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinases licensing cleavage not yet identified\", \"Protection mechanism at centromeres undefined\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Defined a major mammalian REC8 function as restricting synapsis to homologs, since its loss causes inter-sister synapsis and sterility.\",\n      \"evidence\": \"Rec8 knockout mouse cytology in both sexes\",\n      \"pmids\": [\"15935783\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative axis-density requirement not addressed\", \"Recombination/DSB phenotype not detailed\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Showed Rec8 phosphorylation cooperates with shugoshin and recombination to set the stepwise cohesion-removal pattern, and confirmed in oocytes that arm vs. centromeric Rec8 loss drives MI vs MII separation.\",\n      \"evidence\": \"Phosphomutant analysis with Sgo1/recombination genetics in budding yeast; anti-Rec8 antibody microinjection in mouse oocytes\",\n      \"pmids\": [\"16672979\", \"16855401\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific kinases not yet pinned down\", \"Antibody microinjection lacks site resolution\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Reconstituted that separase cleaves Rec8 only when hyper-phosphorylated and showed cleavage is required in vivo for chiasma resolution, coupling phosphoregulation directly to cleavage.\",\n      \"evidence\": \"In vitro cleavage assay and non-cleavable Rec8 transgenic mice; ChIP tiling of Spo11/Rec8 in budding yeast\",\n      \"pmids\": [\"19625504\", \"19439448\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the relevant in vivo kinase(s) still open\", \"Mechanism of Rec8-directed Spo11 prearrangement unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identified CK1δ/ε and DDK as the cohesin kinases licensing Rec8 cleavage and established that PP2A protects centromeric Rec8 by opposing these phosphorylations—resolving the kinase/phosphatase logic of stepwise cohesion loss.\",\n      \"evidence\": \"Phosphomutant/phosphomimetic and kinase-inhibition analyses with MS site mapping in budding and fission yeast\",\n      \"pmids\": [\"20230747\", \"20383139\", \"20581463\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Polo-like kinase role reassigned but its meiotic contribution remained to be reconciled\", \"How site-specific phosphorylation is spatially controlled unclear\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrated by TEV-cleavable knock-in that Rec8 cohesin holds bivalents from birth to ovulation, does not turn over, and is exchanged for Scc1 cohesin at fertilization.\",\n      \"evidence\": \"TEV-cleavable Rec8/Scc1 knock-in mice with TEV microinjection and live imaging in oocytes\",\n      \"pmids\": [\"20971813\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why arrested-oocyte cohesin cannot be renewed not yet explained\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identified STAG3 as the stromalin that stabilizes REC8 cohesin and is required for axis compaction, synapsis, and recombination.\",\n      \"evidence\": \"Hypomorphic Stag3 mouse with cohesin dosage and meiotic phenotype analysis\",\n      \"pmids\": [\"24797475\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Sufficiency of STAG3 for REC8 function not yet shown\", \"Stoichiometry of the complex undefined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Resolved the cohesion lifecycle and axis-density logic: cohesion establishment requires ongoing fetal DNA replication, and high REC8 axis density prevents ectopic inter-sister SC; also revealed a cleavage-independent prophase role of DDK phosphorylation in crossover formation.\",\n      \"evidence\": \"Inducible Rec8 transgene with TEV readout, super-resolution imaging of hypomorphic Stag3 meiocytes, and phospho-alanine Rec8 series in budding yeast\",\n      \"pmids\": [\"26898469\", \"27170622\", \"27484478\", \"27665783\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Replication-coupled establishment mechanism not molecularly defined\", \"How DDK phosphorylation promotes crossovers without cleavage unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Established that the separase-generated C-terminal Rec8 fragment is destroyed by Ate1 arginylation via the N-end rule, a step essential for spermatocyte survival at metaphase I.\",\n      \"evidence\": \"Germ-cell-specific Ate1 knockout mouse with biochemical fragment-stability analysis\",\n      \"pmids\": [\"26858254\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why fragment persistence is lethal mechanistically unclear\", \"Female meiosis dependence not addressed\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrated STAG3 is sufficient to drive REC8 nuclear import, chromatin loading and cohesion in somatic cells, and that REC8-STAG3 obeys WAPL/sororin regulation; also linked Rec8 to the SUN protein Mps3 at the nuclear envelope.\",\n      \"evidence\": \"Ectopic expression, chromatin fractionation and co-IP in HEK293; co-IP and ectopic expression in budding yeast\",\n      \"pmids\": [\"29724914\", \"30417519\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological role of Rec8-Mps3 tethering in meiosis not established\", \"WAPL/sororin regulation in true meiocytes not directly tested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Connected REC8 to recombination hotspot positioning by showing EWSR1 bridges PRDM9-marked hotspots to phosphorylated REC8 on the axis.\",\n      \"evidence\": \"Co-IP of EWSR1 with PRDM9 and pREC8 plus conditional Ewsr1 KO and ChIP-seq in mouse\",\n      \"pmids\": [\"33175657\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs. indirect EWSR1-pREC8 interaction unresolved\", \"Single lab without reciprocal validation in meiocytes\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Established that pericentromeric REC8 cleavage at MI both converts sister kinetochores to bi-orientation and deprotects centromeric cohesion; identified meikin-Plo1 phosphorylation of Rec8 that potentiates Sgo1-PP2A protection; and revealed a gain-of-function capacity of Rec8 to dismantle mitotic centromeres.\",\n      \"evidence\": \"Spindle-chromosome transfers with site-specific TEV cleavage in oocytes; phospho-site epistasis in fission yeast; Rec8 overexpression in fission yeast and human cells\",\n      \"pmids\": [\"34758289\", \"33888556\", \"33658710\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How a single cleavage event couples bi-orientation to deprotection mechanistically unclear\", \"Physiological relevance of centromere dismantlement in normal meiosis uncertain\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified Aurora B/C as the mammalian kinases promoting REC8 cleavage and showed Separase levels are tuned by miR-202 to prevent premature REC8 cleavage; refined fission yeast protection logic to Sgo1/Moa1 turnover and Rec8 S449/S450 phosphorylation.\",\n      \"evidence\": \"Separase biosensor with phosphomutants and Aurora inhibition in oocytes; miR-202 KO with luciferase target validation; non-degradable Sgo1/Moa1 and phosphomutant analysis in fission yeast (preprint)\",\n      \"pmids\": [\"35385691\", \"35712867\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How Aurora B/C activity is spatially restricted to arms vs centromeres unclear\", \"Integration of CK1/DDK/Aurora inputs on the same substrate not unified\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Reported a non-meiotic cytoplasmic role in which SUMOylated REC8 stabilizes MAVS/STING by blocking RNF5-mediated ubiquitination to support innate antiviral signaling.\",\n      \"evidence\": \"Co-IP, ubiquitination assays and REC8 knockdown with viral infection in cells\",\n      \"pmids\": [\"35107381\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab, non-meiotic context not reconciled with germline-restricted expression\", \"Reciprocal/in vivo validation lacking\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Refined meikin-Plo1 control by dissecting Rec8 phosphosites governing mono-orientation versus cohesion protection, and identified Eso1-dependent meikin-directed acetylation of the cohesin SMC subunit underlying reductional segregation.\",\n      \"evidence\": \"Non-phosphorylatable Rec8/Psm3 mutants and MS acetylation mapping in fission yeast\",\n      \"pmids\": [\"38448160\", \"38575358\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Conservation of these acetylation/phospho events in mammals untested\", \"Single-lab findings\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Extended REC8 function to chromatin reorganization at the mitosis-to-meiosis transition, localizing to open promoters and interacting with CCNA2, with distribution shaped by BEND2.\",\n      \"evidence\": \"REC8 ChIP-seq, BEND2 KO, REC8-CCNA2 co-IP and RNA-seq in mouse\",\n      \"pmids\": [\"41476252\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct transcriptional role vs. structural consequence unresolved\", \"Functional significance of REC8-CCNA2 interaction unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the multiple kinase inputs (CK1, DDK, Aurora B/C, Polo/meikin) are spatially and temporally integrated on REC8 to achieve precise arm-then-centromere cleavage, and whether the somatic innate-immunity and chromatin/transcription roles represent bona fide non-meiotic functions, remain open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model of combinatorial phosphocode on REC8\", \"Non-meiotic roles lack independent confirmation\", \"Structural model of meiotic cohesin ring assembly absent\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 4, 5, 18]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [5, 16, 22]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [11, 30, 34]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [0, 4, 5, 30]},\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [4, 5, 18]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [22, 35]},\n      {\"term_id\": \"GO:0005635\", \"supporting_discovery_ids\": [23]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [22, 35]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [0, 6, 15, 25]},\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [7, 15, 17]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [11, 19, 30]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [26, 34]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [35]}\n    ],\n    \"complexes\": [\n      \"meiotic cohesin (REC8-SMC1β-SMC3-STAG3)\",\n      \"synaptonemal complex / axial element\",\n      \"REC8-STAG3-PDS5-WAPL-sororin cohesin\"\n    ],\n    \"partners\": [\n      \"SMC1B\",\n      \"SMC3\",\n      \"STAG3\",\n      \"PDS5\",\n      \"WAPL\",\n      \"EWSR1\",\n      \"CCNA2\",\n      \"MAVS\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}