{"gene":"STAG3","run_date":"2026-04-28T20:42:08","timeline":{"discoveries":[{"year":2001,"finding":"STAG3 physically interacts with SMC1 and SMC3 (structural maintenance of chromosome proteins) and functions as a sister chromatid arm cohesin specific to mammalian meiosis I, localizing to the interchromatid domain in metaphase I and to the axial/lateral element of the synaptonemal complex in prophase I.","method":"Co-immunoprecipitation; immunofluorescence localization in meiotic cells","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP with SMC1/SMC3 plus direct localization experiments, foundational paper with 210 citations","pmids":["11483963"],"is_preprint":false},{"year":2000,"finding":"STAG3 contains a stromalin conservative domain (SCD) and localizes to the synaptonemal complex specifically in testis, suggesting a cohesin-like role in chromosome pairing and synaptonemal complex maintenance during pachytene.","method":"cDNA cloning; immunolocalization in spermatocytes; sequence analysis","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 — direct immunolocalization with domain characterization; 117 citations, foundational identification paper","pmids":["10698974"],"is_preprint":false},{"year":2014,"finding":"STAG3 is required for the stability and chromosomal axis loading of all meiosis-specific cohesin subunits (SMC1β, RAD21L, REC8); loss of STAG3 reduces protein levels of these subunits and disrupts their localization to chromosome axes, causing aberrant DNA repair, failed homolog synapsis, disrupted pericentromeric heterochromatin clustering, and early prophase I arrest in both sexes.","method":"Stag3 knockout mouse; immunofluorescence; meiotic spread analysis; genetic epistasis with Smc1β, Rec8, Rad21l mutants","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined cellular phenotypes and epistasis analysis, replicated across multiple cohesin subunits; 104 citations","pmids":["24992337"],"is_preprint":false},{"year":2014,"finding":"STAG3 deficiency causes complete failure of axial element (AE) formation in meiosis — SYCP3 forms only dot-like structures, HORMAD1 is diffusely distributed, and SYCP1 is largely absent — demonstrating STAG3 is the key STAG cohesin for meiotic chromosome architecture, centromeric and telomeric sister chromatid cohesion.","method":"STAG3-deficient mouse (both sexes); immunofluorescence of synaptonemal complex proteins; meiotic spread analysis","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — clean KO with multiple orthogonal structural markers; 86 citations","pmids":["24797474"],"is_preprint":false},{"year":2014,"finding":"STAG3 preferentially stabilizes REC8-containing cohesin complexes; three α-kleisins (REC8, RAD21L, RAD21) show different dosage-dependent requirements for STAG3, and STAG3-REC8 complexes have a critical role in meiotic chromosome axis compaction and synapsis.","method":"Stag3 hypomorphic mouse allele; immunofluorescence; co-immunoprecipitation of cohesin subunits; meiotic phenotype analysis","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1-2 — Co-IP combined with in vivo hypomorphic model and multiple readouts; 83 citations","pmids":["24797475"],"is_preprint":false},{"year":2014,"finding":"In male Stag3 knockout mice, meiotic arrest occurs at zygonema with shortened axial elements, partial loss of centromeric cohesion, and inability to complete RAD51- and DMC1-mediated DSB repair, establishing STAG3 as a crucial cohesin subunit for mammalian gametogenesis.","method":"Stag3 knockout mouse; immunofluorescence; meiotic spread analysis for RAD51, DMC1, axial element markers","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 — KO with multiple orthogonal readouts (cohesion, DSB repair markers, AE formation)","pmids":["24608227"],"is_preprint":false},{"year":2005,"finding":"E2F6 transcriptionally represses STAG3 (and SMC1β) in somatic cells by binding their promoters and mediating histone H3 methylation on lysine 9 and lysine 27; loss of E2f6 derepresses these meiotic genes in mouse embryonic fibroblasts.","method":"cDNA microarray in E2f6-/- MEFs; chromatin immunoprecipitation (ChIP); E2F6 re-expression rescue","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — ChIP combined with KO and rescue experiment, multiple histone marks identified","pmids":["16236716"],"is_preprint":false},{"year":2013,"finding":"E2f6-mediated repression of Stag3 and Smc1β during embryonic development requires the enzymatic (SET domain) activity of Ezh2 (PRC2), but not the de novo methyltransferase Dnmt3b; repression is established at the transition from ESCs to epiblast stem cells and accompanied by promoter DNA methylation.","method":"Ezh2 SET domain deletion; Dnmt3b knockout; embryoid body differentiation; RT-qPCR; ChIP","journal":"Epigenetics","confidence":"High","confidence_rationale":"Tier 2 — genetic dissection with Ezh2 and Dnmt3b mutants plus epigenetic assays","pmids":["23880518"],"is_preprint":false},{"year":2015,"finding":"In fission yeast, casein kinase 1 (CK1/Hhp1/Hhp2) phosphorylates the STAG3 functional homolog Rec11/SA3, which promotes loading of linear element proteins Rec10/Rec27 and thereby drives meiotic DSB formation and recombination; the mammalian STAG3 is also phosphorylated during meiosis, indicating conservation.","method":"In vitro phosphorylation screen; genetic analysis of CK1 mutants; immunofluorescence; biochemical fractionation in S. pombe","journal":"PLoS genetics","confidence":"Medium","confidence_rationale":"Tier 1 for yeast Rec11 (in vitro assay + genetics), but mammalian STAG3 phosphorylation is only noted as correlative","pmids":["25993311"],"is_preprint":false},{"year":2015,"finding":"CK1-mediated phosphorylation of fission yeast Rec11/SA3 (STAG3 homolog) mediates the interaction with the Rec10/Red1/SCP2 axis component to assemble the meiotic chromosome axis (linear element), independently of sister chromatid cohesion; Rec11-Rec10 fusion protein bypasses the requirement for CK1.","method":"In vitro phosphorylation assay; Rec11-Rec10 fusion rescue; genetic epistasis; immunofluorescence in S. pombe","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with mutagenesis and genetic bypass experiment","pmids":["25979576"],"is_preprint":false},{"year":2016,"finding":"STAG3 is the predominant STAG protein in primary spermatocytes and interacts directly with each α-kleisin subunit (REC8, RAD21L, RAD21); genetic double-mutant analysis shows STAG3/REC8 complexes are the primary cohesins required for centromeric cohesion and axis formation, while STAG3/RAD21L cohesins mediate pericentromeric heterochromatin clustering.","method":"Stag3/Rad21L and Stag3/Rec8 double knockout mice; immunofluorescence; co-immunoprecipitation; meiotic spread analysis","journal":"G3 (Bethesda, Md.)","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with double KO combined with Co-IP for direct interaction","pmids":["27172213"],"is_preprint":false},{"year":2018,"finding":"When expressed in HEK293 somatic cells, REC8 has no affinity for STAG1 or STAG2 and remains cytoplasmic; co-expression of STAG3 is sufficient for REC8 to enter the nucleus, load onto chromatin, and functionally replace RAD21 in 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; co-immunoprecipitation; chromatin fractionation; cohesion assay; Wapl/sororin knockdown","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1-2 — reconstitution in somatic cells with multiple orthogonal assays demonstrating sufficiency","pmids":["29724914"],"is_preprint":false},{"year":2017,"finding":"STAG3 localizes to the spindle apparatus and colocalizes with microtubule fibers during mouse oocyte meiotic maturation; depletion of STAG3 disrupts spindle assembly, chromosome alignment, reduces acetylated tubulin levels and microtubule stability, impairs kinetochore-microtubule attachment, and causes aneuploidy.","method":"Morpholino knockdown in mouse oocytes; immunofluorescence; microtubule depolymerization assay; FISH for aneuploidy","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 — knockdown with defined phenotypic readout (aneuploidy, spindle defects), but single lab study","pmids":["27906670"],"is_preprint":false},{"year":2016,"finding":"Loss of STAG3 (or STAG2) in melanoma cells confers resistance to BRAF inhibition; loss of STAG2 specifically inhibits CTCF-mediated expression of DUSP6, leading to reactivation of MAPK/ERK signaling.","method":"STAG2/STAG3 knockdown in melanoma cells; xenograft tumor model; gene expression analysis; MAPK signaling readout","journal":"Nature medicine","confidence":"Medium","confidence_rationale":"Tier 2 — KD with defined signaling pathway readout, but STAG3-specific mechanism distinct from STAG2 mechanism is less resolved","pmids":["27500726"],"is_preprint":false},{"year":2019,"finding":"In-frame deletion variants in STAG3 (p.293_295del and p.297_298insAsp) prevent both STAG3 and REC8 from entering the nucleus, and abolish the interaction between mutant STAG3 and REC8 or SMC1A, demonstrating that these residues are required for nuclear import and protein–protein interactions within the meiotic cohesin complex.","method":"Fluorescence localization of mutant proteins in cells; co-immunoprecipitation","journal":"Frontiers in genetics","confidence":"Medium","confidence_rationale":"Tier 2-3 — cell-based localization and Co-IP, single lab study","pmids":["31803224"],"is_preprint":false},{"year":2023,"finding":"METTL3-mediated m6A methylation of STAG3 mRNA is read by IGF2BP2, stabilizing STAG3 protein expression in colorectal cancer cells; knockdown of METTL3 or IGF2BP2 decreases STAG3 protein level, inhibits proliferation and migration, and promotes apoptosis, effects rescued by STAG3 overexpression.","method":"m6A RNA immunoprecipitation (MeRIP); RIP assay; pulldown; METTL3/IGF2BP2 knockdown/overexpression; xenograft mouse model","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2-3 — MeRIP + RIP + rescue experiments establish the m6A regulatory axis, single lab study","pmids":["37828232"],"is_preprint":false},{"year":2024,"finding":"STAG3 is expressed in mouse embryonic stem cells and primordial germ cell-like cells, where it localizes to the centrosome independently of cohesin and interacts with mRNA localization/stability proteins; STAG3 knockdown destabilizes the centrosome and RISC component TNRC6C, derepressing P-body mRNAs (e.g., DPPA3), indicating a cytoplasmic post-transcriptional gene regulatory role distinct from its nuclear cohesin function.","method":"siRNA knockdown in mESCs; mass spectrometry interactome; immunofluorescence; RNA-seq; proximity ligation / co-IP","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 — MS interactome + KD phenotype with multiple readouts, but preprint not yet peer-reviewed","pmids":["bio_10.1101_2024.05.31.595485"],"is_preprint":true}],"current_model":"STAG3 is a meiosis-specific subunit of the cohesin complex that directly interacts with SMC1, SMC3, and all three meiotic α-kleisins (REC8, RAD21L, RAD21) to stabilize meiosis-specific cohesin complexes on chromosome axes, where it is essential for axial/lateral element formation, sister chromatid cohesion, homolog synapsis, and DSB repair during prophase I; in somatic cells its meiotic expression is silenced by E2F6/PRC2-mediated histone methylation, and emerging work indicates a cohesin-independent cytoplasmic role in post-transcriptional mRNA regulation via centrosome-associated RISC components."},"narrative":{"teleology":[{"year":2000,"claim":"Identification of STAG3 as a testis-specific stromalin-domain protein localizing to the synaptonemal complex established the first evidence for a meiosis-specific cohesin subunit dedicated to chromosome pairing.","evidence":"cDNA cloning, sequence analysis, and immunolocalization in mouse spermatocytes","pmids":["10698974"],"confidence":"High","gaps":["No biochemical interaction with cohesin ring subunits demonstrated","No functional loss-of-function data"]},{"year":2001,"claim":"Demonstration that STAG3 physically associates with SMC1 and SMC3 and localizes to the interchromatid domain at metaphase I confirmed STAG3 as a bona fide cohesin subunit rather than merely a synaptonemal complex structural protein.","evidence":"Reciprocal co-immunoprecipitation of STAG3 with SMC1/SMC3; immunofluorescence in meiotic cells","pmids":["11483963"],"confidence":"High","gaps":["Kleisin partner identity unknown","No loss-of-function model available"]},{"year":2005,"claim":"Discovery that E2F6 directly represses STAG3 transcription in somatic cells via H3K9 and H3K27 methylation at its promoter explained how meiotic cohesin genes are silenced outside the germline.","evidence":"ChIP for E2F6 and histone marks at STAG3 promoter in E2f6−/− MEFs; rescue by E2F6 re-expression","pmids":["16236716"],"confidence":"High","gaps":["Upstream signals activating STAG3 in germ cells not identified","Relationship between H3K9me and H3K27me in repression hierarchy unclear"]},{"year":2013,"claim":"Demonstration that PRC2/Ezh2 SET-domain activity is required for STAG3 silencing, while Dnmt3b is dispensable, resolved the epigenetic hierarchy: Polycomb-mediated histone methylation initiates repression, with DNA methylation following secondarily.","evidence":"Ezh2 SET-domain deletion and Dnmt3b KO in embryoid body differentiation; RT-qPCR and ChIP","pmids":["23880518"],"confidence":"High","gaps":["Whether PRC1 also contributes to STAG3 silencing not tested","Mechanism of germline-specific derepression unknown"]},{"year":2014,"claim":"Four independent Stag3 knockout studies collectively established that STAG3 is the indispensable STAG subunit for meiosis: its loss destabilizes all meiotic cohesin subunits (SMC1β, REC8, RAD21L), abolishes axial element formation, prevents synapsis, impairs DSB repair, and causes meiotic arrest in both sexes.","evidence":"Stag3 KO and hypomorphic mouse models; immunofluorescence for SYCP3, SYCP1, HORMAD1, RAD51, DMC1; genetic epistasis with Smc1β, Rec8, Rad21l mutants","pmids":["24992337","24797474","24797475","24608227"],"confidence":"High","gaps":["Whether residual RAD21-STAG3 cohesin has any meiotic function not fully resolved","Mechanism by which STAG3 stabilizes kleisin protein levels (transcriptional vs. post-translational) unclear"]},{"year":2015,"claim":"Work in fission yeast showed that CK1 phosphorylation of the STAG3 homolog Rec11 drives meiotic axis assembly by promoting the Rec11–Rec10 interaction independently of cohesion, revealing that STAG proteins have a cohesion-independent structural role in axis formation that is conserved from yeast to mammals.","evidence":"In vitro CK1 phosphorylation; Rec11-Rec10 fusion bypass; genetic epistasis in S. pombe","pmids":["25979576","25993311"],"confidence":"High","gaps":["Mammalian CK1 phosphorylation sites on STAG3 not mapped","Whether a similar phosphorylation-dependent axis-loading mechanism operates in mammals not tested"]},{"year":2016,"claim":"Double-mutant analysis in mice demonstrated that STAG3–REC8 complexes are the primary cohesins for centromeric cohesion and axis formation, while STAG3–RAD21L complexes specifically mediate pericentromeric heterochromatin clustering, functionally partitioning the roles of different STAG3-containing cohesin variants.","evidence":"Stag3/Rad21L and Stag3/Rec8 double KO mice; co-immunoprecipitation; meiotic spread analysis","pmids":["27172213"],"confidence":"High","gaps":["Role of STAG3–RAD21 (somatic kleisin) complexes in meiosis remains poorly understood","Genomic binding profiles of different STAG3-containing complexes not determined"]},{"year":2018,"claim":"Reconstitution of REC8–STAG3 cohesin in somatic cells demonstrated that STAG3 is both necessary and sufficient for REC8 nuclear import and chromatin loading, and that the resulting complex is regulated by the canonical Wapl/sororin cohesion cycle, bridging meiotic and mitotic cohesin biology.","evidence":"Ectopic co-expression in HEK293 cells; chromatin fractionation; cohesion assay; Wapl/sororin knockdown","pmids":["29724914"],"confidence":"High","gaps":["Whether STAG3–REC8 cohesin adopts a distinct ring topology or chromatin binding mode not addressed structurally","Sororin regulation in actual meiotic cells not validated"]},{"year":2019,"claim":"Disease-associated in-frame deletions in STAG3 (residues 293–298) were shown to abolish interactions with both REC8 and SMC1A and prevent nuclear import, mapping a critical interface for cohesin complex assembly.","evidence":"Fluorescence localization and co-immunoprecipitation of mutant STAG3 proteins in cells","pmids":["31803224"],"confidence":"Medium","gaps":["No structural model of the STAG3–kleisin interface available","Only two variants tested; broader structure–function map lacking","Single-lab study without independent replication"]},{"year":2024,"claim":"A preprint reported that STAG3 localizes to centrosomes in embryonic stem cells independently of cohesin and interacts with RISC component TNRC6C to regulate mRNA stability, suggesting a cohesin-independent cytoplasmic function in post-transcriptional gene regulation.","evidence":"(preprint) siRNA knockdown in mESCs; mass spectrometry interactome; RNA-seq; proximity ligation assay","pmids":["bio_10.1101_2024.05.31.595485"],"confidence":"Medium","gaps":["Not yet peer-reviewed","Centrosomal localization not confirmed in meiotic germ cells","Mechanism linking centrosome association to mRNA regulation not established"]},{"year":null,"claim":"Key open questions include: the structural basis of STAG3's selective interaction with meiotic kleisins, whether CK1-dependent phosphorylation regulates mammalian STAG3 axis loading, the genomic binding profiles distinguishing STAG3–REC8 from STAG3–RAD21L complexes, and whether the cytoplasmic mRNA-regulatory role observed in stem cells operates in germ cells.","evidence":"","pmids":[],"confidence":"High","gaps":["No crystal or cryo-EM structure of STAG3 or STAG3–kleisin interface","Mammalian CK1 phosphorylation of STAG3 not validated","ChIP-seq for distinct STAG3-containing complexes not performed"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,2,3,4,10,11]}],"localization":[{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[0,1,2,3,4,5,10]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,11,14]},{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[16]}],"pathway":[{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[0,2,3,4,5,10,11]},{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[2,3,5,10]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[6,7]}],"complexes":["Meiotic cohesin (STAG3-REC8-SMC1-SMC3)","Meiotic cohesin (STAG3-RAD21L-SMC1-SMC3)"],"partners":["SMC1A","SMC3","REC8","RAD21L","RAD21","SMC1B","PDS5","WAPL"],"other_free_text":[]},"mechanistic_narrative":"STAG3 is a meiosis-specific cohesin subunit essential for chromosome axis formation, sister chromatid cohesion, homolog synapsis, and DNA double-strand break repair during prophase I of mammalian meiosis. STAG3 physically interacts with SMC1/SMC3 and all three meiotic α-kleisins (REC8, RAD21L, RAD21), and is required for the stability and chromosomal loading of meiosis-specific cohesin complexes; loss of STAG3 abolishes axial element assembly, disrupts pericentromeric heterochromatin clustering, and causes meiotic arrest and infertility in both sexes [PMID:11483963, PMID:24992337, PMID:24797474, PMID:27172213]. Co-expression of STAG3 with REC8 in somatic cells is sufficient to reconstitute nuclear import, chromatin loading, and functional sister chromatid cohesion regulated by Wapl and sororin [PMID:29724914]. In somatic cells, STAG3 transcription is silenced by E2F6-dependent recruitment of PRC2/Ezh2, which deposits repressive histone marks at the promoter during early embryonic differentiation [PMID:16236716, PMID:23880518]."},"prefetch_data":{"uniprot":{"accession":"Q9UJ98","full_name":"Cohesin subunit SA-3","aliases":["SCC3 homolog 3","Stromal antigen 3","Stromalin-3"],"length_aa":1225,"mass_kda":139.0,"function":"Meiosis specific component of cohesin complex. The cohesin complex is required for the cohesion of sister chromatids after DNA replication. The cohesin complex apparently forms a large proteinaceous ring within which sister chromatids can be trapped. At anaphase, the complex is cleaved and dissociates from chromatin, allowing sister chromatids to segregate. The meiosis-specific cohesin complex probably replaces mitosis specific cohesin complex when it dissociates from chromatin during prophase I","subcellular_location":"Nucleus; Chromosome; Chromosome, centromere","url":"https://www.uniprot.org/uniprotkb/Q9UJ98/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/STAG3","classification":"Not Classified","n_dependent_lines":9,"n_total_lines":1208,"dependency_fraction":0.0074503311258278145},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/STAG3","total_profiled":1310},"omim":[{"mim_id":"619673","title":"SPERMATOGENIC FAILURE 62; SPGF62","url":"https://www.omim.org/entry/619673"},{"mim_id":"619672","title":"SPERMATOGENIC FAILURE 61; SPGF61","url":"https://www.omim.org/entry/619672"},{"mim_id":"619533","title":"RAD21 COHESIN COMPLEX COMPONENT-LIKE 1; RAD21L1","url":"https://www.omim.org/entry/619533"},{"mim_id":"617332","title":"TELOMERE REPEAT-BINDING BOUQUET FORMATION PROTEIN 1; TERB1","url":"https://www.omim.org/entry/617332"},{"mim_id":"617012","title":"POLIOVIRUS RECEPTOR-RELATED IMMUNOGLOBULIN DOMAIN-CONTAINING PROTEIN; PVRIG","url":"https://www.omim.org/entry/617012"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoli","reliability":"Supported"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"testis","ntpm":49.8}],"url":"https://www.proteinatlas.org/search/STAG3"},"hgnc":{"alias_symbol":["SA3"],"prev_symbol":[]},"alphafold":{"accession":"Q9UJ98","domains":[{"cath_id":"-","chopping":"921-1057","consensus_level":"high","plddt":86.814,"start":921,"end":1057},{"cath_id":"1.25.40","chopping":"672-828","consensus_level":"medium","plddt":92.9542,"start":672,"end":828}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UJ98","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UJ98-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UJ98-F1-predicted_aligned_error_v6.png","plddt_mean":77.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=STAG3","jax_strain_url":"https://www.jax.org/strain/search?query=STAG3"},"sequence":{"accession":"Q9UJ98","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9UJ98.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9UJ98/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UJ98"}},"corpus_meta":[{"pmid":"11483963","id":"PMC_11483963","title":"Mammalian STAG3 is a cohesin specific to sister chromatid arms in meiosis I.","date":"2001","source":"Nature cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/11483963","citation_count":210,"is_preprint":false},{"pmid":"10698974","id":"PMC_10698974","title":"STAG3, a novel gene encoding a protein involved in meiotic chromosome pairing and location of STAG3-related genes flanking the Williams-Beuren syndrome deletion.","date":"2000","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/10698974","citation_count":117,"is_preprint":false},{"pmid":"24992337","id":"PMC_24992337","title":"Meiosis-specific cohesin component, Stag3 is essential for maintaining centromere chromatid cohesion, and required for DNA repair and synapsis between homologous chromosomes.","date":"2014","source":"PLoS 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Interactions Between the Meiosis-Specific Cohesin Components, STAG3, REC8, and RAD21L.","date":"2016","source":"G3 (Bethesda, Md.)","url":"https://pubmed.ncbi.nlm.nih.gov/27172213","citation_count":46,"is_preprint":false},{"pmid":"25579976","id":"PMC_25579976","title":"Phosphorylation of cohesin Rec11/SA3 by casein kinase 1 promotes homologous recombination by assembling the meiotic chromosome axis.","date":"2015","source":"Developmental cell","url":"https://pubmed.ncbi.nlm.nih.gov/25579976","citation_count":46,"is_preprint":false},{"pmid":"26059840","id":"PMC_26059840","title":"STAG3 truncating variant as the cause of primary ovarian insufficiency.","date":"2015","source":"European journal of human genetics : EJHG","url":"https://pubmed.ncbi.nlm.nih.gov/26059840","citation_count":43,"is_preprint":false},{"pmid":"32634216","id":"PMC_32634216","title":"STAG3 homozygous missense variant causes primary ovarian insufficiency and male non-obstructive azoospermia.","date":"2020","source":"Molecular human reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/32634216","citation_count":37,"is_preprint":false},{"pmid":"28393351","id":"PMC_28393351","title":"Whole-exome sequencing identifies a homozygous donor splice-site mutation in STAG3 that causes primary ovarian insufficiency.","date":"2017","source":"Clinical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/28393351","citation_count":36,"is_preprint":false},{"pmid":"31363903","id":"PMC_31363903","title":"Novel STAG3 mutations in a Caucasian family with primary ovarian insufficiency.","date":"2019","source":"Molecular genetics and genomics : MGG","url":"https://pubmed.ncbi.nlm.nih.gov/31363903","citation_count":31,"is_preprint":false},{"pmid":"16236716","id":"PMC_16236716","title":"Silencing of the meiotic genes SMC1beta and STAG3 in somatic cells by E2F6.","date":"2005","source":"The Journal of biological 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alcohol by Sphingomonas sp. SA3 and its symbiote.","date":"2003","source":"Journal of industrial microbiology & biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/12545389","citation_count":19,"is_preprint":false},{"pmid":"35176428","id":"PMC_35176428","title":"Novel STAG3 variant associated with primary ovarian insufficiency and non-obstructive azoospermia in an Iranian consanguineous family.","date":"2022","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/35176428","citation_count":18,"is_preprint":false},{"pmid":"29724914","id":"PMC_29724914","title":"Studying meiotic cohesin in somatic cells reveals that Rec8-containing cohesin requires Stag3 to function and is regulated by Wapl and sororin.","date":"2018","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/29724914","citation_count":18,"is_preprint":false},{"pmid":"23880518","id":"PMC_23880518","title":"E2f6-mediated repression of the meiotic Stag3 and Smc1β genes during early embryonic development requires Ezh2 and not the de novo methyltransferase Dnmt3b.","date":"2013","source":"Epigenetics","url":"https://pubmed.ncbi.nlm.nih.gov/23880518","citation_count":16,"is_preprint":false},{"pmid":"37828232","id":"PMC_37828232","title":"METTL3/IGF2BP2 axis affects the progression of colorectal cancer by regulating m6A modification of STAG3.","date":"2023","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/37828232","citation_count":14,"is_preprint":false},{"pmid":"16790336","id":"PMC_16790336","title":"Production of an antimicrobial substance against Cryptococcus neoformans by Paenibacillus brasilensis Sa3 isolated from the rhizosphere of Kalanchoe brasiliensis.","date":"2006","source":"Microbiological research","url":"https://pubmed.ncbi.nlm.nih.gov/16790336","citation_count":14,"is_preprint":false},{"pmid":"34828315","id":"PMC_34828315","title":"A Long Contiguous Stretch of Homozygosity Disclosed a Novel STAG3 Biallelic Pathogenic Variant Causing Primary Ovarian Insufficiency: A Case Report and Review of the Literature.","date":"2021","source":"Genes","url":"https://pubmed.ncbi.nlm.nih.gov/34828315","citation_count":11,"is_preprint":false},{"pmid":"11599053","id":"PMC_11599053","title":"Evaluation of the Stag3 gene and the synaptonemal complex in a rat model (as/as) for male infertility.","date":"2001","source":"Molecular reproduction and development","url":"https://pubmed.ncbi.nlm.nih.gov/11599053","citation_count":10,"is_preprint":false},{"pmid":"31115363","id":"PMC_31115363","title":"The association of stromal antigen 3 (STAG3) sequence variations with spermatogenic impairment in the male Korean population.","date":"2020","source":"Asian journal of andrology","url":"https://pubmed.ncbi.nlm.nih.gov/31115363","citation_count":10,"is_preprint":false},{"pmid":"34497033","id":"PMC_34497033","title":"Biallelic loss of function variants in STAG3 result in primary ovarian insufficiency.","date":"2021","source":"Reproductive biomedicine online","url":"https://pubmed.ncbi.nlm.nih.gov/34497033","citation_count":7,"is_preprint":false},{"pmid":"30420384","id":"PMC_30420384","title":"Retinoic acid-induced CYP51 nuclear translocation promotes meiosis prophase I process and is correlated to the expression of REC8 and STAG3 in mice.","date":"2018","source":"Biology open","url":"https://pubmed.ncbi.nlm.nih.gov/30420384","citation_count":6,"is_preprint":false},{"pmid":"29277047","id":"PMC_29277047","title":"Association of the common SNPs in RNF212, STAG3 and RFX2 gene with male infertility with azoospermia in Chinese population.","date":"2017","source":"European journal of obstetrics, gynecology, and reproductive biology","url":"https://pubmed.ncbi.nlm.nih.gov/29277047","citation_count":5,"is_preprint":false},{"pmid":"11320322","id":"PMC_11320322","title":"Purification, crystallization and preliminary X-ray analysis of two crystal forms of ribonuclease Sa3.","date":"2001","source":"Acta crystallographica. Section D, Biological crystallography","url":"https://pubmed.ncbi.nlm.nih.gov/11320322","citation_count":5,"is_preprint":false},{"pmid":"33980954","id":"PMC_33980954","title":"Analysis of STAG3 variants in Chinese non-obstructive azoospermia patients with germ cell maturation arrest.","date":"2021","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/33980954","citation_count":3,"is_preprint":false},{"pmid":"39932630","id":"PMC_39932630","title":"Novel STAG3 variant causes oligoasthenoteratozoospermia with high sperm aneuploidy rate.","date":"2025","source":"Journal of assisted reproduction and genetics","url":"https://pubmed.ncbi.nlm.nih.gov/39932630","citation_count":3,"is_preprint":false},{"pmid":"35503298","id":"PMC_35503298","title":"New STAG3 gene variant as a cause of premature ovarian insufficiency.","date":"2022","source":"Revista colombiana de obstetricia y ginecologia","url":"https://pubmed.ncbi.nlm.nih.gov/35503298","citation_count":2,"is_preprint":false},{"pmid":"38391498","id":"PMC_38391498","title":"The Role of Prophage ϕSa3 in the Adaption of Staphylococcus aureus ST398 Sublineages from Human to Animal Hosts.","date":"2024","source":"Antibiotics (Basel, Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/38391498","citation_count":2,"is_preprint":false},{"pmid":"26648292","id":"PMC_26648292","title":"[Rab23 enhances invasion of Sa3 cutaneous squamous cell carcinoma cells via up-regulating the expression of Rac1].","date":"2015","source":"Xi bao yu fen zi mian yi xue za zhi = Chinese journal of cellular and molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/26648292","citation_count":2,"is_preprint":false},{"pmid":"22086009","id":"PMC_22086009","title":"Expression of scFv SA3 against hepatoma fused with enhanced green fluorescent protein and its targeted ability in vivo.","date":"2011","source":"Zhong nan da xue xue bao. Yi xue ban = Journal of Central South University. Medical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/22086009","citation_count":1,"is_preprint":false},{"pmid":"38554835","id":"PMC_38554835","title":"Statistical modelling, optimization, and mechanistic exploration of novel ureolytic Enterobacter hormaechei IITISM-SA3 in cadmium immobilization under microbial inclusive and cell-free conditions through microbially induced calcite precipitation.","date":"2024","source":"Environmental pollution (Barking, Essex : 1987)","url":"https://pubmed.ncbi.nlm.nih.gov/38554835","citation_count":1,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.05.31.595485","title":"STAG3 promotes exit from pluripotency through post-transcriptional mRNA regulation in the cytoplasm","date":"2024-05-31","source":"bioRxiv","url":"https://doi.org/10.1101/2024.05.31.595485","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":23372,"output_tokens":4135,"usd":0.066071},"stage2":{"model":"claude-opus-4-6","input_tokens":7604,"output_tokens":2983,"usd":0.168893},"total_usd":0.234964,"stage1_batch_id":"msgbatch_011rkcQdVV1RaFq9XhcG6df6","stage2_batch_id":"msgbatch_01RzgrJafdF4EWHhj5mNi6dh","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2001,\n      \"finding\": \"STAG3 physically interacts with SMC1 and SMC3 (structural maintenance of chromosome proteins) and functions as a sister chromatid arm cohesin specific to mammalian meiosis I, localizing to the interchromatid domain in metaphase I and to the axial/lateral element of the synaptonemal complex in prophase I.\",\n      \"method\": \"Co-immunoprecipitation; immunofluorescence localization in meiotic cells\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP with SMC1/SMC3 plus direct localization experiments, foundational paper with 210 citations\",\n      \"pmids\": [\"11483963\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"STAG3 contains a stromalin conservative domain (SCD) and localizes to the synaptonemal complex specifically in testis, suggesting a cohesin-like role in chromosome pairing and synaptonemal complex maintenance during pachytene.\",\n      \"method\": \"cDNA cloning; immunolocalization in spermatocytes; sequence analysis\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct immunolocalization with domain characterization; 117 citations, foundational identification paper\",\n      \"pmids\": [\"10698974\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"STAG3 is required for the stability and chromosomal axis loading of all meiosis-specific cohesin subunits (SMC1β, RAD21L, REC8); loss of STAG3 reduces protein levels of these subunits and disrupts their localization to chromosome axes, causing aberrant DNA repair, failed homolog synapsis, disrupted pericentromeric heterochromatin clustering, and early prophase I arrest in both sexes.\",\n      \"method\": \"Stag3 knockout mouse; immunofluorescence; meiotic spread analysis; genetic epistasis with Smc1β, Rec8, Rad21l mutants\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined cellular phenotypes and epistasis analysis, replicated across multiple cohesin subunits; 104 citations\",\n      \"pmids\": [\"24992337\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"STAG3 deficiency causes complete failure of axial element (AE) formation in meiosis — SYCP3 forms only dot-like structures, HORMAD1 is diffusely distributed, and SYCP1 is largely absent — demonstrating STAG3 is the key STAG cohesin for meiotic chromosome architecture, centromeric and telomeric sister chromatid cohesion.\",\n      \"method\": \"STAG3-deficient mouse (both sexes); immunofluorescence of synaptonemal complex proteins; meiotic spread analysis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with multiple orthogonal structural markers; 86 citations\",\n      \"pmids\": [\"24797474\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"STAG3 preferentially stabilizes REC8-containing cohesin complexes; three α-kleisins (REC8, RAD21L, RAD21) show different dosage-dependent requirements for STAG3, and STAG3-REC8 complexes have a critical role in meiotic chromosome axis compaction and synapsis.\",\n      \"method\": \"Stag3 hypomorphic mouse allele; immunofluorescence; co-immunoprecipitation of cohesin subunits; meiotic phenotype analysis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — Co-IP combined with in vivo hypomorphic model and multiple readouts; 83 citations\",\n      \"pmids\": [\"24797475\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In male Stag3 knockout mice, meiotic arrest occurs at zygonema with shortened axial elements, partial loss of centromeric cohesion, and inability to complete RAD51- and DMC1-mediated DSB repair, establishing STAG3 as a crucial cohesin subunit for mammalian gametogenesis.\",\n      \"method\": \"Stag3 knockout mouse; immunofluorescence; meiotic spread analysis for RAD51, DMC1, axial element markers\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO with multiple orthogonal readouts (cohesion, DSB repair markers, AE formation)\",\n      \"pmids\": [\"24608227\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"E2F6 transcriptionally represses STAG3 (and SMC1β) in somatic cells by binding their promoters and mediating histone H3 methylation on lysine 9 and lysine 27; loss of E2f6 derepresses these meiotic genes in mouse embryonic fibroblasts.\",\n      \"method\": \"cDNA microarray in E2f6-/- MEFs; chromatin immunoprecipitation (ChIP); E2F6 re-expression rescue\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP combined with KO and rescue experiment, multiple histone marks identified\",\n      \"pmids\": [\"16236716\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"E2f6-mediated repression of Stag3 and Smc1β during embryonic development requires the enzymatic (SET domain) activity of Ezh2 (PRC2), but not the de novo methyltransferase Dnmt3b; repression is established at the transition from ESCs to epiblast stem cells and accompanied by promoter DNA methylation.\",\n      \"method\": \"Ezh2 SET domain deletion; Dnmt3b knockout; embryoid body differentiation; RT-qPCR; ChIP\",\n      \"journal\": \"Epigenetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic dissection with Ezh2 and Dnmt3b mutants plus epigenetic assays\",\n      \"pmids\": [\"23880518\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"In fission yeast, casein kinase 1 (CK1/Hhp1/Hhp2) phosphorylates the STAG3 functional homolog Rec11/SA3, which promotes loading of linear element proteins Rec10/Rec27 and thereby drives meiotic DSB formation and recombination; the mammalian STAG3 is also phosphorylated during meiosis, indicating conservation.\",\n      \"method\": \"In vitro phosphorylation screen; genetic analysis of CK1 mutants; immunofluorescence; biochemical fractionation in S. pombe\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 for yeast Rec11 (in vitro assay + genetics), but mammalian STAG3 phosphorylation is only noted as correlative\",\n      \"pmids\": [\"25993311\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"CK1-mediated phosphorylation of fission yeast Rec11/SA3 (STAG3 homolog) mediates the interaction with the Rec10/Red1/SCP2 axis component to assemble the meiotic chromosome axis (linear element), independently of sister chromatid cohesion; Rec11-Rec10 fusion protein bypasses the requirement for CK1.\",\n      \"method\": \"In vitro phosphorylation assay; Rec11-Rec10 fusion rescue; genetic epistasis; immunofluorescence in S. pombe\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with mutagenesis and genetic bypass experiment\",\n      \"pmids\": [\"25979576\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"STAG3 is the predominant STAG protein in primary spermatocytes and interacts directly with each α-kleisin subunit (REC8, RAD21L, RAD21); genetic double-mutant analysis shows STAG3/REC8 complexes are the primary cohesins required for centromeric cohesion and axis formation, while STAG3/RAD21L cohesins mediate pericentromeric heterochromatin clustering.\",\n      \"method\": \"Stag3/Rad21L and Stag3/Rec8 double knockout mice; immunofluorescence; co-immunoprecipitation; meiotic spread analysis\",\n      \"journal\": \"G3 (Bethesda, Md.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with double KO combined with Co-IP for direct interaction\",\n      \"pmids\": [\"27172213\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"When expressed in HEK293 somatic cells, REC8 has no affinity for STAG1 or STAG2 and remains cytoplasmic; co-expression of STAG3 is sufficient for REC8 to enter the nucleus, load onto chromatin, and functionally replace RAD21 in 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; co-immunoprecipitation; chromatin fractionation; cohesion assay; Wapl/sororin knockdown\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstitution in somatic cells with multiple orthogonal assays demonstrating sufficiency\",\n      \"pmids\": [\"29724914\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"STAG3 localizes to the spindle apparatus and colocalizes with microtubule fibers during mouse oocyte meiotic maturation; depletion of STAG3 disrupts spindle assembly, chromosome alignment, reduces acetylated tubulin levels and microtubule stability, impairs kinetochore-microtubule attachment, and causes aneuploidy.\",\n      \"method\": \"Morpholino knockdown in mouse oocytes; immunofluorescence; microtubule depolymerization assay; FISH for aneuploidy\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — knockdown with defined phenotypic readout (aneuploidy, spindle defects), but single lab study\",\n      \"pmids\": [\"27906670\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Loss of STAG3 (or STAG2) in melanoma cells confers resistance to BRAF inhibition; loss of STAG2 specifically inhibits CTCF-mediated expression of DUSP6, leading to reactivation of MAPK/ERK signaling.\",\n      \"method\": \"STAG2/STAG3 knockdown in melanoma cells; xenograft tumor model; gene expression analysis; MAPK signaling readout\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KD with defined signaling pathway readout, but STAG3-specific mechanism distinct from STAG2 mechanism is less resolved\",\n      \"pmids\": [\"27500726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In-frame deletion variants in STAG3 (p.293_295del and p.297_298insAsp) prevent both STAG3 and REC8 from entering the nucleus, and abolish the interaction between mutant STAG3 and REC8 or SMC1A, demonstrating that these residues are required for nuclear import and protein–protein interactions within the meiotic cohesin complex.\",\n      \"method\": \"Fluorescence localization of mutant proteins in cells; co-immunoprecipitation\",\n      \"journal\": \"Frontiers in genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — cell-based localization and Co-IP, single lab study\",\n      \"pmids\": [\"31803224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"METTL3-mediated m6A methylation of STAG3 mRNA is read by IGF2BP2, stabilizing STAG3 protein expression in colorectal cancer cells; knockdown of METTL3 or IGF2BP2 decreases STAG3 protein level, inhibits proliferation and migration, and promotes apoptosis, effects rescued by STAG3 overexpression.\",\n      \"method\": \"m6A RNA immunoprecipitation (MeRIP); RIP assay; pulldown; METTL3/IGF2BP2 knockdown/overexpression; xenograft mouse model\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — MeRIP + RIP + rescue experiments establish the m6A regulatory axis, single lab study\",\n      \"pmids\": [\"37828232\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"STAG3 is expressed in mouse embryonic stem cells and primordial germ cell-like cells, where it localizes to the centrosome independently of cohesin and interacts with mRNA localization/stability proteins; STAG3 knockdown destabilizes the centrosome and RISC component TNRC6C, derepressing P-body mRNAs (e.g., DPPA3), indicating a cytoplasmic post-transcriptional gene regulatory role distinct from its nuclear cohesin function.\",\n      \"method\": \"siRNA knockdown in mESCs; mass spectrometry interactome; immunofluorescence; RNA-seq; proximity ligation / co-IP\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — MS interactome + KD phenotype with multiple readouts, but preprint not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2024.05.31.595485\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"STAG3 is a meiosis-specific subunit of the cohesin complex that directly interacts with SMC1, SMC3, and all three meiotic α-kleisins (REC8, RAD21L, RAD21) to stabilize meiosis-specific cohesin complexes on chromosome axes, where it is essential for axial/lateral element formation, sister chromatid cohesion, homolog synapsis, and DSB repair during prophase I; in somatic cells its meiotic expression is silenced by E2F6/PRC2-mediated histone methylation, and emerging work indicates a cohesin-independent cytoplasmic role in post-transcriptional mRNA regulation via centrosome-associated RISC components.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"STAG3 is a meiosis-specific cohesin subunit essential for chromosome axis formation, sister chromatid cohesion, homolog synapsis, and DNA double-strand break repair during prophase I of mammalian meiosis. STAG3 physically interacts with SMC1/SMC3 and all three meiotic α-kleisins (REC8, RAD21L, RAD21), and is required for the stability and chromosomal loading of meiosis-specific cohesin complexes; loss of STAG3 abolishes axial element assembly, disrupts pericentromeric heterochromatin clustering, and causes meiotic arrest and infertility in both sexes [PMID:11483963, PMID:24992337, PMID:24797474, PMID:27172213]. Co-expression of STAG3 with REC8 in somatic cells is sufficient to reconstitute nuclear import, chromatin loading, and functional sister chromatid cohesion regulated by Wapl and sororin [PMID:29724914]. In somatic cells, STAG3 transcription is silenced by E2F6-dependent recruitment of PRC2/Ezh2, which deposits repressive histone marks at the promoter during early embryonic differentiation [PMID:16236716, PMID:23880518].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Identification of STAG3 as a testis-specific stromalin-domain protein localizing to the synaptonemal complex established the first evidence for a meiosis-specific cohesin subunit dedicated to chromosome pairing.\",\n      \"evidence\": \"cDNA cloning, sequence analysis, and immunolocalization in mouse spermatocytes\",\n      \"pmids\": [\"10698974\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No biochemical interaction with cohesin ring subunits demonstrated\", \"No functional loss-of-function data\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Demonstration that STAG3 physically associates with SMC1 and SMC3 and localizes to the interchromatid domain at metaphase I confirmed STAG3 as a bona fide cohesin subunit rather than merely a synaptonemal complex structural protein.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation of STAG3 with SMC1/SMC3; immunofluorescence in meiotic cells\",\n      \"pmids\": [\"11483963\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kleisin partner identity unknown\", \"No loss-of-function model available\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Discovery that E2F6 directly represses STAG3 transcription in somatic cells via H3K9 and H3K27 methylation at its promoter explained how meiotic cohesin genes are silenced outside the germline.\",\n      \"evidence\": \"ChIP for E2F6 and histone marks at STAG3 promoter in E2f6−/− MEFs; rescue by E2F6 re-expression\",\n      \"pmids\": [\"16236716\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream signals activating STAG3 in germ cells not identified\", \"Relationship between H3K9me and H3K27me in repression hierarchy unclear\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Demonstration that PRC2/Ezh2 SET-domain activity is required for STAG3 silencing, while Dnmt3b is dispensable, resolved the epigenetic hierarchy: Polycomb-mediated histone methylation initiates repression, with DNA methylation following secondarily.\",\n      \"evidence\": \"Ezh2 SET-domain deletion and Dnmt3b KO in embryoid body differentiation; RT-qPCR and ChIP\",\n      \"pmids\": [\"23880518\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PRC1 also contributes to STAG3 silencing not tested\", \"Mechanism of germline-specific derepression unknown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Four independent Stag3 knockout studies collectively established that STAG3 is the indispensable STAG subunit for meiosis: its loss destabilizes all meiotic cohesin subunits (SMC1β, REC8, RAD21L), abolishes axial element formation, prevents synapsis, impairs DSB repair, and causes meiotic arrest in both sexes.\",\n      \"evidence\": \"Stag3 KO and hypomorphic mouse models; immunofluorescence for SYCP3, SYCP1, HORMAD1, RAD51, DMC1; genetic epistasis with Smc1β, Rec8, Rad21l mutants\",\n      \"pmids\": [\"24992337\", \"24797474\", \"24797475\", \"24608227\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether residual RAD21-STAG3 cohesin has any meiotic function not fully resolved\", \"Mechanism by which STAG3 stabilizes kleisin protein levels (transcriptional vs. post-translational) unclear\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Work in fission yeast showed that CK1 phosphorylation of the STAG3 homolog Rec11 drives meiotic axis assembly by promoting the Rec11–Rec10 interaction independently of cohesion, revealing that STAG proteins have a cohesion-independent structural role in axis formation that is conserved from yeast to mammals.\",\n      \"evidence\": \"In vitro CK1 phosphorylation; Rec11-Rec10 fusion bypass; genetic epistasis in S. pombe\",\n      \"pmids\": [\"25979576\", \"25993311\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mammalian CK1 phosphorylation sites on STAG3 not mapped\", \"Whether a similar phosphorylation-dependent axis-loading mechanism operates in mammals not tested\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Double-mutant analysis in mice demonstrated that STAG3–REC8 complexes are the primary cohesins for centromeric cohesion and axis formation, while STAG3–RAD21L complexes specifically mediate pericentromeric heterochromatin clustering, functionally partitioning the roles of different STAG3-containing cohesin variants.\",\n      \"evidence\": \"Stag3/Rad21L and Stag3/Rec8 double KO mice; co-immunoprecipitation; meiotic spread analysis\",\n      \"pmids\": [\"27172213\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Role of STAG3–RAD21 (somatic kleisin) complexes in meiosis remains poorly understood\", \"Genomic binding profiles of different STAG3-containing complexes not determined\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Reconstitution of REC8–STAG3 cohesin in somatic cells demonstrated that STAG3 is both necessary and sufficient for REC8 nuclear import and chromatin loading, and that the resulting complex is regulated by the canonical Wapl/sororin cohesion cycle, bridging meiotic and mitotic cohesin biology.\",\n      \"evidence\": \"Ectopic co-expression in HEK293 cells; chromatin fractionation; cohesion assay; Wapl/sororin knockdown\",\n      \"pmids\": [\"29724914\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether STAG3–REC8 cohesin adopts a distinct ring topology or chromatin binding mode not addressed structurally\", \"Sororin regulation in actual meiotic cells not validated\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Disease-associated in-frame deletions in STAG3 (residues 293–298) were shown to abolish interactions with both REC8 and SMC1A and prevent nuclear import, mapping a critical interface for cohesin complex assembly.\",\n      \"evidence\": \"Fluorescence localization and co-immunoprecipitation of mutant STAG3 proteins in cells\",\n      \"pmids\": [\"31803224\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of the STAG3–kleisin interface available\", \"Only two variants tested; broader structure–function map lacking\", \"Single-lab study without independent replication\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"A preprint reported that STAG3 localizes to centrosomes in embryonic stem cells independently of cohesin and interacts with RISC component TNRC6C to regulate mRNA stability, suggesting a cohesin-independent cytoplasmic function in post-transcriptional gene regulation.\",\n      \"evidence\": \"(preprint) siRNA knockdown in mESCs; mass spectrometry interactome; RNA-seq; proximity ligation assay\",\n      \"pmids\": [\"bio_10.1101_2024.05.31.595485\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Not yet peer-reviewed\", \"Centrosomal localization not confirmed in meiotic germ cells\", \"Mechanism linking centrosome association to mRNA regulation not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include: the structural basis of STAG3's selective interaction with meiotic kleisins, whether CK1-dependent phosphorylation regulates mammalian STAG3 axis loading, the genomic binding profiles distinguishing STAG3–REC8 from STAG3–RAD21L complexes, and whether the cytoplasmic mRNA-regulatory role observed in stem cells operates in germ cells.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal or cryo-EM structure of STAG3 or STAG3–kleisin interface\", \"Mammalian CK1 phosphorylation of STAG3 not validated\", \"ChIP-seq for distinct STAG3-containing complexes not performed\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 2, 3, 4, 10, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4, 5, 10]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 11, 14]},\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [16]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [0, 2, 3, 4, 5, 10, 11]},\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [2, 3, 5, 10]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [6, 7]}\n    ],\n    \"complexes\": [\n      \"Meiotic cohesin (STAG3-REC8-SMC1-SMC3)\",\n      \"Meiotic cohesin (STAG3-RAD21L-SMC1-SMC3)\"\n    ],\n    \"partners\": [\n      \"SMC1A\",\n      \"SMC3\",\n      \"REC8\",\n      \"RAD21L\",\n      \"RAD21\",\n      \"SMC1B\",\n      \"PDS5\",\n      \"WAPL\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}