{"gene":"TOP6BL","run_date":"2026-06-10T10:51:55","timeline":{"discoveries":[{"year":2016,"finding":"Mouse TOPOVIBL (TOP6BL) physically interacts with SPO11 and forms a complex required for meiotic DNA double-strand break (DSB) formation; loss of TOPOVIBL abolishes meiotic DSBs.","method":"Co-immunoprecipitation, mouse genetics (loss-of-function), functional assay for DSB formation","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP and in vivo loss-of-function with defined DSB phenotype, replicated by multiple subsequent labs","pmids":["26917764"],"is_preprint":false},{"year":2022,"finding":"REC114 is a direct binding partner of TOPOVIBL; their conserved interacting domains were identified by structural analysis. Point mutations in TOPOVIBL that reduce or disrupt REC114 binding strongly reduce DSB activity genome-wide in oocytes and in sub-telomeric regions in spermatocytes, and delay DSB timing in autosomes of spermatocytes.","method":"Structural analysis of interacting domains, point-mutation knock-in mice, genome-wide DSB monitoring","journal":"Nature Communications","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — structural domain mapping combined with in vivo knock-in mouse functional data, multiple orthogonal methods","pmids":["36396648"],"is_preprint":false},{"year":2020,"finding":"An autosomal recessive loss-of-function mutation in TOP6BL abolishes meiotic DSB formation and causes meiotic arrest prior to pachytene stage in male patients (non-obstructive azoospermia) and failure of oocyte maturation in female patients; mouse models carrying equivalent mutations recapitulate these defects.","method":"Whole-exome sequencing, Sanger confirmation, mouse knock-in models, histological and DSB formation assays","journal":"Science Bulletin","confidence":"High","confidence_rationale":"Tier 2 / Strong — human genetics plus mouse knock-in model with defined cellular phenotype (meiotic arrest, DSB absence), replicated in both sexes","pmids":["36732965"],"is_preprint":false},{"year":2025,"finding":"Purified recombinant mouse SPO11 and TOP6BL form a monomeric 1:1 complex in solution. This complex catalyzes DNA double-strand breaks in vitro, forming covalent 5' attachments; cleavage requires SPO11 active-site residues, divalent metal ions, and SPO11 dimerization (2:2 assembly). The SPO11-TOP6BL complex binds DNA ends with higher affinity than SPO11 alone, suggesting a post-cleavage role for TOP6BL. AlphaFold 3 modeling suggests DNA is bent prior to cleavage.","method":"In vitro reconstitution with purified recombinant proteins, active-site mutagenesis, DNA cleavage assay, AlphaFold 3 structural modeling, deep sequencing of cleavage products","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — full biochemical reconstitution with mutagenesis, structural modeling, and replication across two independent labs in the same journal issue","pmids":["39972129","39972130","39972125"],"is_preprint":false},{"year":2025,"finding":"In vitro reconstitution shows the mouse SPO11-TOP6BL complex cleaves DNA and covalently attaches to the 5' terminus of DNA breaks. Mg2+ is essential for this DNA-cleavage activity; a SPO11 point mutation disrupting Mg2+ binding abolishes DSB formation in knock-in mice. The SPO11-TOP6BL complex does not require ATP for its cleavage activity, distinguishing it biochemically from the ancestral topoisomerase VI.","method":"In vitro biochemical reconstitution, point-mutation knock-in mice, metal-ion dependency assays, ATP-independence assay","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution plus knock-in mouse validation with active-site mutagenesis, multiple orthogonal methods in a single rigorous study","pmids":["39972125"],"is_preprint":false},{"year":2024,"finding":"Purified TOPOVIBL (TOPOVIBLΔC25) is monomeric in solution and does not bind ATP (no ATPase activity), adopts a dynamic conformation, and interacts with DNA with a preference for specific geometries (e.g., branched or bent DNA substrates), suggesting TOPOVIBL senses specific DNA architectures.","method":"Protein purification, in vitro biochemical assays (ATP binding, DNA binding), structural analysis (SAXS/SEC-MALS inferred from abstract)","journal":"Nucleic Acids Research","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — direct in vitro biochemical characterization with multiple assays, single lab, no in vivo validation of specific DNA geometry preference","pmids":["38966985"],"is_preprint":false},{"year":2024,"finding":"Cryo-EM structures of the yeast Spo11 core complex (Spo11–Rec102–Rec104–Ski8) bound to DNA at up to 3.3 Å resolution reveal molecular determinants of DNA end-binding and DNA cleavage preferences, and show unexpected structural variation in homologs of the Top6BL component (Rec102), providing insight into metal-ion roles in DNA binding.","method":"Cryo-electron microscopy, functional validation in yeast","journal":"Nature Structural & Molecular Biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — high-resolution cryo-EM structure with in vivo functional validation in yeast; single lab but multiple orthogonal methods","pmids":["39304764"],"is_preprint":false},{"year":2025,"finding":"Two TOP6BL variants causing NOA were functionally characterized: p.Arg515Ter impairs binding to both REC114 and SPO11, whereas p.Pro356Arg does not affect protein binding but impairs TOP6BL self-dimerization. Deletion of the TOP6BL central region in mice causes meiotic arrest, confirming the critical role of this intermediate region in spermatogenesis.","method":"Protein binding assays (Co-IP/pulldown), self-dimerization assay, mouse knock-in/deletion models with meiotic arrest phenotype","journal":"Reproduction (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — protein binding and dimerization assays combined with mouse genetic model, single lab","pmids":["41211863"],"is_preprint":false},{"year":2007,"finding":"Expansion of a CGG repeat at the 5' end of the C11orf80 (TOP6BL) gene causes the folate-sensitive fragile site FRA11A; this repeat expansion coincides with hypermethylation of the adjacent CpG island and transcriptional silencing of the C11orf80 gene.","method":"Molecular cytogenetics, repeat expansion analysis, methylation analysis, family segregation","journal":"Cytogenetic and Genome Research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct molecular characterization of repeat expansion and epigenetic silencing, replicated in a family cohort","pmids":["18160775"],"is_preprint":false},{"year":2023,"finding":"IHO1 directly interacts with the PH domain of REC114 by recognizing the same surface as TOPOVIBL and ANKRD31, suggesting that REC114 acts as a regulatory platform mediating mutually exclusive interactions with TOPOVIBL and other meiotic factors.","method":"AlphaFold2 modeling combined with biochemical characterization (binding assays), structural analysis","journal":"The EMBO Journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical binding assays combined with structural modeling, single lab, TOPOVIBL competition inferred from shared binding surface","pmids":["37431931"],"is_preprint":false}],"current_model":"TOP6BL (TOPOVIBL) is the obligate partner of SPO11, together forming the monomeric (1:1) TOPOVIL complex that catalyzes meiotic DNA double-strand breaks: upon dimerization to a 2:2 assembly, SPO11 active-site residues cleave DNA in a Mg2+-dependent, ATP-independent manner and remain covalently attached to the 5' broken ends, while TOP6BL contributes to DNA-end binding affinity post-cleavage, senses specific DNA geometries, and is regulated through its direct interaction with the accessory factor REC114 (which competes with IHO1 for the same REC114 surface), with disruption of any of these interactions causing meiotic arrest and infertility in both sexes."},"narrative":{"mechanistic_narrative":"TOP6BL (TOPOVIBL) is the obligate partner of SPO11, together forming the TOPOVIL complex that catalyzes the programmed DNA double-strand breaks (DSBs) which initiate meiotic recombination; loss of TOP6BL abolishes meiotic DSBs and arrests gametogenesis [PMID:26917764]. Purified recombinant SPO11 and TOP6BL assemble as a monomeric 1:1 complex that, upon dimerization into a 2:2 assembly, cleaves DNA and remains covalently attached to the 5' broken ends; cleavage depends on SPO11 active-site residues and divalent metal ions but is ATP-independent, and TOP6BL itself binds neither ATP nor exhibits ATPase activity, distinguishing the complex biochemically from ancestral topoisomerase VI [PMID:39972129, PMID:39972130, PMID:39972125, PMID:38966985]. TOP6BL binds DNA with a preference for branched or bent geometries and increases the affinity of the complex for DNA ends beyond that of SPO11 alone, indicating both a DNA-architecture-sensing role and a post-cleavage end-binding function [PMID:39972129, PMID:39972130, PMID:39972125, PMID:38966985]. TOP6BL activity is governed through its central region and through direct interaction with the accessory factor REC114, whose PH domain is bound competitively by TOPOVIBL, IHO1, and ANKRD31, making REC114 a regulatory platform for mutually exclusive meiotic interactions; point mutations that disrupt the TOP6BL–REC114 interaction strongly reduce genome-wide DSB activity, and disruption of TOP6BL self-dimerization or its central region likewise causes meiotic arrest [PMID:36396648, PMID:41211863, PMID:37431931]. In humans, autosomal-recessive loss-of-function mutations in TOP6BL abolish meiotic DSB formation and cause meiotic arrest with non-obstructive azoospermia in males and oocyte maturation failure in females, phenotypes recapitulated in equivalent mouse knock-in models [PMID:36732965, PMID:41211863]. Separately, CGG-repeat expansion at the 5' end of the gene underlies the folate-sensitive fragile site FRA11A through CpG-island hypermethylation and transcriptional silencing [PMID:18160775].","teleology":[{"year":2016,"claim":"Established that TOP6BL is a SPO11 partner essential for the initiating event of meiotic recombination, answering whether SPO11 acts alone or within a defined complex.","evidence":"Reciprocal Co-IP and loss-of-function mouse genetics with DSB-formation assay","pmids":["26917764"],"confidence":"High","gaps":["Did not establish the stoichiometry or catalytic mechanism of the complex","Did not define TOP6BL's specific contribution distinct from SPO11"]},{"year":2020,"claim":"Connected TOP6BL to human disease by showing biallelic loss-of-function causes meiotic arrest and infertility in both sexes, demonstrating conservation of its DSB-initiating role.","evidence":"Whole-exome sequencing of azoospermia/oocyte-failure patients plus mouse knock-in models with DSB and histological readouts","pmids":["36732965"],"confidence":"High","gaps":["Did not resolve which molecular interaction each mutation disrupts","Did not address residual partial-function alleles"]},{"year":2022,"claim":"Identified REC114 as a direct TOPOVIBL partner and mapped the interacting domains, defining how the catalytic complex is recruited or regulated.","evidence":"Structural domain mapping plus point-mutation knock-in mice with genome-wide DSB monitoring","pmids":["36396648"],"confidence":"High","gaps":["Differential effects between oocytes and spermatocytes not mechanistically explained","Did not show how REC114 binding translates into DSB-site selection"]},{"year":2023,"claim":"Reframed REC114 as a competitive regulatory platform by showing IHO1 binds the same PH-domain surface as TOPOVIBL and ANKRD31, implying mutually exclusive partner exchange.","evidence":"AlphaFold2 modeling combined with biochemical binding assays","pmids":["37431931"],"confidence":"Medium","gaps":["TOPOVIBL competition inferred from shared surface rather than directly measured","In vivo consequence of exchange dynamics not tested"]},{"year":2024,"claim":"Characterized TOP6BL as a monomeric, ATP-independent DNA-architecture sensor, dissociating it from the ATPase activity of ancestral topoisomerase VI subunits.","evidence":"Purification and in vitro ATP-binding/DNA-binding and structural assays of TOPOVIBLΔC25","pmids":["38966985"],"confidence":"Medium","gaps":["DNA-geometry preference not validated in vivo","Single-lab biochemistry without functional confirmation of bent-DNA sensing"]},{"year":2024,"claim":"Provided high-resolution structural insight into DNA end-binding and cleavage determinants of the Spo11 core complex, including variation in the Top6BL homolog.","evidence":"Cryo-EM of yeast Spo11–Rec102–Rec104–Ski8 bound to DNA with yeast functional validation","pmids":["39304764"],"confidence":"High","gaps":["Structure is of yeast homologs, not mammalian TOP6BL","Did not capture the catalytically active cleaving state directly"]},{"year":2025,"claim":"Achieved full biochemical reconstitution, proving the SPO11-TOP6BL complex is itself the catalytic DSB machine: a 1:1 monomer that dimerizes to a 2:2 assembly, cleaves DNA Mg2+-dependently and ATP-independently, forms covalent 5' attachments, and uses TOP6BL for enhanced DNA-end binding.","evidence":"In vitro reconstitution with purified proteins, active-site and Mg2+-binding mutagenesis, deep sequencing of products, AlphaFold 3 modeling, and knock-in mouse validation across independent labs","pmids":["39972129","39972130","39972125"],"confidence":"High","gaps":["Trigger for the monomer-to-dimer transition in vivo not defined","How accessory factors gate catalysis in cells not reconstituted"]},{"year":2025,"claim":"Resolved how distinct patient mutations impair TOP6BL function, separating partner-binding defects from self-dimerization defects and pinpointing the central region as critical.","evidence":"Protein-binding and self-dimerization assays for NOA variants plus mouse central-region deletion with meiotic-arrest phenotype","pmids":["41211863"],"confidence":"Medium","gaps":["Single-lab functional characterization","Mechanism by which self-dimerization promotes DSB activity not structurally resolved"]},{"year":null,"claim":"How REC114-mediated partner competition, DNA-architecture sensing, and the monomer-to-dimer transition are coordinated in time and space to select DSB sites in vivo remains open.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No in vivo demonstration of TOP6BL bent-DNA sensing driving site choice","Regulation of dimerization timing during meiotic prophase unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[3,5]},{"term_id":"GO:0140097","term_label":"catalytic activity, acting on DNA","supporting_discovery_ids":[3,4]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[5]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,3]}],"pathway":[{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[0,2]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[3,4]}],"complexes":["TOPOVIL (SPO11-TOP6BL) complex"],"partners":["SPO11","REC114"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8N6T0","full_name":"Type 2 DNA topoisomerase 6 subunit B-like","aliases":["TOP6B like initiator of meiotic double strand breaks","Type 2 DNA topoisomerase VI subunit B-like","TOPOVIBL"],"length_aa":511,"mass_kda":57.0,"function":"Component of a topoisomerase 6 complex specifically required for meiotic recombination. Together with SPO11, mediates DNA cleavage that forms the double-strand breaks (DSB) that initiate meiotic recombination. The complex promotes relaxation of negative and positive supercoiled DNA and DNA decatenation through cleavage and ligation cycles","subcellular_location":"Chromosome","url":"https://www.uniprot.org/uniprotkb/Q8N6T0/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TOP6BL","classification":"Not Classified","n_dependent_lines":10,"n_total_lines":1208,"dependency_fraction":0.008278145695364239},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TOP6BL","total_profiled":1310},"omim":[{"mim_id":"618432","title":"HYDATIDIFORM MOLE, RECURRENT, 4; HYDM4","url":"https://www.omim.org/entry/618432"},{"mim_id":"616109","title":"TOP6B-LIKE INITIATOR OF MEIOTIC DOUBLE STRAND BREAKS; TOP6BL","url":"https://www.omim.org/entry/616109"},{"mim_id":"605114","title":"SPO11 INITIATOR OF MEIOTIC DOUBLE-STRANDED BREAKS; SPO11","url":"https://www.omim.org/entry/605114"},{"mim_id":"231090","title":"HYDATIDIFORM MOLE, RECURRENT, 1; HYDM1","url":"https://www.omim.org/entry/231090"}],"hpa":{"profiled":true,"resolved_as":"C11ORF80","reliability":"Approved","locations":[{"location":"Centrosome","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/C11ORF80"},"hgnc":{"alias_symbol":["FLJ22531","TOPOVIBL"],"prev_symbol":["C11orf80"]},"alphafold":{"accession":"Q8N6T0","domains":[{"cath_id":"3.30.565","chopping":"2-95_103-161","consensus_level":"medium","plddt":78.3662,"start":2,"end":161},{"cath_id":"-","chopping":"163-312_321-382","consensus_level":"medium","plddt":81.5739,"start":163,"end":382},{"cath_id":"-","chopping":"386-449","consensus_level":"medium","plddt":85.2025,"start":386,"end":449}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8N6T0","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8N6T0-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8N6T0-F1-predicted_aligned_error_v6.png","plddt_mean":67.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TOP6BL","jax_strain_url":"https://www.jax.org/strain/search?query=TOP6BL"},"sequence":{"accession":"Q8N6T0","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8N6T0.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8N6T0/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8N6T0"}},"corpus_meta":[{"pmid":"26917764","id":"PMC_26917764","title":"The 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infertility.","date":"2020","source":"Science bulletin","url":"https://pubmed.ncbi.nlm.nih.gov/36732965","citation_count":26,"is_preprint":false},{"pmid":"36256608","id":"PMC_36256608","title":"Evolution and Diversity of the TopoVI and TopoVI-like Subunits With Extensive Divergence of the TOPOVIBL subunit.","date":"2022","source":"Molecular biology and evolution","url":"https://pubmed.ncbi.nlm.nih.gov/36256608","citation_count":24,"is_preprint":false},{"pmid":"39972130","id":"PMC_39972130","title":"SPO11 dimers are sufficient to catalyse DNA double-strand breaks in vitro.","date":"2025","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/39972130","citation_count":21,"is_preprint":false},{"pmid":"18160775","id":"PMC_18160775","title":"The molecular basis of the folate-sensitive fragile site FRA11A at 11q13.","date":"2007","source":"Cytogenetic and genome 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meiotic DNA double-strand break formation","date":"2024-11-20","source":"bioRxiv","url":"https://doi.org/10.1101/2024.11.20.624454","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":13410,"output_tokens":2503,"usd":0.038887,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9756,"output_tokens":3065,"usd":0.062702,"stage2_stop_reason":"end_turn"},"total_usd":0.101589,"stage1_batch_id":"msgbatch_017qqVz33Ga63SCDwzb35XPb","stage2_batch_id":"msgbatch_01Scr2Ei9x4HJMiRGxwrmvLK","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2016,\n      \"finding\": \"Mouse TOPOVIBL (TOP6BL) physically interacts with SPO11 and forms a complex required for meiotic DNA double-strand break (DSB) formation; loss of TOPOVIBL abolishes meiotic DSBs.\",\n      \"method\": \"Co-immunoprecipitation, mouse genetics (loss-of-function), functional assay for DSB formation\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP and in vivo loss-of-function with defined DSB phenotype, replicated by multiple subsequent labs\",\n      \"pmids\": [\"26917764\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"REC114 is a direct binding partner of TOPOVIBL; their conserved interacting domains were identified by structural analysis. Point mutations in TOPOVIBL that reduce or disrupt REC114 binding strongly reduce DSB activity genome-wide in oocytes and in sub-telomeric regions in spermatocytes, and delay DSB timing in autosomes of spermatocytes.\",\n      \"method\": \"Structural analysis of interacting domains, point-mutation knock-in mice, genome-wide DSB monitoring\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — structural domain mapping combined with in vivo knock-in mouse functional data, multiple orthogonal methods\",\n      \"pmids\": [\"36396648\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"An autosomal recessive loss-of-function mutation in TOP6BL abolishes meiotic DSB formation and causes meiotic arrest prior to pachytene stage in male patients (non-obstructive azoospermia) and failure of oocyte maturation in female patients; mouse models carrying equivalent mutations recapitulate these defects.\",\n      \"method\": \"Whole-exome sequencing, Sanger confirmation, mouse knock-in models, histological and DSB formation assays\",\n      \"journal\": \"Science Bulletin\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — human genetics plus mouse knock-in model with defined cellular phenotype (meiotic arrest, DSB absence), replicated in both sexes\",\n      \"pmids\": [\"36732965\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Purified recombinant mouse SPO11 and TOP6BL form a monomeric 1:1 complex in solution. This complex catalyzes DNA double-strand breaks in vitro, forming covalent 5' attachments; cleavage requires SPO11 active-site residues, divalent metal ions, and SPO11 dimerization (2:2 assembly). The SPO11-TOP6BL complex binds DNA ends with higher affinity than SPO11 alone, suggesting a post-cleavage role for TOP6BL. AlphaFold 3 modeling suggests DNA is bent prior to cleavage.\",\n      \"method\": \"In vitro reconstitution with purified recombinant proteins, active-site mutagenesis, DNA cleavage assay, AlphaFold 3 structural modeling, deep sequencing of cleavage products\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — full biochemical reconstitution with mutagenesis, structural modeling, and replication across two independent labs in the same journal issue\",\n      \"pmids\": [\"39972129\", \"39972130\", \"39972125\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In vitro reconstitution shows the mouse SPO11-TOP6BL complex cleaves DNA and covalently attaches to the 5' terminus of DNA breaks. Mg2+ is essential for this DNA-cleavage activity; a SPO11 point mutation disrupting Mg2+ binding abolishes DSB formation in knock-in mice. The SPO11-TOP6BL complex does not require ATP for its cleavage activity, distinguishing it biochemically from the ancestral topoisomerase VI.\",\n      \"method\": \"In vitro biochemical reconstitution, point-mutation knock-in mice, metal-ion dependency assays, ATP-independence assay\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution plus knock-in mouse validation with active-site mutagenesis, multiple orthogonal methods in a single rigorous study\",\n      \"pmids\": [\"39972125\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Purified TOPOVIBL (TOPOVIBLΔC25) is monomeric in solution and does not bind ATP (no ATPase activity), adopts a dynamic conformation, and interacts with DNA with a preference for specific geometries (e.g., branched or bent DNA substrates), suggesting TOPOVIBL senses specific DNA architectures.\",\n      \"method\": \"Protein purification, in vitro biochemical assays (ATP binding, DNA binding), structural analysis (SAXS/SEC-MALS inferred from abstract)\",\n      \"journal\": \"Nucleic Acids Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — direct in vitro biochemical characterization with multiple assays, single lab, no in vivo validation of specific DNA geometry preference\",\n      \"pmids\": [\"38966985\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Cryo-EM structures of the yeast Spo11 core complex (Spo11–Rec102–Rec104–Ski8) bound to DNA at up to 3.3 Å resolution reveal molecular determinants of DNA end-binding and DNA cleavage preferences, and show unexpected structural variation in homologs of the Top6BL component (Rec102), providing insight into metal-ion roles in DNA binding.\",\n      \"method\": \"Cryo-electron microscopy, functional validation in yeast\",\n      \"journal\": \"Nature Structural & Molecular Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — high-resolution cryo-EM structure with in vivo functional validation in yeast; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"39304764\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Two TOP6BL variants causing NOA were functionally characterized: p.Arg515Ter impairs binding to both REC114 and SPO11, whereas p.Pro356Arg does not affect protein binding but impairs TOP6BL self-dimerization. Deletion of the TOP6BL central region in mice causes meiotic arrest, confirming the critical role of this intermediate region in spermatogenesis.\",\n      \"method\": \"Protein binding assays (Co-IP/pulldown), self-dimerization assay, mouse knock-in/deletion models with meiotic arrest phenotype\",\n      \"journal\": \"Reproduction (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — protein binding and dimerization assays combined with mouse genetic model, single lab\",\n      \"pmids\": [\"41211863\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Expansion of a CGG repeat at the 5' end of the C11orf80 (TOP6BL) gene causes the folate-sensitive fragile site FRA11A; this repeat expansion coincides with hypermethylation of the adjacent CpG island and transcriptional silencing of the C11orf80 gene.\",\n      \"method\": \"Molecular cytogenetics, repeat expansion analysis, methylation analysis, family segregation\",\n      \"journal\": \"Cytogenetic and Genome Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct molecular characterization of repeat expansion and epigenetic silencing, replicated in a family cohort\",\n      \"pmids\": [\"18160775\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"IHO1 directly interacts with the PH domain of REC114 by recognizing the same surface as TOPOVIBL and ANKRD31, suggesting that REC114 acts as a regulatory platform mediating mutually exclusive interactions with TOPOVIBL and other meiotic factors.\",\n      \"method\": \"AlphaFold2 modeling combined with biochemical characterization (binding assays), structural analysis\",\n      \"journal\": \"The EMBO Journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical binding assays combined with structural modeling, single lab, TOPOVIBL competition inferred from shared binding surface\",\n      \"pmids\": [\"37431931\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TOP6BL (TOPOVIBL) is the obligate partner of SPO11, together forming the monomeric (1:1) TOPOVIL complex that catalyzes meiotic DNA double-strand breaks: upon dimerization to a 2:2 assembly, SPO11 active-site residues cleave DNA in a Mg2+-dependent, ATP-independent manner and remain covalently attached to the 5' broken ends, while TOP6BL contributes to DNA-end binding affinity post-cleavage, senses specific DNA geometries, and is regulated through its direct interaction with the accessory factor REC114 (which competes with IHO1 for the same REC114 surface), with disruption of any of these interactions causing meiotic arrest and infertility in both sexes.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TOP6BL (TOPOVIBL) is the obligate partner of SPO11, together forming the TOPOVIL complex that catalyzes the programmed DNA double-strand breaks (DSBs) which initiate meiotic recombination; loss of TOP6BL abolishes meiotic DSBs and arrests gametogenesis [#0]. Purified recombinant SPO11 and TOP6BL assemble as a monomeric 1:1 complex that, upon dimerization into a 2:2 assembly, cleaves DNA and remains covalently attached to the 5' broken ends; cleavage depends on SPO11 active-site residues and divalent metal ions but is ATP-independent, and TOP6BL itself binds neither ATP nor exhibits ATPase activity, distinguishing the complex biochemically from ancestral topoisomerase VI [#3, #4, #5]. TOP6BL binds DNA with a preference for branched or bent geometries and increases the affinity of the complex for DNA ends beyond that of SPO11 alone, indicating both a DNA-architecture-sensing role and a post-cleavage end-binding function [#3, #5]. TOP6BL activity is governed through its central region and through direct interaction with the accessory factor REC114, whose PH domain is bound competitively by TOPOVIBL, IHO1, and ANKRD31, making REC114 a regulatory platform for mutually exclusive meiotic interactions; point mutations that disrupt the TOP6BL–REC114 interaction strongly reduce genome-wide DSB activity, and disruption of TOP6BL self-dimerization or its central region likewise causes meiotic arrest [#1, #7, #9]. In humans, autosomal-recessive loss-of-function mutations in TOP6BL abolish meiotic DSB formation and cause meiotic arrest with non-obstructive azoospermia in males and oocyte maturation failure in females, phenotypes recapitulated in equivalent mouse knock-in models [#2, #7]. Separately, CGG-repeat expansion at the 5' end of the gene underlies the folate-sensitive fragile site FRA11A through CpG-island hypermethylation and transcriptional silencing [#8].\",\n  \"teleology\": [\n    {\n      \"year\": 2016,\n      \"claim\": \"Established that TOP6BL is a SPO11 partner essential for the initiating event of meiotic recombination, answering whether SPO11 acts alone or within a defined complex.\",\n      \"evidence\": \"Reciprocal Co-IP and loss-of-function mouse genetics with DSB-formation assay\",\n      \"pmids\": [\"26917764\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish the stoichiometry or catalytic mechanism of the complex\", \"Did not define TOP6BL's specific contribution distinct from SPO11\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Connected TOP6BL to human disease by showing biallelic loss-of-function causes meiotic arrest and infertility in both sexes, demonstrating conservation of its DSB-initiating role.\",\n      \"evidence\": \"Whole-exome sequencing of azoospermia/oocyte-failure patients plus mouse knock-in models with DSB and histological readouts\",\n      \"pmids\": [\"36732965\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve which molecular interaction each mutation disrupts\", \"Did not address residual partial-function alleles\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified REC114 as a direct TOPOVIBL partner and mapped the interacting domains, defining how the catalytic complex is recruited or regulated.\",\n      \"evidence\": \"Structural domain mapping plus point-mutation knock-in mice with genome-wide DSB monitoring\",\n      \"pmids\": [\"36396648\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Differential effects between oocytes and spermatocytes not mechanistically explained\", \"Did not show how REC114 binding translates into DSB-site selection\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Reframed REC114 as a competitive regulatory platform by showing IHO1 binds the same PH-domain surface as TOPOVIBL and ANKRD31, implying mutually exclusive partner exchange.\",\n      \"evidence\": \"AlphaFold2 modeling combined with biochemical binding assays\",\n      \"pmids\": [\"37431931\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"TOPOVIBL competition inferred from shared surface rather than directly measured\", \"In vivo consequence of exchange dynamics not tested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Characterized TOP6BL as a monomeric, ATP-independent DNA-architecture sensor, dissociating it from the ATPase activity of ancestral topoisomerase VI subunits.\",\n      \"evidence\": \"Purification and in vitro ATP-binding/DNA-binding and structural assays of TOPOVIBLΔC25\",\n      \"pmids\": [\"38966985\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"DNA-geometry preference not validated in vivo\", \"Single-lab biochemistry without functional confirmation of bent-DNA sensing\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Provided high-resolution structural insight into DNA end-binding and cleavage determinants of the Spo11 core complex, including variation in the Top6BL homolog.\",\n      \"evidence\": \"Cryo-EM of yeast Spo11–Rec102–Rec104–Ski8 bound to DNA with yeast functional validation\",\n      \"pmids\": [\"39304764\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure is of yeast homologs, not mammalian TOP6BL\", \"Did not capture the catalytically active cleaving state directly\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Achieved full biochemical reconstitution, proving the SPO11-TOP6BL complex is itself the catalytic DSB machine: a 1:1 monomer that dimerizes to a 2:2 assembly, cleaves DNA Mg2+-dependently and ATP-independently, forms covalent 5' attachments, and uses TOP6BL for enhanced DNA-end binding.\",\n      \"evidence\": \"In vitro reconstitution with purified proteins, active-site and Mg2+-binding mutagenesis, deep sequencing of products, AlphaFold 3 modeling, and knock-in mouse validation across independent labs\",\n      \"pmids\": [\"39972129\", \"39972130\", \"39972125\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Trigger for the monomer-to-dimer transition in vivo not defined\", \"How accessory factors gate catalysis in cells not reconstituted\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Resolved how distinct patient mutations impair TOP6BL function, separating partner-binding defects from self-dimerization defects and pinpointing the central region as critical.\",\n      \"evidence\": \"Protein-binding and self-dimerization assays for NOA variants plus mouse central-region deletion with meiotic-arrest phenotype\",\n      \"pmids\": [\"41211863\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab functional characterization\", \"Mechanism by which self-dimerization promotes DSB activity not structurally resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How REC114-mediated partner competition, DNA-architecture sensing, and the monomer-to-dimer transition are coordinated in time and space to select DSB sites in vivo remains open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No in vivo demonstration of TOP6BL bent-DNA sensing driving site choice\", \"Regulation of dimerization timing during meiotic prophase unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [3, 5]},\n      {\"term_id\": \"GO:0140097\", \"supporting_discovery_ids\": [3, 4]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [3, 4]}\n    ],\n    \"complexes\": [\"TOPOVIL (SPO11-TOP6BL) complex\"],\n    \"partners\": [\"SPO11\", \"REC114\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}