{"gene":"SHOC1","run_date":"2026-06-10T07:46:31","timeline":{"discoveries":[{"year":2008,"finding":"SHOC1 (Arabidopsis ortholog) is required for class I meiotic crossover formation; shoc1 mutants show striking reduction in CO number with normal early recombination (DMC1 foci) and synapsis completion. Double-mutant analysis showed SHOC1 acts in the same pathway as AtMSH5 (a ZMM protein). SHOC1 shows sequence similarity to the XPF endonuclease protein family, suggesting direct involvement in maturation of DNA intermediates leading to COs.","method":"Genetic mutant analysis in Arabidopsis, cytological DMC1 foci quantification, double-mutant epistasis analysis, sequence similarity analysis","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 2 / Strong — epistasis with ZMM pathway established by double mutants, orthogonal cytological methods, replicated across subsequent studies","pmids":["18812090"],"is_preprint":false},{"year":2011,"finding":"Arabidopsis SHOC1 interacts with PTD (an ERCC1-like protein) through its XPF-like nuclease-(HhH)2 domain to form an XPF-ERCC1-like heterodimer required for class I interfering crossovers. Both SHOC1 and PTD are required for class-I-interfering COs alongside MSH4, MSH5, MER3, and MLH3. The authors propose that the human ortholog C9orf84 (SHOC1) forms an analogous heterodimer with Zip2 in yeast.","method":"Yeast two-hybrid assay, genetic mutant analysis, double-mutant epistasis","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct protein interaction via two-hybrid mapped to specific domain, epistasis confirmed, independently consistent with structural family assignment","pmids":["21771883"],"is_preprint":false},{"year":2018,"finding":"Purified recombinant human SHOC1 (an XPF/MUS81 family member with conserved ERCC4-(HhH)2 core structure) preferentially binds branched DNA molecules in vitro but apparently lacks in vitro endonuclease activity despite conserved catalytic domain. In SHOC1 hypomorphic mice, MLH1 chromosomal localization is reduced, chiasma formation is reduced, and cells arrest at metaphase I with lagging chromosomes. SHOC1 localizes to a subset of recombination sites, axial element formation and homologous pairing are normal, but synapsis is altered. SHOC1 interacts with TEX11, connecting SHOC1 to chromosome axis and crossover structure.","method":"In vitro DNA binding assay with purified recombinant protein, in vitro endonuclease assay (negative result for nuclease), cytological analysis of SHOC1 hypomorphic mice, Co-immunoprecipitation/interaction assay with TEX11","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro biochemical assays with recombinant protein, in vivo cytology in mouse model, protein interaction, multiple orthogonal methods in single study","pmids":["29742103"],"is_preprint":false},{"year":2018,"finding":"MZIP2 (SHOC1 mammalian ortholog) is the mammalian ortholog of yeast Zip2. Complete MZIP2 knockout in mice causes sterility in both males and females and defects in repairing meiotic DNA double-strand breaks. MZIP2 forms discrete foci on chromosome axes and is required for localization of TEX11 (mammalian Zip4 ortholog) and MSH4 to form crossover-prone recombination intermediates. In MZIP2-null meiocytes, crossover formation is abolished, synaptonemal complex formation is incomplete, and meiosis arrests at a zygotene-like stage.","method":"Mouse knockout, cytological analysis (foci localization, chromosome spreads), immunofluorescence","journal":"Communications biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — complete KO mouse with defined cellular phenotypes, multiple cytological readouts, localization of downstream factors established","pmids":["30272023"],"is_preprint":false},{"year":2019,"finding":"SPO16 (mammalian ortholog of yeast Spo16) physically interacts with SHOC1 (MZIP2/mammalian Zip2 ortholog) and forms a complex. SPO16 localizes to recombination nodules alongside SHOC1 and TEX11. SPO16 is required for stabilization of SHOC1 protein levels and proper localization of other ZMM proteins. In SPO16-deleted meiocytes, DSBs are repaired without CO formation though synapsis is less affected. The SPO16-SHOC1 complex-associated recombination intermediate is a key step facilitating meiotic recombination that produces COs.","method":"Co-immunoprecipitation, mouse KO, cytological localization studies, immunofluorescence","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal interaction confirmed, KO phenotype with defined downstream effects on SHOC1 stability and ZMM localization, multiple methods","pmids":["30746471"],"is_preprint":false},{"year":2022,"finding":"Bi-allelic SHOC1 loss-of-function variants in NOA patients and Shoc1-knockout mice show meiotic defects including comprehensive defects in homologous pairing and synapsis, along with abnormal expression/localization of DMC1, RAD51, and RPA2 in spermatocyte spreads, suggesting SHOC1 has a presynaptic function during meiotic recombination in addition to its role in crossover formation.","method":"Whole-exome sequencing in patients, mouse KO (germ-cell-specific and general), meiotic chromosome spread analysis, immunofluorescence for DMC1/RAD51/RPA2","journal":"Molecular human reproduction","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse with defined cytological phenotype, but presynaptic role is a new mechanistic inference from single lab","pmids":["35485979"],"is_preprint":false},{"year":2022,"finding":"M1AP interacts with the mammalian ZZS complex components SHOC1, TEX11, and SPO16. M1AP localizes to chromosomal axes in a SPO16-dependent manner. Ablation of M1AP does not alter SHOC1 localization but reduces the recruitment of TEX11 to recombination intermediates and decreases crossover formation in males.","method":"Co-immunoprecipitation, mouse KO, cytological immunofluorescence, chromosome spread analysis","journal":"EMBO reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP for interaction, KO for localization hierarchy, single lab with multiple methods","pmids":["36440627"],"is_preprint":false},{"year":2024,"finding":"In RNF212B mutant mice, MZIP2 (SHOC1) localization to recombination intermediates is reduced, placing SHOC1 downstream of the RNF212B E3 ligase in the CO maturation pathway.","method":"Mouse KO of RNF212B, cytological immunofluorescence for MZIP2 foci","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — single lab, KO with localization readout, but SHOC1 is not the primary subject","pmids":["38865271"],"is_preprint":false},{"year":2023,"finding":"FLIP-FIGNL1 complex promotes RAD51/DMC1 dissociation; FLIP-null meiocytes arrest at zygotene-like stage with massive RAD51 and DMC1 foci that frequently co-localize with SHOC1 and TEX11, indicating that SHOC1-positive recombination intermediates accumulate when RAD51/DMC1 are not properly dissociated.","method":"Mouse germline-specific KO, cytological co-localization immunofluorescence","journal":"Nucleic acids research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — SHOC1 is used as a marker here, not the primary subject; co-localization observation only","pmids":["37439366"],"is_preprint":false},{"year":2025,"finding":"In human SHOC1, the XPF-like domain is required for binding branched DNA structures and for CO formation. A missense variant (p.Q590R) within the XPF-like domain impairs DNA double-strand break repair by compromising branched DNA binding and recruitment of M1AP, REDIC1, and ZMM factors to recombination intermediates. The XPF-like domain also prevents autosome intrusion into the sex body, protecting autosomal loci from meiotic silencing of unsynapsed chromatin (MSUC). The variant disrupts 3D chromatin structure in pachytene spermatocytes and induces synapsis defects.","method":"Patient variant identification, in vitro DNA binding assay (branched DNA), cytological immunofluorescence, 3D chromatin analysis","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro biochemical assay for branched DNA binding with disease variant, in vivo cytology, multiple orthogonal methods, peer-reviewed publication","pmids":["42258546"],"is_preprint":false},{"year":2025,"finding":"Men with ZZS (SHOC1/TEX11/SPO16) deficiency show early meiotic arrest with incorrect synapsis of homologous chromosomes, unrepaired DNA double-strand breaks, and incomplete recombination, phenotypically distinct from M1AP deficiency (which causes metaphase I arrest). This establishes SHOC1/ZZS function as essential for early meiotic recombination steps leading to synapsis in humans.","method":"In-depth testicular phenotyping of men with biallelic LoF variants, meiotic spread analysis, immunofluorescence","journal":"EMBO molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — human tissue analysis with defined cytological phenotype, but limited to observational characterization of patient material","pmids":["40374915"],"is_preprint":false},{"year":2023,"finding":"During meiotic prophase I, SHOC1 binds to branched DNA and recruits SPO16 and other ZMM proteins to facilitate crossover formation (mechanistic model stated in context of SPO16 POI findings, consistent with prior experimental evidence from PMID:29742103 and PMID:30746471).","method":"Synthesis of experimental evidence cited in paper; SPO16 variant functional assay (minigene); prior biochemical data from referenced studies","journal":"Clinical genetics","confidence":"Low","confidence_rationale":"Tier 3 / Weak — mechanistic statement based on cited prior work, no new direct SHOC1 experiment performed in this paper","pmids":["37270785"],"is_preprint":false}],"current_model":"SHOC1 (also MZIP2/C9orf84) is a ZMM protein with an XPF/ERCC1-like ERCC4-(HhH)2 domain that forms a trimeric ZZS complex with SPO16 and TEX11 to bind branched (recombination intermediate) DNA structures and promote class I meiotic crossover formation; its XPF-like domain is required for branched DNA binding, recruitment of downstream recombination factors (TEX11, MSH4, M1AP), and proper synapsis, and also protects autosomes from meiotic silencing of unsynapsed chromatin (MSUC), while lacking detectable in vitro endonuclease activity despite its conserved catalytic domain architecture."},"narrative":{"mechanistic_narrative":"SHOC1 (MZIP2/C9orf84) is a ZMM-class meiotic recombination factor required for class I, interference-dependent crossover formation during meiotic prophase I [PMID:18812090, PMID:30272023]. It is the structural homolog of XPF/MUS81-family nucleases, carrying a conserved ERCC4-(HhH)2 core, and its XPF-like domain mediates preferential binding to branched (recombination intermediate) DNA structures, yet the purified protein lacks detectable in vitro endonuclease activity [PMID:29742103, PMID:42258546]. SHOC1 partners with the ERCC1-like protein SPO16 and with TEX11 to form the trimeric ZZS complex; SPO16 stabilizes SHOC1 protein and SHOC1 in turn is required to recruit downstream recombination factors including TEX11, MSH4, and M1AP to recombination intermediates, with this branched-DNA-binding activity essential for crossover formation [PMID:29742103, PMID:30272023, PMID:30746471, PMID:42258546]. Loss of SHOC1 abolishes crossovers, leaves meiotic double-strand breaks unrepaired, and produces incomplete or aberrant synapsis with arrest at a zygotene-like stage in mice and early meiotic arrest in men [PMID:30272023, PMID:40374915]. The XPF-like domain additionally protects autosomes from meiotic silencing of unsynapsed chromatin by preventing autosome intrusion into the sex body [PMID:42258546]. Biallelic loss-of-function SHOC1 variants cause non-obstructive azoospermia in human males [PMID:35485979, PMID:42258546, PMID:40374915].","teleology":[{"year":2008,"claim":"Established that SHOC1 acts specifically in the class I crossover pathway rather than in early recombination, defining its position downstream of strand invasion.","evidence":"Genetic mutant and double-mutant epistasis analysis with cytological DMC1 quantification in Arabidopsis","pmids":["18812090"],"confidence":"High","gaps":["Did not identify the biochemical substrate or interacting proteins","XPF-family role inferred from sequence similarity only"]},{"year":2011,"claim":"Identified the heterodimeric architecture by showing the XPF-like domain mediates interaction with an ERCC1-like partner (PTD), framing SHOC1 as half of an XPF-ERCC1-like module for class I crossovers.","evidence":"Yeast two-hybrid domain mapping and genetic epistasis in Arabidopsis","pmids":["21771883"],"confidence":"High","gaps":["Interaction shown in plant ortholog; mammalian complex not directly tested","No demonstration of catalytic activity"]},{"year":2018,"claim":"Defined the biochemical activity of human SHOC1 as branched-DNA binding without detectable nuclease activity, and connected it in mammals to TEX11, crossover maturation, and proper synapsis.","evidence":"In vitro DNA binding and endonuclease assays with recombinant human protein, plus cytology and Co-IP in SHOC1 hypomorphic mice","pmids":["29742103"],"confidence":"High","gaps":["Reason for absent nuclease activity despite conserved catalytic domain unresolved","Whether a partner subunit confers catalysis untested"]},{"year":2018,"claim":"Demonstrated that SHOC1/MZIP2 is essential for recruiting TEX11 and MSH4 to recombination intermediates, establishing it as an upstream organizer of the ZMM module in mammalian meiosis.","evidence":"Complete mouse knockout with chromosome spreads and immunofluorescence of downstream factors","pmids":["30272023"],"confidence":"High","gaps":["Mechanism of branched-DNA recognition coupling to recruitment not resolved","Female versus male requirement detail limited"]},{"year":2019,"claim":"Completed the trimeric ZZS complex by showing reciprocal SHOC1-SPO16 interaction and that SPO16 stabilizes SHOC1, separating its crossover function from synapsis.","evidence":"Co-IP, mouse knockout, and cytological localization of ZMM proteins","pmids":["30746471"],"confidence":"High","gaps":["Stoichiometry and structure of the ZZS complex not determined","How SPO16 stabilizes SHOC1 mechanistically unknown"]},{"year":2022,"claim":"Placed M1AP within the ZZS network downstream of SHOC1 localization, showing M1AP loss reduces TEX11 recruitment and crossovers without disturbing SHOC1.","evidence":"Co-IP, mouse knockout, and chromosome spread immunofluorescence","pmids":["36440627"],"confidence":"Medium","gaps":["Direct versus indirect SHOC1-M1AP contact not resolved","Sex-specific differences in M1AP requirement not fully explained"]},{"year":2022,"claim":"Extended SHOC1 function to a presynaptic role by linking biallelic loss to abnormal DMC1/RAD51/RPA2 dynamics and pairing/synapsis defects in azoospermic men and mice.","evidence":"Whole-exome sequencing of NOA patients, mouse knockout, and meiotic spread immunofluorescence","pmids":["35485979"],"confidence":"Medium","gaps":["Presynaptic mechanism is a single-lab inference","Molecular link between SHOC1 and strand-exchange protein loading undefined"]},{"year":2024,"claim":"Positioned SHOC1 downstream of the RNF212B E3 ligase in the crossover maturation pathway by showing reduced SHOC1 focus formation in RNF212B mutants.","evidence":"RNF212B knockout mouse with cytological MZIP2 focus quantification","pmids":["38865271"],"confidence":"Medium","gaps":["SHOC1 was not the primary subject","Whether RNF212B acts on SHOC1 directly is untested"]},{"year":2025,"claim":"Pinpointed the XPF-like domain via a disease missense variant (p.Q590R) as required for branched-DNA binding, factor recruitment, and protection of autosomes from MSUC, mechanistically linking domain function to chromatin architecture and disease.","evidence":"Patient variant identification, in vitro branched-DNA binding assay, cytology, and 3D chromatin analysis","pmids":["42258546"],"confidence":"High","gaps":["Structural basis of branched-DNA recognition not resolved","How the domain prevents autosome intrusion into the sex body mechanistically unknown"]},{"year":2025,"claim":"Distinguished ZZS deficiency (early meiotic arrest with synapsis and DSB-repair failure) from M1AP deficiency (metaphase I arrest) in human males, defining SHOC1/ZZS as essential for early recombination steps leading to synapsis.","evidence":"Testicular phenotyping of men with biallelic LoF variants, meiotic spreads, immunofluorescence","pmids":["40374915"],"confidence":"Medium","gaps":["Observational human characterization without manipulation","Molecular step distinguishing ZZS from M1AP arrest not defined"]},{"year":null,"claim":"Why SHOC1 retains a conserved XPF/ERCC4 catalytic architecture yet shows no detectable endonuclease activity, and whether catalysis is acquired in the assembled ZZS complex or has been functionally replaced by branched-DNA recognition, remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No structure of the ZZS complex bound to branched DNA","No reconstituted assay testing catalysis in complex context","Mechanism coupling branched-DNA binding to downstream ZMM recruitment undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[2,9]}],"localization":[{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[2,3,4]}],"pathway":[{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[3,5,10]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[0,2,3]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[3,5,9]}],"complexes":["ZZS complex (SHOC1-SPO16-TEX11)"],"partners":["SPO16","TEX11","M1AP","PTD"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q5VXU9","full_name":"Protein shortage in chiasmata 1 ortholog","aliases":["Protein ZIP2 homolog","MZIP2"],"length_aa":1444,"mass_kda":165.2,"function":"ATPase required during meiosis for the formation of crossover recombination intermediates (By similarity). Binds DNA: preferentially binds to single-stranded DNA and DNA branched structures (PubMed:29742103). Does not show nuclease activity in vitro, but shows ATPase activity, which is stimulated by the presence of single-stranded DNA (PubMed:29742103). Plays a key role in homologous recombination and crossing-over in meiotic prophase I in male and female germ cells (By similarity). Required for proper synaptonemal complex assembly and homologous chromosome pairing (By similarity). Requiref for recruitment TEX11 and MSH4 to recombination intermediates (By similarity)","subcellular_location":"Chromosome","url":"https://www.uniprot.org/uniprotkb/Q5VXU9/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SHOC1","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SHOC1","total_profiled":1310},"omim":[{"mim_id":"619949","title":"SPERMATOGENIC FAILURE 75; SPGF75","url":"https://www.omim.org/entry/619949"},{"mim_id":"618968","title":"CHROMOSOME 1 OPEN READING FRAME 146; C1ORF146","url":"https://www.omim.org/entry/618968"},{"mim_id":"618038","title":"SHORTAGE IN CHIASMATA 1; SHOC1","url":"https://www.omim.org/entry/618038"},{"mim_id":"258150","title":"SPERMATOGENIC FAILURE 1; SPGF1","url":"https://www.omim.org/entry/258150"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Nuclear bodies","reliability":"Additional"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"testis","ntpm":20.5}],"url":"https://www.proteinatlas.org/search/SHOC1"},"hgnc":{"alias_symbol":["FLJ32779","Zip2","MZIP2"],"prev_symbol":["C9orf84"]},"alphafold":{"accession":"Q5VXU9","domains":[{"cath_id":"-","chopping":"582-777_785-851","consensus_level":"medium","plddt":75.5056,"start":582,"end":851},{"cath_id":"3.40.50.10130","chopping":"865-1033","consensus_level":"high","plddt":80.1031,"start":865,"end":1033},{"cath_id":"1.10.150","chopping":"1054-1100","consensus_level":"medium","plddt":85.0919,"start":1054,"end":1100}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5VXU9","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q5VXU9-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q5VXU9-F1-predicted_aligned_error_v6.png","plddt_mean":49.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SHOC1","jax_strain_url":"https://www.jax.org/strain/search?query=SHOC1"},"sequence":{"accession":"Q5VXU9","fasta_url":"https://rest.uniprot.org/uniprotkb/Q5VXU9.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q5VXU9/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5VXU9"}},"corpus_meta":[{"pmid":"32741963","id":"PMC_32741963","title":"Genetic 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chromatin","date":"2025-06-01","source":"bioRxiv","url":"https://doi.org/10.1101/2025.05.28.656576","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15212,"output_tokens":3352,"usd":0.047958,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10812,"output_tokens":3269,"usd":0.067892,"stage2_stop_reason":"end_turn"},"total_usd":0.11585,"stage1_batch_id":"msgbatch_013LWZZT6MWaqB9qyTSeQBmU","stage2_batch_id":"msgbatch_0194ZzQaTGNpruoNJBbEMbt3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2008,\n      \"finding\": \"SHOC1 (Arabidopsis ortholog) is required for class I meiotic crossover formation; shoc1 mutants show striking reduction in CO number with normal early recombination (DMC1 foci) and synapsis completion. Double-mutant analysis showed SHOC1 acts in the same pathway as AtMSH5 (a ZMM protein). SHOC1 shows sequence similarity to the XPF endonuclease protein family, suggesting direct involvement in maturation of DNA intermediates leading to COs.\",\n      \"method\": \"Genetic mutant analysis in Arabidopsis, cytological DMC1 foci quantification, double-mutant epistasis analysis, sequence similarity analysis\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — epistasis with ZMM pathway established by double mutants, orthogonal cytological methods, replicated across subsequent studies\",\n      \"pmids\": [\"18812090\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Arabidopsis SHOC1 interacts with PTD (an ERCC1-like protein) through its XPF-like nuclease-(HhH)2 domain to form an XPF-ERCC1-like heterodimer required for class I interfering crossovers. Both SHOC1 and PTD are required for class-I-interfering COs alongside MSH4, MSH5, MER3, and MLH3. The authors propose that the human ortholog C9orf84 (SHOC1) forms an analogous heterodimer with Zip2 in yeast.\",\n      \"method\": \"Yeast two-hybrid assay, genetic mutant analysis, double-mutant epistasis\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct protein interaction via two-hybrid mapped to specific domain, epistasis confirmed, independently consistent with structural family assignment\",\n      \"pmids\": [\"21771883\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Purified recombinant human SHOC1 (an XPF/MUS81 family member with conserved ERCC4-(HhH)2 core structure) preferentially binds branched DNA molecules in vitro but apparently lacks in vitro endonuclease activity despite conserved catalytic domain. In SHOC1 hypomorphic mice, MLH1 chromosomal localization is reduced, chiasma formation is reduced, and cells arrest at metaphase I with lagging chromosomes. SHOC1 localizes to a subset of recombination sites, axial element formation and homologous pairing are normal, but synapsis is altered. SHOC1 interacts with TEX11, connecting SHOC1 to chromosome axis and crossover structure.\",\n      \"method\": \"In vitro DNA binding assay with purified recombinant protein, in vitro endonuclease assay (negative result for nuclease), cytological analysis of SHOC1 hypomorphic mice, Co-immunoprecipitation/interaction assay with TEX11\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro biochemical assays with recombinant protein, in vivo cytology in mouse model, protein interaction, multiple orthogonal methods in single study\",\n      \"pmids\": [\"29742103\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"MZIP2 (SHOC1 mammalian ortholog) is the mammalian ortholog of yeast Zip2. Complete MZIP2 knockout in mice causes sterility in both males and females and defects in repairing meiotic DNA double-strand breaks. MZIP2 forms discrete foci on chromosome axes and is required for localization of TEX11 (mammalian Zip4 ortholog) and MSH4 to form crossover-prone recombination intermediates. In MZIP2-null meiocytes, crossover formation is abolished, synaptonemal complex formation is incomplete, and meiosis arrests at a zygotene-like stage.\",\n      \"method\": \"Mouse knockout, cytological analysis (foci localization, chromosome spreads), immunofluorescence\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — complete KO mouse with defined cellular phenotypes, multiple cytological readouts, localization of downstream factors established\",\n      \"pmids\": [\"30272023\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SPO16 (mammalian ortholog of yeast Spo16) physically interacts with SHOC1 (MZIP2/mammalian Zip2 ortholog) and forms a complex. SPO16 localizes to recombination nodules alongside SHOC1 and TEX11. SPO16 is required for stabilization of SHOC1 protein levels and proper localization of other ZMM proteins. In SPO16-deleted meiocytes, DSBs are repaired without CO formation though synapsis is less affected. The SPO16-SHOC1 complex-associated recombination intermediate is a key step facilitating meiotic recombination that produces COs.\",\n      \"method\": \"Co-immunoprecipitation, mouse KO, cytological localization studies, immunofluorescence\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal interaction confirmed, KO phenotype with defined downstream effects on SHOC1 stability and ZMM localization, multiple methods\",\n      \"pmids\": [\"30746471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Bi-allelic SHOC1 loss-of-function variants in NOA patients and Shoc1-knockout mice show meiotic defects including comprehensive defects in homologous pairing and synapsis, along with abnormal expression/localization of DMC1, RAD51, and RPA2 in spermatocyte spreads, suggesting SHOC1 has a presynaptic function during meiotic recombination in addition to its role in crossover formation.\",\n      \"method\": \"Whole-exome sequencing in patients, mouse KO (germ-cell-specific and general), meiotic chromosome spread analysis, immunofluorescence for DMC1/RAD51/RPA2\",\n      \"journal\": \"Molecular human reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse with defined cytological phenotype, but presynaptic role is a new mechanistic inference from single lab\",\n      \"pmids\": [\"35485979\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"M1AP interacts with the mammalian ZZS complex components SHOC1, TEX11, and SPO16. M1AP localizes to chromosomal axes in a SPO16-dependent manner. Ablation of M1AP does not alter SHOC1 localization but reduces the recruitment of TEX11 to recombination intermediates and decreases crossover formation in males.\",\n      \"method\": \"Co-immunoprecipitation, mouse KO, cytological immunofluorescence, chromosome spread analysis\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP for interaction, KO for localization hierarchy, single lab with multiple methods\",\n      \"pmids\": [\"36440627\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In RNF212B mutant mice, MZIP2 (SHOC1) localization to recombination intermediates is reduced, placing SHOC1 downstream of the RNF212B E3 ligase in the CO maturation pathway.\",\n      \"method\": \"Mouse KO of RNF212B, cytological immunofluorescence for MZIP2 foci\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — single lab, KO with localization readout, but SHOC1 is not the primary subject\",\n      \"pmids\": [\"38865271\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"FLIP-FIGNL1 complex promotes RAD51/DMC1 dissociation; FLIP-null meiocytes arrest at zygotene-like stage with massive RAD51 and DMC1 foci that frequently co-localize with SHOC1 and TEX11, indicating that SHOC1-positive recombination intermediates accumulate when RAD51/DMC1 are not properly dissociated.\",\n      \"method\": \"Mouse germline-specific KO, cytological co-localization immunofluorescence\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — SHOC1 is used as a marker here, not the primary subject; co-localization observation only\",\n      \"pmids\": [\"37439366\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In human SHOC1, the XPF-like domain is required for binding branched DNA structures and for CO formation. A missense variant (p.Q590R) within the XPF-like domain impairs DNA double-strand break repair by compromising branched DNA binding and recruitment of M1AP, REDIC1, and ZMM factors to recombination intermediates. The XPF-like domain also prevents autosome intrusion into the sex body, protecting autosomal loci from meiotic silencing of unsynapsed chromatin (MSUC). The variant disrupts 3D chromatin structure in pachytene spermatocytes and induces synapsis defects.\",\n      \"method\": \"Patient variant identification, in vitro DNA binding assay (branched DNA), cytological immunofluorescence, 3D chromatin analysis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro biochemical assay for branched DNA binding with disease variant, in vivo cytology, multiple orthogonal methods, peer-reviewed publication\",\n      \"pmids\": [\"42258546\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Men with ZZS (SHOC1/TEX11/SPO16) deficiency show early meiotic arrest with incorrect synapsis of homologous chromosomes, unrepaired DNA double-strand breaks, and incomplete recombination, phenotypically distinct from M1AP deficiency (which causes metaphase I arrest). This establishes SHOC1/ZZS function as essential for early meiotic recombination steps leading to synapsis in humans.\",\n      \"method\": \"In-depth testicular phenotyping of men with biallelic LoF variants, meiotic spread analysis, immunofluorescence\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — human tissue analysis with defined cytological phenotype, but limited to observational characterization of patient material\",\n      \"pmids\": [\"40374915\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"During meiotic prophase I, SHOC1 binds to branched DNA and recruits SPO16 and other ZMM proteins to facilitate crossover formation (mechanistic model stated in context of SPO16 POI findings, consistent with prior experimental evidence from PMID:29742103 and PMID:30746471).\",\n      \"method\": \"Synthesis of experimental evidence cited in paper; SPO16 variant functional assay (minigene); prior biochemical data from referenced studies\",\n      \"journal\": \"Clinical genetics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — mechanistic statement based on cited prior work, no new direct SHOC1 experiment performed in this paper\",\n      \"pmids\": [\"37270785\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SHOC1 (also MZIP2/C9orf84) is a ZMM protein with an XPF/ERCC1-like ERCC4-(HhH)2 domain that forms a trimeric ZZS complex with SPO16 and TEX11 to bind branched (recombination intermediate) DNA structures and promote class I meiotic crossover formation; its XPF-like domain is required for branched DNA binding, recruitment of downstream recombination factors (TEX11, MSH4, M1AP), and proper synapsis, and also protects autosomes from meiotic silencing of unsynapsed chromatin (MSUC), while lacking detectable in vitro endonuclease activity despite its conserved catalytic domain architecture.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SHOC1 (MZIP2/C9orf84) is a ZMM-class meiotic recombination factor required for class I, interference-dependent crossover formation during meiotic prophase I [#0, #3]. It is the structural homolog of XPF/MUS81-family nucleases, carrying a conserved ERCC4-(HhH)2 core, and its XPF-like domain mediates preferential binding to branched (recombination intermediate) DNA structures, yet the purified protein lacks detectable in vitro endonuclease activity [#2, #9]. SHOC1 partners with the ERCC1-like protein SPO16 and with TEX11 to form the trimeric ZZS complex; SPO16 stabilizes SHOC1 protein and SHOC1 in turn is required to recruit downstream recombination factors including TEX11, MSH4, and M1AP to recombination intermediates, with this branched-DNA-binding activity essential for crossover formation [#2, #3, #4, #9]. Loss of SHOC1 abolishes crossovers, leaves meiotic double-strand breaks unrepaired, and produces incomplete or aberrant synapsis with arrest at a zygotene-like stage in mice and early meiotic arrest in men [#3, #10]. The XPF-like domain additionally protects autosomes from meiotic silencing of unsynapsed chromatin by preventing autosome intrusion into the sex body [#9]. Biallelic loss-of-function SHOC1 variants cause non-obstructive azoospermia in human males [#5, #9, #10].\",\n  \"teleology\": [\n    {\n      \"year\": 2008,\n      \"claim\": \"Established that SHOC1 acts specifically in the class I crossover pathway rather than in early recombination, defining its position downstream of strand invasion.\",\n      \"evidence\": \"Genetic mutant and double-mutant epistasis analysis with cytological DMC1 quantification in Arabidopsis\",\n      \"pmids\": [\"18812090\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the biochemical substrate or interacting proteins\", \"XPF-family role inferred from sequence similarity only\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identified the heterodimeric architecture by showing the XPF-like domain mediates interaction with an ERCC1-like partner (PTD), framing SHOC1 as half of an XPF-ERCC1-like module for class I crossovers.\",\n      \"evidence\": \"Yeast two-hybrid domain mapping and genetic epistasis in Arabidopsis\",\n      \"pmids\": [\"21771883\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Interaction shown in plant ortholog; mammalian complex not directly tested\", \"No demonstration of catalytic activity\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Defined the biochemical activity of human SHOC1 as branched-DNA binding without detectable nuclease activity, and connected it in mammals to TEX11, crossover maturation, and proper synapsis.\",\n      \"evidence\": \"In vitro DNA binding and endonuclease assays with recombinant human protein, plus cytology and Co-IP in SHOC1 hypomorphic mice\",\n      \"pmids\": [\"29742103\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Reason for absent nuclease activity despite conserved catalytic domain unresolved\", \"Whether a partner subunit confers catalysis untested\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrated that SHOC1/MZIP2 is essential for recruiting TEX11 and MSH4 to recombination intermediates, establishing it as an upstream organizer of the ZMM module in mammalian meiosis.\",\n      \"evidence\": \"Complete mouse knockout with chromosome spreads and immunofluorescence of downstream factors\",\n      \"pmids\": [\"30272023\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of branched-DNA recognition coupling to recruitment not resolved\", \"Female versus male requirement detail limited\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Completed the trimeric ZZS complex by showing reciprocal SHOC1-SPO16 interaction and that SPO16 stabilizes SHOC1, separating its crossover function from synapsis.\",\n      \"evidence\": \"Co-IP, mouse knockout, and cytological localization of ZMM proteins\",\n      \"pmids\": [\"30746471\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and structure of the ZZS complex not determined\", \"How SPO16 stabilizes SHOC1 mechanistically unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Placed M1AP within the ZZS network downstream of SHOC1 localization, showing M1AP loss reduces TEX11 recruitment and crossovers without disturbing SHOC1.\",\n      \"evidence\": \"Co-IP, mouse knockout, and chromosome spread immunofluorescence\",\n      \"pmids\": [\"36440627\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct versus indirect SHOC1-M1AP contact not resolved\", \"Sex-specific differences in M1AP requirement not fully explained\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Extended SHOC1 function to a presynaptic role by linking biallelic loss to abnormal DMC1/RAD51/RPA2 dynamics and pairing/synapsis defects in azoospermic men and mice.\",\n      \"evidence\": \"Whole-exome sequencing of NOA patients, mouse knockout, and meiotic spread immunofluorescence\",\n      \"pmids\": [\"35485979\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Presynaptic mechanism is a single-lab inference\", \"Molecular link between SHOC1 and strand-exchange protein loading undefined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Positioned SHOC1 downstream of the RNF212B E3 ligase in the crossover maturation pathway by showing reduced SHOC1 focus formation in RNF212B mutants.\",\n      \"evidence\": \"RNF212B knockout mouse with cytological MZIP2 focus quantification\",\n      \"pmids\": [\"38865271\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"SHOC1 was not the primary subject\", \"Whether RNF212B acts on SHOC1 directly is untested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Pinpointed the XPF-like domain via a disease missense variant (p.Q590R) as required for branched-DNA binding, factor recruitment, and protection of autosomes from MSUC, mechanistically linking domain function to chromatin architecture and disease.\",\n      \"evidence\": \"Patient variant identification, in vitro branched-DNA binding assay, cytology, and 3D chromatin analysis\",\n      \"pmids\": [\"42258546\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of branched-DNA recognition not resolved\", \"How the domain prevents autosome intrusion into the sex body mechanistically unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Distinguished ZZS deficiency (early meiotic arrest with synapsis and DSB-repair failure) from M1AP deficiency (metaphase I arrest) in human males, defining SHOC1/ZZS as essential for early recombination steps leading to synapsis.\",\n      \"evidence\": \"Testicular phenotyping of men with biallelic LoF variants, meiotic spreads, immunofluorescence\",\n      \"pmids\": [\"40374915\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Observational human characterization without manipulation\", \"Molecular step distinguishing ZZS from M1AP arrest not defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Why SHOC1 retains a conserved XPF/ERCC4 catalytic architecture yet shows no detectable endonuclease activity, and whether catalysis is acquired in the assembled ZZS complex or has been functionally replaced by branched-DNA recognition, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structure of the ZZS complex bound to branched DNA\", \"No reconstituted assay testing catalysis in complex context\", \"Mechanism coupling branched-DNA binding to downstream ZMM recruitment undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [2, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [2, 3, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [3, 5, 10]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [0, 2, 3]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [3, 5, 9]}\n    ],\n    \"complexes\": [\"ZZS complex (SHOC1-SPO16-TEX11)\"],\n    \"partners\": [\"SPO16\", \"TEX11\", \"M1AP\", \"PTD\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}