{"gene":"SYCP2","run_date":"2026-06-10T10:51:54","timeline":{"discoveries":[{"year":2006,"finding":"SYCP2 forms heterodimers with SYCP3 both in vitro and in vivo, mediated by an evolutionarily conserved coiled-coil domain in SYCP2. Deletion of this coiled-coil domain prevents SYCP3 incorporation into axial/lateral elements (AEs/LEs) of the synaptonemal complex, while the mutant SYCP2 still localizes to axial chromosomal cores, establishing SYCP2 as the primary determinant of AE/LE formation.","method":"In vitro binding assay, in vivo co-immunoprecipitation, coiled-coil domain deletion mouse mutant, immunofluorescence on spermatocyte spreads","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro reconstitution of heterodimer, in vivo Co-IP, domain mutagenesis (deletion allele in mice), and direct localization experiments with functional phenotype in same study","pmids":["16717126"],"is_preprint":false},{"year":2006,"finding":"SYCP2 is required for synaptonemal complex assembly and chromosomal synapsis during male meiosis; Sycp2 mutant male mice are sterile due to a block in meiosis with failure of AE formation, whereas females are subfertile with reduced litter size, demonstrating sexually dimorphic requirement.","method":"Conditional/targeted mouse knockout (Sycp2 coiled-coil deletion allele), fertility assays, meiotic spread immunofluorescence","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic knockout with defined meiotic arrest phenotype, replicated across sexes, multiple orthogonal readouts","pmids":["16717126"],"is_preprint":false},{"year":2005,"finding":"SYCP2 and SYCP3 are required for maintaining cohesin core integrity at the diplotene stage of meiosis; in the absence of SYCP3 (which also removes SYCP2 from cores), cohesin cores in female meiotic chromosomes disassemble prematurely at diplotene. However, SYCP2 and SYCP3 are not required for centromere cohesion at metaphase I in male germ cells.","method":"Sycp3-deficient mouse analysis, immunofluorescence of cohesin-complex proteins on meiotic chromosome spreads from both sexes","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO mouse model, sex-specific analysis, but SYCP2 not directly deleted (loss inferred through SYCP3 KO context)","pmids":["15870106"],"is_preprint":false},{"year":2008,"finding":"SYCP2 directly interacts with the transverse filament protein SYCP1 via its C-terminal region, and SYCP1's C-terminus mediates this interaction, establishing SYCP2 as a molecular linker between lateral elements (via SYCP3) and transverse filaments (via SYCP1) of the synaptonemal complex.","method":"Immunoprecipitation from meiotic cell extracts, yeast two-hybrid system, interaction trap assays, domain-mapping experiments","journal":"Chromosoma","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal interaction confirmed by co-IP and two independent yeast two-hybrid/interaction-trap methods, domain mapping performed","pmids":["19034475"],"is_preprint":false},{"year":2004,"finding":"In the absence of SYCP2 and SYCP3, meiotic chromosome core alignment between homologs is preserved, indicating that homology recognition/alignment is not a function of these core components but may be mediated by chromatin-chromatin interactions. However, SYCP2 and SYCP3 are required for the specificity of chromatin loop attachment to the chromosome core.","method":"Sycp3-null mouse (which also lacks SYCP2 on cores), whole-chromosome painting for homolog alignment, measurement of chromatin loop sizes with centromeric satellite and exogenous transgene sequences","journal":"Cytogenetic and genome research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis using KO mouse, multiple orthogonal chromatin assays, but SYCP2 not independently deleted","pmids":["15237206"],"is_preprint":false},{"year":2020,"finding":"In zebrafish spermatocytes, Sycp2 is required for synaptonemal complex assembly (initiated near telomeres), homologous pairing, formation of Dmc1/Rad51 and RPA recombinase foci, and γH2AX signals, demonstrating that Sycp2 is essential for early meiotic recombination initiation in addition to SC structural assembly.","method":"ENU mutagenesis hypomorphic allele and TALEN-generated knockout in zebrafish, immunofluorescence for SC proteins and recombination markers, meiotic chromosome spreads","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — two independent alleles (hypomorphic and null) with graded phenotypes, multiple orthogonal meiotic markers examined, replicates mammalian findings in vertebrate model","pmids":["32092049"],"is_preprint":false},{"year":2024,"finding":"In cancer cells, SYCP2 promotes repair of DNA double-strand breaks through transcription-coupled homologous recombination (TC-HR) by facilitating R-loop formation at DSBs and recruiting RAD51 independently of BRCA1; SYCP2 loss impairs RAD51 localization and reduces TC-HR, rendering tumor cells sensitive to PARP and TOP1 inhibitors.","method":"SYCP2 knockdown/overexpression in breast and ovarian cancer cell lines, R-loop immunofluorescence assays, RAD51 recruitment assays, PARP and TOP1 inhibitor sensitivity assays, BRCA1-independent pathway analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function with defined molecular phenotype (RAD51 localization, R-loop formation), multiple orthogonal functional readouts, supported by clinical cohort correlation","pmids":["38383600"],"is_preprint":false},{"year":2025,"finding":"ABL1 tyrosine kinase phosphorylates SYCP2 at tyrosine Y739 within a conserved phosphorylation motif [RK]-x(2,3)-[DE]-x(2,3)-Y; this phosphorylation promotes SYCP2 function at R-loop sites, facilitates RAD51 localization and DSB repair via transcription-coupled homologous recombination, and contributes to platinum resistance in ovarian cancer. ABL1 and SYCP2 colocalize at sites of R-loops after DNA damage.","method":"Site-directed mutagenesis (Y739 phospho-null mutant), ABL1 inhibitor treatment, co-localization immunofluorescence at R-loop/damage sites, RAD51 recruitment assay, in vivo tumor growth assay","journal":"NAR cancer","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — site-specific mutagenesis of phosphorylation site with functional rescue/loss assay, in vitro and in vivo validation, single lab but multiple orthogonal methods","pmids":["40918650"],"is_preprint":false},{"year":2023,"finding":"A homozygous frameshift variant in SYCP2 (c.2689_2690insT) causes meiotic arrest at the zygotene stage and non-obstructive azoospermia, demonstrating that complete loss of SYCP2 function leads to a block in spermatogenesis at the zygotene stage in humans, and that SYCP2-associated azoospermia can follow an autosomal recessive inheritance pattern.","method":"Whole exome sequencing, Sanger sequencing, histological (HE) and immunofluorescence analysis of testicular biopsy, meiotic chromosomal spread analysis","journal":"Clinical genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct patient genetics with meiotic spread confirmation, single patient/family, but phenotype clearly defined at cellular level","pmids":["37337432"],"is_preprint":false},{"year":2015,"finding":"Evolutionary analysis combined with RNA and protein expression data established that SYCP2 is an ancient metazoan SC protein present in basal-branching metazoans, predating more recently evolved SC components such as SYCE1 and SYCE3, indicating it was a constituent of the ancestral synaptonemal complex more than 500 million years ago.","method":"Bioinformatic phylogenetic analysis, RNA expression analysis, protein expression analysis across metazoan species","journal":"Cytogenetic and genome research","confidence":"Low","confidence_rationale":"Tier 4 / Moderate — primarily bioinformatic/comparative analysis with expression validation, no direct functional experiment","pmids":["25831978"],"is_preprint":false}],"current_model":"SYCP2 is a core structural component of the synaptonemal complex lateral element that heterodimerizes with SYCP3 via a conserved coiled-coil domain to nucleate axial/lateral element assembly during meiotic prophase I, links transverse filaments to lateral elements by directly binding the C-terminus of SYCP1, and is required for chromosomal synapsis, homologous pairing, and early meiotic recombination (Dmc1/Rad51 recruitment); additionally, when aberrantly expressed in cancer cells, SYCP2 promotes transcription-coupled homologous recombination at DNA double-strand breaks by facilitating R-loop formation and RAD51 recruitment independently of BRCA1, a function regulated by ABL1-mediated phosphorylation at Y739."},"narrative":{"mechanistic_narrative":"SYCP2 is a core structural component of the synaptonemal complex (SC) lateral/axial elements that organizes chromosome architecture during meiotic prophase I [PMID:16717126]. It heterodimerizes with SYCP3 through an evolutionarily conserved coiled-coil domain, and this interaction is the primary determinant of axial/lateral element (AE/LE) assembly: deletion of the coiled-coil prevents SYCP3 incorporation into AEs/LEs while leaving SYCP2 itself on axial cores [PMID:16717126]. Through its C-terminal region SYCP2 directly binds the C-terminus of the transverse filament protein SYCP1, positioning it as the molecular linker that couples lateral elements to transverse filaments [PMID:19034475]. Genetically, SYCP2 is required for SC assembly and chromosomal synapsis: loss causes meiotic arrest with failed AE formation, manifesting as male sterility and female subfertility in mice, and as zygotene-stage meiotic arrest in zebrafish, where it is additionally required for homologous pairing and for formation of Dmc1/Rad51, RPA, and γH2AX recombination foci [PMID:16717126, PMID:32092049]. In humans, a homozygous frameshift variant causes zygotene-stage meiotic arrest and autosomal-recessive non-obstructive azoospermia [PMID:37337432]. Beyond meiosis, when aberrantly expressed in cancer cells SYCP2 promotes transcription-coupled homologous recombination at DNA double-strand breaks by facilitating R-loop formation and recruiting RAD51 independently of BRCA1, sensitizing tumors to PARP and TOP1 inhibitors; this activity is enhanced by ABL1-mediated phosphorylation at Y739 and contributes to platinum resistance [PMID:38383600, PMID:40918650].","teleology":[{"year":2005,"claim":"Established that the SYCP3/SYCP2 core is needed to maintain cohesin integrity and proper chromatin loop attachment, distinguishing core structural roles from cohesion per se.","evidence":"Sycp3-deficient mouse meiotic spreads with cohesin immunofluorescence and chromatin loop measurements in both sexes","pmids":["15870106","15237206"],"confidence":"Medium","gaps":["SYCP2 was not independently deleted; its role inferred from SYCP3 loss","Mechanism by which the core specifies loop attachment is undefined","Homology alignment shown to be core-independent, leaving its mediator unidentified"]},{"year":2006,"claim":"Defined SYCP2 as the primary determinant of axial/lateral element formation by showing it heterodimerizes with SYCP3 via a conserved coiled-coil domain required for SYCP3 incorporation, and that its loss blocks meiosis.","evidence":"In vitro binding, in vivo Co-IP, coiled-coil deletion mouse mutant, fertility assays, and spermatocyte spread immunofluorescence","pmids":["16717126"],"confidence":"High","gaps":["Structural basis of the heterodimer not resolved","Reason for sexually dimorphic requirement (sterile males vs subfertile females) unexplained"]},{"year":2008,"claim":"Identified the molecular bridge between SC substructures by mapping a direct SYCP2 C-terminus–SYCP1 C-terminus interaction, linking lateral elements to transverse filaments.","evidence":"Co-IP from meiotic extracts, yeast two-hybrid/interaction trap, and domain mapping","pmids":["19034475"],"confidence":"High","gaps":["Stoichiometry and structure of the SYCP2–SYCP1 interface not determined","Whether this linkage is regulated during synapsis is unknown"]},{"year":2020,"claim":"Extended SYCP2 function beyond structural assembly by showing it is also required for homologous pairing and recombination initiation in a vertebrate model.","evidence":"ENU hypomorphic and TALEN-null zebrafish alleles with immunofluorescence for SC and recombination markers (Dmc1/Rad51, RPA, γH2AX)","pmids":["32092049"],"confidence":"High","gaps":["Whether recombination defects are direct or secondary to failed SC assembly is unresolved","Molecular link between SYCP2 and recombinase loading not defined"]},{"year":2023,"claim":"Established SYCP2 as a human meiosis gene by linking a loss-of-function variant to zygotene arrest and azoospermia.","evidence":"Whole exome sequencing of an azoospermia patient with testicular histology and meiotic spread analysis","pmids":["37337432"],"confidence":"Medium","gaps":["Single patient/family limits genetic generalizability","Functional consequence of the variant confirmed only at cellular level"]},{"year":2024,"claim":"Revealed an unexpected somatic role for SYCP2 in promoting transcription-coupled homologous recombination at DSBs through R-loop formation and BRCA1-independent RAD51 recruitment, with therapeutic implications.","evidence":"Knockdown/overexpression in breast and ovarian cancer lines, R-loop and RAD51 recruitment assays, PARP/TOP1 inhibitor sensitivity, clinical cohort correlation","pmids":["38383600"],"confidence":"High","gaps":["Direct biochemical mechanism by which SYCP2 facilitates R-loop formation unknown","Relationship between meiotic and cancer-associated functions unclear"]},{"year":2025,"claim":"Identified ABL1 phosphorylation of SYCP2 at Y739 as a regulatory switch that promotes its R-loop-associated repair function and platinum resistance.","evidence":"Y739 phospho-null mutagenesis, ABL1 inhibition, colocalization at R-loop/damage sites, RAD51 recruitment, and in vivo tumor growth assays","pmids":["40918650"],"confidence":"High","gaps":["Whether Y739 phosphorylation regulates the meiotic function is untested","Single-lab finding; structural effect of phosphorylation not resolved"]},{"year":null,"claim":"How a meiosis-specific structural protein is co-opted into somatic DSB repair, and whether its R-loop/RAD51 functions share mechanistic logic with its SC-organizing role, remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No structural model of SYCP2 or its complexes","Mechanism connecting SC architecture to recombinase recruitment undefined","Direct molecular basis of SYCP2-driven R-loop formation unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,1]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[3]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0]}],"localization":[{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[0,4]},{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[0,5]}],"pathway":[{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[1,5,8]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[6,7]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[1,5]}],"complexes":["synaptonemal complex (lateral/axial element)"],"partners":["SYCP3","SYCP1","RAD51","ABL1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9BX26","full_name":"Synaptonemal complex protein 2","aliases":["Synaptonemal complex lateral element protein","hsSCP2"],"length_aa":1530,"mass_kda":175.6,"function":"Major component of the axial/lateral elements of synaptonemal complexes (SCS) during meiotic prophase. Plays a role in the assembly of synaptonemal complexes. Required for normal meiotic chromosome synapsis during oocyte and spermatocyte development and for normal male and female fertility. Required for insertion of SYCP3 into synaptonemal complexes. May be involved in the organization of chromatin by temporarily binding to DNA scaffold attachment regions. Requires SYCP3, but not SYCP1, in order to be incorporated into the axial/lateral elements","subcellular_location":"Nucleus; Chromosome","url":"https://www.uniprot.org/uniprotkb/Q9BX26/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SYCP2","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SYCP2","total_profiled":1310},"omim":[{"mim_id":"616799","title":"SYNAPTONEMAL COMPLEX PROTEIN 2-LIKE; SYCP2L","url":"https://www.omim.org/entry/616799"},{"mim_id":"604759","title":"SYNAPTONEMAL COMPLEX PROTEIN 3; SYCP3","url":"https://www.omim.org/entry/604759"},{"mim_id":"604105","title":"SYNAPTONEMAL COMPLEX PROTEIN 2; SYCP2","url":"https://www.omim.org/entry/604105"},{"mim_id":"300311","title":"TESTIS-EXPRESSED GENE 11; TEX11","url":"https://www.omim.org/entry/300311"},{"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"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"breast","ntpm":13.0},{"tissue":"testis","ntpm":40.2}],"url":"https://www.proteinatlas.org/search/SYCP2"},"hgnc":{"alias_symbol":["SCP2"],"prev_symbol":[]},"alphafold":{"accession":"Q9BX26","domains":[{"cath_id":"-","chopping":"142-277","consensus_level":"medium","plddt":92.5082,"start":142,"end":277},{"cath_id":"2.30.29","chopping":"282-394","consensus_level":"medium","plddt":90.094,"start":282,"end":394},{"cath_id":"1.20.5","chopping":"1438-1485","consensus_level":"medium","plddt":86.3542,"start":1438,"end":1485}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BX26","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BX26-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BX26-F1-predicted_aligned_error_v6.png","plddt_mean":53.97},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SYCP2","jax_strain_url":"https://www.jax.org/strain/search?query=SYCP2"},"sequence":{"accession":"Q9BX26","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9BX26.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9BX26/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BX26"}},"corpus_meta":[{"pmid":"16717126","id":"PMC_16717126","title":"Mouse SYCP2 is required for synaptonemal complex assembly and chromosomal synapsis during male meiosis.","date":"2006","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/16717126","citation_count":223,"is_preprint":false},{"pmid":"15870106","id":"PMC_15870106","title":"SYCP2 and SYCP3 are required for cohesin core integrity at diplotene but not for centromere cohesion at the first meiotic division.","date":"2005","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/15870106","citation_count":83,"is_preprint":false},{"pmid":"26334652","id":"PMC_26334652","title":"Deregulation of SYCP2 predicts early stage human papillomavirus-positive oropharyngeal carcinoma: A prospective whole transcriptome analysis.","date":"2015","source":"Cancer science","url":"https://pubmed.ncbi.nlm.nih.gov/26334652","citation_count":48,"is_preprint":false},{"pmid":"19034475","id":"PMC_19034475","title":"Protein SYCP2 provides a link between transverse filaments and lateral elements of mammalian synaptonemal complexes.","date":"2008","source":"Chromosoma","url":"https://pubmed.ncbi.nlm.nih.gov/19034475","citation_count":44,"is_preprint":false},{"pmid":"32092049","id":"PMC_32092049","title":"Sycp2 is essential for synaptonemal complex assembly, early meiotic recombination and homologous pairing in zebrafish spermatocytes.","date":"2020","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/32092049","citation_count":44,"is_preprint":false},{"pmid":"15237206","id":"PMC_15237206","title":"Male mouse meiotic chromosome cores deficient in structural proteins SYCP3 and SYCP2 align by homology but fail to synapse and have possible impaired specificity of chromatin loop attachment.","date":"2004","source":"Cytogenetic and genome research","url":"https://pubmed.ncbi.nlm.nih.gov/15237206","citation_count":41,"is_preprint":false},{"pmid":"38383600","id":"PMC_38383600","title":"Meiotic protein SYCP2 confers resistance to DNA-damaging agents through R-loop-mediated DNA repair.","date":"2024","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/38383600","citation_count":15,"is_preprint":false},{"pmid":"25831978","id":"PMC_25831978","title":"Protein SYCP2 is an ancient component of the metazoan synaptonemal complex.","date":"2015","source":"Cytogenetic and genome research","url":"https://pubmed.ncbi.nlm.nih.gov/25831978","citation_count":14,"is_preprint":false},{"pmid":"35596132","id":"PMC_35596132","title":"Recombination rates in pigs differ between breeds, sexes and individuals, and are associated with the RNF212, SYCP2, PRDM7, MEI1 and MSH4 loci.","date":"2022","source":"Genetics, selection, evolution : GSE","url":"https://pubmed.ncbi.nlm.nih.gov/35596132","citation_count":14,"is_preprint":false},{"pmid":"37337432","id":"PMC_37337432","title":"A homozygous frameshift variant in SYCP2 caused meiotic arrest and non-obstructive azoospermia.","date":"2023","source":"Clinical 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positioning, rate and interference are associated with distinct genetic processes in domestic pigs","date":"2024-06-24","source":"bioRxiv","url":"https://doi.org/10.1101/2024.06.20.599484","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10668,"output_tokens":2761,"usd":0.036709,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10072,"output_tokens":3024,"usd":0.06298,"stage2_stop_reason":"end_turn"},"total_usd":0.099689,"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\": 2006,\n      \"finding\": \"SYCP2 forms heterodimers with SYCP3 both in vitro and in vivo, mediated by an evolutionarily conserved coiled-coil domain in SYCP2. Deletion of this coiled-coil domain prevents SYCP3 incorporation into axial/lateral elements (AEs/LEs) of the synaptonemal complex, while the mutant SYCP2 still localizes to axial chromosomal cores, establishing SYCP2 as the primary determinant of AE/LE formation.\",\n      \"method\": \"In vitro binding assay, in vivo co-immunoprecipitation, coiled-coil domain deletion mouse mutant, immunofluorescence on spermatocyte spreads\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro reconstitution of heterodimer, in vivo Co-IP, domain mutagenesis (deletion allele in mice), and direct localization experiments with functional phenotype in same study\",\n      \"pmids\": [\"16717126\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"SYCP2 is required for synaptonemal complex assembly and chromosomal synapsis during male meiosis; Sycp2 mutant male mice are sterile due to a block in meiosis with failure of AE formation, whereas females are subfertile with reduced litter size, demonstrating sexually dimorphic requirement.\",\n      \"method\": \"Conditional/targeted mouse knockout (Sycp2 coiled-coil deletion allele), fertility assays, meiotic spread immunofluorescence\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic knockout with defined meiotic arrest phenotype, replicated across sexes, multiple orthogonal readouts\",\n      \"pmids\": [\"16717126\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"SYCP2 and SYCP3 are required for maintaining cohesin core integrity at the diplotene stage of meiosis; in the absence of SYCP3 (which also removes SYCP2 from cores), cohesin cores in female meiotic chromosomes disassemble prematurely at diplotene. However, SYCP2 and SYCP3 are not required for centromere cohesion at metaphase I in male germ cells.\",\n      \"method\": \"Sycp3-deficient mouse analysis, immunofluorescence of cohesin-complex proteins on meiotic chromosome spreads from both sexes\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO mouse model, sex-specific analysis, but SYCP2 not directly deleted (loss inferred through SYCP3 KO context)\",\n      \"pmids\": [\"15870106\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SYCP2 directly interacts with the transverse filament protein SYCP1 via its C-terminal region, and SYCP1's C-terminus mediates this interaction, establishing SYCP2 as a molecular linker between lateral elements (via SYCP3) and transverse filaments (via SYCP1) of the synaptonemal complex.\",\n      \"method\": \"Immunoprecipitation from meiotic cell extracts, yeast two-hybrid system, interaction trap assays, domain-mapping experiments\",\n      \"journal\": \"Chromosoma\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal interaction confirmed by co-IP and two independent yeast two-hybrid/interaction-trap methods, domain mapping performed\",\n      \"pmids\": [\"19034475\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"In the absence of SYCP2 and SYCP3, meiotic chromosome core alignment between homologs is preserved, indicating that homology recognition/alignment is not a function of these core components but may be mediated by chromatin-chromatin interactions. However, SYCP2 and SYCP3 are required for the specificity of chromatin loop attachment to the chromosome core.\",\n      \"method\": \"Sycp3-null mouse (which also lacks SYCP2 on cores), whole-chromosome painting for homolog alignment, measurement of chromatin loop sizes with centromeric satellite and exogenous transgene sequences\",\n      \"journal\": \"Cytogenetic and genome research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis using KO mouse, multiple orthogonal chromatin assays, but SYCP2 not independently deleted\",\n      \"pmids\": [\"15237206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In zebrafish spermatocytes, Sycp2 is required for synaptonemal complex assembly (initiated near telomeres), homologous pairing, formation of Dmc1/Rad51 and RPA recombinase foci, and γH2AX signals, demonstrating that Sycp2 is essential for early meiotic recombination initiation in addition to SC structural assembly.\",\n      \"method\": \"ENU mutagenesis hypomorphic allele and TALEN-generated knockout in zebrafish, immunofluorescence for SC proteins and recombination markers, meiotic chromosome spreads\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — two independent alleles (hypomorphic and null) with graded phenotypes, multiple orthogonal meiotic markers examined, replicates mammalian findings in vertebrate model\",\n      \"pmids\": [\"32092049\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In cancer cells, SYCP2 promotes repair of DNA double-strand breaks through transcription-coupled homologous recombination (TC-HR) by facilitating R-loop formation at DSBs and recruiting RAD51 independently of BRCA1; SYCP2 loss impairs RAD51 localization and reduces TC-HR, rendering tumor cells sensitive to PARP and TOP1 inhibitors.\",\n      \"method\": \"SYCP2 knockdown/overexpression in breast and ovarian cancer cell lines, R-loop immunofluorescence assays, RAD51 recruitment assays, PARP and TOP1 inhibitor sensitivity assays, BRCA1-independent pathway analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function with defined molecular phenotype (RAD51 localization, R-loop formation), multiple orthogonal functional readouts, supported by clinical cohort correlation\",\n      \"pmids\": [\"38383600\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ABL1 tyrosine kinase phosphorylates SYCP2 at tyrosine Y739 within a conserved phosphorylation motif [RK]-x(2,3)-[DE]-x(2,3)-Y; this phosphorylation promotes SYCP2 function at R-loop sites, facilitates RAD51 localization and DSB repair via transcription-coupled homologous recombination, and contributes to platinum resistance in ovarian cancer. ABL1 and SYCP2 colocalize at sites of R-loops after DNA damage.\",\n      \"method\": \"Site-directed mutagenesis (Y739 phospho-null mutant), ABL1 inhibitor treatment, co-localization immunofluorescence at R-loop/damage sites, RAD51 recruitment assay, in vivo tumor growth assay\",\n      \"journal\": \"NAR cancer\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — site-specific mutagenesis of phosphorylation site with functional rescue/loss assay, in vitro and in vivo validation, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"40918650\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"A homozygous frameshift variant in SYCP2 (c.2689_2690insT) causes meiotic arrest at the zygotene stage and non-obstructive azoospermia, demonstrating that complete loss of SYCP2 function leads to a block in spermatogenesis at the zygotene stage in humans, and that SYCP2-associated azoospermia can follow an autosomal recessive inheritance pattern.\",\n      \"method\": \"Whole exome sequencing, Sanger sequencing, histological (HE) and immunofluorescence analysis of testicular biopsy, meiotic chromosomal spread analysis\",\n      \"journal\": \"Clinical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct patient genetics with meiotic spread confirmation, single patient/family, but phenotype clearly defined at cellular level\",\n      \"pmids\": [\"37337432\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Evolutionary analysis combined with RNA and protein expression data established that SYCP2 is an ancient metazoan SC protein present in basal-branching metazoans, predating more recently evolved SC components such as SYCE1 and SYCE3, indicating it was a constituent of the ancestral synaptonemal complex more than 500 million years ago.\",\n      \"method\": \"Bioinformatic phylogenetic analysis, RNA expression analysis, protein expression analysis across metazoan species\",\n      \"journal\": \"Cytogenetic and genome research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Moderate — primarily bioinformatic/comparative analysis with expression validation, no direct functional experiment\",\n      \"pmids\": [\"25831978\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SYCP2 is a core structural component of the synaptonemal complex lateral element that heterodimerizes with SYCP3 via a conserved coiled-coil domain to nucleate axial/lateral element assembly during meiotic prophase I, links transverse filaments to lateral elements by directly binding the C-terminus of SYCP1, and is required for chromosomal synapsis, homologous pairing, and early meiotic recombination (Dmc1/Rad51 recruitment); additionally, when aberrantly expressed in cancer cells, SYCP2 promotes transcription-coupled homologous recombination at DNA double-strand breaks by facilitating R-loop formation and RAD51 recruitment independently of BRCA1, a function regulated by ABL1-mediated phosphorylation at Y739.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SYCP2 is a core structural component of the synaptonemal complex (SC) lateral/axial elements that organizes chromosome architecture during meiotic prophase I [#0, #1]. It heterodimerizes with SYCP3 through an evolutionarily conserved coiled-coil domain, and this interaction is the primary determinant of axial/lateral element (AE/LE) assembly: deletion of the coiled-coil prevents SYCP3 incorporation into AEs/LEs while leaving SYCP2 itself on axial cores [#0]. Through its C-terminal region SYCP2 directly binds the C-terminus of the transverse filament protein SYCP1, positioning it as the molecular linker that couples lateral elements to transverse filaments [#3]. Genetically, SYCP2 is required for SC assembly and chromosomal synapsis: loss causes meiotic arrest with failed AE formation, manifesting as male sterility and female subfertility in mice, and as zygotene-stage meiotic arrest in zebrafish, where it is additionally required for homologous pairing and for formation of Dmc1/Rad51, RPA, and \\u03b3H2AX recombination foci [#1, #5]. In humans, a homozygous frameshift variant causes zygotene-stage meiotic arrest and autosomal-recessive non-obstructive azoospermia [#8]. Beyond meiosis, when aberrantly expressed in cancer cells SYCP2 promotes transcription-coupled homologous recombination at DNA double-strand breaks by facilitating R-loop formation and recruiting RAD51 independently of BRCA1, sensitizing tumors to PARP and TOP1 inhibitors; this activity is enhanced by ABL1-mediated phosphorylation at Y739 and contributes to platinum resistance [#6, #7].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Established that the SYCP3/SYCP2 core is needed to maintain cohesin integrity and proper chromatin loop attachment, distinguishing core structural roles from cohesion per se.\",\n      \"evidence\": \"Sycp3-deficient mouse meiotic spreads with cohesin immunofluorescence and chromatin loop measurements in both sexes\",\n      \"pmids\": [\"15870106\", \"15237206\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"SYCP2 was not independently deleted; its role inferred from SYCP3 loss\",\n        \"Mechanism by which the core specifies loop attachment is undefined\",\n        \"Homology alignment shown to be core-independent, leaving its mediator unidentified\"\n      ]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Defined SYCP2 as the primary determinant of axial/lateral element formation by showing it heterodimerizes with SYCP3 via a conserved coiled-coil domain required for SYCP3 incorporation, and that its loss blocks meiosis.\",\n      \"evidence\": \"In vitro binding, in vivo Co-IP, coiled-coil deletion mouse mutant, fertility assays, and spermatocyte spread immunofluorescence\",\n      \"pmids\": [\"16717126\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of the heterodimer not resolved\",\n        \"Reason for sexually dimorphic requirement (sterile males vs subfertile females) unexplained\"\n      ]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identified the molecular bridge between SC substructures by mapping a direct SYCP2 C-terminus–SYCP1 C-terminus interaction, linking lateral elements to transverse filaments.\",\n      \"evidence\": \"Co-IP from meiotic extracts, yeast two-hybrid/interaction trap, and domain mapping\",\n      \"pmids\": [\"19034475\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Stoichiometry and structure of the SYCP2–SYCP1 interface not determined\",\n        \"Whether this linkage is regulated during synapsis is unknown\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Extended SYCP2 function beyond structural assembly by showing it is also required for homologous pairing and recombination initiation in a vertebrate model.\",\n      \"evidence\": \"ENU hypomorphic and TALEN-null zebrafish alleles with immunofluorescence for SC and recombination markers (Dmc1/Rad51, RPA, \\u03b3H2AX)\",\n      \"pmids\": [\"32092049\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether recombination defects are direct or secondary to failed SC assembly is unresolved\",\n        \"Molecular link between SYCP2 and recombinase loading not defined\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Established SYCP2 as a human meiosis gene by linking a loss-of-function variant to zygotene arrest and azoospermia.\",\n      \"evidence\": \"Whole exome sequencing of an azoospermia patient with testicular histology and meiotic spread analysis\",\n      \"pmids\": [\"37337432\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single patient/family limits genetic generalizability\",\n        \"Functional consequence of the variant confirmed only at cellular level\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Revealed an unexpected somatic role for SYCP2 in promoting transcription-coupled homologous recombination at DSBs through R-loop formation and BRCA1-independent RAD51 recruitment, with therapeutic implications.\",\n      \"evidence\": \"Knockdown/overexpression in breast and ovarian cancer lines, R-loop and RAD51 recruitment assays, PARP/TOP1 inhibitor sensitivity, clinical cohort correlation\",\n      \"pmids\": [\"38383600\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Direct biochemical mechanism by which SYCP2 facilitates R-loop formation unknown\",\n        \"Relationship between meiotic and cancer-associated functions unclear\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified ABL1 phosphorylation of SYCP2 at Y739 as a regulatory switch that promotes its R-loop-associated repair function and platinum resistance.\",\n      \"evidence\": \"Y739 phospho-null mutagenesis, ABL1 inhibition, colocalization at R-loop/damage sites, RAD51 recruitment, and in vivo tumor growth assays\",\n      \"pmids\": [\"40918650\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether Y739 phosphorylation regulates the meiotic function is untested\",\n        \"Single-lab finding; structural effect of phosphorylation not resolved\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a meiosis-specific structural protein is co-opted into somatic DSB repair, and whether its R-loop/RAD51 functions share mechanistic logic with its SC-organizing role, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No structural model of SYCP2 or its complexes\",\n        \"Mechanism connecting SC architecture to recombinase recruitment undefined\",\n        \"Direct molecular basis of SYCP2-driven R-loop formation unknown\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [0, 4]},\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [0, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": []},\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [1, 5, 8]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [6, 7]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [1, 5]}\n    ],\n    \"complexes\": [\n      \"synaptonemal complex (lateral/axial element)\"\n    ],\n    \"partners\": [\n      \"SYCP3\",\n      \"SYCP1\",\n      \"RAD51\",\n      \"ABL1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":6,"faith_pct":83.33333333333333}}