{"gene":"EQTN","run_date":"2026-06-09T23:54:43","timeline":{"discoveries":[{"year":1998,"finding":"Equatorin (MN9 antigenic molecule) localized at the equatorial segment of the acrosome is required for sperm-oocyte fusion in mice. The MN9 antibody did not affect sperm motility, zona binding, or zona penetration, but significantly inhibited fertilization by blocking sperm-oocyte fusion, as evidenced by accumulation of sperm in the perivitelline space with unreleased cortical granules beneath the oolemma.","method":"In vitro fertilization inhibition assay with monoclonal antibody mMN9, electron microscopy, confocal laser scanning immunofluorescence microscopy","journal":"Biology of reproduction","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (IVF inhibition, EM, immunofluorescence) in a focused study establishing a specific cellular function with defined molecular localization","pmids":["9674989"],"is_preprint":false},{"year":2001,"finding":"Equatorin in the posterior acrosome is not exposed on intact spermatozoa but becomes detectable after acrosome reaction (spontaneous or induced). After sperm-egg fusion during IVF, equatorin dissociates from the sperm head equatorial region, remains near decondensing male pronuclei, is pushed away during pronuclear apposition, and is inherited by one proembryonic cell after first cleavage, disappearing after the second cleavage.","method":"Immunofluorescence with permeabilization assays, in vitro fertilization, confocal microscopy, microinjection of sperm into MII oocytes","journal":"Biology of reproduction","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple methods (IVF, microinjection, immunofluorescence) in a single lab, clearly defining equatorin behavior during fertilization","pmids":["11673259"],"is_preprint":false},{"year":2006,"finding":"Afaf (EQTN/SPACA8), a novel membrane protein, is expressed abundantly in round spermatids and localizes to the inner and outer membranes of forming acrosomes during spermiogenesis, then declines in maturing acrosomes. In transfected HeLa cells, Afaf localizes to the plasma membrane and EEA1-positive early endosomes, suggesting involvement of early endosomes and plasma membrane in acrosome biogenesis.","method":"Cloning, immunofluorescence, subcellular fractionation/localization in transfected HeLa cells, co-localization with EEA1 marker","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single lab, immunofluorescence and co-localization, defines subcellular localization with partial mechanistic follow-up on acrosome biogenesis","pmids":["16831425"],"is_preprint":false},{"year":2009,"finding":"Afaf (EQTN) participates in calcium-triggered acrosomal exocytosis by acting upstream of calcium efflux from the acrosome interior. Afaf interacts with SNAP25 (a SNARE complex component critical for exocytosis and endosomal trafficking), as demonstrated by co-immunoprecipitation and co-localization. Afaf antibodies inhibit sperm penetration of eggs and reduce in vitro fertilization rates. Afaf also regulates endocytic pathway by down-regulating transferrin endocytosis in HeLa cells.","method":"Co-immunoprecipitation, co-localization, acrosomal exocytosis assay with streptolysin O permeabilization, transferrin uptake assay, RNAi, in vitro fertilization, sperm penetration assay","journal":"Fertility and sterility","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP plus functional assays (IVF, AE, transferrin uptake) in a single lab, multiple orthogonal methods establishing interaction and mechanism","pmids":["19285662"],"is_preprint":false},{"year":2009,"finding":"Equatorin is a highly glycosylated, sperm-specific type 1 transmembrane N,O-sialoglycoprotein. The gamete interaction-related domain recognized by the MN9 antibody is post-translationally modified near threonine 138, most likely via O-glycosylation. The MN9 epitope (N-terminus) localizes on the acrosomal membrane facing the acrosomal lumen as shown by immunogold electron microscopy.","method":"cDNA cloning, mass spectrometry, carbohydrate staining, glycosidase treatment, recombinant protein assays, amino acid substitution mutagenesis, dephosphorylation assay, O-glycosylation inhibitor assay, immunogold electron microscopy","journal":"Biology of reproduction","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal biochemical methods (mass spectrometry, mutagenesis, glycosidase treatment, immunogold EM) in a single rigorous study establishing molecular identity and post-translational modification","pmids":["19605790"],"is_preprint":false},{"year":2009,"finding":"During the acrosome reaction on zona pellucida, equatorin undergoes a defined progression: it spreads from the peripheral anterior acrosome to the equatorial segment in four stages (initial, early, advanced, final). Equatorin decreases in molecular mass from 40–60 kDa to 35 kDa as the acrosome reaction progresses, and accumulates on hybrid vesicles surrounded by amorphous substances at the advanced stage.","method":"MN9 antibody immunofluorescence staging, PNA-FITC staining, immunogold electron microscopy, Western blot of acrosome-reacted sperm","journal":"Reproduction (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple methods (immunofluorescence staging, immunogold EM, Western blot) in a single lab defining mechanistic progression","pmids":["20032212"],"is_preprint":false},{"year":2012,"finding":"Galnt3-mediated mucin-type O-glycosylation of equatorin is required for the MN9 antibody epitope recognition. In Galnt3-deficient mice, the O-glycosylated moiety of equatorin (recognized by MN9 antibody, which inhibits sperm-egg interaction) was drastically reduced, linking Galnt3-catalyzed O-glycosylation of equatorin to the fertilization process.","method":"Galnt3 knockout mouse model, immunohistochemistry, Western blot with MN9 antibody, VVA lectin binding (Tn antigen detection)","journal":"Histochemistry and cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with defined biochemical readout (loss of O-glycan epitope on equatorin), single lab","pmids":["23052838"],"is_preprint":false},{"year":2013,"finding":"During spermatogenesis, equatorin mRNA is first detected in round spermatids but disappears in early elongating spermatids. The protein (~65 kDa in testis) is first detected on nascent acrosomal membrane at step 3 round spermatids, actively integrates into acrosomal membranes in subsequent steps, and participates in acrosome remodeling in elongating spermatids. Immunogold EM showed the epitope region lying 5–70 nm from the acrosomal membrane, associated with the electron-dense acrosomal matrix.","method":"In situ hybridization, super-resolution STED nanoscopy, immunogold electron microscopy, GFP-tagged transgenic mice, high-resolution fluorescence microscopy","journal":"Cell and tissue research","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal methods including super-resolution nanoscopy, immunogold EM, transgenic mice, and in situ hybridization in a rigorous single study","pmids":["23564009"],"is_preprint":false},{"year":2014,"finding":"Equatorin (Eqtn) is not required for acrosome biogenesis but is essential for the acrosome reaction. Eqtn-knockout males are subfertile (~50% of plugged females pregnant vs >90% for controls). Eqtn-deficient sperm have normal motility and morphology but dramatically reduced fertilization rates and induced acrosome exocytosis rates. Equatorin protein interacts with Syntaxin1a and SNAP25 (SNARE complex components), but loss of Eqtn does not affect protein levels of these partners.","method":"Gene knockout mouse model, in vitro fertilization assay, acrosome exocytosis assay, co-immunoprecipitation with Syntaxin1a and SNAP25, Western blot","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO mouse with defined cellular phenotypes plus co-IP identifying SNARE complex interaction; multiple orthogonal methods in a single focused study","pmids":["24480441"],"is_preprint":false},{"year":2018,"finding":"EQTN-knockout males have reduced fertility and reduced sperm-egg adhesion. Eqtn−/− sperm can travel to the oviduct and penetrate the zona pellucida but show significant reduction in sperm attached to zona-free oocytes. SPESP1 behaved aberrantly in Eqtn−/− sperm during the acrosome reaction. EQTN/SPESP1-double KO males showed more severe fertility impairment than single Eqtn−/− males. Fertility was rescued in Eqtn−/−-Tg(Eqtn) males. IZUMO1 and egg CD9 behaved normally in Eqtn−/− sperm.","method":"Eqtn knockout and double KO (Eqtn/Spesp1) mouse models, transgenic rescue (Eqtn−/−-Tg(Eqtn)), zona-free oocyte sperm binding assay, acrosome reporter (Acr-Egfp) transgenic mice, immunofluorescence for IZUMO1, CD9, and SPESP1","journal":"Reproduction (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO with genetic rescue, double KO epistasis, and multiple molecular readouts; multiple orthogonal methods establishing role in sperm-egg adhesion specifically","pmids":["30328350"],"is_preprint":false},{"year":2000,"finding":"C9orf11 (an alias for EQTN) encodes a protein of 294 amino acids (predicted 32.8 kDa) with a putative leucine zipper at the C-terminal end, organized in eight exons spanning ~13 kb on chromosome 9p21. Expression analysis showed C9orf11 is highly expressed in testis with minor expression in other tissues.","method":"cDNA cloning, sequence analysis, Northern blot/expression analysis, mutation screening in CMM families","journal":"Biochimica et biophysica acta","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, cloning and expression analysis only, no functional mechanistic data beyond identification","pmids":["11118625"],"is_preprint":false},{"year":2023,"finding":"Equatorin (EQTN) is among the most highly O-glycosylated proteins in human sperm and seminal plasma, detected in a comprehensive O-glycoproteome map. EQTN was identified as one of three highly abundant, highly complex, and highly O-glycosylated proteins, with multiple novel O-glycosites identified for the first time, primarily modified by core 1 O-glycans.","method":"Glycoproteomics using two complementary fragmentation methods (GlycoTCFM), mass spectrometry-based intact O-glycopeptide analysis of human sperm and seminal plasma","journal":"Journal of proteome research","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — mass spectrometry-based glycoproteomics with site-level resolution, single study, establishes specific O-glycosylation sites on human EQTN","pmids":["37943980"],"is_preprint":false}],"current_model":"Equatorin (EQTN/SPACA8/AFAF/C9orf11) is a sperm-specific type 1 transmembrane N,O-sialoglycoprotein that integrates into the acrosomal membrane during spermatogenesis, where it is required for the acrosome reaction and sperm-egg adhesion/fusion: it interacts with SNARE complex components Syntaxin1a and SNAP25 to mediate outer acrosomal membrane–plasma membrane fusion during the acrosome reaction, and its O-glycosylated extracellular domain (near Thr138, modified by Galnt3) is functionally important for gamete interaction, with loss-of-function causing subfertility due to defective acrosome exocytosis and reduced sperm attachment to the oolemma."},"narrative":{"mechanistic_narrative":"Equatorin (EQTN/SPACA8/AFAF/C9orf11) is a sperm-specific type 1 transmembrane N,O-sialoglycoprotein that integrates into the acrosomal membrane during spermiogenesis and is essential for the acrosome reaction and sperm–egg interaction [PMID:9674989, PMID:19605790, PMID:24480441]. The protein is first expressed in round spermatids and deposited onto nascent acrosomal membranes, where it associates with the electron-dense acrosomal matrix and participates in acrosome remodeling, though it is dispensable for acrosome biogenesis itself [PMID:16831425, PMID:23564009, PMID:24480441]. On intact sperm equatorin is sequestered facing the acrosomal lumen and becomes exposed only after the acrosome reaction, during which it undergoes a staged redistribution from the anterior acrosome to the equatorial segment accompanied by a reduction in molecular mass [PMID:11673259, PMID:19605790, PMID:20032212]. Mechanistically, equatorin acts upstream of acrosomal calcium efflux and physically interacts with the SNARE proteins SNAP25 and Syntaxin1a to support the membrane fusion underlying acrosomal exocytosis; in transfected cells it also modulates endosomal trafficking, down-regulating transferrin endocytosis [PMID:19285662, PMID:24480441]. Its extracellular gamete-interaction domain is heavily O-glycosylated near threonine 138 by Galnt3-dependent mucin-type glycosylation, a modification required for the MN9 fertility-blocking epitope and for normal sperm–egg adhesion [PMID:19605790, PMID:23052838, PMID:37943980]. Loss of Eqtn causes subfertility marked by defective induced acrosome exocytosis and reduced attachment of sperm to the oolemma, with aberrant behavior of the partner protein SPESP1 and a more severe phenotype in Eqtn/Spesp1 double knockouts, while fertility is restored by transgenic rescue [PMID:24480441, PMID:30328350].","teleology":[{"year":1998,"claim":"Established that an equatorial-segment acrosomal molecule is specifically required for the gamete fusion step rather than earlier fertilization events, defining EQTN's functional niche.","evidence":"IVF inhibition with the MN9 monoclonal antibody, electron microscopy, and immunofluorescence in mouse","pmids":["9674989"],"confidence":"High","gaps":["Molecular identity of the antigen not yet defined","Mechanism of how blocking the molecule prevents fusion unknown"]},{"year":2000,"claim":"Identified the gene (C9orf11) encoding a testis-enriched 294-aa protein, providing the genomic and sequence framework for the antigen.","evidence":"cDNA cloning, sequence/expression analysis, and mutation screening on chromosome 9p21","pmids":["11118625"],"confidence":"Low","gaps":["No functional data beyond identification","Link to the equatorin/MN9 antigen not established in this study"]},{"year":2001,"claim":"Showed that equatorin is masked on intact sperm and exposed after the acrosome reaction, then tracked through fertilization, clarifying when and where it becomes accessible to act.","evidence":"Permeabilization immunofluorescence, IVF, sperm microinjection, and confocal microscopy","pmids":["11673259"],"confidence":"Medium","gaps":["Biochemical basis of post-fertilization dissociation unknown","Functional consequence of inheritance pattern unclear"]},{"year":2006,"claim":"Defined the developmental timing and subcellular targeting of the protein, linking acrosome formation to plasma membrane and early endosome compartments.","evidence":"Cloning, immunofluorescence, and EEA1 co-localization in transfected HeLa cells","pmids":["16831425"],"confidence":"Medium","gaps":["Endosomal role inferred from heterologous cells, not sperm","No direct mechanism linking trafficking to acrosome biogenesis"]},{"year":2009,"claim":"Connected equatorin to the exocytic machinery by demonstrating it acts upstream of acrosomal calcium efflux, interacts with SNAP25, and modulates endocytosis, providing a molecular mechanism for its role in exocytosis.","evidence":"Co-IP and co-localization with SNAP25, permeabilized acrosomal exocytosis and transferrin uptake assays, RNAi, and IVF","pmids":["19285662"],"confidence":"Medium","gaps":["Single-lab co-IP without reciprocal validation","Direct vs indirect nature of SNAP25 interaction unresolved"]},{"year":2009,"claim":"Resolved the molecular identity and topology of equatorin as a glycosylated type 1 transmembrane N,O-sialoglycoprotein and mapped the gamete-interaction epitope to an O-glycosylation site near Thr138.","evidence":"cDNA cloning, mass spectrometry, glycosidase and mutagenesis assays, O-glycosylation inhibition, and immunogold EM","pmids":["19605790"],"confidence":"High","gaps":["Identity of the egg-side binding partner not established","Functional role of N-glycans/sialylation not dissected"]},{"year":2009,"claim":"Mapped the staged redistribution and proteolytic/molecular-mass change of equatorin during the acrosome reaction on the zona, defining its dynamic behavior during exocytosis.","evidence":"MN9 immunofluorescence staging, PNA-FITC, immunogold EM, and Western blot of acrosome-reacted sperm","pmids":["20032212"],"confidence":"Medium","gaps":["Enzyme(s) responsible for mass reduction unknown","Functional significance of hybrid-vesicle accumulation unclear"]},{"year":2012,"claim":"Identified Galnt3 as the glycosyltransferase generating the functional O-glycan epitope on equatorin, tying a specific glycosylation enzyme to the fertilization-relevant modification.","evidence":"Galnt3 knockout mice, immunohistochemistry, MN9 Western blot, and VVA lectin Tn-antigen detection","pmids":["23052838"],"confidence":"Medium","gaps":["Whether Galnt3 loss impairs fertility through equatorin specifically not shown","Other glycosyltransferases acting on equatorin unidentified"]},{"year":2013,"claim":"Defined the precise expression timing, membrane integration, and nanoscale matrix association of equatorin during spermatogenesis at super-resolution.","evidence":"In situ hybridization, STED nanoscopy, immunogold EM, and GFP-tagged transgenic mice","pmids":["23564009"],"confidence":"High","gaps":["Targeting machinery directing acrosomal integration unknown","Functional necessity at each developmental step not tested genetically here"]},{"year":2014,"claim":"Provided genetic proof via knockout that equatorin is dispensable for acrosome biogenesis but essential for the acrosome reaction, and confirmed interaction with both Syntaxin1a and SNAP25.","evidence":"Eqtn knockout mice, IVF and acrosome exocytosis assays, and co-IP with Syntaxin1a/SNAP25","pmids":["24480441"],"confidence":"High","gaps":["How equatorin promotes SNARE-mediated fusion mechanistically unresolved","Residual fertility implies redundant pathways not identified"]},{"year":2018,"claim":"Localized the fertility defect specifically to reduced sperm–oolemma adhesion and revealed genetic interaction with SPESP1, refining the step at which EQTN acts during gamete interaction.","evidence":"Eqtn and Eqtn/Spesp1 double knockouts, transgenic rescue, zona-free oocyte binding assays, and immunofluorescence for IZUMO1/CD9/SPESP1","pmids":["30328350"],"confidence":"High","gaps":["Molecular basis of EQTN-SPESP1 functional interaction unknown","Direct adhesion receptor on the oolemma not identified"]},{"year":2023,"claim":"Confirmed and extended the human O-glycoproteome of equatorin, establishing it as one of the most heavily core-1 O-glycosylated sperm proteins with multiple novel sites.","evidence":"Glycoproteomics (GlycoTCFM) and intact O-glycopeptide mass spectrometry of human sperm and seminal plasma","pmids":["37943980"],"confidence":"Medium","gaps":["Functional role of individual human glycosites untested","Species conservation of site-level glycosylation not addressed"]},{"year":null,"claim":"The egg-side receptor that engages equatorin's O-glycosylated extracellular domain and the precise biochemical mechanism by which equatorin promotes SNARE-mediated acrosomal membrane fusion remain undefined.","evidence":"","pmids":[],"confidence":"High","gaps":["No oolemmal binding partner identified","Direct biochemical role of equatorin in the fusion reaction not reconstituted"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[3,8]}],"localization":[{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[2,4,7]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[2,3]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[2,3]}],"pathway":[{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[0,8,9]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[3,8]}],"complexes":[],"partners":["SNAP25","STX1A","SPESP1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9NQ60","full_name":"Equatorin","aliases":["Acrosome formation-associated factor"],"length_aa":294,"mass_kda":32.8,"function":"Acrosomal membrane-anchored protein involved in the process of fertilization and in acrosome biogenesis","subcellular_location":"Cytoplasmic vesicle, secretory vesicle, acrosome membrane; Cytoplasmic vesicle, secretory vesicle, acrosome inner membrane; Cytoplasmic vesicle, secretory vesicle, acrosome outer membrane","url":"https://www.uniprot.org/uniprotkb/Q9NQ60/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/EQTN","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/EQTN","total_profiled":1310},"omim":[{"mim_id":"617653","title":"EQUATORIN; EQTN","url":"https://www.omim.org/entry/617653"},{"mim_id":"617652","title":"MOB KINASE ACTIVATOR 3B; MOB3B","url":"https://www.omim.org/entry/617652"},{"mim_id":"617651","title":"EQTN, MOB3B, IFNK, AND C9ORF72 ENHANCER RNA I, NONCODING","url":"https://www.omim.org/entry/617651"},{"mim_id":"615326","title":"INTERFERON, KAPPA; IFNK","url":"https://www.omim.org/entry/615326"},{"mim_id":"614260","title":"CHROMOSOME 9 OPEN READING FRAME 72; C9ORF72","url":"https://www.omim.org/entry/614260"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Actin filaments","reliability":"Approved"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in single","driving_tissues":[{"tissue":"testis","ntpm":35.3}],"url":"https://www.proteinatlas.org/search/EQTN"},"hgnc":{"alias_symbol":["AFAF","SPACA8","equatorin"],"prev_symbol":["C9orf11"]},"alphafold":{"accession":"Q9NQ60","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NQ60","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NQ60-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NQ60-F1-predicted_aligned_error_v6.png","plddt_mean":58.91},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=EQTN","jax_strain_url":"https://www.jax.org/strain/search?query=EQTN"},"sequence":{"accession":"Q9NQ60","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9NQ60.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9NQ60/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NQ60"}},"corpus_meta":[{"pmid":"20495015","id":"PMC_20495015","title":"Association of left atrial endothelin-1 with atrial rhythm, size, and fibrosis in patients with structural heart disease.","date":"2010","source":"Circulation. Arrhythmia and electrophysiology","url":"https://pubmed.ncbi.nlm.nih.gov/20495015","citation_count":132,"is_preprint":false},{"pmid":"18439551","id":"PMC_18439551","title":"Genetic architecture of transcript-level variation in humans.","date":"2008","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/18439551","citation_count":113,"is_preprint":false},{"pmid":"25693803","id":"PMC_25693803","title":"Discovery of predictive biomarkers for litter size in boar spermatozoa.","date":"2015","source":"Molecular & cellular proteomics : MCP","url":"https://pubmed.ncbi.nlm.nih.gov/25693803","citation_count":93,"is_preprint":false},{"pmid":"9674989","id":"PMC_9674989","title":"An MN9 antigenic molecule, equatorin, is required for successful sperm-oocyte fusion in mice.","date":"1998","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/9674989","citation_count":73,"is_preprint":false},{"pmid":"26489431","id":"PMC_26489431","title":"Increased male fertility using fertility-related biomarkers.","date":"2015","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/26489431","citation_count":69,"is_preprint":false},{"pmid":"8002584","id":"PMC_8002584","title":"Nucleotide sequence of the afimbrial-adhesin-encoding afa-3 gene cluster and its translocation via flanking IS1 insertion sequences.","date":"1994","source":"Journal of bacteriology","url":"https://pubmed.ncbi.nlm.nih.gov/8002584","citation_count":68,"is_preprint":false},{"pmid":"8820639","id":"PMC_8820639","title":"The afimbrial adhesive sheath encoded by the afa-3 gene cluster of pathogenic Escherichia coli is composed of two adhesins.","date":"1996","source":"Molecular microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/8820639","citation_count":65,"is_preprint":false},{"pmid":"29947466","id":"PMC_29947466","title":"Genetic architecture underlying the lignin biosynthesis pathway involves noncoding RNAs and transcription factors for growth and wood properties in Populus.","date":"2018","source":"Plant biotechnology journal","url":"https://pubmed.ncbi.nlm.nih.gov/29947466","citation_count":50,"is_preprint":false},{"pmid":"16831425","id":"PMC_16831425","title":"Afaf, a novel vesicle membrane protein, is related to acrosome formation in murine testis.","date":"2006","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/16831425","citation_count":34,"is_preprint":false},{"pmid":"11673259","id":"PMC_11673259","title":"Exposure of sperm head equatorin after acrosome reaction and its fate after fertilization in mice.","date":"2001","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/11673259","citation_count":31,"is_preprint":false},{"pmid":"23052838","id":"PMC_23052838","title":"Galnt3 deficiency disrupts acrosome formation and leads to oligoasthenoteratozoospermia.","date":"2012","source":"Histochemistry and cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/23052838","citation_count":31,"is_preprint":false},{"pmid":"24480441","id":"PMC_24480441","title":"Equatorin is not essential for acrosome biogenesis but is required for the acrosome reaction.","date":"2014","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/24480441","citation_count":26,"is_preprint":false},{"pmid":"8858583","id":"PMC_8858583","title":"The clp (CS31A) operon is negatively controlled by Lrp, ClpB, and L-alanine at the transcriptional level.","date":"1996","source":"Molecular microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/8858583","citation_count":24,"is_preprint":false},{"pmid":"19605790","id":"PMC_19605790","title":"Equatorin: identification and characterization of the epitope of the MN9 antibody in the mouse.","date":"2009","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/19605790","citation_count":23,"is_preprint":false},{"pmid":"30328350","id":"PMC_30328350","title":"Deletion of Eqtn in mice reduces male fertility and sperm-egg adhesion.","date":"2018","source":"Reproduction (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/30328350","citation_count":23,"is_preprint":false},{"pmid":"20032212","id":"PMC_20032212","title":"A model of the acrosome reaction progression via the acrosomal membrane-anchored protein equatorin.","date":"2009","source":"Reproduction (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/20032212","citation_count":22,"is_preprint":false},{"pmid":"10946147","id":"PMC_10946147","title":"The afa-related gene cluster in necrotoxigenic and other Escherichia coli from animals belongs to the afa-8 variant.","date":"2000","source":"Veterinary microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/10946147","citation_count":22,"is_preprint":false},{"pmid":"36535002","id":"PMC_36535002","title":"Enhanced genome-wide association reveals the role of YABBY11-NGATHA-LIKE1 in leaf serration development of Populus.","date":"2023","source":"Plant physiology","url":"https://pubmed.ncbi.nlm.nih.gov/36535002","citation_count":22,"is_preprint":false},{"pmid":"37782577","id":"PMC_37782577","title":"Bull Sperm SWATH-MS-Based Proteomics Reveals Link between High Fertility and Energy Production, Motility Structures, and Sperm-Oocyte Interaction.","date":"2023","source":"Journal of proteome research","url":"https://pubmed.ncbi.nlm.nih.gov/37782577","citation_count":21,"is_preprint":false},{"pmid":"31560799","id":"PMC_31560799","title":"Linkage-linkage disequilibrium dissection of the epigenetic quantitative trait loci (epiQTLs) underlying growth and wood properties in Populus.","date":"2019","source":"The New phytologist","url":"https://pubmed.ncbi.nlm.nih.gov/31560799","citation_count":21,"is_preprint":false},{"pmid":"34256996","id":"PMC_34256996","title":"Membrane lipid replacement with nano-micelles in human sperm cryopreservation improves post-thaw function and acrosome protein integrity.","date":"2021","source":"Reproductive biomedicine online","url":"https://pubmed.ncbi.nlm.nih.gov/34256996","citation_count":21,"is_preprint":false},{"pmid":"32665575","id":"PMC_32665575","title":"Optimization of sperm RNA processing for developmental research.","date":"2020","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/32665575","citation_count":20,"is_preprint":false},{"pmid":"19285662","id":"PMC_19285662","title":"Acrosome formation-associated factor is involved in fertilization.","date":"2009","source":"Fertility and sterility","url":"https://pubmed.ncbi.nlm.nih.gov/19285662","citation_count":20,"is_preprint":false},{"pmid":"35794675","id":"PMC_35794675","title":"Establishment of a male fertility prediction model with sperm RNA markers in pigs as a translational animal model.","date":"2022","source":"Journal of animal science and biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/35794675","citation_count":18,"is_preprint":false},{"pmid":"33258949","id":"PMC_33258949","title":"Miniature inverted repeat transposable elements cis-regulate circular RNA expression and promote ethylene biosynthesis, reducing heat tolerance in Populus tomentosa.","date":"2021","source":"Journal of experimental botany","url":"https://pubmed.ncbi.nlm.nih.gov/33258949","citation_count":16,"is_preprint":false},{"pmid":"12618452","id":"PMC_12618452","title":"Leucine-responsive regulatory protein-mediated repression of clp (encoding CS31A) expression by L-leucine and L-alanine in Escherichia coli.","date":"2003","source":"Journal of bacteriology","url":"https://pubmed.ncbi.nlm.nih.gov/12618452","citation_count":16,"is_preprint":false},{"pmid":"31649710","id":"PMC_31649710","title":"Finding New Cell Wall Regulatory Genes in Populus trichocarpa Using Multiple Lines of Evidence.","date":"2019","source":"Frontiers in plant science","url":"https://pubmed.ncbi.nlm.nih.gov/31649710","citation_count":15,"is_preprint":false},{"pmid":"33999454","id":"PMC_33999454","title":"Integration of genome wide association studies and co-expression networks reveal roles of PtoWRKY 42-PtoUGT76C1-1 in trans-zeatin metabolism and cytokinin sensitivity in poplar.","date":"2021","source":"The New phytologist","url":"https://pubmed.ncbi.nlm.nih.gov/33999454","citation_count":15,"is_preprint":false},{"pmid":"23564009","id":"PMC_23564009","title":"Integration of the mouse sperm fertilization-related protein equatorin into the acrosome during spermatogenesis as revealed by super-resolution and immunoelectron microscopy.","date":"2013","source":"Cell and tissue research","url":"https://pubmed.ncbi.nlm.nih.gov/23564009","citation_count":14,"is_preprint":false},{"pmid":"37943980","id":"PMC_37943980","title":"GlycoTCFM: Glycoproteomics Based on Two Complementary Fragmentation Methods Reveals Distinctive O-Glycosylation in Human Sperm and Seminal Plasma.","date":"2023","source":"Journal of proteome research","url":"https://pubmed.ncbi.nlm.nih.gov/37943980","citation_count":12,"is_preprint":false},{"pmid":"36050562","id":"PMC_36050562","title":"The vertebrate- and testis- specific transmembrane protein C11ORF94 plays a critical role in sperm-oocyte membrane binding.","date":"2022","source":"Molecular biomedicine","url":"https://pubmed.ncbi.nlm.nih.gov/36050562","citation_count":11,"is_preprint":false},{"pmid":"27676172","id":"PMC_27676172","title":"Novel Sperm and Gonadotropin-releasing Hormone-based Recombinant Fusion Protein: Achievement of 100% Contraceptive Efficacy by Co-immunization of Male and Female Mice.","date":"2016","source":"Molecular reproduction and development","url":"https://pubmed.ncbi.nlm.nih.gov/27676172","citation_count":10,"is_preprint":false},{"pmid":"24914179","id":"PMC_24914179","title":"Leucine-responsive regulatory protein Lrp and PapI homologues influence phase variation of CS31A fimbriae.","date":"2014","source":"Journal of bacteriology","url":"https://pubmed.ncbi.nlm.nih.gov/24914179","citation_count":10,"is_preprint":false},{"pmid":"38837425","id":"PMC_38837425","title":"afila, the origin and nature of a major innovation in the history of pea breeding.","date":"2024","source":"The New phytologist","url":"https://pubmed.ncbi.nlm.nih.gov/38837425","citation_count":9,"is_preprint":false},{"pmid":"36714547","id":"PMC_36714547","title":"High-throughput proteomic characterization of seminal plasma from bulls with contrasting semen quality.","date":"2023","source":"3 Biotech","url":"https://pubmed.ncbi.nlm.nih.gov/36714547","citation_count":8,"is_preprint":false},{"pmid":"39800247","id":"PMC_39800247","title":"Dahuang-Gancao decoction ameliorates testosterone-induced androgenetic alopecia in mice.","date":"2025","source":"Journal of ethnopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/39800247","citation_count":7,"is_preprint":false},{"pmid":"24452736","id":"PMC_24452736","title":"Preoperative hepatic CT perfusion as an early predictor for the recurrence of esophageal squamous cell carcinoma: initial clinical results.","date":"2014","source":"Oncology reports","url":"https://pubmed.ncbi.nlm.nih.gov/24452736","citation_count":7,"is_preprint":false},{"pmid":"11118625","id":"PMC_11118625","title":"Isolation and characterisation of a novel human gene (C9orf11) on chromosome 9p21, a region frequently deleted in human cancer.","date":"2000","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/11118625","citation_count":6,"is_preprint":false},{"pmid":"25430742","id":"PMC_25430742","title":"Analysis of the complexity of the sperm acrosomal membrane by super-resolution stimulated emission depletion microscopy compared with transmission electron microscopy.","date":"2014","source":"Microscopy (Oxford, England)","url":"https://pubmed.ncbi.nlm.nih.gov/25430742","citation_count":6,"is_preprint":false},{"pmid":"33673666","id":"PMC_33673666","title":"Genetic Architecture Underlying the Metabolites of Chlorogenic Acid Biosynthesis in Populus tomentosa.","date":"2021","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/33673666","citation_count":6,"is_preprint":false},{"pmid":"37079096","id":"PMC_37079096","title":"Cryostress induces fragmentation and alters the abundance of sperm transcripts associated with fertilizing competence and reproductive processes in buffalo.","date":"2023","source":"Cell and tissue research","url":"https://pubmed.ncbi.nlm.nih.gov/37079096","citation_count":6,"is_preprint":false},{"pmid":"30941430","id":"PMC_30941430","title":"Transcription factors involved in the regulatory networks governing the Calvin-Benson-Bassham cycle.","date":"2019","source":"Tree physiology","url":"https://pubmed.ncbi.nlm.nih.gov/30941430","citation_count":5,"is_preprint":false},{"pmid":"37988335","id":"PMC_37988335","title":"Allelic variations of WAK106-E2Fa-DPb1-UGT74E2 module regulate fibre properties in Populus tomentosa.","date":"2023","source":"Plant biotechnology journal","url":"https://pubmed.ncbi.nlm.nih.gov/37988335","citation_count":3,"is_preprint":false},{"pmid":"31695175","id":"PMC_31695175","title":"A multimodal attempt to follow-up linkage regions using RNA expression, SNPs and CpG methylation in schizophrenia and bipolar disorder kindreds.","date":"2019","source":"European journal of human genetics : EJHG","url":"https://pubmed.ncbi.nlm.nih.gov/31695175","citation_count":3,"is_preprint":false},{"pmid":"39648428","id":"PMC_39648428","title":"Exploring the Biological Effects of Polystyrene Nanoplastics on Spermatogenesis: Insights From Transcriptomic Analysis in Mouse Spermatocytes.","date":"2024","source":"International journal of toxicology","url":"https://pubmed.ncbi.nlm.nih.gov/39648428","citation_count":3,"is_preprint":false},{"pmid":"29690710","id":"PMC_29690710","title":"[Relationship between FGF23/FGFR4 expression in atrial tissue and atrial fibrosis in patients with atrial fibrillation].","date":"2018","source":"Zhonghua yi xue za zhi","url":"https://pubmed.ncbi.nlm.nih.gov/29690710","citation_count":3,"is_preprint":false},{"pmid":"35968119","id":"PMC_35968119","title":"Transcriptome and association mapping revealed functional genes respond to drought stress in Populus.","date":"2022","source":"Frontiers in plant science","url":"https://pubmed.ncbi.nlm.nih.gov/35968119","citation_count":2,"is_preprint":false},{"pmid":"17161877","id":"PMC_17161877","title":"Analysis of alcohol-related phenotypes in F2 progeny derived from FH/Wjd and ACI/N rat strains reveals independent measures and sex differences.","date":"2006","source":"Behavioural brain research","url":"https://pubmed.ncbi.nlm.nih.gov/17161877","citation_count":2,"is_preprint":false},{"pmid":"40263929","id":"PMC_40263929","title":"Identification of Anoikis-Related Genes in Gastric Cancer: Bioinformatics and Experimental Validation.","date":"2025","source":"Cancer medicine","url":"https://pubmed.ncbi.nlm.nih.gov/40263929","citation_count":0,"is_preprint":false},{"pmid":"37283433","id":"PMC_37283433","title":"Transitions experienced by mothers of children/adolescents with sickle cell disease in the context of the COVID-19 pandemic.","date":"2023","source":"Revista gaucha de enfermagem","url":"https://pubmed.ncbi.nlm.nih.gov/37283433","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":28120,"output_tokens":3616,"usd":0.0693,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":11202,"output_tokens":3775,"usd":0.075192,"stage2_stop_reason":"end_turn"},"total_usd":0.144492,"stage1_batch_id":"msgbatch_01AsR7g8dGTEiEw9U83bJeWn","stage2_batch_id":"msgbatch_01YV5ZyxtFNUZEjxRcpd9jzb","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1998,\n      \"finding\": \"Equatorin (MN9 antigenic molecule) localized at the equatorial segment of the acrosome is required for sperm-oocyte fusion in mice. The MN9 antibody did not affect sperm motility, zona binding, or zona penetration, but significantly inhibited fertilization by blocking sperm-oocyte fusion, as evidenced by accumulation of sperm in the perivitelline space with unreleased cortical granules beneath the oolemma.\",\n      \"method\": \"In vitro fertilization inhibition assay with monoclonal antibody mMN9, electron microscopy, confocal laser scanning immunofluorescence microscopy\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (IVF inhibition, EM, immunofluorescence) in a focused study establishing a specific cellular function with defined molecular localization\",\n      \"pmids\": [\"9674989\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Equatorin in the posterior acrosome is not exposed on intact spermatozoa but becomes detectable after acrosome reaction (spontaneous or induced). After sperm-egg fusion during IVF, equatorin dissociates from the sperm head equatorial region, remains near decondensing male pronuclei, is pushed away during pronuclear apposition, and is inherited by one proembryonic cell after first cleavage, disappearing after the second cleavage.\",\n      \"method\": \"Immunofluorescence with permeabilization assays, in vitro fertilization, confocal microscopy, microinjection of sperm into MII oocytes\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple methods (IVF, microinjection, immunofluorescence) in a single lab, clearly defining equatorin behavior during fertilization\",\n      \"pmids\": [\"11673259\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Afaf (EQTN/SPACA8), a novel membrane protein, is expressed abundantly in round spermatids and localizes to the inner and outer membranes of forming acrosomes during spermiogenesis, then declines in maturing acrosomes. In transfected HeLa cells, Afaf localizes to the plasma membrane and EEA1-positive early endosomes, suggesting involvement of early endosomes and plasma membrane in acrosome biogenesis.\",\n      \"method\": \"Cloning, immunofluorescence, subcellular fractionation/localization in transfected HeLa cells, co-localization with EEA1 marker\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single lab, immunofluorescence and co-localization, defines subcellular localization with partial mechanistic follow-up on acrosome biogenesis\",\n      \"pmids\": [\"16831425\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Afaf (EQTN) participates in calcium-triggered acrosomal exocytosis by acting upstream of calcium efflux from the acrosome interior. Afaf interacts with SNAP25 (a SNARE complex component critical for exocytosis and endosomal trafficking), as demonstrated by co-immunoprecipitation and co-localization. Afaf antibodies inhibit sperm penetration of eggs and reduce in vitro fertilization rates. Afaf also regulates endocytic pathway by down-regulating transferrin endocytosis in HeLa cells.\",\n      \"method\": \"Co-immunoprecipitation, co-localization, acrosomal exocytosis assay with streptolysin O permeabilization, transferrin uptake assay, RNAi, in vitro fertilization, sperm penetration assay\",\n      \"journal\": \"Fertility and sterility\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP plus functional assays (IVF, AE, transferrin uptake) in a single lab, multiple orthogonal methods establishing interaction and mechanism\",\n      \"pmids\": [\"19285662\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Equatorin is a highly glycosylated, sperm-specific type 1 transmembrane N,O-sialoglycoprotein. The gamete interaction-related domain recognized by the MN9 antibody is post-translationally modified near threonine 138, most likely via O-glycosylation. The MN9 epitope (N-terminus) localizes on the acrosomal membrane facing the acrosomal lumen as shown by immunogold electron microscopy.\",\n      \"method\": \"cDNA cloning, mass spectrometry, carbohydrate staining, glycosidase treatment, recombinant protein assays, amino acid substitution mutagenesis, dephosphorylation assay, O-glycosylation inhibitor assay, immunogold electron microscopy\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal biochemical methods (mass spectrometry, mutagenesis, glycosidase treatment, immunogold EM) in a single rigorous study establishing molecular identity and post-translational modification\",\n      \"pmids\": [\"19605790\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"During the acrosome reaction on zona pellucida, equatorin undergoes a defined progression: it spreads from the peripheral anterior acrosome to the equatorial segment in four stages (initial, early, advanced, final). Equatorin decreases in molecular mass from 40–60 kDa to 35 kDa as the acrosome reaction progresses, and accumulates on hybrid vesicles surrounded by amorphous substances at the advanced stage.\",\n      \"method\": \"MN9 antibody immunofluorescence staging, PNA-FITC staining, immunogold electron microscopy, Western blot of acrosome-reacted sperm\",\n      \"journal\": \"Reproduction (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple methods (immunofluorescence staging, immunogold EM, Western blot) in a single lab defining mechanistic progression\",\n      \"pmids\": [\"20032212\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Galnt3-mediated mucin-type O-glycosylation of equatorin is required for the MN9 antibody epitope recognition. In Galnt3-deficient mice, the O-glycosylated moiety of equatorin (recognized by MN9 antibody, which inhibits sperm-egg interaction) was drastically reduced, linking Galnt3-catalyzed O-glycosylation of equatorin to the fertilization process.\",\n      \"method\": \"Galnt3 knockout mouse model, immunohistochemistry, Western blot with MN9 antibody, VVA lectin binding (Tn antigen detection)\",\n      \"journal\": \"Histochemistry and cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with defined biochemical readout (loss of O-glycan epitope on equatorin), single lab\",\n      \"pmids\": [\"23052838\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"During spermatogenesis, equatorin mRNA is first detected in round spermatids but disappears in early elongating spermatids. The protein (~65 kDa in testis) is first detected on nascent acrosomal membrane at step 3 round spermatids, actively integrates into acrosomal membranes in subsequent steps, and participates in acrosome remodeling in elongating spermatids. Immunogold EM showed the epitope region lying 5–70 nm from the acrosomal membrane, associated with the electron-dense acrosomal matrix.\",\n      \"method\": \"In situ hybridization, super-resolution STED nanoscopy, immunogold electron microscopy, GFP-tagged transgenic mice, high-resolution fluorescence microscopy\",\n      \"journal\": \"Cell and tissue research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal methods including super-resolution nanoscopy, immunogold EM, transgenic mice, and in situ hybridization in a rigorous single study\",\n      \"pmids\": [\"23564009\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Equatorin (Eqtn) is not required for acrosome biogenesis but is essential for the acrosome reaction. Eqtn-knockout males are subfertile (~50% of plugged females pregnant vs >90% for controls). Eqtn-deficient sperm have normal motility and morphology but dramatically reduced fertilization rates and induced acrosome exocytosis rates. Equatorin protein interacts with Syntaxin1a and SNAP25 (SNARE complex components), but loss of Eqtn does not affect protein levels of these partners.\",\n      \"method\": \"Gene knockout mouse model, in vitro fertilization assay, acrosome exocytosis assay, co-immunoprecipitation with Syntaxin1a and SNAP25, Western blot\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO mouse with defined cellular phenotypes plus co-IP identifying SNARE complex interaction; multiple orthogonal methods in a single focused study\",\n      \"pmids\": [\"24480441\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"EQTN-knockout males have reduced fertility and reduced sperm-egg adhesion. Eqtn−/− sperm can travel to the oviduct and penetrate the zona pellucida but show significant reduction in sperm attached to zona-free oocytes. SPESP1 behaved aberrantly in Eqtn−/− sperm during the acrosome reaction. EQTN/SPESP1-double KO males showed more severe fertility impairment than single Eqtn−/− males. Fertility was rescued in Eqtn−/−-Tg(Eqtn) males. IZUMO1 and egg CD9 behaved normally in Eqtn−/− sperm.\",\n      \"method\": \"Eqtn knockout and double KO (Eqtn/Spesp1) mouse models, transgenic rescue (Eqtn−/−-Tg(Eqtn)), zona-free oocyte sperm binding assay, acrosome reporter (Acr-Egfp) transgenic mice, immunofluorescence for IZUMO1, CD9, and SPESP1\",\n      \"journal\": \"Reproduction (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO with genetic rescue, double KO epistasis, and multiple molecular readouts; multiple orthogonal methods establishing role in sperm-egg adhesion specifically\",\n      \"pmids\": [\"30328350\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"C9orf11 (an alias for EQTN) encodes a protein of 294 amino acids (predicted 32.8 kDa) with a putative leucine zipper at the C-terminal end, organized in eight exons spanning ~13 kb on chromosome 9p21. Expression analysis showed C9orf11 is highly expressed in testis with minor expression in other tissues.\",\n      \"method\": \"cDNA cloning, sequence analysis, Northern blot/expression analysis, mutation screening in CMM families\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, cloning and expression analysis only, no functional mechanistic data beyond identification\",\n      \"pmids\": [\"11118625\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Equatorin (EQTN) is among the most highly O-glycosylated proteins in human sperm and seminal plasma, detected in a comprehensive O-glycoproteome map. EQTN was identified as one of three highly abundant, highly complex, and highly O-glycosylated proteins, with multiple novel O-glycosites identified for the first time, primarily modified by core 1 O-glycans.\",\n      \"method\": \"Glycoproteomics using two complementary fragmentation methods (GlycoTCFM), mass spectrometry-based intact O-glycopeptide analysis of human sperm and seminal plasma\",\n      \"journal\": \"Journal of proteome research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mass spectrometry-based glycoproteomics with site-level resolution, single study, establishes specific O-glycosylation sites on human EQTN\",\n      \"pmids\": [\"37943980\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Equatorin (EQTN/SPACA8/AFAF/C9orf11) is a sperm-specific type 1 transmembrane N,O-sialoglycoprotein that integrates into the acrosomal membrane during spermatogenesis, where it is required for the acrosome reaction and sperm-egg adhesion/fusion: it interacts with SNARE complex components Syntaxin1a and SNAP25 to mediate outer acrosomal membrane–plasma membrane fusion during the acrosome reaction, and its O-glycosylated extracellular domain (near Thr138, modified by Galnt3) is functionally important for gamete interaction, with loss-of-function causing subfertility due to defective acrosome exocytosis and reduced sperm attachment to the oolemma.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"Equatorin (EQTN/SPACA8/AFAF/C9orf11) is a sperm-specific type 1 transmembrane N,O-sialoglycoprotein that integrates into the acrosomal membrane during spermiogenesis and is essential for the acrosome reaction and sperm–egg interaction [#0, #4, #8]. The protein is first expressed in round spermatids and deposited onto nascent acrosomal membranes, where it associates with the electron-dense acrosomal matrix and participates in acrosome remodeling, though it is dispensable for acrosome biogenesis itself [#2, #7, #8]. On intact sperm equatorin is sequestered facing the acrosomal lumen and becomes exposed only after the acrosome reaction, during which it undergoes a staged redistribution from the anterior acrosome to the equatorial segment accompanied by a reduction in molecular mass [#1, #4, #5]. Mechanistically, equatorin acts upstream of acrosomal calcium efflux and physically interacts with the SNARE proteins SNAP25 and Syntaxin1a to support the membrane fusion underlying acrosomal exocytosis; in transfected cells it also modulates endosomal trafficking, down-regulating transferrin endocytosis [#3, #8]. Its extracellular gamete-interaction domain is heavily O-glycosylated near threonine 138 by Galnt3-dependent mucin-type glycosylation, a modification required for the MN9 fertility-blocking epitope and for normal sperm–egg adhesion [#4, #6, #11]. Loss of Eqtn causes subfertility marked by defective induced acrosome exocytosis and reduced attachment of sperm to the oolemma, with aberrant behavior of the partner protein SPESP1 and a more severe phenotype in Eqtn/Spesp1 double knockouts, while fertility is restored by transgenic rescue [#8, #9].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Established that an equatorial-segment acrosomal molecule is specifically required for the gamete fusion step rather than earlier fertilization events, defining EQTN's functional niche.\",\n      \"evidence\": \"IVF inhibition with the MN9 monoclonal antibody, electron microscopy, and immunofluorescence in mouse\",\n      \"pmids\": [\"9674989\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular identity of the antigen not yet defined\", \"Mechanism of how blocking the molecule prevents fusion unknown\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Identified the gene (C9orf11) encoding a testis-enriched 294-aa protein, providing the genomic and sequence framework for the antigen.\",\n      \"evidence\": \"cDNA cloning, sequence/expression analysis, and mutation screening on chromosome 9p21\",\n      \"pmids\": [\"11118625\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No functional data beyond identification\", \"Link to the equatorin/MN9 antigen not established in this study\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Showed that equatorin is masked on intact sperm and exposed after the acrosome reaction, then tracked through fertilization, clarifying when and where it becomes accessible to act.\",\n      \"evidence\": \"Permeabilization immunofluorescence, IVF, sperm microinjection, and confocal microscopy\",\n      \"pmids\": [\"11673259\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Biochemical basis of post-fertilization dissociation unknown\", \"Functional consequence of inheritance pattern unclear\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Defined the developmental timing and subcellular targeting of the protein, linking acrosome formation to plasma membrane and early endosome compartments.\",\n      \"evidence\": \"Cloning, immunofluorescence, and EEA1 co-localization in transfected HeLa cells\",\n      \"pmids\": [\"16831425\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Endosomal role inferred from heterologous cells, not sperm\", \"No direct mechanism linking trafficking to acrosome biogenesis\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Connected equatorin to the exocytic machinery by demonstrating it acts upstream of acrosomal calcium efflux, interacts with SNAP25, and modulates endocytosis, providing a molecular mechanism for its role in exocytosis.\",\n      \"evidence\": \"Co-IP and co-localization with SNAP25, permeabilized acrosomal exocytosis and transferrin uptake assays, RNAi, and IVF\",\n      \"pmids\": [\"19285662\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab co-IP without reciprocal validation\", \"Direct vs indirect nature of SNAP25 interaction unresolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Resolved the molecular identity and topology of equatorin as a glycosylated type 1 transmembrane N,O-sialoglycoprotein and mapped the gamete-interaction epitope to an O-glycosylation site near Thr138.\",\n      \"evidence\": \"cDNA cloning, mass spectrometry, glycosidase and mutagenesis assays, O-glycosylation inhibition, and immunogold EM\",\n      \"pmids\": [\"19605790\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the egg-side binding partner not established\", \"Functional role of N-glycans/sialylation not dissected\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Mapped the staged redistribution and proteolytic/molecular-mass change of equatorin during the acrosome reaction on the zona, defining its dynamic behavior during exocytosis.\",\n      \"evidence\": \"MN9 immunofluorescence staging, PNA-FITC, immunogold EM, and Western blot of acrosome-reacted sperm\",\n      \"pmids\": [\"20032212\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Enzyme(s) responsible for mass reduction unknown\", \"Functional significance of hybrid-vesicle accumulation unclear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identified Galnt3 as the glycosyltransferase generating the functional O-glycan epitope on equatorin, tying a specific glycosylation enzyme to the fertilization-relevant modification.\",\n      \"evidence\": \"Galnt3 knockout mice, immunohistochemistry, MN9 Western blot, and VVA lectin Tn-antigen detection\",\n      \"pmids\": [\"23052838\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether Galnt3 loss impairs fertility through equatorin specifically not shown\", \"Other glycosyltransferases acting on equatorin unidentified\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Defined the precise expression timing, membrane integration, and nanoscale matrix association of equatorin during spermatogenesis at super-resolution.\",\n      \"evidence\": \"In situ hybridization, STED nanoscopy, immunogold EM, and GFP-tagged transgenic mice\",\n      \"pmids\": [\"23564009\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Targeting machinery directing acrosomal integration unknown\", \"Functional necessity at each developmental step not tested genetically here\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Provided genetic proof via knockout that equatorin is dispensable for acrosome biogenesis but essential for the acrosome reaction, and confirmed interaction with both Syntaxin1a and SNAP25.\",\n      \"evidence\": \"Eqtn knockout mice, IVF and acrosome exocytosis assays, and co-IP with Syntaxin1a/SNAP25\",\n      \"pmids\": [\"24480441\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How equatorin promotes SNARE-mediated fusion mechanistically unresolved\", \"Residual fertility implies redundant pathways not identified\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Localized the fertility defect specifically to reduced sperm–oolemma adhesion and revealed genetic interaction with SPESP1, refining the step at which EQTN acts during gamete interaction.\",\n      \"evidence\": \"Eqtn and Eqtn/Spesp1 double knockouts, transgenic rescue, zona-free oocyte binding assays, and immunofluorescence for IZUMO1/CD9/SPESP1\",\n      \"pmids\": [\"30328350\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of EQTN-SPESP1 functional interaction unknown\", \"Direct adhesion receptor on the oolemma not identified\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Confirmed and extended the human O-glycoproteome of equatorin, establishing it as one of the most heavily core-1 O-glycosylated sperm proteins with multiple novel sites.\",\n      \"evidence\": \"Glycoproteomics (GlycoTCFM) and intact O-glycopeptide mass spectrometry of human sperm and seminal plasma\",\n      \"pmids\": [\"37943980\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional role of individual human glycosites untested\", \"Species conservation of site-level glycosylation not addressed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The egg-side receptor that engages equatorin's O-glycosylated extracellular domain and the precise biochemical mechanism by which equatorin promotes SNARE-mediated acrosomal membrane fusion remain undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No oolemmal binding partner identified\", \"Direct biochemical role of equatorin in the fusion reaction not reconstituted\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [3, 8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [2, 4, 7]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2, 3]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [2, 3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [0, 8, 9]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [3, 8]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"SNAP25\", \"STX1A\", \"SPESP1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}