{"gene":"CABS1","run_date":"2026-04-28T17:28:52","timeline":{"discoveries":[{"year":2009,"finding":"CABS1 is a calcium-binding protein specifically expressed in elongate spermatids (steps 13–16) that localizes to the principal piece of flagellum of mature sperm in the cauda epididymis, and binds calcium during epididymal maturation.","method":"Two-dimensional gel electrophoresis, mass spectrometry, immunolocalization, calcium-binding assay; busulfan-depletion/recovery model","journal":"Biology of reproduction","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (2-DE, MS, IHC, calcium overlay) in a single rigorous study establishing identity, localization, and calcium-binding activity","pmids":["19208547"],"is_preprint":false},{"year":2009,"finding":"The rat CABS1 ortholog CLPH is phosphorylated in vitro and in vivo by casein kinase 2, localizes to cytoplasm and mitochondrial inner membrane in elongated spermatids, and is an intrinsically disordered calcium-binding protein.","method":"In vitro kinase assay with casein kinase 2, immunohistochemistry, electron microscopy, trypsin digestion assay, circular dichroism, fluorescence spectroscopy, calcium overlay","journal":"Journal of proteome research","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro kinase assay plus multiple biophysical and structural methods confirming intrinsic disorder, calcium binding, and CK2-mediated phosphorylation","pmids":["19271754"],"is_preprint":false},{"year":2016,"finding":"Porcine CABS1 localizes to the acrosome and flagellum of epididymal sperm; the acrosomal immunoreactivity disappears during the acrosome reaction, and neutralization with anti-pCABS1 antiserum significantly decreases acrosome reactions, implicating CABS1 in calcium ion signaling during acrosome reaction.","method":"Immunolocalization, functional antibody-blocking assay of acrosome reaction, computational transmembrane domain prediction","journal":"Experimental animals","confidence":"Medium","confidence_rationale":"Tier 2–3 — antibody inhibition assay with immunolocalization, single lab, porcine ortholog","pmids":["26960363"],"is_preprint":false},{"year":2021,"finding":"Genetic loss of Cabs1 in mice (CRISPR-Cas9 KO) causes defects in sperm flagellar differentiation including abnormal annulus and disorganization of the midpiece-principal piece junction, bent-tail sperm accumulating during epididymal transit, and subfertility; Cabs1 deficiency also decreases Septin 4 and Krt1 and increases Ccnyl1 levels, indicating disruption of cytoskeleton-related protein expression.","method":"CRISPR-Cas9 knockout mice, ultrastructural electron microscopy, Western blot, immunofluorescence, fertility assays","journal":"International journal of molecular sciences","confidence":"High","confidence_rationale":"Tier 2 — clean CRISPR KO with ultrastructural phenotype, protein-level changes, and fertility readout; multiple orthogonal methods","pmids":["33440775"],"is_preprint":false},{"year":2024,"finding":"CABS1 is present in epididymal lumen fluid; Cabs1 KO mice show no change in luminal calcium concentration but exhibit significant metabolomic perturbations in cauda epididymal fluid (34 differential metabolites), with pathway analysis implicating mitochondrial dysfunction and inflammation as contributors to sperm deformity.","method":"HPLC-MS/MS metabolomics, ICP-MS for metal ions, in vivo microperfusion, immunofluorescence","journal":"Frontiers in endocrinology","confidence":"Medium","confidence_rationale":"Tier 2–3 — metabolomics in KO model with ICP-MS, single lab, indirect mechanistic inference","pmids":["39234505"],"is_preprint":false},{"year":2024,"finding":"CABS1 localizes to the midsection of flagellum in testicular sperm and to the principal piece in epididymal sperm; loss of CABS1 impairs progressive sperm motility, disrupts calcium signaling responses to alkaline high-salt buffer and progesterone, alters PKA substrate phosphorylation and tyrosine phosphorylation, and causes defective fibrous sheath structure with abnormal doublet microtubule configuration.","method":"CRISPR KO mice, immunofluorescence localization, calcium imaging, phosphorylation assays (PKA substrates, tyrosine), electron microscopy of fibrous sheath","journal":"Molecular reproduction and development","confidence":"High","confidence_rationale":"Tier 2 — KO with multiple orthogonal functional assays (calcium flux, kinase signaling, ultrastructure, motility)","pmids":["39526486"],"is_preprint":false},{"year":2025,"finding":"A homozygous nonsense mutation in CABS1 in an infertile man causes protein truncation, reduces CABS1 interaction with the perinuclear theca protein ACTL9 (shown by Co-IP), leads to absence of acrosome in spermatozoa, and causes abnormal localization of the sperm oocyte-activation factor PLCζ, resulting in total fertilization failure.","method":"Whole-exome sequencing, Co-immunoprecipitation of wild-type vs. mutant CABS1 with ACTL9, immunofluorescence, Western blot, transmission electron microscopy","journal":"Journal of assisted reproduction and genetics","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP establishing CABS1–ACTL9 interaction plus mutant validation, single case/single lab","pmids":["40407971"],"is_preprint":false}],"current_model":"CABS1 is an intrinsically disordered, casein kinase 2-phosphorylated calcium-binding protein expressed in elongate spermatids that localizes sequentially from the flagellar midsection (testicular sperm) to the principal piece (epididymal sperm), where it maintains fibrous sheath and annulus integrity, regulates sperm calcium signaling and PKA-dependent phosphorylation cascades, interacts with the perinuclear theca protein ACTL9 to support acrosome formation and PLCζ localization, and whose loss causes structural flagellar defects, impaired motility, and male subfertility/infertility."},"narrative":{"teleology":[{"year":2009,"claim":"Identification of CABS1 as a testis-specific calcium-binding protein of elongate spermatids resolved a key unknown — what calcium-responsive factors are acquired during spermiogenesis and where they reside on mature sperm.","evidence":"2-DE/MS identification, calcium overlay assay, immunolocalization, and busulfan depletion/recovery model in rat","pmids":["19208547"],"confidence":"High","gaps":["No functional loss-of-function data to establish necessity","Calcium-binding stoichiometry and affinity not quantified","Mechanism by which CABS1 reaches the principal piece unknown"]},{"year":2009,"claim":"Demonstration that CABS1 (CLPH ortholog) is intrinsically disordered and phosphorylated by casein kinase 2 established its post-translational regulation and structural class, suggesting it functions as a flexible signaling scaffold rather than a conventional enzyme.","evidence":"In vitro/in vivo CK2 kinase assay, circular dichroism, fluorescence spectroscopy, trypsin sensitivity, immunoEM in rat spermatids","pmids":["19271754"],"confidence":"High","gaps":["Functional consequence of CK2 phosphorylation on CABS1 activity unknown","No interacting partners identified at this stage","Mitochondrial inner membrane localization not reconciled with later flagellar principal-piece localization"]},{"year":2016,"claim":"Antibody-blocking experiments in porcine sperm linked CABS1 to calcium-dependent acrosome reaction, providing the first functional evidence that CABS1 participates in a specific sperm signaling event beyond passive calcium binding.","evidence":"Immunolocalization and anti-CABS1 antiserum neutralization assay measuring acrosome reaction rates in porcine epididymal sperm","pmids":["26960363"],"confidence":"Medium","gaps":["Antibody-blocking is indirect; off-target effects not excluded","Porcine system — relevance to mouse/human CABS1 not yet confirmed genetically","Downstream targets in acrosome reaction signaling unidentified"]},{"year":2021,"claim":"CRISPR knockout of Cabs1 in mice revealed that it is required for annulus integrity, midpiece–principal piece junction organization, and normal sperm morphology during epididymal transit, establishing CABS1 as a structural organizer of the flagellar cytoskeleton.","evidence":"Cabs1-null mice generated by CRISPR-Cas9; ultrastructural EM, Western blot showing reduced Septin 4 and Krt1, fertility assays","pmids":["33440775"],"confidence":"High","gaps":["Direct molecular mechanism linking CABS1 to Septin 4/Krt1 stability unknown","Whether subfertility reflects motility defects, signaling defects, or both not resolved","No rescue experiment to confirm specificity of KO phenotype"]},{"year":2024,"claim":"Detailed analysis of Cabs1 KO sperm demonstrated that CABS1 is required for calcium signaling responses, PKA substrate phosphorylation during capacitation, and fibrous sheath/doublet microtubule architecture — unifying its calcium-binding and structural roles into a single signaling-to-cytoskeleton axis.","evidence":"CRISPR KO mice with calcium imaging (response to progesterone/alkaline buffer), anti-phospho-PKA substrate and phosphotyrosine Western blots, EM of fibrous sheath","pmids":["39526486"],"confidence":"High","gaps":["Whether CABS1 directly modulates PKA activity or acts upstream via calcium unclear","Relocalization mechanism from midsection to principal piece not elucidated","Whether metabolomic perturbations in epididymal fluid are cause or consequence of structural defects unresolved"]},{"year":2025,"claim":"A human homozygous nonsense CABS1 mutation linked the protein to acrosome biogenesis through its interaction with ACTL9 and to oocyte activation through PLCζ localization, establishing CABS1 deficiency as a cause of human male infertility with total fertilization failure.","evidence":"WES of infertile patient, Co-IP of wild-type and truncated CABS1 with ACTL9, immunofluorescence and TEM showing acrosome absence and PLCζ mislocalization","pmids":["40407971"],"confidence":"Medium","gaps":["Single patient/family — additional cases needed to confirm causality","CABS1–ACTL9 interaction demonstrated by Co-IP only; reciprocal and in vivo validation lacking","How CABS1 influences PLCζ localization mechanistically is unknown"]},{"year":null,"claim":"The mechanism by which CABS1 relocalizes along the flagellum during epididymal maturation, the structural basis of its calcium-dependent conformational changes, and the full repertoire of its direct binding partners remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No crystal or cryo-EM structure available for the intrinsically disordered CABS1","Full interactome beyond ACTL9 unknown","Whether CK2 phosphorylation regulates relocalization or calcium binding untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,1,2]}],"localization":[{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[0,3,5]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[1]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[0,3,5,6]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,5]}],"complexes":[],"partners":["ACTL9","CSNK2A1","SEPT4"],"other_free_text":[]},"mechanistic_narrative":"CABS1 is an intrinsically disordered, calcium-binding protein expressed exclusively in elongate spermatids that is essential for sperm flagellar differentiation, calcium signaling, and male fertility. Phosphorylated by casein kinase 2, CABS1 undergoes a dynamic relocalization from the flagellar midsection in testicular sperm to the principal piece during epididymal maturation, where it maintains fibrous sheath integrity, annulus architecture (via Septin 4 and Krt1 expression), and proper doublet microtubule organization [PMID:19208547, PMID:33440775, PMID:39526486]. Loss of CABS1 impairs progressive motility, disrupts calcium influx responses to progesterone and alkaline stimuli, and alters PKA-dependent phosphorylation cascades required for capacitation [PMID:39526486, PMID:26960363]. A homozygous nonsense mutation in human CABS1 abolishes its interaction with the perinuclear theca protein ACTL9, causes acrosome absence and mislocalization of the oocyte-activation factor PLCζ, and results in total fertilization failure [PMID:40407971]."},"prefetch_data":{"uniprot":{"accession":"Q96KC9","full_name":"Calcium-binding and spermatid-specific protein 1","aliases":["Testis development protein NYD-SP26"],"length_aa":395,"mass_kda":43.0,"function":"Calcium-binding protein (By similarity). Essential for maintaining the structural integrity of the sperm flagella (By similarity)","subcellular_location":"Cytoplasm; Mitochondrion inner membrane; Cell projection, cilium, flagellum; Cytoplasmic vesicle, secretory vesicle, acrosome","url":"https://www.uniprot.org/uniprotkb/Q96KC9/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CABS1","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CABS1","total_profiled":1310},"omim":[{"mim_id":"618600","title":"CALCIUM-BINDING PROTEIN, SPERMATID-ASSOCIATED 1; CABS1","url":"https://www.omim.org/entry/618600"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"testis","ntpm":101.9}],"url":"https://www.proteinatlas.org/search/CABS1"},"hgnc":{"alias_symbol":["NYD-SP26","FLJ32897","CLPH"],"prev_symbol":["C4orf35"]},"alphafold":{"accession":"Q96KC9","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96KC9","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96KC9-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96KC9-F1-predicted_aligned_error_v6.png","plddt_mean":39.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CABS1","jax_strain_url":"https://www.jax.org/strain/search?query=CABS1"},"sequence":{"accession":"Q96KC9","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96KC9.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96KC9/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96KC9"}},"corpus_meta":[{"pmid":"23616745","id":"PMC_23616745","title":"Calibration and functional analysis of three genetically encoded Cl(-)/pH sensors.","date":"2013","source":"Frontiers in molecular neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/23616745","citation_count":41,"is_preprint":false},{"pmid":"19208547","id":"PMC_19208547","title":"CABS1 is a novel calcium-binding protein specifically expressed in elongate spermatids of mice.","date":"2009","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/19208547","citation_count":29,"is_preprint":false},{"pmid":"33440775","id":"PMC_33440775","title":"Cabs1 Maintains Structural Integrity of Mouse Sperm Flagella during Epididymal Transit of Sperm.","date":"2021","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/33440775","citation_count":19,"is_preprint":false},{"pmid":"19271754","id":"PMC_19271754","title":"CLPH, a novel casein kinase 2-phosphorylated disordered protein, is specifically associated with postmeiotic germ cells in rat spermatogenesis.","date":"2009","source":"Journal of proteome research","url":"https://pubmed.ncbi.nlm.nih.gov/19271754","citation_count":18,"is_preprint":false},{"pmid":"26960363","id":"PMC_26960363","title":"Identification, localization, and functional analysis of the homologues of mouse CABS1 protein in porcine testis.","date":"2016","source":"Experimental animals","url":"https://pubmed.ncbi.nlm.nih.gov/26960363","citation_count":18,"is_preprint":false},{"pmid":"38453924","id":"PMC_38453924","title":"CRISPR/Cas9 model of prostate cancer identifies Kmt2c deficiency as a metastatic driver by Odam/Cabs1 gene cluster expression.","date":"2024","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/38453924","citation_count":17,"is_preprint":false},{"pmid":"28381457","id":"PMC_28381457","title":"A novel biomarker associated with distress in humans: calcium-binding protein, spermatid-specific 1 (CABS1).","date":"2017","source":"American journal of physiology. Regulatory, integrative and comparative physiology","url":"https://pubmed.ncbi.nlm.nih.gov/28381457","citation_count":7,"is_preprint":false},{"pmid":"31302264","id":"PMC_31302264","title":"CLARITY analysis of the Cl/pH sensor expression in the brain of transgenic mice.","date":"2019","source":"Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/31302264","citation_count":7,"is_preprint":false},{"pmid":"38187237","id":"PMC_38187237","title":"FTHL17, PRM2, CABYR, CPXCR1, ADAM29, and CABS1 are highly expressed in colon cancer patients and are regulated in vitro by epigenetic alterations.","date":"2023","source":"Heliyon","url":"https://pubmed.ncbi.nlm.nih.gov/38187237","citation_count":5,"is_preprint":false},{"pmid":"39234505","id":"PMC_39234505","title":"The metabolomics changes in epididymal lumen fluid of CABS1 deficient male mice potentially contribute to sperm deformity.","date":"2024","source":"Frontiers in endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/39234505","citation_count":3,"is_preprint":false},{"pmid":"39526486","id":"PMC_39526486","title":"CABS1 Is Essential for Progressive Motility and the Integrity of Fibrous Sheath in Mouse Epididymal Spermatozoa.","date":"2024","source":"Molecular reproduction and development","url":"https://pubmed.ncbi.nlm.nih.gov/39526486","citation_count":2,"is_preprint":false},{"pmid":"38753592","id":"PMC_38753592","title":"Identification and characterization of calcium binding protein, spermatid-associated 1 (CABS1)# in selected human tissues and fluids.","date":"2024","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/38753592","citation_count":2,"is_preprint":false},{"pmid":"40407971","id":"PMC_40407971","title":"Identification of nonfunctional CABS1 causing fertilization failure and male infertility in humans: a case report.","date":"2025","source":"Journal of assisted reproduction and genetics","url":"https://pubmed.ncbi.nlm.nih.gov/40407971","citation_count":1,"is_preprint":false},{"pmid":"40490738","id":"PMC_40490738","title":"SEQSIM: A novel bioinformatics tool for comparisons of promoter regions-a case study of calcium binding protein spermatid associated 1 (CABS1).","date":"2025","source":"BMC bioinformatics","url":"https://pubmed.ncbi.nlm.nih.gov/40490738","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8425,"output_tokens":1839,"usd":0.02643},"stage2":{"model":"claude-opus-4-6","input_tokens":5110,"output_tokens":2092,"usd":0.116775},"total_usd":0.143205,"stage1_batch_id":"msgbatch_011kfMfE81o6CTcyhVUqumuW","stage2_batch_id":"msgbatch_01DTputS6WNkH745x1nVSoBo","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2009,\n      \"finding\": \"CABS1 is a calcium-binding protein specifically expressed in elongate spermatids (steps 13–16) that localizes to the principal piece of flagellum of mature sperm in the cauda epididymis, and binds calcium during epididymal maturation.\",\n      \"method\": \"Two-dimensional gel electrophoresis, mass spectrometry, immunolocalization, calcium-binding assay; busulfan-depletion/recovery model\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (2-DE, MS, IHC, calcium overlay) in a single rigorous study establishing identity, localization, and calcium-binding activity\",\n      \"pmids\": [\"19208547\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The rat CABS1 ortholog CLPH is phosphorylated in vitro and in vivo by casein kinase 2, localizes to cytoplasm and mitochondrial inner membrane in elongated spermatids, and is an intrinsically disordered calcium-binding protein.\",\n      \"method\": \"In vitro kinase assay with casein kinase 2, immunohistochemistry, electron microscopy, trypsin digestion assay, circular dichroism, fluorescence spectroscopy, calcium overlay\",\n      \"journal\": \"Journal of proteome research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro kinase assay plus multiple biophysical and structural methods confirming intrinsic disorder, calcium binding, and CK2-mediated phosphorylation\",\n      \"pmids\": [\"19271754\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Porcine CABS1 localizes to the acrosome and flagellum of epididymal sperm; the acrosomal immunoreactivity disappears during the acrosome reaction, and neutralization with anti-pCABS1 antiserum significantly decreases acrosome reactions, implicating CABS1 in calcium ion signaling during acrosome reaction.\",\n      \"method\": \"Immunolocalization, functional antibody-blocking assay of acrosome reaction, computational transmembrane domain prediction\",\n      \"journal\": \"Experimental animals\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — antibody inhibition assay with immunolocalization, single lab, porcine ortholog\",\n      \"pmids\": [\"26960363\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Genetic loss of Cabs1 in mice (CRISPR-Cas9 KO) causes defects in sperm flagellar differentiation including abnormal annulus and disorganization of the midpiece-principal piece junction, bent-tail sperm accumulating during epididymal transit, and subfertility; Cabs1 deficiency also decreases Septin 4 and Krt1 and increases Ccnyl1 levels, indicating disruption of cytoskeleton-related protein expression.\",\n      \"method\": \"CRISPR-Cas9 knockout mice, ultrastructural electron microscopy, Western blot, immunofluorescence, fertility assays\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean CRISPR KO with ultrastructural phenotype, protein-level changes, and fertility readout; multiple orthogonal methods\",\n      \"pmids\": [\"33440775\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CABS1 is present in epididymal lumen fluid; Cabs1 KO mice show no change in luminal calcium concentration but exhibit significant metabolomic perturbations in cauda epididymal fluid (34 differential metabolites), with pathway analysis implicating mitochondrial dysfunction and inflammation as contributors to sperm deformity.\",\n      \"method\": \"HPLC-MS/MS metabolomics, ICP-MS for metal ions, in vivo microperfusion, immunofluorescence\",\n      \"journal\": \"Frontiers in endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — metabolomics in KO model with ICP-MS, single lab, indirect mechanistic inference\",\n      \"pmids\": [\"39234505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CABS1 localizes to the midsection of flagellum in testicular sperm and to the principal piece in epididymal sperm; loss of CABS1 impairs progressive sperm motility, disrupts calcium signaling responses to alkaline high-salt buffer and progesterone, alters PKA substrate phosphorylation and tyrosine phosphorylation, and causes defective fibrous sheath structure with abnormal doublet microtubule configuration.\",\n      \"method\": \"CRISPR KO mice, immunofluorescence localization, calcium imaging, phosphorylation assays (PKA substrates, tyrosine), electron microscopy of fibrous sheath\",\n      \"journal\": \"Molecular reproduction and development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO with multiple orthogonal functional assays (calcium flux, kinase signaling, ultrastructure, motility)\",\n      \"pmids\": [\"39526486\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A homozygous nonsense mutation in CABS1 in an infertile man causes protein truncation, reduces CABS1 interaction with the perinuclear theca protein ACTL9 (shown by Co-IP), leads to absence of acrosome in spermatozoa, and causes abnormal localization of the sperm oocyte-activation factor PLCζ, resulting in total fertilization failure.\",\n      \"method\": \"Whole-exome sequencing, Co-immunoprecipitation of wild-type vs. mutant CABS1 with ACTL9, immunofluorescence, Western blot, transmission electron microscopy\",\n      \"journal\": \"Journal of assisted reproduction and genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP establishing CABS1–ACTL9 interaction plus mutant validation, single case/single lab\",\n      \"pmids\": [\"40407971\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CABS1 is an intrinsically disordered, casein kinase 2-phosphorylated calcium-binding protein expressed in elongate spermatids that localizes sequentially from the flagellar midsection (testicular sperm) to the principal piece (epididymal sperm), where it maintains fibrous sheath and annulus integrity, regulates sperm calcium signaling and PKA-dependent phosphorylation cascades, interacts with the perinuclear theca protein ACTL9 to support acrosome formation and PLCζ localization, and whose loss causes structural flagellar defects, impaired motility, and male subfertility/infertility.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CABS1 is an intrinsically disordered, calcium-binding protein expressed exclusively in elongate spermatids that is essential for sperm flagellar differentiation, calcium signaling, and male fertility. Phosphorylated by casein kinase 2, CABS1 undergoes a dynamic relocalization from the flagellar midsection in testicular sperm to the principal piece during epididymal maturation, where it maintains fibrous sheath integrity, annulus architecture (via Septin 4 and Krt1 expression), and proper doublet microtubule organization [PMID:19208547, PMID:33440775, PMID:39526486]. Loss of CABS1 impairs progressive motility, disrupts calcium influx responses to progesterone and alkaline stimuli, and alters PKA-dependent phosphorylation cascades required for capacitation [PMID:39526486, PMID:26960363]. A homozygous nonsense mutation in human CABS1 abolishes its interaction with the perinuclear theca protein ACTL9, causes acrosome absence and mislocalization of the oocyte-activation factor PLCζ, and results in total fertilization failure [PMID:40407971].\",\n  \"teleology\": [\n    {\n      \"year\": 2009,\n      \"claim\": \"Identification of CABS1 as a testis-specific calcium-binding protein of elongate spermatids resolved a key unknown — what calcium-responsive factors are acquired during spermiogenesis and where they reside on mature sperm.\",\n      \"evidence\": \"2-DE/MS identification, calcium overlay assay, immunolocalization, and busulfan depletion/recovery model in rat\",\n      \"pmids\": [\"19208547\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No functional loss-of-function data to establish necessity\",\n        \"Calcium-binding stoichiometry and affinity not quantified\",\n        \"Mechanism by which CABS1 reaches the principal piece unknown\"\n      ]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstration that CABS1 (CLPH ortholog) is intrinsically disordered and phosphorylated by casein kinase 2 established its post-translational regulation and structural class, suggesting it functions as a flexible signaling scaffold rather than a conventional enzyme.\",\n      \"evidence\": \"In vitro/in vivo CK2 kinase assay, circular dichroism, fluorescence spectroscopy, trypsin sensitivity, immunoEM in rat spermatids\",\n      \"pmids\": [\"19271754\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Functional consequence of CK2 phosphorylation on CABS1 activity unknown\",\n        \"No interacting partners identified at this stage\",\n        \"Mitochondrial inner membrane localization not reconciled with later flagellar principal-piece localization\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Antibody-blocking experiments in porcine sperm linked CABS1 to calcium-dependent acrosome reaction, providing the first functional evidence that CABS1 participates in a specific sperm signaling event beyond passive calcium binding.\",\n      \"evidence\": \"Immunolocalization and anti-CABS1 antiserum neutralization assay measuring acrosome reaction rates in porcine epididymal sperm\",\n      \"pmids\": [\"26960363\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Antibody-blocking is indirect; off-target effects not excluded\",\n        \"Porcine system — relevance to mouse/human CABS1 not yet confirmed genetically\",\n        \"Downstream targets in acrosome reaction signaling unidentified\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"CRISPR knockout of Cabs1 in mice revealed that it is required for annulus integrity, midpiece–principal piece junction organization, and normal sperm morphology during epididymal transit, establishing CABS1 as a structural organizer of the flagellar cytoskeleton.\",\n      \"evidence\": \"Cabs1-null mice generated by CRISPR-Cas9; ultrastructural EM, Western blot showing reduced Septin 4 and Krt1, fertility assays\",\n      \"pmids\": [\"33440775\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Direct molecular mechanism linking CABS1 to Septin 4/Krt1 stability unknown\",\n        \"Whether subfertility reflects motility defects, signaling defects, or both not resolved\",\n        \"No rescue experiment to confirm specificity of KO phenotype\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Detailed analysis of Cabs1 KO sperm demonstrated that CABS1 is required for calcium signaling responses, PKA substrate phosphorylation during capacitation, and fibrous sheath/doublet microtubule architecture — unifying its calcium-binding and structural roles into a single signaling-to-cytoskeleton axis.\",\n      \"evidence\": \"CRISPR KO mice with calcium imaging (response to progesterone/alkaline buffer), anti-phospho-PKA substrate and phosphotyrosine Western blots, EM of fibrous sheath\",\n      \"pmids\": [\"39526486\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether CABS1 directly modulates PKA activity or acts upstream via calcium unclear\",\n        \"Relocalization mechanism from midsection to principal piece not elucidated\",\n        \"Whether metabolomic perturbations in epididymal fluid are cause or consequence of structural defects unresolved\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A human homozygous nonsense CABS1 mutation linked the protein to acrosome biogenesis through its interaction with ACTL9 and to oocyte activation through PLCζ localization, establishing CABS1 deficiency as a cause of human male infertility with total fertilization failure.\",\n      \"evidence\": \"WES of infertile patient, Co-IP of wild-type and truncated CABS1 with ACTL9, immunofluorescence and TEM showing acrosome absence and PLCζ mislocalization\",\n      \"pmids\": [\"40407971\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single patient/family — additional cases needed to confirm causality\",\n        \"CABS1–ACTL9 interaction demonstrated by Co-IP only; reciprocal and in vivo validation lacking\",\n        \"How CABS1 influences PLCζ localization mechanistically is unknown\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The mechanism by which CABS1 relocalizes along the flagellum during epididymal maturation, the structural basis of its calcium-dependent conformational changes, and the full repertoire of its direct binding partners remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No crystal or cryo-EM structure available for the intrinsically disordered CABS1\",\n        \"Full interactome beyond ACTL9 unknown\",\n        \"Whether CK2 phosphorylation regulates relocalization or calcium binding untested\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 1, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [0, 3, 5]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [0, 3, 5, 6]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 5]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"ACTL9\",\n      \"CSNK2A1\",\n      \"SEPT4\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}