{"gene":"CABS1","run_date":"2026-06-09T22:57:17","timeline":{"discoveries":[{"year":2009,"finding":"CABS1 is a calcium-binding protein specifically expressed in elongate spermatids (steps 13–16) and localizes to the principal piece of flagellum of mature sperm in the cauda epididymis; calcium binding occurs during epididymal maturation.","method":"Two-dimensional gel electrophoresis, mass spectrometry identification, immunolocalization, calcium overlay experiment","journal":"Biology of reproduction","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct calcium-binding assay (overlay) combined with immunolocalization and stage-specific expression analysis in a single focused study","pmids":["19208547"],"is_preprint":false},{"year":2009,"finding":"CABS1 (CLPH) is phosphorylated in vitro and in vivo by casein kinase 2; it is an intrinsically disordered protein with calcium-binding activity and associates with the mitochondrial inner membrane during the last steps of spermatid differentiation.","method":"In vitro kinase assay with casein kinase 2, trypsin digestion assay, circular dichroism, fluorescence spectroscopy, calcium overlay experiment, electron microscopy, immunohistochemistry","journal":"Journal of proteome research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple orthogonal biochemical methods (in vitro kinase assay, CD, calcium overlay, EM) in a single focused study establishing CK2 as the kinase writer and characterizing enzymatic/structural properties","pmids":["19271754"],"is_preprint":false},{"year":2016,"finding":"Porcine CABS1 localizes to the acrosome region and flagellum of epididymal sperm; immunoreactivity in the acrosomal region disappears during the acrosome reaction, and treatment of capacitated sperm with anti-pCABS1 antiserum significantly decreases acrosome reactions, indicating a role in calcium ion signaling during acrosome reaction.","method":"Immunolocalization, functional antibody-blocking assay of acrosome reaction in capacitated porcine sperm, computational transmembrane domain prediction","journal":"Experimental animals","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional antibody-blocking experiment with defined readout (acrosome reaction rate), supported by localization data, single lab","pmids":["26960363"],"is_preprint":false},{"year":2021,"finding":"Genetic loss of Cabs1 in mice causes defects in sperm flagellar structure including abnormal annulus and disorganization of the midpiece–principal piece junction, leading to bent-tail sperm and subfertility; Cabs1 deficiency reduces Septin 4 and Krt1 protein levels and increases Ccnyl1, demonstrating that Cabs1 maintains cytoskeletal protein homeostasis at the sperm annulus.","method":"CRISPR-Cas9 knockout, ultrastructural analysis (electron microscopy), Western blot, immunofluorescence, fertility assays","journal":"International journal of molecular sciences","confidence":"High","confidence_rationale":"Tier 2 / Strong — CRISPR KO with ultrastructural phenotype, biochemical (WB) confirmation of downstream protein changes, and fertility readout; replicated in subsequent studies","pmids":["33440775"],"is_preprint":false},{"year":2024,"finding":"CABS1 is present in epididymal lumen fluid and its loss in knockout mice does not change luminal calcium concentration, but alters the metabolic profile of cauda epididymal lumen fluid (21 upregulated, 13 downregulated metabolites), with pathway analysis implicating mitochondrial dysfunction and inflammation as contributors to sperm defects.","method":"HPLC-MS/MS metabolomics, ICP-MS for metal ion quantification, in vivo cauda epididymis microperfusion, CRISPR KO mouse model","journal":"Frontiers in endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct metabolomic and ion quantification in KO versus WT, single lab, multiple analytical methods","pmids":["39234505"],"is_preprint":false},{"year":2024,"finding":"CABS1 localizes to the midsection of testicular sperm flagella and the principal piece of epididymal sperm; knockout mice show defective progressive sperm motility, altered calcium response to alkalized buffer and progesterone, reduced PKA substrate phosphorylation and tyrosine phosphorylation, and disorganization of the fibrous sheath and doublet microtubules in post-testicular sperm.","method":"Immunofluorescence localization, CRISPR KO mouse model, calcium imaging, Western blot for phosphorylation, electron microscopy of fibrous sheath","journal":"Molecular reproduction and development","confidence":"High","confidence_rationale":"Tier 2 / Moderate — CRISPR KO with multiple orthogonal functional readouts (motility, Ca2+ signaling, phosphorylation cascades, ultrastructure) in a single focused study","pmids":["39526486"],"is_preprint":false},{"year":2024,"finding":"Depletion of Odam and Cabs1 in a CRISPR-Cas9 mouse prostate cancer model prevents lung metastasis that otherwise occurs upon combined loss of tumor suppressors and epigenetic regulators including Kmt2c, establishing that the Odam/Cabs1 gene cluster is regulated by KMT2C and functionally drives metastasis.","method":"CRISPR-Cas9 in vivo gene depletion, whole genome sequencing, RNA sequencing, epistasis via sequential gene targeting","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis via in vivo CRISPR depletion with clear metastasis endpoint, single lab","pmids":["38453924"],"is_preprint":false},{"year":2025,"finding":"A homozygous nonsense mutation in CABS1 causes protein truncation, reduced interaction with the perinuclear theca protein ACTL9 (identified by Co-IP), absent acrosome in spermatozoa, and abnormal localization of the sperm-borne oocyte activation factor PLCζ, leading to total fertilization failure.","method":"Whole-exome sequencing, Co-immunoprecipitation (wild-type vs. mutant CABS1 with ACTL9), immunofluorescence, Western blot, transmission electron microscopy, transfection of mutant plasmids","journal":"Journal of assisted reproduction and genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP demonstrating interaction with ACTL9 plus functional consequence (PLCζ mislocalization, acrosome absence) supported by multiple methods; single lab, case-report context","pmids":["40407971"],"is_preprint":false},{"year":2024,"finding":"CABS1 protein is detectable in multiple human tissues and fluids (salivary glands, saliva, serum, testes) and exhibits multiple molecular weight forms consistent with its intrinsically disordered character; in human testes, CABS1 is distributed across Leydig cells, primary spermatogonia, Sertoli cells, and developing spermatocytes and spermatids — a broader and distinct localization compared to rodents and pigs.","method":"Western blot, immunohistochemistry with polyclonal and monoclonal antibodies to distinct protein sections, overexpression cell lysate analysis","journal":"PloS one","confidence":"Low","confidence_rationale":"Tier 3 / Weak — descriptive localization across tissues with antibody-based methods, single lab, no functional consequence established","pmids":["38753592"],"is_preprint":false},{"year":2023,"finding":"CABS1 gene expression in colon cancer cell lines is activated by histone deacetylase inhibitor trichostatin but not by the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine, indicating that CABS1 transcription is regulated by histone acetylation rather than DNA methylation in this context.","method":"qRT-PCR after pharmacological inhibition of HDAC (trichostatin) or DNMT (5-aza-2'-deoxycytidine) in HCT116 and Caco-2 cells","journal":"Heliyon","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single pharmacological treatment readout for epigenetic regulation, no mechanistic follow-up, single lab","pmids":["38187237"],"is_preprint":false}],"current_model":"CABS1 is an intrinsically disordered, calcium-binding protein expressed in post-meiotic spermatids that is phosphorylated by casein kinase 2; it localizes to the sperm annulus and principal piece of the flagellum, where it maintains structural integrity of the fibrous sheath and annulus, regulates calcium signaling and PKA/tyrosine phosphorylation cascades required for progressive motility, and interacts with the perinuclear theca protein ACTL9 to support acrosome formation and correct localization of the oocyte-activating factor PLCζ — loss of function causing subfertility or total fertilization failure."},"narrative":{"mechanistic_narrative":"CABS1 is an intrinsically disordered, calcium-binding protein expressed in post-meiotic elongate spermatids that supports the structural and signaling competence of the sperm flagellum [PMID:19208547, PMID:19271754]. It is phosphorylated by casein kinase 2 and acquires calcium-binding capacity during epididymal maturation, localizing to the principal piece and annulus of the flagellum [PMID:19208547, PMID:19271754]. Genetic loss in mice disorganizes the midpiece–principal piece junction and annulus and disrupts the fibrous sheath and doublet microtubules, producing bent-tail sperm and subfertility; mechanistically, CABS1 maintains cytoskeletal protein homeostasis at the annulus, since its loss reduces Septin 4 and Krt1 and elevates Ccnyl1 [PMID:33440775, PMID:39526486]. CABS1 is also required for the calcium-dependent signaling that drives capacitation and progressive motility: knockout sperm show altered calcium responses to alkalinization and progesterone and reduced PKA-substrate and tyrosine phosphorylation [PMID:39526486]. Through interaction with the perinuclear theca protein ACTL9, CABS1 supports acrosome formation and correct localization of the oocyte-activating factor PLCζ; a homozygous nonsense mutation truncating CABS1 causes absent acrosome, PLCζ mislocalization, and total fertilization failure in humans [PMID:40407971]. Separately, the Odam/Cabs1 gene cluster, regulated by KMT2C, functionally drives lung metastasis in a mouse prostate cancer model [PMID:38453924].","teleology":[{"year":2009,"claim":"Establishing that a previously uncharacterized spermatid protein binds calcium and is restricted to late spermatogenesis defined CABS1 as a candidate effector of flagellar maturation.","evidence":"2D gel/MS identification, calcium overlay, and stage-specific immunolocalization in elongate spermatids and mature sperm","pmids":["19208547"],"confidence":"Medium","gaps":["Calcium-binding stoichiometry and affinity not quantified","Functional consequence of calcium binding not tested","Subdomain responsible for calcium binding not mapped"]},{"year":2009,"claim":"Identifying CK2 as the kinase that phosphorylates CABS1 and showing the protein is intrinsically disordered established the upstream regulatory writer and structural class.","evidence":"In vitro CK2 kinase assay, circular dichroism, fluorescence spectroscopy, calcium overlay, and EM in differentiating spermatids","pmids":["19271754"],"confidence":"High","gaps":["Functional role of CK2 phosphorylation in vivo not established","Mitochondrial inner membrane association mechanism unclear","Link between disorder and calcium binding not resolved"]},{"year":2016,"claim":"Antibody-blocking of CABS1 in capacitated sperm reduced acrosome reactions, providing the first functional evidence that CABS1 participates in calcium signaling during the acrosome reaction.","evidence":"Immunolocalization and functional anti-pCABS1 antibody-blocking assay in capacitated porcine sperm","pmids":["26960363"],"confidence":"Medium","gaps":["Antibody-blocking is indirect and may have off-target effects","Molecular target of CABS1 in the acrosome reaction unknown","Species generalization uncertain"]},{"year":2021,"claim":"CRISPR knockout demonstrated that CABS1 is required for annulus integrity and cytoskeletal protein homeostasis, converting correlative localization into a causal structural role.","evidence":"Cabs1 CRISPR-Cas9 KO mice with EM ultrastructure, Western blot of Septin 4/Krt1/Ccnyl1, and fertility assays","pmids":["33440775"],"confidence":"High","gaps":["Whether protein-level changes are direct or secondary not resolved","Direct binding partners at the annulus not identified","Mechanism connecting CABS1 to Septin 4 stability unknown"]},{"year":2024,"claim":"Extending the KO phenotype to calcium signaling and phosphorylation cascades placed CABS1 within the pathway controlling progressive motility, not just static structure.","evidence":"Calcium imaging, PKA-substrate and tyrosine phosphorylation Western blots, and fibrous sheath EM in Cabs1 KO sperm","pmids":["39526486"],"confidence":"High","gaps":["Whether motility defects derive from structural or signaling roles not separable","Direct calcium-channel or PKA target interaction not mapped","Order of causation among Ca2+, PKA, and structural defects unclear"]},{"year":2024,"claim":"Metabolomic profiling of KO epididymal fluid showed CABS1 loss does not alter luminal calcium but perturbs metabolism, refining where its effects act in the epididymal environment.","evidence":"HPLC-MS/MS metabolomics, ICP-MS metal quantification, and microperfusion in Cabs1 KO versus WT cauda epididymis","pmids":["39234505"],"confidence":"Medium","gaps":["Causality between metabolite changes and sperm defects not established","Source of altered metabolites (sperm vs epithelium) unclear","Mechanism linking mitochondrial dysfunction to CABS1 loss undefined"]},{"year":2025,"claim":"A human nonsense mutation linked CABS1 to acrosome biogenesis and oocyte activation via its interaction with ACTL9, establishing a Mendelian fertilization-failure phenotype.","evidence":"Whole-exome sequencing, Co-IP of WT vs mutant CABS1 with ACTL9, immunofluorescence of PLCζ, and EM in a patient","pmids":["40407971"],"confidence":"Medium","gaps":["Single case/family limits generalization","Co-IP not reciprocally validated and binding interface unmapped","Mechanism by which CABS1–ACTL9 directs PLCζ localization unknown"]},{"year":2024,"claim":"Demonstrating a metastasis-driving role of the KMT2C-regulated Odam/Cabs1 cluster revealed a function outside spermatogenesis.","evidence":"In vivo CRISPR-Cas9 depletion with epistasis, WGS, and RNA-seq in a mouse prostate cancer metastasis model","pmids":["38453924"],"confidence":"Medium","gaps":["Relative contributions of Odam versus Cabs1 not dissected","Molecular mechanism of CABS1 in metastasis unknown","Relevance to human cancer not established"]},{"year":null,"claim":"How CABS1 phosphorylation and calcium binding mechanistically couple to annulus cytoskeletal homeostasis, PKA/tyrosine phosphorylation cascades, and acrosome/PLCζ positioning remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural model of the calcium-bound or CK2-phosphorylated protein","Direct molecular targets of CABS1 at the flagellum unmapped","Unified mechanism linking structural and signaling phenotypes lacking"]}],"mechanism_profile":{"molecular_activity":[],"localization":[{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[0,2,5]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[1]}],"pathway":[{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[3,5,7]}],"complexes":[],"partners":["ACTL9","CK2"],"other_free_text":[]}},"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":20,"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":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":"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":4,"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":3,"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":9200,"output_tokens":2596,"usd":0.03327,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9834,"output_tokens":2957,"usd":0.061547,"stage2_stop_reason":"end_turn"},"total_usd":0.094817,"stage1_batch_id":"msgbatch_01ACAxJQabDsht39JXeWG22d","stage2_batch_id":"msgbatch_01QEU22A9U5sbPTgsMzTmvSf","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) and localizes to the principal piece of flagellum of mature sperm in the cauda epididymis; calcium binding occurs during epididymal maturation.\",\n      \"method\": \"Two-dimensional gel electrophoresis, mass spectrometry identification, immunolocalization, calcium overlay experiment\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct calcium-binding assay (overlay) combined with immunolocalization and stage-specific expression analysis in a single focused study\",\n      \"pmids\": [\"19208547\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"CABS1 (CLPH) is phosphorylated in vitro and in vivo by casein kinase 2; it is an intrinsically disordered protein with calcium-binding activity and associates with the mitochondrial inner membrane during the last steps of spermatid differentiation.\",\n      \"method\": \"In vitro kinase assay with casein kinase 2, trypsin digestion assay, circular dichroism, fluorescence spectroscopy, calcium overlay experiment, electron microscopy, immunohistochemistry\",\n      \"journal\": \"Journal of proteome research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple orthogonal biochemical methods (in vitro kinase assay, CD, calcium overlay, EM) in a single focused study establishing CK2 as the kinase writer and characterizing enzymatic/structural properties\",\n      \"pmids\": [\"19271754\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Porcine CABS1 localizes to the acrosome region and flagellum of epididymal sperm; immunoreactivity in the acrosomal region disappears during the acrosome reaction, and treatment of capacitated sperm with anti-pCABS1 antiserum significantly decreases acrosome reactions, indicating a role in calcium ion signaling during acrosome reaction.\",\n      \"method\": \"Immunolocalization, functional antibody-blocking assay of acrosome reaction in capacitated porcine sperm, computational transmembrane domain prediction\",\n      \"journal\": \"Experimental animals\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional antibody-blocking experiment with defined readout (acrosome reaction rate), supported by localization data, single lab\",\n      \"pmids\": [\"26960363\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Genetic loss of Cabs1 in mice causes defects in sperm flagellar structure including abnormal annulus and disorganization of the midpiece–principal piece junction, leading to bent-tail sperm and subfertility; Cabs1 deficiency reduces Septin 4 and Krt1 protein levels and increases Ccnyl1, demonstrating that Cabs1 maintains cytoskeletal protein homeostasis at the sperm annulus.\",\n      \"method\": \"CRISPR-Cas9 knockout, ultrastructural analysis (electron microscopy), Western blot, immunofluorescence, fertility assays\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — CRISPR KO with ultrastructural phenotype, biochemical (WB) confirmation of downstream protein changes, and fertility readout; replicated in subsequent studies\",\n      \"pmids\": [\"33440775\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CABS1 is present in epididymal lumen fluid and its loss in knockout mice does not change luminal calcium concentration, but alters the metabolic profile of cauda epididymal lumen fluid (21 upregulated, 13 downregulated metabolites), with pathway analysis implicating mitochondrial dysfunction and inflammation as contributors to sperm defects.\",\n      \"method\": \"HPLC-MS/MS metabolomics, ICP-MS for metal ion quantification, in vivo cauda epididymis microperfusion, CRISPR KO mouse model\",\n      \"journal\": \"Frontiers in endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct metabolomic and ion quantification in KO versus WT, single lab, multiple analytical methods\",\n      \"pmids\": [\"39234505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CABS1 localizes to the midsection of testicular sperm flagella and the principal piece of epididymal sperm; knockout mice show defective progressive sperm motility, altered calcium response to alkalized buffer and progesterone, reduced PKA substrate phosphorylation and tyrosine phosphorylation, and disorganization of the fibrous sheath and doublet microtubules in post-testicular sperm.\",\n      \"method\": \"Immunofluorescence localization, CRISPR KO mouse model, calcium imaging, Western blot for phosphorylation, electron microscopy of fibrous sheath\",\n      \"journal\": \"Molecular reproduction and development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR KO with multiple orthogonal functional readouts (motility, Ca2+ signaling, phosphorylation cascades, ultrastructure) in a single focused study\",\n      \"pmids\": [\"39526486\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Depletion of Odam and Cabs1 in a CRISPR-Cas9 mouse prostate cancer model prevents lung metastasis that otherwise occurs upon combined loss of tumor suppressors and epigenetic regulators including Kmt2c, establishing that the Odam/Cabs1 gene cluster is regulated by KMT2C and functionally drives metastasis.\",\n      \"method\": \"CRISPR-Cas9 in vivo gene depletion, whole genome sequencing, RNA sequencing, epistasis via sequential gene targeting\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis via in vivo CRISPR depletion with clear metastasis endpoint, single lab\",\n      \"pmids\": [\"38453924\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A homozygous nonsense mutation in CABS1 causes protein truncation, reduced interaction with the perinuclear theca protein ACTL9 (identified by Co-IP), absent acrosome in spermatozoa, and abnormal localization of the sperm-borne oocyte activation factor PLCζ, leading to total fertilization failure.\",\n      \"method\": \"Whole-exome sequencing, Co-immunoprecipitation (wild-type vs. mutant CABS1 with ACTL9), immunofluorescence, Western blot, transmission electron microscopy, transfection of mutant plasmids\",\n      \"journal\": \"Journal of assisted reproduction and genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP demonstrating interaction with ACTL9 plus functional consequence (PLCζ mislocalization, acrosome absence) supported by multiple methods; single lab, case-report context\",\n      \"pmids\": [\"40407971\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CABS1 protein is detectable in multiple human tissues and fluids (salivary glands, saliva, serum, testes) and exhibits multiple molecular weight forms consistent with its intrinsically disordered character; in human testes, CABS1 is distributed across Leydig cells, primary spermatogonia, Sertoli cells, and developing spermatocytes and spermatids — a broader and distinct localization compared to rodents and pigs.\",\n      \"method\": \"Western blot, immunohistochemistry with polyclonal and monoclonal antibodies to distinct protein sections, overexpression cell lysate analysis\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — descriptive localization across tissues with antibody-based methods, single lab, no functional consequence established\",\n      \"pmids\": [\"38753592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CABS1 gene expression in colon cancer cell lines is activated by histone deacetylase inhibitor trichostatin but not by the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine, indicating that CABS1 transcription is regulated by histone acetylation rather than DNA methylation in this context.\",\n      \"method\": \"qRT-PCR after pharmacological inhibition of HDAC (trichostatin) or DNMT (5-aza-2'-deoxycytidine) in HCT116 and Caco-2 cells\",\n      \"journal\": \"Heliyon\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single pharmacological treatment readout for epigenetic regulation, no mechanistic follow-up, single lab\",\n      \"pmids\": [\"38187237\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CABS1 is an intrinsically disordered, calcium-binding protein expressed in post-meiotic spermatids that is phosphorylated by casein kinase 2; it localizes to the sperm annulus and principal piece of the flagellum, where it maintains structural integrity of the fibrous sheath and annulus, regulates calcium signaling and PKA/tyrosine phosphorylation cascades required for progressive motility, and interacts with the perinuclear theca protein ACTL9 to support acrosome formation and correct localization of the oocyte-activating factor PLCζ — loss of function causing subfertility or total fertilization failure.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CABS1 is an intrinsically disordered, calcium-binding protein expressed in post-meiotic elongate spermatids that supports the structural and signaling competence of the sperm flagellum [#0, #1]. It is phosphorylated by casein kinase 2 and acquires calcium-binding capacity during epididymal maturation, localizing to the principal piece and annulus of the flagellum [#0, #1]. Genetic loss in mice disorganizes the midpiece\\u2013principal piece junction and annulus and disrupts the fibrous sheath and doublet microtubules, producing bent-tail sperm and subfertility; mechanistically, CABS1 maintains cytoskeletal protein homeostasis at the annulus, since its loss reduces Septin 4 and Krt1 and elevates Ccnyl1 [#3, #5]. CABS1 is also required for the calcium-dependent signaling that drives capacitation and progressive motility: knockout sperm show altered calcium responses to alkalinization and progesterone and reduced PKA-substrate and tyrosine phosphorylation [#5]. Through interaction with the perinuclear theca protein ACTL9, CABS1 supports acrosome formation and correct localization of the oocyte-activating factor PLC\\u03b6; a homozygous nonsense mutation truncating CABS1 causes absent acrosome, PLC\\u03b6 mislocalization, and total fertilization failure in humans [#7]. Separately, the Odam/Cabs1 gene cluster, regulated by KMT2C, functionally drives lung metastasis in a mouse prostate cancer model [#6].\",\n  \"teleology\": [\n    {\n      \"year\": 2009,\n      \"claim\": \"Establishing that a previously uncharacterized spermatid protein binds calcium and is restricted to late spermatogenesis defined CABS1 as a candidate effector of flagellar maturation.\",\n      \"evidence\": \"2D gel/MS identification, calcium overlay, and stage-specific immunolocalization in elongate spermatids and mature sperm\",\n      \"pmids\": [\"19208547\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Calcium-binding stoichiometry and affinity not quantified\", \"Functional consequence of calcium binding not tested\", \"Subdomain responsible for calcium binding not mapped\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identifying CK2 as the kinase that phosphorylates CABS1 and showing the protein is intrinsically disordered established the upstream regulatory writer and structural class.\",\n      \"evidence\": \"In vitro CK2 kinase assay, circular dichroism, fluorescence spectroscopy, calcium overlay, and EM in differentiating spermatids\",\n      \"pmids\": [\"19271754\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional role of CK2 phosphorylation in vivo not established\", \"Mitochondrial inner membrane association mechanism unclear\", \"Link between disorder and calcium binding not resolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Antibody-blocking of CABS1 in capacitated sperm reduced acrosome reactions, providing the first functional evidence that CABS1 participates in calcium signaling during the acrosome reaction.\",\n      \"evidence\": \"Immunolocalization and functional anti-pCABS1 antibody-blocking assay in capacitated porcine sperm\",\n      \"pmids\": [\"26960363\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Antibody-blocking is indirect and may have off-target effects\", \"Molecular target of CABS1 in the acrosome reaction unknown\", \"Species generalization uncertain\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"CRISPR knockout demonstrated that CABS1 is required for annulus integrity and cytoskeletal protein homeostasis, converting correlative localization into a causal structural role.\",\n      \"evidence\": \"Cabs1 CRISPR-Cas9 KO mice with EM ultrastructure, Western blot of Septin 4/Krt1/Ccnyl1, and fertility assays\",\n      \"pmids\": [\"33440775\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether protein-level changes are direct or secondary not resolved\", \"Direct binding partners at the annulus not identified\", \"Mechanism connecting CABS1 to Septin 4 stability unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Extending the KO phenotype to calcium signaling and phosphorylation cascades placed CABS1 within the pathway controlling progressive motility, not just static structure.\",\n      \"evidence\": \"Calcium imaging, PKA-substrate and tyrosine phosphorylation Western blots, and fibrous sheath EM in Cabs1 KO sperm\",\n      \"pmids\": [\"39526486\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether motility defects derive from structural or signaling roles not separable\", \"Direct calcium-channel or PKA target interaction not mapped\", \"Order of causation among Ca2+, PKA, and structural defects unclear\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Metabolomic profiling of KO epididymal fluid showed CABS1 loss does not alter luminal calcium but perturbs metabolism, refining where its effects act in the epididymal environment.\",\n      \"evidence\": \"HPLC-MS/MS metabolomics, ICP-MS metal quantification, and microperfusion in Cabs1 KO versus WT cauda epididymis\",\n      \"pmids\": [\"39234505\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causality between metabolite changes and sperm defects not established\", \"Source of altered metabolites (sperm vs epithelium) unclear\", \"Mechanism linking mitochondrial dysfunction to CABS1 loss undefined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A human nonsense mutation linked CABS1 to acrosome biogenesis and oocyte activation via its interaction with ACTL9, establishing a Mendelian fertilization-failure phenotype.\",\n      \"evidence\": \"Whole-exome sequencing, Co-IP of WT vs mutant CABS1 with ACTL9, immunofluorescence of PLC\\u03b6, and EM in a patient\",\n      \"pmids\": [\"40407971\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single case/family limits generalization\", \"Co-IP not reciprocally validated and binding interface unmapped\", \"Mechanism by which CABS1\\u2013ACTL9 directs PLC\\u03b6 localization unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrating a metastasis-driving role of the KMT2C-regulated Odam/Cabs1 cluster revealed a function outside spermatogenesis.\",\n      \"evidence\": \"In vivo CRISPR-Cas9 depletion with epistasis, WGS, and RNA-seq in a mouse prostate cancer metastasis model\",\n      \"pmids\": [\"38453924\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relative contributions of Odam versus Cabs1 not dissected\", \"Molecular mechanism of CABS1 in metastasis unknown\", \"Relevance to human cancer not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How CABS1 phosphorylation and calcium binding mechanistically couple to annulus cytoskeletal homeostasis, PKA/tyrosine phosphorylation cascades, and acrosome/PLC\\u03b6 positioning remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural model of the calcium-bound or CK2-phosphorylated protein\", \"Direct molecular targets of CABS1 at the flagellum unmapped\", \"Unified mechanism linking structural and signaling phenotypes lacking\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [],\n    \"localization\": [\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [0, 2, 5]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [3, 5, 7]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"ACTL9\", \"CK2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}