{"gene":"SPACA1","run_date":"2026-04-28T20:42:08","timeline":{"discoveries":[{"year":2012,"finding":"SPACA1 is a membrane protein localizing to the equatorial segment of spermatozoa; Spaca1 knockout male mice are infertile due to abnormal sperm head shaping reminiscent of globozoospermia. Loss of SPACA1 causes disappearance of the nuclear plate (dense lining of nuclear envelope facing inner acrosomal membrane), failure of acrosomal expansion during spermiogenesis, and degeneration/disappearance of the acrosome in mature spermatozoa.","method":"Gene knockout mouse model (Spaca1-disrupted), immunofluorescence localization, electron microscopy of spermiogenesis","journal":"Development","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined cellular phenotype, multiple orthogonal methods, replicated by independent labs","pmids":["22949614"],"is_preprint":false},{"year":2002,"finding":"SPACA1 (originally named SAMP32) is a transmembrane protein associated with the inner acrosomal membrane in the principal and equatorial segments of the sperm acrosome; it is phosphorylated in vivo on serine 256; antibodies against SPACA1 inhibit both binding and fusion of human sperm to zona-free hamster eggs, establishing a direct role in sperm-egg interaction.","method":"Immunoelectron microscopy, 2D gel electrophoresis, mass spectrometry, cDNA cloning, in vitro sperm-egg binding/fusion inhibition assay, immunofluorescence","journal":"Biology of Reproduction","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including functional inhibition assay, structural localization by immunoEM, and in vivo phosphorylation demonstrated","pmids":["11870081"],"is_preprint":false},{"year":2021,"finding":"Biallelic loss-of-function nonsense variant in SPACA1 (p.Trp18*, causing premature termination in the signal peptide) causes human globozoospermia by damaging the acrosome-acroplaxome complex. SPACA1 physically interacts with ACTL7A (an acrosome-acroplaxome complex component), confirmed by co-immunoprecipitation and yeast two-hybrid assay; SPACA1 and ACTL7A co-localize in mature sperm.","method":"Exome sequencing, western blotting, co-immunoprecipitation, yeast two-hybrid, immunofluorescence colocalization, transmission electron microscopy, mass spectrometry proteomics","journal":"Human Reproduction","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (co-IP, Y2H, TEM, proteomics) identifying SPACA1-ACTL7A interaction and defining its role in acrosome-acroplaxome complex integrity","pmids":["34172998"],"is_preprint":false},{"year":2022,"finding":"ACTRT1 anchors developing acrosomes to the nucleus in part by interacting with the inner acrosomal membrane protein SPACA1 and nuclear envelope proteins PARP11 and SPATA46. Loss of ACTRT1 weakens the interaction between ACTL7A and SPACA1, demonstrating SPACA1's role in a PT-specific complex mediating the acrosome-nucleus connection.","method":"Co-immunoprecipitation, Actrt1-knockout mouse model, immunofluorescence, electron microscopy","journal":"Development","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP, clean KO with defined cellular phenotype, and functional consequence of SPACA1 interaction disruption demonstrated","pmids":["35616329"],"is_preprint":false},{"year":2022,"finding":"Calicin (perinuclear theca protein) interacts with SPACA1 (inner acrosomal membrane protein) and nuclear envelope components to form an 'IAM-PT-NE' structure. Loss of Calicin specifically causes surface subsidence of sperm heads during nuclear condensation, DNA damage, and fertilization failure, placing SPACA1 within this structural scaffold.","method":"Co-immunoprecipitation, Calicin-knockout mouse model, immunofluorescence, electron microscopy","journal":"Cell Reports","confidence":"Medium","confidence_rationale":"Tier 2-3 — SPACA1 identified as binding partner by co-IP within larger complex; primary phenotype attributed to Calicin loss, single lab","pmids":["35793634"],"is_preprint":false},{"year":2024,"finding":"Cylicin-1 (CYLC1) interacts with SPACA1 (inner acrosomal membrane protein) and FAM209 (nuclear envelope protein) to form an 'IAM-cylicins-NE' sandwich structure that anchors the acrosome to the nucleus. Loss of cylicin-1 causes acrosome detachment from sperm nuclei and sperm head deformity.","method":"Co-immunoprecipitation, Cylc1-knockout mouse model, whole exome sequencing, immunofluorescence, electron microscopy","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP identifying SPACA1 in the complex, validated by KO mouse model with defined acrosome detachment phenotype","pmids":["38573307"],"is_preprint":false},{"year":2021,"finding":"CFAP65 forms a cytoplasmic protein network comprising MNS1, RSPH1, TPPP2, ZPBP1, and SPACA1, as demonstrated by endogenous immunoprecipitation and immunostaining in spermatids. Loss of CFAP65 disrupts acrosome biogenesis and sperm head shaping.","method":"Endogenous co-immunoprecipitation, immunostaining, Cfap65-knockout mouse, proteomic analysis","journal":"Human Molecular Genetics","confidence":"Medium","confidence_rationale":"Tier 2-3 — endogenous co-IP identifying SPACA1 in complex with CFAP65; SPACA1's specific role in the network not independently validated","pmids":["34231842"],"is_preprint":false},{"year":2024,"finding":"MFSD6L, an acrosome membrane protein, interacts with SPACA1 (inner acrosomal membrane protein). Loss of MFSD6L causes deformed acrosomes and oligoasthenoteratozoospermia in humans and mice, with SPACA1 interaction required for acrosome anchoring and head shaping.","method":"Co-immunoprecipitation, Mfsd6l-knockout mouse model, exome sequencing, electron microscopy","journal":"Journal of Genetics and Genomics","confidence":"Medium","confidence_rationale":"Tier 2-3 — co-IP identifying SPACA1 as MFSD6L interactor; functional consequence of lost interaction demonstrated in KO model","pmids":["38909778"],"is_preprint":false},{"year":2024,"finding":"CCDC28A interacts with SPACA1; Ccdc28a-knockout mice display acrosomal defects and bent sperm heads, placing CCDC28A-SPACA1 interaction in sperm head morphology regulation.","method":"Co-immunoprecipitation, Ccdc28a-knockout mouse model, immunofluorescence, electron microscopy","journal":"Cellular and Molecular Life Sciences","confidence":"Medium","confidence_rationale":"Tier 2-3 — co-IP demonstrates interaction, KO phenotype confirms functional relevance; SPACA1's specific role in complex not fully resolved","pmids":["38597936"],"is_preprint":false},{"year":2023,"finding":"SPACA1 in boar spermatozoa is N-glycosylated and tyrosine-phosphorylated (at 32 and 35-45 kDa forms). Inhibition of the calcium-sensing receptor (CASR) by NPS2143 induces calcium-dependent serine protease-mediated proteolysis of glycosylated/phosphorylated SPACA1 (35-45 kDa) to generate a 32 kDa fragment (p32), coinciding with loss of acrosomal integrity.","method":"Mass spectrometry, immunoprecipitation, immunofluorescence, PNGase F treatment (glycosylation), serine protease inhibitor (STI), flow cytometry","journal":"Reproduction","confidence":"Medium","confidence_rationale":"Tier 1-2 — N-glycosylation confirmed biochemically, proteolysis mechanism defined by inhibitor and mass spectrometry, single lab","pmids":["36821514"],"is_preprint":false},{"year":2016,"finding":"During the true (extracellular Ca2+-dependent) acrosome reaction in boar spermatozoa, SPACA1 proteins redistribute from the acrosome to the postacrosomal region and undergo a shift to smaller molecular weight forms (15-28 kDa), distinguishing the true acrosome reaction from acrosomal damage.","method":"Immunofluorescence double staining (anti-SPACA1 + FITC-PNA), Western blotting, calcium-dependent acrosome reaction induction, cyclodextrin treatment","journal":"Animal Reproduction Science","confidence":"Medium","confidence_rationale":"Tier 2 — direct biochemical and localization evidence for SPACA1 redistribution during acrosome reaction, single lab with multiple methods","pmids":["27449406"],"is_preprint":false},{"year":2020,"finding":"SPACA1 is associated with lipid rafts (membrane raft microdomains) in boar spermatozoa, as demonstrated by sucrose gradient centrifugation fractionation and lectin-glycoprotein identification, and is glycosylated.","method":"Sucrose gradient centrifugation fractionation, lectin blot assay, mass spectrometry","journal":"Animal Reproduction Science / Glycoconjugate Journal","confidence":"Medium","confidence_rationale":"Tier 2-3 — membrane raft association shown by fractionation in two independent studies; single methods per study","pmids":["32507260","32367480"],"is_preprint":false},{"year":2012,"finding":"FSIP2 co-immunoprecipitates with SPACA1 and other acrosome biogenesis proteins (DPY19L2, HSP90B1, KIAA1210, HSPA2, CLTC); FSIP2-mutant human sperm show downregulated SPACA1 protein, linking FSIP2-SPACA1 interaction to acrosome development.","method":"Co-immunoprecipitation, proteomics (LC-MS/MS), western blotting, immunofluorescence","journal":"Journal of Medical Genetics","confidence":"Low","confidence_rationale":"Tier 3 — co-IP demonstrates interaction but SPACA1's specific mechanistic role in the FSIP2 pathway not independently resolved","pmids":["35654582"],"is_preprint":false}],"current_model":"SPACA1 is a transmembrane inner acrosomal membrane protein, phosphorylated and N-glycosylated, that serves as a structural scaffold anchoring the acrosome to the sperm nucleus by interacting with perinuclear theca proteins (ACTRT1, ACTL7A, Calicin/CCIN, cylicin-1/CYLC1) and nuclear envelope components (PARP11, SPATA46, FAM209), and its loss causes failure of acrosomal expansion and nuclear plate formation during spermiogenesis, resulting in globozoospermia and male infertility; during the acrosome reaction, SPACA1 redistributes to the postacrosomal region and undergoes proteolytic cleavage, and antibodies against it inhibit sperm-egg fusion."},"narrative":{"teleology":[{"year":2002,"claim":"Identification of SPACA1 as a phosphorylated inner acrosomal membrane protein with a functional role in sperm–egg interaction established the gene's basic molecular identity and biological relevance.","evidence":"Immunoelectron microscopy, 2D gel/MS, cDNA cloning, and antibody-mediated inhibition of sperm–egg binding/fusion using human sperm and zona-free hamster eggs","pmids":["11870081"],"confidence":"High","gaps":["Identity of SPACA1 binding partners on the egg surface unknown","In vivo functional requirement not yet tested by genetic ablation"]},{"year":2012,"claim":"Genetic ablation of Spaca1 in mice revealed its essential role in nuclear plate formation, acrosomal expansion, and sperm head shaping, establishing it as a causative factor for globozoospermia-like infertility.","evidence":"Spaca1-knockout mouse model with immunofluorescence and electron microscopy of spermiogenesis stages","pmids":["22949614"],"confidence":"High","gaps":["Molecular partners mediating SPACA1's connection to the nuclear envelope not identified","Human genetic validation pending"]},{"year":2016,"claim":"Demonstration that SPACA1 redistributes from the acrosome to the postacrosomal region and undergoes proteolytic processing during the true acrosome reaction linked SPACA1 dynamics to acrosomal exocytosis.","evidence":"Immunofluorescence double staining and western blotting during calcium-dependent acrosome reaction induction in boar spermatozoa","pmids":["27449406"],"confidence":"Medium","gaps":["Protease responsible for SPACA1 cleavage not identified at this stage","Functional significance of redistribution for fertilization not directly tested"]},{"year":2020,"claim":"Association of glycosylated SPACA1 with lipid raft microdomains placed the protein within a signaling-competent membrane environment on sperm.","evidence":"Sucrose gradient fractionation, lectin blot, and mass spectrometry in boar spermatozoa","pmids":["32507260","32367480"],"confidence":"Medium","gaps":["Functional significance of raft association for SPACA1 activity not tested","Whether raft association is conserved across species is unknown"]},{"year":2021,"claim":"Identification of ACTL7A as a direct SPACA1 binding partner and demonstration that a biallelic human SPACA1 nonsense mutation causes globozoospermia validated the acrosome–acroplaxome anchoring model in humans.","evidence":"Co-immunoprecipitation, yeast two-hybrid, exome sequencing of infertile patient, TEM, and proteomics","pmids":["34172998"],"confidence":"High","gaps":["Only one human family reported","Stoichiometry and topology of the SPACA1–ACTL7A interaction unresolved"]},{"year":2022,"claim":"Placement of SPACA1 within multi-protein IAM–PT–NE complexes bridging inner acrosomal membrane to nuclear envelope via ACTRT1, Calicin, PARP11, and SPATA46 defined the structural scaffold mechanism for acrosome anchoring.","evidence":"Reciprocal co-immunoprecipitation in Actrt1-KO and Calicin-KO mouse models with immunofluorescence and electron microscopy","pmids":["35616329","35793634"],"confidence":"High","gaps":["Direct structural data for the complex absent","Hierarchy of assembly during spermiogenesis not resolved"]},{"year":2023,"claim":"Biochemical characterization of SPACA1 N-glycosylation and identification of calcium-dependent serine protease-mediated cleavage of its glycosylated forms defined the proteolytic mechanism linked to acrosomal integrity loss.","evidence":"PNGase F deglycosylation, serine protease inhibitor treatment, mass spectrometry, and CASR inhibition in boar spermatozoa","pmids":["36821514"],"confidence":"Medium","gaps":["Specific serine protease responsible not identified","Whether proteolysis is required for normal acrosome reaction or is pathological remains unclear"]},{"year":2024,"claim":"Expansion of the SPACA1 interaction network to include Cylicin-1/CYLC1-FAM209 and additional partners MFSD6L and CCDC28A reinforced SPACA1 as a central hub connecting acrosomal membrane to nuclear envelope through multiple parallel complexes.","evidence":"Co-immunoprecipitation and knockout mouse models (Cylc1-KO, Mfsd6l-KO, Ccdc28a-KO) with electron microscopy and exome sequencing","pmids":["38573307","38909778","38597936"],"confidence":"High","gaps":["Whether these complexes function independently or cooperatively is unknown","No reconstitution of the full complex in vitro"]},{"year":null,"claim":"The precise structural organization of the IAM–PT–NE super-complex, the temporal hierarchy of SPACA1 complex assembly during spermiogenesis, and the identity of the protease(s) cleaving SPACA1 during the acrosome reaction remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structural model of SPACA1 or its complexes","Temporal sequence of partner recruitment during acrosome biogenesis unknown","Identity of the SPACA1-cleaving serine protease unresolved","Whether SPACA1 has a direct role in membrane fusion beyond scaffolding not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,3,4,5]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,11]}],"pathway":[{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[0,1,2]}],"complexes":["IAM-PT-NE acrosome-nucleus anchoring complex"],"partners":["ACTL7A","ACTRT1","CCIN","CYLC1","MFSD6L","CCDC28A","CFAP65","FSIP2"],"other_free_text":[]},"mechanistic_narrative":"SPACA1 is a transmembrane inner acrosomal membrane protein that serves as a central structural scaffold anchoring the acrosome to the sperm nucleus during spermiogenesis. It physically bridges inner acrosomal membrane components to perinuclear theca proteins (ACTRT1, ACTL7A, Calicin/CCIN, Cylicin-1/CYLC1) and nuclear envelope proteins (PARP11, SPATA46, FAM209), forming an IAM–PT–NE complex essential for acrosomal expansion, nuclear plate formation, and sperm head shaping [PMID:22949614, PMID:35616329, PMID:38573307]. Biallelic loss-of-function mutations in human SPACA1 cause globozoospermia and male infertility by disrupting the acrosome–acroplaxome complex [PMID:34172998]. SPACA1 is N-glycosylated and phosphorylated, resides in lipid raft microdomains, and during the acrosome reaction undergoes calcium-dependent serine protease-mediated proteolytic cleavage and redistribution to the postacrosomal region, consistent with a functional role in sperm–egg fusion supported by antibody inhibition of sperm–egg binding [PMID:11870081, PMID:36821514, PMID:27449406]."},"prefetch_data":{"uniprot":{"accession":"Q9HBV2","full_name":"Sperm acrosome membrane-associated protein 1","aliases":["Sperm acrosomal membrane-associated protein 32"],"length_aa":294,"mass_kda":32.1,"function":"Plays a role in acrosome formation and establishment of normal sperm morphology during spermatogenesis (PubMed:34172998). Important for male fertility (PubMed:11870081)","subcellular_location":"Cytoplasmic vesicle, secretory vesicle, acrosome inner membrane","url":"https://www.uniprot.org/uniprotkb/Q9HBV2/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SPACA1","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SPACA1","total_profiled":1310},"omim":[{"mim_id":"620490","title":"SPERMATOGENIC FAILURE 85; SPGF85","url":"https://www.omim.org/entry/620490"},{"mim_id":"620353","title":"SPERMATOGENIC FAILURE 82; SPGF82","url":"https://www.omim.org/entry/620353"},{"mim_id":"619905","title":"GOLGI-ASSOCIATED RAB2 INTERACTOR 1B; GARIN1B","url":"https://www.omim.org/entry/619905"},{"mim_id":"612739","title":"SPERM ACROSOME-ASSOCIATED PROTEIN 1; SPACA1","url":"https://www.omim.org/entry/612739"},{"mim_id":"301119","title":"SPERMATOGENIC FAILURE, X-LINKED, 8; SPGFX8","url":"https://www.omim.org/entry/301119"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Acrosome","reliability":"Supported"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in single","driving_tissues":[{"tissue":"testis","ntpm":39.5}],"url":"https://www.proteinatlas.org/search/SPACA1"},"hgnc":{"alias_symbol":["SAMP32"],"prev_symbol":[]},"alphafold":{"accession":"Q9HBV2","domains":[{"cath_id":"-","chopping":"78-119","consensus_level":"medium","plddt":91.6074,"start":78,"end":119},{"cath_id":"2.60.40,2.60.40","chopping":"121-212","consensus_level":"high","plddt":90.0514,"start":121,"end":212},{"cath_id":"1.20.5","chopping":"216-250","consensus_level":"medium","plddt":86.1466,"start":216,"end":250}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9HBV2","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9HBV2-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9HBV2-F1-predicted_aligned_error_v6.png","plddt_mean":71.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SPACA1","jax_strain_url":"https://www.jax.org/strain/search?query=SPACA1"},"sequence":{"accession":"Q9HBV2","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9HBV2.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9HBV2/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9HBV2"}},"corpus_meta":[{"pmid":"22949614","id":"PMC_22949614","title":"SPACA1-deficient 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dynamics","url":"https://pubmed.ncbi.nlm.nih.gov/41616039","citation_count":0,"is_preprint":false},{"pmid":"40544175","id":"PMC_40544175","title":"Evaluation of aptamers binding ability towards bovine X-specific sperm.","date":"2025","source":"Molecular biology reports","url":"https://pubmed.ncbi.nlm.nih.gov/40544175","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":19287,"output_tokens":3324,"usd":0.05386},"stage2":{"model":"claude-opus-4-6","input_tokens":6687,"output_tokens":2180,"usd":0.131903},"total_usd":0.185763,"stage1_batch_id":"msgbatch_011rkcQdVV1RaFq9XhcG6df6","stage2_batch_id":"msgbatch_01RzgrJafdF4EWHhj5mNi6dh","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2012,\n      \"finding\": \"SPACA1 is a membrane protein localizing to the equatorial segment of spermatozoa; Spaca1 knockout male mice are infertile due to abnormal sperm head shaping reminiscent of globozoospermia. Loss of SPACA1 causes disappearance of the nuclear plate (dense lining of nuclear envelope facing inner acrosomal membrane), failure of acrosomal expansion during spermiogenesis, and degeneration/disappearance of the acrosome in mature spermatozoa.\",\n      \"method\": \"Gene knockout mouse model (Spaca1-disrupted), immunofluorescence localization, electron microscopy of spermiogenesis\",\n      \"journal\": \"Development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined cellular phenotype, multiple orthogonal methods, replicated by independent labs\",\n      \"pmids\": [\"22949614\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"SPACA1 (originally named SAMP32) is a transmembrane protein associated with the inner acrosomal membrane in the principal and equatorial segments of the sperm acrosome; it is phosphorylated in vivo on serine 256; antibodies against SPACA1 inhibit both binding and fusion of human sperm to zona-free hamster eggs, establishing a direct role in sperm-egg interaction.\",\n      \"method\": \"Immunoelectron microscopy, 2D gel electrophoresis, mass spectrometry, cDNA cloning, in vitro sperm-egg binding/fusion inhibition assay, immunofluorescence\",\n      \"journal\": \"Biology of Reproduction\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including functional inhibition assay, structural localization by immunoEM, and in vivo phosphorylation demonstrated\",\n      \"pmids\": [\"11870081\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Biallelic loss-of-function nonsense variant in SPACA1 (p.Trp18*, causing premature termination in the signal peptide) causes human globozoospermia by damaging the acrosome-acroplaxome complex. SPACA1 physically interacts with ACTL7A (an acrosome-acroplaxome complex component), confirmed by co-immunoprecipitation and yeast two-hybrid assay; SPACA1 and ACTL7A co-localize in mature sperm.\",\n      \"method\": \"Exome sequencing, western blotting, co-immunoprecipitation, yeast two-hybrid, immunofluorescence colocalization, transmission electron microscopy, mass spectrometry proteomics\",\n      \"journal\": \"Human Reproduction\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (co-IP, Y2H, TEM, proteomics) identifying SPACA1-ACTL7A interaction and defining its role in acrosome-acroplaxome complex integrity\",\n      \"pmids\": [\"34172998\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ACTRT1 anchors developing acrosomes to the nucleus in part by interacting with the inner acrosomal membrane protein SPACA1 and nuclear envelope proteins PARP11 and SPATA46. Loss of ACTRT1 weakens the interaction between ACTL7A and SPACA1, demonstrating SPACA1's role in a PT-specific complex mediating the acrosome-nucleus connection.\",\n      \"method\": \"Co-immunoprecipitation, Actrt1-knockout mouse model, immunofluorescence, electron microscopy\",\n      \"journal\": \"Development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP, clean KO with defined cellular phenotype, and functional consequence of SPACA1 interaction disruption demonstrated\",\n      \"pmids\": [\"35616329\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Calicin (perinuclear theca protein) interacts with SPACA1 (inner acrosomal membrane protein) and nuclear envelope components to form an 'IAM-PT-NE' structure. Loss of Calicin specifically causes surface subsidence of sperm heads during nuclear condensation, DNA damage, and fertilization failure, placing SPACA1 within this structural scaffold.\",\n      \"method\": \"Co-immunoprecipitation, Calicin-knockout mouse model, immunofluorescence, electron microscopy\",\n      \"journal\": \"Cell Reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — SPACA1 identified as binding partner by co-IP within larger complex; primary phenotype attributed to Calicin loss, single lab\",\n      \"pmids\": [\"35793634\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Cylicin-1 (CYLC1) interacts with SPACA1 (inner acrosomal membrane protein) and FAM209 (nuclear envelope protein) to form an 'IAM-cylicins-NE' sandwich structure that anchors the acrosome to the nucleus. Loss of cylicin-1 causes acrosome detachment from sperm nuclei and sperm head deformity.\",\n      \"method\": \"Co-immunoprecipitation, Cylc1-knockout mouse model, whole exome sequencing, immunofluorescence, electron microscopy\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP identifying SPACA1 in the complex, validated by KO mouse model with defined acrosome detachment phenotype\",\n      \"pmids\": [\"38573307\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CFAP65 forms a cytoplasmic protein network comprising MNS1, RSPH1, TPPP2, ZPBP1, and SPACA1, as demonstrated by endogenous immunoprecipitation and immunostaining in spermatids. Loss of CFAP65 disrupts acrosome biogenesis and sperm head shaping.\",\n      \"method\": \"Endogenous co-immunoprecipitation, immunostaining, Cfap65-knockout mouse, proteomic analysis\",\n      \"journal\": \"Human Molecular Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — endogenous co-IP identifying SPACA1 in complex with CFAP65; SPACA1's specific role in the network not independently validated\",\n      \"pmids\": [\"34231842\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"MFSD6L, an acrosome membrane protein, interacts with SPACA1 (inner acrosomal membrane protein). Loss of MFSD6L causes deformed acrosomes and oligoasthenoteratozoospermia in humans and mice, with SPACA1 interaction required for acrosome anchoring and head shaping.\",\n      \"method\": \"Co-immunoprecipitation, Mfsd6l-knockout mouse model, exome sequencing, electron microscopy\",\n      \"journal\": \"Journal of Genetics and Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — co-IP identifying SPACA1 as MFSD6L interactor; functional consequence of lost interaction demonstrated in KO model\",\n      \"pmids\": [\"38909778\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CCDC28A interacts with SPACA1; Ccdc28a-knockout mice display acrosomal defects and bent sperm heads, placing CCDC28A-SPACA1 interaction in sperm head morphology regulation.\",\n      \"method\": \"Co-immunoprecipitation, Ccdc28a-knockout mouse model, immunofluorescence, electron microscopy\",\n      \"journal\": \"Cellular and Molecular Life Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — co-IP demonstrates interaction, KO phenotype confirms functional relevance; SPACA1's specific role in complex not fully resolved\",\n      \"pmids\": [\"38597936\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SPACA1 in boar spermatozoa is N-glycosylated and tyrosine-phosphorylated (at 32 and 35-45 kDa forms). Inhibition of the calcium-sensing receptor (CASR) by NPS2143 induces calcium-dependent serine protease-mediated proteolysis of glycosylated/phosphorylated SPACA1 (35-45 kDa) to generate a 32 kDa fragment (p32), coinciding with loss of acrosomal integrity.\",\n      \"method\": \"Mass spectrometry, immunoprecipitation, immunofluorescence, PNGase F treatment (glycosylation), serine protease inhibitor (STI), flow cytometry\",\n      \"journal\": \"Reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 — N-glycosylation confirmed biochemically, proteolysis mechanism defined by inhibitor and mass spectrometry, single lab\",\n      \"pmids\": [\"36821514\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"During the true (extracellular Ca2+-dependent) acrosome reaction in boar spermatozoa, SPACA1 proteins redistribute from the acrosome to the postacrosomal region and undergo a shift to smaller molecular weight forms (15-28 kDa), distinguishing the true acrosome reaction from acrosomal damage.\",\n      \"method\": \"Immunofluorescence double staining (anti-SPACA1 + FITC-PNA), Western blotting, calcium-dependent acrosome reaction induction, cyclodextrin treatment\",\n      \"journal\": \"Animal Reproduction Science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct biochemical and localization evidence for SPACA1 redistribution during acrosome reaction, single lab with multiple methods\",\n      \"pmids\": [\"27449406\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SPACA1 is associated with lipid rafts (membrane raft microdomains) in boar spermatozoa, as demonstrated by sucrose gradient centrifugation fractionation and lectin-glycoprotein identification, and is glycosylated.\",\n      \"method\": \"Sucrose gradient centrifugation fractionation, lectin blot assay, mass spectrometry\",\n      \"journal\": \"Animal Reproduction Science / Glycoconjugate Journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — membrane raft association shown by fractionation in two independent studies; single methods per study\",\n      \"pmids\": [\"32507260\", \"32367480\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"FSIP2 co-immunoprecipitates with SPACA1 and other acrosome biogenesis proteins (DPY19L2, HSP90B1, KIAA1210, HSPA2, CLTC); FSIP2-mutant human sperm show downregulated SPACA1 protein, linking FSIP2-SPACA1 interaction to acrosome development.\",\n      \"method\": \"Co-immunoprecipitation, proteomics (LC-MS/MS), western blotting, immunofluorescence\",\n      \"journal\": \"Journal of Medical Genetics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — co-IP demonstrates interaction but SPACA1's specific mechanistic role in the FSIP2 pathway not independently resolved\",\n      \"pmids\": [\"35654582\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SPACA1 is a transmembrane inner acrosomal membrane protein, phosphorylated and N-glycosylated, that serves as a structural scaffold anchoring the acrosome to the sperm nucleus by interacting with perinuclear theca proteins (ACTRT1, ACTL7A, Calicin/CCIN, cylicin-1/CYLC1) and nuclear envelope components (PARP11, SPATA46, FAM209), and its loss causes failure of acrosomal expansion and nuclear plate formation during spermiogenesis, resulting in globozoospermia and male infertility; during the acrosome reaction, SPACA1 redistributes to the postacrosomal region and undergoes proteolytic cleavage, and antibodies against it inhibit sperm-egg fusion.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SPACA1 is a transmembrane inner acrosomal membrane protein that serves as a central structural scaffold anchoring the acrosome to the sperm nucleus during spermiogenesis. It physically bridges inner acrosomal membrane components to perinuclear theca proteins (ACTRT1, ACTL7A, Calicin/CCIN, Cylicin-1/CYLC1) and nuclear envelope proteins (PARP11, SPATA46, FAM209), forming an IAM–PT–NE complex essential for acrosomal expansion, nuclear plate formation, and sperm head shaping [PMID:22949614, PMID:35616329, PMID:38573307]. Biallelic loss-of-function mutations in human SPACA1 cause globozoospermia and male infertility by disrupting the acrosome–acroplaxome complex [PMID:34172998]. SPACA1 is N-glycosylated and phosphorylated, resides in lipid raft microdomains, and during the acrosome reaction undergoes calcium-dependent serine protease-mediated proteolytic cleavage and redistribution to the postacrosomal region, consistent with a functional role in sperm–egg fusion supported by antibody inhibition of sperm–egg binding [PMID:11870081, PMID:36821514, PMID:27449406].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Identification of SPACA1 as a phosphorylated inner acrosomal membrane protein with a functional role in sperm–egg interaction established the gene's basic molecular identity and biological relevance.\",\n      \"evidence\": \"Immunoelectron microscopy, 2D gel/MS, cDNA cloning, and antibody-mediated inhibition of sperm–egg binding/fusion using human sperm and zona-free hamster eggs\",\n      \"pmids\": [\"11870081\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of SPACA1 binding partners on the egg surface unknown\", \"In vivo functional requirement not yet tested by genetic ablation\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Genetic ablation of Spaca1 in mice revealed its essential role in nuclear plate formation, acrosomal expansion, and sperm head shaping, establishing it as a causative factor for globozoospermia-like infertility.\",\n      \"evidence\": \"Spaca1-knockout mouse model with immunofluorescence and electron microscopy of spermiogenesis stages\",\n      \"pmids\": [\"22949614\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular partners mediating SPACA1's connection to the nuclear envelope not identified\", \"Human genetic validation pending\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Demonstration that SPACA1 redistributes from the acrosome to the postacrosomal region and undergoes proteolytic processing during the true acrosome reaction linked SPACA1 dynamics to acrosomal exocytosis.\",\n      \"evidence\": \"Immunofluorescence double staining and western blotting during calcium-dependent acrosome reaction induction in boar spermatozoa\",\n      \"pmids\": [\"27449406\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Protease responsible for SPACA1 cleavage not identified at this stage\", \"Functional significance of redistribution for fertilization not directly tested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Association of glycosylated SPACA1 with lipid raft microdomains placed the protein within a signaling-competent membrane environment on sperm.\",\n      \"evidence\": \"Sucrose gradient fractionation, lectin blot, and mass spectrometry in boar spermatozoa\",\n      \"pmids\": [\"32507260\", \"32367480\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional significance of raft association for SPACA1 activity not tested\", \"Whether raft association is conserved across species is unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identification of ACTL7A as a direct SPACA1 binding partner and demonstration that a biallelic human SPACA1 nonsense mutation causes globozoospermia validated the acrosome–acroplaxome anchoring model in humans.\",\n      \"evidence\": \"Co-immunoprecipitation, yeast two-hybrid, exome sequencing of infertile patient, TEM, and proteomics\",\n      \"pmids\": [\"34172998\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Only one human family reported\", \"Stoichiometry and topology of the SPACA1–ACTL7A interaction unresolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Placement of SPACA1 within multi-protein IAM–PT–NE complexes bridging inner acrosomal membrane to nuclear envelope via ACTRT1, Calicin, PARP11, and SPATA46 defined the structural scaffold mechanism for acrosome anchoring.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation in Actrt1-KO and Calicin-KO mouse models with immunofluorescence and electron microscopy\",\n      \"pmids\": [\"35616329\", \"35793634\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct structural data for the complex absent\", \"Hierarchy of assembly during spermiogenesis not resolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Biochemical characterization of SPACA1 N-glycosylation and identification of calcium-dependent serine protease-mediated cleavage of its glycosylated forms defined the proteolytic mechanism linked to acrosomal integrity loss.\",\n      \"evidence\": \"PNGase F deglycosylation, serine protease inhibitor treatment, mass spectrometry, and CASR inhibition in boar spermatozoa\",\n      \"pmids\": [\"36821514\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific serine protease responsible not identified\", \"Whether proteolysis is required for normal acrosome reaction or is pathological remains unclear\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Expansion of the SPACA1 interaction network to include Cylicin-1/CYLC1-FAM209 and additional partners MFSD6L and CCDC28A reinforced SPACA1 as a central hub connecting acrosomal membrane to nuclear envelope through multiple parallel complexes.\",\n      \"evidence\": \"Co-immunoprecipitation and knockout mouse models (Cylc1-KO, Mfsd6l-KO, Ccdc28a-KO) with electron microscopy and exome sequencing\",\n      \"pmids\": [\"38573307\", \"38909778\", \"38597936\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether these complexes function independently or cooperatively is unknown\", \"No reconstitution of the full complex in vitro\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The precise structural organization of the IAM–PT–NE super-complex, the temporal hierarchy of SPACA1 complex assembly during spermiogenesis, and the identity of the protease(s) cleaving SPACA1 during the acrosome reaction remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structural model of SPACA1 or its complexes\", \"Temporal sequence of partner recruitment during acrosome biogenesis unknown\", \"Identity of the SPACA1-cleaving serine protease unresolved\", \"Whether SPACA1 has a direct role in membrane fusion beyond scaffolding not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 3, 4, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [0, 1, 2]}\n    ],\n    \"complexes\": [\n      \"IAM-PT-NE acrosome-nucleus anchoring complex\"\n    ],\n    \"partners\": [\n      \"ACTL7A\",\n      \"ACTRT1\",\n      \"CCIN\",\n      \"CYLC1\",\n      \"MFSD6L\",\n      \"CCDC28A\",\n      \"CFAP65\",\n      \"FSIP2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}