{"gene":"ACTRT1","run_date":"2026-06-09T22:02:40","timeline":{"discoveries":[{"year":2002,"finding":"ARP-T1 (ACTRT1) is a novel actin-related protein that localizes specifically to the calyx of the mammalian sperm head perinuclear theca, identified as a major acidic component by partial amino acid sequencing of calyx preparations from bull spermatozoa and confirmed by immunoblotting and immunofluorescence microscopy. Its expression is restricted to the testis, appearing late in spermatid differentiation.","method":"Partial amino acid sequencing, immunoblotting, immunofluorescence microscopy, subcellular fractionation","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct biochemical identification and localization with antibody validation, single lab, two orthogonal methods","pmids":["12243744"],"is_preprint":false},{"year":2017,"finding":"ARP-T1 directly binds to the GLI1 promoter, thereby inhibiting GLI1 expression and suppressing Hedgehog signaling pathway activation; loss of ARP-T1 leads to Hedgehog pathway activation, and exogenous ACTRT1 expression reduces in vitro and in vivo proliferation of cell lines with aberrant Hedgehog signaling.","method":"Chromatin binding assays (GLI1 promoter binding), loss-of-function experiments, exogenous expression assays, in vitro and in vivo proliferation assays","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct promoter binding established, functional rescue with exogenous expression, in vitro and in vivo validation, multiple orthogonal approaches in a rigorous study","pmids":["28869610"],"is_preprint":false},{"year":2021,"finding":"ARP-T1 (ACTRT1) localizes to the midbody during cytokinesis and to the basal body of primary cilia during interphase; an ARP-T1 interactome includes proteins involved in ciliogenesis, endosomal recycling, and septin ring formation. ACTRT1 knockdown in cultured cells reduces ciliary length, and tissue from BDCS patients with ACTRT1 mutations shows reduced ciliary length correlating with ARP-T1 protein levels.","method":"Immunofluorescence localization, mass spectrometry interactome (PXD016557), ACTRT1 knockdown, ciliary length measurement in patient tissue and knockdown cells","journal":"Communications biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — interactome by MS, direct localization, functional KD with quantitative phenotype, validated in patient tissue and cell culture","pmids":["33972689"],"is_preprint":false},{"year":2022,"finding":"ACTRT1, ACTRT2, ACTL7A, and ACTL9 proteins interact to form a multimeric complex localizing to the subacrosomal region of spermatids. ACTRT1 anchors developing acrosomes to the nucleus by interacting with inner acrosomal membrane protein SPACA1 and nuclear envelope proteins PARP11 and SPATA46. Loss of ACTRT1 in knockout mice causes loosened acroplaxome structure during spermiogenesis, acrosome detachment from sperm nuclei, malformed heads, reduced ACTL7A and PLCζ protein content, and severe subfertility despite normal sperm count and motility.","method":"Co-immunoprecipitation, Actrt1-knockout mouse generation and phenotyping, immunofluorescence, Western blotting, fertility assays","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP for multiple interactors, knockout mouse with defined cellular and fertility phenotype, multiple orthogonal methods in one rigorous study","pmids":["35616329"],"is_preprint":false},{"year":2024,"finding":"ACTRT1 deficiency in humans (whole-gene deletion) causes sperm acrosomal ultrastructural defects (acrosomal detachment) and fertilization failure; ACTL7A and PLCζ (phospholipase C zeta) are decreased and ectopically distributed in sperm from ACTRT1-deleted men, consistent with findings in Actrt1-KO mice.","method":"Whole exome sequencing, whole genome sequencing, PCR, quantitative PCR, Western blotting, immunostaining, electron microscopy, Papanicolaou staining","journal":"Human reproduction (Oxford, England)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct mechanistic link to ACTL7A and PLCζ mislocalization, validated by multiple methods, but limited to two human cases","pmids":["38414365"],"is_preprint":false},{"year":2025,"finding":"Actrt1 promotes tumor growth through non-hematopoietic endothelium by sustaining endothelial sprouting and vessel maturation. Actrt1-/- mice show reduced growth of B16F1 and MC38 tumors; bone marrow chimera experiments localize the phenotype to the non-hematopoietic compartment. ACTRT1 protein is detected in CD31+ tumor vessels. Actrt1 deficiency reduces endothelial sprouting from aortic rings, delays recovery after hindlimb ischemia, and shifts endothelial transcriptome toward immaturity by single-cell RNA-seq, while developmental retinal vascularization is preserved.","method":"Actrt1-knockout mice, bone marrow chimera experiments, immunofluorescence, aortic ring sprouting assay, hindlimb ischemia model, Matrigel plug assay, single-cell RNA-seq, histology","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — knockout mouse with tumor models, bone marrow chimeras localizing phenotype to non-hematopoietic compartment, multiple orthogonal functional assays and mechanistic readouts","pmids":["41197408"],"is_preprint":false},{"year":2026,"finding":"ACTRT3 (ACTRT1 paralog, distinct gene) co-immunoprecipitates with ACTRT1, confirming that ACTRT1 is a component of the perinuclear theca protein complex also containing ACTRT2, ACTL7A, SPEM2, and ZPBP.","method":"Co-immunoprecipitation in Actrt3-/- mouse model","journal":"Development (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct Co-IP confirming complex membership, but this is incidental to the primary ACTRT3 study; single method for the ACTRT1 interaction","pmids":["41668650"],"is_preprint":false}],"current_model":"ACTRT1 (ARP-T1) is a testis-enriched actin-related protein that forms a multimeric complex with ACTRT2, ACTL7A, ACTL9, and ACTRT3 in the subacrosomal perinuclear theca of spermatids, where it anchors the acrosome to the nucleus via interactions with SPACA1, PARP11, and SPATA46, ensuring proper sperm head morphology and fertilization competence; in somatic cells, it localizes to the basal body of primary cilia and regulates ciliary length, and it directly binds the GLI1 promoter to suppress Hedgehog signaling as a tumor suppressor; additionally, ACTRT1 sustains pathological angiogenesis by promoting endothelial sprouting and vessel maturation in tumors."},"narrative":{"mechanistic_narrative":"ACTRT1 (ARP-T1) is a testis-enriched actin-related protein that acts as a structural organizer of the sperm head and, in somatic contexts, as a regulator of ciliary length, Hedgehog signaling, and tumor vasculature [PMID:12243744, PMID:28869610, PMID:33972689, PMID:35616329]. In differentiating spermatids it is a major acidic component of the perinuclear theca/calyx and assembles into a multimeric complex with ACTRT2, ACTL7A, ACTL9, and ACTRT3 in the subacrosomal region [PMID:12243744, PMID:35616329, PMID:41668650]. Within this complex, ACTRT1 anchors the developing acrosome to the nucleus by bridging the inner acrosomal membrane protein SPACA1 to the nuclear envelope proteins PARP11 and SPATA46; its loss loosens the acroplaxome, detaches the acrosome, produces malformed heads, and depletes and mislocalizes ACTL7A and PLCζ, causing severe subfertility in knockout mice and acrosomal detachment with fertilization failure in men carrying whole-gene ACTRT1 deletions [PMID:35616329, PMID:38414365]. Beyond the testis, ACTRT1 localizes to the basal body of primary cilia and the midbody and sustains ciliary length, with patient tissue bearing ACTRT1 mutations showing reduced cilia [PMID:33972689]. As a tumor suppressor it binds the GLI1 promoter directly to repress GLI1 expression and dampen Hedgehog pathway activation [PMID:28869610], yet in tumor endothelium it promotes growth by driving endothelial sprouting and vessel maturation [PMID:41197408]. Whether these somatic activities share a common molecular basis with its structural role in the perinuclear theca has not been resolved in the available corpus.","teleology":[{"year":2002,"claim":"Established ACTRT1 as a bona fide actin-related protein and pinpointed its identity as a testis-restricted structural component of the sperm head, framing it as a candidate cytoskeletal organizer rather than a generic actin.","evidence":"Partial amino acid sequencing of bull sperm calyx preparations with immunoblot and immunofluorescence localization to the perinuclear theca","pmids":["12243744"],"confidence":"Medium","gaps":["No interacting partners or molecular function defined","Functional consequence of localization not tested","Single species (bull) without genetic perturbation"]},{"year":2017,"claim":"Revealed an unexpected nuclear, gene-regulatory function: ACTRT1 directly represses the Hedgehog effector GLI1, defining it as a tumor suppressor in Hedgehog-driven cancers and decoupling its somatic role from a purely structural one.","evidence":"GLI1 promoter binding assays, loss-of-function, and exogenous expression rescue with in vitro and in vivo proliferation assays","pmids":["28869610"],"confidence":"High","gaps":["Mechanism of promoter recognition by an actin-related protein not resolved","Whether ACTRT1 acts alone or within a chromatin complex unknown","No structural basis for DNA binding"]},{"year":2021,"claim":"Connected ACTRT1 to ciliary and cytokinetic structures, showing it controls ciliary length and providing an interactome linking it to ciliogenesis, endosomal recycling, and septin machinery — a candidate route to its somatic phenotypes.","evidence":"Immunofluorescence localization to basal body and midbody, mass-spectrometry interactome, knockdown with ciliary length measurement, and patient tissue correlation","pmids":["33972689"],"confidence":"High","gaps":["Direct partner mediating ciliary length control not isolated from the interactome","Relationship between ciliary defect and Hedgehog repression not integrated","Mechanism of basal body recruitment unknown"]},{"year":2022,"claim":"Defined ACTRT1's core spermatogenic mechanism: it nucleates a perinuclear theca complex and physically tethers the acrosome to the nucleus, explaining the structural requirement for normal sperm head morphology and fertility.","evidence":"Reciprocal co-immunoprecipitation of ACTRT2/ACTL7A/ACTL9, Actrt1-knockout mouse phenotyping, and interaction mapping to SPACA1, PARP11, and SPATA46","pmids":["35616329"],"confidence":"High","gaps":["Stoichiometry and architecture of the multimeric complex unresolved","Why ACTL7A and PLCζ levels drop upon ACTRT1 loss mechanistically unclear","No structural model of the anchoring interface"]},{"year":2024,"claim":"Translated the mouse mechanism to human disease, showing whole-gene ACTRT1 deletion causes acrosomal detachment and fertilization failure with the same ACTL7A/PLCζ mislocalization, confirming conserved relevance to human male infertility.","evidence":"Whole exome/genome sequencing of affected men with Western blot, immunostaining, and electron microscopy of patient sperm","pmids":["38414365"],"confidence":"Medium","gaps":["Limited to two human cases","Whether residual fertility or assisted-reproduction outcomes vary not addressed","Causal chain from deletion to PLCζ loss not mechanistically dissected"]},{"year":2025,"claim":"Uncovered a pro-angiogenic role distinct from its tumor-suppressor function, showing ACTRT1 in tumor endothelium drives sprouting and vessel maturation, revealing context-dependent and even opposing effects on tumor growth.","evidence":"Actrt1-knockout mice with B16F1/MC38 tumor models, bone marrow chimeras, aortic ring sprouting, hindlimb ischemia, Matrigel plug, and single-cell RNA-seq of endothelium","pmids":["41197408"],"confidence":"High","gaps":["Molecular effector linking ACTRT1 to endothelial maturation not identified","Relationship to its Hedgehog/GLI1 activity in endothelium untested","No structural or biochemical mechanism for the angiogenic function"]},{"year":2026,"claim":"Extended the perinuclear theca complex roster by showing ACTRT3 associates with ACTRT1, reinforcing ACTRT1 as a stable subunit of a multi-actin-related-protein assembly that also contains SPEM2 and ZPBP.","evidence":"Co-immunoprecipitation in an Actrt3-knockout mouse model","pmids":["41668650"],"confidence":"Medium","gaps":["Single-method Co-IP, incidental to the ACTRT3-focused study","Functional consequence of the ACTRT1–ACTRT3 interaction not tested","No reciprocal validation for this specific pairing"]},{"year":null,"claim":"Whether ACTRT1's structural role in the perinuclear theca and its somatic activities (GLI1 repression, ciliary length control, endothelial sprouting) reflect a shared biochemical mechanism or distinct context-specific functions remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unifying molecular activity reconciling cytoskeletal, chromatin, and ciliary roles","No high-resolution structure of any ACTRT1 complex","Mechanism of nuclear DNA binding by an actin-related protein undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[1]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,3]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0]}],"localization":[{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[2]},{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[2]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[1,3]},{"term_id":"GO:0005635","term_label":"nuclear envelope","supporting_discovery_ids":[3]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1]},{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[3,4]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[1,5]}],"complexes":["perinuclear theca subacrosomal complex (ACTRT1/ACTRT2/ACTL7A/ACTL9/ACTRT3)"],"partners":["ACTRT2","ACTL7A","ACTL9","ACTRT3","SPACA1","PARP11","SPATA46","ZPBP"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8TDG2","full_name":"Actin-related protein T1","aliases":[],"length_aa":376,"mass_kda":41.7,"function":"Negatively regulates the Hedgehog (SHH) signaling. Binds to the promoter of the SHH signaling mediator, GLI1, and inhibits its expression","subcellular_location":"Cytoplasm, cytoskeleton; Cytoplasm; Nucleus; Cytoplasmic vesicle, secretory vesicle, acrosome","url":"https://www.uniprot.org/uniprotkb/Q8TDG2/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ACTRT1","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/ACTRT1","total_profiled":1310},"omim":[{"mim_id":"301845","title":"BAZEX-DUPRE-CHRISTOL SYNDROME; BDCS","url":"https://www.omim.org/entry/301845"},{"mim_id":"300768","title":"CYLICIN 1; CYLC1","url":"https://www.omim.org/entry/300768"},{"mim_id":"300487","title":"ACTIN-RELATED PROTEIN T1; ACTRT1","url":"https://www.omim.org/entry/300487"},{"mim_id":"258150","title":"SPERMATOGENIC FAILURE 1; SPGF1","url":"https://www.omim.org/entry/258150"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in single","driving_tissues":[{"tissue":"testis","ntpm":3.9}],"url":"https://www.proteinatlas.org/search/ACTRT1"},"hgnc":{"alias_symbol":["AIP1","KIAA0705","ARIP1","Arp-T1"],"prev_symbol":[]},"alphafold":{"accession":"Q8TDG2","domains":[{"cath_id":"3.30.420.40","chopping":"5-143_341-375","consensus_level":"medium","plddt":92.5844,"start":5,"end":375},{"cath_id":"3.30.420.40","chopping":"149-184_273-337","consensus_level":"medium","plddt":96.9569,"start":149,"end":337},{"cath_id":"3.90.640.10","chopping":"186-263","consensus_level":"high","plddt":90.7255,"start":186,"end":263}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8TDG2","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8TDG2-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8TDG2-F1-predicted_aligned_error_v6.png","plddt_mean":93.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ACTRT1","jax_strain_url":"https://www.jax.org/strain/search?query=ACTRT1"},"sequence":{"accession":"Q8TDG2","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8TDG2.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8TDG2/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8TDG2"}},"corpus_meta":[{"pmid":"12243744","id":"PMC_12243744","title":"Novel actin-related proteins Arp-T1 and Arp-T2 as components of the cytoskeletal calyx of the mammalian sperm head.","date":"2002","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/12243744","citation_count":60,"is_preprint":false},{"pmid":"28869610","id":"PMC_28869610","title":"Mutations in ACTRT1 and its enhancer RNA elements lead to aberrant activation of Hedgehog signaling in inherited and sporadic basal cell carcinomas.","date":"2017","source":"Nature medicine","url":"https://pubmed.ncbi.nlm.nih.gov/28869610","citation_count":54,"is_preprint":false},{"pmid":"38614076","id":"PMC_38614076","title":"Toward clinical exomes in diagnostics and management of male infertility.","date":"2024","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/38614076","citation_count":39,"is_preprint":false},{"pmid":"35616329","id":"PMC_35616329","title":"Loss of perinuclear theca ACTRT1 causes acrosome detachment and severe male subfertility in mice.","date":"2022","source":"Development (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/35616329","citation_count":29,"is_preprint":false},{"pmid":"39267058","id":"PMC_39267058","title":"Whole exome sequencing analysis of 167 men with primary infertility.","date":"2024","source":"BMC medical genomics","url":"https://pubmed.ncbi.nlm.nih.gov/39267058","citation_count":17,"is_preprint":false},{"pmid":"34422805","id":"PMC_34422805","title":"Pathogenic Variants in ACTRT1 Cause Acephalic Spermatozoa Syndrome.","date":"2021","source":"Frontiers in cell and developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/34422805","citation_count":16,"is_preprint":false},{"pmid":"35986704","id":"PMC_35986704","title":"Germline intergenic duplications at Xq26.1 underlie Bazex-Dupré-Christol basal cell carcinoma susceptibility syndrome.","date":"2022","source":"The British journal of dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/35986704","citation_count":16,"is_preprint":false},{"pmid":"33972689","id":"PMC_33972689","title":"ARP-T1-associated Bazex-Dupré-Christol syndrome is an inherited basal cell cancer with ciliary defects characteristic of ciliopathies.","date":"2021","source":"Communications biology","url":"https://pubmed.ncbi.nlm.nih.gov/33972689","citation_count":12,"is_preprint":false},{"pmid":"38414365","id":"PMC_38414365","title":"Deletion of ACTRT1 is associated with male infertility as sperm acrosomal ultrastructural defects and fertilization failure in human.","date":"2024","source":"Human reproduction (Oxford, England)","url":"https://pubmed.ncbi.nlm.nih.gov/38414365","citation_count":11,"is_preprint":false},{"pmid":"38872096","id":"PMC_38872096","title":"Silencing immune-infiltrating biomarker CCDC80 inhibits malignant characterization and tumor formation in gastric cancer.","date":"2024","source":"BMC cancer","url":"https://pubmed.ncbi.nlm.nih.gov/38872096","citation_count":8,"is_preprint":false},{"pmid":"36355490","id":"PMC_36355490","title":"The Expression Patterns of Human Cancer-Testis Genes Are Induced through Epigenetic Drugs in Colon Cancer Cells.","date":"2022","source":"Pharmaceuticals (Basel, Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/36355490","citation_count":7,"is_preprint":false},{"pmid":"41197408","id":"PMC_41197408","title":"Loss of Actrt1 in non-hematopoietic stroma suppresses pathological angiogenesis and tumor progression.","date":"2025","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/41197408","citation_count":0,"is_preprint":false},{"pmid":"41465095","id":"PMC_41465095","title":"A Novel Variant of the ACTRT1 Gene Is Potentially Associated with Oligoasthenoteratozoospermia, Acrosome Detachment, and Fertilization Failure.","date":"2025","source":"Genes","url":"https://pubmed.ncbi.nlm.nih.gov/41465095","citation_count":0,"is_preprint":false},{"pmid":"41668650","id":"PMC_41668650","title":"Actin-related protein T3 is required for acrosome biogenesis and sperm function in mice.","date":"2026","source":"Development (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/41668650","citation_count":0,"is_preprint":false},{"pmid":"41913266","id":"PMC_41913266","title":"Testis-specific lncRNA Teshl regulates acrosome biogenesis to maintain sperm structure and function.","date":"2026","source":"Cell & bioscience","url":"https://pubmed.ncbi.nlm.nih.gov/41913266","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.03.27.645694","title":"Actin-related protein M1 (ARPM1) required for acrosome biogenesis and sperm function in mice","date":"2025-04-01","source":"bioRxiv","url":"https://doi.org/10.1101/2025.03.27.645694","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11220,"output_tokens":2097,"usd":0.032558,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9096,"output_tokens":3483,"usd":0.066278,"stage2_stop_reason":"end_turn"},"total_usd":0.098836,"stage1_batch_id":"msgbatch_0179Z2pxRYBsXi2xADneafRw","stage2_batch_id":"msgbatch_01LaY9ZaVdgjWArcZo9eqQE5","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2002,\n      \"finding\": \"ARP-T1 (ACTRT1) is a novel actin-related protein that localizes specifically to the calyx of the mammalian sperm head perinuclear theca, identified as a major acidic component by partial amino acid sequencing of calyx preparations from bull spermatozoa and confirmed by immunoblotting and immunofluorescence microscopy. Its expression is restricted to the testis, appearing late in spermatid differentiation.\",\n      \"method\": \"Partial amino acid sequencing, immunoblotting, immunofluorescence microscopy, subcellular fractionation\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct biochemical identification and localization with antibody validation, single lab, two orthogonal methods\",\n      \"pmids\": [\"12243744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"ARP-T1 directly binds to the GLI1 promoter, thereby inhibiting GLI1 expression and suppressing Hedgehog signaling pathway activation; loss of ARP-T1 leads to Hedgehog pathway activation, and exogenous ACTRT1 expression reduces in vitro and in vivo proliferation of cell lines with aberrant Hedgehog signaling.\",\n      \"method\": \"Chromatin binding assays (GLI1 promoter binding), loss-of-function experiments, exogenous expression assays, in vitro and in vivo proliferation assays\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct promoter binding established, functional rescue with exogenous expression, in vitro and in vivo validation, multiple orthogonal approaches in a rigorous study\",\n      \"pmids\": [\"28869610\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ARP-T1 (ACTRT1) localizes to the midbody during cytokinesis and to the basal body of primary cilia during interphase; an ARP-T1 interactome includes proteins involved in ciliogenesis, endosomal recycling, and septin ring formation. ACTRT1 knockdown in cultured cells reduces ciliary length, and tissue from BDCS patients with ACTRT1 mutations shows reduced ciliary length correlating with ARP-T1 protein levels.\",\n      \"method\": \"Immunofluorescence localization, mass spectrometry interactome (PXD016557), ACTRT1 knockdown, ciliary length measurement in patient tissue and knockdown cells\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — interactome by MS, direct localization, functional KD with quantitative phenotype, validated in patient tissue and cell culture\",\n      \"pmids\": [\"33972689\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ACTRT1, ACTRT2, ACTL7A, and ACTL9 proteins interact to form a multimeric complex localizing to the subacrosomal region of spermatids. ACTRT1 anchors developing acrosomes to the nucleus by interacting with inner acrosomal membrane protein SPACA1 and nuclear envelope proteins PARP11 and SPATA46. Loss of ACTRT1 in knockout mice causes loosened acroplaxome structure during spermiogenesis, acrosome detachment from sperm nuclei, malformed heads, reduced ACTL7A and PLCζ protein content, and severe subfertility despite normal sperm count and motility.\",\n      \"method\": \"Co-immunoprecipitation, Actrt1-knockout mouse generation and phenotyping, immunofluorescence, Western blotting, fertility assays\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP for multiple interactors, knockout mouse with defined cellular and fertility phenotype, multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"35616329\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ACTRT1 deficiency in humans (whole-gene deletion) causes sperm acrosomal ultrastructural defects (acrosomal detachment) and fertilization failure; ACTL7A and PLCζ (phospholipase C zeta) are decreased and ectopically distributed in sperm from ACTRT1-deleted men, consistent with findings in Actrt1-KO mice.\",\n      \"method\": \"Whole exome sequencing, whole genome sequencing, PCR, quantitative PCR, Western blotting, immunostaining, electron microscopy, Papanicolaou staining\",\n      \"journal\": \"Human reproduction (Oxford, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct mechanistic link to ACTL7A and PLCζ mislocalization, validated by multiple methods, but limited to two human cases\",\n      \"pmids\": [\"38414365\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Actrt1 promotes tumor growth through non-hematopoietic endothelium by sustaining endothelial sprouting and vessel maturation. Actrt1-/- mice show reduced growth of B16F1 and MC38 tumors; bone marrow chimera experiments localize the phenotype to the non-hematopoietic compartment. ACTRT1 protein is detected in CD31+ tumor vessels. Actrt1 deficiency reduces endothelial sprouting from aortic rings, delays recovery after hindlimb ischemia, and shifts endothelial transcriptome toward immaturity by single-cell RNA-seq, while developmental retinal vascularization is preserved.\",\n      \"method\": \"Actrt1-knockout mice, bone marrow chimera experiments, immunofluorescence, aortic ring sprouting assay, hindlimb ischemia model, Matrigel plug assay, single-cell RNA-seq, histology\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — knockout mouse with tumor models, bone marrow chimeras localizing phenotype to non-hematopoietic compartment, multiple orthogonal functional assays and mechanistic readouts\",\n      \"pmids\": [\"41197408\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"ACTRT3 (ACTRT1 paralog, distinct gene) co-immunoprecipitates with ACTRT1, confirming that ACTRT1 is a component of the perinuclear theca protein complex also containing ACTRT2, ACTL7A, SPEM2, and ZPBP.\",\n      \"method\": \"Co-immunoprecipitation in Actrt3-/- mouse model\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct Co-IP confirming complex membership, but this is incidental to the primary ACTRT3 study; single method for the ACTRT1 interaction\",\n      \"pmids\": [\"41668650\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ACTRT1 (ARP-T1) is a testis-enriched actin-related protein that forms a multimeric complex with ACTRT2, ACTL7A, ACTL9, and ACTRT3 in the subacrosomal perinuclear theca of spermatids, where it anchors the acrosome to the nucleus via interactions with SPACA1, PARP11, and SPATA46, ensuring proper sperm head morphology and fertilization competence; in somatic cells, it localizes to the basal body of primary cilia and regulates ciliary length, and it directly binds the GLI1 promoter to suppress Hedgehog signaling as a tumor suppressor; additionally, ACTRT1 sustains pathological angiogenesis by promoting endothelial sprouting and vessel maturation in tumors.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ACTRT1 (ARP-T1) is a testis-enriched actin-related protein that acts as a structural organizer of the sperm head and, in somatic contexts, as a regulator of ciliary length, Hedgehog signaling, and tumor vasculature [#0, #1, #2, #3]. In differentiating spermatids it is a major acidic component of the perinuclear theca/calyx and assembles into a multimeric complex with ACTRT2, ACTL7A, ACTL9, and ACTRT3 in the subacrosomal region [#0, #3, #6]. Within this complex, ACTRT1 anchors the developing acrosome to the nucleus by bridging the inner acrosomal membrane protein SPACA1 to the nuclear envelope proteins PARP11 and SPATA46; its loss loosens the acroplaxome, detaches the acrosome, produces malformed heads, and depletes and mislocalizes ACTL7A and PLCζ, causing severe subfertility in knockout mice and acrosomal detachment with fertilization failure in men carrying whole-gene ACTRT1 deletions [#3, #4]. Beyond the testis, ACTRT1 localizes to the basal body of primary cilia and the midbody and sustains ciliary length, with patient tissue bearing ACTRT1 mutations showing reduced cilia [#2]. As a tumor suppressor it binds the GLI1 promoter directly to repress GLI1 expression and dampen Hedgehog pathway activation [#1], yet in tumor endothelium it promotes growth by driving endothelial sprouting and vessel maturation [#5]. Whether these somatic activities share a common molecular basis with its structural role in the perinuclear theca has not been resolved in the available corpus.\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Established ACTRT1 as a bona fide actin-related protein and pinpointed its identity as a testis-restricted structural component of the sperm head, framing it as a candidate cytoskeletal organizer rather than a generic actin.\",\n      \"evidence\": \"Partial amino acid sequencing of bull sperm calyx preparations with immunoblot and immunofluorescence localization to the perinuclear theca\",\n      \"pmids\": [\"12243744\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\n        \"No interacting partners or molecular function defined\",\n        \"Functional consequence of localization not tested\",\n        \"Single species (bull) without genetic perturbation\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Revealed an unexpected nuclear, gene-regulatory function: ACTRT1 directly represses the Hedgehog effector GLI1, defining it as a tumor suppressor in Hedgehog-driven cancers and decoupling its somatic role from a purely structural one.\",\n      \"evidence\": \"GLI1 promoter binding assays, loss-of-function, and exogenous expression rescue with in vitro and in vivo proliferation assays\",\n      \"pmids\": [\"28869610\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\n        \"Mechanism of promoter recognition by an actin-related protein not resolved\",\n        \"Whether ACTRT1 acts alone or within a chromatin complex unknown\",\n        \"No structural basis for DNA binding\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Connected ACTRT1 to ciliary and cytokinetic structures, showing it controls ciliary length and providing an interactome linking it to ciliogenesis, endosomal recycling, and septin machinery — a candidate route to its somatic phenotypes.\",\n      \"evidence\": \"Immunofluorescence localization to basal body and midbody, mass-spectrometry interactome, knockdown with ciliary length measurement, and patient tissue correlation\",\n      \"pmids\": [\"33972689\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\n        \"Direct partner mediating ciliary length control not isolated from the interactome\",\n        \"Relationship between ciliary defect and Hedgehog repression not integrated\",\n        \"Mechanism of basal body recruitment unknown\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined ACTRT1's core spermatogenic mechanism: it nucleates a perinuclear theca complex and physically tethers the acrosome to the nucleus, explaining the structural requirement for normal sperm head morphology and fertility.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation of ACTRT2/ACTL7A/ACTL9, Actrt1-knockout mouse phenotyping, and interaction mapping to SPACA1, PARP11, and SPATA46\",\n      \"pmids\": [\"35616329\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\n        \"Stoichiometry and architecture of the multimeric complex unresolved\",\n        \"Why ACTL7A and PLCζ levels drop upon ACTRT1 loss mechanistically unclear\",\n        \"No structural model of the anchoring interface\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Translated the mouse mechanism to human disease, showing whole-gene ACTRT1 deletion causes acrosomal detachment and fertilization failure with the same ACTL7A/PLCζ mislocalization, confirming conserved relevance to human male infertility.\",\n      \"evidence\": \"Whole exome/genome sequencing of affected men with Western blot, immunostaining, and electron microscopy of patient sperm\",\n      \"pmids\": [\"38414365\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\n        \"Limited to two human cases\",\n        \"Whether residual fertility or assisted-reproduction outcomes vary not addressed\",\n        \"Causal chain from deletion to PLCζ loss not mechanistically dissected\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Uncovered a pro-angiogenic role distinct from its tumor-suppressor function, showing ACTRT1 in tumor endothelium drives sprouting and vessel maturation, revealing context-dependent and even opposing effects on tumor growth.\",\n      \"evidence\": \"Actrt1-knockout mice with B16F1/MC38 tumor models, bone marrow chimeras, aortic ring sprouting, hindlimb ischemia, Matrigel plug, and single-cell RNA-seq of endothelium\",\n      \"pmids\": [\"41197408\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\n        \"Molecular effector linking ACTRT1 to endothelial maturation not identified\",\n        \"Relationship to its Hedgehog/GLI1 activity in endothelium untested\",\n        \"No structural or biochemical mechanism for the angiogenic function\"\n      ]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Extended the perinuclear theca complex roster by showing ACTRT3 associates with ACTRT1, reinforcing ACTRT1 as a stable subunit of a multi-actin-related-protein assembly that also contains SPEM2 and ZPBP.\",\n      \"evidence\": \"Co-immunoprecipitation in an Actrt3-knockout mouse model\",\n      \"pmids\": [\"41668650\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\n        \"Single-method Co-IP, incidental to the ACTRT3-focused study\",\n        \"Functional consequence of the ACTRT1–ACTRT3 interaction not tested\",\n        \"No reciprocal validation for this specific pairing\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Whether ACTRT1's structural role in the perinuclear theca and its somatic activities (GLI1 repression, ciliary length control, endothelial sprouting) reflect a shared biochemical mechanism or distinct context-specific functions remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\n        \"No unifying molecular activity reconciling cytoskeletal, chromatin, and ciliary roles\",\n        \"No high-resolution structure of any ACTRT1 complex\",\n        \"Mechanism of nuclear DNA binding by an actin-related protein undefined\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1, 3]},\n      {\"term_id\": \"GO:0005635\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [3, 4]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [1, 5]}\n    ],\n    \"complexes\": [\n      \"perinuclear theca subacrosomal complex (ACTRT1/ACTRT2/ACTL7A/ACTL9/ACTRT3)\"\n    ],\n    \"partners\": [\n      \"ACTRT2\",\n      \"ACTL7A\",\n      \"ACTL9\",\n      \"ACTRT3\",\n      \"SPACA1\",\n      \"PARP11\",\n      \"SPATA46\",\n      \"ZPBP\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":5,"faith_total":5,"faith_pct":100.0}}