{"gene":"ACTRT2","run_date":"2026-04-28T17:12:37","timeline":{"discoveries":[{"year":2002,"finding":"ACTRT2 (Arp-T2) 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 of the cytoskeletal calyx structure resistant to high ionic strength and detergents.","method":"Partial amino acid sequencing of calyx preparations from bull spermatozoa, immunoblotting, and immunofluorescence microscopy with antibodies raised against human Arp-T2","journal":"Experimental cell research","confidence":"High","confidence_rationale":"Tier 2 — direct protein identification, localization by immunofluorescence, replicated across species","pmids":["12243744"],"is_preprint":false},{"year":2022,"finding":"ACTRT2 interacts with ACTRT1, ACTL7A, and ACTL9 to form a multimeric complex localizing to the subacrosomal region of spermatids, and this complex is required for anchoring the developing acrosome to the nucleus.","method":"Co-immunoprecipitation and immunostaining in mouse spermatids; Actrt1-knockout mouse model showing disrupted complex and acrosomal detachment","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP plus KO mouse with defined cellular phenotype, replicated in subsequent studies","pmids":["35616329"],"is_preprint":false},{"year":2025,"finding":"ACTRT2 deficiency in spermatogonia increases vulnerability to ferroptosis by causing intracellular iron overload (upregulation of SLC11A2, IREB2, TFRC), mitochondrial damage, upregulation of ACSL4 and ALOX15, and downregulation of SLC7A11 and GPX4.","method":"In vitro knockdown in GC-1 spermatogonial cells with busulfan treatment; in vivo ACTRT2-/- and ACTRT2+/- mouse models; western blotting and ROS measurement","journal":"Molecular human reproduction","confidence":"Medium","confidence_rationale":"Tier 2 — KO/KD with defined cellular phenotype and pathway placement, single lab","pmids":["40811009"],"is_preprint":false},{"year":2026,"finding":"ACTRT2 interacts with ACTRT3 (ARPM1/ACTRT3) as part of the perinuclear theca protein complex in spermatids, co-immunoprecipitated together with ACTRT1, ACTL7A, SPEM2, and ZPBP.","method":"Co-immunoprecipitation in mouse spermatids from Actrt3-/- model","journal":"Development (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP with multiple PT complex members, single study","pmids":["41668650"],"is_preprint":false},{"year":2025,"finding":"ACTRT2 (ARPM1/ACTRT3 study context) interacts with ACTRT1, ACTL7A, and ZPBP as part of the perinuclear theca scaffold in spermatids, contributing to the cytoskeletal network connecting acrosome and nucleus.","method":"Co-immunoprecipitation in Arpm1-deficient mouse model","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP in KO model, preprint, single lab","pmids":["bio_10.1101_2025.03.27.645694"],"is_preprint":true},{"year":2014,"finding":"ACTRT2 localizes to the post-acrosomal region and middle piece of human spermatozoa, and its reduced expression is associated with obesity-induced asthenozoospermia and impaired sperm motility.","method":"Immunofluorescence, Western blot, and flow cytometry on human sperm samples from obese individuals with asthenozoospermia","journal":"Andrology","confidence":"Low","confidence_rationale":"Tier 3 — localization established but functional link is correlative, not mechanistic","pmids":["25293813"],"is_preprint":false},{"year":2024,"finding":"ACTRT1 deficiency in humans (caused by a 110-kb X-chromosome microdeletion) disrupts the ACTRT1-ACTRT2-ACTL7A-ACTL9 complex in the subacrosomal region, leading to acrosomal detachment and fertilization failure, consistent with the role of ACTRT2 as part of this multimeric complex.","method":"Whole genome sequencing, western blotting, immunostaining of human patient sperm","journal":"Human reproduction (Oxford, England)","confidence":"Medium","confidence_rationale":"Tier 2 — human genetic KO validates complex membership established in mice","pmids":["38414365"],"is_preprint":false}],"current_model":"ACTRT2 is a testis-specific actin-related protein that localizes to the perinuclear theca (subacrosomal region and calyx) of spermatids, where it forms a multimeric complex with ACTRT1, ACTL7A, ACTL9, and ACTRT3 to anchor the developing acrosome to the sperm nucleus; additionally, in spermatogonia, ACTRT2 suppresses ferroptosis by maintaining iron homeostasis and supporting the antioxidant GPX4/SLC7A11 pathway."},"narrative":{"teleology":[{"year":2002,"claim":"Identifying ACTRT2 as a novel actin-related protein and localizing it to the sperm calyx established that the perinuclear theca contains a specialized ARP distinct from conventional actins.","evidence":"Partial amino acid sequencing of bull sperm calyx preparations combined with immunofluorescence on human spermatozoa","pmids":["12243744"],"confidence":"High","gaps":["No interaction partners identified","Function beyond structural residence in the calyx unknown","No loss-of-function data"]},{"year":2022,"claim":"Demonstrating that ACTRT2 forms a multimeric complex with ACTRT1, ACTL7A, and ACTL9 in the subacrosomal region, and that disruption of this complex causes acrosomal detachment, established the first mechanistic role for ACTRT2 in acrosome–nucleus anchoring.","evidence":"Reciprocal co-immunoprecipitation and immunostaining in mouse spermatids; Actrt1-knockout mouse phenotype showing acrosomal detachment","pmids":["35616329"],"confidence":"High","gaps":["Direct ACTRT2 knockout phenotype not yet characterized","Stoichiometry and architecture of the complex unresolved","Whether ACTRT2 binds nucleotides like conventional actins unknown"]},{"year":2024,"claim":"Validation in a human patient with an ACTRT1 microdeletion confirmed that the ACTRT1–ACTRT2–ACTL7A–ACTL9 complex is essential for human acrosome integrity and fertilization, extending the mouse findings to clinical relevance.","evidence":"Whole genome sequencing and immunostaining of patient sperm showing loss of complex members and acrosomal detachment","pmids":["38414365"],"confidence":"Medium","gaps":["Human ACTRT2-specific mutations have not been reported","Whether residual ACTRT2 protein persists in ACTRT1-deficient sperm not quantified"]},{"year":2025,"claim":"Discovery that ACTRT2 deficiency in spermatogonia causes ferroptosis through iron overload and collapse of the GPX4/SLC7A11 axis revealed an unexpected non-structural role in iron homeostasis and cell survival during early spermatogenesis.","evidence":"ACTRT2 knockdown in GC-1 spermatogonial cells and ACTRT2-knockout mouse model with western blotting and ROS measurement","pmids":["40811009"],"confidence":"Medium","gaps":["Mechanism by which an actin-related protein regulates iron uptake genes is unknown","Single-lab finding not yet independently replicated","Whether the ferroptosis phenotype is cell-autonomous or secondary to structural defects is unclear"]},{"year":2026,"claim":"Identification of ACTRT3 and ZPBP as additional complex partners expanded the perinuclear theca scaffold model beyond the original four-member complex.","evidence":"Co-immunoprecipitation in mouse spermatids from Actrt3-knockout model","pmids":["41668650"],"confidence":"Medium","gaps":["Direct binary interactions among all six partners not mapped","Structural organization of the expanded complex unknown","Functional hierarchy among subunits not determined"]},{"year":null,"claim":"A direct ACTRT2 loss-of-function model with full phenotypic characterization, the biochemical basis by which ACTRT2 regulates ferroptosis, and the structural architecture of the perinuclear theca complex remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No Actrt2-specific conditional knockout with spermatogenesis phenotyping reported","No structural or biophysical data on ACTRT2 or its complexes","Molecular link between ACTRT2 and iron homeostasis gene regulation is undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,1]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,1,3]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,1]}],"pathway":[{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[1,2,6]}],"complexes":["Perinuclear theca actin-related protein complex"],"partners":["ACTRT1","ACTL7A","ACTL9","ACTRT3","ZPBP"],"other_free_text":[]},"mechanistic_narrative":"ACTRT2 is a testis-specific actin-related protein that functions as a structural component of the sperm perinuclear theca, where it participates in anchoring the acrosome to the nucleus during spermiogenesis. ACTRT2 forms a multimeric complex with ACTRT1, ACTL7A, ACTL9, and ACTRT3 in the subacrosomal region of spermatids; disruption of this complex—as demonstrated in Actrt1-knockout mice and in a human ACTRT1 microdeletion—results in acrosomal detachment and fertilization failure [PMID:35616329, PMID:38414365, PMID:41668650]. Originally identified as a major acidic, detergent-resistant component of the bull sperm calyx, ACTRT2 is tightly integrated into the cytoskeletal scaffold of the perinuclear theca [PMID:12243744]. In spermatogonia, ACTRT2 deficiency promotes ferroptosis through intracellular iron overload, mitochondrial damage, and downregulation of the GPX4/SLC7A11 antioxidant axis [PMID:40811009]."},"prefetch_data":{"uniprot":{"accession":"Q8TDY3","full_name":"Actin-related protein T2","aliases":["Actin-related protein M2"],"length_aa":377,"mass_kda":41.7,"function":"","subcellular_location":"Cytoplasm, cytoskeleton","url":"https://www.uniprot.org/uniprotkb/Q8TDY3/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ACTRT2","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/ACTRT2","total_profiled":1310},"omim":[{"mim_id":"608535","title":"ACTIN-RELATED PROTEIN T2; ACTRT2","url":"https://www.omim.org/entry/608535"},{"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"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in single","driving_tissues":[{"tissue":"testis","ntpm":146.1}],"url":"https://www.proteinatlas.org/search/ACTRT2"},"hgnc":{"alias_symbol":["Arp-T2","ARPM2","FLJ25424"],"prev_symbol":[]},"alphafold":{"accession":"Q8TDY3","domains":[{"cath_id":"3.30.420.40","chopping":"5-142_342-376","consensus_level":"medium","plddt":92.7324,"start":5,"end":376},{"cath_id":"3.30.420.40","chopping":"148-185_272-338","consensus_level":"medium","plddt":96.7737,"start":148,"end":338},{"cath_id":"3.90.640.10","chopping":"187-264","consensus_level":"high","plddt":91.7319,"start":187,"end":264}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8TDY3","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8TDY3-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8TDY3-F1-predicted_aligned_error_v6.png","plddt_mean":93.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ACTRT2","jax_strain_url":"https://www.jax.org/strain/search?query=ACTRT2"},"sequence":{"accession":"Q8TDY3","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8TDY3.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8TDY3/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8TDY3"}},"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":"25293813","id":"PMC_25293813","title":"Proteomic pattern changes associated with obesity-induced asthenozoospermia.","date":"2014","source":"Andrology","url":"https://pubmed.ncbi.nlm.nih.gov/25293813","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":"32787870","id":"PMC_32787870","title":"Effect of transient scrotal hyperthermia on human sperm: an iTRAQ-based proteomic analysis.","date":"2020","source":"Reproductive biology and endocrinology : RB&E","url":"https://pubmed.ncbi.nlm.nih.gov/32787870","citation_count":22,"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":"31122248","id":"PMC_31122248","title":"Exome-wide search and functional annotation of genes associated in patients with severe tick-borne encephalitis in a Russian population.","date":"2019","source":"BMC medical genomics","url":"https://pubmed.ncbi.nlm.nih.gov/31122248","citation_count":6,"is_preprint":false},{"pmid":"35751016","id":"PMC_35751016","title":"Ectopic expression of a combination of 5 genes detects high risk forms of T-cell acute lymphoblastic leukemia.","date":"2022","source":"BMC genomics","url":"https://pubmed.ncbi.nlm.nih.gov/35751016","citation_count":5,"is_preprint":false},{"pmid":"40811009","id":"PMC_40811009","title":"ACTRT2 deficiency increases spermatogonia vulnerability to ferroptosis.","date":"2025","source":"Molecular human reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/40811009","citation_count":2,"is_preprint":false},{"pmid":"38179408","id":"PMC_38179408","title":"Whole genome sequencing reveals population diversity and variation in HIV-1 specific host genes.","date":"2023","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/38179408","citation_count":2,"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":"41610073","id":"PMC_41610073","title":"Methylation-specific, universal, and highly sensitive identification of ctDNA in prostate cancer by multiplex droplet digital PCR.","date":"2026","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/41610073","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":8093,"output_tokens":1584,"usd":0.024019},"stage2":{"model":"claude-opus-4-6","input_tokens":4837,"output_tokens":1669,"usd":0.098865},"total_usd":0.122884,"stage1_batch_id":"msgbatch_01TqNM6p6FsoMBT2jzQTwKBr","stage2_batch_id":"msgbatch_01Ya473eco8sTHbvRymQaU8o","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2002,\n      \"finding\": \"ACTRT2 (Arp-T2) 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 of the cytoskeletal calyx structure resistant to high ionic strength and detergents.\",\n      \"method\": \"Partial amino acid sequencing of calyx preparations from bull spermatozoa, immunoblotting, and immunofluorescence microscopy with antibodies raised against human Arp-T2\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct protein identification, localization by immunofluorescence, replicated across species\",\n      \"pmids\": [\"12243744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ACTRT2 interacts with ACTRT1, ACTL7A, and ACTL9 to form a multimeric complex localizing to the subacrosomal region of spermatids, and this complex is required for anchoring the developing acrosome to the nucleus.\",\n      \"method\": \"Co-immunoprecipitation and immunostaining in mouse spermatids; Actrt1-knockout mouse model showing disrupted complex and acrosomal detachment\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus KO mouse with defined cellular phenotype, replicated in subsequent studies\",\n      \"pmids\": [\"35616329\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ACTRT2 deficiency in spermatogonia increases vulnerability to ferroptosis by causing intracellular iron overload (upregulation of SLC11A2, IREB2, TFRC), mitochondrial damage, upregulation of ACSL4 and ALOX15, and downregulation of SLC7A11 and GPX4.\",\n      \"method\": \"In vitro knockdown in GC-1 spermatogonial cells with busulfan treatment; in vivo ACTRT2-/- and ACTRT2+/- mouse models; western blotting and ROS measurement\",\n      \"journal\": \"Molecular human reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO/KD with defined cellular phenotype and pathway placement, single lab\",\n      \"pmids\": [\"40811009\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"ACTRT2 interacts with ACTRT3 (ARPM1/ACTRT3) as part of the perinuclear theca protein complex in spermatids, co-immunoprecipitated together with ACTRT1, ACTL7A, SPEM2, and ZPBP.\",\n      \"method\": \"Co-immunoprecipitation in mouse spermatids from Actrt3-/- model\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP with multiple PT complex members, single study\",\n      \"pmids\": [\"41668650\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ACTRT2 (ARPM1/ACTRT3 study context) interacts with ACTRT1, ACTL7A, and ZPBP as part of the perinuclear theca scaffold in spermatids, contributing to the cytoskeletal network connecting acrosome and nucleus.\",\n      \"method\": \"Co-immunoprecipitation in Arpm1-deficient mouse model\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP in KO model, preprint, single lab\",\n      \"pmids\": [\"bio_10.1101_2025.03.27.645694\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"ACTRT2 localizes to the post-acrosomal region and middle piece of human spermatozoa, and its reduced expression is associated with obesity-induced asthenozoospermia and impaired sperm motility.\",\n      \"method\": \"Immunofluorescence, Western blot, and flow cytometry on human sperm samples from obese individuals with asthenozoospermia\",\n      \"journal\": \"Andrology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — localization established but functional link is correlative, not mechanistic\",\n      \"pmids\": [\"25293813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ACTRT1 deficiency in humans (caused by a 110-kb X-chromosome microdeletion) disrupts the ACTRT1-ACTRT2-ACTL7A-ACTL9 complex in the subacrosomal region, leading to acrosomal detachment and fertilization failure, consistent with the role of ACTRT2 as part of this multimeric complex.\",\n      \"method\": \"Whole genome sequencing, western blotting, immunostaining of human patient sperm\",\n      \"journal\": \"Human reproduction (Oxford, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — human genetic KO validates complex membership established in mice\",\n      \"pmids\": [\"38414365\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ACTRT2 is a testis-specific actin-related protein that localizes to the perinuclear theca (subacrosomal region and calyx) of spermatids, where it forms a multimeric complex with ACTRT1, ACTL7A, ACTL9, and ACTRT3 to anchor the developing acrosome to the sperm nucleus; additionally, in spermatogonia, ACTRT2 suppresses ferroptosis by maintaining iron homeostasis and supporting the antioxidant GPX4/SLC7A11 pathway.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"ACTRT2 is a testis-specific actin-related protein that functions as a structural component of the sperm perinuclear theca, where it participates in anchoring the acrosome to the nucleus during spermiogenesis. ACTRT2 forms a multimeric complex with ACTRT1, ACTL7A, ACTL9, and ACTRT3 in the subacrosomal region of spermatids; disruption of this complex—as demonstrated in Actrt1-knockout mice and in a human ACTRT1 microdeletion—results in acrosomal detachment and fertilization failure [PMID:35616329, PMID:38414365, PMID:41668650]. Originally identified as a major acidic, detergent-resistant component of the bull sperm calyx, ACTRT2 is tightly integrated into the cytoskeletal scaffold of the perinuclear theca [PMID:12243744]. In spermatogonia, ACTRT2 deficiency promotes ferroptosis through intracellular iron overload, mitochondrial damage, and downregulation of the GPX4/SLC7A11 antioxidant axis [PMID:40811009].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Identifying ACTRT2 as a novel actin-related protein and localizing it to the sperm calyx established that the perinuclear theca contains a specialized ARP distinct from conventional actins.\",\n      \"evidence\": \"Partial amino acid sequencing of bull sperm calyx preparations combined with immunofluorescence on human spermatozoa\",\n      \"pmids\": [\"12243744\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No interaction partners identified\",\n        \"Function beyond structural residence in the calyx unknown\",\n        \"No loss-of-function data\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrating that ACTRT2 forms a multimeric complex with ACTRT1, ACTL7A, and ACTL9 in the subacrosomal region, and that disruption of this complex causes acrosomal detachment, established the first mechanistic role for ACTRT2 in acrosome–nucleus anchoring.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation and immunostaining in mouse spermatids; Actrt1-knockout mouse phenotype showing acrosomal detachment\",\n      \"pmids\": [\"35616329\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Direct ACTRT2 knockout phenotype not yet characterized\",\n        \"Stoichiometry and architecture of the complex unresolved\",\n        \"Whether ACTRT2 binds nucleotides like conventional actins unknown\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Validation in a human patient with an ACTRT1 microdeletion confirmed that the ACTRT1–ACTRT2–ACTL7A–ACTL9 complex is essential for human acrosome integrity and fertilization, extending the mouse findings to clinical relevance.\",\n      \"evidence\": \"Whole genome sequencing and immunostaining of patient sperm showing loss of complex members and acrosomal detachment\",\n      \"pmids\": [\"38414365\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Human ACTRT2-specific mutations have not been reported\",\n        \"Whether residual ACTRT2 protein persists in ACTRT1-deficient sperm not quantified\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Discovery that ACTRT2 deficiency in spermatogonia causes ferroptosis through iron overload and collapse of the GPX4/SLC7A11 axis revealed an unexpected non-structural role in iron homeostasis and cell survival during early spermatogenesis.\",\n      \"evidence\": \"ACTRT2 knockdown in GC-1 spermatogonial cells and ACTRT2-knockout mouse model with western blotting and ROS measurement\",\n      \"pmids\": [\"40811009\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism by which an actin-related protein regulates iron uptake genes is unknown\",\n        \"Single-lab finding not yet independently replicated\",\n        \"Whether the ferroptosis phenotype is cell-autonomous or secondary to structural defects is unclear\"\n      ]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Identification of ACTRT3 and ZPBP as additional complex partners expanded the perinuclear theca scaffold model beyond the original four-member complex.\",\n      \"evidence\": \"Co-immunoprecipitation in mouse spermatids from Actrt3-knockout model\",\n      \"pmids\": [\"41668650\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct binary interactions among all six partners not mapped\",\n        \"Structural organization of the expanded complex unknown\",\n        \"Functional hierarchy among subunits not determined\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A direct ACTRT2 loss-of-function model with full phenotypic characterization, the biochemical basis by which ACTRT2 regulates ferroptosis, and the structural architecture of the perinuclear theca complex remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No Actrt2-specific conditional knockout with spermatogenesis phenotyping reported\",\n        \"No structural or biophysical data on ACTRT2 or its complexes\",\n        \"Molecular link between ACTRT2 and iron homeostasis gene regulation is undefined\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 1, 3]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [1, 2, 6]}\n    ],\n    \"complexes\": [\n      \"Perinuclear theca actin-related protein complex\"\n    ],\n    \"partners\": [\n      \"ACTRT1\",\n      \"ACTL7A\",\n      \"ACTL9\",\n      \"ACTRT3\",\n      \"ZPBP\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}