{"gene":"SEPTIN3","run_date":"2026-06-10T07:46:30","timeline":{"discoveries":[{"year":2007,"finding":"SEPT3 directly binds SEPT5 and SEPT7, forming a heteromeric complex at nerve terminals adjacent to synaptophysin-positive synaptic vesicle compartments in mature neurons. In HEK293 cells, overexpressed SEPT3 forms filamentous structures dependent on its GTP- and phosphoinositide-binding domains.","method":"Co-immunoprecipitation (direct binding), overexpression in HEK293 cells with domain mutants, immunofluorescence localization in primary hippocampal neurons","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — reciprocal binding demonstrated, domain-dependence of filament formation shown, localization to synaptic terminals established; single lab, multiple methods","pmids":["17564677"],"is_preprint":false},{"year":2007,"finding":"Sept3 knockout mice show no apparent abnormalities in histogenesis or neuronal differentiation, and expression of synaptic proteins and other septins is unaltered, indicating SEPT3 is dispensable for normal neuronal development.","method":"Genetic knockout (Sept3-deficient mice), histology, Western blotting","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO with defined cellular phenotype readout; single lab, negative result well-controlled","pmids":["17564677"],"is_preprint":false},{"year":2014,"finding":"SEPT3 (along with SEPT9 and SEPT12, the SEPT3 subgroup) functions as a cognate subunit in heterooctameric septin complexes but not hexamers; tissue-specific expression of SEPT3 subgroup members controls whether heterooctamers or atypical tetramers (equivalent in composition to half an octamer) are assembled, thereby shaping higher-order septin filament properties.","method":"Native complex analysis in genetically manipulated human cells, size-exclusion chromatography, immunoblotting of septin subunit composition","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetically manipulated cells with biochemical fractionation, replicated concept across multiple cell types and tissues in a single rigorous study","pmids":["24648497"],"is_preprint":false},{"year":2020,"finding":"Crystal structures of the GTP-binding domains of all SEPT3 subgroup members (SEPT3, SEPT9, SEPT12) bound to GDP or GTPγS reveal unique plasticity at the NC (non-coiled-coil) filament interface. GDP/GTPγS-bound states of SEPT9 reveal a squeezing mechanism that expels a polybasic region from the NC interface, rendering it free to interact with negatively charged membranes; a polyacidic region near helix α5' sequesters the polybasic region when retracted. This suggests GTP binding/hydrolysis is coupled to membrane association, implying a unique role for the SEPT3 subgroup in membrane interactions.","method":"X-ray crystallography of GTP-binding domains with GDP and GTPγS ligands; structural comparison across all SEPT3 subgroup members","journal":"IUCrJ","confidence":"High","confidence_rationale":"Tier 1 / Strong — complete crystal structure compendium for all subgroup members with ligand-state comparisons; mechanistic model supported by structural evidence across multiple structures","pmids":["32431830"],"is_preprint":false},{"year":2022,"finding":"SEPT3 binds the autophagy protein LC3B (Atg8 homolog) and also GABARAPL2; colocalization of SEPT3 and LC3B increases upon chemical autophagy induction in primary neurons. Electron microscopy shows SEPT3 localizes to LC3B-positive membranes and at mitochondria. SEPT3 accumulates in primary neurons upon autophagy enhancement or blockade, similar to autophagy proteins.","method":"Co-immunoprecipitation (SEPT3–LC3B binding), immunofluorescence colocalization in primary neurons with chemical autophagy induction/blockade, electron microscopy","journal":"Cellular and molecular life sciences : CMLS","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — direct binding shown by Co-IP, localization confirmed by EM, functional context established in primary neurons; single lab with multiple orthogonal methods","pmids":["35932293"],"is_preprint":false},{"year":2022,"finding":"SEPT3 colocalization with the early mitophagy marker PINK1 does not support a mitophagy-specific role for SEPT3 binding to mitochondria (negative result).","method":"Immunofluorescence colocalization in primary neurons","journal":"Cellular and molecular life sciences : CMLS","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single method, negative colocalization result","pmids":["35932293"],"is_preprint":false},{"year":2023,"finding":"SEPT3 knockdown in TNBC cell lines reduces cell growth, invasion, and migration, whereas SEPT3 overexpression has the opposite effects. SEPT3 promotes cell aggressiveness and proliferation via activation of the Wnt signaling pathway, as assessed by functional enrichment analysis and Western blotting of Wnt pathway components.","method":"Lentiviral knockdown and overexpression in TNBC cell lines, CCK8/colony formation/scratch/transwell functional assays, in vivo xenograft with Ki-67 staining, Western blotting for Wnt pathway markers","journal":"International journal of general medicine","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, pathway placement based on Western blotting without mechanistic reconstitution; no direct binding or epistasis experiment","pmids":["37720177"],"is_preprint":false}],"current_model":"SEPTIN3 is a brain-enriched GTPase that assembles with SEPT5 and SEPT7 into heteromeric complexes at neuronal axon terminals, and—as part of the SEPT3 subgroup (with SEPT9 and SEPT12)—serves as a cognate subunit exclusively in heterooctameric (not hexameric) septin protofilaments; structural studies reveal that GTP binding/hydrolysis drives conformational changes at the NC interface that couple to membrane association via a polybasic region, while in neurons SEPT3 also binds the autophagy receptor LC3B and localizes to autophagic membranes, implicating it in synaptic autophagy."},"narrative":{"mechanistic_narrative":"SEPTIN3 is a brain-enriched, GTP-binding septin subunit that assembles into heteromeric filaments and participates in neuronal membrane-associated processes [PMID:17564677, PMID:24648497]. It directly binds SEPT5 and SEPT7 to form a heteromeric complex localized to nerve terminals adjacent to synaptic vesicle compartments, and its ability to form filaments in cells depends on its GTP- and phosphoinositide-binding domains [PMID:17564677]. As a member of the SEPT3 subgroup (with SEPT9 and SEPT12), it serves as a cognate subunit specifically in heterooctameric—rather than hexameric—septin complexes, so that tissue-specific expression of subgroup members dictates whether octamers or atypical tetramers are assembled, shaping higher-order filament properties [PMID:24648497]. Crystallographic comparison across the SEPT3 subgroup reveals plasticity at the NC filament interface in which nucleotide-state changes expel a polybasic region that is otherwise sequestered by a polyacidic region, coupling GTP binding/hydrolysis to interaction with negatively charged membranes [PMID:32431830]. In neurons, SEPT3 binds the autophagy proteins LC3B and GABARAPL2, increases its colocalization with LC3B upon autophagy induction, localizes to LC3B-positive membranes and mitochondria, and accumulates with autophagy proteins upon autophagy modulation, implicating it in synaptic autophagy [PMID:35932293]. SEPT3 is dispensable for normal neuronal development, as knockout mice show no histogenesis or differentiation defects [PMID:17564677].","teleology":[{"year":2007,"claim":"Established that SEPT3 is not an isolated protein but a direct binding partner of other septins, defining its place in a neuronal heteromeric complex at synaptic terminals.","evidence":"Co-immunoprecipitation, domain-mutant overexpression in HEK293 cells, and immunofluorescence in primary hippocampal neurons","pmids":["17564677"],"confidence":"Medium","gaps":["Stoichiometry and architecture of the SEPT3-SEPT5-SEPT7 complex not resolved","Functional consequence of complex assembly at terminals untested"]},{"year":2007,"claim":"Tested whether SEPT3 is required for nervous system development; loss-of-function showed it is dispensable, redirecting attention to non-developmental roles.","evidence":"Sept3 knockout mice with histology and Western blotting of synaptic proteins and other septins","pmids":["17564677"],"confidence":"Medium","gaps":["Possible functional redundancy with other septins not excluded","Behavioral or synaptic-function phenotypes not assessed"]},{"year":2014,"claim":"Defined the precise role of SEPT3 in septin assembly: it is a cognate octamer-specific subunit whose expression governs filament composition, explaining how tissue context tunes septin architecture.","evidence":"Native complex analysis in genetically manipulated human cells with size-exclusion chromatography and immunoblotting","pmids":["24648497"],"confidence":"High","gaps":["Functional difference between octamer- and tetramer-based filaments not defined","In vivo relevance of composition control not tested"]},{"year":2020,"claim":"Provided the structural mechanism by which the SEPT3 subgroup couples nucleotide state to membrane binding, explaining the subgroup's distinctive membrane-association behavior.","evidence":"X-ray crystallography of SEPT3-subgroup GTP-binding domains in GDP and GTPgammaS states","pmids":["32431830"],"confidence":"High","gaps":["Squeezing/polybasic mechanism directly demonstrated for SEPT9, inferred for SEPT3","Membrane association in cells not directly tested from these structures"]},{"year":2022,"claim":"Connected SEPT3 to autophagy by identifying direct binding to Atg8-family proteins and localization to autophagic membranes in neurons, implicating it in synaptic autophagy.","evidence":"Co-immunoprecipitation, immunofluorescence with chemical autophagy modulation, and electron microscopy in primary neurons","pmids":["35932293"],"confidence":"Medium","gaps":["Functional requirement of SEPT3 for autophagic flux not established","LIR motif or binding interface with LC3B/GABARAPL2 not mapped"]},{"year":2022,"claim":"Tested whether SEPT3 mitochondrial localization reflects a mitophagy role; lack of PINK1 colocalization argued against a mitophagy-specific function.","evidence":"Immunofluorescence colocalization with PINK1 in primary neurons","pmids":["35932293"],"confidence":"Low","gaps":["Single method, single marker negative result","Alternative mitochondrial functions not explored"]},{"year":2023,"claim":"Examined a possible role for SEPT3 in cancer, linking its expression to TNBC aggressiveness through Wnt pathway activation.","evidence":"Lentiviral knockdown/overexpression in TNBC cell lines, functional assays, xenograft, and Western blotting of Wnt components","pmids":["37720177"],"confidence":"Low","gaps":["Pathway placement inferred from Western blotting without direct binding or epistasis","No mechanistic reconstitution of SEPT3-Wnt link"]},{"year":null,"claim":"How GTP-state-dependent membrane association and Atg8-family binding are integrated into a defined function of SEPT3 in synaptic autophagy remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No loss-of-function autophagy phenotype demonstrated for SEPT3","Recruitment mechanism linking septin filaments to autophagic membranes unknown","Physiological substrate or cargo of SEPT3-associated autophagy undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003924","term_label":"GTPase activity","supporting_discovery_ids":[0,3]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[2]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,3]}],"localization":[{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[4]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[4]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,2]}],"pathway":[{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[4]}],"complexes":["SEPT3-SEPT5-SEPT7 heteromeric complex","heterooctameric septin filament"],"partners":["SEPT5","SEPT7","SEPT9","SEPT12","LC3B","GABARAPL2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9UH03","full_name":"Neuronal-specific septin-3","aliases":[],"length_aa":358,"mass_kda":40.7,"function":"Filament-forming cytoskeletal GTPase (By similarity). May play a role in cytokinesis (Potential)","subcellular_location":"Cytoplasm; Cytoplasm, cytoskeleton; Synapse","url":"https://www.uniprot.org/uniprotkb/Q9UH03/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SEPTIN3","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1090,"dependency_fraction":0.0009174311926605505},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"SEPT8","stoichiometry":4.0},{"gene":"COPB2","stoichiometry":0.2},{"gene":"SEPT11","stoichiometry":0.2},{"gene":"SEPT2","stoichiometry":0.2},{"gene":"SEPT7","stoichiometry":0.2},{"gene":"SEPT9","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/SEPTIN3","total_profiled":1310},"omim":[],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Actin filaments","reliability":"Approved"},{"location":"Nucleoplasm","reliability":"Additional"},{"location":"Primary cilium","reliability":"Additional"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":253.5}],"url":"https://www.proteinatlas.org/search/SEPTIN3"},"hgnc":{"alias_symbol":[],"prev_symbol":["SEP3","SEPT3"]},"alphafold":{"accession":"Q9UH03","domains":[{"cath_id":"3.40.50.300","chopping":"58-263_295-331","consensus_level":"high","plddt":90.713,"start":58,"end":331}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UH03","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UH03-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UH03-F1-predicted_aligned_error_v6.png","plddt_mean":81.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SEPTIN3","jax_strain_url":"https://www.jax.org/strain/search?query=SEPTIN3"},"sequence":{"accession":"Q9UH03","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9UH03.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9UH03/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UH03"}},"corpus_meta":[{"pmid":"17564677","id":"PMC_17564677","title":"Targeted disruption of Sept3, a heteromeric assembly partner of Sept5 and Sept7 in axons, has no effect on developing CNS neurons.","date":"2007","source":"Journal of neurochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17564677","citation_count":58,"is_preprint":false},{"pmid":"24648497","id":"PMC_24648497","title":"Cell type-specific expression of SEPT3-homology subgroup members controls the subunit number of heteromeric septin complexes.","date":"2014","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/24648497","citation_count":43,"is_preprint":false},{"pmid":"22899051","id":"PMC_22899051","title":"Role of SEPALLATA3 (SEP3) as a downstream gene of miR156-SPL3-FT circuitry in ambient temperature-responsive flowering.","date":"2012","source":"Plant signaling & behavior","url":"https://pubmed.ncbi.nlm.nih.gov/22899051","citation_count":28,"is_preprint":false},{"pmid":"32431830","id":"PMC_32431830","title":"A complete compendium of crystal structures for the human SEPT3 subgroup reveals functional plasticity at a specific septin interface.","date":"2020","source":"IUCrJ","url":"https://pubmed.ncbi.nlm.nih.gov/32431830","citation_count":27,"is_preprint":false},{"pmid":"36997937","id":"PMC_36997937","title":"Septin-3 autoimmunity in patients with paraneoplastic cerebellar ataxia.","date":"2023","source":"Journal of neuroinflammation","url":"https://pubmed.ncbi.nlm.nih.gov/36997937","citation_count":18,"is_preprint":false},{"pmid":"35932293","id":"PMC_35932293","title":"Neuronal-specific septin-3 binds Atg8/LC3B, accumulates and localizes to autophagosomes during induced autophagy.","date":"2022","source":"Cellular and molecular life sciences : CMLS","url":"https://pubmed.ncbi.nlm.nih.gov/35932293","citation_count":13,"is_preprint":false},{"pmid":"28261064","id":"PMC_28261064","title":"Expression of sept3, sept5a and sept5b in the Developing and Adult Nervous System of the Zebrafish (Danio rerio).","date":"2017","source":"Frontiers in neuroanatomy","url":"https://pubmed.ncbi.nlm.nih.gov/28261064","citation_count":5,"is_preprint":false},{"pmid":"31347183","id":"PMC_31347183","title":"Characterization of SE-P3, P16, P37, and P47 bacteriophages infecting Salmonella Enteritidis.","date":"2019","source":"Journal of basic microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/31347183","citation_count":3,"is_preprint":false},{"pmid":"38686040","id":"PMC_38686040","title":"SEPT3 as a Potential Molecular Target of Triple-Negative Breast Cancer.","date":"2024","source":"International journal of general medicine","url":"https://pubmed.ncbi.nlm.nih.gov/38686040","citation_count":3,"is_preprint":false},{"pmid":"37720177","id":"PMC_37720177","title":"SEPTIN3 Promotes Progression of Triple-Negative Breast Cancer via Activating Wnt Pathway.","date":"2023","source":"International journal of general medicine","url":"https://pubmed.ncbi.nlm.nih.gov/37720177","citation_count":2,"is_preprint":false},{"pmid":"36976188","id":"PMC_36976188","title":"Repair and Mechanism of Oligopeptide SEP-3 on Oxidative Stress Liver Injury Induced by Sleep Deprivation in Mice.","date":"2023","source":"Marine drugs","url":"https://pubmed.ncbi.nlm.nih.gov/36976188","citation_count":2,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.09.08.674588","title":"Guided multi-agent AI invents highly accurate, uncertainty-aware transcriptomic aging clocks","date":"2025-09-12","source":"bioRxiv","url":"https://doi.org/10.1101/2025.09.08.674588","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8014,"output_tokens":1835,"usd":0.025784,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8784,"output_tokens":2639,"usd":0.054948,"stage2_stop_reason":"end_turn"},"total_usd":0.080732,"stage1_batch_id":"msgbatch_013LWZZT6MWaqB9qyTSeQBmU","stage2_batch_id":"msgbatch_0194ZzQaTGNpruoNJBbEMbt3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2007,\n      \"finding\": \"SEPT3 directly binds SEPT5 and SEPT7, forming a heteromeric complex at nerve terminals adjacent to synaptophysin-positive synaptic vesicle compartments in mature neurons. In HEK293 cells, overexpressed SEPT3 forms filamentous structures dependent on its GTP- and phosphoinositide-binding domains.\",\n      \"method\": \"Co-immunoprecipitation (direct binding), overexpression in HEK293 cells with domain mutants, immunofluorescence localization in primary hippocampal neurons\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — reciprocal binding demonstrated, domain-dependence of filament formation shown, localization to synaptic terminals established; single lab, multiple methods\",\n      \"pmids\": [\"17564677\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Sept3 knockout mice show no apparent abnormalities in histogenesis or neuronal differentiation, and expression of synaptic proteins and other septins is unaltered, indicating SEPT3 is dispensable for normal neuronal development.\",\n      \"method\": \"Genetic knockout (Sept3-deficient mice), histology, Western blotting\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO with defined cellular phenotype readout; single lab, negative result well-controlled\",\n      \"pmids\": [\"17564677\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"SEPT3 (along with SEPT9 and SEPT12, the SEPT3 subgroup) functions as a cognate subunit in heterooctameric septin complexes but not hexamers; tissue-specific expression of SEPT3 subgroup members controls whether heterooctamers or atypical tetramers (equivalent in composition to half an octamer) are assembled, thereby shaping higher-order septin filament properties.\",\n      \"method\": \"Native complex analysis in genetically manipulated human cells, size-exclusion chromatography, immunoblotting of septin subunit composition\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetically manipulated cells with biochemical fractionation, replicated concept across multiple cell types and tissues in a single rigorous study\",\n      \"pmids\": [\"24648497\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Crystal structures of the GTP-binding domains of all SEPT3 subgroup members (SEPT3, SEPT9, SEPT12) bound to GDP or GTPγS reveal unique plasticity at the NC (non-coiled-coil) filament interface. GDP/GTPγS-bound states of SEPT9 reveal a squeezing mechanism that expels a polybasic region from the NC interface, rendering it free to interact with negatively charged membranes; a polyacidic region near helix α5' sequesters the polybasic region when retracted. This suggests GTP binding/hydrolysis is coupled to membrane association, implying a unique role for the SEPT3 subgroup in membrane interactions.\",\n      \"method\": \"X-ray crystallography of GTP-binding domains with GDP and GTPγS ligands; structural comparison across all SEPT3 subgroup members\",\n      \"journal\": \"IUCrJ\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — complete crystal structure compendium for all subgroup members with ligand-state comparisons; mechanistic model supported by structural evidence across multiple structures\",\n      \"pmids\": [\"32431830\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SEPT3 binds the autophagy protein LC3B (Atg8 homolog) and also GABARAPL2; colocalization of SEPT3 and LC3B increases upon chemical autophagy induction in primary neurons. Electron microscopy shows SEPT3 localizes to LC3B-positive membranes and at mitochondria. SEPT3 accumulates in primary neurons upon autophagy enhancement or blockade, similar to autophagy proteins.\",\n      \"method\": \"Co-immunoprecipitation (SEPT3–LC3B binding), immunofluorescence colocalization in primary neurons with chemical autophagy induction/blockade, electron microscopy\",\n      \"journal\": \"Cellular and molecular life sciences : CMLS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — direct binding shown by Co-IP, localization confirmed by EM, functional context established in primary neurons; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"35932293\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SEPT3 colocalization with the early mitophagy marker PINK1 does not support a mitophagy-specific role for SEPT3 binding to mitochondria (negative result).\",\n      \"method\": \"Immunofluorescence colocalization in primary neurons\",\n      \"journal\": \"Cellular and molecular life sciences : CMLS\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single method, negative colocalization result\",\n      \"pmids\": [\"35932293\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SEPT3 knockdown in TNBC cell lines reduces cell growth, invasion, and migration, whereas SEPT3 overexpression has the opposite effects. SEPT3 promotes cell aggressiveness and proliferation via activation of the Wnt signaling pathway, as assessed by functional enrichment analysis and Western blotting of Wnt pathway components.\",\n      \"method\": \"Lentiviral knockdown and overexpression in TNBC cell lines, CCK8/colony formation/scratch/transwell functional assays, in vivo xenograft with Ki-67 staining, Western blotting for Wnt pathway markers\",\n      \"journal\": \"International journal of general medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, pathway placement based on Western blotting without mechanistic reconstitution; no direct binding or epistasis experiment\",\n      \"pmids\": [\"37720177\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SEPTIN3 is a brain-enriched GTPase that assembles with SEPT5 and SEPT7 into heteromeric complexes at neuronal axon terminals, and—as part of the SEPT3 subgroup (with SEPT9 and SEPT12)—serves as a cognate subunit exclusively in heterooctameric (not hexameric) septin protofilaments; structural studies reveal that GTP binding/hydrolysis drives conformational changes at the NC interface that couple to membrane association via a polybasic region, while in neurons SEPT3 also binds the autophagy receptor LC3B and localizes to autophagic membranes, implicating it in synaptic autophagy.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SEPTIN3 is a brain-enriched, GTP-binding septin subunit that assembles into heteromeric filaments and participates in neuronal membrane-associated processes [#0, #2]. It directly binds SEPT5 and SEPT7 to form a heteromeric complex localized to nerve terminals adjacent to synaptic vesicle compartments, and its ability to form filaments in cells depends on its GTP- and phosphoinositide-binding domains [#0]. As a member of the SEPT3 subgroup (with SEPT9 and SEPT12), it serves as a cognate subunit specifically in heterooctameric—rather than hexameric—septin complexes, so that tissue-specific expression of subgroup members dictates whether octamers or atypical tetramers are assembled, shaping higher-order filament properties [#2]. Crystallographic comparison across the SEPT3 subgroup reveals plasticity at the NC filament interface in which nucleotide-state changes expel a polybasic region that is otherwise sequestered by a polyacidic region, coupling GTP binding/hydrolysis to interaction with negatively charged membranes [#3]. In neurons, SEPT3 binds the autophagy proteins LC3B and GABARAPL2, increases its colocalization with LC3B upon autophagy induction, localizes to LC3B-positive membranes and mitochondria, and accumulates with autophagy proteins upon autophagy modulation, implicating it in synaptic autophagy [#4]. SEPT3 is dispensable for normal neuronal development, as knockout mice show no histogenesis or differentiation defects [#1].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"Established that SEPT3 is not an isolated protein but a direct binding partner of other septins, defining its place in a neuronal heteromeric complex at synaptic terminals.\",\n      \"evidence\": \"Co-immunoprecipitation, domain-mutant overexpression in HEK293 cells, and immunofluorescence in primary hippocampal neurons\",\n      \"pmids\": [\"17564677\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Stoichiometry and architecture of the SEPT3-SEPT5-SEPT7 complex not resolved\", \"Functional consequence of complex assembly at terminals untested\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Tested whether SEPT3 is required for nervous system development; loss-of-function showed it is dispensable, redirecting attention to non-developmental roles.\",\n      \"evidence\": \"Sept3 knockout mice with histology and Western blotting of synaptic proteins and other septins\",\n      \"pmids\": [\"17564677\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Possible functional redundancy with other septins not excluded\", \"Behavioral or synaptic-function phenotypes not assessed\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defined the precise role of SEPT3 in septin assembly: it is a cognate octamer-specific subunit whose expression governs filament composition, explaining how tissue context tunes septin architecture.\",\n      \"evidence\": \"Native complex analysis in genetically manipulated human cells with size-exclusion chromatography and immunoblotting\",\n      \"pmids\": [\"24648497\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional difference between octamer- and tetramer-based filaments not defined\", \"In vivo relevance of composition control not tested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Provided the structural mechanism by which the SEPT3 subgroup couples nucleotide state to membrane binding, explaining the subgroup's distinctive membrane-association behavior.\",\n      \"evidence\": \"X-ray crystallography of SEPT3-subgroup GTP-binding domains in GDP and GTPgammaS states\",\n      \"pmids\": [\"32431830\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Squeezing/polybasic mechanism directly demonstrated for SEPT9, inferred for SEPT3\", \"Membrane association in cells not directly tested from these structures\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Connected SEPT3 to autophagy by identifying direct binding to Atg8-family proteins and localization to autophagic membranes in neurons, implicating it in synaptic autophagy.\",\n      \"evidence\": \"Co-immunoprecipitation, immunofluorescence with chemical autophagy modulation, and electron microscopy in primary neurons\",\n      \"pmids\": [\"35932293\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional requirement of SEPT3 for autophagic flux not established\", \"LIR motif or binding interface with LC3B/GABARAPL2 not mapped\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Tested whether SEPT3 mitochondrial localization reflects a mitophagy role; lack of PINK1 colocalization argued against a mitophagy-specific function.\",\n      \"evidence\": \"Immunofluorescence colocalization with PINK1 in primary neurons\",\n      \"pmids\": [\"35932293\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single method, single marker negative result\", \"Alternative mitochondrial functions not explored\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Examined a possible role for SEPT3 in cancer, linking its expression to TNBC aggressiveness through Wnt pathway activation.\",\n      \"evidence\": \"Lentiviral knockdown/overexpression in TNBC cell lines, functional assays, xenograft, and Western blotting of Wnt components\",\n      \"pmids\": [\"37720177\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Pathway placement inferred from Western blotting without direct binding or epistasis\", \"No mechanistic reconstitution of SEPT3-Wnt link\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How GTP-state-dependent membrane association and Atg8-family binding are integrated into a defined function of SEPT3 in synaptic autophagy remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No loss-of-function autophagy phenotype demonstrated for SEPT3\", \"Recruitment mechanism linking septin filaments to autophagic membranes unknown\", \"Physiological substrate or cargo of SEPT3-associated autophagy undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003924\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"complexes\": [\"SEPT3-SEPT5-SEPT7 heteromeric complex\", \"heterooctameric septin filament\"],\n    \"partners\": [\"SEPT5\", \"SEPT7\", \"SEPT9\", \"SEPT12\", \"LC3B\", \"GABARAPL2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":6,"faith_pct":83.33333333333333}}