{"gene":"SYT1","run_date":"2026-06-10T10:51:54","timeline":{"discoveries":[{"year":2018,"finding":"De novo heterozygous missense mutations in the SYT1 C2B domain (M303K, D304G, D366E, I368T, N371K) cause a dominant-negative impairment of synaptic vesicle exocytosis; SYT1D304G and SYT1D366E fail to relocalize to nerve terminals following stimulation, indicating defective endocytic retrieval, while all variants slow exocytic rate following sustained action potential stimulation in hippocampal neurons.","method":"Expression of rat SYT1 mutants in wild-type mouse primary hippocampal cultures; live imaging of SYT1 localization at rest and after stimulation; synaptic vesicle kinetics assays","journal":"Brain : a journal of neurology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple mutant variants tested in neurons with defined functional readouts (localization, exocytic rate), replicated across five variants with graded phenotypes matching patient severity","pmids":["30107533"],"is_preprint":false},{"year":2024,"finding":"Pathogenic SYT1 variants in both the C2A domain (L159R, T196K, E209K, E219Q) and additional C2B domain positions (M303V, S309P, Y365C, G369D) cause a graded, variant-dependent dominant-negative impairment of evoked exocytosis; the extent of exocytic impairment correlates quantitatively with the severity of neurodevelopmental outcomes in affected individuals.","method":"Cultured hippocampal neurons transfected with SYT1-pHluorin; measurement of evoked exocytosis for each variant","journal":"EBioMedicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct functional assay in neurons for eight distinct variants with quantitative genotype-function-phenotype correlation","pmids":["39481209"],"is_preprint":false},{"year":2024,"finding":"SYT1 forms surface nanoclusters on the neuronal plasma membrane through interaction of its C2B domain with SV2A; this nanoclustering is disrupted by the Syt1K326A/K328A mutation or SV2A knockdown. SV2A-Syt1 nanoclustering segregates SYT1 from the endocytic machinery by limiting dynamin-1 recruitment, thereby negatively regulating the rate of SYT1 entry into recycling synaptic vesicles.","method":"Single-molecule imaging in hippocampal neurons; C2B domain point mutations; SV2A knockdown; dynamin-1 recruitment assay; Rab5 sorting assay","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — single-molecule imaging plus mutagenesis plus knockdown with multiple orthogonal readouts (nanoclustering, dynamin recruitment, endocytic rate, intracellular sorting)","pmids":["39091022"],"is_preprint":false},{"year":2023,"finding":"Targeted endocytosis of botulinum neurotoxin type A (BoNT/A) into synaptic vesicles requires simultaneous binding to a preassembled PSG-SYT1 complex and SV2 on the neuronal plasma membrane, facilitating SYT1-SV2 nanoclustering that controls endocytic sorting of the toxin; SYT1 CRISPRi knockdown suppressed BoNT/A- and BoNT/E-induced neurointoxication (SNAP-25 cleavage).","method":"Live-cell super-resolution imaging and electron microscopy of catalytically inactivated BoNT/A wildtype and receptor-binding-deficient mutants in hippocampal neurons; SYT1 CRISPRi knockdown with SNAP-25 cleavage readout","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (super-resolution imaging, EM, CRISPRi knockdown, functional toxin assay) in a single rigorous study","pmids":["37226896"],"is_preprint":false},{"year":2017,"finding":"At fast-releasing inhibitory synapses (MNTB-LSO glycinergic and basket/stellate-Purkinje GABAergic), SYT1 and SYT2 are co-expressed and function redundantly as Ca2+ sensors for evoked transmitter release; genetic inactivation of both Syt1 and Syt2 is required to significantly reduce and desynchronize fast release, whereas Syt2 KO alone has only minor effects.","method":"Conditional and conventional knockout mouse lines; viral Cre expression; optical stimulation; electrophysiological recording; immunohistochemistry","journal":"The Journal of neuroscience : the official journal of the Society for Neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with single and double KO, electrophysiology, replicated at two synapse types","pmids":["28363983"],"is_preprint":false},{"year":2024,"finding":"STON2 (Stonin 2) dephosphorylation caused by schizophrenia-related variants reduces its interaction with SYT1, impairing clathrin-mediated endocytosis (CME) of synaptic vesicles and synaptic transmission; acute haloperidol administration recovers Syt1 sorting and synaptic transmission deficits in STON2307Pro851Ala knockin mice.","method":"Co-immunoprecipitation; STON2307Pro851Ala knockin mouse electrophysiology; Syt1 sorting assay; haloperidol rescue experiment","journal":"Science bulletin","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP plus knockin mouse electrophysiology and pharmacological rescue, single lab","pmids":["38402028"],"is_preprint":false},{"year":2024,"finding":"Neutralization of highly conserved polybasic patches in either the C2A or C2B domain of SYT1 impairs both dense core vesicle (DCV) docking to the plasma membrane and efficient serotonin release; the same mutations result in larger fusion pores and faster serotonin release during individual fusion events, linking SYT1's polybasic regions to vesicle docking, fusion triggering, and fusion pore regulation.","method":"Site-directed mutagenesis of polybasic patches; DCV docking assay; single-vesicle serotonin release measurement in human neuroendocrine cell line","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — mutagenesis with functional in vitro assays but preprint, single lab","pmids":["bio_10.1101_2024.09.12.612660"],"is_preprint":true},{"year":2025,"finding":"In bronchial epithelial cells, SYT1 localizes to late endo-lysosomes and MR1 vesicles; loss of Syt1 (and Syt7) results in enlarged MR1 vesicles and increased proximity of MR1 vesicles to Mtb-containing vacuoles, impairing MR1-mediated presentation of Mycobacterium tuberculosis antigens to MAIT cells.","method":"Immunofluorescence localization; Syt1/Syt7 loss-of-function in bronchial epithelial cells; MR1 vesicle morphology and MAIT cell activation assay","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct localization plus loss-of-function with defined functional readout, preprint, single lab","pmids":["bio_10.1101_2025.06.23.660389"],"is_preprint":true},{"year":2025,"finding":"In human monocyte-derived macrophages treated with 4-HNE, SYT1 is strongly upregulated and localizes predominantly to the plasma membrane; SYT1 overexpression inhibits phagocytosis of pathogenic bacteria, revealing a non-neuronal role for SYT1 in suppressing macrophage phagocytic function.","method":"Transcriptomics; overexpression of fluorescent-reporter-tagged SYT1; phagocytosis functional assay in macrophages","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — overexpression with single functional readout, preprint, single lab","pmids":["bio_10.1101_2025.11.24.690103"],"is_preprint":true},{"year":2025,"finding":"SNT-1 (C. elegans functional analog of Syt1) mediates fast evoked neurotransmitter release through C2B–SNARE complex interactions and polybasic motifs within its C2 domains; these interactions are required for both synchronous evoked and spontaneous release, with spontaneous release involving multiple SNARE-binding pathways beyond the primary C2B–SNARE interface.","method":"AlphaFold3 structural modeling; targeted mutagenesis; electrophysiology at C. elegans NMJ","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — mutagenesis combined with electrophysiology and structural modeling, preprint, ortholog study in C. elegans","pmids":["bio_10.1101_2025.09.30.679486"],"is_preprint":true}],"current_model":"SYT1 (synaptotagmin-1) is a presynaptic vesicle protein that acts as the primary Ca²⁺ sensor for fast, synchronous neurotransmitter release via its C2A and C2B domains interacting with the SNARE complex, negatively charged phospholipids, and polybasic patches; it additionally regulates synaptic vesicle docking, fusion pore dynamics, and endocytic retrieval through interaction with SV2A and stonin-2 (STON2), and its C2B-domain pathogenic variants cause a dominant-negative impairment of evoked exocytosis whose severity correlates quantitatively with the degree of neurodevelopmental disability in Baker-Gordon syndrome."},"narrative":{"mechanistic_narrative":"SYT1 (synaptotagmin-1) is a presynaptic Ca²⁺ sensor that triggers fast, synchronous neurotransmitter release through its tandem C2A and C2B domains, which engage the SNARE complex and membrane phospholipids via conserved polybasic patches [PMID:bio_10.1101_2024.09.12.612660, PMID:bio_10.1101_2025.09.30.679486]. At fast inhibitory synapses SYT1 functions redundantly with SYT2 as the evoked-release Ca²⁺ sensor, with loss of both required to desynchronize and reduce release [PMID:28363983]. Beyond fusion triggering, SYT1 controls vesicle docking and fusion pore dynamics — neutralization of its C2A/C2B polybasic patches impairs dense-core-vesicle docking and produces enlarged, faster-releasing fusion pores [PMID:bio_10.1101_2024.09.12.612660]. SYT1 also governs its own endocytic retrieval: its C2B domain binds SV2A to form surface nanoclusters that limit dynamin-1 recruitment and tune the rate of SYT1 entry into recycling vesicles [PMID:39091022], and efficient clathrin-mediated endocytic sorting of SYT1 depends on its interaction with STON2 [PMID:38402028]. The SV2-SYT1 nanocluster is hijacked as the entry route for botulinum neurotoxins A and E into synaptic vesicles [PMID:37226896]. De novo heterozygous missense variants across the C2A and C2B domains cause a dominant-negative impairment of evoked exocytosis whose magnitude correlates quantitatively with neurodevelopmental severity in affected individuals (Baker-Gordon syndrome) [PMID:30107533, PMID:39481209]. Emerging non-neuronal roles in late endo-lysosomal/MR1 vesicle trafficking and macrophage phagocytosis have been described but are not yet well characterized in the available corpus [PMID:bio_10.1101_2025.06.23.660389, PMID:bio_10.1101_2025.11.24.690103].","teleology":[{"year":2017,"claim":"Established which Ca²⁺ sensor drives fast evoked release at inhibitory synapses, resolving whether SYT1 acts alone or redundantly.","evidence":"Conditional and conventional Syt1/Syt2 knockout mice with optical stimulation and electrophysiology at glycinergic and GABAergic synapses","pmids":["28363983"],"confidence":"High","gaps":["Does not resolve the molecular basis of redundancy between SYT1 and SYT2","Excitatory synapse dependence not addressed in this study"]},{"year":2018,"claim":"Linked C2B-domain SYT1 missense variants to a dominant-negative human disease mechanism, distinguishing exocytic from endocytic defects.","evidence":"Expression of five rat SYT1 C2B mutants in mouse hippocampal cultures with live imaging of localization and synaptic vesicle kinetics","pmids":["30107533"],"confidence":"High","gaps":["Mechanism by which mutant SYT1 dominantly interferes with wild-type protein not defined at molecular level","Only C2B variants tested"]},{"year":2023,"claim":"Showed that botulinum neurotoxins exploit the preassembled SV2-SYT1 nanocluster for endocytic entry into synaptic vesicles.","evidence":"Super-resolution imaging and EM of inactivated BoNT/A in hippocampal neurons plus SYT1 CRISPRi knockdown with SNAP-25 cleavage readout","pmids":["37226896"],"confidence":"High","gaps":["Stoichiometry of the PSG-SYT1-SV2 toxin complex not resolved","Generalizability to other BoNT serotypes beyond A and E untested"]},{"year":2024,"claim":"Defined the SV2A-dependent C2B nanoclustering mechanism that segregates SYT1 from endocytic machinery and sets its recycling rate.","evidence":"Single-molecule imaging, C2B point mutations, SV2A knockdown, and dynamin-1 recruitment / Rab5 sorting assays in hippocampal neurons","pmids":["39091022"],"confidence":"High","gaps":["Whether nanoclustering also modulates the exocytic Ca²⁺-sensing function not addressed","Structural basis of the C2B-SV2A interface not determined"]},{"year":2024,"claim":"Extended the disease-variant catalog to C2A-domain positions and quantitatively tied exocytic impairment to clinical severity.","evidence":"SYT1-pHluorin evoked exocytosis assays in hippocampal neurons across eight C2A and C2B variants","pmids":["39481209"],"confidence":"High","gaps":["Does not separate fusion-triggering defects from docking or endocytic contributions per variant","In vivo neurodevelopmental correlate not modeled"]},{"year":2024,"claim":"Connected SYT1 endocytic sorting to a STON2-dependent pathway with disease and pharmacological relevance.","evidence":"Co-immunoprecipitation, STON2 knockin mouse electrophysiology, Syt1 sorting assay, and haloperidol rescue","pmids":["38402028"],"confidence":"Medium","gaps":["Single-lab Co-IP without reciprocal structural mapping of the STON2-SYT1 interface","Direct causal link between Syt1 mis-sorting and behavioral phenotype not established"]},{"year":2024,"claim":"Assigned the C2A/C2B polybasic patches to vesicle docking and fusion pore regulation, separating these roles from Ca²⁺ binding.","evidence":"Polybasic-patch mutagenesis with DCV docking and single-vesicle serotonin release measurements in a human neuroendocrine cell line (preprint)","pmids":["bio_10.1101_2024.09.12.612660"],"confidence":"Medium","gaps":["Preprint, single lab","Neuroendocrine DCV findings not validated at central synapses"]},{"year":2025,"claim":"Reported non-neuronal SYT1 functions in endo-lysosomal/MR1 trafficking and macrophage phagocytosis.","evidence":"Immunofluorescence localization and Syt1 loss/overexpression with MR1-MAIT and phagocytosis functional assays (preprints)","pmids":["bio_10.1101_2025.06.23.660389","bio_10.1101_2025.11.24.690103"],"confidence":"Low","gaps":["Overexpression and single functional readouts in preprints","Molecular partners mediating non-neuronal roles unidentified","Physiological relevance untested in vivo"]},{"year":2025,"claim":"Dissected C2B-SNARE and polybasic-motif contributions to evoked versus spontaneous release using an invertebrate ortholog.","evidence":"AlphaFold3 modeling, mutagenesis, and electrophysiology at the C. elegans NMJ (preprint, ortholog SNT-1)","pmids":["bio_10.1101_2025.09.30.679486"],"confidence":"Medium","gaps":["Ortholog study, preprint","Multiple SNARE-binding pathways for spontaneous release not individually resolved"]},{"year":null,"claim":"How the disease variants dominantly poison wild-type SYT1 function and whether the non-neuronal trafficking roles are conserved physiological functions remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural model of the dominant-negative interference mechanism","Non-neuronal roles rest only on preprint overexpression/loss-of-function data","Direct partners for endo-lysosomal SYT1 unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[4]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[6]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[2,3]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[2,8]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[0,2]},{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[7]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[0,1,4]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[2,3,5]},{"term_id":"R-HSA-1500931","term_label":"Cell-Cell communication","supporting_discovery_ids":[4]}],"complexes":["SV2-SYT1 surface nanocluster","SNARE complex"],"partners":["SV2A","STON2","DNM1","SNAP25"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P21579","full_name":"Synaptotagmin-1","aliases":["Synaptotagmin I","SytI","p65"],"length_aa":422,"mass_kda":47.6,"function":"Calcium sensor that participates in triggering neurotransmitter release at the synapse (By similarity). May have a regulatory role in the membrane interactions during trafficking of synaptic vesicles at the active zone of the synapse (By similarity). It binds acidic phospholipids with a specificity that requires the presence of both an acidic head group and a diacyl backbone. A Ca(2+)-dependent interaction between synaptotagmin and putative receptors for activated protein kinase C has also been reported. It can bind to at least three additional proteins in a Ca(2+)-independent manner; these are neurexins, syntaxin and AP2. Plays a role in dendrite formation by melanocytes (PubMed:23999003)","subcellular_location":"Cytoplasmic vesicle, secretory vesicle membrane; Cytoplasmic vesicle, secretory vesicle, synaptic vesicle membrane; Cytoplasmic vesicle, secretory vesicle, chromaffin granule membrane; Cytoplasm","url":"https://www.uniprot.org/uniprotkb/P21579/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SYT1","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SYT1","total_profiled":1310},"omim":[{"mim_id":"621427","title":"N-TERMINAL EF-HAND CALCIUM-BINDING PROTEIN 1; NECAB1","url":"https://www.omim.org/entry/621427"},{"mim_id":"620772","title":"DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 113; DEE113","url":"https://www.omim.org/entry/620772"},{"mim_id":"619461","title":"MYASTHENIC SYNDROME, CONGENITAL, 7B, PRESYNAPTIC, AUTOSOMAL RECESSIVE; CMS7B","url":"https://www.omim.org/entry/619461"},{"mim_id":"618218","title":"BAKER-GORDON SYNDROME; BAGOS","url":"https://www.omim.org/entry/618218"},{"mim_id":"618044","title":"C2 CALCIUM-DEPENDENT DOMAIN-CONTAINING PROTEIN 5; C2CD5","url":"https://www.omim.org/entry/618044"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":280.3},{"tissue":"retina","ntpm":187.2}],"url":"https://www.proteinatlas.org/search/SYT1"},"hgnc":{"alias_symbol":["P65"],"prev_symbol":["SYT","SVP65"]},"alphafold":{"accession":"P21579","domains":[{"cath_id":"2.60.40.150","chopping":"143-262","consensus_level":"high","plddt":93.7236,"start":143,"end":262},{"cath_id":"2.60.40.150","chopping":"275-419","consensus_level":"high","plddt":94.9479,"start":275,"end":419}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P21579","model_url":"https://alphafold.ebi.ac.uk/files/AF-P21579-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P21579-F1-predicted_aligned_error_v6.png","plddt_mean":81.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SYT1","jax_strain_url":"https://www.jax.org/strain/search?query=SYT1"},"sequence":{"accession":"P21579","fasta_url":"https://rest.uniprot.org/uniprotkb/P21579.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P21579/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P21579"}},"corpus_meta":[{"pmid":"24183667","id":"PMC_24183667","title":"Feedback regulation of receptor-induced Ca2+ signaling mediated by E-Syt1 and Nir2 at endoplasmic reticulum-plasma membrane junctions.","date":"2013","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/24183667","citation_count":300,"is_preprint":false},{"pmid":"30107533","id":"PMC_30107533","title":"SYT1-associated neurodevelopmental disorder: a case series.","date":"2018","source":"Brain : a journal of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/30107533","citation_count":112,"is_preprint":false},{"pmid":"22659450","id":"PMC_22659450","title":"The oncogenic lung cancer fusion kinase CD74-ROS activates a novel invasiveness pathway through E-Syt1 phosphorylation.","date":"2012","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/22659450","citation_count":88,"is_preprint":false},{"pmid":"8872307","id":"PMC_8872307","title":"Two synaptotagmin genes, Syt1 and Syt4, are differentially regulated in adult brain and during postnatal development following kainic acid-induced seizures.","date":"1996","source":"Brain research. Molecular brain research","url":"https://pubmed.ncbi.nlm.nih.gov/8872307","citation_count":54,"is_preprint":false},{"pmid":"19255425","id":"PMC_19255425","title":"The atypical kinase Cdk5 is activated by insulin, regulates the association between GLUT4 and E-Syt1, and modulates glucose transport in 3T3-L1 adipocytes.","date":"2009","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/19255425","citation_count":52,"is_preprint":false},{"pmid":"36821088","id":"PMC_36821088","title":"PERK recruits E-Syt1 at ER-mitochondria contacts for mitochondrial lipid transport and respiration.","date":"2023","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/36821088","citation_count":49,"is_preprint":false},{"pmid":"20222955","id":"PMC_20222955","title":"A meta-analysis of genome-wide data from five European isolates reveals an association of COL22A1, SYT1, and GABRR2 with serum creatinine 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SYT1D304G and SYT1D366E fail to relocalize to nerve terminals following stimulation, indicating defective endocytic retrieval, while all variants slow exocytic rate following sustained action potential stimulation in hippocampal neurons.\",\n      \"method\": \"Expression of rat SYT1 mutants in wild-type mouse primary hippocampal cultures; live imaging of SYT1 localization at rest and after stimulation; synaptic vesicle kinetics assays\",\n      \"journal\": \"Brain : a journal of neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple mutant variants tested in neurons with defined functional readouts (localization, exocytic rate), replicated across five variants with graded phenotypes matching patient severity\",\n      \"pmids\": [\"30107533\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Pathogenic SYT1 variants in both the C2A domain (L159R, T196K, E209K, E219Q) and additional C2B domain positions (M303V, S309P, Y365C, G369D) cause a graded, variant-dependent dominant-negative impairment of evoked exocytosis; the extent of exocytic impairment correlates quantitatively with the severity of neurodevelopmental outcomes in affected individuals.\",\n      \"method\": \"Cultured hippocampal neurons transfected with SYT1-pHluorin; measurement of evoked exocytosis for each variant\",\n      \"journal\": \"EBioMedicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct functional assay in neurons for eight distinct variants with quantitative genotype-function-phenotype correlation\",\n      \"pmids\": [\"39481209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SYT1 forms surface nanoclusters on the neuronal plasma membrane through interaction of its C2B domain with SV2A; this nanoclustering is disrupted by the Syt1K326A/K328A mutation or SV2A knockdown. SV2A-Syt1 nanoclustering segregates SYT1 from the endocytic machinery by limiting dynamin-1 recruitment, thereby negatively regulating the rate of SYT1 entry into recycling synaptic vesicles.\",\n      \"method\": \"Single-molecule imaging in hippocampal neurons; C2B domain point mutations; SV2A knockdown; dynamin-1 recruitment assay; Rab5 sorting assay\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — single-molecule imaging plus mutagenesis plus knockdown with multiple orthogonal readouts (nanoclustering, dynamin recruitment, endocytic rate, intracellular sorting)\",\n      \"pmids\": [\"39091022\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Targeted endocytosis of botulinum neurotoxin type A (BoNT/A) into synaptic vesicles requires simultaneous binding to a preassembled PSG-SYT1 complex and SV2 on the neuronal plasma membrane, facilitating SYT1-SV2 nanoclustering that controls endocytic sorting of the toxin; SYT1 CRISPRi knockdown suppressed BoNT/A- and BoNT/E-induced neurointoxication (SNAP-25 cleavage).\",\n      \"method\": \"Live-cell super-resolution imaging and electron microscopy of catalytically inactivated BoNT/A wildtype and receptor-binding-deficient mutants in hippocampal neurons; SYT1 CRISPRi knockdown with SNAP-25 cleavage readout\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (super-resolution imaging, EM, CRISPRi knockdown, functional toxin assay) in a single rigorous study\",\n      \"pmids\": [\"37226896\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"At fast-releasing inhibitory synapses (MNTB-LSO glycinergic and basket/stellate-Purkinje GABAergic), SYT1 and SYT2 are co-expressed and function redundantly as Ca2+ sensors for evoked transmitter release; genetic inactivation of both Syt1 and Syt2 is required to significantly reduce and desynchronize fast release, whereas Syt2 KO alone has only minor effects.\",\n      \"method\": \"Conditional and conventional knockout mouse lines; viral Cre expression; optical stimulation; electrophysiological recording; immunohistochemistry\",\n      \"journal\": \"The Journal of neuroscience : the official journal of the Society for Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with single and double KO, electrophysiology, replicated at two synapse types\",\n      \"pmids\": [\"28363983\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"STON2 (Stonin 2) dephosphorylation caused by schizophrenia-related variants reduces its interaction with SYT1, impairing clathrin-mediated endocytosis (CME) of synaptic vesicles and synaptic transmission; acute haloperidol administration recovers Syt1 sorting and synaptic transmission deficits in STON2307Pro851Ala knockin mice.\",\n      \"method\": \"Co-immunoprecipitation; STON2307Pro851Ala knockin mouse electrophysiology; Syt1 sorting assay; haloperidol rescue experiment\",\n      \"journal\": \"Science bulletin\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP plus knockin mouse electrophysiology and pharmacological rescue, single lab\",\n      \"pmids\": [\"38402028\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Neutralization of highly conserved polybasic patches in either the C2A or C2B domain of SYT1 impairs both dense core vesicle (DCV) docking to the plasma membrane and efficient serotonin release; the same mutations result in larger fusion pores and faster serotonin release during individual fusion events, linking SYT1's polybasic regions to vesicle docking, fusion triggering, and fusion pore regulation.\",\n      \"method\": \"Site-directed mutagenesis of polybasic patches; DCV docking assay; single-vesicle serotonin release measurement in human neuroendocrine cell line\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — mutagenesis with functional in vitro assays but preprint, single lab\",\n      \"pmids\": [\"bio_10.1101_2024.09.12.612660\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In bronchial epithelial cells, SYT1 localizes to late endo-lysosomes and MR1 vesicles; loss of Syt1 (and Syt7) results in enlarged MR1 vesicles and increased proximity of MR1 vesicles to Mtb-containing vacuoles, impairing MR1-mediated presentation of Mycobacterium tuberculosis antigens to MAIT cells.\",\n      \"method\": \"Immunofluorescence localization; Syt1/Syt7 loss-of-function in bronchial epithelial cells; MR1 vesicle morphology and MAIT cell activation assay\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct localization plus loss-of-function with defined functional readout, preprint, single lab\",\n      \"pmids\": [\"bio_10.1101_2025.06.23.660389\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In human monocyte-derived macrophages treated with 4-HNE, SYT1 is strongly upregulated and localizes predominantly to the plasma membrane; SYT1 overexpression inhibits phagocytosis of pathogenic bacteria, revealing a non-neuronal role for SYT1 in suppressing macrophage phagocytic function.\",\n      \"method\": \"Transcriptomics; overexpression of fluorescent-reporter-tagged SYT1; phagocytosis functional assay in macrophages\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — overexpression with single functional readout, preprint, single lab\",\n      \"pmids\": [\"bio_10.1101_2025.11.24.690103\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SNT-1 (C. elegans functional analog of Syt1) mediates fast evoked neurotransmitter release through C2B–SNARE complex interactions and polybasic motifs within its C2 domains; these interactions are required for both synchronous evoked and spontaneous release, with spontaneous release involving multiple SNARE-binding pathways beyond the primary C2B–SNARE interface.\",\n      \"method\": \"AlphaFold3 structural modeling; targeted mutagenesis; electrophysiology at C. elegans NMJ\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis combined with electrophysiology and structural modeling, preprint, ortholog study in C. elegans\",\n      \"pmids\": [\"bio_10.1101_2025.09.30.679486\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"SYT1 (synaptotagmin-1) is a presynaptic vesicle protein that acts as the primary Ca²⁺ sensor for fast, synchronous neurotransmitter release via its C2A and C2B domains interacting with the SNARE complex, negatively charged phospholipids, and polybasic patches; it additionally regulates synaptic vesicle docking, fusion pore dynamics, and endocytic retrieval through interaction with SV2A and stonin-2 (STON2), and its C2B-domain pathogenic variants cause a dominant-negative impairment of evoked exocytosis whose severity correlates quantitatively with the degree of neurodevelopmental disability in Baker-Gordon syndrome.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SYT1 (synaptotagmin-1) is a presynaptic Ca²⁺ sensor that triggers fast, synchronous neurotransmitter release through its tandem C2A and C2B domains, which engage the SNARE complex and membrane phospholipids via conserved polybasic patches [#6, #9]. At fast inhibitory synapses SYT1 functions redundantly with SYT2 as the evoked-release Ca²⁺ sensor, with loss of both required to desynchronize and reduce release [#4]. Beyond fusion triggering, SYT1 controls vesicle docking and fusion pore dynamics — neutralization of its C2A/C2B polybasic patches impairs dense-core-vesicle docking and produces enlarged, faster-releasing fusion pores [#6]. SYT1 also governs its own endocytic retrieval: its C2B domain binds SV2A to form surface nanoclusters that limit dynamin-1 recruitment and tune the rate of SYT1 entry into recycling vesicles [#2], and efficient clathrin-mediated endocytic sorting of SYT1 depends on its interaction with STON2 [#5]. The SV2-SYT1 nanocluster is hijacked as the entry route for botulinum neurotoxins A and E into synaptic vesicles [#3]. De novo heterozygous missense variants across the C2A and C2B domains cause a dominant-negative impairment of evoked exocytosis whose magnitude correlates quantitatively with neurodevelopmental severity in affected individuals (Baker-Gordon syndrome) [#0, #1]. Emerging non-neuronal roles in late endo-lysosomal/MR1 vesicle trafficking and macrophage phagocytosis have been described but are not yet well characterized in the available corpus [#7, #8].\",\n  \"teleology\": [\n    {\n      \"year\": 2017,\n      \"claim\": \"Established which Ca²⁺ sensor drives fast evoked release at inhibitory synapses, resolving whether SYT1 acts alone or redundantly.\",\n      \"evidence\": \"Conditional and conventional Syt1/Syt2 knockout mice with optical stimulation and electrophysiology at glycinergic and GABAergic synapses\",\n      \"pmids\": [\"28363983\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not resolve the molecular basis of redundancy between SYT1 and SYT2\", \"Excitatory synapse dependence not addressed in this study\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Linked C2B-domain SYT1 missense variants to a dominant-negative human disease mechanism, distinguishing exocytic from endocytic defects.\",\n      \"evidence\": \"Expression of five rat SYT1 C2B mutants in mouse hippocampal cultures with live imaging of localization and synaptic vesicle kinetics\",\n      \"pmids\": [\"30107533\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which mutant SYT1 dominantly interferes with wild-type protein not defined at molecular level\", \"Only C2B variants tested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Showed that botulinum neurotoxins exploit the preassembled SV2-SYT1 nanocluster for endocytic entry into synaptic vesicles.\",\n      \"evidence\": \"Super-resolution imaging and EM of inactivated BoNT/A in hippocampal neurons plus SYT1 CRISPRi knockdown with SNAP-25 cleavage readout\",\n      \"pmids\": [\"37226896\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of the PSG-SYT1-SV2 toxin complex not resolved\", \"Generalizability to other BoNT serotypes beyond A and E untested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defined the SV2A-dependent C2B nanoclustering mechanism that segregates SYT1 from endocytic machinery and sets its recycling rate.\",\n      \"evidence\": \"Single-molecule imaging, C2B point mutations, SV2A knockdown, and dynamin-1 recruitment / Rab5 sorting assays in hippocampal neurons\",\n      \"pmids\": [\"39091022\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether nanoclustering also modulates the exocytic Ca²⁺-sensing function not addressed\", \"Structural basis of the C2B-SV2A interface not determined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Extended the disease-variant catalog to C2A-domain positions and quantitatively tied exocytic impairment to clinical severity.\",\n      \"evidence\": \"SYT1-pHluorin evoked exocytosis assays in hippocampal neurons across eight C2A and C2B variants\",\n      \"pmids\": [\"39481209\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not separate fusion-triggering defects from docking or endocytic contributions per variant\", \"In vivo neurodevelopmental correlate not modeled\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Connected SYT1 endocytic sorting to a STON2-dependent pathway with disease and pharmacological relevance.\",\n      \"evidence\": \"Co-immunoprecipitation, STON2 knockin mouse electrophysiology, Syt1 sorting assay, and haloperidol rescue\",\n      \"pmids\": [\"38402028\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab Co-IP without reciprocal structural mapping of the STON2-SYT1 interface\", \"Direct causal link between Syt1 mis-sorting and behavioral phenotype not established\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Assigned the C2A/C2B polybasic patches to vesicle docking and fusion pore regulation, separating these roles from Ca²⁺ binding.\",\n      \"evidence\": \"Polybasic-patch mutagenesis with DCV docking and single-vesicle serotonin release measurements in a human neuroendocrine cell line (preprint)\",\n      \"pmids\": [\"bio_10.1101_2024.09.12.612660\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, single lab\", \"Neuroendocrine DCV findings not validated at central synapses\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Reported non-neuronal SYT1 functions in endo-lysosomal/MR1 trafficking and macrophage phagocytosis.\",\n      \"evidence\": \"Immunofluorescence localization and Syt1 loss/overexpression with MR1-MAIT and phagocytosis functional assays (preprints)\",\n      \"pmids\": [\"bio_10.1101_2025.06.23.660389\", \"bio_10.1101_2025.11.24.690103\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Overexpression and single functional readouts in preprints\", \"Molecular partners mediating non-neuronal roles unidentified\", \"Physiological relevance untested in vivo\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Dissected C2B-SNARE and polybasic-motif contributions to evoked versus spontaneous release using an invertebrate ortholog.\",\n      \"evidence\": \"AlphaFold3 modeling, mutagenesis, and electrophysiology at the C. elegans NMJ (preprint, ortholog SNT-1)\",\n      \"pmids\": [\"bio_10.1101_2025.09.30.679486\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ortholog study, preprint\", \"Multiple SNARE-binding pathways for spontaneous release not individually resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the disease variants dominantly poison wild-type SYT1 function and whether the non-neuronal trafficking roles are conserved physiological functions remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural model of the dominant-negative interference mechanism\", \"Non-neuronal roles rest only on preprint overexpression/loss-of-function data\", \"Direct partners for endo-lysosomal SYT1 unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [2, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2, 8]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [0, 1, 4]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [2, 3, 5]},\n      {\"term_id\": \"R-HSA-1500931\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"complexes\": [\"SV2-SYT1 surface nanocluster\", \"SNARE complex\"],\n    \"partners\": [\"SV2A\", \"STON2\", \"DNM1\", \"SNAP25\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":4,"faith_pct":100.0}}