{"gene":"VTI1A","run_date":"2026-06-11T09:02:06","timeline":{"discoveries":[{"year":1998,"finding":"VTI1A (Vti1-rp2) is a 29-kDa integral membrane SNARE protein enriched in the Golgi membrane. It binds alpha-SNAP (retained on GST-alpha-SNAP affinity resin from Golgi extracts), co-immunoprecipitates with syntaxin 5 and syntaxin 6, indicating participation in at least two distinct Golgi SNARE complexes. Antibody microinjection against Vti1-rp2 arrested VSV-G protein transport at the Golgi, establishing a functional role in the secretory pathway.","method":"Subcellular fractionation, indirect immunofluorescence, GST-alpha-SNAP pulldown, co-immunoprecipitation, antibody microinjection with VSV-G trafficking assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (pulldown, Co-IP, functional antibody microinjection) in a single study establishing mechanism","pmids":["9705316"],"is_preprint":false},{"year":2000,"finding":"A brain-specific splice variant, Vti1a-beta (with a 7-amino-acid insertion near the SNARE-interacting helix), is enriched in small synaptic vesicles and clathrin-coated vesicles from nerve terminals. It co-purifies with synaptobrevin during immunoisolation of synaptic vesicles and forms a distinct SNARE complex that binds NSF and alpha-SNAP but does not co-immunoprecipitate with syntaxin 1 or SNAP-25, indicating it functions in a recycling/biogenesis step rather than exocytosis.","method":"Subcellular fractionation, immunoisolation of synaptic vesicles, co-immunoprecipitation, SDS-PAGE/immunoblot","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, immunoisolation, and negative result (no syntaxin 1/SNAP-25 association) with multiple orthogonal methods in a single study","pmids":["10908612"],"is_preprint":false},{"year":2005,"finding":"Vti1a is a component of insulin-sensitive GLUT4-containing vesicles in 3T3-L1 adipocytes (identified by mass spectrometry in purified GLUT4 membranes). Insulin treatment depletes Vti1a from these membranes. siRNA-mediated knockdown of Vti1a significantly inhibited both adiponectin (Acrp30) secretion and insulin-stimulated glucose uptake, establishing Vti1a as a regulator of a common trafficking step for GLUT4 and Acrp30.","method":"Proteomics/mass spectrometry of purified vesicles, siRNA knockdown, deoxyglucose uptake assay, secretion assay, immunofluorescence colocalization","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mass spectrometry identification plus functional siRNA knockdown with two orthogonal readouts, single lab","pmids":["16131485"],"is_preprint":false},{"year":2009,"finding":"Vti1a co-localizes with VAMP7 on KChIP1-expressing intracellular vesicles in HeLa and Neuro2A cells. siRNA knockdown of either Vti1a or VAMP7 inhibited Kv4/KChIP1 traffic to the plasma membrane but had no effect on conventional VSVG traffic or KChIP2-stimulated Kv4.2 traffic, defining a VAMP7/Vti1a-containing SNARE complex that mediates a non-conventional trafficking route to the cell surface.","method":"siRNA knockdown, immunofluorescence colocalization, cell-surface trafficking assay","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with specific trafficking readout and parallel negative controls, single lab","pmids":["19138172"],"is_preprint":false},{"year":2011,"finding":"Double knockout of vti1a and vti1b in mice results in perinatal lethality with major axon tract defects and >95% neuron loss in dorsal root and geniculate ganglia at E18.5, while single knockouts are viable without these defects. Fibroblasts lacking both SNAREs survive with intact organelle morphology and minor trafficking defects, indicating that more distantly related SNAREs can substitute in endosomal traffic in non-neuronal cells but not in neurons.","method":"Genetic knockout (double and single null mice), histology, immunofluorescence, cell viability assays in fibroblasts","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic KO with defined neurodegeneration phenotype, genetic epistasis between vti1a and vti1b established by single vs. double KO comparison","pmids":["21262811"],"is_preprint":false},{"year":2011,"finding":"A VTI1A-TCF7L2 in-frame gene fusion is found in 3/97 colorectal cancers. The fusion protein lacks the TCF4 β-catenin-binding domain. The colorectal carcinoma cell line NCI-H508 harboring the fusion is dependent on VTI1A-TCF7L2 for anchorage-independent growth, as demonstrated by RNAi-mediated knockdown.","method":"Whole-genome sequencing, RNAi knockdown, anchorage-independent growth assay","journal":"Nature genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional dependency demonstrated by RNAi in a relevant cell line, single lab","pmids":["21892161"],"is_preprint":false},{"year":2012,"finding":"Vti1a marks a synaptic vesicle pool that recycles preferentially under resting conditions and selectively maintains high-frequency spontaneous neurotransmitter release. Loss of vti1a function specifically reduced spontaneous miniature release detected postsynaptically. Expression of a truncated vti1a augmented spontaneous release more than full-length vti1a, indicating an autoinhibitory mechanism regulates vti1a function.","method":"Multicolor live imaging at individual synapses, loss-of-function (dominant-negative truncation), electrophysiological recordings (mEPSC/mIPSC frequency)","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 / Strong — live imaging combined with electrophysiology and truncation analysis, multiple orthogonal methods establishing selective role in spontaneous release","pmids":["22243751"],"is_preprint":false},{"year":2014,"finding":"Vti1a is absent from mature dense-core vesicles (DCVs) in adrenal chromaffin cells but localizes near the trans-Golgi network (partially overlapping with syntaxin-6). Vti1a null cells have fewer and smaller DCVs with reduced synaptobrevin-2 content and fewer Ca2+-channels at the plasma membrane, impairing exocytosis. Release kinetics and Ca2+-sensitivity are unchanged. Long-term (days) but not short-term (hours) re-expression restores secretion, placing vti1a function in an upstream vesicle biogenesis/generation step rather than in the final fusion reaction. Additional deletion of vti1b did not exacerbate the phenotype; vti1b null cells showed no secretion defects.","method":"Immunofluorescence/localization, null mouse chromaffin cells, carbon-fiber amperometry, Ca2+ imaging, electron microscopy, rescue by long-term vs. short-term re-expression","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (amperometry, Ca2+ imaging, EM, re-expression timing) in null cells establishing upstream biogenesis role","pmids":["24902738"],"is_preprint":false},{"year":2018,"finding":"Vti1a/b-deficient neurons show severely impaired synaptic vesicle and dense-core vesicle secretion. Synaptic levels of SNAP-25 are reduced to ~50%, and both SNAP-25 and DCV cargo accumulate in the Golgi. Cargo exits the Golgi less efficiently but enters normally. Retrograde cholera toxin trafficking is compromised while Sortilin/Sorcs1 distribution is unaffected. Either Vti1a or Vti1b expression alone rescues these defects. Distended Golgi cisternae and vacuoles are observed. Conclusion: Vti1a/b support regulated secretion by sorting secretory cargo and secretion machinery at the Golgi.","method":"Vti1a/b double KO neurons, live-cell imaging of cargo trafficking, immunofluorescence, electrophysiology (SV secretion), electron microscopy","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — null neurons with multiple orthogonal methods (EM, live imaging, electrophysiology, rescue experiments) establishing Golgi-sorting mechanism","pmids":["30143604"],"is_preprint":false},{"year":2018,"finding":"The VTI1A-TCF4 fusion protein acts as a dominant-negative regulator of Wnt signaling: NCI-H508 cells carrying the fusion show no active Wnt signaling, and overexpression of the fusion in LS174T cells inhibits a Wnt signaling luciferase reporter. The VTI1A promoter is highly active in colon cancer cells and is transcriptionally activated by the intestinal homeodomain factor CDX2.","method":"Luciferase reporter assay (Wnt signaling), overexpression in colon cancer cell lines, promoter-reporter assay, CDX2 transcription factor assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — luciferase reporter assay in two cell lines with defined molecular readout, single lab","pmids":["29975781"],"is_preprint":false},{"year":2021,"finding":"Synaptotagmin-11 (Syt11) directly interacts with vti1a and suppresses spontaneous neurotransmission through it. GST pulldown, co-immunoprecipitation, and affinity purification demonstrated direct Syt11–vti1a interaction. The C2A domain of Syt11 binds vti1a with high affinity. Knockdown of vti1a reversed the elevated spontaneous release phenotype of Syt11 knockout neurons, placing vti1a downstream of Syt11 inhibition.","method":"GST pulldown, co-immunoprecipitation, affinity purification, domain deletion analysis, siRNA knockdown of vti1a in Syt11 KO neurons, electrophysiology (mEPSC frequency)","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — direct interaction validated by three independent biochemical methods plus genetic epistasis (vti1a KD rescues Syt11 KO phenotype), single lab","pmids":["34599505"],"is_preprint":false},{"year":2021,"finding":"Vti1a and Vti1b are required for cortical development: their double null mutation depletes neural progenitor pools and causes distinctive disorganization of cortical layer 5, with apoptosis of Ctip2-expressing L5 neurons and loss of corticospinal and callosal projections.","method":"Vti1a/b double null mouse, histology, immunofluorescence, apoptosis assays","journal":"Neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean genetic KO with defined cellular phenotype (layer 5 disorganization, progenitor depletion), single lab","pmids":["33774122"],"is_preprint":false},{"year":2022,"finding":"In the absence of vti1a and vti1b, hippocampal neurons lack Golgi outposts in dendrites and cortical neurons have significantly shorter neurites. Neurite elongation stimulated by neurotrophic factors (NGF, BDNF, NT-3, GDNF) or ROCK inhibitor Y27632 (enlargeosome exocytosis) is abolished in double-deficient neurons. vti1a or vti1b functions as the Qb-SNARE in a complex with VAMP-4 (R-SNARE), syntaxin 16 (Qa-SNARE), and syntaxin 6 (Qc-SNARE) required for induced neurite outgrowth.","method":"Double KO primary neurons (hippocampal and cortical), immunofluorescence for Golgi outposts, neurite length measurement, neurotrophic factor/Y27632 stimulation, Western blotting of postsynaptic densities","journal":"Neural development","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with defined morphological and stimulation-response phenotype, SNARE complex composition inferred from genetic data, single lab","pmids":["36419086"],"is_preprint":false},{"year":2022,"finding":"In Vti1a/b-deficient neurons, the cis-/medial Golgi (GM130, giantin staining) is increased while TGN recycling proteins TGN38 and TMEM87A are decreased, without overall reduction in Golgi size or absence of TGN compartment. DCV cargo markers and LAMP1/KDEL distribution are altered. Cholera Toxin retrograde trafficking is disrupted. Partial phenocopy is achieved by disturbing sphingolipid homeostasis, but overexpression of sphingomyelin synthases or myriocin treatment does not rescue, indicating that Vti1a/b are required for distinct aspects of TGN and cis-/medial Golgi organization beyond sphingolipid regulation.","method":"Vti1a/b double KO neurons, immunofluorescence for Golgi markers, live retrograde trafficking assay (Cholera Toxin), sphingolipid pathway perturbation","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple Golgi markers and trafficking assays in null neurons, single lab","pmids":["36460703"],"is_preprint":false},{"year":2024,"finding":"CRISPR/Cas9-generated Vti1a/Vti1b double knockout in N1E-115 neuroblastoma cells impairs differentiation, reduces synaptic protein levels, and reduces neurite formation and elongation. Y27632 (enlargeosome exocytosis via Rho kinase inhibition) fails to stimulate neurite elongation in DKO cells, and Akt signaling during enlargeosome-mediated outgrowth is disrupted. BDNF-induced neurite outgrowth is also impaired, with disrupted Erk signaling, placing vti1a/b upstream of these growth factor signaling cascades.","method":"CRISPR/Cas9 double KO, neurite length measurement, Western blotting (Akt, Erk phosphorylation), neurotrophic factor stimulation assays","journal":"European journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR-generated KO with defined signaling readouts (Akt, Erk), single lab","pmids":["39406055"],"is_preprint":false}],"current_model":"VTI1A is a Qb-SNARE protein residing on trans-Golgi network/endosomal membranes that forms distinct SNARE complexes (with syntaxin 5/6 at the Golgi, and with VAMP-4/syntaxin 16/syntaxin 6 for neurite outgrowth) to mediate vesicle biogenesis and cargo sorting at the Golgi—supporting delivery of secretory machinery (e.g., SNAP-25), dense-core vesicle generation, and regulated exocytosis—while a brain-specific splice variant (Vti1a-beta) on synaptic vesicles selectively maintains spontaneous neurotransmitter release through a mechanism inhibited by direct interaction with the C2A domain of synaptotagmin-11."},"narrative":{"mechanistic_narrative":"VTI1A is a Qb-SNARE protein of the trans-Golgi network and endosomal membranes that organizes vesicle biogenesis and cargo sorting by assembling into multiple distinct SNARE complexes, supporting both constitutive secretory traffic and regulated exocytosis [PMID:9705316, PMID:30143604]. At the Golgi it binds alpha-SNAP and co-immunoprecipitates with syntaxin 5 and syntaxin 6, defining at least two Golgi SNARE complexes, and functional antibody microinjection arrests VSV-G secretory transport, establishing a direct role in the secretory pathway [PMID:9705316]. Loss of VTI1A (together with its paralog VTI1B) impairs efficient exit of secretory cargo and secretory machinery — including SNAP-25 and dense-core vesicle cargo — from the Golgi, reducing synaptic SNAP-25 levels, disrupting retrograde cholera toxin trafficking, and yielding fewer, smaller dense-core vesicles; rescue requires long-term re-expression, placing VTI1A function in an upstream vesicle-generation step rather than the final fusion reaction [PMID:24902738, PMID:30143604]. VTI1A and VTI1B act redundantly in this role, and their combined loss causes perinatal lethality with massive neurodegeneration, cortical layer 5 disorganization, and abolished neurotrophin- and enlargeosome-stimulated neurite outgrowth, the latter mediated by a complex of VTI1A/B with VAMP-4, syntaxin 16, and syntaxin 6 [PMID:21262811, PMID:33774122, PMID:36419086]. A brain-specific splice variant, Vti1a-beta, resides on synaptic vesicles, co-purifies with synaptobrevin, and selectively maintains high-frequency spontaneous neurotransmitter release through a pool that recycles under resting conditions; this activity is held in check by autoinhibition and by direct binding of the synaptotagmin-11 C2A domain to VTI1A [PMID:10908612, PMID:22243751, PMID:34599505]. Beyond its trafficking roles, a VTI1A-TCF7L2 (TCF4) gene fusion in colorectal cancer drives anchorage-independent growth and acts as a dominant-negative regulator of Wnt signaling [PMID:21892161, PMID:29975781].","teleology":[{"year":1998,"claim":"Establishing whether VTI1A is a functional SNARE answered how a newly identified Golgi membrane protein participates in secretory traffic, defining it as a component of multiple Golgi SNARE complexes essential for transport.","evidence":"GST-alpha-SNAP pulldown, Co-IP with syntaxin 5/6, and antibody microinjection blocking VSV-G transport from Golgi extracts","pmids":["9705316"],"confidence":"High","gaps":["Did not resolve which complex serves which cargo step","No structural model of the SNARE complexes","Endosomal versus Golgi partitioning not delineated"]},{"year":2000,"claim":"Identifying a brain-specific splice variant on synaptic vesicles distinguished a neuronal recycling/biogenesis pool of VTI1A from its exocytic Golgi role.","evidence":"Subcellular fractionation, synaptic vesicle immunoisolation, and Co-IP showing co-purification with synaptobrevin but not syntaxin 1/SNAP-25","pmids":["10908612"],"confidence":"High","gaps":["Functional consequence of the 7-aa insertion not tested in vivo","Composition of the Vti1a-beta SNARE complex incomplete","Did not establish role in release versus recycling"]},{"year":2005,"claim":"Finding VTI1A on GLUT4 vesicles extended its trafficking role to insulin-regulated secretion in adipocytes, identifying a shared step for GLUT4 and adiponectin.","evidence":"Mass spectrometry of purified GLUT4 vesicles plus siRNA knockdown with glucose uptake and Acrp30 secretion readouts in 3T3-L1 cells","pmids":["16131485"],"confidence":"Medium","gaps":["SNARE complex partners on GLUT4 vesicles not defined","Direct versus indirect role in glucose uptake unresolved","Single cell-line system"]},{"year":2009,"claim":"Demonstrating a VAMP7/VTI1A route for Kv4/KChIP1 channels showed VTI1A mediates a non-conventional, cargo-selective trafficking pathway to the cell surface.","evidence":"siRNA knockdown of Vti1a or VAMP7 with surface-trafficking readouts and parallel negative controls (VSVG, KChIP2) in HeLa and Neuro2A","pmids":["19138172"],"confidence":"Medium","gaps":["Full SNARE complex composition not biochemically reconstituted","Mechanism of cargo selectivity unknown","Single lab"]},{"year":2011,"claim":"Comparing single versus double vti1a/vti1b knockouts established genetic redundancy and revealed a neuron-specific essentiality, since only neurons cannot substitute other SNAREs.","evidence":"Single and double null mice with histology and fibroblast viability/trafficking assays","pmids":["21262811"],"confidence":"High","gaps":["Molecular basis of neuronal non-redundancy not defined","Which trafficking step causes neurodegeneration unresolved","Compensating SNAREs in fibroblasts not identified"]},{"year":2011,"claim":"Discovery of a recurrent VTI1A-TCF7L2 fusion in colorectal cancer linked the locus to oncogenic dependency independent of its SNARE function.","evidence":"Whole-genome sequencing of colorectal tumors and RNAi knockdown with anchorage-independent growth assay in NCI-H508","pmids":["21892161"],"confidence":"Medium","gaps":["Mechanism of growth dependency not defined at the time","Fusion frequency low (3/97)","Contribution of VTI1A portion unclear"]},{"year":2012,"claim":"Live imaging plus electrophysiology defined a resting-recycling synaptic vesicle pool marked by VTI1A that selectively sustains spontaneous release, and truncation analysis revealed autoinhibition.","evidence":"Multicolor live imaging at single synapses, dominant-negative truncation, and mEPSC/mIPSC recordings","pmids":["22243751"],"confidence":"High","gaps":["Molecular basis of autoinhibition not identified","How VTI1A distinguishes spontaneous from evoked pools unknown","SNARE partners for spontaneous release not specified"]},{"year":2014,"claim":"Re-expression timing in null chromaffin cells placed VTI1A function at an upstream dense-core vesicle biogenesis step rather than the final Ca2+-triggered fusion event.","evidence":"Null mouse chromaffin cells with amperometry, Ca2+ imaging, EM, and long- versus short-term rescue","pmids":["24902738"],"confidence":"High","gaps":["Identity of the biogenesis-step SNARE complex unresolved","Why vti1b cannot compensate here unexplained","Link between DCV size and synaptobrevin loading not mechanistic"]},{"year":2018,"claim":"Double-null neuron studies unified the secretory phenotype into a Golgi cargo-sorting mechanism, showing VTI1A/B sort both secretion machinery (SNAP-25) and DCV cargo for efficient Golgi exit.","evidence":"Vti1a/b double KO neurons with live cargo imaging, EM, electrophysiology, and rescue by either paralog","pmids":["30143604"],"confidence":"High","gaps":["Cargo recognition/sorting determinants not identified","Distinction between TGN sorting and earlier Golgi steps incomplete","Mechanism of retrograde cholera toxin defect unresolved"]},{"year":2018,"claim":"Functional analysis of the cancer fusion showed VTI1A-TCF4 acts as a dominant-negative Wnt regulator and that the VTI1A promoter is driven by CDX2, clarifying the fusion's signaling consequence.","evidence":"Wnt luciferase reporter assays, overexpression in colon cancer lines, and promoter/CDX2 transcription assays","pmids":["29975781"],"confidence":"Medium","gaps":["How dominant-negative Wnt activity promotes growth is paradoxical and unexplained","In vivo relevance not tested","Single-lab reporter readouts"]},{"year":2021,"claim":"Identifying synaptotagmin-11 as a direct VTI1A partner provided the molecular brake on spontaneous release, with genetic epistasis placing VTI1A downstream of Syt11 inhibition.","evidence":"GST pulldown, Co-IP, affinity purification, C2A domain mapping, and vti1a knockdown rescuing Syt11 KO release in electrophysiology","pmids":["34599505"],"confidence":"High","gaps":["Structural basis of C2A-VTI1A binding unresolved","Whether this interaction underlies the earlier autoinhibition not connected","Regulation of the interaction in vivo unknown"]},{"year":2021,"claim":"Cortical development studies showed VTI1A/B are required for neural progenitor maintenance and survival of layer 5 projection neurons, extending the trafficking role to developmental neurogenesis.","evidence":"Vti1a/b double null mouse with histology, immunofluorescence, and apoptosis assays","pmids":["33774122"],"confidence":"Medium","gaps":["Cell-autonomous versus non-autonomous mechanism unclear","Specific cargo whose mistrafficking causes L5 loss not identified","Single lab"]},{"year":2022,"claim":"Defining the SNARE complex for induced neurite outgrowth (VTI1A/B Qb with VAMP-4, syntaxin 16, syntaxin 6) and the loss of dendritic Golgi outposts connected VTI1A trafficking to neuronal morphogenesis.","evidence":"Double KO hippocampal/cortical neurons with Golgi outpost imaging, neurite measurement, and neurotrophic factor/Y27632 stimulation","pmids":["36419086"],"confidence":"Medium","gaps":["Complex composition inferred genetically, not reconstituted","How outpost loss limits neurite elongation mechanistically unclear","Cargo delivered by this complex not defined"]},{"year":2022,"claim":"Detailed Golgi marker analysis showed VTI1A/B maintain TGN recycling-protein distribution and cis-/medial Golgi organization through a mechanism only partly attributable to sphingolipid homeostasis.","evidence":"Double KO neurons with multiple Golgi markers, retrograde cholera toxin assay, and sphingolipid pathway perturbation/rescue attempts","pmids":["36460703"],"confidence":"Medium","gaps":["Sphingolipid-independent mechanism not identified","Causal link between marker mislocalization and secretion defect incomplete","Single lab"]},{"year":2024,"claim":"A neuroblastoma double-knockout model placed VTI1A/B upstream of BDNF/Erk and enlargeosome/Akt growth-factor signaling during differentiation and neurite outgrowth.","evidence":"CRISPR/Cas9 double KO N1E-115 cells with neurite measurement, Akt/Erk phosphorylation blots, and neurotrophic factor/Y27632 stimulation","pmids":["39406055"],"confidence":"Medium","gaps":["How a trafficking SNARE controls Akt/Erk signaling mechanistically unclear","Receptor whose trafficking is affected not identified","Single cell-line system"]},{"year":null,"claim":"The molecular determinants by which VTI1A selects specific cargo at the Golgi/TGN, the structural basis of its autoinhibition and synaptotagmin-11 binding, and how its trafficking loss feeds into growth-factor signaling cascades remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of VTI1A SNARE complexes or the Syt11 interaction","Cargo-sorting recognition code at the TGN undefined","Mechanistic link between SNARE function and Akt/Erk/Wnt signaling unestablished"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,1,12]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0,1]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[0,7,8,13]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[1,2,3]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,7,8]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[8,13]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[6,10,12]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[4,11,12]}],"complexes":["Golgi SNARE complex (syntaxin 5/syntaxin 6)","VAMP-4/syntaxin 16/syntaxin 6 SNARE complex","VAMP7/Vti1a SNARE complex","synaptic vesicle SNARE complex (with synaptobrevin)"],"partners":["STX5","STX6","STX16","VAMP4","VAMP7","SYT11","NAPA","VTI1B"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q96AJ9","full_name":"Vesicle transport through interaction with t-SNAREs homolog 1A","aliases":["Vesicle transport v-SNARE protein Vti1-like 2","Vti1-rp2"],"length_aa":217,"mass_kda":25.2,"function":"V-SNARE that mediates vesicle transport pathways through interactions with t-SNAREs on the target membrane. These interactions are proposed to mediate aspects of the specificity of vesicle trafficking and to promote fusion of the lipid bilayers. Involved in vesicular transport from the late endosomes to the trans-Golgi network. Along with VAMP7, involved in an non-conventional RAB1-dependent traffic route to the cell surface used by KCNIP1 and KCND2. May be involved in increased cytokine secretion associated with cellular senescence","subcellular_location":"Cytoplasmic vesicle; Golgi apparatus membrane","url":"https://www.uniprot.org/uniprotkb/Q96AJ9/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/VTI1A","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000151532","cell_line_id":"CID000759","localizations":[{"compartment":"vesicles","grade":3},{"compartment":"golgi","grade":2}],"interactors":[{"gene":"VAMP4","stoichiometry":10.0},{"gene":"STX6","stoichiometry":10.0},{"gene":"NSF","stoichiometry":10.0},{"gene":"STX16;STX16-NPEPL1","stoichiometry":10.0},{"gene":"NAPG","stoichiometry":10.0},{"gene":"GOLPH3","stoichiometry":10.0},{"gene":"STX8","stoichiometry":10.0},{"gene":"VTI1B","stoichiometry":10.0},{"gene":"STX10","stoichiometry":10.0},{"gene":"CLCN5","stoichiometry":4.0}],"url":"https://opencell.sf.czbiohub.org/target/CID000759","total_profiled":1310},"omim":[{"mim_id":"620986","title":"T-SNARE DOMAIN-CONTAINING PROTEIN 1; TSNARE1","url":"https://www.omim.org/entry/620986"},{"mim_id":"614316","title":"VESICLE TRANSPORT THROUGH INTERACTION WITH T-SNARES 1A; VTI1A","url":"https://www.omim.org/entry/614316"},{"mim_id":"605410","title":"POTASSIUM VOLTAGE-GATED CHANNEL, SHAL-RELATED SUBFAMILY, MEMBER 2; KCND2","url":"https://www.omim.org/entry/605410"},{"mim_id":"604660","title":"POTASSIUM CHANNEL-INTERACTING PROTEIN 1; KCNIP1","url":"https://www.omim.org/entry/604660"},{"mim_id":"602228","title":"TRANSCRIPTION FACTOR 7-LIKE 2; TCF7L2","url":"https://www.omim.org/entry/602228"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Golgi apparatus","reliability":"Approved"},{"location":"Vesicles","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/VTI1A"},"hgnc":{"alias_symbol":["MVti1","Vti1-rp2"],"prev_symbol":[]},"alphafold":{"accession":"Q96AJ9","domains":[{"cath_id":"1.20.58.400","chopping":"1-102","consensus_level":"medium","plddt":82.1856,"start":1,"end":102}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96AJ9","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96AJ9-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96AJ9-F1-predicted_aligned_error_v6.png","plddt_mean":84.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=VTI1A","jax_strain_url":"https://www.jax.org/strain/search?query=VTI1A"},"sequence":{"accession":"Q96AJ9","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96AJ9.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96AJ9/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96AJ9"}},"corpus_meta":[{"pmid":"21892161","id":"PMC_21892161","title":"Genomic sequencing of colorectal adenocarcinomas identifies a recurrent VTI1A-TCF7L2 fusion.","date":"2011","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/21892161","citation_count":246,"is_preprint":false},{"pmid":"22243751","id":"PMC_22243751","title":"Vti1a identifies a vesicle pool that preferentially recycles at rest and maintains spontaneous neurotransmission.","date":"2012","source":"Neuron","url":"https://pubmed.ncbi.nlm.nih.gov/22243751","citation_count":143,"is_preprint":false},{"pmid":"10908612","id":"PMC_10908612","title":"The SNARE Vti1a-beta is localized to small synaptic vesicles and participates in a novel SNARE complex.","date":"2000","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/10908612","citation_count":80,"is_preprint":false},{"pmid":"21262811","id":"PMC_21262811","title":"Lack of the endosomal SNAREs vti1a and vti1b led to significant impairments in neuronal development.","date":"2011","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/21262811","citation_count":55,"is_preprint":false},{"pmid":"9705316","id":"PMC_9705316","title":"A 29-kilodalton Golgi soluble N-ethylmaleimide-sensitive factor attachment protein receptor (Vti1-rp2) implicated in protein trafficking in the secretory pathway.","date":"1998","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/9705316","citation_count":54,"is_preprint":false},{"pmid":"30143604","id":"PMC_30143604","title":"Vti1a/b regulate synaptic vesicle and dense core vesicle secretion via protein sorting at the Golgi.","date":"2018","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/30143604","citation_count":47,"is_preprint":false},{"pmid":"16131485","id":"PMC_16131485","title":"The v-SNARE Vti1a regulates insulin-stimulated glucose transport and Acrp30 secretion in 3T3-L1 adipocytes.","date":"2005","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16131485","citation_count":43,"is_preprint":false},{"pmid":"19138172","id":"PMC_19138172","title":"A VAMP7/Vti1a SNARE complex distinguishes a non-conventional traffic route to the cell surface used by KChIP1 and Kv4 potassium channels.","date":"2009","source":"The Biochemical journal","url":"https://pubmed.ncbi.nlm.nih.gov/19138172","citation_count":41,"is_preprint":false},{"pmid":"24902738","id":"PMC_24902738","title":"The SNARE protein vti1a functions in dense-core vesicle biogenesis.","date":"2014","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/24902738","citation_count":37,"is_preprint":false},{"pmid":"28949031","id":"PMC_28949031","title":"Cumulative evidence for relationships between multiple variants in the VTI1A and TCF7L2 genes and cancer incidence.","date":"2017","source":"International journal of cancer","url":"https://pubmed.ncbi.nlm.nih.gov/28949031","citation_count":18,"is_preprint":false},{"pmid":"32775753","id":"PMC_32775753","title":"Vesicle transport through interaction with t-SNAREs 1a (Vti1a)'s roles in neurons.","date":"2020","source":"Heliyon","url":"https://pubmed.ncbi.nlm.nih.gov/32775753","citation_count":14,"is_preprint":false},{"pmid":"29975781","id":"PMC_29975781","title":"The VTI1A-TCF4 colon cancer fusion protein is a dominant negative regulator of Wnt signaling and is transcriptionally regulated by intestinal homeodomain factor CDX2.","date":"2018","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/29975781","citation_count":13,"is_preprint":false},{"pmid":"36419086","id":"PMC_36419086","title":"Primary neurons lacking the SNAREs vti1a and vti1b show altered neuronal development.","date":"2022","source":"Neural 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exercise","url":"https://pubmed.ncbi.nlm.nih.gov/35700439","citation_count":8,"is_preprint":false},{"pmid":"33774122","id":"PMC_33774122","title":"Ablation of Vti1a/1b Triggers Neural Progenitor Pool Depletion and Cortical Layer 5 Malformation in Late-embryonic Mouse Cortex.","date":"2021","source":"Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/33774122","citation_count":8,"is_preprint":false},{"pmid":"25744365","id":"PMC_25744365","title":"Single nucleotide polymorphisms in VTI1A gene contribute to the susceptibility of Chinese population to non-small cell lung cancer.","date":"2015","source":"The International journal of biological markers","url":"https://pubmed.ncbi.nlm.nih.gov/25744365","citation_count":7,"is_preprint":false},{"pmid":"36460703","id":"PMC_36460703","title":"Vti1a/b support distinct aspects of TGN and cis-/medial Golgi organization.","date":"2022","source":"Scientific 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Vti1b.","date":"2026","source":"Proteomics","url":"https://pubmed.ncbi.nlm.nih.gov/41859820","citation_count":0,"is_preprint":false},{"pmid":"41838692","id":"PMC_41838692","title":"Alterations in bone malformation in the absence of the endosomal SNAREs Vti1a and Vti1b.","date":"2026","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/41838692","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":14071,"output_tokens":4537,"usd":0.055134,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12497,"output_tokens":5310,"usd":0.097617,"stage2_stop_reason":"end_turn"},"total_usd":0.152751,"stage1_batch_id":"msgbatch_01UT1AahFPCAyn2uVweS7A9z","stage2_batch_id":"msgbatch_01HuKWtKNT4Pqj1bc8eEP5RV","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1998,\n      \"finding\": \"VTI1A (Vti1-rp2) is a 29-kDa integral membrane SNARE protein enriched in the Golgi membrane. It binds alpha-SNAP (retained on GST-alpha-SNAP affinity resin from Golgi extracts), co-immunoprecipitates with syntaxin 5 and syntaxin 6, indicating participation in at least two distinct Golgi SNARE complexes. Antibody microinjection against Vti1-rp2 arrested VSV-G protein transport at the Golgi, establishing a functional role in the secretory pathway.\",\n      \"method\": \"Subcellular fractionation, indirect immunofluorescence, GST-alpha-SNAP pulldown, co-immunoprecipitation, antibody microinjection with VSV-G trafficking assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (pulldown, Co-IP, functional antibody microinjection) in a single study establishing mechanism\",\n      \"pmids\": [\"9705316\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"A brain-specific splice variant, Vti1a-beta (with a 7-amino-acid insertion near the SNARE-interacting helix), is enriched in small synaptic vesicles and clathrin-coated vesicles from nerve terminals. It co-purifies with synaptobrevin during immunoisolation of synaptic vesicles and forms a distinct SNARE complex that binds NSF and alpha-SNAP but does not co-immunoprecipitate with syntaxin 1 or SNAP-25, indicating it functions in a recycling/biogenesis step rather than exocytosis.\",\n      \"method\": \"Subcellular fractionation, immunoisolation of synaptic vesicles, co-immunoprecipitation, SDS-PAGE/immunoblot\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, immunoisolation, and negative result (no syntaxin 1/SNAP-25 association) with multiple orthogonal methods in a single study\",\n      \"pmids\": [\"10908612\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Vti1a is a component of insulin-sensitive GLUT4-containing vesicles in 3T3-L1 adipocytes (identified by mass spectrometry in purified GLUT4 membranes). Insulin treatment depletes Vti1a from these membranes. siRNA-mediated knockdown of Vti1a significantly inhibited both adiponectin (Acrp30) secretion and insulin-stimulated glucose uptake, establishing Vti1a as a regulator of a common trafficking step for GLUT4 and Acrp30.\",\n      \"method\": \"Proteomics/mass spectrometry of purified vesicles, siRNA knockdown, deoxyglucose uptake assay, secretion assay, immunofluorescence colocalization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mass spectrometry identification plus functional siRNA knockdown with two orthogonal readouts, single lab\",\n      \"pmids\": [\"16131485\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Vti1a co-localizes with VAMP7 on KChIP1-expressing intracellular vesicles in HeLa and Neuro2A cells. siRNA knockdown of either Vti1a or VAMP7 inhibited Kv4/KChIP1 traffic to the plasma membrane but had no effect on conventional VSVG traffic or KChIP2-stimulated Kv4.2 traffic, defining a VAMP7/Vti1a-containing SNARE complex that mediates a non-conventional trafficking route to the cell surface.\",\n      \"method\": \"siRNA knockdown, immunofluorescence colocalization, cell-surface trafficking assay\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with specific trafficking readout and parallel negative controls, single lab\",\n      \"pmids\": [\"19138172\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Double knockout of vti1a and vti1b in mice results in perinatal lethality with major axon tract defects and >95% neuron loss in dorsal root and geniculate ganglia at E18.5, while single knockouts are viable without these defects. Fibroblasts lacking both SNAREs survive with intact organelle morphology and minor trafficking defects, indicating that more distantly related SNAREs can substitute in endosomal traffic in non-neuronal cells but not in neurons.\",\n      \"method\": \"Genetic knockout (double and single null mice), histology, immunofluorescence, cell viability assays in fibroblasts\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic KO with defined neurodegeneration phenotype, genetic epistasis between vti1a and vti1b established by single vs. double KO comparison\",\n      \"pmids\": [\"21262811\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"A VTI1A-TCF7L2 in-frame gene fusion is found in 3/97 colorectal cancers. The fusion protein lacks the TCF4 β-catenin-binding domain. The colorectal carcinoma cell line NCI-H508 harboring the fusion is dependent on VTI1A-TCF7L2 for anchorage-independent growth, as demonstrated by RNAi-mediated knockdown.\",\n      \"method\": \"Whole-genome sequencing, RNAi knockdown, anchorage-independent growth assay\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional dependency demonstrated by RNAi in a relevant cell line, single lab\",\n      \"pmids\": [\"21892161\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Vti1a marks a synaptic vesicle pool that recycles preferentially under resting conditions and selectively maintains high-frequency spontaneous neurotransmitter release. Loss of vti1a function specifically reduced spontaneous miniature release detected postsynaptically. Expression of a truncated vti1a augmented spontaneous release more than full-length vti1a, indicating an autoinhibitory mechanism regulates vti1a function.\",\n      \"method\": \"Multicolor live imaging at individual synapses, loss-of-function (dominant-negative truncation), electrophysiological recordings (mEPSC/mIPSC frequency)\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — live imaging combined with electrophysiology and truncation analysis, multiple orthogonal methods establishing selective role in spontaneous release\",\n      \"pmids\": [\"22243751\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Vti1a is absent from mature dense-core vesicles (DCVs) in adrenal chromaffin cells but localizes near the trans-Golgi network (partially overlapping with syntaxin-6). Vti1a null cells have fewer and smaller DCVs with reduced synaptobrevin-2 content and fewer Ca2+-channels at the plasma membrane, impairing exocytosis. Release kinetics and Ca2+-sensitivity are unchanged. Long-term (days) but not short-term (hours) re-expression restores secretion, placing vti1a function in an upstream vesicle biogenesis/generation step rather than in the final fusion reaction. Additional deletion of vti1b did not exacerbate the phenotype; vti1b null cells showed no secretion defects.\",\n      \"method\": \"Immunofluorescence/localization, null mouse chromaffin cells, carbon-fiber amperometry, Ca2+ imaging, electron microscopy, rescue by long-term vs. short-term re-expression\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (amperometry, Ca2+ imaging, EM, re-expression timing) in null cells establishing upstream biogenesis role\",\n      \"pmids\": [\"24902738\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Vti1a/b-deficient neurons show severely impaired synaptic vesicle and dense-core vesicle secretion. Synaptic levels of SNAP-25 are reduced to ~50%, and both SNAP-25 and DCV cargo accumulate in the Golgi. Cargo exits the Golgi less efficiently but enters normally. Retrograde cholera toxin trafficking is compromised while Sortilin/Sorcs1 distribution is unaffected. Either Vti1a or Vti1b expression alone rescues these defects. Distended Golgi cisternae and vacuoles are observed. Conclusion: Vti1a/b support regulated secretion by sorting secretory cargo and secretion machinery at the Golgi.\",\n      \"method\": \"Vti1a/b double KO neurons, live-cell imaging of cargo trafficking, immunofluorescence, electrophysiology (SV secretion), electron microscopy\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — null neurons with multiple orthogonal methods (EM, live imaging, electrophysiology, rescue experiments) establishing Golgi-sorting mechanism\",\n      \"pmids\": [\"30143604\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The VTI1A-TCF4 fusion protein acts as a dominant-negative regulator of Wnt signaling: NCI-H508 cells carrying the fusion show no active Wnt signaling, and overexpression of the fusion in LS174T cells inhibits a Wnt signaling luciferase reporter. The VTI1A promoter is highly active in colon cancer cells and is transcriptionally activated by the intestinal homeodomain factor CDX2.\",\n      \"method\": \"Luciferase reporter assay (Wnt signaling), overexpression in colon cancer cell lines, promoter-reporter assay, CDX2 transcription factor assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — luciferase reporter assay in two cell lines with defined molecular readout, single lab\",\n      \"pmids\": [\"29975781\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Synaptotagmin-11 (Syt11) directly interacts with vti1a and suppresses spontaneous neurotransmission through it. GST pulldown, co-immunoprecipitation, and affinity purification demonstrated direct Syt11–vti1a interaction. The C2A domain of Syt11 binds vti1a with high affinity. Knockdown of vti1a reversed the elevated spontaneous release phenotype of Syt11 knockout neurons, placing vti1a downstream of Syt11 inhibition.\",\n      \"method\": \"GST pulldown, co-immunoprecipitation, affinity purification, domain deletion analysis, siRNA knockdown of vti1a in Syt11 KO neurons, electrophysiology (mEPSC frequency)\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — direct interaction validated by three independent biochemical methods plus genetic epistasis (vti1a KD rescues Syt11 KO phenotype), single lab\",\n      \"pmids\": [\"34599505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Vti1a and Vti1b are required for cortical development: their double null mutation depletes neural progenitor pools and causes distinctive disorganization of cortical layer 5, with apoptosis of Ctip2-expressing L5 neurons and loss of corticospinal and callosal projections.\",\n      \"method\": \"Vti1a/b double null mouse, histology, immunofluorescence, apoptosis assays\",\n      \"journal\": \"Neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic KO with defined cellular phenotype (layer 5 disorganization, progenitor depletion), single lab\",\n      \"pmids\": [\"33774122\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In the absence of vti1a and vti1b, hippocampal neurons lack Golgi outposts in dendrites and cortical neurons have significantly shorter neurites. Neurite elongation stimulated by neurotrophic factors (NGF, BDNF, NT-3, GDNF) or ROCK inhibitor Y27632 (enlargeosome exocytosis) is abolished in double-deficient neurons. vti1a or vti1b functions as the Qb-SNARE in a complex with VAMP-4 (R-SNARE), syntaxin 16 (Qa-SNARE), and syntaxin 6 (Qc-SNARE) required for induced neurite outgrowth.\",\n      \"method\": \"Double KO primary neurons (hippocampal and cortical), immunofluorescence for Golgi outposts, neurite length measurement, neurotrophic factor/Y27632 stimulation, Western blotting of postsynaptic densities\",\n      \"journal\": \"Neural development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with defined morphological and stimulation-response phenotype, SNARE complex composition inferred from genetic data, single lab\",\n      \"pmids\": [\"36419086\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In Vti1a/b-deficient neurons, the cis-/medial Golgi (GM130, giantin staining) is increased while TGN recycling proteins TGN38 and TMEM87A are decreased, without overall reduction in Golgi size or absence of TGN compartment. DCV cargo markers and LAMP1/KDEL distribution are altered. Cholera Toxin retrograde trafficking is disrupted. Partial phenocopy is achieved by disturbing sphingolipid homeostasis, but overexpression of sphingomyelin synthases or myriocin treatment does not rescue, indicating that Vti1a/b are required for distinct aspects of TGN and cis-/medial Golgi organization beyond sphingolipid regulation.\",\n      \"method\": \"Vti1a/b double KO neurons, immunofluorescence for Golgi markers, live retrograde trafficking assay (Cholera Toxin), sphingolipid pathway perturbation\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple Golgi markers and trafficking assays in null neurons, single lab\",\n      \"pmids\": [\"36460703\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CRISPR/Cas9-generated Vti1a/Vti1b double knockout in N1E-115 neuroblastoma cells impairs differentiation, reduces synaptic protein levels, and reduces neurite formation and elongation. Y27632 (enlargeosome exocytosis via Rho kinase inhibition) fails to stimulate neurite elongation in DKO cells, and Akt signaling during enlargeosome-mediated outgrowth is disrupted. BDNF-induced neurite outgrowth is also impaired, with disrupted Erk signaling, placing vti1a/b upstream of these growth factor signaling cascades.\",\n      \"method\": \"CRISPR/Cas9 double KO, neurite length measurement, Western blotting (Akt, Erk phosphorylation), neurotrophic factor stimulation assays\",\n      \"journal\": \"European journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR-generated KO with defined signaling readouts (Akt, Erk), single lab\",\n      \"pmids\": [\"39406055\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"VTI1A is a Qb-SNARE protein residing on trans-Golgi network/endosomal membranes that forms distinct SNARE complexes (with syntaxin 5/6 at the Golgi, and with VAMP-4/syntaxin 16/syntaxin 6 for neurite outgrowth) to mediate vesicle biogenesis and cargo sorting at the Golgi—supporting delivery of secretory machinery (e.g., SNAP-25), dense-core vesicle generation, and regulated exocytosis—while a brain-specific splice variant (Vti1a-beta) on synaptic vesicles selectively maintains spontaneous neurotransmitter release through a mechanism inhibited by direct interaction with the C2A domain of synaptotagmin-11.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"VTI1A is a Qb-SNARE protein of the trans-Golgi network and endosomal membranes that organizes vesicle biogenesis and cargo sorting by assembling into multiple distinct SNARE complexes, supporting both constitutive secretory traffic and regulated exocytosis [#0, #8]. At the Golgi it binds alpha-SNAP and co-immunoprecipitates with syntaxin 5 and syntaxin 6, defining at least two Golgi SNARE complexes, and functional antibody microinjection arrests VSV-G secretory transport, establishing a direct role in the secretory pathway [#0]. Loss of VTI1A (together with its paralog VTI1B) impairs efficient exit of secretory cargo and secretory machinery — including SNAP-25 and dense-core vesicle cargo — from the Golgi, reducing synaptic SNAP-25 levels, disrupting retrograde cholera toxin trafficking, and yielding fewer, smaller dense-core vesicles; rescue requires long-term re-expression, placing VTI1A function in an upstream vesicle-generation step rather than the final fusion reaction [#7, #8]. VTI1A and VTI1B act redundantly in this role, and their combined loss causes perinatal lethality with massive neurodegeneration, cortical layer 5 disorganization, and abolished neurotrophin- and enlargeosome-stimulated neurite outgrowth, the latter mediated by a complex of VTI1A/B with VAMP-4, syntaxin 16, and syntaxin 6 [#4, #11, #12]. A brain-specific splice variant, Vti1a-beta, resides on synaptic vesicles, co-purifies with synaptobrevin, and selectively maintains high-frequency spontaneous neurotransmitter release through a pool that recycles under resting conditions; this activity is held in check by autoinhibition and by direct binding of the synaptotagmin-11 C2A domain to VTI1A [#1, #6, #10]. Beyond its trafficking roles, a VTI1A-TCF7L2 (TCF4) gene fusion in colorectal cancer drives anchorage-independent growth and acts as a dominant-negative regulator of Wnt signaling [#5, #9].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Establishing whether VTI1A is a functional SNARE answered how a newly identified Golgi membrane protein participates in secretory traffic, defining it as a component of multiple Golgi SNARE complexes essential for transport.\",\n      \"evidence\": \"GST-alpha-SNAP pulldown, Co-IP with syntaxin 5/6, and antibody microinjection blocking VSV-G transport from Golgi extracts\",\n      \"pmids\": [\"9705316\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve which complex serves which cargo step\", \"No structural model of the SNARE complexes\", \"Endosomal versus Golgi partitioning not delineated\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Identifying a brain-specific splice variant on synaptic vesicles distinguished a neuronal recycling/biogenesis pool of VTI1A from its exocytic Golgi role.\",\n      \"evidence\": \"Subcellular fractionation, synaptic vesicle immunoisolation, and Co-IP showing co-purification with synaptobrevin but not syntaxin 1/SNAP-25\",\n      \"pmids\": [\"10908612\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of the 7-aa insertion not tested in vivo\", \"Composition of the Vti1a-beta SNARE complex incomplete\", \"Did not establish role in release versus recycling\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Finding VTI1A on GLUT4 vesicles extended its trafficking role to insulin-regulated secretion in adipocytes, identifying a shared step for GLUT4 and adiponectin.\",\n      \"evidence\": \"Mass spectrometry of purified GLUT4 vesicles plus siRNA knockdown with glucose uptake and Acrp30 secretion readouts in 3T3-L1 cells\",\n      \"pmids\": [\"16131485\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"SNARE complex partners on GLUT4 vesicles not defined\", \"Direct versus indirect role in glucose uptake unresolved\", \"Single cell-line system\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrating a VAMP7/VTI1A route for Kv4/KChIP1 channels showed VTI1A mediates a non-conventional, cargo-selective trafficking pathway to the cell surface.\",\n      \"evidence\": \"siRNA knockdown of Vti1a or VAMP7 with surface-trafficking readouts and parallel negative controls (VSVG, KChIP2) in HeLa and Neuro2A\",\n      \"pmids\": [\"19138172\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Full SNARE complex composition not biochemically reconstituted\", \"Mechanism of cargo selectivity unknown\", \"Single lab\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Comparing single versus double vti1a/vti1b knockouts established genetic redundancy and revealed a neuron-specific essentiality, since only neurons cannot substitute other SNAREs.\",\n      \"evidence\": \"Single and double null mice with histology and fibroblast viability/trafficking assays\",\n      \"pmids\": [\"21262811\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of neuronal non-redundancy not defined\", \"Which trafficking step causes neurodegeneration unresolved\", \"Compensating SNAREs in fibroblasts not identified\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Discovery of a recurrent VTI1A-TCF7L2 fusion in colorectal cancer linked the locus to oncogenic dependency independent of its SNARE function.\",\n      \"evidence\": \"Whole-genome sequencing of colorectal tumors and RNAi knockdown with anchorage-independent growth assay in NCI-H508\",\n      \"pmids\": [\"21892161\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of growth dependency not defined at the time\", \"Fusion frequency low (3/97)\", \"Contribution of VTI1A portion unclear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Live imaging plus electrophysiology defined a resting-recycling synaptic vesicle pool marked by VTI1A that selectively sustains spontaneous release, and truncation analysis revealed autoinhibition.\",\n      \"evidence\": \"Multicolor live imaging at single synapses, dominant-negative truncation, and mEPSC/mIPSC recordings\",\n      \"pmids\": [\"22243751\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of autoinhibition not identified\", \"How VTI1A distinguishes spontaneous from evoked pools unknown\", \"SNARE partners for spontaneous release not specified\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Re-expression timing in null chromaffin cells placed VTI1A function at an upstream dense-core vesicle biogenesis step rather than the final Ca2+-triggered fusion event.\",\n      \"evidence\": \"Null mouse chromaffin cells with amperometry, Ca2+ imaging, EM, and long- versus short-term rescue\",\n      \"pmids\": [\"24902738\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the biogenesis-step SNARE complex unresolved\", \"Why vti1b cannot compensate here unexplained\", \"Link between DCV size and synaptobrevin loading not mechanistic\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Double-null neuron studies unified the secretory phenotype into a Golgi cargo-sorting mechanism, showing VTI1A/B sort both secretion machinery (SNAP-25) and DCV cargo for efficient Golgi exit.\",\n      \"evidence\": \"Vti1a/b double KO neurons with live cargo imaging, EM, electrophysiology, and rescue by either paralog\",\n      \"pmids\": [\"30143604\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cargo recognition/sorting determinants not identified\", \"Distinction between TGN sorting and earlier Golgi steps incomplete\", \"Mechanism of retrograde cholera toxin defect unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Functional analysis of the cancer fusion showed VTI1A-TCF4 acts as a dominant-negative Wnt regulator and that the VTI1A promoter is driven by CDX2, clarifying the fusion's signaling consequence.\",\n      \"evidence\": \"Wnt luciferase reporter assays, overexpression in colon cancer lines, and promoter/CDX2 transcription assays\",\n      \"pmids\": [\"29975781\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How dominant-negative Wnt activity promotes growth is paradoxical and unexplained\", \"In vivo relevance not tested\", \"Single-lab reporter readouts\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identifying synaptotagmin-11 as a direct VTI1A partner provided the molecular brake on spontaneous release, with genetic epistasis placing VTI1A downstream of Syt11 inhibition.\",\n      \"evidence\": \"GST pulldown, Co-IP, affinity purification, C2A domain mapping, and vti1a knockdown rescuing Syt11 KO release in electrophysiology\",\n      \"pmids\": [\"34599505\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of C2A-VTI1A binding unresolved\", \"Whether this interaction underlies the earlier autoinhibition not connected\", \"Regulation of the interaction in vivo unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Cortical development studies showed VTI1A/B are required for neural progenitor maintenance and survival of layer 5 projection neurons, extending the trafficking role to developmental neurogenesis.\",\n      \"evidence\": \"Vti1a/b double null mouse with histology, immunofluorescence, and apoptosis assays\",\n      \"pmids\": [\"33774122\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cell-autonomous versus non-autonomous mechanism unclear\", \"Specific cargo whose mistrafficking causes L5 loss not identified\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defining the SNARE complex for induced neurite outgrowth (VTI1A/B Qb with VAMP-4, syntaxin 16, syntaxin 6) and the loss of dendritic Golgi outposts connected VTI1A trafficking to neuronal morphogenesis.\",\n      \"evidence\": \"Double KO hippocampal/cortical neurons with Golgi outpost imaging, neurite measurement, and neurotrophic factor/Y27632 stimulation\",\n      \"pmids\": [\"36419086\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Complex composition inferred genetically, not reconstituted\", \"How outpost loss limits neurite elongation mechanistically unclear\", \"Cargo delivered by this complex not defined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Detailed Golgi marker analysis showed VTI1A/B maintain TGN recycling-protein distribution and cis-/medial Golgi organization through a mechanism only partly attributable to sphingolipid homeostasis.\",\n      \"evidence\": \"Double KO neurons with multiple Golgi markers, retrograde cholera toxin assay, and sphingolipid pathway perturbation/rescue attempts\",\n      \"pmids\": [\"36460703\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Sphingolipid-independent mechanism not identified\", \"Causal link between marker mislocalization and secretion defect incomplete\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"A neuroblastoma double-knockout model placed VTI1A/B upstream of BDNF/Erk and enlargeosome/Akt growth-factor signaling during differentiation and neurite outgrowth.\",\n      \"evidence\": \"CRISPR/Cas9 double KO N1E-115 cells with neurite measurement, Akt/Erk phosphorylation blots, and neurotrophic factor/Y27632 stimulation\",\n      \"pmids\": [\"39406055\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How a trafficking SNARE controls Akt/Erk signaling mechanistically unclear\", \"Receptor whose trafficking is affected not identified\", \"Single cell-line system\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The molecular determinants by which VTI1A selects specific cargo at the Golgi/TGN, the structural basis of its autoinhibition and synaptotagmin-11 binding, and how its trafficking loss feeds into growth-factor signaling cascades remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of VTI1A SNARE complexes or the Syt11 interaction\", \"Cargo-sorting recognition code at the TGN undefined\", \"Mechanistic link between SNARE function and Akt/Erk/Wnt signaling unestablished\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 1, 12]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [0, 7, 8, 13]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [1, 2, 3]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 7, 8]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [8, 13]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [6, 10, 12]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [4, 11, 12]}\n    ],\n    \"complexes\": [\n      \"Golgi SNARE complex (syntaxin 5/syntaxin 6)\",\n      \"VAMP-4/syntaxin 16/syntaxin 6 SNARE complex\",\n      \"VAMP7/Vti1a SNARE complex\",\n      \"synaptic vesicle SNARE complex (with synaptobrevin)\"\n    ],\n    \"partners\": [\n      \"STX5\",\n      \"STX6\",\n      \"STX16\",\n      \"VAMP4\",\n      \"VAMP7\",\n      \"SYT11\",\n      \"NAPA\",\n      \"VTI1B\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}