{"gene":"UNC13B","run_date":"2026-06-10T10:51:56","timeline":{"discoveries":[{"year":1991,"finding":"The C1/C2-like domain region of UNC-13 (C. elegans ortholog) binds phorbol esters with high affinity in a zinc- and phospholipid-dependent, stereospecific manner, and diacylglycerol competitively inhibits this binding, establishing UNC-13 as a DAG/phorbol ester receptor.","method":"Recombinant protein expression in E. coli, radioligand binding assay with [3H]phorbol ester, competitive inhibition with diacylglycerol","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro biochemical reconstitution with purified recombinant domain, replicated independently (PMIDs 2062851, 1445255, 7537738)","pmids":["2062851","1445255","7537738"],"is_preprint":false},{"year":1995,"finding":"Munc13-2 (UNC13B) is a mammalian homologue of C. elegans UNC-13 expressed in rat brain; it is a brain-specific large protein with conserved C1- and C2-domains and is enriched as a peripheral membrane protein in synaptosomes localized to plasma membranes but absent from synaptic vesicles.","method":"Molecular cloning, Western blot with specific antibodies, subcellular fractionation of rat brain synaptosomes","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — antibody-based subcellular fractionation plus cloning, single lab, two orthogonal methods","pmids":["7559667"],"is_preprint":false},{"year":1997,"finding":"Munc13-1 (the closest paralog, but the interaction paradigm is the founding mechanism for Munc13 family including Munc13-2/UNC13B) directly interacts with the N-terminal coiled-coil domain of syntaxin via its C terminus; through this interaction it associates with a subpopulation of the SNARE core complex (synaptobrevin/SNAP-25/syntaxin) but not with other syntaxin-interacting proteins.","method":"Yeast two-hybrid, in vitro GST pulldown, co-immunoprecipitation — three independent methods on Munc13-1/syntaxin interaction; the binding site in syntaxin overlaps with Munc18 binding site","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — three independent in vitro methods (Y2H, pulldown, co-IP) in one study establishing direct protein–protein interaction","pmids":["8999968"],"is_preprint":false},{"year":1999,"finding":"UNC-13 (C. elegans) is required for a post-docking priming step of synaptic vesicle exocytosis: null mutants have morphologically docked vesicles but these are not competent for fusion as shown by absent evoked release and failure to release with hyperosmotic saline or in calcium-free solution.","method":"Whole-cell voltage-clamp electrophysiology at C. elegans NMJ, hyperosmotic saline stimulation, calcium-free recording, electron microscopy of synapse morphology","journal":"Nature neuroscience","confidence":"High","confidence_rationale":"Tier 1 / Strong — rigorous null-mutant electrophysiology with multiple stimulation paradigms, independently replicated in Drosophila and mouse","pmids":["10526333"],"is_preprint":false},{"year":1999,"finding":"Neurotransmitter release at C. elegans NMJs is facilitated by a presynaptic Gqα (EGL-30) → PLCβ (EGL-8) → DAG pathway, and this effect requires DAG binding to UNC-13: a mutation abolishing phorbol ester/DAG binding to UNC-13 blocks the stimulatory effect of phorbol esters on acetylcholine release.","method":"Genetic epistasis in C. elegans, phorbol ester pharmacology, constitutively membrane-targeted UNC-13 rescue, confocal imaging of UNC-13 localization","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis combined with pharmacology and domain-specific rescue, replicated in subsequent studies","pmids":["10571228"],"is_preprint":false},{"year":1999,"finding":"Serotonin inhibits acetylcholine release at C. elegans NMJs via GOA-1 (Gα0) and DGK-1 (DAG kinase), and this inhibition correlates with decreased abundance of UNC-13 at release sites; loss of GOA-1 leads to abnormally high levels of UNC-13 at nerve terminals.","method":"Aldicarb sensitivity assay in intact C. elegans, immunofluorescence quantification of UNC-13 at synapses, genetic epistasis with goa-1 and dgk-1 mutants","journal":"Neuron","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis plus quantitative immunofluorescence, single lab","pmids":["10677040"],"is_preprint":false},{"year":1999,"finding":"UNC-13 transiently interacts with the UNC-18–syntaxin complex and causes rapid displacement of UNC-18 from syntaxin, providing a mechanism by which UNC-13 modulates SNARE complex availability.","method":"Co-immunoprecipitation, GST pulldown (biochemical), genetic epistasis in C. elegans unc-13/unc-18/unc-64 double mutants","journal":"The Journal of neuroscience : the official journal of the Society for Neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal biochemical pulldown plus genetic epistasis, single lab","pmids":["10366611"],"is_preprint":false},{"year":1999,"finding":"Drosophila UNC-13 (Dunc-13) is essential for synaptic transmission at a post-docking priming step: null mutants accumulate docked vesicles at release sites but have no evoked or hyperosmotic-saline-evoked release.","method":"Electrophysiology (EJPs, miniature EJPs), hyperosmotic saline stimulation, electron microscopy of presynaptic terminals in Dunc-13 null Drosophila","journal":"Nature neuroscience","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal methods (electrophysiology + EM) in null mutant, independently replicating C. elegans findings","pmids":["10526334"],"is_preprint":false},{"year":2001,"finding":"UNC-13 primes synaptic vesicles by promoting the open conformation of syntaxin: an open-form syntaxin mutant (constitutively open) bypasses the requirement for UNC-13 in synaptic vesicle priming in C. elegans, placing UNC-13 upstream of syntaxin opening in the exocytic pathway.","method":"Genetic epistasis — engineered open-form syntaxin mutations introduced into C. elegans unc-13 null background; electrophysiology and behavioral rescue assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic epistasis with structure-informed mutations, clear bypass of null phenotype, replicated across multiple assays","pmids":["11460165"],"is_preprint":false},{"year":2003,"finding":"Synaptic levels of Drosophila UNC-13 (Dunc-13) are regulated by proteasome-mediated degradation downstream of both GαS/cAMP/PKA and Gαq/PLC/DAG pathways; both pathways converge to control synaptic UNC-13 abundance by modulating the rate of proteasomal degradation rather than translocation.","method":"Immunofluorescence quantification of Dunc-13 at NMJ boutons, pharmacological manipulation of cAMP/PKA and PLC/DAG pathways, proteasome inhibitor treatment in Drosophila","journal":"Journal of neurobiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — quantitative imaging with pharmacological and genetic pathway perturbations, single lab","pmids":["12532395"],"is_preprint":false},{"year":2005,"finding":"UNC-13 interaction with syntaxin is required for nerve-evoked synaptic vesicle fusion but not for vesicle priming: a double mutation in MHD2 (F1000A/K1002A) that disrupts the UNC-13/syntaxin interaction reduces evoked EPSCs but leaves the primed vesicle pool normal, indicating UNC-13 regulates multiple steps of the vesicle cycle.","method":"Site-directed mutagenesis of UNC-13 MHD2 domain, whole-cell electrophysiology at C. elegans NMJ, behavioral rescue assays","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 1 / Strong — active-site mutagenesis combined with electrophysiology, clear separation of priming from fusion-step function","pmids":["16271476"],"is_preprint":false},{"year":2005,"finding":"Diacylglycerol-activated Hmunc13 (UNC13B) translocates to the Golgi and binds GTP-bound Rab34 via its MHD2 domain; this interaction requires the GTP-loaded form of Rab34, establishing UNC13B as an effector of Rab34 in intracellular vesicle/lysosome positioning.","method":"Bacterial two-hybrid screen, co-immunoprecipitation from cell lysates, GST pulldown with GTP/GDP-loaded Rab34 mutants (Q111L, T66N), radioactive GTP overlay assay, deletion mutagenesis of MHD2","journal":"Traffic (Copenhagen, Denmark)","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple orthogonal biochemical methods (Y2H, co-IP, GST pulldown with nucleotide-state mutants, mutagenesis), single lab","pmids":["16138900"],"is_preprint":false},{"year":2006,"finding":"UNC-13 localizes to the plasma membrane within ~100 nm of dense projections at C. elegans NMJs; in unc-13 null mutants, synaptic vesicles that normally contact the plasma membrane are nearly absent, identifying membrane-contacting vesicles as morphological correlates of primed vesicles and defining UNC-13's spatial domain for priming.","method":"Rapid physical fixation, immunogold electron microscopy, high-resolution morphometric analysis at C. elegans NMJ","journal":"The Journal of neuroscience : the official journal of the Society for Neuroscience","confidence":"High","confidence_rationale":"Tier 1 / Strong — quantitative immunogold EM with null mutant comparison, precise nanoscale spatial mapping with functional consequence","pmids":["16885217"],"is_preprint":false},{"year":2008,"finding":"Munc13-2 (UNC13B) knockout mice show accumulation of mucins (Muc5b) in Clara cells and goblet cells of multiple mucosal tissues, demonstrating that Munc13-2 is required for constitutive/baseline priming and secretion of a specific population of secretory granules; agonist-regulated secretion via Munc13-4 is preserved, revealing isoform-specific priming requirements.","method":"Munc13-2 knockout mouse histology (AB/PAS staining), BAL cell counts, qPCR, electron microscopy of Clara cells, agonist stimulation (ATP/UTP) in Munc13-2−/− airways","journal":"The Journal of physiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — knockout mouse with multiple orthogonal readouts (histology, EM, qPCR, pharmacology), clear cell-biological phenotype","pmids":["18258655"],"is_preprint":false},{"year":2009,"finding":"Munc13-2 (UNC13B) upregulation by high glucose in mesangial cells increases constitutive protein secretion via Rab34 interaction; siRNA knockdown of munc13-2 or rab34 abolishes high-glucose-induced VSVG-GFP secretion and fibronectin secretion; deletion of MHD2 abolishes the effect, confirming the MHD2–Rab34 interaction as the mechanistic basis.","method":"siRNA knockdown in rat mesangial cells, VSVG-GFP secretion assay, fibronectin secretion assay, MHD2-deletion mutant transfection in HeLa cells","journal":"American journal of physiology. Cell physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown and domain-deletion mutagenesis with functional secretion assay, single lab","pmids":["19641095"],"is_preprint":false},{"year":2009,"finding":"Munc13-2 (UNC13B) is essential for normal release probability at hippocampal mossy fiber synapses: Munc13-2 knockout mice show strongly increased paired-pulse and frequency facilitation at mossy fiber synapses, consistent with reduced basal release probability, while mossy fiber LTP is unaffected; other hippocampal synapse types are unaffected.","method":"Munc13-2 knockout mouse electrophysiology — patch-clamp recordings of mossy fiber synapses, paired-pulse and frequency facilitation protocols, LTP induction","journal":"Cerebral cortex (New York, N.Y. : 1991)","confidence":"High","confidence_rationale":"Tier 2 / Strong — knockout mouse with rigorous electrophysiological characterization at multiple synapse types, clear isoform-specific phenotype","pmids":["19700493"],"is_preprint":false},{"year":2013,"finding":"The N-terminal C2A domain of UNC-13 regulates active zone localization of UNC-13, release probability of evoked release, and is specifically required for spontaneous release; proximity of UNC-13 to Ca2+ entry sites mediated by the C2A-containing N-terminus accelerates neurotransmitter release kinetics.","method":"C2A domain deletion and mutagenesis in C. elegans, whole-cell voltage-clamp electrophysiology, kinetic analysis of synaptic vesicle release, immunofluorescence localization","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 / Strong — domain mutagenesis combined with quantitative electrophysiology and localization, multiple orthogonal assays in one study","pmids":["24220508"],"is_preprint":false},{"year":2015,"finding":"NLP-12 neuropeptide potentiates tonic ACh release through a Gαq/PLCβ-independent DAG pathway requiring DAG binding to UNC-13L (but not UNC-13S), while potentiation of evoked release uses both UNC-13 isoforms via the Gαq/PLCβ/DAG pathway, demonstrating isoform-specific and pathway-specific roles of UNC-13 in tonic versus evoked release.","method":"Genetic epistasis in C. elegans (egl-30, egl-8 mutants combined with unc-13 isoform-specific mutants), aldicarb sensitivity assay, electrophysiology","journal":"The Journal of neuroscience : the official journal of the Society for Neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean genetic epistasis with isoform-specific mutants, single lab","pmids":["25609620"],"is_preprint":false},{"year":2016,"finding":"The Drosophila Unc13B isoform is recruited to nascent active zones by scaffolding proteins Syd-1 and Liprin-α and localizes ~120 nm from Ca2+ channels, while Unc13A is positioned ~70 nm from Ca2+ channels by Bruchpilot/RIM-binding protein complexes and is responsible for docking SVs at that distance; Unc13A null mutants show inefficient, delayed, and EGTA-supersensitive release, demonstrating that isoform positioning defines release probability and kinetics.","method":"Super-resolution microscopy (STORM/STED), intravital imaging in Drosophila, electrophysiology (TEVC), EGTA chelation, mathematical modeling, isoform-specific null mutants","journal":"Nature neuroscience","confidence":"High","confidence_rationale":"Tier 1 / Strong — super-resolution imaging + electrophysiology + mathematical modeling + multiple genetic nulls in a single rigorous study","pmids":["27526206"],"is_preprint":false},{"year":2016,"finding":"Munc13-2 (UNC13B) level differences between C57BL/6J and DBA/2J mice underlie strain-dependent differences in presynaptic release probability, vesicle recycling, and short-term plasticity at BLA glutamatergic synapses; shRNA knockdown of Munc13-2 in B6 mice recapitulates the DBA/2J presynaptic phenotype.","method":"shRNA knockdown in vivo, electrophysiology (paired-pulse, frequency facilitation), biochemical quantification of presynaptic proteins, BXD recombinant inbred strain in silico QTL analysis","journal":"The Journal of neuroscience : the official journal of the Society for Neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — shRNA knockdown with electrophysiological phenotyping, supported by in silico QTL mapping and protein quantification","pmids":["27798178"],"is_preprint":false},{"year":2017,"finding":"Munc18-1/UNC-18 primes vesicle fusion downstream of Munc13-1/UNC-13 by templating SNARE complex assembly; a gain-of-function UNC-18(P334A) mutation partially bypasses the requirement for UNC-13, and this bypass is synergistically enhanced by loss of Tomosyn/TOM-1; Munc18-1(P335A) shows enhanced SNARE complex formation and partially bypasses Munc13-1 requirement in liposome fusion assays.","method":"Genetic epistasis in C. elegans, electrophysiology (C. elegans and mammalian neurons), liposome fusion reconstitution assay, biochemical SNARE complex formation assay","journal":"The Journal of neuroscience : the official journal of the Society for Neuroscience","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution in liposome fusion assay plus genetic epistasis plus electrophysiology, multiple orthogonal methods placing UNC-13 upstream of UNC-18","pmids":["28821673"],"is_preprint":false},{"year":2017,"finding":"Doc2B requires interaction with ubMunc13-2 (a ubiquitous isoform of UNC13B/Munc13-2) for its downstream vesicle priming function in chromaffin cells: Doc2B Ca2+-binding mutations and SNARE-binding mutations block distinct priming steps, and the downstream priming step is dependent on both ubMunc13-2 and synaptotagmin-1.","method":"Overexpression and mutagenesis of Doc2B in mouse chromaffin cells, capacitance measurements, Ca2+ uncaging, genetic deletion of synaptotagmin-1 and Munc13-2","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis in primary cells with functional exocytosis readout; Munc13-2 involvement established by genetic deletion, single lab","pmids":["29274147"],"is_preprint":false},{"year":2019,"finding":"UNC-13L has three inhibitory domains (X region between C2A and C1, C1 domain, and C2B domain) that suppress synaptic vesicle exocytosis; removing all three produces a hyperactive UNC-13 with dramatically increased neurotransmitter release, Ca2+ sensitivity, and release probability, and this hyperactivity increases syntaxin open probability to enhance tonic release.","method":"Domain deletion mutagenesis in C. elegans, electrophysiology, Ca2+ sensitivity assay, synaptic recovery/replenishment kinetics, double mutant epistasis with syntaxin open-form mutants","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 1 / Strong — systematic domain deletion mutagenesis combined with multiple electrophysiology assays and epistasis, defining inhibitory domain architecture","pmids":["31509756"],"is_preprint":false},{"year":2021,"finding":"Synaptotagmin-7 promotes ubMunc13-2- and phorbol ester-dependent priming of dense-core vesicles, especially at low resting Ca2+; without synaptotagmin-7, vesicles accumulate 20–40 nm from the membrane rather than in close (<6 nm) apposition, indicating synaptotagmin-7 mediates a membrane-approach step upstream of Munc13-2-dependent priming.","method":"Synaptotagmin-7 knockout and overexpression in mouse chromaffin cells, capacitance measurements, TIRF microscopy with vesicle distance measurements, phorbol ester stimulation, genetic epistasis with Munc13-2","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic deletion combined with TIRF nanoscale distance measurements and functional exocytosis assay; Munc13-2 involvement established by epistasis, single lab","pmids":["33749593"],"is_preprint":false},{"year":2022,"finding":"Endogenously tagged Unc-13 (all isoforms) in Drosophila undergoes nanoscale reorganization during presynaptic homeostatic potentiation (PHP): localization microscopy shows Unc-13 subclusters move toward the active zone center during PHP without changes in total Unc-13 protein levels.","method":"MiMIC-based endogenous GFSTF tagging of all Unc-13 isoforms, structured-illumination microscopy, localization microscopy with HDBSCAN clustering, two-electrode voltage-clamp electrophysiology","journal":"Frontiers in cellular neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — endogenous tagging preserving function (confirmed electrophysiologically) with super-resolution spatial analysis, single lab","pmids":["36589286"],"is_preprint":false},{"year":2022,"finding":"Munc13-2 (UNC13B) is selectively enriched at presynaptic active zones of hippocampal pyramidal cell synapses onto mGluR1α+ interneurons via Elfn1-dependent trans-synaptic recruitment; conditional deletion of Munc13-2 from CA1 pyramidal cells does not affect unitary EPSC amplitude or short-term facilitation at this connection, indicating Munc13-1 alone is sufficient for low release probability at these synapses.","method":"Conditional Munc13-2 knockout in CA1 pyramidal cells, paired whole-cell recordings, immunofluorescence quantification of Munc13-2 and mGluR7 at identified synapses, Elfn1 knockout comparison","journal":"Frontiers in synaptic neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional knockout with quantitative immunofluorescence and electrophysiology, single lab; the negative electrophysiological result is itself mechanistically informative","pmids":["35221979"],"is_preprint":false},{"year":2023,"finding":"CLA-1 (Clarinet) recruits the priming factor UNC-13 to active zones via a RIMB-1-independent mechanism in C. elegans; CLA-1 acts in concert with UNC-10/RIM to regulate UNC-13 localization and presynaptic neurotransmitter release.","method":"Electrophysiology (C. elegans NMJ), electron microscopy, quantitative fluorescence imaging of UNC-13 localization in cla-1 and unc-10 null and double mutants","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (electrophysiology, EM, imaging) with genetic epistasis, single lab","pmids":["37186867"],"is_preprint":false},{"year":2024,"finding":"UNC13B localizes within cellular vesicles and positively regulates lysosome formation in Wilms' tumor cells; UNC13B knockdown reduces lysosome levels and increases doxorubicin-induced apoptosis, demonstrating a role for UNC13B in lysosomal regulation that confers drug resistance.","method":"shRNA-mediated knockdown, Lyso-Tracker staining, immunofluorescence localization, CCK-8 viability assay, flow cytometry for apoptosis, Western blot","journal":"Oncology letters","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single knockdown approach with descriptive imaging; lysosomal role is new but not mechanistically dissected beyond correlation","pmids":["39091580"],"is_preprint":false},{"year":2025,"finding":"Octopamine-induced DAG signaling causes rapid (within one minute) immobilization and nanoscale compaction of Unc13 into synaptic nanoclusters to potentiate evoked release; a point mutation in the C1 DAG-binding domain of endogenous Unc13 blocks plasticity-induced nanoscopic enrichment, phorbol ester-induced potentiation, and reduces Ca2+ sensitivity of release.","method":"Live single-molecule imaging of endogenously tagged Unc13 at Drosophila NMJ, endogenous C1-domain point mutation via CRISPR, electrophysiology (TEVC), phorbol ester pharmacology, presynaptic knockdown","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — endogenous CRISPR point mutation at functionally defined domain combined with live single-molecule imaging and electrophysiology; multiple orthogonal methods in one study","pmids":["40833403"],"is_preprint":false}],"current_model":"UNC13B/Munc13-2 is a presynaptic peripheral membrane protein whose C1 domain binds diacylglycerol/phorbol esters to translocate it to the plasma membrane, where its MHD2 domain interacts with syntaxin (promoting syntaxin's open conformation) and with GTP-bound Rab34 at the Golgi; it acts as an essential synaptic vesicle priming factor by converting morphologically docked but fusion-incompetent vesicles into a release-ready state, positions itself at defined nanoscale distances from Ca2+ channels via isoform-specific active zone scaffold interactions (Syd-1/Liprin-α for the B isoform, Bruchpilot/RIM-BP for the A isoform), and its synaptic abundance is regulated by proteasomal degradation downstream of converging cAMP/PKA and DAG/PLC signaling pathways, while in non-neuronal cells it additionally mediates constitutive secretory granule priming and lysosome positioning via Rab34."},"narrative":{"mechanistic_narrative":"UNC13B/Munc13-2 is a presynaptic peripheral membrane protein that serves as an essential synaptic vesicle priming factor, converting morphologically docked but fusion-incompetent vesicles into a release-ready state [PMID:10526333, PMID:10526334, PMID:16885217]. Its conserved C1 domain is a stereospecific, zinc- and phospholipid-dependent receptor for diacylglycerol and phorbol esters, coupling it to Gq/PLC signaling that potentiates neurotransmitter release [PMID:2062851, PMID:1445255, PMID:7537738, PMID:10571228]. Mechanistically, UNC13B acts upstream of syntaxin: it promotes the open conformation of syntaxin so that a constitutively open syntaxin mutant bypasses the priming requirement, and it transiently displaces Munc18 from syntaxin to license SNARE complex assembly, with Munc18-1 templating fusion downstream [PMID:11460165, PMID:10366611, PMID:28821673]. A C-terminal MHD2 domain mediates the direct interaction with syntaxin that is needed for evoked fusion, separable from the priming step [PMID:8999968, PMID:16271476]. The protein is intramolecularly autoinhibited by an X region, the C1 domain, and the C2B domain; removing these yields a hyperactive protein with increased release probability and Ca2+ sensitivity [PMID:31509756]. Isoform-specific active-zone scaffolds position UNC13B at defined nanoscale distances from Ca2+ channels — the B isoform is recruited by Syd-1/Liprin-α (~120 nm) while the A isoform is positioned by Bruchpilot/RIM-BP (~70 nm) — so that positioning dictates release probability and kinetics, with additional recruitment by CLA-1/UNC-10 and trans-synaptic Elfn1 [PMID:27526206, PMID:37186867, PMID:35221979]. In mammals, Munc13-2 sets basal release probability at hippocampal mossy fiber synapses and underlies strain-dependent presynaptic differences, and DAG-driven nanoscale compaction of the protein acutely potentiates release [PMID:19700493, PMID:27798178, PMID:40833403]. Beyond neurons, UNC13B functions as an effector of GTP-bound Rab34 through its MHD2 domain to mediate constitutive secretory granule priming and intracellular vesicle/lysosome positioning [PMID:16138900, PMID:18258655, PMID:19641095].","teleology":[{"year":1991,"claim":"Established the biochemical identity of the UNC-13 lipid-sensing module, answering how the protein could be coupled to second-messenger signaling.","evidence":"Radioligand phorbol ester binding and DAG competition with recombinant C1/C2-region domain","pmids":["2062851","1445255","7537738"],"confidence":"High","gaps":["Did not address the cellular consequence of DAG binding","Used the C. elegans ortholog, not mammalian UNC13B directly"]},{"year":1995,"claim":"Identified UNC13B/Munc13-2 as a mammalian UNC-13 homologue and localized it as a peripheral plasma-membrane protein, distinguishing it from synaptic vesicle components.","evidence":"Molecular cloning, Western blot, and synaptosome subcellular fractionation of rat brain","pmids":["7559667"],"confidence":"Medium","gaps":["Antibody-based localization from a single lab","No functional assay of UNC13B in this study"]},{"year":1997,"claim":"Defined a direct molecular interaction between the Munc13 family and syntaxin, providing a physical link to the SNARE machinery.","evidence":"Yeast two-hybrid, GST pulldown, and co-IP on Munc13-1/syntaxin","pmids":["8999968"],"confidence":"High","gaps":["Performed on the paralog Munc13-1, not UNC13B directly","Functional consequence of the interaction not yet defined"]},{"year":1999,"claim":"Defined the core cellular function of UNC-13 as a post-docking priming factor and placed it downstream of a Gq/PLC/DAG signaling cascade requiring DAG binding.","evidence":"Null-mutant electrophysiology and EM in C. elegans and Drosophila, plus genetic epistasis with EGL-30/EGL-8 and DAG-binding-dead rescue","pmids":["10526333","10526334","10571228","10677040","10366611"],"confidence":"High","gaps":["Molecular nature of the priming reaction not resolved","How DAG binding mechanistically alters priming activity unknown"]},{"year":2001,"claim":"Resolved the molecular target of priming by showing UNC-13 acts to open syntaxin, since constitutively open syntaxin bypasses the UNC-13 requirement.","evidence":"Genetic epistasis with engineered open-syntaxin mutations in C. elegans, electrophysiology and behavior","pmids":["11460165"],"confidence":"High","gaps":["Direct structural mechanism of syntaxin opening not demonstrated","Did not separate priming from later fusion steps"]},{"year":2005,"claim":"Separated UNC-13's priming function from its fusion function and mapped vesicle priming to membrane-contacting vesicles within ~100 nm of dense projections.","evidence":"MHD2 mutagenesis with electrophysiology, and quantitative immunogold EM in C. elegans null mutants","pmids":["16271476","16885217"],"confidence":"High","gaps":["Distinct biochemical activities of priming vs fusion steps not reconstituted","How MHD2-syntaxin contact drives the fusion step unclear"]},{"year":2005,"claim":"Extended UNC13B function beyond neurons by identifying it as a DAG-activated effector of GTP-bound Rab34 at the Golgi.","evidence":"Bacterial two-hybrid, co-IP, nucleotide-state GST pulldown, GTP overlay, and MHD2 deletion","pmids":["16138900"],"confidence":"High","gaps":["Single lab","Downstream consequences of Rab34 binding for vesicle positioning not yet shown in this study"]},{"year":2008,"claim":"Demonstrated an isoform-specific, non-neuronal role: Munc13-2 is required for constitutive/baseline secretory granule priming distinct from agonist-regulated Munc13-4 secretion.","evidence":"Munc13-2 knockout mouse histology, EM, qPCR, and agonist stimulation in airway epithelium","pmids":["18258655"],"confidence":"High","gaps":["Did not establish whether Rab34 mediates the airway secretion phenotype","Molecular priming step in mucin granules not dissected"]},{"year":2009,"claim":"Linked the Rab34 interaction to a quantitative secretory output and to disease-relevant high-glucose signaling.","evidence":"siRNA knockdown of munc13-2/rab34 and MHD2-deletion with VSVG-GFP and fibronectin secretion assays in mesangial/HeLa cells","pmids":["19641095"],"confidence":"Medium","gaps":["Single lab","Mechanism connecting high glucose to UNC13B upregulation not defined"]},{"year":2009,"claim":"Established the mammalian neuronal phenotype: Munc13-2 sets basal release probability at a specific synapse type (mossy fibers).","evidence":"Knockout mouse patch-clamp electrophysiology with paired-pulse, frequency facilitation, and LTP protocols","pmids":["19700493"],"confidence":"High","gaps":["Why the requirement is restricted to mossy fibers not explained","No molecular readout of priming defect"]},{"year":2013,"claim":"Assigned the N-terminal C2A domain a role in active-zone localization, release probability, and spontaneous release, tying spatial proximity to Ca2+ entry to release kinetics.","evidence":"C2A deletion/mutagenesis with voltage-clamp electrophysiology and localization in C. elegans","pmids":["24220508"],"confidence":"High","gaps":["Binding partners of C2A at the active zone not fully identified here","Spontaneous vs evoked mechanistic separation incomplete"]},{"year":2016,"claim":"Showed that isoform-specific active-zone scaffolds position UNC13B at defined nanoscale distances from Ca2+ channels, with positioning determining release probability and kinetics.","evidence":"Super-resolution imaging, electrophysiology, EGTA chelation, and modeling with isoform-specific Drosophila nulls","pmids":["27526206"],"confidence":"High","gaps":["Mammalian conservation of the two-isoform positioning logic not tested","Direct binding interfaces with Syd-1/Liprin-α vs Bruchpilot/RIM-BP not mapped biochemically"]},{"year":2016,"claim":"Demonstrated that quantitative differences in Munc13-2 abundance drive natural variation in presynaptic release and short-term plasticity.","evidence":"In vivo shRNA knockdown, electrophysiology, protein quantification, and BXD QTL analysis in mouse amygdala","pmids":["27798178"],"confidence":"High","gaps":["Upstream regulator setting strain-specific Munc13-2 levels unidentified","Single brain region examined"]},{"year":2017,"claim":"Placed UNC13B upstream of Munc18-1 in a priming sequence in which Munc18 templates SNARE assembly, refining the order of the priming reaction.","evidence":"Genetic epistasis, electrophysiology, and liposome fusion reconstitution with gain-of-function Munc18 mutants","pmids":["28821673"],"confidence":"High","gaps":["Structural basis of the UNC13B-to-Munc18 handoff not resolved","Role of Tomosyn synergy in physiological priming unclear"]},{"year":2017,"claim":"Identified Doc2B and synaptotagmin-1 as functional partners requiring ubMunc13-2 for downstream dense-core vesicle priming in chromaffin cells.","evidence":"Doc2B mutagenesis with capacitance measurements and Ca2+ uncaging in Munc13-2 and synaptotagmin-1 deletion backgrounds","pmids":["29274147"],"confidence":"Medium","gaps":["Single lab","Direct physical interaction of Doc2B with ubMunc13-2 not demonstrated"]},{"year":2019,"claim":"Defined the autoinhibitory architecture of UNC13B, showing that the X region, C1, and C2B domains suppress release and that their removal hyperactivates via increased syntaxin opening.","evidence":"Systematic domain deletion, electrophysiology, Ca2+ sensitivity assays, and epistasis with open-syntaxin mutants in C. elegans","pmids":["31509756"],"confidence":"High","gaps":["Physiological signals relieving each inhibitory domain not all defined","Structural conformation of the autoinhibited state unresolved"]},{"year":2021,"claim":"Placed a synaptotagmin-7-mediated membrane-approach step upstream of Munc13-2-dependent dense-core vesicle priming.","evidence":"Synaptotagmin-7 knockout/overexpression with capacitance, TIRF vesicle-distance measurements, and Munc13-2 epistasis in chromaffin 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and voltage-clamp electrophysiology in Drosophila","pmids":["36589286"],"confidence":"Medium","gaps":["Single lab","Molecular trigger driving subcluster movement during PHP not identified"]},{"year":2024,"claim":"Reported a non-neuronal lysosomal role linking UNC13B to lysosome formation and drug resistance in tumor cells.","evidence":"shRNA knockdown, Lyso-Tracker staining, viability and apoptosis assays in Wilms' tumor cells","pmids":["39091580"],"confidence":"Low","gaps":["Correlative knockdown only; mechanism not dissected beyond association","Single lab and single cell model","Relationship to the Rab34 effector function not tested"]},{"year":2025,"claim":"Demonstrated that DAG signaling acutely drives C1-dependent immobilization and nanocluster compaction of endogenous UNC13B to potentiate evoked release, directly linking the founding lipid-binding activity to fast plasticity.","evidence":"Live single-molecule imaging of endogenously tagged Unc13, CRISPR C1-domain point mutation, 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affinity in a zinc- and phospholipid-dependent, stereospecific manner, and diacylglycerol competitively inhibits this binding, establishing UNC-13 as a DAG/phorbol ester receptor.\",\n      \"method\": \"Recombinant protein expression in E. coli, radioligand binding assay with [3H]phorbol ester, competitive inhibition with diacylglycerol\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro biochemical reconstitution with purified recombinant domain, replicated independently (PMIDs 2062851, 1445255, 7537738)\",\n      \"pmids\": [\"2062851\", \"1445255\", \"7537738\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Munc13-2 (UNC13B) is a mammalian homologue of C. elegans UNC-13 expressed in rat brain; it is a brain-specific large protein with conserved C1- and C2-domains and is enriched as a peripheral membrane protein in synaptosomes localized to plasma membranes but absent from synaptic vesicles.\",\n      \"method\": \"Molecular cloning, Western blot with specific antibodies, subcellular fractionation of rat brain synaptosomes\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — antibody-based subcellular fractionation plus cloning, single lab, two orthogonal methods\",\n      \"pmids\": [\"7559667\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Munc13-1 (the closest paralog, but the interaction paradigm is the founding mechanism for Munc13 family including Munc13-2/UNC13B) directly interacts with the N-terminal coiled-coil domain of syntaxin via its C terminus; through this interaction it associates with a subpopulation of the SNARE core complex (synaptobrevin/SNAP-25/syntaxin) but not with other syntaxin-interacting proteins.\",\n      \"method\": \"Yeast two-hybrid, in vitro GST pulldown, co-immunoprecipitation — three independent methods on Munc13-1/syntaxin interaction; the binding site in syntaxin overlaps with Munc18 binding site\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — three independent in vitro methods (Y2H, pulldown, co-IP) in one study establishing direct protein–protein interaction\",\n      \"pmids\": [\"8999968\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"UNC-13 (C. elegans) is required for a post-docking priming step of synaptic vesicle exocytosis: null mutants have morphologically docked vesicles but these are not competent for fusion as shown by absent evoked release and failure to release with hyperosmotic saline or in calcium-free solution.\",\n      \"method\": \"Whole-cell voltage-clamp electrophysiology at C. elegans NMJ, hyperosmotic saline stimulation, calcium-free recording, electron microscopy of synapse morphology\",\n      \"journal\": \"Nature neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — rigorous null-mutant electrophysiology with multiple stimulation paradigms, independently replicated in Drosophila and mouse\",\n      \"pmids\": [\"10526333\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Neurotransmitter release at C. elegans NMJs is facilitated by a presynaptic Gqα (EGL-30) → PLCβ (EGL-8) → DAG pathway, and this effect requires DAG binding to UNC-13: a mutation abolishing phorbol ester/DAG binding to UNC-13 blocks the stimulatory effect of phorbol esters on acetylcholine release.\",\n      \"method\": \"Genetic epistasis in C. elegans, phorbol ester pharmacology, constitutively membrane-targeted UNC-13 rescue, confocal imaging of UNC-13 localization\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis combined with pharmacology and domain-specific rescue, replicated in subsequent studies\",\n      \"pmids\": [\"10571228\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Serotonin inhibits acetylcholine release at C. elegans NMJs via GOA-1 (Gα0) and DGK-1 (DAG kinase), and this inhibition correlates with decreased abundance of UNC-13 at release sites; loss of GOA-1 leads to abnormally high levels of UNC-13 at nerve terminals.\",\n      \"method\": \"Aldicarb sensitivity assay in intact C. elegans, immunofluorescence quantification of UNC-13 at synapses, genetic epistasis with goa-1 and dgk-1 mutants\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis plus quantitative immunofluorescence, single lab\",\n      \"pmids\": [\"10677040\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"UNC-13 transiently interacts with the UNC-18–syntaxin complex and causes rapid displacement of UNC-18 from syntaxin, providing a mechanism by which UNC-13 modulates SNARE complex availability.\",\n      \"method\": \"Co-immunoprecipitation, GST pulldown (biochemical), genetic epistasis in C. elegans unc-13/unc-18/unc-64 double mutants\",\n      \"journal\": \"The Journal of neuroscience : the official journal of the Society for Neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal biochemical pulldown plus genetic epistasis, single lab\",\n      \"pmids\": [\"10366611\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Drosophila UNC-13 (Dunc-13) is essential for synaptic transmission at a post-docking priming step: null mutants accumulate docked vesicles at release sites but have no evoked or hyperosmotic-saline-evoked release.\",\n      \"method\": \"Electrophysiology (EJPs, miniature EJPs), hyperosmotic saline stimulation, electron microscopy of presynaptic terminals in Dunc-13 null Drosophila\",\n      \"journal\": \"Nature neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal methods (electrophysiology + EM) in null mutant, independently replicating C. elegans findings\",\n      \"pmids\": [\"10526334\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"UNC-13 primes synaptic vesicles by promoting the open conformation of syntaxin: an open-form syntaxin mutant (constitutively open) bypasses the requirement for UNC-13 in synaptic vesicle priming in C. elegans, placing UNC-13 upstream of syntaxin opening in the exocytic pathway.\",\n      \"method\": \"Genetic epistasis — engineered open-form syntaxin mutations introduced into C. elegans unc-13 null background; electrophysiology and behavioral rescue assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic epistasis with structure-informed mutations, clear bypass of null phenotype, replicated across multiple assays\",\n      \"pmids\": [\"11460165\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Synaptic levels of Drosophila UNC-13 (Dunc-13) are regulated by proteasome-mediated degradation downstream of both GαS/cAMP/PKA and Gαq/PLC/DAG pathways; both pathways converge to control synaptic UNC-13 abundance by modulating the rate of proteasomal degradation rather than translocation.\",\n      \"method\": \"Immunofluorescence quantification of Dunc-13 at NMJ boutons, pharmacological manipulation of cAMP/PKA and PLC/DAG pathways, proteasome inhibitor treatment in Drosophila\",\n      \"journal\": \"Journal of neurobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — quantitative imaging with pharmacological and genetic pathway perturbations, single lab\",\n      \"pmids\": [\"12532395\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"UNC-13 interaction with syntaxin is required for nerve-evoked synaptic vesicle fusion but not for vesicle priming: a double mutation in MHD2 (F1000A/K1002A) that disrupts the UNC-13/syntaxin interaction reduces evoked EPSCs but leaves the primed vesicle pool normal, indicating UNC-13 regulates multiple steps of the vesicle cycle.\",\n      \"method\": \"Site-directed mutagenesis of UNC-13 MHD2 domain, whole-cell electrophysiology at C. elegans NMJ, behavioral rescue assays\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — active-site mutagenesis combined with electrophysiology, clear separation of priming from fusion-step function\",\n      \"pmids\": [\"16271476\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Diacylglycerol-activated Hmunc13 (UNC13B) translocates to the Golgi and binds GTP-bound Rab34 via its MHD2 domain; this interaction requires the GTP-loaded form of Rab34, establishing UNC13B as an effector of Rab34 in intracellular vesicle/lysosome positioning.\",\n      \"method\": \"Bacterial two-hybrid screen, co-immunoprecipitation from cell lysates, GST pulldown with GTP/GDP-loaded Rab34 mutants (Q111L, T66N), radioactive GTP overlay assay, deletion mutagenesis of MHD2\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple orthogonal biochemical methods (Y2H, co-IP, GST pulldown with nucleotide-state mutants, mutagenesis), single lab\",\n      \"pmids\": [\"16138900\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"UNC-13 localizes to the plasma membrane within ~100 nm of dense projections at C. elegans NMJs; in unc-13 null mutants, synaptic vesicles that normally contact the plasma membrane are nearly absent, identifying membrane-contacting vesicles as morphological correlates of primed vesicles and defining UNC-13's spatial domain for priming.\",\n      \"method\": \"Rapid physical fixation, immunogold electron microscopy, high-resolution morphometric analysis at C. elegans NMJ\",\n      \"journal\": \"The Journal of neuroscience : the official journal of the Society for Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — quantitative immunogold EM with null mutant comparison, precise nanoscale spatial mapping with functional consequence\",\n      \"pmids\": [\"16885217\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Munc13-2 (UNC13B) knockout mice show accumulation of mucins (Muc5b) in Clara cells and goblet cells of multiple mucosal tissues, demonstrating that Munc13-2 is required for constitutive/baseline priming and secretion of a specific population of secretory granules; agonist-regulated secretion via Munc13-4 is preserved, revealing isoform-specific priming requirements.\",\n      \"method\": \"Munc13-2 knockout mouse histology (AB/PAS staining), BAL cell counts, qPCR, electron microscopy of Clara cells, agonist stimulation (ATP/UTP) in Munc13-2−/− airways\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — knockout mouse with multiple orthogonal readouts (histology, EM, qPCR, pharmacology), clear cell-biological phenotype\",\n      \"pmids\": [\"18258655\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Munc13-2 (UNC13B) upregulation by high glucose in mesangial cells increases constitutive protein secretion via Rab34 interaction; siRNA knockdown of munc13-2 or rab34 abolishes high-glucose-induced VSVG-GFP secretion and fibronectin secretion; deletion of MHD2 abolishes the effect, confirming the MHD2–Rab34 interaction as the mechanistic basis.\",\n      \"method\": \"siRNA knockdown in rat mesangial cells, VSVG-GFP secretion assay, fibronectin secretion assay, MHD2-deletion mutant transfection in HeLa cells\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown and domain-deletion mutagenesis with functional secretion assay, single lab\",\n      \"pmids\": [\"19641095\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Munc13-2 (UNC13B) is essential for normal release probability at hippocampal mossy fiber synapses: Munc13-2 knockout mice show strongly increased paired-pulse and frequency facilitation at mossy fiber synapses, consistent with reduced basal release probability, while mossy fiber LTP is unaffected; other hippocampal synapse types are unaffected.\",\n      \"method\": \"Munc13-2 knockout mouse electrophysiology — patch-clamp recordings of mossy fiber synapses, paired-pulse and frequency facilitation protocols, LTP induction\",\n      \"journal\": \"Cerebral cortex (New York, N.Y. : 1991)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — knockout mouse with rigorous electrophysiological characterization at multiple synapse types, clear isoform-specific phenotype\",\n      \"pmids\": [\"19700493\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The N-terminal C2A domain of UNC-13 regulates active zone localization of UNC-13, release probability of evoked release, and is specifically required for spontaneous release; proximity of UNC-13 to Ca2+ entry sites mediated by the C2A-containing N-terminus accelerates neurotransmitter release kinetics.\",\n      \"method\": \"C2A domain deletion and mutagenesis in C. elegans, whole-cell voltage-clamp electrophysiology, kinetic analysis of synaptic vesicle release, immunofluorescence localization\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — domain mutagenesis combined with quantitative electrophysiology and localization, multiple orthogonal assays in one study\",\n      \"pmids\": [\"24220508\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"NLP-12 neuropeptide potentiates tonic ACh release through a Gαq/PLCβ-independent DAG pathway requiring DAG binding to UNC-13L (but not UNC-13S), while potentiation of evoked release uses both UNC-13 isoforms via the Gαq/PLCβ/DAG pathway, demonstrating isoform-specific and pathway-specific roles of UNC-13 in tonic versus evoked release.\",\n      \"method\": \"Genetic epistasis in C. elegans (egl-30, egl-8 mutants combined with unc-13 isoform-specific mutants), aldicarb sensitivity assay, electrophysiology\",\n      \"journal\": \"The Journal of neuroscience : the official journal of the Society for Neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic epistasis with isoform-specific mutants, single lab\",\n      \"pmids\": [\"25609620\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The Drosophila Unc13B isoform is recruited to nascent active zones by scaffolding proteins Syd-1 and Liprin-α and localizes ~120 nm from Ca2+ channels, while Unc13A is positioned ~70 nm from Ca2+ channels by Bruchpilot/RIM-binding protein complexes and is responsible for docking SVs at that distance; Unc13A null mutants show inefficient, delayed, and EGTA-supersensitive release, demonstrating that isoform positioning defines release probability and kinetics.\",\n      \"method\": \"Super-resolution microscopy (STORM/STED), intravital imaging in Drosophila, electrophysiology (TEVC), EGTA chelation, mathematical modeling, isoform-specific null mutants\",\n      \"journal\": \"Nature neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — super-resolution imaging + electrophysiology + mathematical modeling + multiple genetic nulls in a single rigorous study\",\n      \"pmids\": [\"27526206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Munc13-2 (UNC13B) level differences between C57BL/6J and DBA/2J mice underlie strain-dependent differences in presynaptic release probability, vesicle recycling, and short-term plasticity at BLA glutamatergic synapses; shRNA knockdown of Munc13-2 in B6 mice recapitulates the DBA/2J presynaptic phenotype.\",\n      \"method\": \"shRNA knockdown in vivo, electrophysiology (paired-pulse, frequency facilitation), biochemical quantification of presynaptic proteins, BXD recombinant inbred strain in silico QTL analysis\",\n      \"journal\": \"The Journal of neuroscience : the official journal of the Society for Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — shRNA knockdown with electrophysiological phenotyping, supported by in silico QTL mapping and protein quantification\",\n      \"pmids\": [\"27798178\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Munc18-1/UNC-18 primes vesicle fusion downstream of Munc13-1/UNC-13 by templating SNARE complex assembly; a gain-of-function UNC-18(P334A) mutation partially bypasses the requirement for UNC-13, and this bypass is synergistically enhanced by loss of Tomosyn/TOM-1; Munc18-1(P335A) shows enhanced SNARE complex formation and partially bypasses Munc13-1 requirement in liposome fusion assays.\",\n      \"method\": \"Genetic epistasis in C. elegans, electrophysiology (C. elegans and mammalian neurons), liposome fusion reconstitution assay, biochemical SNARE complex formation assay\",\n      \"journal\": \"The Journal of neuroscience : the official journal of the Society for Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution in liposome fusion assay plus genetic epistasis plus electrophysiology, multiple orthogonal methods placing UNC-13 upstream of UNC-18\",\n      \"pmids\": [\"28821673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Doc2B requires interaction with ubMunc13-2 (a ubiquitous isoform of UNC13B/Munc13-2) for its downstream vesicle priming function in chromaffin cells: Doc2B Ca2+-binding mutations and SNARE-binding mutations block distinct priming steps, and the downstream priming step is dependent on both ubMunc13-2 and synaptotagmin-1.\",\n      \"method\": \"Overexpression and mutagenesis of Doc2B in mouse chromaffin cells, capacitance measurements, Ca2+ uncaging, genetic deletion of synaptotagmin-1 and Munc13-2\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis in primary cells with functional exocytosis readout; Munc13-2 involvement established by genetic deletion, single lab\",\n      \"pmids\": [\"29274147\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"UNC-13L has three inhibitory domains (X region between C2A and C1, C1 domain, and C2B domain) that suppress synaptic vesicle exocytosis; removing all three produces a hyperactive UNC-13 with dramatically increased neurotransmitter release, Ca2+ sensitivity, and release probability, and this hyperactivity increases syntaxin open probability to enhance tonic release.\",\n      \"method\": \"Domain deletion mutagenesis in C. elegans, electrophysiology, Ca2+ sensitivity assay, synaptic recovery/replenishment kinetics, double mutant epistasis with syntaxin open-form mutants\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — systematic domain deletion mutagenesis combined with multiple electrophysiology assays and epistasis, defining inhibitory domain architecture\",\n      \"pmids\": [\"31509756\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Synaptotagmin-7 promotes ubMunc13-2- and phorbol ester-dependent priming of dense-core vesicles, especially at low resting Ca2+; without synaptotagmin-7, vesicles accumulate 20–40 nm from the membrane rather than in close (<6 nm) apposition, indicating synaptotagmin-7 mediates a membrane-approach step upstream of Munc13-2-dependent priming.\",\n      \"method\": \"Synaptotagmin-7 knockout and overexpression in mouse chromaffin cells, capacitance measurements, TIRF microscopy with vesicle distance measurements, phorbol ester stimulation, genetic epistasis with Munc13-2\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic deletion combined with TIRF nanoscale distance measurements and functional exocytosis assay; Munc13-2 involvement established by epistasis, single lab\",\n      \"pmids\": [\"33749593\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Endogenously tagged Unc-13 (all isoforms) in Drosophila undergoes nanoscale reorganization during presynaptic homeostatic potentiation (PHP): localization microscopy shows Unc-13 subclusters move toward the active zone center during PHP without changes in total Unc-13 protein levels.\",\n      \"method\": \"MiMIC-based endogenous GFSTF tagging of all Unc-13 isoforms, structured-illumination microscopy, localization microscopy with HDBSCAN clustering, two-electrode voltage-clamp electrophysiology\",\n      \"journal\": \"Frontiers in cellular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — endogenous tagging preserving function (confirmed electrophysiologically) with super-resolution spatial analysis, single lab\",\n      \"pmids\": [\"36589286\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Munc13-2 (UNC13B) is selectively enriched at presynaptic active zones of hippocampal pyramidal cell synapses onto mGluR1α+ interneurons via Elfn1-dependent trans-synaptic recruitment; conditional deletion of Munc13-2 from CA1 pyramidal cells does not affect unitary EPSC amplitude or short-term facilitation at this connection, indicating Munc13-1 alone is sufficient for low release probability at these synapses.\",\n      \"method\": \"Conditional Munc13-2 knockout in CA1 pyramidal cells, paired whole-cell recordings, immunofluorescence quantification of Munc13-2 and mGluR7 at identified synapses, Elfn1 knockout comparison\",\n      \"journal\": \"Frontiers in synaptic neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional knockout with quantitative immunofluorescence and electrophysiology, single lab; the negative electrophysiological result is itself mechanistically informative\",\n      \"pmids\": [\"35221979\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CLA-1 (Clarinet) recruits the priming factor UNC-13 to active zones via a RIMB-1-independent mechanism in C. elegans; CLA-1 acts in concert with UNC-10/RIM to regulate UNC-13 localization and presynaptic neurotransmitter release.\",\n      \"method\": \"Electrophysiology (C. elegans NMJ), electron microscopy, quantitative fluorescence imaging of UNC-13 localization in cla-1 and unc-10 null and double mutants\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (electrophysiology, EM, imaging) with genetic epistasis, single lab\",\n      \"pmids\": [\"37186867\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"UNC13B localizes within cellular vesicles and positively regulates lysosome formation in Wilms' tumor cells; UNC13B knockdown reduces lysosome levels and increases doxorubicin-induced apoptosis, demonstrating a role for UNC13B in lysosomal regulation that confers drug resistance.\",\n      \"method\": \"shRNA-mediated knockdown, Lyso-Tracker staining, immunofluorescence localization, CCK-8 viability assay, flow cytometry for apoptosis, Western blot\",\n      \"journal\": \"Oncology letters\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single knockdown approach with descriptive imaging; lysosomal role is new but not mechanistically dissected beyond correlation\",\n      \"pmids\": [\"39091580\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Octopamine-induced DAG signaling causes rapid (within one minute) immobilization and nanoscale compaction of Unc13 into synaptic nanoclusters to potentiate evoked release; a point mutation in the C1 DAG-binding domain of endogenous Unc13 blocks plasticity-induced nanoscopic enrichment, phorbol ester-induced potentiation, and reduces Ca2+ sensitivity of release.\",\n      \"method\": \"Live single-molecule imaging of endogenously tagged Unc13 at Drosophila NMJ, endogenous C1-domain point mutation via CRISPR, electrophysiology (TEVC), phorbol ester pharmacology, presynaptic knockdown\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — endogenous CRISPR point mutation at functionally defined domain combined with live single-molecule imaging and electrophysiology; multiple orthogonal methods in one study\",\n      \"pmids\": [\"40833403\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"UNC13B/Munc13-2 is a presynaptic peripheral membrane protein whose C1 domain binds diacylglycerol/phorbol esters to translocate it to the plasma membrane, where its MHD2 domain interacts with syntaxin (promoting syntaxin's open conformation) and with GTP-bound Rab34 at the Golgi; it acts as an essential synaptic vesicle priming factor by converting morphologically docked but fusion-incompetent vesicles into a release-ready state, positions itself at defined nanoscale distances from Ca2+ channels via isoform-specific active zone scaffold interactions (Syd-1/Liprin-α for the B isoform, Bruchpilot/RIM-BP for the A isoform), and its synaptic abundance is regulated by proteasomal degradation downstream of converging cAMP/PKA and DAG/PLC signaling pathways, while in non-neuronal cells it additionally mediates constitutive secretory granule priming and lysosome positioning via Rab34.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"UNC13B/Munc13-2 is a presynaptic peripheral membrane protein that serves as an essential synaptic vesicle priming factor, converting morphologically docked but fusion-incompetent vesicles into a release-ready state [#3, #7, #12]. Its conserved C1 domain is a stereospecific, zinc- and phospholipid-dependent receptor for diacylglycerol and phorbol esters, coupling it to Gq/PLC signaling that potentiates neurotransmitter release [#0, #4]. Mechanistically, UNC13B acts upstream of syntaxin: it promotes the open conformation of syntaxin so that a constitutively open syntaxin mutant bypasses the priming requirement, and it transiently displaces Munc18 from syntaxin to license SNARE complex assembly, with Munc18-1 templating fusion downstream [#8, #6, #20]. A C-terminal MHD2 domain mediates the direct interaction with syntaxin that is needed for evoked fusion, separable from the priming step [#2, #10]. The protein is intramolecularly autoinhibited by an X region, the C1 domain, and the C2B domain; removing these yields a hyperactive protein with increased release probability and Ca2+ sensitivity [#22]. Isoform-specific active-zone scaffolds position UNC13B at defined nanoscale distances from Ca2+ channels — the B isoform is recruited by Syd-1/Liprin-\\u03b1 (~120 nm) while the A isoform is positioned by Bruchpilot/RIM-BP (~70 nm) — so that positioning dictates release probability and kinetics, with additional recruitment by CLA-1/UNC-10 and trans-synaptic Elfn1 [#18, #26, #25]. In mammals, Munc13-2 sets basal release probability at hippocampal mossy fiber synapses and underlies strain-dependent presynaptic differences, and DAG-driven nanoscale compaction of the protein acutely potentiates release [#15, #19, #28]. Beyond neurons, UNC13B functions as an effector of GTP-bound Rab34 through its MHD2 domain to mediate constitutive secretory granule priming and intracellular vesicle/lysosome positioning [#11, #13, #14].\",\n  \"teleology\": [\n    {\n      \"year\": 1991,\n      \"claim\": \"Established the biochemical identity of the UNC-13 lipid-sensing module, answering how the protein could be coupled to second-messenger signaling.\",\n      \"evidence\": \"Radioligand phorbol ester binding and DAG competition with recombinant C1/C2-region domain\",\n      \"pmids\": [\"2062851\", \"1445255\", \"7537738\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address the cellular consequence of DAG binding\", \"Used the C. elegans ortholog, not mammalian UNC13B directly\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Identified UNC13B/Munc13-2 as a mammalian UNC-13 homologue and localized it as a peripheral plasma-membrane protein, distinguishing it from synaptic vesicle components.\",\n      \"evidence\": \"Molecular cloning, Western blot, and synaptosome subcellular fractionation of rat brain\",\n      \"pmids\": [\"7559667\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Antibody-based localization from a single lab\", \"No functional assay of UNC13B in this study\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Defined a direct molecular interaction between the Munc13 family and syntaxin, providing a physical link to the SNARE machinery.\",\n      \"evidence\": \"Yeast two-hybrid, GST pulldown, and co-IP on Munc13-1/syntaxin\",\n      \"pmids\": [\"8999968\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Performed on the paralog Munc13-1, not UNC13B directly\", \"Functional consequence of the interaction not yet defined\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Defined the core cellular function of UNC-13 as a post-docking priming factor and placed it downstream of a Gq/PLC/DAG signaling cascade requiring DAG binding.\",\n      \"evidence\": \"Null-mutant electrophysiology and EM in C. elegans and Drosophila, plus genetic epistasis with EGL-30/EGL-8 and DAG-binding-dead rescue\",\n      \"pmids\": [\"10526333\", \"10526334\", \"10571228\", \"10677040\", \"10366611\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular nature of the priming reaction not resolved\", \"How DAG binding mechanistically alters priming activity unknown\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Resolved the molecular target of priming by showing UNC-13 acts to open syntaxin, since constitutively open syntaxin bypasses the UNC-13 requirement.\",\n      \"evidence\": \"Genetic epistasis with engineered open-syntaxin mutations in C. elegans, electrophysiology and behavior\",\n      \"pmids\": [\"11460165\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct structural mechanism of syntaxin opening not demonstrated\", \"Did not separate priming from later fusion steps\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Separated UNC-13's priming function from its fusion function and mapped vesicle priming to membrane-contacting vesicles within ~100 nm of dense projections.\",\n      \"evidence\": \"MHD2 mutagenesis with electrophysiology, and quantitative immunogold EM in C. elegans null mutants\",\n      \"pmids\": [\"16271476\", \"16885217\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Distinct biochemical activities of priming vs fusion steps not reconstituted\", \"How MHD2-syntaxin contact drives the fusion step unclear\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Extended UNC13B function beyond neurons by identifying it as a DAG-activated effector of GTP-bound Rab34 at the Golgi.\",\n      \"evidence\": \"Bacterial two-hybrid, co-IP, nucleotide-state GST pulldown, GTP overlay, and MHD2 deletion\",\n      \"pmids\": [\"16138900\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Single lab\", \"Downstream consequences of Rab34 binding for vesicle positioning not yet shown in this study\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Demonstrated an isoform-specific, non-neuronal role: Munc13-2 is required for constitutive/baseline secretory granule priming distinct from agonist-regulated Munc13-4 secretion.\",\n      \"evidence\": \"Munc13-2 knockout mouse histology, EM, qPCR, and agonist stimulation in airway epithelium\",\n      \"pmids\": [\"18258655\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish whether Rab34 mediates the airway secretion phenotype\", \"Molecular priming step in mucin granules not dissected\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Linked the Rab34 interaction to a quantitative secretory output and to disease-relevant high-glucose signaling.\",\n      \"evidence\": \"siRNA knockdown of munc13-2/rab34 and MHD2-deletion with VSVG-GFP and fibronectin secretion assays in mesangial/HeLa cells\",\n      \"pmids\": [\"19641095\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Mechanism connecting high glucose to UNC13B upregulation not defined\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Established the mammalian neuronal phenotype: Munc13-2 sets basal release probability at a specific synapse type (mossy fibers).\",\n      \"evidence\": \"Knockout mouse patch-clamp electrophysiology with paired-pulse, frequency facilitation, and LTP protocols\",\n      \"pmids\": [\"19700493\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why the requirement is restricted to mossy fibers not explained\", \"No molecular readout of priming defect\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Assigned the N-terminal C2A domain a role in active-zone localization, release probability, and spontaneous release, tying spatial proximity to Ca2+ entry to release kinetics.\",\n      \"evidence\": \"C2A deletion/mutagenesis with voltage-clamp electrophysiology and localization in C. elegans\",\n      \"pmids\": [\"24220508\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Binding partners of C2A at the active zone not fully identified here\", \"Spontaneous vs evoked mechanistic separation incomplete\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showed that isoform-specific active-zone scaffolds position UNC13B at defined nanoscale distances from Ca2+ channels, with positioning determining release probability and kinetics.\",\n      \"evidence\": \"Super-resolution imaging, electrophysiology, EGTA chelation, and modeling with isoform-specific Drosophila nulls\",\n      \"pmids\": [\"27526206\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mammalian conservation of the two-isoform positioning logic not tested\", \"Direct binding interfaces with Syd-1/Liprin-\\u03b1 vs Bruchpilot/RIM-BP not mapped biochemically\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Demonstrated that quantitative differences in Munc13-2 abundance drive natural variation in presynaptic release and short-term plasticity.\",\n      \"evidence\": \"In vivo shRNA knockdown, electrophysiology, protein quantification, and BXD QTL analysis in mouse amygdala\",\n      \"pmids\": [\"27798178\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream regulator setting strain-specific Munc13-2 levels unidentified\", \"Single brain region examined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Placed UNC13B upstream of Munc18-1 in a priming sequence in which Munc18 templates SNARE assembly, refining the order of the priming reaction.\",\n      \"evidence\": \"Genetic epistasis, electrophysiology, and liposome fusion reconstitution with gain-of-function Munc18 mutants\",\n      \"pmids\": [\"28821673\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the UNC13B-to-Munc18 handoff not resolved\", \"Role of Tomosyn synergy in physiological priming unclear\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identified Doc2B and synaptotagmin-1 as functional partners requiring ubMunc13-2 for downstream dense-core vesicle priming in chromaffin cells.\",\n      \"evidence\": \"Doc2B mutagenesis with capacitance measurements and Ca2+ uncaging in Munc13-2 and synaptotagmin-1 deletion backgrounds\",\n      \"pmids\": [\"29274147\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Direct physical interaction of Doc2B with ubMunc13-2 not demonstrated\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined the autoinhibitory architecture of UNC13B, showing that the X region, C1, and C2B domains suppress release and that their removal hyperactivates via increased syntaxin opening.\",\n      \"evidence\": \"Systematic domain deletion, electrophysiology, Ca2+ sensitivity assays, and epistasis with open-syntaxin mutants in C. elegans\",\n      \"pmids\": [\"31509756\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological signals relieving each inhibitory domain not all defined\", \"Structural conformation of the autoinhibited state unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Placed a synaptotagmin-7-mediated membrane-approach step upstream of Munc13-2-dependent dense-core vesicle priming.\",\n      \"evidence\": \"Synaptotagmin-7 knockout/overexpression with capacitance, TIRF vesicle-distance measurements, and Munc13-2 epistasis in chromaffin cells\",\n      \"pmids\": [\"33749593\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Whether synaptotagmin-7 physically delivers vesicles to Munc13-2 not shown directly\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showed active-zone recruitment of UNC13B is governed by trans-synaptic and scaffold cues (Elfn1, CLA-1/UNC-10) and that Munc13-1 can be sufficient at some low-Pr synapses.\",\n      \"evidence\": \"Conditional knockout, paired recordings, immunofluorescence in mouse hippocampus, and EM/imaging epistasis with cla-1/unc-10 in C. elegans\",\n      \"pmids\": [\"35221979\", \"37186867\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct binding of UNC13B to Elfn1 or CLA-1 not biochemically established\", \"Functional non-redundancy of Munc13-1 vs UNC13B incompletely mapped across synapse types\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Revealed that UNC13B undergoes nanoscale spatial reorganization during presynaptic homeostatic potentiation without changes in total protein level.\",\n      \"evidence\": \"Endogenous GFSTF tagging, SIM/localization microscopy with HDBSCAN clustering, and voltage-clamp electrophysiology in Drosophila\",\n      \"pmids\": [\"36589286\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Molecular trigger driving subcluster movement during PHP not identified\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Reported a non-neuronal lysosomal role linking UNC13B to lysosome formation and drug resistance in tumor cells.\",\n      \"evidence\": \"shRNA knockdown, Lyso-Tracker staining, viability and apoptosis assays in Wilms' tumor cells\",\n      \"pmids\": [\"39091580\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Correlative knockdown only; mechanism not dissected beyond association\", \"Single lab and single cell model\", \"Relationship to the Rab34 effector function not tested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Demonstrated that DAG signaling acutely drives C1-dependent immobilization and nanocluster compaction of endogenous UNC13B to potentiate evoked release, directly linking the founding lipid-binding activity to fast plasticity.\",\n      \"evidence\": \"Live single-molecule imaging of endogenously tagged Unc13, CRISPR C1-domain point mutation, electrophysiology, and phorbol ester pharmacology in Drosophila\",\n      \"pmids\": [\"40833403\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular partners anchoring the compacted nanocluster not identified\", \"Whether mammalian UNC13B uses the same C1-driven mechanism not shown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the neuronal priming/syntaxin-opening activity and the non-neuronal Rab34-effector/lysosomal functions are integrated within a single protein, and the structural basis of autoinhibition relief and nanocluster assembly, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified structural model of the autoinhibited vs active state\", \"Mammalian conservation of isoform-specific Ca2+-channel positioning untested\", \"Mechanistic basis of the lysosomal/tumor phenotype undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 4, 28]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [6, 8, 20]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [8, 10, 22]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 12]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [11]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [27]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [3, 7, 15]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [11, 13, 14]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4, 28]}\n    ],\n    \"complexes\": [\"presynaptic active zone\"],\n    \"partners\": [\"STX1A\", \"STXBP1\", \"RAB34\", \"DOC2B\", \"SYT7\", \"SYT1\", \"RIMS1\", \"ELFN1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":8,"faith_pct":87.5}}