{"gene":"GRM7","run_date":"2026-06-10T01:55:21","timeline":{"discoveries":[{"year":1994,"finding":"mGluR7 is a Gi/o-coupled GPCR that inhibits forskolin-stimulated cyclic AMP accumulation in response to agonist (L-AP4, L-serine-O-phosphate) in transfected CHO cells, establishing it as a negatively coupled adenylyl cyclase receptor.","method":"Heterologous expression in CHO cells with cAMP accumulation assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct functional reconstitution in transfected cells, foundational characterization replicated across subsequent studies","pmids":["8288585"],"is_preprint":false},{"year":1995,"finding":"mGluR7 protein is localized presynaptically in axon terminals of primary afferent fibers projecting to laminae I and II of the spinal dorsal horn, as demonstrated by immunoreactivity reduced after dorsal rhizotomy.","method":"Immunohistochemistry with dorsal rhizotomy lesion; electron microscopy","journal":"Neuroscience letters","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct localization with lesion control confirming presynaptic terminal origin, replicated in subsequent EM studies","pmids":["8787837"],"is_preprint":false},{"year":1996,"finding":"mGluR7 is localized both presynaptically as an autoreceptor at cone bipolar cell ribbon synapses and postsynaptically in amacrine cells in the rat retina, with the presynaptic pool restricted to one half of the active zone.","method":"Electron microscopy immunohistochemistry with double-labeling in rat retina","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — EM-level subcellular localization with double-labeling, defining two distinct active sites","pmids":["8764662"],"is_preprint":false},{"year":1998,"finding":"Alternative splicing of mGluR7 produces a 'b' isoform (mGluR7b) with a different C-terminal sequence; both mGluR7a and mGluR7b show identical pharmacological profiles when expressed in heterologous systems, indicating the C-terminal differences do not alter agonist pharmacology.","method":"RT-PCR cloning, expression in HEK293 cells and Xenopus oocytes with pharmacological profiling","journal":"The European journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct functional characterization of splice variants in two heterologous systems, single lab","pmids":["9875342"],"is_preprint":false},{"year":1999,"finding":"mGluR7-like receptor activation by high concentrations of L-AP4 inhibits NMDA-induced glutamate release and excitotoxicity in cerebellar granule neurons via a pertussis toxin-sensitive Gi/o protein, suggesting a presynaptic neuroprotective mechanism.","method":"Cell culture excitotoxicity assay with pertussis toxin, glutamate release measurement, immunocytochemistry for mGluR7 protein","journal":"The European journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — functional assay with pharmacological dissection (pertussis toxin) in primary neurons, single lab","pmids":["10051767"],"is_preprint":false},{"year":2000,"finding":"PICK1 binds to the extreme C-terminus (PDZ-binding motif) of mGluR7a via its PDZ domain, forms a trimeric complex with PKCα, and reduces PKCα-evoked phosphorylation of mGluR7a in vitro.","method":"Yeast two-hybrid, GST pulldown, co-immunoprecipitation from COS-7 cells and rat brain tissue, confocal colocalization in hippocampal neurons, in vitro phosphorylation assay","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (Y2H, pulldown, co-IP from native brain, in vitro kinase assay), replicated in heterologous and native contexts","pmids":["11007882"],"is_preprint":false},{"year":2002,"finding":"PKC, PKA, and PKG all inhibit calmodulin (CaM) binding to mGluR7 by phosphorylating a single serine residue, Ser862, in the C-terminal tail; however, PKC-mediated inhibition of mGluR7-coupled GIRK currents is independent of Ser862 phosphorylation and CaM binding.","method":"Site-directed mutagenesis of Ser862, in vitro kinase assays, CaM binding assays, GIRK current recordings in heterologous expression system","journal":"Molecular pharmacology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstitution with mutagenesis and multiple kinase substrates, electrophysiological functional readout, single lab","pmids":["12021391"],"is_preprint":false},{"year":2002,"finding":"mGluR7 knockout mice display attenuated short-term potentiation (STP), reduced frequency facilitation during high-frequency trains, and decreased post-tetanic potentiation at hippocampal Schaffer collateral-CA1 synapses, while long-term potentiation is preserved.","method":"Electrophysiological field recordings in hippocampal slices from mGluR7-/- knockout mice","journal":"TheScientificWorldJournal","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — clean KO with specific electrophysiological phenotype, single lab, limited mechanistic follow-up","pmids":["12805997"],"is_preprint":false},{"year":2003,"finding":"mGluR7a is highly enriched in the presynaptic active zones of GABAergic terminals (particularly VIP-positive interneurons) that innervate somatostatin- and mGluR1α-positive interneurons in the hippocampus, demonstrating target-cell-specific expression of mGluR7 in GABAergic terminals.","method":"Quantitative immunocytochemistry and electron microscopy with multiple antibody markers in rat hippocampus","journal":"The European journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — EM-level quantitative analysis of 466 synapses with multiple markers defining cell-type specificity","pmids":["12823458"],"is_preprint":false},{"year":2004,"finding":"mGluR7, but not mGluR8, mediates presynaptic inhibition at medial perforant path synapses in the dentate gyrus, and this mGluR7-mediated inhibition is significantly reduced 3–9 days after pilocarpine-induced status epilepticus.","method":"Field EPSP recordings in hippocampal slices from wild-type, mGluR8-KO, and mGluR4/8 double-KO mice with selective pharmacological agonists","journal":"Journal of neurophysiology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with multiple KO strains plus selective pharmacology to assign pathway position, single lab","pmids":["15152022"],"is_preprint":false},{"year":2005,"finding":"mGluR7 acts as a metaplastic switch at mossy fiber–stratum lucidum interneuron (MF-SLIN) synapses: its activation during high-frequency stimulation induces LTD through a PKC-dependent reduction in presynaptic release, and subsequent agonist-induced internalization of mGluR7 unmasks the ability of the same stimulation to induce LTP.","method":"Hippocampal slice electrophysiology, pharmacological activation/blockade of mGluR7, PKC inhibitors, immunofluorescence for receptor surface expression","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (electrophysiology, pharmacology, imaging), mechanistic pathway dissected with PKC inhibitors, single lab","pmids":["15820696"],"is_preprint":false},{"year":2006,"finding":"mGluR7 constitutively internalizes via a clathrin-independent, Arf6-positive endosomal pathway in both heterologous cells and neurons.","method":"Immunofluorescence internalization assay, dominant-negative Arf6 and clathrin inhibition, co-localization with Arf6 endosomes in heterologous cells and neurons","journal":"Neuropharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — pathway assigned using dominant-negative constructs and inhibitors, single lab, single study","pmids":["16890965"],"is_preprint":false},{"year":2006,"finding":"The allosteric agonist AMN082 induces rapid mGluR7 internalization in hippocampal neurons, resistant to competitive orthosteric antagonists, as confirmed by pHluorin-tagged live imaging of surface receptor loss.","method":"Immunofluorescence internalization assay and live imaging with N-terminal pHluorin-tagged mGluR7 in dissociated hippocampal neurons","journal":"Neuropharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two orthogonal imaging methods, single lab","pmids":["16914173"],"is_preprint":false},{"year":2007,"finding":"mGluR7 inhibits glutamate release at hippocampal nerve terminals primarily by inhibiting P/Q-type Ca2+ channels through a pertussis toxin-sensitive (Gi/o) PKC-independent mechanism; a separate pathway decreases cAMP when cAMP is elevated by forskolin.","method":"Glutamate release assays in rat hippocampal synaptosomes with selective Ca2+ channel blockers (ω-conotoxin), pertussis toxin, PKC inhibitors, PKA inhibitors, cAMP measurements","journal":"The European journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro synaptosome assay with multiple pharmacological dissections and direct cAMP measurement, single lab with multiple orthogonal approaches","pmids":["17650109"],"is_preprint":false},{"year":2007,"finding":"mGluR7 activation blocks LTP acquisition in the lateral amygdala and facilitates extinction of aversive memories; siRNA knockdown of mGluR7 attenuates extinction, demonstrating a required role for mGluR7 in amygdala plasticity and fear memory extinction.","method":"AMN082 pharmacological activation, siRNA knockdown in vivo, fear conditioning behavioral assays, lateral amygdala LTP electrophysiology in mice","journal":"Molecular psychiatry","confidence":"High","confidence_rationale":"Tier 2 / Strong — bidirectional manipulation (agonist + siRNA KD) with matched electrophysiological and behavioral readouts","pmids":["17712315"],"is_preprint":false},{"year":2008,"finding":"mGluR7 surface expression requires both PKC phosphorylation at Ser862 (which inhibits CaM binding) and PICK1 binding; in PICK1 knockout mice, PKC-dependent increases in mGluR7 phosphorylation and surface expression are diminished, and mGluR7-dependent plasticity at mossy fiber–interneuron synapses is impaired.","method":"Site-directed mutagenesis of Ser862, surface biotinylation assays, co-immunoprecipitation, CaM binding assays, hippocampal slice electrophysiology in PICK1-/- mice","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis, biochemical assays, and electrophysiological validation in KO mice, multiple orthogonal methods, single lab","pmids":["18549785"],"is_preprint":false},{"year":2008,"finding":"mGluR7a signaling (GIRK channel activation) is potentiated by physiological increases in intracellular Ca2+, mediated through calmodulin binding to the C-terminal tail; light-gated Ca2+ influx via ChR2 markedly enhanced L-AP4-dependent GIRK currents, an effect attenuated by intracellular Ca2+ chelation.","method":"Xenopus oocyte electrophysiology with ChR2-mediated Ca2+ influx, BAPTA chelation, GIRK3.1/3.2 concatemer reporter","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — functional reconstitution in oocytes with optogenetic Ca2+ control and chelation, single lab, two orthogonal approaches","pmids":["18599484"],"is_preprint":false},{"year":2010,"finding":"Prolonged activation of mGlu7 receptors at cerebrocortical nerve terminals switches signaling from inhibition to potentiation of glutamate release; this potentiation involves phospholipase C activation, PIP2 hydrolysis, a pertussis toxin-insensitive G protein, and translocation of Munc13-1 from soluble to particulate fractions, independent of PKC.","method":"Glutamate release assays in synaptosomes with pertussis toxin, PLC inhibitors, calphostin C (DAG-binding site inhibitor), Ca2+ ionophore ionomycin, Munc13-1 subcellular fractionation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro synaptosome reconstitution with multiple pharmacological tools and biochemical fractionation, single lab","pmids":["20375012"],"is_preprint":false},{"year":2012,"finding":"Presynaptic mGlu7 receptors on hippocampal GABAergic terminals inhibit GABA release via an adenylyl cyclase-dependent (cAMP-mediated) mechanism; these mGlu7 heteroreceptors colocalize with syntaxin-1A, VGAT, and GABAB receptor subunits but do not functionally cross-talk with GABAB autoreceptors.","method":"[3H]GABA release from hippocampal synaptosomes with selective pharmacological tools (AMN082, MMPIP, cAMP pathway modulators, GABAB antagonists), confocal colocalization","journal":"Neuropharmacology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — functional release assays with selective NAM, pathway dissection with cAMP modulators, colocalization, single lab","pmids":["22564442"],"is_preprint":false},{"year":2013,"finding":"GRK4 regulates mGluR7-dependent adenylyl cyclase and JNK pathways, while GRK2 selectively regulates the ERK1/2 pathway; β-arrestin1 and β-arrestin2 exert reciprocally opposite effects on ERK1/2 and JNK signaling downstream of mGluR7, with β-arrestin1 amplifying ERK1/2 activation by the orthosteric agonist L-AP4 but not by the allosteric agonist AMN082.","method":"Overexpression of GRK subtypes and β-arrestin isoforms in recombinant cells expressing mGluR7, with adenylyl cyclase, ERK1/2, and JNK pathway readouts","journal":"Neuropharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — multiple signaling pathway readouts in heterologous cells, single lab, no in vivo validation","pmids":["24148810"],"is_preprint":false},{"year":2013,"finding":"PP1γ1 dephosphorylates Ser862 on mGluR7 and regulates agonist-induced (but not NMDA-induced) dephosphorylation and surface expression of mGluR7; PP1 inhibitors increase Ser862 phosphorylation and mGluR7 surface expression in neurons.","method":"Phospho-specific immunoblotting, surface biotinylation, PP1 inhibitor pharmacology, and PP1γ1 overexpression/knockdown in neurons","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — biochemical assays with pharmacological and genetic manipulation, demonstrated in primary neurons, single lab","pmids":["23612982"],"is_preprint":false},{"year":2014,"finding":"Elfn1 recruits mGluR7 to presynaptic sites of excitatory synapses onto somatostatin interneurons via a transsynaptic interaction; Elfn1 knockout mice show deficits in mGluR7 recruitment to these synapses and impaired presynaptic plasticity.","method":"Immunohistochemistry, co-immunoprecipitation, electrophysiology in Elfn1-KO mice, identification of damaging ELFN1 mutations in epilepsy/ADHD patients","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO mouse with matched biochemical (recruitment) and electrophysiological phenotype, confirmed transsynaptic interaction, replicated with human genetics","pmids":["25047565"],"is_preprint":false},{"year":2014,"finding":"The mGlu7-selective antagonist XAP044 acts via a binding pocket in the extracellular Venus flytrap domain (VFTD), not the transmembrane region; this was demonstrated by chimeric receptor studies in which the VFTD of mGlu7 conferred XAP044 sensitivity.","method":"Chimeric receptor construction and functional assays in recombinant cell lines; lateral amygdala LTP electrophysiology in wild-type and mGlu7-KO mice","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — chimeric receptor reconstitution defining binding domain, validated with KO electrophysiology, single lab with two orthogonal approaches","pmids":["24596089"],"is_preprint":false},{"year":2014,"finding":"mGluR7 activation decreases NMDAR-mediated currents and NR1 surface expression in basal forebrain cholinergic neurons via cofilin-regulated actin dynamics; Aβ selectively impairs this mGluR7 regulation by increasing PAK activity and decreasing cofilin-mediated actin depolymerization through a p75NTR-dependent mechanism.","method":"Whole-cell patch-clamp recordings, surface biotinylation, actin dynamics assays (cofilin phosphorylation), PAK activity assays, p75NTR neutralization in rodent BF neurons","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (electrophysiology, biochemistry, actin dynamics) with mechanistic pathway dissection in primary neurons","pmids":["25297090"],"is_preprint":false},{"year":2015,"finding":"mGlu7 receptor activation on cerebellar Purkinje cells mediates adaptively timed pauses in firing that constitute intrinsic cellular temporal memory; antagonists of mGlu7 but not other glutamate receptor subtypes abolished these learned responses in vivo.","method":"In vivo single-unit recordings in rat cerebellum with pharmacological blockade of mGlu7 and GABA receptors during conditioned stimulus presentation","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — in vivo electrophysiology with selective pharmacology, single lab","pmids":["26655894"],"is_preprint":false},{"year":2015,"finding":"GRM7 knockdown reduces neural progenitor cell proliferation and promotes neuronal differentiation during cortical development; mGlu7 regulates CREB phosphorylation and YAP expression by directly interacting with calmodulin, controlling CyclinD1 expression.","method":"In utero electroporation knockdown/overexpression, immunofluorescence, co-immunoprecipitation (mGlu7-CaM interaction), Western blot in mouse cortex","journal":"Stem cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo knockdown with rescue experiments and biochemical co-IP, single lab","pmids":["25921811"],"is_preprint":false},{"year":2015,"finding":"mGluR7 is SUMOylated at Lys889; this SUMOylation is reversed by SENP1 and is reduced by agonist (L-AP4) treatment. DeSUMOylation or SENP1 overexpression markedly increases mGluR7 internalization in hippocampal neurons, and Ser862 phosphorylation facilitates SUMO conjugation.","method":"SUMO conjugation assays in HEK293T cells, identification of SUMOylated mGluR7 in brain and cortical neurons by immunoprecipitation, SENP1 overexpression, mGluR7 internalization assays in hippocampal neurons","journal":"Neuropharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical SUMOylation mapping in native neurons and heterologous cells, functional trafficking readout, single lab","pmids":["26631532"],"is_preprint":false},{"year":2016,"finding":"mGlu7 receptors are functionally expressed at both glutamatergic and GABAergic thalamic synapses where they inhibit neurotransmission and regulate short-term plasticity in a PDZ-ligand-dependent manner; constitutive (tonic) mGlu7 activity prevents pathological thalamocortical synchrony, as in vivo NAM application induces absence-like seizures.","method":"Thalamic slice electrophysiology, optogenetics, pharmacology with NAM ADX71743, and in vivo EEG in mice with PDZ-domain mutant mGlu7","journal":"Frontiers in neural circuits","confidence":"High","confidence_rationale":"Tier 2 / Strong — combination of electrophysiology, optogenetics, pharmacology and in vivo EEG, mechanistic link to PDZ domain via mutant mice","pmids":["27199672"],"is_preprint":false},{"year":2017,"finding":"mGlu7 is the predominant mGlu receptor expressed presynaptically at Schaffer collateral–CA1 synapses in adult mice; its activation on GABAergic interneurons is necessary for LTP induction; MECP2 mutations reduce mGlu7 protein expression, and positive allosteric modulation of mGlu7 restores LTP and improves cognitive and social behaviors in RTT mouse models.","method":"Immunohistochemistry, hippocampal slice LTP recordings, behavioral testing (fear learning, novel object recognition, social memory), in vivo pharmacology in Mecp2 mutant mice","journal":"Science translational medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — combined electrophysiology, behavioral and molecular phenotyping with positive allosteric modulation rescue, validated in patient tissue","pmids":["28814546"],"is_preprint":false},{"year":2019,"finding":"Nedd4 E3 ubiquitin ligase ubiquitinates mGluR7 upon agonist stimulation; β-arrestins recruit Nedd4 to mGluR7 and facilitate ubiquitination; Nedd4 and β-arrestins are required for constitutive and agonist-induced endocytosis of mGluR7 and for mGluR7-dependent MAPK signaling; Nedd4-mediated ubiquitination leads to mGluR7 degradation via both the ubiquitin-proteasome system and lysosomal pathway.","method":"Co-immunoprecipitation, ubiquitination assays in heterologous cells and rat neurons, endocytosis assays, MAPK signaling assays, proteasome/lysosome inhibitors","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (co-IP, functional endocytosis, signaling assays) in both heterologous cells and neurons, single lab","pmids":["31373553"],"is_preprint":false},{"year":2019,"finding":"Elfn1 produces glutamate-independent (constitutive) activation of mGluR7 through presynaptic clustering, tonically suppressing initial release probability at synapses onto somatostatin interneurons, which is distinct from canonical autoreceptor function.","method":"Electrophysiology in cortical slices from Elfn1-KO mice, pharmacological mGluR7 activation/blockade, assessment of short-term synaptic facilitation in Layer 2/3 and Layer 5","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with electrophysiology and pharmacological dissection, layer-specific comparisons providing mechanistic insight, single lab","pmids":["30940718"],"is_preprint":false},{"year":2020,"finding":"mGluR7 is N-glycosylated at four asparagine residues; N-glycosylation is essential for ER exit and forward trafficking to the plasma membrane; deglycosylated mGluR7 is retained in the ER and degraded via the autophagolysosomal pathway; N-glycosylation also promotes the mGluR7–Elfn1 transsynaptic interaction.","method":"Glycosylation-deficient mutagenesis, surface biotinylation, ER retention assays, co-immunoprecipitation with Elfn1, autophagy/lysosome inhibitor studies in heterologous cells and neurons","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis plus multiple biochemical readouts (trafficking, degradation, protein interaction) in heterologous and neuronal contexts, single lab","pmids":["32931036"],"is_preprint":false},{"year":2021,"finding":"mGluR7 neddylation is required for presynaptic clustering and stabilization of mGluR7 protein; agonist treatment reduces neddylation; neddylation facilitates ubiquitination of mGluR7 and is necessary for maturation of excitatory presynaptic terminals.","method":"Neddylation assays in heterologous cells and primary neurons, neddylation inhibitor (MLN4924), presynaptic clustering immunostaining, synaptosome fractionation","journal":"Experimental & molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical modification assays with functional clustering and maturation readouts in neurons, single lab","pmids":["33767338"],"is_preprint":false},{"year":2021,"finding":"Pathogenic GRM7 mutations I154T and R658W/T675K cause degradation and loss of surface expression of mGluR7 protein; I154T and R658W/T675K mutations impair axon outgrowth and reduce presynaptic terminal number through the MAPK-cAMP-PKA signaling pathway; mGluR7 agonist treatment rescues I154T (which retains partial surface expression) but not R658W/T675K phenotypes.","method":"Expression of mutant constructs in HEK293A cells and rat primary neurons, surface biotinylation, axon outgrowth measurements, presynaptic terminal counting, MAPK/cAMP/PKA pathway assays, pharmacological rescue","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple mutations studied with biochemical, morphological, and signaling readouts including pharmacological rescue, in both heterologous and neuronal contexts","pmids":["33500274"],"is_preprint":false},{"year":2021,"finding":"Cryo-EM structures of mGlu2 and mGlu7 homo- and heterodimers reveal that mGlu7 forms a distinct homodimer interface and a heterodimer with mGlu2; in the mGlu2–mGlu7 heterodimer, the mGlu7 subunit has a dominant role in controlling dimeric association and G-protein activation.","method":"Cryo-electron microscopy structure determination; functional studies of mGlu2–mGlu7 heterodimer G-protein activation","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structures at near-atomic resolution with functional validation of heterodimer G-protein coupling, high-impact journal","pmids":["34135509"],"is_preprint":false},{"year":2022,"finding":"mGlu7/8 heterodimers modulate Schaffer collateral–CA1 synaptic transmission and LTP; ADX71743 (mGlu7 NAM) blocks responses of both mGlu7/7 homodimers and mGlu7/8 heterodimers, whereas MMPIP only antagonizes mGlu7/7 homodimers, explaining the differential pharmacology observed at SC-CA1 synapses.","method":"complemented donor-acceptor FRET (CODA-RET) to study heterodimer activation in vitro; hippocampal slice electrophysiology with differential NAM pharmacology","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — two orthogonal approaches (FRET-based in vitro heterodimer assay plus matched electrophysiology) with multiple structurally related compounds, single lab","pmids":["36063995"],"is_preprint":false}],"current_model":"mGluR7 (GRM7) is a presynaptic, Gi/o-coupled class C GPCR that inhibits adenylyl cyclase and modulates neurotransmitter release primarily by suppressing P/Q- and N-type Ca2+ channel activity; it exists as homodimers and heterodimers (e.g., with mGlu2 and mGlu8) with the mGlu7 subunit dominant for G-protein activation in heterodimers; its surface expression and trafficking are tightly regulated by a network of post-translational modifications (PKC phosphorylation of Ser862, CaM competitive binding, PICK1 PDZ interaction, PP1γ1-mediated dephosphorylation, SUMO conjugation at Lys889, Nedd4/β-arrestin-mediated ubiquitination and endocytosis, and N-glycosylation for ER exit) and by the transsynaptic Elfn1 interaction that constitutively activates and clusters mGluR7 at synapses onto somatostatin interneurons; pathogenic GRM7 mutations cause protein degradation, impair axon outgrowth via MAPK-cAMP-PKA signaling, and are linked to neurodevelopmental disorders including epileptic encephalopathy."},"narrative":{"mechanistic_narrative":"GRM7 encodes mGluR7, a presynaptic Gi/o-coupled class C GPCR that inhibits forskolin-stimulated adenylyl cyclase upon agonist binding and serves as a low-affinity autoreceptor and heteroreceptor controlling neurotransmitter release at central synapses [PMID:8288585, PMID:17650109]. It is concentrated in presynaptic active zones of both glutamatergic and GABAergic terminals, including target-cell-specific GABAergic terminals innervating somatostatin and other interneurons [PMID:8787837, PMID:12823458, PMID:22564442]. Mechanistically, mGluR7 suppresses glutamate release principally by inhibiting P/Q-type Ca2+ channels through a pertussis-toxin-sensitive, PKC-independent Gi/o pathway, with a parallel cAMP-lowering arm; prolonged activation can switch signaling from inhibition to PLC/Munc13-1-dependent potentiation of release [PMID:17650109, PMID:20375012]. Through these actions it sets short-term plasticity, acting as a metaplastic switch that gates LTD versus LTP at mossy fiber–interneuron synapses and is required for STP and frequency facilitation, perforant-path presynaptic inhibition, amygdala fear-memory extinction, and tonic suppression of pathological thalamocortical synchrony [PMID:12805997, PMID:15152022, PMID:15820696, PMID:17712315, PMID:27199672]. Surface availability is governed by an integrated post-translational network: PKC/PKA/PKG phosphorylation of Ser862 competitively blocks calmodulin binding, PICK1 PDZ-domain binding and Ser862 phosphorylation jointly maintain surface expression, PP1γ1 dephosphorylates Ser862, SUMOylation at Lys889 and Nedd4/β-arrestin-mediated ubiquitination regulate constitutive Arf6- and clathrin-independent endocytosis and degradation, neddylation stabilizes presynaptic clusters, and N-glycosylation is required for ER exit and forward trafficking [PMID:11007882, PMID:12021391, PMID:18549785, PMID:23612982, PMID:26631532, PMID:31373553, PMID:16890965, PMID:32931036, PMID:33767338]. The transsynaptic ligand Elfn1 recruits and constitutively (glutamate-independently) activates and clusters mGluR7 at synapses onto somatostatin interneurons, tonically lowering release probability [PMID:25047565, PMID:30940718]. mGluR7 forms homodimers and an mGlu2–mGlu7 heterodimer in which the mGlu7 subunit dominates G-protein activation, and assembles mGlu7/8 heterodimers with distinct allosteric pharmacology [PMID:34135509, PMID:36063995]. Pathogenic GRM7 mutations cause receptor degradation, loss of surface expression, and impaired axon outgrowth via MAPK-cAMP-PKA signaling, linking the gene to neurodevelopmental disorders; reduced mGlu7 expression also underlies plasticity and behavioral deficits in Rett syndrome models, where positive allosteric modulation restores function [PMID:33500274, PMID:28814546].","teleology":[{"year":1994,"claim":"Established mGluR7 as a functional receptor by showing it couples negatively to adenylyl cyclase, defining its core signaling output.","evidence":"Heterologous expression in CHO cells with agonist-driven cAMP accumulation assay","pmids":["8288585"],"confidence":"High","gaps":["Did not address subcellular localization or native synaptic role","Downstream effectors beyond cAMP unresolved"]},{"year":1996,"claim":"Determined where the receptor acts by localizing it presynaptically in axon terminals and at ribbon-synapse active zones, supporting an autoreceptor function.","evidence":"Immunohistochemistry with dorsal rhizotomy lesion and EM double-labeling in spinal cord and retina","pmids":["8787837","8764662"],"confidence":"High","gaps":["Functional consequence of active-zone restriction not tested","Postsynaptic pool function in amacrine cells uncharacterized"]},{"year":2000,"claim":"Identified scaffolding and phosphoregulatory control by showing PICK1 binds the C-terminal PDZ motif and assembles a complex with PKCα that regulates receptor phosphorylation.","evidence":"Yeast two-hybrid, GST pulldown, co-IP from brain, and in vitro kinase assays","pmids":["11007882"],"confidence":"High","gaps":["Functional impact on surface expression not yet shown","Phosphosite not yet mapped"]},{"year":2002,"claim":"Mapped the phosphoregulatory switch to Ser862, where PKC/PKA/PKG phosphorylation blocks calmodulin binding, defining a competitive CaM/phosphorylation node.","evidence":"Ser862 mutagenesis, in vitro kinase and CaM-binding assays, GIRK current recordings","pmids":["12021391"],"confidence":"High","gaps":["GIRK inhibition shown independent of Ser862/CaM, leaving that effector pathway unexplained","In vivo relevance not tested"]},{"year":2004,"claim":"Assigned mGluR7 a specific circuit role in presynaptic inhibition at perforant-path synapses and linked its loss to epileptogenesis.","evidence":"Field EPSP recordings in multiple KO strains with selective agonists; pilocarpine status epilepticus model","pmids":["15152022"],"confidence":"High","gaps":["Mechanism of post-seizure downregulation unresolved","Molecular effector at this synapse not defined"]},{"year":2007,"claim":"Defined the proximal release-inhibition mechanism as P/Q-type Ca2+ channel suppression via Gi/o, distinguishing it from the cAMP-lowering arm.","evidence":"Synaptosome glutamate release assays with conotoxin, pertussis toxin, and kinase inhibitors plus cAMP measurement","pmids":["17650109"],"confidence":"High","gaps":["Direct Gβγ-channel interaction not demonstrated","Relative contribution of two arms in vivo unclear"]},{"year":2008,"claim":"Integrated trafficking control by demonstrating that both Ser862 phosphorylation and PICK1 binding are required for surface expression and mGluR7-dependent plasticity.","evidence":"Ser862 mutagenesis, surface biotinylation, co-IP, and slice electrophysiology in PICK1-KO mice","pmids":["18549785"],"confidence":"High","gaps":["Endocytic machinery executing internalization not identified here","Temporal dynamics of surface regulation unresolved"]},{"year":2010,"claim":"Revealed signaling plasticity: prolonged activation switches mGluR7 from release inhibition to PLC/Munc13-1-dependent potentiation via a PTX-insensitive G protein.","evidence":"Cerebrocortical synaptosome release assays with PLC inhibitors, ionomycin, and Munc13-1 fractionation","pmids":["20375012"],"confidence":"High","gaps":["Identity of the PTX-insensitive G protein not defined","In vivo behavioral relevance of the switch untested"]},{"year":2013,"claim":"Expanded the post-translational network by identifying PP1γ1 as the Ser862 phosphatase and GRK/β-arrestin isoform-specific control of downstream MAPK arms.","evidence":"Phospho-immunoblotting, surface biotinylation, PP1 manipulation in neurons; GRK/β-arrestin overexpression with AC/ERK/JNK readouts","pmids":["23612982","24148810"],"confidence":"Medium","gaps":["GRK/β-arrestin study lacks in vivo validation","Biased agonism between L-AP4 and AMN082 not mechanistically resolved"]},{"year":2014,"claim":"Identified Elfn1 as the transsynaptic organizer that recruits mGluR7 to specific somatostatin-interneuron synapses, defining target-cell-specific receptor placement.","evidence":"Co-IP, immunohistochemistry, and electrophysiology in Elfn1-KO mice with human genetic correlation","pmids":["25047565"],"confidence":"High","gaps":["Whether recruitment alters receptor signaling state not yet shown here","Structural basis of the interaction undefined"]},{"year":2015,"claim":"Showed Ca2+/calmodulin potentiates mGluR7 signaling and that the receptor also regulates neural progenitor proliferation via CaM-dependent CREB/YAP/CyclinD1 control, extending its role to development.","evidence":"Oocyte GIRK recordings with optogenetic Ca2+ control; in utero electroporation knockdown with co-IP in mouse cortex","pmids":["18599484","25921811"],"confidence":"Medium","gaps":["Developmental signaling shown in single lab without genetic KO","Link between CaM binding and proliferation effectors incompletely mapped"]},{"year":2015,"claim":"Established SUMOylation at Lys889 as an agonist-sensitive modification gating receptor internalization, adding a further trafficking control layer.","evidence":"SUMO conjugation assays, SENP1 manipulation, and internalization assays in neurons","pmids":["26631532"],"confidence":"Medium","gaps":["Effector linking deSUMOylation to endocytosis not identified","In vivo synaptic consequence untested"]},{"year":2017,"claim":"Connected mGluR7 to disease by showing MECP2 mutations reduce its expression and that positive allosteric modulation restores LTP and behavior in Rett models.","evidence":"Immunohistochemistry, slice LTP, behavior, and in vivo pharmacology in Mecp2 mutant mice with patient tissue","pmids":["28814546"],"confidence":"High","gaps":["Mechanism by which MECP2 controls GRM7 expression unresolved","Durability of PAM rescue not addressed"]},{"year":2019,"claim":"Resolved the constitutive endocytic and degradation machinery: β-arrestins recruit Nedd4 to ubiquitinate mGluR7, driving proteasomal and lysosomal degradation and MAPK signaling.","evidence":"Co-IP, ubiquitination, endocytosis, and signaling assays with proteasome/lysosome inhibitors in cells and neurons","pmids":["31373553"],"confidence":"High","gaps":["Ubiquitination site(s) not mapped","Balance between proteasomal and lysosomal routing not quantified"]},{"year":2019,"claim":"Clarified that Elfn1 produces glutamate-independent constitutive activation and clustering of mGluR7, distinguishing it from canonical autoreceptor signaling.","evidence":"Cortical slice electrophysiology in Elfn1-KO mice with pharmacological dissection across cortical layers","pmids":["30940718"],"confidence":"High","gaps":["Structural mechanism of ligand-independent activation undefined","Whether other partners drive constitutive activity elsewhere unknown"]},{"year":2020,"claim":"Defined N-glycosylation as a prerequisite for ER exit and forward trafficking, with deglycosylated receptor degraded autophagolysosomally and impaired Elfn1 binding.","evidence":"Glycosylation-deficient mutagenesis, surface biotinylation, ER-retention and co-IP assays in cells and neurons","pmids":["32931036"],"confidence":"High","gaps":["Quality-control machinery recognizing unglycosylated receptor not identified","Whether glycosylation tunes signaling beyond trafficking unknown"]},{"year":2021,"claim":"Identified neddylation as a stabilizing modification required for presynaptic clustering and terminal maturation, and provided high-resolution structures of mGlu7 dimers showing mGlu7 dominance in heterodimeric G-protein activation.","evidence":"Neddylation assays with MLN4924 and clustering readouts; cryo-EM of mGlu2/mGlu7 homo- and heterodimers with functional validation","pmids":["33767338","34135509"],"confidence":"High","gaps":["Neddylation site and interplay with ubiquitination not fully resolved","Functional role of mGlu7 homodimer interface in vivo untested"]},{"year":2021,"claim":"Demonstrated disease causality by showing pathogenic GRM7 mutations cause receptor degradation, loss of surface expression, and impaired axon outgrowth via MAPK-cAMP-PKA signaling, with mutation-dependent pharmacological rescue.","evidence":"Mutant expression in cells and neurons with biotinylation, axon outgrowth, terminal counting, signaling assays, and agonist rescue","pmids":["33500274"],"confidence":"High","gaps":["In vivo modeling of patient mutations not performed","Genotype–phenotype correlation across the disorder spectrum incomplete"]},{"year":2022,"claim":"Defined heterodimer-specific pharmacology by showing mGlu7/8 heterodimers and mGlu7/7 homodimers respond differentially to NAMs, explaining native synaptic drug responses.","evidence":"CODA-RET heterodimer activation assays plus hippocampal slice electrophysiology with differential NAMs","pmids":["36063995"],"confidence":"High","gaps":["Stoichiometry and abundance of native heterodimers unresolved","Distinct signaling outputs of each dimer species not fully mapped"]},{"year":null,"claim":"How the multiple post-translational modifications, dimerization states, and Elfn1-driven constitutive activation are coordinated in space and time to set synapse-specific output remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No integrated model linking glycosylation, SUMOylation, ubiquitination, neddylation, and phosphorylation dynamics","Native dimer composition at defined synapses unknown","Structural basis of Elfn1-induced constitutive activation undetermined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,13,34]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[13,18]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,2,8,15]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[31]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[11,29]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,13,19]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[7,9,10,27]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[29,31,32]}],"complexes":["mGlu2–mGlu7 heterodimer","mGlu7/8 heterodimer","mGluR7–PICK1–PKCα complex"],"partners":["PICK1","ELFN1","CALM1","PPP1CC","NEDD4","GRM2","GRM8"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q14831","full_name":"Metabotropic glutamate receptor 7","aliases":[],"length_aa":915,"mass_kda":102.3,"function":"G-protein coupled receptor activated by glutamate that regulates axon outgrowth through the MAPK-cAMP-PKA signaling pathway during neuronal development (PubMed:33500274). 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\"mGluR7 is a Gi/o-coupled GPCR that inhibits forskolin-stimulated cyclic AMP accumulation in response to agonist (L-AP4, L-serine-O-phosphate) in transfected CHO cells, establishing it as a negatively coupled adenylyl cyclase receptor.\",\n      \"method\": \"Heterologous expression in CHO cells with cAMP accumulation assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct functional reconstitution in transfected cells, foundational characterization replicated across subsequent studies\",\n      \"pmids\": [\"8288585\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"mGluR7 protein is localized presynaptically in axon terminals of primary afferent fibers projecting to laminae I and II of the spinal dorsal horn, as demonstrated by immunoreactivity reduced after dorsal rhizotomy.\",\n      \"method\": \"Immunohistochemistry with dorsal rhizotomy lesion; electron microscopy\",\n      \"journal\": \"Neuroscience letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct localization with lesion control confirming presynaptic terminal origin, replicated in subsequent EM studies\",\n      \"pmids\": [\"8787837\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"mGluR7 is localized both presynaptically as an autoreceptor at cone bipolar cell ribbon synapses and postsynaptically in amacrine cells in the rat retina, with the presynaptic pool restricted to one half of the active zone.\",\n      \"method\": \"Electron microscopy immunohistochemistry with double-labeling in rat retina\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — EM-level subcellular localization with double-labeling, defining two distinct active sites\",\n      \"pmids\": [\"8764662\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Alternative splicing of mGluR7 produces a 'b' isoform (mGluR7b) with a different C-terminal sequence; both mGluR7a and mGluR7b show identical pharmacological profiles when expressed in heterologous systems, indicating the C-terminal differences do not alter agonist pharmacology.\",\n      \"method\": \"RT-PCR cloning, expression in HEK293 cells and Xenopus oocytes with pharmacological profiling\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct functional characterization of splice variants in two heterologous systems, single lab\",\n      \"pmids\": [\"9875342\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"mGluR7-like receptor activation by high concentrations of L-AP4 inhibits NMDA-induced glutamate release and excitotoxicity in cerebellar granule neurons via a pertussis toxin-sensitive Gi/o protein, suggesting a presynaptic neuroprotective mechanism.\",\n      \"method\": \"Cell culture excitotoxicity assay with pertussis toxin, glutamate release measurement, immunocytochemistry for mGluR7 protein\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — functional assay with pharmacological dissection (pertussis toxin) in primary neurons, single lab\",\n      \"pmids\": [\"10051767\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"PICK1 binds to the extreme C-terminus (PDZ-binding motif) of mGluR7a via its PDZ domain, forms a trimeric complex with PKCα, and reduces PKCα-evoked phosphorylation of mGluR7a in vitro.\",\n      \"method\": \"Yeast two-hybrid, GST pulldown, co-immunoprecipitation from COS-7 cells and rat brain tissue, confocal colocalization in hippocampal neurons, in vitro phosphorylation assay\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (Y2H, pulldown, co-IP from native brain, in vitro kinase assay), replicated in heterologous and native contexts\",\n      \"pmids\": [\"11007882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"PKC, PKA, and PKG all inhibit calmodulin (CaM) binding to mGluR7 by phosphorylating a single serine residue, Ser862, in the C-terminal tail; however, PKC-mediated inhibition of mGluR7-coupled GIRK currents is independent of Ser862 phosphorylation and CaM binding.\",\n      \"method\": \"Site-directed mutagenesis of Ser862, in vitro kinase assays, CaM binding assays, GIRK current recordings in heterologous expression system\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstitution with mutagenesis and multiple kinase substrates, electrophysiological functional readout, single lab\",\n      \"pmids\": [\"12021391\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"mGluR7 knockout mice display attenuated short-term potentiation (STP), reduced frequency facilitation during high-frequency trains, and decreased post-tetanic potentiation at hippocampal Schaffer collateral-CA1 synapses, while long-term potentiation is preserved.\",\n      \"method\": \"Electrophysiological field recordings in hippocampal slices from mGluR7-/- knockout mice\",\n      \"journal\": \"TheScientificWorldJournal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — clean KO with specific electrophysiological phenotype, single lab, limited mechanistic follow-up\",\n      \"pmids\": [\"12805997\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"mGluR7a is highly enriched in the presynaptic active zones of GABAergic terminals (particularly VIP-positive interneurons) that innervate somatostatin- and mGluR1α-positive interneurons in the hippocampus, demonstrating target-cell-specific expression of mGluR7 in GABAergic terminals.\",\n      \"method\": \"Quantitative immunocytochemistry and electron microscopy with multiple antibody markers in rat hippocampus\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — EM-level quantitative analysis of 466 synapses with multiple markers defining cell-type specificity\",\n      \"pmids\": [\"12823458\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"mGluR7, but not mGluR8, mediates presynaptic inhibition at medial perforant path synapses in the dentate gyrus, and this mGluR7-mediated inhibition is significantly reduced 3–9 days after pilocarpine-induced status epilepticus.\",\n      \"method\": \"Field EPSP recordings in hippocampal slices from wild-type, mGluR8-KO, and mGluR4/8 double-KO mice with selective pharmacological agonists\",\n      \"journal\": \"Journal of neurophysiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with multiple KO strains plus selective pharmacology to assign pathway position, single lab\",\n      \"pmids\": [\"15152022\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"mGluR7 acts as a metaplastic switch at mossy fiber–stratum lucidum interneuron (MF-SLIN) synapses: its activation during high-frequency stimulation induces LTD through a PKC-dependent reduction in presynaptic release, and subsequent agonist-induced internalization of mGluR7 unmasks the ability of the same stimulation to induce LTP.\",\n      \"method\": \"Hippocampal slice electrophysiology, pharmacological activation/blockade of mGluR7, PKC inhibitors, immunofluorescence for receptor surface expression\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (electrophysiology, pharmacology, imaging), mechanistic pathway dissected with PKC inhibitors, single lab\",\n      \"pmids\": [\"15820696\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"mGluR7 constitutively internalizes via a clathrin-independent, Arf6-positive endosomal pathway in both heterologous cells and neurons.\",\n      \"method\": \"Immunofluorescence internalization assay, dominant-negative Arf6 and clathrin inhibition, co-localization with Arf6 endosomes in heterologous cells and neurons\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — pathway assigned using dominant-negative constructs and inhibitors, single lab, single study\",\n      \"pmids\": [\"16890965\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The allosteric agonist AMN082 induces rapid mGluR7 internalization in hippocampal neurons, resistant to competitive orthosteric antagonists, as confirmed by pHluorin-tagged live imaging of surface receptor loss.\",\n      \"method\": \"Immunofluorescence internalization assay and live imaging with N-terminal pHluorin-tagged mGluR7 in dissociated hippocampal neurons\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal imaging methods, single lab\",\n      \"pmids\": [\"16914173\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"mGluR7 inhibits glutamate release at hippocampal nerve terminals primarily by inhibiting P/Q-type Ca2+ channels through a pertussis toxin-sensitive (Gi/o) PKC-independent mechanism; a separate pathway decreases cAMP when cAMP is elevated by forskolin.\",\n      \"method\": \"Glutamate release assays in rat hippocampal synaptosomes with selective Ca2+ channel blockers (ω-conotoxin), pertussis toxin, PKC inhibitors, PKA inhibitors, cAMP measurements\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro synaptosome assay with multiple pharmacological dissections and direct cAMP measurement, single lab with multiple orthogonal approaches\",\n      \"pmids\": [\"17650109\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"mGluR7 activation blocks LTP acquisition in the lateral amygdala and facilitates extinction of aversive memories; siRNA knockdown of mGluR7 attenuates extinction, demonstrating a required role for mGluR7 in amygdala plasticity and fear memory extinction.\",\n      \"method\": \"AMN082 pharmacological activation, siRNA knockdown in vivo, fear conditioning behavioral assays, lateral amygdala LTP electrophysiology in mice\",\n      \"journal\": \"Molecular psychiatry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — bidirectional manipulation (agonist + siRNA KD) with matched electrophysiological and behavioral readouts\",\n      \"pmids\": [\"17712315\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"mGluR7 surface expression requires both PKC phosphorylation at Ser862 (which inhibits CaM binding) and PICK1 binding; in PICK1 knockout mice, PKC-dependent increases in mGluR7 phosphorylation and surface expression are diminished, and mGluR7-dependent plasticity at mossy fiber–interneuron synapses is impaired.\",\n      \"method\": \"Site-directed mutagenesis of Ser862, surface biotinylation assays, co-immunoprecipitation, CaM binding assays, hippocampal slice electrophysiology in PICK1-/- mice\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis, biochemical assays, and electrophysiological validation in KO mice, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"18549785\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"mGluR7a signaling (GIRK channel activation) is potentiated by physiological increases in intracellular Ca2+, mediated through calmodulin binding to the C-terminal tail; light-gated Ca2+ influx via ChR2 markedly enhanced L-AP4-dependent GIRK currents, an effect attenuated by intracellular Ca2+ chelation.\",\n      \"method\": \"Xenopus oocyte electrophysiology with ChR2-mediated Ca2+ influx, BAPTA chelation, GIRK3.1/3.2 concatemer reporter\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — functional reconstitution in oocytes with optogenetic Ca2+ control and chelation, single lab, two orthogonal approaches\",\n      \"pmids\": [\"18599484\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Prolonged activation of mGlu7 receptors at cerebrocortical nerve terminals switches signaling from inhibition to potentiation of glutamate release; this potentiation involves phospholipase C activation, PIP2 hydrolysis, a pertussis toxin-insensitive G protein, and translocation of Munc13-1 from soluble to particulate fractions, independent of PKC.\",\n      \"method\": \"Glutamate release assays in synaptosomes with pertussis toxin, PLC inhibitors, calphostin C (DAG-binding site inhibitor), Ca2+ ionophore ionomycin, Munc13-1 subcellular fractionation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro synaptosome reconstitution with multiple pharmacological tools and biochemical fractionation, single lab\",\n      \"pmids\": [\"20375012\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Presynaptic mGlu7 receptors on hippocampal GABAergic terminals inhibit GABA release via an adenylyl cyclase-dependent (cAMP-mediated) mechanism; these mGlu7 heteroreceptors colocalize with syntaxin-1A, VGAT, and GABAB receptor subunits but do not functionally cross-talk with GABAB autoreceptors.\",\n      \"method\": \"[3H]GABA release from hippocampal synaptosomes with selective pharmacological tools (AMN082, MMPIP, cAMP pathway modulators, GABAB antagonists), confocal colocalization\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional release assays with selective NAM, pathway dissection with cAMP modulators, colocalization, single lab\",\n      \"pmids\": [\"22564442\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"GRK4 regulates mGluR7-dependent adenylyl cyclase and JNK pathways, while GRK2 selectively regulates the ERK1/2 pathway; β-arrestin1 and β-arrestin2 exert reciprocally opposite effects on ERK1/2 and JNK signaling downstream of mGluR7, with β-arrestin1 amplifying ERK1/2 activation by the orthosteric agonist L-AP4 but not by the allosteric agonist AMN082.\",\n      \"method\": \"Overexpression of GRK subtypes and β-arrestin isoforms in recombinant cells expressing mGluR7, with adenylyl cyclase, ERK1/2, and JNK pathway readouts\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — multiple signaling pathway readouts in heterologous cells, single lab, no in vivo validation\",\n      \"pmids\": [\"24148810\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PP1γ1 dephosphorylates Ser862 on mGluR7 and regulates agonist-induced (but not NMDA-induced) dephosphorylation and surface expression of mGluR7; PP1 inhibitors increase Ser862 phosphorylation and mGluR7 surface expression in neurons.\",\n      \"method\": \"Phospho-specific immunoblotting, surface biotinylation, PP1 inhibitor pharmacology, and PP1γ1 overexpression/knockdown in neurons\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical assays with pharmacological and genetic manipulation, demonstrated in primary neurons, single lab\",\n      \"pmids\": [\"23612982\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Elfn1 recruits mGluR7 to presynaptic sites of excitatory synapses onto somatostatin interneurons via a transsynaptic interaction; Elfn1 knockout mice show deficits in mGluR7 recruitment to these synapses and impaired presynaptic plasticity.\",\n      \"method\": \"Immunohistochemistry, co-immunoprecipitation, electrophysiology in Elfn1-KO mice, identification of damaging ELFN1 mutations in epilepsy/ADHD patients\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO mouse with matched biochemical (recruitment) and electrophysiological phenotype, confirmed transsynaptic interaction, replicated with human genetics\",\n      \"pmids\": [\"25047565\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The mGlu7-selective antagonist XAP044 acts via a binding pocket in the extracellular Venus flytrap domain (VFTD), not the transmembrane region; this was demonstrated by chimeric receptor studies in which the VFTD of mGlu7 conferred XAP044 sensitivity.\",\n      \"method\": \"Chimeric receptor construction and functional assays in recombinant cell lines; lateral amygdala LTP electrophysiology in wild-type and mGlu7-KO mice\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — chimeric receptor reconstitution defining binding domain, validated with KO electrophysiology, single lab with two orthogonal approaches\",\n      \"pmids\": [\"24596089\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"mGluR7 activation decreases NMDAR-mediated currents and NR1 surface expression in basal forebrain cholinergic neurons via cofilin-regulated actin dynamics; Aβ selectively impairs this mGluR7 regulation by increasing PAK activity and decreasing cofilin-mediated actin depolymerization through a p75NTR-dependent mechanism.\",\n      \"method\": \"Whole-cell patch-clamp recordings, surface biotinylation, actin dynamics assays (cofilin phosphorylation), PAK activity assays, p75NTR neutralization in rodent BF neurons\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (electrophysiology, biochemistry, actin dynamics) with mechanistic pathway dissection in primary neurons\",\n      \"pmids\": [\"25297090\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"mGlu7 receptor activation on cerebellar Purkinje cells mediates adaptively timed pauses in firing that constitute intrinsic cellular temporal memory; antagonists of mGlu7 but not other glutamate receptor subtypes abolished these learned responses in vivo.\",\n      \"method\": \"In vivo single-unit recordings in rat cerebellum with pharmacological blockade of mGlu7 and GABA receptors during conditioned stimulus presentation\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — in vivo electrophysiology with selective pharmacology, single lab\",\n      \"pmids\": [\"26655894\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"GRM7 knockdown reduces neural progenitor cell proliferation and promotes neuronal differentiation during cortical development; mGlu7 regulates CREB phosphorylation and YAP expression by directly interacting with calmodulin, controlling CyclinD1 expression.\",\n      \"method\": \"In utero electroporation knockdown/overexpression, immunofluorescence, co-immunoprecipitation (mGlu7-CaM interaction), Western blot in mouse cortex\",\n      \"journal\": \"Stem cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo knockdown with rescue experiments and biochemical co-IP, single lab\",\n      \"pmids\": [\"25921811\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"mGluR7 is SUMOylated at Lys889; this SUMOylation is reversed by SENP1 and is reduced by agonist (L-AP4) treatment. DeSUMOylation or SENP1 overexpression markedly increases mGluR7 internalization in hippocampal neurons, and Ser862 phosphorylation facilitates SUMO conjugation.\",\n      \"method\": \"SUMO conjugation assays in HEK293T cells, identification of SUMOylated mGluR7 in brain and cortical neurons by immunoprecipitation, SENP1 overexpression, mGluR7 internalization assays in hippocampal neurons\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical SUMOylation mapping in native neurons and heterologous cells, functional trafficking readout, single lab\",\n      \"pmids\": [\"26631532\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"mGlu7 receptors are functionally expressed at both glutamatergic and GABAergic thalamic synapses where they inhibit neurotransmission and regulate short-term plasticity in a PDZ-ligand-dependent manner; constitutive (tonic) mGlu7 activity prevents pathological thalamocortical synchrony, as in vivo NAM application induces absence-like seizures.\",\n      \"method\": \"Thalamic slice electrophysiology, optogenetics, pharmacology with NAM ADX71743, and in vivo EEG in mice with PDZ-domain mutant mGlu7\",\n      \"journal\": \"Frontiers in neural circuits\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — combination of electrophysiology, optogenetics, pharmacology and in vivo EEG, mechanistic link to PDZ domain via mutant mice\",\n      \"pmids\": [\"27199672\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"mGlu7 is the predominant mGlu receptor expressed presynaptically at Schaffer collateral–CA1 synapses in adult mice; its activation on GABAergic interneurons is necessary for LTP induction; MECP2 mutations reduce mGlu7 protein expression, and positive allosteric modulation of mGlu7 restores LTP and improves cognitive and social behaviors in RTT mouse models.\",\n      \"method\": \"Immunohistochemistry, hippocampal slice LTP recordings, behavioral testing (fear learning, novel object recognition, social memory), in vivo pharmacology in Mecp2 mutant mice\",\n      \"journal\": \"Science translational medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — combined electrophysiology, behavioral and molecular phenotyping with positive allosteric modulation rescue, validated in patient tissue\",\n      \"pmids\": [\"28814546\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Nedd4 E3 ubiquitin ligase ubiquitinates mGluR7 upon agonist stimulation; β-arrestins recruit Nedd4 to mGluR7 and facilitate ubiquitination; Nedd4 and β-arrestins are required for constitutive and agonist-induced endocytosis of mGluR7 and for mGluR7-dependent MAPK signaling; Nedd4-mediated ubiquitination leads to mGluR7 degradation via both the ubiquitin-proteasome system and lysosomal pathway.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays in heterologous cells and rat neurons, endocytosis assays, MAPK signaling assays, proteasome/lysosome inhibitors\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (co-IP, functional endocytosis, signaling assays) in both heterologous cells and neurons, single lab\",\n      \"pmids\": [\"31373553\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Elfn1 produces glutamate-independent (constitutive) activation of mGluR7 through presynaptic clustering, tonically suppressing initial release probability at synapses onto somatostatin interneurons, which is distinct from canonical autoreceptor function.\",\n      \"method\": \"Electrophysiology in cortical slices from Elfn1-KO mice, pharmacological mGluR7 activation/blockade, assessment of short-term synaptic facilitation in Layer 2/3 and Layer 5\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with electrophysiology and pharmacological dissection, layer-specific comparisons providing mechanistic insight, single lab\",\n      \"pmids\": [\"30940718\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"mGluR7 is N-glycosylated at four asparagine residues; N-glycosylation is essential for ER exit and forward trafficking to the plasma membrane; deglycosylated mGluR7 is retained in the ER and degraded via the autophagolysosomal pathway; N-glycosylation also promotes the mGluR7–Elfn1 transsynaptic interaction.\",\n      \"method\": \"Glycosylation-deficient mutagenesis, surface biotinylation, ER retention assays, co-immunoprecipitation with Elfn1, autophagy/lysosome inhibitor studies in heterologous cells and neurons\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis plus multiple biochemical readouts (trafficking, degradation, protein interaction) in heterologous and neuronal contexts, single lab\",\n      \"pmids\": [\"32931036\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"mGluR7 neddylation is required for presynaptic clustering and stabilization of mGluR7 protein; agonist treatment reduces neddylation; neddylation facilitates ubiquitination of mGluR7 and is necessary for maturation of excitatory presynaptic terminals.\",\n      \"method\": \"Neddylation assays in heterologous cells and primary neurons, neddylation inhibitor (MLN4924), presynaptic clustering immunostaining, synaptosome fractionation\",\n      \"journal\": \"Experimental & molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical modification assays with functional clustering and maturation readouts in neurons, single lab\",\n      \"pmids\": [\"33767338\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Pathogenic GRM7 mutations I154T and R658W/T675K cause degradation and loss of surface expression of mGluR7 protein; I154T and R658W/T675K mutations impair axon outgrowth and reduce presynaptic terminal number through the MAPK-cAMP-PKA signaling pathway; mGluR7 agonist treatment rescues I154T (which retains partial surface expression) but not R658W/T675K phenotypes.\",\n      \"method\": \"Expression of mutant constructs in HEK293A cells and rat primary neurons, surface biotinylation, axon outgrowth measurements, presynaptic terminal counting, MAPK/cAMP/PKA pathway assays, pharmacological rescue\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple mutations studied with biochemical, morphological, and signaling readouts including pharmacological rescue, in both heterologous and neuronal contexts\",\n      \"pmids\": [\"33500274\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cryo-EM structures of mGlu2 and mGlu7 homo- and heterodimers reveal that mGlu7 forms a distinct homodimer interface and a heterodimer with mGlu2; in the mGlu2–mGlu7 heterodimer, the mGlu7 subunit has a dominant role in controlling dimeric association and G-protein activation.\",\n      \"method\": \"Cryo-electron microscopy structure determination; functional studies of mGlu2–mGlu7 heterodimer G-protein activation\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structures at near-atomic resolution with functional validation of heterodimer G-protein coupling, high-impact journal\",\n      \"pmids\": [\"34135509\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"mGlu7/8 heterodimers modulate Schaffer collateral–CA1 synaptic transmission and LTP; ADX71743 (mGlu7 NAM) blocks responses of both mGlu7/7 homodimers and mGlu7/8 heterodimers, whereas MMPIP only antagonizes mGlu7/7 homodimers, explaining the differential pharmacology observed at SC-CA1 synapses.\",\n      \"method\": \"complemented donor-acceptor FRET (CODA-RET) to study heterodimer activation in vitro; hippocampal slice electrophysiology with differential NAM pharmacology\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — two orthogonal approaches (FRET-based in vitro heterodimer assay plus matched electrophysiology) with multiple structurally related compounds, single lab\",\n      \"pmids\": [\"36063995\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"mGluR7 (GRM7) is a presynaptic, Gi/o-coupled class C GPCR that inhibits adenylyl cyclase and modulates neurotransmitter release primarily by suppressing P/Q- and N-type Ca2+ channel activity; it exists as homodimers and heterodimers (e.g., with mGlu2 and mGlu8) with the mGlu7 subunit dominant for G-protein activation in heterodimers; its surface expression and trafficking are tightly regulated by a network of post-translational modifications (PKC phosphorylation of Ser862, CaM competitive binding, PICK1 PDZ interaction, PP1γ1-mediated dephosphorylation, SUMO conjugation at Lys889, Nedd4/β-arrestin-mediated ubiquitination and endocytosis, and N-glycosylation for ER exit) and by the transsynaptic Elfn1 interaction that constitutively activates and clusters mGluR7 at synapses onto somatostatin interneurons; pathogenic GRM7 mutations cause protein degradation, impair axon outgrowth via MAPK-cAMP-PKA signaling, and are linked to neurodevelopmental disorders including epileptic encephalopathy.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"GRM7 encodes mGluR7, a presynaptic Gi/o-coupled class C GPCR that inhibits forskolin-stimulated adenylyl cyclase upon agonist binding and serves as a low-affinity autoreceptor and heteroreceptor controlling neurotransmitter release at central synapses [#0, #13]. It is concentrated in presynaptic active zones of both glutamatergic and GABAergic terminals, including target-cell-specific GABAergic terminals innervating somatostatin and other interneurons [#1, #8, #18]. Mechanistically, mGluR7 suppresses glutamate release principally by inhibiting P/Q-type Ca2+ channels through a pertussis-toxin-sensitive, PKC-independent Gi/o pathway, with a parallel cAMP-lowering arm; prolonged activation can switch signaling from inhibition to PLC/Munc13-1-dependent potentiation of release [#13, #17]. Through these actions it sets short-term plasticity, acting as a metaplastic switch that gates LTD versus LTP at mossy fiber–interneuron synapses and is required for STP and frequency facilitation, perforant-path presynaptic inhibition, amygdala fear-memory extinction, and tonic suppression of pathological thalamocortical synchrony [#7, #9, #10, #14, #27]. Surface availability is governed by an integrated post-translational network: PKC/PKA/PKG phosphorylation of Ser862 competitively blocks calmodulin binding, PICK1 PDZ-domain binding and Ser862 phosphorylation jointly maintain surface expression, PP1γ1 dephosphorylates Ser862, SUMOylation at Lys889 and Nedd4/β-arrestin-mediated ubiquitination regulate constitutive Arf6- and clathrin-independent endocytosis and degradation, neddylation stabilizes presynaptic clusters, and N-glycosylation is required for ER exit and forward trafficking [#5, #6, #15, #20, #26, #29, #11, #31, #32]. The transsynaptic ligand Elfn1 recruits and constitutively (glutamate-independently) activates and clusters mGluR7 at synapses onto somatostatin interneurons, tonically lowering release probability [#21, #30]. mGluR7 forms homodimers and an mGlu2–mGlu7 heterodimer in which the mGlu7 subunit dominates G-protein activation, and assembles mGlu7/8 heterodimers with distinct allosteric pharmacology [#34, #35]. Pathogenic GRM7 mutations cause receptor degradation, loss of surface expression, and impaired axon outgrowth via MAPK-cAMP-PKA signaling, linking the gene to neurodevelopmental disorders; reduced mGlu7 expression also underlies plasticity and behavioral deficits in Rett syndrome models, where positive allosteric modulation restores function [#33, #28].\",\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Established mGluR7 as a functional receptor by showing it couples negatively to adenylyl cyclase, defining its core signaling output.\",\n      \"evidence\": \"Heterologous expression in CHO cells with agonist-driven cAMP accumulation assay\",\n      \"pmids\": [\"8288585\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address subcellular localization or native synaptic role\", \"Downstream effectors beyond cAMP unresolved\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Determined where the receptor acts by localizing it presynaptically in axon terminals and at ribbon-synapse active zones, supporting an autoreceptor function.\",\n      \"evidence\": \"Immunohistochemistry with dorsal rhizotomy lesion and EM double-labeling in spinal cord and retina\",\n      \"pmids\": [\"8787837\", \"8764662\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of active-zone restriction not tested\", \"Postsynaptic pool function in amacrine cells uncharacterized\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Identified scaffolding and phosphoregulatory control by showing PICK1 binds the C-terminal PDZ motif and assembles a complex with PKCα that regulates receptor phosphorylation.\",\n      \"evidence\": \"Yeast two-hybrid, GST pulldown, co-IP from brain, and in vitro kinase assays\",\n      \"pmids\": [\"11007882\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional impact on surface expression not yet shown\", \"Phosphosite not yet mapped\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Mapped the phosphoregulatory switch to Ser862, where PKC/PKA/PKG phosphorylation blocks calmodulin binding, defining a competitive CaM/phosphorylation node.\",\n      \"evidence\": \"Ser862 mutagenesis, in vitro kinase and CaM-binding assays, GIRK current recordings\",\n      \"pmids\": [\"12021391\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"GIRK inhibition shown independent of Ser862/CaM, leaving that effector pathway unexplained\", \"In vivo relevance not tested\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Assigned mGluR7 a specific circuit role in presynaptic inhibition at perforant-path synapses and linked its loss to epileptogenesis.\",\n      \"evidence\": \"Field EPSP recordings in multiple KO strains with selective agonists; pilocarpine status epilepticus model\",\n      \"pmids\": [\"15152022\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of post-seizure downregulation unresolved\", \"Molecular effector at this synapse not defined\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Defined the proximal release-inhibition mechanism as P/Q-type Ca2+ channel suppression via Gi/o, distinguishing it from the cAMP-lowering arm.\",\n      \"evidence\": \"Synaptosome glutamate release assays with conotoxin, pertussis toxin, and kinase inhibitors plus cAMP measurement\",\n      \"pmids\": [\"17650109\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct Gβγ-channel interaction not demonstrated\", \"Relative contribution of two arms in vivo unclear\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Integrated trafficking control by demonstrating that both Ser862 phosphorylation and PICK1 binding are required for surface expression and mGluR7-dependent plasticity.\",\n      \"evidence\": \"Ser862 mutagenesis, surface biotinylation, co-IP, and slice electrophysiology in PICK1-KO mice\",\n      \"pmids\": [\"18549785\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endocytic machinery executing internalization not identified here\", \"Temporal dynamics of surface regulation unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Revealed signaling plasticity: prolonged activation switches mGluR7 from release inhibition to PLC/Munc13-1-dependent potentiation via a PTX-insensitive G protein.\",\n      \"evidence\": \"Cerebrocortical synaptosome release assays with PLC inhibitors, ionomycin, and Munc13-1 fractionation\",\n      \"pmids\": [\"20375012\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the PTX-insensitive G protein not defined\", \"In vivo behavioral relevance of the switch untested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Expanded the post-translational network by identifying PP1γ1 as the Ser862 phosphatase and GRK/β-arrestin isoform-specific control of downstream MAPK arms.\",\n      \"evidence\": \"Phospho-immunoblotting, surface biotinylation, PP1 manipulation in neurons; GRK/β-arrestin overexpression with AC/ERK/JNK readouts\",\n      \"pmids\": [\"23612982\", \"24148810\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"GRK/β-arrestin study lacks in vivo validation\", \"Biased agonism between L-AP4 and AMN082 not mechanistically resolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identified Elfn1 as the transsynaptic organizer that recruits mGluR7 to specific somatostatin-interneuron synapses, defining target-cell-specific receptor placement.\",\n      \"evidence\": \"Co-IP, immunohistochemistry, and electrophysiology in Elfn1-KO mice with human genetic correlation\",\n      \"pmids\": [\"25047565\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether recruitment alters receptor signaling state not yet shown here\", \"Structural basis of the interaction undefined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Showed Ca2+/calmodulin potentiates mGluR7 signaling and that the receptor also regulates neural progenitor proliferation via CaM-dependent CREB/YAP/CyclinD1 control, extending its role to development.\",\n      \"evidence\": \"Oocyte GIRK recordings with optogenetic Ca2+ control; in utero electroporation knockdown with co-IP in mouse cortex\",\n      \"pmids\": [\"18599484\", \"25921811\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Developmental signaling shown in single lab without genetic KO\", \"Link between CaM binding and proliferation effectors incompletely mapped\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Established SUMOylation at Lys889 as an agonist-sensitive modification gating receptor internalization, adding a further trafficking control layer.\",\n      \"evidence\": \"SUMO conjugation assays, SENP1 manipulation, and internalization assays in neurons\",\n      \"pmids\": [\"26631532\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Effector linking deSUMOylation to endocytosis not identified\", \"In vivo synaptic consequence untested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Connected mGluR7 to disease by showing MECP2 mutations reduce its expression and that positive allosteric modulation restores LTP and behavior in Rett models.\",\n      \"evidence\": \"Immunohistochemistry, slice LTP, behavior, and in vivo pharmacology in Mecp2 mutant mice with patient tissue\",\n      \"pmids\": [\"28814546\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which MECP2 controls GRM7 expression unresolved\", \"Durability of PAM rescue not addressed\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Resolved the constitutive endocytic and degradation machinery: β-arrestins recruit Nedd4 to ubiquitinate mGluR7, driving proteasomal and lysosomal degradation and MAPK signaling.\",\n      \"evidence\": \"Co-IP, ubiquitination, endocytosis, and signaling assays with proteasome/lysosome inhibitors in cells and neurons\",\n      \"pmids\": [\"31373553\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Ubiquitination site(s) not mapped\", \"Balance between proteasomal and lysosomal routing not quantified\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Clarified that Elfn1 produces glutamate-independent constitutive activation and clustering of mGluR7, distinguishing it from canonical autoreceptor signaling.\",\n      \"evidence\": \"Cortical slice electrophysiology in Elfn1-KO mice with pharmacological dissection across cortical layers\",\n      \"pmids\": [\"30940718\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural mechanism of ligand-independent activation undefined\", \"Whether other partners drive constitutive activity elsewhere unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Defined N-glycosylation as a prerequisite for ER exit and forward trafficking, with deglycosylated receptor degraded autophagolysosomally and impaired Elfn1 binding.\",\n      \"evidence\": \"Glycosylation-deficient mutagenesis, surface biotinylation, ER-retention and co-IP assays in cells and neurons\",\n      \"pmids\": [\"32931036\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quality-control machinery recognizing unglycosylated receptor not identified\", \"Whether glycosylation tunes signaling beyond trafficking unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identified neddylation as a stabilizing modification required for presynaptic clustering and terminal maturation, and provided high-resolution structures of mGlu7 dimers showing mGlu7 dominance in heterodimeric G-protein activation.\",\n      \"evidence\": \"Neddylation assays with MLN4924 and clustering readouts; cryo-EM of mGlu2/mGlu7 homo- and heterodimers with functional validation\",\n      \"pmids\": [\"33767338\", \"34135509\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Neddylation site and interplay with ubiquitination not fully resolved\", \"Functional role of mGlu7 homodimer interface in vivo untested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstrated disease causality by showing pathogenic GRM7 mutations cause receptor degradation, loss of surface expression, and impaired axon outgrowth via MAPK-cAMP-PKA signaling, with mutation-dependent pharmacological rescue.\",\n      \"evidence\": \"Mutant expression in cells and neurons with biotinylation, axon outgrowth, terminal counting, signaling assays, and agonist rescue\",\n      \"pmids\": [\"33500274\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo modeling of patient mutations not performed\", \"Genotype–phenotype correlation across the disorder spectrum incomplete\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined heterodimer-specific pharmacology by showing mGlu7/8 heterodimers and mGlu7/7 homodimers respond differentially to NAMs, explaining native synaptic drug responses.\",\n      \"evidence\": \"CODA-RET heterodimer activation assays plus hippocampal slice electrophysiology with differential NAMs\",\n      \"pmids\": [\"36063995\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and abundance of native heterodimers unresolved\", \"Distinct signaling outputs of each dimer species not fully mapped\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the multiple post-translational modifications, dimerization states, and Elfn1-driven constitutive activation are coordinated in space and time to set synapse-specific output remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No integrated model linking glycosylation, SUMOylation, ubiquitination, neddylation, and phosphorylation dynamics\", \"Native dimer composition at defined synapses unknown\", \"Structural basis of Elfn1-induced constitutive activation undetermined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 13, 34]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [13, 18]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 2, 8, 15]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [31]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [11, 29]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 13, 19]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [7, 9, 10, 27]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [29, 31, 32]}\n    ],\n    \"complexes\": [\"mGlu2–mGlu7 heterodimer\", \"mGlu7/8 heterodimer\", \"mGluR7–PICK1–PKCα complex\"],\n    \"partners\": [\"PICK1\", \"ELFN1\", \"CALM1\", \"PPP1CC\", \"NEDD4\", \"GRM2\", \"GRM8\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":7,"faith_total":7,"faith_pct":100.0}}