{"gene":"LRRTM2","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":2009,"finding":"LRRTM2 localizes to excitatory synapses in hippocampal neurons and its shRNA-mediated knockdown decreases excitatory (but not inhibitory) synapse number. LRRTM2 interacts with PSD-95 and regulates surface expression of AMPA receptors. Lentivirus-mediated knockdown in vivo decreases evoked excitatory synaptic current strength. The extracellular LRR domain is required for inducing presynaptic differentiation.","method":"shRNA knockdown in hippocampal neurons, lentiviral in vivo knockdown, immunostaining, electrophysiology, structure-function mutagenesis","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (KD, in vivo electrophysiology, domain deletion) replicated across two independent papers in the same issue","pmids":["20064388"],"is_preprint":false},{"year":2009,"finding":"LRRTM2 binds specifically to alpha- and beta-neurexins lacking an insert at splice site #4 (but not neurexins with the SS4 insert), identified by affinity chromatography. This binding is distinct from neuroligin-1 which binds neurexins regardless of SS4. Recombinant neurexin-1beta blocks LRRTM2-induced presynaptic differentiation, confirming the trans-synaptic interaction.","method":"Affinity chromatography, cell-adhesion assay, blocking experiments with recombinant neurexin","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — affinity chromatography plus functional blocking, independently replicated in two simultaneous papers","pmids":["20064387","20064388"],"is_preprint":false},{"year":2009,"finding":"LRRTM2 expressed in non-neuronal cells induces exclusively excitatory (not inhibitory) presynaptic differentiation in contacting axons, and when expressed in transfected neurons induces synapses similarly to neuroligin-1.","method":"Coculture synaptogenic assay with non-neuronal cells and neurons, immunostaining for synaptic markers","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 / Strong — coculture assay replicated in two independent labs simultaneously","pmids":["20064387","20064388"],"is_preprint":false},{"year":2016,"finding":"Crystal structure of a thermostabilized mouse LRRTM2 was solved, revealing the concave LRR surface as the neurexin-binding site, determined by protein engineering, sequence conservation analysis, and binding affinity measurements. Wild-type LRRTM1 and LRRTM2 bind neurexin-beta1 in a Ca2+-dependent manner.","method":"X-ray crystallography, protein engineering (thermostabilization), surface plasmon resonance/binding affinity measurements, cell culture synaptogenic assay","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure with mutagenesis mapping of binding site and functional validation in cell culture, single lab","pmids":["26785044"],"is_preprint":false},{"year":2018,"finding":"Conditional knockout of LRRTM1 and LRRTM2 in CA1 neurons in vivo impairs LTP and reduces AMPA receptor-mediated (but not NMDA receptor-mediated) synaptic transmission without affecting presynaptic function. LRRTM2 (but not LRRTM4) rescues both LTP and AMPA transmission. Mutation of LRRTM2's neurexin-binding interface prevents rescue of LTP, while deletion of the intracellular tail does not. Photo-activated GluA1 is less stable at spines lacking LRRTM1/2.","method":"Conditional knockout mouse, Cre lentivirus, whole-cell patch-clamp electrophysiology, site-directed mutagenesis, single-molecule photoactivation imaging (PAGFP-GluA1)","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — conditional genetic KO with multiple orthogonal methods (electrophysiology, mutagenesis, live imaging), rigorous domain-specific rescue experiments","pmids":["29784826"],"is_preprint":false},{"year":2021,"finding":"Acute severing of the LRRTM2 extracellular domain (using engineered rapid proteolysis) causes rapid nanoscale declustering of AMPARs away from presynaptic release sites before any loss of total receptor number, producing deficits in evoked but not spontaneous postsynaptic currents. This dissociates receptor number from subsynaptic nano-positioning as independent determinants of synaptic strength.","method":"Engineered LRRTM2 extracellular domain cleavage (TEV-based), STORM super-resolution microscopy, electrophysiology (evoked vs. spontaneous EPSCs)","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — acute domain-specific manipulation combined with super-resolution imaging and electrophysiology, single lab but multiple orthogonal methods","pmids":["34417170"],"is_preprint":false},{"year":2021,"finding":"The LRRTM2 C-terminal intracellular domain is required for synaptic confinement and membrane dynamics: deletion of the C-terminal domain abolishes dendritic compartmentalization and increases diffusion. Synaptic confinement depends critically on a YxxC motif in the C-terminal domain, not on the PDZ-like binding motif (ECEV). The nanoscale organization of LRRTM2 requires both the PDZ-binding and YxxC motifs.","method":"shRNA knockdown, single-molecule tracking (uPAINT), super-resolution dSTORM microscopy, C-terminal domain deletion/point mutants","journal":"Biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — single molecule tracking and super-resolution with domain mutants, single lab","pmids":["34498765"],"is_preprint":false},{"year":2019,"finding":"LRRTM2 synaptogenic activity in cortical neurons is independent of N-cadherin expression and function at both immature (6-7 DIV) and mature (14-15 DIV) stages, whereas neuroligin-1 synaptogenic activity requires N-cadherin in immature neurons. LRRTM2 retains significant synaptogenic activity at more mature stages (12-13 DIV) when neuroligin-1 activity diminishes.","method":"Overexpression in cultured mouse cortical neurons, immunostaining for VAMP2 and VGLUT1/Homer1, N-cadherin knockdown/function blocking","journal":"Frontiers in molecular neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — coculture synaptogenic assay with genetic manipulation of N-cadherin, single lab, two orthogonal readouts","pmids":["31780894"],"is_preprint":false},{"year":2014,"finding":"Lrrtm2 expression is upregulated by nuclear calcium signaling downstream of synaptic NMDA receptor activation in hippocampal neurons, in a manner dependent on calcium/calmodulin-dependent protein kinases and the CREB-binding protein. A functional cAMP response element in the proximal Lrrtm2 promoter mediates regulation via the CaMKIV-CREB/CBP pathway, independent of new protein synthesis.","method":"Neuronal activity induction, reporter gene constructs, pharmacological inhibition of CaMK and CBP, calcium buffering experiments","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reporter gene assay plus pharmacological dissection, single lab, multiple pathway components tested","pmids":["25527504"],"is_preprint":false},{"year":2024,"finding":"The N-terminal extracellular domain of LRRTM2 (specifically the recently identified Neurexin-binding interface/C-terminal cap of the LRR domain) controls presynaptic nano-organization and postsynaptic AMPAR sub-positioning and stabilization. The C-terminal intracellular domain controls surface expression, synaptic clustering, and membrane dynamics through selective motifs. LRRTM2 cKO specifically impairs excitatory synapse formation and function in mice.","method":"Conditional knockout mouse, domain-specific mutants, super-resolution microscopy, electrophysiology","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — conditional KO with domain-specific mutagenesis, super-resolution imaging, and electrophysiology in a single rigorous study","pmids":["39394199"],"is_preprint":false},{"year":2025,"finding":"Using whole-CDS CRISPR replacement, endogenous N-terminally tagged LRRTM2 was found in ~80% of synapses, and synaptic LRRTM2 content positively correlates with PSD-95 and AMPAR levels. LRRTM2 is also enriched with AMPARs outside synapses. Mutation of the C-terminal domain increases synaptic LRRTM2 levels but does not correspondingly increase AMPAR enrichment.","method":"Two-guide CRISPR knock-in of tagged endogenous LRRTM2 in rat hippocampal neurons, quantitative fluorescence imaging","journal":"The Journal of neuroscience : the official journal of the Society for Neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — endogenous tagging via CRISPR with quantitative imaging and C-terminal domain mutation, single lab","pmids":["39824639"],"is_preprint":false},{"year":2022,"finding":"Double knockout of LRRTM1 and LRRTM2 in mice impairs excitatory synapse density and morphological integrity on CA1 pyramidal neurons during development but not in the mature circuit. Both proteins are required for LTP in the CA3-CA1 pathway and dentate gyrus, and for enduring fear memory, in both developing and mature brain.","method":"Double conditional knockout mouse, electron and confocal microscopy, LTP electrophysiology, fear conditioning behavioral assay","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with electrophysiology and behavior, but findings are for the LRRTM1/2 double KO and cannot always be attributed solely to LRRTM2","pmids":["35662394"],"is_preprint":false},{"year":2026,"finding":"In callosal projection neurons (CPN), deletion of transcription factor Bcl11a disrupts targeting of Lrrtm2 to growth cone membranes, causing cytoplasmic sequestration of key surface proteins and aberrant innervation of basolateral amygdala. This identifies a non-canonical, presynaptic (growth cone) role for LRRTM2 in regulating axon targeting and circuit specificity.","method":"CPN-specific Bcl11a deletion, in vivo growth cone proteomics, ex vivo localization validation, axonal projection tracing","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — preprint, proteomics plus projection tracing but limited direct mechanistic dissection of LRRTM2 itself; novel non-canonical role not yet peer-reviewed","pmids":["41993341"],"is_preprint":true}],"current_model":"LRRTM2 is a postsynaptic leucine-rich repeat transmembrane protein that localizes to excitatory synapses where its extracellular LRR domain binds specifically to splice-site-4-lacking neurexins (both α and β) on the presynaptic membrane to induce and organize presynaptic differentiation; intracellularly it associates with PSD-95 and its C-terminal YxxC and PDZ-binding motifs control synaptic confinement and nanoscale organization, while the transsynaptic neurexin interaction positions and stabilizes AMPA receptors within postsynaptic nanocolumns to set the strength of evoked excitatory transmission and enable LTP; its expression is transcriptionally upregulated by nuclear calcium signaling via CaMKIV-CREB/CBP following synaptic NMDA receptor activation."},"narrative":{"mechanistic_narrative":"LRRTM2 is a postsynaptic leucine-rich repeat transmembrane protein that localizes to excitatory synapses and organizes excitatory synapse formation, strength, and plasticity [PMID:20064388, PMID:20064387]. Its extracellular LRR domain induces presynaptic differentiation by binding specifically to α- and β-neurexins lacking an insert at splice site 4 [PMID:20064387, PMID:20064388]; crystallography maps this trans-synaptic interaction to the concave LRR surface and shows it is Ca2+-dependent [PMID:26785044]. Through this neurexin interface, LRRTM2 stabilizes AMPA receptors and positions them in register with presynaptic release sites: conditional knockout of LRRTM1/2 selectively reduces AMPAR-mediated transmission and impairs LTP, and rescue requires an intact neurexin-binding interface but not the intracellular tail [PMID:29784826]. Acute cleavage of the extracellular domain rapidly disperses AMPAR nanoclusters from release sites before total receptor number falls, dissociating nano-positioning from receptor abundance as independent determinants of evoked strength [PMID:34417170]. The C-terminal intracellular domain governs surface expression, synaptic confinement, and membrane diffusion via a YxxC motif together with a PDZ-binding motif, and LRRTM2 associates with PSD-95 [PMID:20064388, PMID:34498765, PMID:39394199]. Endogenous tagging shows LRRTM2 occupies most synapses and its level correlates with PSD-95 and AMPAR content [PMID:39824639]. Lrrtm2 transcription is induced by synaptic NMDA-receptor activity through a nuclear calcium–CaMKIV–CREB/CBP pathway acting on a promoter cAMP response element [PMID:25527504].","teleology":[{"year":2009,"claim":"Established LRRTM2 as a postsynaptic organizer that selectively builds excitatory synapses and sets their strength, answering whether it has a defined synaptic function.","evidence":"shRNA and lentiviral in vivo knockdown, immunostaining, electrophysiology, and domain deletion in hippocampal neurons; coculture synaptogenic assays","pmids":["20064388","20064387"],"confidence":"High","gaps":["Did not identify the presynaptic receptor for the LRR domain","Mechanism linking LRRTM2 to AMPAR surface expression unresolved"]},{"year":2009,"claim":"Identified the trans-synaptic ligand as SS4-lacking neurexins, defining the molecular basis for LRRTM2-induced presynaptic differentiation and distinguishing it from neuroligin-1.","evidence":"Affinity chromatography, cell-adhesion assays, and blocking with recombinant neurexin-1β","pmids":["20064387","20064388"],"confidence":"High","gaps":["Did not resolve the structural binding interface","Did not establish how binding controls postsynaptic AMPARs"]},{"year":2014,"claim":"Showed that Lrrtm2 is an activity-regulated gene, linking synaptic NMDA-receptor signaling to its transcription and explaining how its expression is tuned by activity.","evidence":"Activity induction with reporter constructs, pharmacological inhibition of CaMK/CBP, and calcium buffering in hippocampal neurons","pmids":["25527504"],"confidence":"Medium","gaps":["Functional consequence of activity-dependent upregulation on synaptic strength not tested","Single-lab reporter dissection"]},{"year":2016,"claim":"Resolved the atomic basis of neurexin binding, mapping the interaction to the concave LRR surface and confirming Ca2+ dependence.","evidence":"X-ray crystallography of thermostabilized mouse LRRTM2, protein engineering, binding affinity measurements, and synaptogenic assays","pmids":["26785044"],"confidence":"High","gaps":["No co-crystal structure of the LRRTM2-neurexin complex","Did not address intracellular signaling"]},{"year":2018,"claim":"Demonstrated through genetic knockout and domain-specific rescue that the neurexin-binding interface, not the cytoplasmic tail, drives AMPAR transmission and LTP in vivo.","evidence":"Conditional LRRTM1/2 knockout, Cre lentivirus, patch-clamp, site-directed mutagenesis, and PAGFP-GluA1 photoactivation imaging","pmids":["29784826"],"confidence":"High","gaps":["Redundancy between LRRTM1 and LRRTM2 not fully separated","Did not resolve subsynaptic positioning of AMPARs"]},{"year":2021,"claim":"Separated AMPAR nano-positioning from receptor number as independent strength determinants by acutely severing the extracellular domain.","evidence":"Engineered TEV-based extracellular domain cleavage, STORM super-resolution microscopy, and evoked-versus-spontaneous EPSC recordings","pmids":["34417170"],"confidence":"High","gaps":["Molecular link from the extracellular interaction to nanocolumn alignment not defined","Single lab"]},{"year":2021,"claim":"Assigned synaptic confinement and membrane dynamics to a YxxC motif in the C-terminal tail, distinguishing its role from the PDZ-binding motif.","evidence":"shRNA knockdown, uPAINT single-molecule tracking, dSTORM, and C-terminal deletion/point mutants","pmids":["34498765"],"confidence":"Medium","gaps":["Trafficking machinery engaging the YxxC motif unidentified","Single lab"]},{"year":2022,"claim":"Showed LRRTM1/2 are developmentally required for excitatory synapse density and morphology and continuously required for LTP and fear memory.","evidence":"Double conditional knockout, electron/confocal microscopy, LTP electrophysiology, and fear conditioning","pmids":["35662394"],"confidence":"Medium","gaps":["Phenotypes cannot be attributed to LRRTM2 alone due to double-KO design","Cell-type specificity beyond CA1/dentate not addressed"]},{"year":2024,"claim":"Integrated extracellular and intracellular determinants, attributing presynaptic nano-organization and AMPAR sub-positioning to the neurexin interface and surface expression/clustering to selective C-terminal motifs.","evidence":"Conditional knockout, domain-specific mutants, super-resolution microscopy, and electrophysiology","pmids":["39394199"],"confidence":"High","gaps":["Quantitative stoichiometry of LRRTM2-AMPAR coupling not defined"]},{"year":2025,"claim":"Quantified endogenous LRRTM2 distribution, showing it occupies most synapses and scales with PSD-95 and AMPAR levels, including extrasynaptic AMPAR co-enrichment.","evidence":"Two-guide CRISPR knock-in of N-terminally tagged endogenous LRRTM2 in rat hippocampal neurons with quantitative imaging","pmids":["39824639"],"confidence":"Medium","gaps":["C-terminal mutation raised LRRTM2 without matching AMPAR gain, leaving the coupling rule unexplained","Single lab"]},{"year":2026,"claim":"Proposed a non-canonical presynaptic role in which Bcl11a-dependent trafficking of Lrrtm2 to growth cone membranes governs axon targeting and circuit specificity.","evidence":"CPN-specific Bcl11a deletion, in vivo growth cone proteomics, localization validation, and projection tracing (preprint)","pmids":["41993341"],"confidence":"Low","gaps":["Preprint, not peer-reviewed","Limited direct mechanistic dissection of LRRTM2 in the growth cone","Whether the targeting role is direct or secondary to broad surface-protein mislocalization is unclear"]},{"year":null,"claim":"How the trans-synaptic neurexin interaction is mechanistically transduced across the membrane to align and stabilize AMPAR nanoclusters remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No defined molecular chain linking extracellular neurexin binding to intracellular AMPAR anchoring","No co-structure of the trans-synaptic complex","Quantitative rule coupling LRRTM2 abundance to AMPAR content unexplained"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098631","term_label":"cell adhesion mediator activity","supporting_discovery_ids":[1,2,3]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,4,5]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,6,10]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[0,4]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[2,11]}],"complexes":[],"partners":["NRXN1","DLG4"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O43300","full_name":"Leucine-rich repeat transmembrane neuronal protein 2","aliases":["Leucine-rich repeat neuronal 2 protein"],"length_aa":516,"mass_kda":59.1,"function":"Involved in the development and maintenance of excitatory synapses in the vertebrate nervous system. Regulates surface expression of AMPA receptors and instructs the development of functional glutamate release sites. Acts as a ligand for the presynaptic receptors NRXN1-A and NRXN1-B (By similarity)","subcellular_location":"Cell membrane; Postsynaptic cell membrane","url":"https://www.uniprot.org/uniprotkb/O43300/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/LRRTM2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/LRRTM2","total_profiled":1310},"omim":[{"mim_id":"610868","title":"LEUCINE-RICH REPEAT TRANSMEMBRANE PROTEIN 2; LRRTM2","url":"https://www.omim.org/entry/610868"},{"mim_id":"610867","title":"LEUCINE-RICH REPEAT TRANSMEMBRANE PROTEIN 1: LRRTM1","url":"https://www.omim.org/entry/610867"},{"mim_id":"603731","title":"CCR4-NOT TRANSCRIPTION COMPLEX, SUBUNIT 8; CNOT8","url":"https://www.omim.org/entry/603731"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"brain","ntpm":16.3}],"url":"https://www.proteinatlas.org/search/LRRTM2"},"hgnc":{"alias_symbol":["KIAA0416"],"prev_symbol":[]},"alphafold":{"accession":"O43300","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O43300","model_url":"https://alphafold.ebi.ac.uk/files/AF-O43300-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O43300-F1-predicted_aligned_error_v6.png","plddt_mean":79.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=LRRTM2","jax_strain_url":"https://www.jax.org/strain/search?query=LRRTM2"},"sequence":{"accession":"O43300","fasta_url":"https://rest.uniprot.org/uniprotkb/O43300.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O43300/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O43300"}},"corpus_meta":[{"pmid":"20064388","id":"PMC_20064388","title":"LRRTM2 interacts with Neurexin1 and regulates excitatory synapse formation.","date":"2009","source":"Neuron","url":"https://pubmed.ncbi.nlm.nih.gov/20064388","citation_count":309,"is_preprint":false},{"pmid":"20064387","id":"PMC_20064387","title":"LRRTM2 functions as a neurexin ligand in promoting excitatory synapse formation.","date":"2009","source":"Neuron","url":"https://pubmed.ncbi.nlm.nih.gov/20064387","citation_count":303,"is_preprint":false},{"pmid":"34417170","id":"PMC_34417170","title":"Subsynaptic positioning of AMPARs by LRRTM2 controls synaptic strength.","date":"2021","source":"Science advances","url":"https://pubmed.ncbi.nlm.nih.gov/34417170","citation_count":83,"is_preprint":false},{"pmid":"29784826","id":"PMC_29784826","title":"Deletion of LRRTM1 and LRRTM2 in adult mice impairs basal AMPA receptor transmission and LTP in hippocampal CA1 pyramidal neurons.","date":"2018","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/29784826","citation_count":61,"is_preprint":false},{"pmid":"35662394","id":"PMC_35662394","title":"Distinct but overlapping roles of LRRTM1 and LRRTM2 in developing and mature hippocampal circuits.","date":"2022","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/35662394","citation_count":18,"is_preprint":false},{"pmid":"26785044","id":"PMC_26785044","title":"Crystal Structure of an Engineered LRRTM2 Synaptic Adhesion Molecule and a Model for Neurexin Binding.","date":"2016","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/26785044","citation_count":17,"is_preprint":false},{"pmid":"23326251","id":"PMC_23326251","title":"5q31 Microdeletions: Definition of a Critical Region and Analysis of LRRTM2, a Candidate Gene for Intellectual Disability.","date":"2012","source":"Molecular syndromology","url":"https://pubmed.ncbi.nlm.nih.gov/23326251","citation_count":13,"is_preprint":false},{"pmid":"21708131","id":"PMC_21708131","title":"Bidirectional transcription from human LRRTM2/CTNNA1 and LRRTM1/CTNNA2 gene loci leads to expression of N-terminally truncated CTNNA1 and CTNNA2 isoforms.","date":"2011","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/21708131","citation_count":10,"is_preprint":false},{"pmid":"31780894","id":"PMC_31780894","title":"Differential Properties of the Synaptogenic Activities of the Neurexin Ligands Neuroligin1 and LRRTM2.","date":"2019","source":"Frontiers in molecular neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/31780894","citation_count":7,"is_preprint":false},{"pmid":"39394199","id":"PMC_39394199","title":"LRRTM2 controls presynapse nano-organization and AMPA receptor sub-positioning through Neurexin-binding interface.","date":"2024","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/39394199","citation_count":6,"is_preprint":false},{"pmid":"34498765","id":"PMC_34498765","title":"Role of regulatory C-terminal motifs in synaptic confinement of LRRTM2.","date":"2021","source":"Biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/34498765","citation_count":5,"is_preprint":false},{"pmid":"25527504","id":"PMC_25527504","title":"Nuclear calcium signaling induces expression of the synaptic organizers Lrrtm1 and Lrrtm2.","date":"2014","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/25527504","citation_count":3,"is_preprint":false},{"pmid":"39824639","id":"PMC_39824639","title":"Large Donor CRISPR for Whole-Coding Sequence Replacement of Cell Adhesion Molecule LRRTM2.","date":"2025","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/39824639","citation_count":0,"is_preprint":false},{"pmid":"41993341","id":"PMC_41993341","title":"Sequestration of growth cone surface proteins by cytoplasmic Lrrtm2 induces de novo amygdala innervation by cerebral cortex associative neurons.","date":"2026","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/41993341","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":9005,"output_tokens":3500,"usd":0.039758,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":11095,"output_tokens":3494,"usd":0.071413,"stage2_stop_reason":"end_turn"},"total_usd":0.111171,"stage1_batch_id":"msgbatch_01BbTCMyrRPyhtEq6b1MdwCN","stage2_batch_id":"msgbatch_011dEed5bbxYvTAaQWKJevxu","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2009,\n      \"finding\": \"LRRTM2 localizes to excitatory synapses in hippocampal neurons and its shRNA-mediated knockdown decreases excitatory (but not inhibitory) synapse number. LRRTM2 interacts with PSD-95 and regulates surface expression of AMPA receptors. Lentivirus-mediated knockdown in vivo decreases evoked excitatory synaptic current strength. The extracellular LRR domain is required for inducing presynaptic differentiation.\",\n      \"method\": \"shRNA knockdown in hippocampal neurons, lentiviral in vivo knockdown, immunostaining, electrophysiology, structure-function mutagenesis\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (KD, in vivo electrophysiology, domain deletion) replicated across two independent papers in the same issue\",\n      \"pmids\": [\"20064388\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"LRRTM2 binds specifically to alpha- and beta-neurexins lacking an insert at splice site #4 (but not neurexins with the SS4 insert), identified by affinity chromatography. This binding is distinct from neuroligin-1 which binds neurexins regardless of SS4. Recombinant neurexin-1beta blocks LRRTM2-induced presynaptic differentiation, confirming the trans-synaptic interaction.\",\n      \"method\": \"Affinity chromatography, cell-adhesion assay, blocking experiments with recombinant neurexin\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — affinity chromatography plus functional blocking, independently replicated in two simultaneous papers\",\n      \"pmids\": [\"20064387\", \"20064388\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"LRRTM2 expressed in non-neuronal cells induces exclusively excitatory (not inhibitory) presynaptic differentiation in contacting axons, and when expressed in transfected neurons induces synapses similarly to neuroligin-1.\",\n      \"method\": \"Coculture synaptogenic assay with non-neuronal cells and neurons, immunostaining for synaptic markers\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — coculture assay replicated in two independent labs simultaneously\",\n      \"pmids\": [\"20064387\", \"20064388\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Crystal structure of a thermostabilized mouse LRRTM2 was solved, revealing the concave LRR surface as the neurexin-binding site, determined by protein engineering, sequence conservation analysis, and binding affinity measurements. Wild-type LRRTM1 and LRRTM2 bind neurexin-beta1 in a Ca2+-dependent manner.\",\n      \"method\": \"X-ray crystallography, protein engineering (thermostabilization), surface plasmon resonance/binding affinity measurements, cell culture synaptogenic assay\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure with mutagenesis mapping of binding site and functional validation in cell culture, single lab\",\n      \"pmids\": [\"26785044\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Conditional knockout of LRRTM1 and LRRTM2 in CA1 neurons in vivo impairs LTP and reduces AMPA receptor-mediated (but not NMDA receptor-mediated) synaptic transmission without affecting presynaptic function. LRRTM2 (but not LRRTM4) rescues both LTP and AMPA transmission. Mutation of LRRTM2's neurexin-binding interface prevents rescue of LTP, while deletion of the intracellular tail does not. Photo-activated GluA1 is less stable at spines lacking LRRTM1/2.\",\n      \"method\": \"Conditional knockout mouse, Cre lentivirus, whole-cell patch-clamp electrophysiology, site-directed mutagenesis, single-molecule photoactivation imaging (PAGFP-GluA1)\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — conditional genetic KO with multiple orthogonal methods (electrophysiology, mutagenesis, live imaging), rigorous domain-specific rescue experiments\",\n      \"pmids\": [\"29784826\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Acute severing of the LRRTM2 extracellular domain (using engineered rapid proteolysis) causes rapid nanoscale declustering of AMPARs away from presynaptic release sites before any loss of total receptor number, producing deficits in evoked but not spontaneous postsynaptic currents. This dissociates receptor number from subsynaptic nano-positioning as independent determinants of synaptic strength.\",\n      \"method\": \"Engineered LRRTM2 extracellular domain cleavage (TEV-based), STORM super-resolution microscopy, electrophysiology (evoked vs. spontaneous EPSCs)\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — acute domain-specific manipulation combined with super-resolution imaging and electrophysiology, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"34417170\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The LRRTM2 C-terminal intracellular domain is required for synaptic confinement and membrane dynamics: deletion of the C-terminal domain abolishes dendritic compartmentalization and increases diffusion. Synaptic confinement depends critically on a YxxC motif in the C-terminal domain, not on the PDZ-like binding motif (ECEV). The nanoscale organization of LRRTM2 requires both the PDZ-binding and YxxC motifs.\",\n      \"method\": \"shRNA knockdown, single-molecule tracking (uPAINT), super-resolution dSTORM microscopy, C-terminal domain deletion/point mutants\",\n      \"journal\": \"Biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — single molecule tracking and super-resolution with domain mutants, single lab\",\n      \"pmids\": [\"34498765\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"LRRTM2 synaptogenic activity in cortical neurons is independent of N-cadherin expression and function at both immature (6-7 DIV) and mature (14-15 DIV) stages, whereas neuroligin-1 synaptogenic activity requires N-cadherin in immature neurons. LRRTM2 retains significant synaptogenic activity at more mature stages (12-13 DIV) when neuroligin-1 activity diminishes.\",\n      \"method\": \"Overexpression in cultured mouse cortical neurons, immunostaining for VAMP2 and VGLUT1/Homer1, N-cadherin knockdown/function blocking\",\n      \"journal\": \"Frontiers in molecular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — coculture synaptogenic assay with genetic manipulation of N-cadherin, single lab, two orthogonal readouts\",\n      \"pmids\": [\"31780894\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Lrrtm2 expression is upregulated by nuclear calcium signaling downstream of synaptic NMDA receptor activation in hippocampal neurons, in a manner dependent on calcium/calmodulin-dependent protein kinases and the CREB-binding protein. A functional cAMP response element in the proximal Lrrtm2 promoter mediates regulation via the CaMKIV-CREB/CBP pathway, independent of new protein synthesis.\",\n      \"method\": \"Neuronal activity induction, reporter gene constructs, pharmacological inhibition of CaMK and CBP, calcium buffering experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reporter gene assay plus pharmacological dissection, single lab, multiple pathway components tested\",\n      \"pmids\": [\"25527504\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The N-terminal extracellular domain of LRRTM2 (specifically the recently identified Neurexin-binding interface/C-terminal cap of the LRR domain) controls presynaptic nano-organization and postsynaptic AMPAR sub-positioning and stabilization. The C-terminal intracellular domain controls surface expression, synaptic clustering, and membrane dynamics through selective motifs. LRRTM2 cKO specifically impairs excitatory synapse formation and function in mice.\",\n      \"method\": \"Conditional knockout mouse, domain-specific mutants, super-resolution microscopy, electrophysiology\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — conditional KO with domain-specific mutagenesis, super-resolution imaging, and electrophysiology in a single rigorous study\",\n      \"pmids\": [\"39394199\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Using whole-CDS CRISPR replacement, endogenous N-terminally tagged LRRTM2 was found in ~80% of synapses, and synaptic LRRTM2 content positively correlates with PSD-95 and AMPAR levels. LRRTM2 is also enriched with AMPARs outside synapses. Mutation of the C-terminal domain increases synaptic LRRTM2 levels but does not correspondingly increase AMPAR enrichment.\",\n      \"method\": \"Two-guide CRISPR knock-in of tagged endogenous LRRTM2 in rat hippocampal neurons, quantitative fluorescence imaging\",\n      \"journal\": \"The Journal of neuroscience : the official journal of the Society for Neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — endogenous tagging via CRISPR with quantitative imaging and C-terminal domain mutation, single lab\",\n      \"pmids\": [\"39824639\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Double knockout of LRRTM1 and LRRTM2 in mice impairs excitatory synapse density and morphological integrity on CA1 pyramidal neurons during development but not in the mature circuit. Both proteins are required for LTP in the CA3-CA1 pathway and dentate gyrus, and for enduring fear memory, in both developing and mature brain.\",\n      \"method\": \"Double conditional knockout mouse, electron and confocal microscopy, LTP electrophysiology, fear conditioning behavioral assay\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with electrophysiology and behavior, but findings are for the LRRTM1/2 double KO and cannot always be attributed solely to LRRTM2\",\n      \"pmids\": [\"35662394\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"In callosal projection neurons (CPN), deletion of transcription factor Bcl11a disrupts targeting of Lrrtm2 to growth cone membranes, causing cytoplasmic sequestration of key surface proteins and aberrant innervation of basolateral amygdala. This identifies a non-canonical, presynaptic (growth cone) role for LRRTM2 in regulating axon targeting and circuit specificity.\",\n      \"method\": \"CPN-specific Bcl11a deletion, in vivo growth cone proteomics, ex vivo localization validation, axonal projection tracing\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — preprint, proteomics plus projection tracing but limited direct mechanistic dissection of LRRTM2 itself; novel non-canonical role not yet peer-reviewed\",\n      \"pmids\": [\"41993341\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"LRRTM2 is a postsynaptic leucine-rich repeat transmembrane protein that localizes to excitatory synapses where its extracellular LRR domain binds specifically to splice-site-4-lacking neurexins (both α and β) on the presynaptic membrane to induce and organize presynaptic differentiation; intracellularly it associates with PSD-95 and its C-terminal YxxC and PDZ-binding motifs control synaptic confinement and nanoscale organization, while the transsynaptic neurexin interaction positions and stabilizes AMPA receptors within postsynaptic nanocolumns to set the strength of evoked excitatory transmission and enable LTP; its expression is transcriptionally upregulated by nuclear calcium signaling via CaMKIV-CREB/CBP following synaptic NMDA receptor activation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"LRRTM2 is a postsynaptic leucine-rich repeat transmembrane protein that localizes to excitatory synapses and organizes excitatory synapse formation, strength, and plasticity [#0, #2]. Its extracellular LRR domain induces presynaptic differentiation by binding specifically to α- and β-neurexins lacking an insert at splice site 4 [#1]; crystallography maps this trans-synaptic interaction to the concave LRR surface and shows it is Ca2+-dependent [#3]. Through this neurexin interface, LRRTM2 stabilizes AMPA receptors and positions them in register with presynaptic release sites: conditional knockout of LRRTM1/2 selectively reduces AMPAR-mediated transmission and impairs LTP, and rescue requires an intact neurexin-binding interface but not the intracellular tail [#4]. Acute cleavage of the extracellular domain rapidly disperses AMPAR nanoclusters from release sites before total receptor number falls, dissociating nano-positioning from receptor abundance as independent determinants of evoked strength [#5]. The C-terminal intracellular domain governs surface expression, synaptic confinement, and membrane diffusion via a YxxC motif together with a PDZ-binding motif, and LRRTM2 associates with PSD-95 [#0, #6, #9]. Endogenous tagging shows LRRTM2 occupies most synapses and its level correlates with PSD-95 and AMPAR content [#10]. Lrrtm2 transcription is induced by synaptic NMDA-receptor activity through a nuclear calcium–CaMKIV–CREB/CBP pathway acting on a promoter cAMP response element [#8].\",\n  \"teleology\": [\n    {\n      \"year\": 2009,\n      \"claim\": \"Established LRRTM2 as a postsynaptic organizer that selectively builds excitatory synapses and sets their strength, answering whether it has a defined synaptic function.\",\n      \"evidence\": \"shRNA and lentiviral in vivo knockdown, immunostaining, electrophysiology, and domain deletion in hippocampal neurons; coculture synaptogenic assays\",\n      \"pmids\": [\"20064388\", \"20064387\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the presynaptic receptor for the LRR domain\", \"Mechanism linking LRRTM2 to AMPAR surface expression unresolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identified the trans-synaptic ligand as SS4-lacking neurexins, defining the molecular basis for LRRTM2-induced presynaptic differentiation and distinguishing it from neuroligin-1.\",\n      \"evidence\": \"Affinity chromatography, cell-adhesion assays, and blocking with recombinant neurexin-1β\",\n      \"pmids\": [\"20064387\", \"20064388\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve the structural binding interface\", \"Did not establish how binding controls postsynaptic AMPARs\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Showed that Lrrtm2 is an activity-regulated gene, linking synaptic NMDA-receptor signaling to its transcription and explaining how its expression is tuned by activity.\",\n      \"evidence\": \"Activity induction with reporter constructs, pharmacological inhibition of CaMK/CBP, and calcium buffering in hippocampal neurons\",\n      \"pmids\": [\"25527504\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of activity-dependent upregulation on synaptic strength not tested\", \"Single-lab reporter dissection\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Resolved the atomic basis of neurexin binding, mapping the interaction to the concave LRR surface and confirming Ca2+ dependence.\",\n      \"evidence\": \"X-ray crystallography of thermostabilized mouse LRRTM2, protein engineering, binding affinity measurements, and synaptogenic assays\",\n      \"pmids\": [\"26785044\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No co-crystal structure of the LRRTM2-neurexin complex\", \"Did not address intracellular signaling\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrated through genetic knockout and domain-specific rescue that the neurexin-binding interface, not the cytoplasmic tail, drives AMPAR transmission and LTP in vivo.\",\n      \"evidence\": \"Conditional LRRTM1/2 knockout, Cre lentivirus, patch-clamp, site-directed mutagenesis, and PAGFP-GluA1 photoactivation imaging\",\n      \"pmids\": [\"29784826\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Redundancy between LRRTM1 and LRRTM2 not fully separated\", \"Did not resolve subsynaptic positioning of AMPARs\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Separated AMPAR nano-positioning from receptor number as independent strength determinants by acutely severing the extracellular domain.\",\n      \"evidence\": \"Engineered TEV-based extracellular domain cleavage, STORM super-resolution microscopy, and evoked-versus-spontaneous EPSC recordings\",\n      \"pmids\": [\"34417170\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular link from the extracellular interaction to nanocolumn alignment not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Assigned synaptic confinement and membrane dynamics to a YxxC motif in the C-terminal tail, distinguishing its role from the PDZ-binding motif.\",\n      \"evidence\": \"shRNA knockdown, uPAINT single-molecule tracking, dSTORM, and C-terminal deletion/point mutants\",\n      \"pmids\": [\"34498765\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Trafficking machinery engaging the YxxC motif unidentified\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showed LRRTM1/2 are developmentally required for excitatory synapse density and morphology and continuously required for LTP and fear memory.\",\n      \"evidence\": \"Double conditional knockout, electron/confocal microscopy, LTP electrophysiology, and fear conditioning\",\n      \"pmids\": [\"35662394\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Phenotypes cannot be attributed to LRRTM2 alone due to double-KO design\", \"Cell-type specificity beyond CA1/dentate not addressed\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Integrated extracellular and intracellular determinants, attributing presynaptic nano-organization and AMPAR sub-positioning to the neurexin interface and surface expression/clustering to selective C-terminal motifs.\",\n      \"evidence\": \"Conditional knockout, domain-specific mutants, super-resolution microscopy, and electrophysiology\",\n      \"pmids\": [\"39394199\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative stoichiometry of LRRTM2-AMPAR coupling not defined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Quantified endogenous LRRTM2 distribution, showing it occupies most synapses and scales with PSD-95 and AMPAR levels, including extrasynaptic AMPAR co-enrichment.\",\n      \"evidence\": \"Two-guide CRISPR knock-in of N-terminally tagged endogenous LRRTM2 in rat hippocampal neurons with quantitative imaging\",\n      \"pmids\": [\"39824639\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"C-terminal mutation raised LRRTM2 without matching AMPAR gain, leaving the coupling rule unexplained\", \"Single lab\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Proposed a non-canonical presynaptic role in which Bcl11a-dependent trafficking of Lrrtm2 to growth cone membranes governs axon targeting and circuit specificity.\",\n      \"evidence\": \"CPN-specific Bcl11a deletion, in vivo growth cone proteomics, localization validation, and projection tracing (preprint)\",\n      \"pmids\": [\"41993341\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Preprint, not peer-reviewed\", \"Limited direct mechanistic dissection of LRRTM2 in the growth cone\", \"Whether the targeting role is direct or secondary to broad surface-protein mislocalization is unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the trans-synaptic neurexin interaction is mechanistically transduced across the membrane to align and stabilize AMPAR nanoclusters remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No defined molecular chain linking extracellular neurexin binding to intracellular AMPAR anchoring\", \"No co-structure of the trans-synaptic complex\", \"Quantitative rule coupling LRRTM2 abundance to AMPAR content unexplained\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098631\", \"supporting_discovery_ids\": [1, 2, 3]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 4, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 6, 10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [0, 4]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [2, 11]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"NRXN1\", \"DLG4\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}