{"gene":"LRRTM2","run_date":"2026-04-28T18:30:27","timeline":{"discoveries":[{"year":2009,"finding":"LRRTM2 localizes to excitatory synapses, interacts with PSD-95 via its intracellular domain, and its extracellular LRR domain induces presynaptic differentiation. LRRTM2 binds both Neurexin1α and Neurexin1β (identified by affinity chromatography), and shRNA knockdown of Neurexin1 abrogates LRRTM2-induced presynaptic differentiation. shRNA knockdown of LRRTM2 reduces excitatory (but not inhibitory) synapse number and decreases AMPA receptor surface expression.","method":"Affinity chromatography, shRNA knockdown, immunocytochemistry, electrophysiology, structure-function mutagenesis","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (affinity chromatography, shRNA epistasis, electrophysiology), replicated in same year by independent lab","pmids":["20064388"],"is_preprint":false},{"year":2009,"finding":"LRRTM2 induces exclusively excitatory synapses and binds α- and β-neurexins lacking an insert at splice site #4 (SS4−), whereas neuroligin-1 binds neurexins with or without SS4 insert. Recombinant neurexin-1β blocks LRRTM2-induced presynaptic differentiation, and neurexin–LRRTM2 interaction can form cell-adhesion junctions in trans.","method":"Affinity chromatography, cell-adhesion junction assay, neurexin-splice-site binding assay, presynaptic differentiation assay, recombinant protein blocking experiment","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 1–2 — reconstitution of binding specificity with splice-site variants, independently replicated alongside PMID:20064388","pmids":["20064387"],"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; affinities of LRRTM2 for neurexin-β1 were determined with and without Ca²⁺, and the engineered protein retained the ability to form synapse-like contacts in cell culture.","method":"X-ray crystallography, protein engineering/thermostabilization, binding affinity measurements, cell culture synapse-formation assay","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — crystal structure combined with functional binding assays and cell-based validation","pmids":["26785044"],"is_preprint":false},{"year":2018,"finding":"Conditional knockout of LRRTM1/2 in CA1 neurons impairs LTP and reduces AMPA receptor-mediated (but not NMDA receptor-mediated) synaptic transmission without affecting presynaptic function. LTP rescue required the LRRTM2 neurexin-binding extracellular domain but not its intracellular tail. Photoactivatable GluA1 imaging showed that AMPA receptors are less stable in dendritic spines in the absence of LRRTM1/2.","method":"Conditional knockout mouse, Cre lentivirus, electrophysiology, rescue with domain-deletion/point-mutant constructs, photoactivatable GluA1 live imaging","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — clean genetic KO with multiple electrophysiological readouts, domain-specific rescue, and live imaging of receptor dynamics","pmids":["29784826"],"is_preprint":false},{"year":2021,"finding":"Acute proteolytic severing of the LRRTM2 extracellular domain rapidly declusters AMPARs away from presynaptic release sites at the nanoscale level, reducing evoked but not spontaneous postsynaptic currents, demonstrating that LRRTM2 acutely positions AMPARs within nanocolumns to control synaptic strength independently of total receptor number.","method":"Engineered rapid proteolysis of extracellular domain, super-resolution imaging, electrophysiology (evoked vs. spontaneous EPSCs)","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 1–2 — acute loss-of-function with rapid proteolysis combined with super-resolution imaging and electrophysiology, multiple orthogonal readouts","pmids":["34417170"],"is_preprint":false},{"year":2021,"finding":"LRRTM2 synaptic confinement and nanoscale organization require its intracellular C-terminal domain: deletion abolishes dendritic compartmentalization and synaptic enrichment. A YxxC motif (not the PDZ-binding ECEV motif) is primarily responsible for synaptic confinement, while both motifs contribute to nanoscale organization, as shown by single-molecule tracking and dSTORM super-resolution microscopy.","method":"shRNA knockdown, C-terminal deletion/point mutants, single-molecule tracking, dSTORM super-resolution microscopy","journal":"Biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 — domain-deletion/point-mutant analysis with super-resolution imaging, single lab","pmids":["34498765"],"is_preprint":false},{"year":2014,"finding":"Lrrtm2 expression in hippocampal neurons is induced by nuclear calcium signaling downstream of synaptic NMDA receptor activation, requiring calcium/calmodulin-dependent protein kinases and CBP; a functional CRE element in the Lrrtm2 proximal promoter mediates regulation via the CaMKIV–CREB/CBP pathway, independent of new protein synthesis.","method":"Reporter gene assays, pharmacological inhibition of CaMKs and NMDA receptors, nuclear calcium buffering, promoter deletion analysis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — promoter reporter assays plus pharmacological pathway dissection, single lab","pmids":["25527504"],"is_preprint":false},{"year":2024,"finding":"LRRTM2's N-terminal domain (Neurexin-binding interface at the C-terminal cap of the LRR) controls presynaptic nano-organization and postsynaptic AMPAR sub-positioning and stabilization, while C-terminal domain motifs control surface expression, synaptic clustering, and membrane dynamics of LRRTM2 itself. Conditional KO of LRRTM2 specifically impairs excitatory synapse formation and function.","method":"Conditional KO mouse, domain-deletion/point mutants targeting Neurexin-binding interface, super-resolution imaging of presynaptic and postsynaptic nanostructure, electrophysiology","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — conditional KO combined with domain-specific mutants, super-resolution imaging, and electrophysiology in multiple orthogonal assays","pmids":["39394199"],"is_preprint":false},{"year":2025,"finding":"Endogenous N-terminally tagged LRRTM2 (via whole-CDS CRISPR replacement) is present in ~80% of synapses and its synaptic content correlates with PSD-95 and AMPAR levels; LRRTM2 is also enriched with AMPARs outside synapses. Mutation of the C-terminal domain increased synaptic LRRTM2 levels without correspondingly increasing AMPAR enrichment, dissociating LRRTM2 accumulation from AMPAR recruitment.","method":"Two-guide CRISPR whole-CDS knock-in, endogenous tagging, quantitative fluorescence imaging, C-terminal domain point mutation","journal":"The Journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 — endogenous tagging via CRISPR with structure-function mutant analysis, single lab","pmids":["39824639"],"is_preprint":false},{"year":2019,"finding":"The synaptogenic activity of LRRTM2 (inducing presynaptic vesicle clusters and glutamatergic synapses) is independent of N-cadherin expression and function in both immature and mature cortical neurons, whereas Neuroligin-1 synaptogenic activity is strongly dependent on N-cadherin, revealing mechanistically distinct pathways despite both ligands signaling through presynaptic neurexins.","method":"Overexpression in cultured cortical neurons, N-cadherin knockdown/blocking, immunostaining for VAMP2 and VGLUT1/Homer1","journal":"Frontiers in molecular neuroscience","confidence":"Medium","confidence_rationale":"Tier 3 — genetic epistasis via knockdown combined with immunostaining readout, single lab","pmids":["31780894"],"is_preprint":false},{"year":2026,"finding":"In cortical callosal projection neurons, Lrrtm2 (canonically postsynaptic) is present in growth cones and controls axon targeting; deletion of Bcl11a causes cytoplasmic sequestration of Lrrtm2 away from growth cone membranes, leading to aberrant sequestration of other growth cone surface proteins and de novo innervation of the basolateral amygdala.","method":"CPN-specific Bcl11a conditional deletion, in vivo growth cone proteomics, ex vivo localization validation, subcellular fractionation of growth cones","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 — preprint, single lab, indirect mechanism via TF deletion with proteomics","pmids":["41993341"],"is_preprint":true}],"current_model":"LRRTM2 is a postsynaptic leucine-rich repeat transmembrane adhesion molecule that localizes to excitatory synapses via C-terminal motifs (including a YxxC motif and a PDZ-binding ECEV motif interacting with PSD-95), binds presynaptic neurexins lacking splice-site-4 inserts through its concave LRR surface in a trans-synaptic interaction that organizes both presynaptic nanocolumn structure and the sub-synaptic positioning and stabilization of AMPA receptors, thereby controlling both synapse formation and the strength of evoked synaptic transmission; its expression is induced by nuclear calcium/CaMKIV–CREB signaling downstream of synaptic NMDA receptor activation."},"narrative":{"teleology":[{"year":2009,"claim":"Identification of neurexins as the presynaptic binding partner of LRRTM2 established it as a trans-synaptic adhesion molecule that induces excitatory presynaptic differentiation and revealed a splice-code: LRRTM2 selectively binds neurexins lacking splice-site 4 inserts.","evidence":"Affinity chromatography, shRNA epistasis, cell-adhesion junction assays, and splice-variant binding assays in two independent studies","pmids":["20064388","20064387"],"confidence":"High","gaps":["Structural basis of neurexin–LRRTM2 interaction unknown","Whether LRRTM2 has postsynaptic roles beyond synapse number not tested","In vivo loss-of-function phenotype not established"]},{"year":2014,"claim":"Demonstrating that Lrrtm2 transcription is driven by nuclear calcium/CaMKIV–CREB/CBP signaling downstream of synaptic NMDA receptor activation established LRRTM2 as an activity-regulated synapse organizer, linking synaptic activity to structural synapse remodeling.","evidence":"Promoter reporter assays, pharmacological inhibition of CaMKs and NMDA receptors, nuclear calcium buffering in hippocampal neurons","pmids":["25527504"],"confidence":"Medium","gaps":["Regulation shown at promoter/mRNA level; activity-dependent changes in LRRTM2 protein levels not demonstrated","Functional consequences of activity-induced LRRTM2 upregulation on synaptic strength not tested"]},{"year":2016,"claim":"Solving the LRRTM2 crystal structure identified the concave LRR surface as the neurexin-binding interface and provided quantitative binding affinities, establishing the structural framework for understanding trans-synaptic adhesion specificity.","evidence":"X-ray crystallography of thermostabilized mouse LRRTM2, binding affinity measurements with neurexin-β1 ± Ca²⁺, cell-based synapse formation assay","pmids":["26785044"],"confidence":"High","gaps":["Co-crystal structure of LRRTM2–neurexin complex not obtained","Contribution of individual LRR residues to binding and synaptogenesis not mapped"]},{"year":2018,"claim":"Conditional knockout of LRRTM1/2 revealed that these proteins are required for LTP and selectively maintain AMPA receptor-mediated (not NMDA receptor-mediated) transmission, with the extracellular neurexin-binding domain being necessary and sufficient for LTP rescue, establishing a postsynaptic signaling role beyond synapse formation.","evidence":"Conditional KO in CA1 neurons, electrophysiology, domain-deletion rescue, photoactivatable GluA1 live imaging","pmids":["29784826"],"confidence":"High","gaps":["Individual contributions of LRRTM1 vs LRRTM2 not resolved (double KO used)","Mechanism by which the extracellular domain stabilizes AMPARs at spines not defined"]},{"year":2019,"claim":"Showing that LRRTM2 synaptogenic activity is independent of N-cadherin distinguished its mechanism from that of Neuroligin-1, which requires N-cadherin, indicating mechanistically distinct trans-synaptic signaling pathways despite shared neurexin binding.","evidence":"N-cadherin knockdown/blocking in cultured cortical neurons with immunostaining for presynaptic markers","pmids":["31780894"],"confidence":"Medium","gaps":["Downstream presynaptic signaling pathway activated by LRRTM2 not identified","Result limited to cultured cortical neurons; in vivo epistasis not tested"]},{"year":2021,"claim":"Acute proteolytic removal of the LRRTM2 extracellular domain demonstrated that LRRTM2 acutely positions AMPARs within trans-synaptic nanocolumns to control evoked transmission, separating its role in receptor positioning from its role in total receptor number.","evidence":"Engineered rapid proteolysis, super-resolution imaging, and evoked vs. spontaneous EPSC electrophysiology","pmids":["34417170"],"confidence":"High","gaps":["Identity of presynaptic nanocolumn partners organized by LRRTM2 not fully resolved","Whether other LRRTMs can substitute for nanocolumn organization not tested"]},{"year":2021,"claim":"Dissection of the intracellular domain revealed that a YxxC motif (not the PDZ-binding ECEV motif) is the primary determinant of LRRTM2 synaptic confinement, while both motifs contribute to nanoscale organization, identifying the molecular determinants of postsynaptic anchoring.","evidence":"C-terminal deletion/point mutants, single-molecule tracking, dSTORM super-resolution microscopy","pmids":["34498765"],"confidence":"Medium","gaps":["Binding partner of the YxxC motif not identified","How intracellular motifs coordinate with the extracellular domain to organize nanocolumns not determined"]},{"year":2024,"claim":"Domain-specific mutant analysis in conditional KO mice unified the model: the N-terminal neurexin-binding interface controls both presynaptic nano-organization and postsynaptic AMPAR sub-positioning, while C-terminal motifs control LRRTM2's own surface expression and synaptic clustering.","evidence":"Conditional KO, domain-deletion/point mutants targeting the neurexin-binding C-terminal LRR cap, super-resolution imaging, electrophysiology","pmids":["39394199"],"confidence":"High","gaps":["Whether the neurexin-binding interface acts solely through neurexin or additional cis/trans partners contribute remains untested","In vivo behavioral consequences of domain-specific mutations not assessed"]},{"year":2025,"claim":"Endogenous tagging via CRISPR showed LRRTM2 is present at ~80% of excitatory synapses and its levels correlate with PSD-95 and AMPAR content, but C-terminal mutations that increase synaptic LRRTM2 do not proportionally increase AMPARs, dissociating LRRTM2 accumulation from AMPAR recruitment.","evidence":"Two-guide CRISPR whole-CDS knock-in for endogenous tagging, quantitative fluorescence imaging, C-terminal domain point mutations","pmids":["39824639"],"confidence":"Medium","gaps":["Mechanism by which LRRTM2 recruits AMPARs (direct binding vs. scaffold intermediates) not resolved","Findings from single lab; independent replication needed"]},{"year":null,"claim":"Key open questions include the identity of the intracellular YxxC-motif binding partner, the structural basis of the neurexin–LRRTM2 complex, and the mechanism by which extracellular neurexin binding is transduced into postsynaptic AMPAR positioning and stabilization.","evidence":"","pmids":[],"confidence":"High","gaps":["No co-crystal structure of neurexin–LRRTM2 complex exists","The intracellular binding partner of the YxxC motif is unknown","How LRRTM2's extracellular domain mechanistically couples to AMPAR stabilization machinery remains unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098631","term_label":"cell adhesion mediator activity","supporting_discovery_ids":[0,1,4,7]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,5,8]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[0,1,3,4,7]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,6]}],"complexes":[],"partners":["NRXN1","DLG4","GRIA1"],"other_free_text":[]},"mechanistic_narrative":"LRRTM2 is a postsynaptic leucine-rich repeat transmembrane protein that functions as a trans-synaptic organizer of excitatory synapses by binding presynaptic neurexins and positioning AMPA receptors within synaptic nanocolumns. It selectively binds α- and β-neurexins lacking a splice-site 4 insert through its concave LRR surface, and this interaction induces presynaptic differentiation and is required for LTP and AMPA receptor-mediated transmission but not NMDA receptor-mediated transmission [PMID:20064387, PMID:20064388, PMID:29784826]. Acute severing of the LRRTM2 extracellular domain rapidly declusters AMPARs from presynaptic release sites, reducing evoked but not spontaneous transmission, demonstrating that LRRTM2 acutely controls synaptic strength by positioning receptors within nanocolumns independently of total receptor number [PMID:34417170]. Its intracellular C-terminal YxxC and PDZ-binding motifs govern synaptic confinement and surface dynamics, while its transcription is induced by nuclear calcium/CaMKIV–CREB signaling downstream of synaptic NMDA receptor activation [PMID:34498765, PMID:25527504]."},"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":306,"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":299,"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":79,"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":58,"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":17,"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":5,"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":4,"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":8243,"output_tokens":2940,"usd":0.034415},"stage2":{"model":"claude-opus-4-6","input_tokens":6314,"output_tokens":2655,"usd":0.146918},"total_usd":0.181333,"stage1_batch_id":"msgbatch_01Mgbec4vM6c9vXht7JVJzss","stage2_batch_id":"msgbatch_01JkuuH5RB2BdJNsgnhjbC6s","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2009,\n      \"finding\": \"LRRTM2 localizes to excitatory synapses, interacts with PSD-95 via its intracellular domain, and its extracellular LRR domain induces presynaptic differentiation. LRRTM2 binds both Neurexin1α and Neurexin1β (identified by affinity chromatography), and shRNA knockdown of Neurexin1 abrogates LRRTM2-induced presynaptic differentiation. shRNA knockdown of LRRTM2 reduces excitatory (but not inhibitory) synapse number and decreases AMPA receptor surface expression.\",\n      \"method\": \"Affinity chromatography, shRNA knockdown, immunocytochemistry, electrophysiology, structure-function mutagenesis\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (affinity chromatography, shRNA epistasis, electrophysiology), replicated in same year by independent lab\",\n      \"pmids\": [\"20064388\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"LRRTM2 induces exclusively excitatory synapses and binds α- and β-neurexins lacking an insert at splice site #4 (SS4−), whereas neuroligin-1 binds neurexins with or without SS4 insert. Recombinant neurexin-1β blocks LRRTM2-induced presynaptic differentiation, and neurexin–LRRTM2 interaction can form cell-adhesion junctions in trans.\",\n      \"method\": \"Affinity chromatography, cell-adhesion junction assay, neurexin-splice-site binding assay, presynaptic differentiation assay, recombinant protein blocking experiment\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — reconstitution of binding specificity with splice-site variants, independently replicated alongside PMID:20064388\",\n      \"pmids\": [\"20064387\"],\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; affinities of LRRTM2 for neurexin-β1 were determined with and without Ca²⁺, and the engineered protein retained the ability to form synapse-like contacts in cell culture.\",\n      \"method\": \"X-ray crystallography, protein engineering/thermostabilization, binding affinity measurements, cell culture synapse-formation assay\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure combined with functional binding assays and cell-based validation\",\n      \"pmids\": [\"26785044\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Conditional knockout of LRRTM1/2 in CA1 neurons impairs LTP and reduces AMPA receptor-mediated (but not NMDA receptor-mediated) synaptic transmission without affecting presynaptic function. LTP rescue required the LRRTM2 neurexin-binding extracellular domain but not its intracellular tail. Photoactivatable GluA1 imaging showed that AMPA receptors are less stable in dendritic spines in the absence of LRRTM1/2.\",\n      \"method\": \"Conditional knockout mouse, Cre lentivirus, electrophysiology, rescue with domain-deletion/point-mutant constructs, photoactivatable GluA1 live imaging\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with multiple electrophysiological readouts, domain-specific rescue, and live imaging of receptor dynamics\",\n      \"pmids\": [\"29784826\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Acute proteolytic severing of the LRRTM2 extracellular domain rapidly declusters AMPARs away from presynaptic release sites at the nanoscale level, reducing evoked but not spontaneous postsynaptic currents, demonstrating that LRRTM2 acutely positions AMPARs within nanocolumns to control synaptic strength independently of total receptor number.\",\n      \"method\": \"Engineered rapid proteolysis of extracellular domain, super-resolution imaging, electrophysiology (evoked vs. spontaneous EPSCs)\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — acute loss-of-function with rapid proteolysis combined with super-resolution imaging and electrophysiology, multiple orthogonal readouts\",\n      \"pmids\": [\"34417170\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"LRRTM2 synaptic confinement and nanoscale organization require its intracellular C-terminal domain: deletion abolishes dendritic compartmentalization and synaptic enrichment. A YxxC motif (not the PDZ-binding ECEV motif) is primarily responsible for synaptic confinement, while both motifs contribute to nanoscale organization, as shown by single-molecule tracking and dSTORM super-resolution microscopy.\",\n      \"method\": \"shRNA knockdown, C-terminal deletion/point mutants, single-molecule tracking, dSTORM super-resolution microscopy\",\n      \"journal\": \"Biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — domain-deletion/point-mutant analysis with super-resolution imaging, single lab\",\n      \"pmids\": [\"34498765\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Lrrtm2 expression in hippocampal neurons is induced by nuclear calcium signaling downstream of synaptic NMDA receptor activation, requiring calcium/calmodulin-dependent protein kinases and CBP; a functional CRE element in the Lrrtm2 proximal promoter mediates regulation via the CaMKIV–CREB/CBP pathway, independent of new protein synthesis.\",\n      \"method\": \"Reporter gene assays, pharmacological inhibition of CaMKs and NMDA receptors, nuclear calcium buffering, promoter deletion analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — promoter reporter assays plus pharmacological pathway dissection, single lab\",\n      \"pmids\": [\"25527504\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"LRRTM2's N-terminal domain (Neurexin-binding interface at the C-terminal cap of the LRR) controls presynaptic nano-organization and postsynaptic AMPAR sub-positioning and stabilization, while C-terminal domain motifs control surface expression, synaptic clustering, and membrane dynamics of LRRTM2 itself. Conditional KO of LRRTM2 specifically impairs excitatory synapse formation and function.\",\n      \"method\": \"Conditional KO mouse, domain-deletion/point mutants targeting Neurexin-binding interface, super-resolution imaging of presynaptic and postsynaptic nanostructure, electrophysiology\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO combined with domain-specific mutants, super-resolution imaging, and electrophysiology in multiple orthogonal assays\",\n      \"pmids\": [\"39394199\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Endogenous N-terminally tagged LRRTM2 (via whole-CDS CRISPR replacement) is present in ~80% of synapses and its synaptic content correlates with PSD-95 and AMPAR levels; LRRTM2 is also enriched with AMPARs outside synapses. Mutation of the C-terminal domain increased synaptic LRRTM2 levels without correspondingly increasing AMPAR enrichment, dissociating LRRTM2 accumulation from AMPAR recruitment.\",\n      \"method\": \"Two-guide CRISPR whole-CDS knock-in, endogenous tagging, quantitative fluorescence imaging, C-terminal domain point mutation\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — endogenous tagging via CRISPR with structure-function mutant analysis, single lab\",\n      \"pmids\": [\"39824639\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The synaptogenic activity of LRRTM2 (inducing presynaptic vesicle clusters and glutamatergic synapses) is independent of N-cadherin expression and function in both immature and mature cortical neurons, whereas Neuroligin-1 synaptogenic activity is strongly dependent on N-cadherin, revealing mechanistically distinct pathways despite both ligands signaling through presynaptic neurexins.\",\n      \"method\": \"Overexpression in cultured cortical neurons, N-cadherin knockdown/blocking, immunostaining for VAMP2 and VGLUT1/Homer1\",\n      \"journal\": \"Frontiers in molecular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — genetic epistasis via knockdown combined with immunostaining readout, single lab\",\n      \"pmids\": [\"31780894\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"In cortical callosal projection neurons, Lrrtm2 (canonically postsynaptic) is present in growth cones and controls axon targeting; deletion of Bcl11a causes cytoplasmic sequestration of Lrrtm2 away from growth cone membranes, leading to aberrant sequestration of other growth cone surface proteins and de novo innervation of the basolateral amygdala.\",\n      \"method\": \"CPN-specific Bcl11a conditional deletion, in vivo growth cone proteomics, ex vivo localization validation, subcellular fractionation of growth cones\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — preprint, single lab, indirect mechanism via TF deletion with proteomics\",\n      \"pmids\": [\"41993341\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"LRRTM2 is a postsynaptic leucine-rich repeat transmembrane adhesion molecule that localizes to excitatory synapses via C-terminal motifs (including a YxxC motif and a PDZ-binding ECEV motif interacting with PSD-95), binds presynaptic neurexins lacking splice-site-4 inserts through its concave LRR surface in a trans-synaptic interaction that organizes both presynaptic nanocolumn structure and the sub-synaptic positioning and stabilization of AMPA receptors, thereby controlling both synapse formation and the strength of evoked synaptic transmission; its expression is induced by nuclear calcium/CaMKIV–CREB signaling downstream of synaptic NMDA receptor activation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"LRRTM2 is a postsynaptic leucine-rich repeat transmembrane protein that functions as a trans-synaptic organizer of excitatory synapses by binding presynaptic neurexins and positioning AMPA receptors within synaptic nanocolumns. It selectively binds α- and β-neurexins lacking a splice-site 4 insert through its concave LRR surface, and this interaction induces presynaptic differentiation and is required for LTP and AMPA receptor-mediated transmission but not NMDA receptor-mediated transmission [PMID:20064387, PMID:20064388, PMID:29784826]. Acute severing of the LRRTM2 extracellular domain rapidly declusters AMPARs from presynaptic release sites, reducing evoked but not spontaneous transmission, demonstrating that LRRTM2 acutely controls synaptic strength by positioning receptors within nanocolumns independently of total receptor number [PMID:34417170]. Its intracellular C-terminal YxxC and PDZ-binding motifs govern synaptic confinement and surface dynamics, while its transcription is induced by nuclear calcium/CaMKIV–CREB signaling downstream of synaptic NMDA receptor activation [PMID:34498765, PMID:25527504].\",\n  \"teleology\": [\n    {\n      \"year\": 2009,\n      \"claim\": \"Identification of neurexins as the presynaptic binding partner of LRRTM2 established it as a trans-synaptic adhesion molecule that induces excitatory presynaptic differentiation and revealed a splice-code: LRRTM2 selectively binds neurexins lacking splice-site 4 inserts.\",\n      \"evidence\": \"Affinity chromatography, shRNA epistasis, cell-adhesion junction assays, and splice-variant binding assays in two independent studies\",\n      \"pmids\": [\"20064388\", \"20064387\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of neurexin–LRRTM2 interaction unknown\",\n        \"Whether LRRTM2 has postsynaptic roles beyond synapse number not tested\",\n        \"In vivo loss-of-function phenotype not established\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Demonstrating that Lrrtm2 transcription is driven by nuclear calcium/CaMKIV–CREB/CBP signaling downstream of synaptic NMDA receptor activation established LRRTM2 as an activity-regulated synapse organizer, linking synaptic activity to structural synapse remodeling.\",\n      \"evidence\": \"Promoter reporter assays, pharmacological inhibition of CaMKs and NMDA receptors, nuclear calcium buffering in hippocampal neurons\",\n      \"pmids\": [\"25527504\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Regulation shown at promoter/mRNA level; activity-dependent changes in LRRTM2 protein levels not demonstrated\",\n        \"Functional consequences of activity-induced LRRTM2 upregulation on synaptic strength not tested\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Solving the LRRTM2 crystal structure identified the concave LRR surface as the neurexin-binding interface and provided quantitative binding affinities, establishing the structural framework for understanding trans-synaptic adhesion specificity.\",\n      \"evidence\": \"X-ray crystallography of thermostabilized mouse LRRTM2, binding affinity measurements with neurexin-β1 ± Ca²⁺, cell-based synapse formation assay\",\n      \"pmids\": [\"26785044\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Co-crystal structure of LRRTM2–neurexin complex not obtained\",\n        \"Contribution of individual LRR residues to binding and synaptogenesis not mapped\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Conditional knockout of LRRTM1/2 revealed that these proteins are required for LTP and selectively maintain AMPA receptor-mediated (not NMDA receptor-mediated) transmission, with the extracellular neurexin-binding domain being necessary and sufficient for LTP rescue, establishing a postsynaptic signaling role beyond synapse formation.\",\n      \"evidence\": \"Conditional KO in CA1 neurons, electrophysiology, domain-deletion rescue, photoactivatable GluA1 live imaging\",\n      \"pmids\": [\"29784826\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Individual contributions of LRRTM1 vs LRRTM2 not resolved (double KO used)\",\n        \"Mechanism by which the extracellular domain stabilizes AMPARs at spines not defined\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Showing that LRRTM2 synaptogenic activity is independent of N-cadherin distinguished its mechanism from that of Neuroligin-1, which requires N-cadherin, indicating mechanistically distinct trans-synaptic signaling pathways despite shared neurexin binding.\",\n      \"evidence\": \"N-cadherin knockdown/blocking in cultured cortical neurons with immunostaining for presynaptic markers\",\n      \"pmids\": [\"31780894\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Downstream presynaptic signaling pathway activated by LRRTM2 not identified\",\n        \"Result limited to cultured cortical neurons; in vivo epistasis not tested\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Acute proteolytic removal of the LRRTM2 extracellular domain demonstrated that LRRTM2 acutely positions AMPARs within trans-synaptic nanocolumns to control evoked transmission, separating its role in receptor positioning from its role in total receptor number.\",\n      \"evidence\": \"Engineered rapid proteolysis, super-resolution imaging, and evoked vs. spontaneous EPSC electrophysiology\",\n      \"pmids\": [\"34417170\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Identity of presynaptic nanocolumn partners organized by LRRTM2 not fully resolved\",\n        \"Whether other LRRTMs can substitute for nanocolumn organization not tested\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Dissection of the intracellular domain revealed that a YxxC motif (not the PDZ-binding ECEV motif) is the primary determinant of LRRTM2 synaptic confinement, while both motifs contribute to nanoscale organization, identifying the molecular determinants of postsynaptic anchoring.\",\n      \"evidence\": \"C-terminal deletion/point mutants, single-molecule tracking, dSTORM super-resolution microscopy\",\n      \"pmids\": [\"34498765\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Binding partner of the YxxC motif not identified\",\n        \"How intracellular motifs coordinate with the extracellular domain to organize nanocolumns not determined\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Domain-specific mutant analysis in conditional KO mice unified the model: the N-terminal neurexin-binding interface controls both presynaptic nano-organization and postsynaptic AMPAR sub-positioning, while C-terminal motifs control LRRTM2's own surface expression and synaptic clustering.\",\n      \"evidence\": \"Conditional KO, domain-deletion/point mutants targeting the neurexin-binding C-terminal LRR cap, super-resolution imaging, electrophysiology\",\n      \"pmids\": [\"39394199\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether the neurexin-binding interface acts solely through neurexin or additional cis/trans partners contribute remains untested\",\n        \"In vivo behavioral consequences of domain-specific mutations not assessed\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Endogenous tagging via CRISPR showed LRRTM2 is present at ~80% of excitatory synapses and its levels correlate with PSD-95 and AMPAR content, but C-terminal mutations that increase synaptic LRRTM2 do not proportionally increase AMPARs, dissociating LRRTM2 accumulation from AMPAR recruitment.\",\n      \"evidence\": \"Two-guide CRISPR whole-CDS knock-in for endogenous tagging, quantitative fluorescence imaging, C-terminal domain point mutations\",\n      \"pmids\": [\"39824639\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism by which LRRTM2 recruits AMPARs (direct binding vs. scaffold intermediates) not resolved\",\n        \"Findings from single lab; independent replication needed\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include the identity of the intracellular YxxC-motif binding partner, the structural basis of the neurexin–LRRTM2 complex, and the mechanism by which extracellular neurexin binding is transduced into postsynaptic AMPAR positioning and stabilization.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No co-crystal structure of neurexin–LRRTM2 complex exists\",\n        \"The intracellular binding partner of the YxxC motif is unknown\",\n        \"How LRRTM2's extracellular domain mechanistically couples to AMPAR stabilization machinery remains unresolved\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098631\", \"supporting_discovery_ids\": [0, 1, 4, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 5, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [0, 1, 3, 4, 7]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 6]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"NRXN1\",\n      \"DLG4\",\n      \"GRIA1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}