{"gene":"NCAM2","run_date":"2026-04-29T11:37:56","timeline":{"discoveries":[{"year":1997,"finding":"NCAM2 encodes a 837-amino acid protein with five immunoglobulin-like domains, two fibronectin type III domains, a transmembrane domain, and a cytoplasmic domain, showing 62% similarity to NCAM1, and is expressed most strongly in human adult and fetal brain.","method":"cDNA cloning and sequence analysis from human fetal brain cDNA library","journal":"Genomics","confidence":"High","confidence_rationale":"Tier 1 — direct sequence determination and domain mapping from cloned cDNA","pmids":["9226371"],"is_preprint":false},{"year":2008,"finding":"The crystal structure of NCAM2 Ig1 domain reveals domain swapping of the two N-terminal beta-strands between two molecules, and gel-filtration chromatography confirmed Ig1 forms dimers in solution, suggesting beta-strand swapping underlies homophilic binding.","method":"X-ray crystallography at 2.7 Å resolution and gel-filtration chromatography","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with solution-state validation by gel filtration","pmids":["18706912"],"is_preprint":false},{"year":2015,"finding":"Aβ binds directly to NCAM2 at the cell surface of cultured hippocampal neurons, induces removal of NCAM2 from synapses, and promotes cleavage of the membrane-proximal extracellular region of NCAM2 generating soluble extracellular fragments (NCAM2-ED). Knockdown of NCAM2 or addition of NCAM2-ED induces disassembly of GluR1-containing glutamatergic synapses. A cleavage-resistant NCAM2 mutant inhibits Aβ-dependent synapse disassembly.","method":"Surface binding assays, live-cell imaging, shRNA knockdown, overexpression of cleavage-resistant mutant, immunofluorescence in cultured hippocampal neurons and AD patient hippocampus","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (binding, KD, mutant rescue) in cultured neurons and human tissue","pmids":["26611261"],"is_preprint":false},{"year":2018,"finding":"The NCAM2 FnIII1-2 double domain forms a rigid, low-flexibility structure (by SAXS), does not bind ATP via its Walker A motif (unlike NCAM1, shown by NMR titration), binds FGFR in vitro, and induces neurite outgrowth in a concentration-dependent manner through FGFR activation and downstream Ras-MAPK signaling.","method":"NMR spectroscopy, SAXS, in vitro FGFR binding assay, neurite outgrowth assay with FGFR inhibitors and Ras-MAPK pathway inhibitors","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1 — structure by NMR/SAXS plus in vitro binding and functional assay with pathway inhibition","pmids":["29895898"],"is_preprint":false},{"year":2019,"finding":"NCAM2 overexpression induces L-type voltage-gated Ca2+ channel-dependent submembrane Ca2+ spikes in individual dendritic protrusions, propagates these spikes along dendrites via c-Src kinase, increases instability of dendritic protrusions, reduces their conversion to mature spines, and results in synaptic boutons enriched in immature marker GAP43 with reduced activity-dependent vesicle recycling.","method":"Ca2+ imaging in live mouse cortical neurons, NCAM2 overexpression, L-type Ca2+ channel blockers, c-Src inhibition, synaptic vesicle recycling assay","journal":"Cerebral cortex","confidence":"High","confidence_rationale":"Tier 2 — live-cell Ca2+ imaging with pharmacological dissection of pathway, replicated with multiple inhibitors","pmids":["29522129"],"is_preprint":false},{"year":2020,"finding":"NCAM2 forms a protein complex with cytoskeletal-associated proteins MAP2 and 14-3-3γ/ζ. NCAM2 knockdown destabilizes the microtubular network and reduces MAP2 signal, leading to shortened dendritic trees, dendritic retraction, somatic neurite emergence, axonal defects, impaired neuronal polarization, and cortical migration deficits in vivo.","method":"Co-immunoprecipitation (proteomic/cell biology validation), shRNA knockdown in hippocampal neurons and in vivo cortical electroporation, immunofluorescence, microtubule stability assays","journal":"Cerebral cortex","confidence":"High","confidence_rationale":"Tier 2 — reciprocal interaction validated by proteomics and Co-IP, combined with in vitro and in vivo KD phenotype","pmids":["32043120"],"is_preprint":false},{"year":2021,"finding":"Mass spectrometry-based interactome analysis identified NCAM2 binding partners in mouse cerebral cortex including Neurofilaments (NEFs), MAP2, CaMKIIα, Actin, and Nogo, validated by co-immunoprecipitation; in silico analysis of the NCAM2.1 cytosolic tail revealed phosphorylation site motifs with affinity for these interactors.","method":"Mass spectrometry immunoprecipitation, co-immunoprecipitation validation, in silico phosphorylation site analysis","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 — MS interactome with Co-IP validation, single lab","pmids":["34299022"],"is_preprint":false},{"year":2022,"finding":"BACE1 cleaves NCAM2 in cultured hippocampal neurons and transfected CHO cells. The resulting C-terminal fragment of NCAM2 (comprising intracellular domain and small extracellular portion) associates with BACE1 before endocytosis, and co-localizes with BACE1 in Rab11-positive recycling endosomes. Overexpression of full-length NCAM2 or the transmembrane/intracellular fragment increases BACE1 in Rab11+ endosomes; NCAM2 deficiency increases BACE1 at the cell surface and reduces intracellular BACE1, correlating with increased BACE1 shedding and reduced Sez6 cleavage in vivo.","method":"Co-immunoprecipitation, confocal co-localization, overexpression and KO in neurons and CHO cells, endocytosis inhibition, BACE1 shedding assay in NCAM2-deficient mice","journal":"Cellular and molecular life sciences","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (Co-IP, co-localization, gain- and loss-of-function) across two cell systems and in vivo","pmids":["36251052"],"is_preprint":false},{"year":2023,"finding":"NCAM2 increases axonal levels of BACE1 in hippocampal mossy fiber projections; NCAM2-deficient mice have reduced BACE1 in mossy fiber axons, a shortened infrapyramidal bundle, and behavioral deficits including impaired short-term spatial memory, reduced cognitive flexibility, and increased self-grooming.","method":"NCAM2-deficient mouse model, immunofluorescence quantification of BACE1 in axonal projections, behavioral tests (spatial memory, cognitive flexibility, grooming)","journal":"Cerebral cortex","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with defined axonal and behavioral phenotypes, single lab","pmids":["37522285"],"is_preprint":false},{"year":2023,"finding":"NCAM2 overexpression in adult mice arrests radial glial progenitors (RGPs) in an RGP-like state in the dentate gyrus, disrupting normal young-adult neurogenesis progression, while changes in NCAM2 levels during corticogenesis cause transient migratory deficits without affecting RGP survival or proliferation.","method":"In vivo NCAM2 overexpression in adult mice via viral vectors, immunofluorescence characterization of neurogenic cell types, BrdU/EdU proliferation assays, cortical electroporation","journal":"Cerebral cortex","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo gain-of-function with defined cellular phenotype, single lab","pmids":["37724425"],"is_preprint":false},{"year":2025,"finding":"APP binds to the extracellular domain of NCAM2; the intracellular domain of NCAM2 binds the Rab11 adaptor protein Rab11-FIP5. The NCAM2/APP complex is endocytosed from the cell surface and targeted to BACE1-containing Rab11-positive recycling endosomes where APP is processed. NCAM2 expression increases amyloidogenic APP cleavage products; NCAM2 deficiency causes APP accumulation at the cell surface and in early endosomes with reduced APP in recycling endosomes. Aβ oligomers and synaptic NMDA receptor activation increase NCAM2-APP binding.","method":"Co-immunoprecipitation (extracellular and intracellular domain interactions), confocal co-localization, overexpression in CHO cells and neurons, NCAM2-deficient neurons, endocytosis assays, Aβ oligomer and NMDA receptor stimulation experiments","journal":"Progress in neurobiology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (Co-IP of distinct domains, gain- and loss-of-function, two cell systems), single lab with comprehensive mechanistic dissection","pmids":["40721030"],"is_preprint":false}],"current_model":"NCAM2 is a synaptic cell adhesion molecule that mediates homophilic binding via Ig-domain swapping, activates FGFR/Ras-MAPK signaling through its rigid FnIII domains to promote neurite outgrowth, organizes the dendritic cytoskeleton by complexing with MAP2 and 14-3-3 proteins, regulates synapse maturation by triggering c-Src-dependent propagation of L-type Ca2+-channel-mediated submembrane Ca2+ spikes, and controls amyloidogenic processing by binding APP extracellularly and Rab11-FIP5 intracellularly to co-traffic APP with BACE1 into Rab11-positive recycling endosomes, while its BACE1-generated C-terminal fragment reciprocally promotes BACE1 targeting to those same endosomes."},"narrative":{"teleology":[{"year":1997,"claim":"Cloning of NCAM2 established it as a brain-enriched Ig-superfamily member structurally related to NCAM1, defining the domain architecture (five Ig, two FnIII, TM, cytoplasmic tail) that subsequent work would parse for discrete functions.","evidence":"cDNA cloning and sequence analysis from human fetal brain library","pmids":["9226371"],"confidence":"High","gaps":["No functional data at this stage","Expression pattern limited to Northern blot survey"]},{"year":2008,"claim":"Crystal structure of the Ig1 domain revealed that homophilic binding is mediated by reciprocal beta-strand swapping, providing the first molecular mechanism for NCAM2 trans-adhesion.","evidence":"X-ray crystallography at 2.7 Å resolution with gel-filtration confirmation of Ig1 dimerization","pmids":["18706912"],"confidence":"High","gaps":["Full-length extracellular domain structure not determined","Contribution of other Ig domains to binding affinity unknown","No cell-based validation of the swapping interface"]},{"year":2015,"claim":"Discovery that Aβ binds NCAM2 at the neuronal surface, induces its proteolytic cleavage and synaptic removal, and thereby triggers GluR1-positive glutamatergic synapse disassembly provided the first link between NCAM2 and Alzheimer's disease-related synaptotoxicity.","evidence":"Surface binding assays, shRNA knockdown, cleavage-resistant mutant rescue in cultured hippocampal neurons; confirmation in AD patient hippocampus","pmids":["26611261"],"confidence":"High","gaps":["Identity of the protease cleaving NCAM2 in this context was not established","Whether NCAM2 cleavage is necessary or sufficient for synapse loss in vivo was not resolved"]},{"year":2018,"claim":"Structural and functional dissection of the FnIII domains showed they form a rigid unit that binds FGFR and activates Ras-MAPK signaling to drive neurite outgrowth, assigning a signaling output to a specific extracellular region distinct from the homophilic Ig1 domain.","evidence":"NMR and SAXS structural analysis; in vitro FGFR binding; neurite outgrowth with FGFR and MAPK inhibitors","pmids":["29895898"],"confidence":"High","gaps":["Direct FnIII–FGFR binding interface not mapped at residue level","Relevance to in vivo neurite outgrowth not tested"]},{"year":2019,"claim":"NCAM2 overexpression was shown to induce L-type Ca²⁺ channel-dependent submembrane Ca²⁺ spikes in dendritic protrusions, propagated by c-Src, that increase protrusion instability and impair spine maturation, linking NCAM2 levels to calcium-dependent control of synapse development.","evidence":"Live Ca²⁺ imaging in mouse cortical neurons with pharmacological dissection (L-type Ca²⁺ channel blockers, c-Src inhibitors)","pmids":["29522129"],"confidence":"High","gaps":["Whether endogenous NCAM2 loss-of-function has reciprocal effects on Ca²⁺ dynamics not shown","Direct physical interaction between NCAM2 and L-type channels or c-Src not demonstrated"]},{"year":2020,"claim":"Identification of a NCAM2–MAP2–14-3-3γ/ζ complex and demonstration that NCAM2 knockdown destabilizes microtubules, shortens dendrites, and impairs neuronal polarization and cortical migration established a cytoskeletal organizing function for NCAM2.","evidence":"Co-immunoprecipitation with proteomic validation; shRNA knockdown in hippocampal neurons and in vivo cortical electroporation","pmids":["32043120"],"confidence":"High","gaps":["Whether NCAM2 directly binds MAP2 or the interaction is bridged by 14-3-3 unknown","Phosphorylation-dependence of complex formation not functionally tested"]},{"year":2021,"claim":"A broader interactome (neurofilaments, CaMKIIα, actin, Nogo) was identified for NCAM2 in cerebral cortex, expanding the scope of cytoskeletal and signaling partners beyond the MAP2/14-3-3 complex.","evidence":"Mass spectrometry immunoprecipitation with co-IP validation from mouse cortex","pmids":["34299022"],"confidence":"Medium","gaps":["Single-lab MS interactome; independent validation in other systems needed","Functional significance of individual interactions not tested","In silico phosphorylation site predictions not experimentally confirmed"]},{"year":2022,"claim":"BACE1 was identified as the protease that cleaves NCAM2, and the resulting C-terminal fragment was shown to associate with BACE1 and promote its targeting to Rab11-positive recycling endosomes, revealing a reciprocal trafficking relationship.","evidence":"Co-IP, confocal co-localization, gain- and loss-of-function in neurons and CHO cells; NCAM2-KO mice show increased surface BACE1 and altered Sez6 cleavage","pmids":["36251052"],"confidence":"High","gaps":["Exact BACE1 cleavage site on NCAM2 not mapped","Whether NCAM2 CTF has signaling activity beyond BACE1 trafficking unknown"]},{"year":2023,"claim":"In vivo loss of NCAM2 reduces axonal BACE1 in hippocampal mossy fibers, shortens the infrapyramidal bundle, and causes behavioral deficits in spatial memory and cognitive flexibility, demonstrating a physiological role for the NCAM2–BACE1 trafficking axis in circuit function.","evidence":"NCAM2-deficient mouse model with immunofluorescence quantification and behavioral testing","pmids":["37522285"],"confidence":"Medium","gaps":["Single-lab KO model; replication in independent cohorts needed","Whether behavioral phenotypes are BACE1-dependent or reflect other NCAM2 functions not dissected"]},{"year":2023,"claim":"NCAM2 overexpression in the adult dentate gyrus arrests radial glial progenitors in an undifferentiated state, revealing a role in regulating adult neurogenesis progression beyond its known synaptogenic and cytoskeletal functions.","evidence":"In vivo viral overexpression in adult mice with immunofluorescence characterization of neurogenic stages","pmids":["37724425"],"confidence":"Medium","gaps":["Mechanism by which NCAM2 maintains RGP-like state not identified","Whether NCAM2 loss-of-function accelerates RGP differentiation not tested"]},{"year":2025,"claim":"A complete trafficking model was established: NCAM2 binds APP extracellularly and Rab11-FIP5 intracellularly, internalizes APP from the surface into BACE1-containing Rab11+ recycling endosomes for amyloidogenic processing, with Aβ oligomers and synaptic NMDA receptor activation enhancing NCAM2–APP association, creating a potential pathogenic feed-forward loop.","evidence":"Domain-specific co-IP, confocal co-localization, gain- and loss-of-function in CHO cells and neurons, Aβ oligomer and NMDA receptor stimulation","pmids":["40721030"],"confidence":"High","gaps":["Whether the NCAM2–APP–BACE1 axis operates identically in vivo in AD models not shown","Stoichiometry and structural basis of the NCAM2–APP and NCAM2–Rab11-FIP5 interactions not determined"]},{"year":null,"claim":"Key unresolved questions include: the structural basis of full-length NCAM2 extracellular domain interactions (only Ig1 and FnIII structures are known), the identity and regulation of proteases other than BACE1 that cleave NCAM2 in synaptic contexts, whether the NCAM2–APP–BACE1 trafficking axis is a viable therapeutic target in Alzheimer's disease in vivo, and how the cytoskeletal, signaling, and trafficking functions of NCAM2 are coordinated through its phosphorylation state.","evidence":"","pmids":[],"confidence":"Low","gaps":["Full-length ectodomain structure unavailable","Non-BACE1 proteases responsible for Aβ-induced cleavage unidentified","In vivo AD model validation of the trafficking axis lacking","Phosphorylation-dependent regulation of NCAM2 complexes unexplored"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098631","term_label":"cell adhesion mediator activity","supporting_discovery_ids":[1,2]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3,4,10]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[2,7,10]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[10]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[7,10]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[5,6]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,4]},{"term_id":"R-HSA-1500931","term_label":"Cell-Cell communication","supporting_discovery_ids":[1,2,5]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[4,5,8]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[5,9]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[7,10]}],"complexes":[],"partners":["MAP2","FGFR1","BACE1","APP","RAB11FIP5","YWHAG","YWHAZ","CAMK2A"],"other_free_text":[]},"mechanistic_narrative":"NCAM2 is a brain-enriched immunoglobulin superfamily cell adhesion molecule that mediates homophilic trans-interactions, organizes dendritic and axonal cytoskeletal architecture, regulates synapse maturation, and controls the intracellular trafficking and amyloidogenic processing of APP and BACE1. Its Ig1 domain undergoes beta-strand swapping to form homophilic dimers [PMID:18706912], while its rigid FnIII domains bind FGFR and activate Ras-MAPK signaling to promote neurite outgrowth [PMID:29895898]. NCAM2 complexes with MAP2 and 14-3-3 proteins to stabilize dendritic microtubules and support neuronal polarization and cortical migration [PMID:32043120], and triggers c-Src-dependent propagation of L-type Ca²⁺ channel-mediated submembrane Ca²⁺ spikes that regulate dendritic protrusion dynamics and synaptic vesicle maturation [PMID:29522129]. NCAM2 binds APP extracellularly and Rab11-FIP5 intracellularly to direct APP into BACE1-containing Rab11-positive recycling endosomes for amyloidogenic processing, while BACE1-generated NCAM2 C-terminal fragments reciprocally promote BACE1 targeting to those endosomes; Aβ oligomers in turn bind NCAM2 and induce its cleavage and removal from synapses, driving disassembly of GluR1-containing glutamatergic synapses [PMID:40721030, PMID:36251052, PMID:26611261]."},"prefetch_data":{"uniprot":{"accession":"O15394","full_name":"Neural cell adhesion molecule 2","aliases":[],"length_aa":837,"mass_kda":93.0,"function":"May play important roles in selective fasciculation and zone-to-zone projection of the primary olfactory axons","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/O15394/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/NCAM2","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/NCAM2","total_profiled":1310},"omim":[{"mim_id":"605686","title":"CELL ADHESION MOLECULE 1; CADM1","url":"https://www.omim.org/entry/605686"},{"mim_id":"602040","title":"CELL ADHESION MOLECULE, NEURAL, 2; NCAM2","url":"https://www.omim.org/entry/602040"},{"mim_id":"601511","title":"SIGNAL TRANSDUCER AND ACTIVATOR OF TRANSCRIPTION 5A; STAT5A","url":"https://www.omim.org/entry/601511"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nuclear bodies","reliability":"Supported"},{"location":"Plasma membrane","reliability":"Supported"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"adrenal gland","ntpm":11.3},{"tissue":"brain","ntpm":38.9}],"url":"https://www.proteinatlas.org/search/NCAM2"},"hgnc":{"alias_symbol":["NCAM21","MGC51008"],"prev_symbol":[]},"alphafold":{"accession":"O15394","domains":[{"cath_id":"2.60.40.10","chopping":"19-114","consensus_level":"high","plddt":90.2928,"start":19,"end":114},{"cath_id":"2.60.40.10","chopping":"120-208","consensus_level":"medium","plddt":90.1522,"start":120,"end":208},{"cath_id":"2.60.40.10","chopping":"214-300","consensus_level":"medium","plddt":91.6026,"start":214,"end":300},{"cath_id":"2.60.40.10","chopping":"309-400","consensus_level":"medium","plddt":93.3155,"start":309,"end":400},{"cath_id":"2.60.40.10","chopping":"405-493","consensus_level":"medium","plddt":94.1388,"start":405,"end":493},{"cath_id":"2.60.40.10","chopping":"501-588","consensus_level":"high","plddt":95.5125,"start":501,"end":588},{"cath_id":"2.60.40.10","chopping":"599-685","consensus_level":"high","plddt":90.9072,"start":599,"end":685}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O15394","model_url":"https://alphafold.ebi.ac.uk/files/AF-O15394-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O15394-F1-predicted_aligned_error_v6.png","plddt_mean":81.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=NCAM2","jax_strain_url":"https://www.jax.org/strain/search?query=NCAM2"},"sequence":{"accession":"O15394","fasta_url":"https://rest.uniprot.org/uniprotkb/O15394.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O15394/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O15394"}},"corpus_meta":[{"pmid":"26611261","id":"PMC_26611261","title":"Aβ-dependent 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Regulating Multiple Neural Functions.","date":"2021","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/34576185","citation_count":32,"is_preprint":false},{"pmid":"32043120","id":"PMC_32043120","title":"NCAM2 Regulates Dendritic and Axonal Differentiation through the Cytoskeletal Proteins MAP2 and 14-3-3.","date":"2020","source":"Cerebral cortex (New York, N.Y. : 1991)","url":"https://pubmed.ncbi.nlm.nih.gov/32043120","citation_count":30,"is_preprint":false},{"pmid":"25464110","id":"PMC_25464110","title":"21q21 deletion involving NCAM2: report of 3 cases with neurodevelopmental disorders.","date":"2014","source":"European journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/25464110","citation_count":28,"is_preprint":false},{"pmid":"29522129","id":"PMC_29522129","title":"Neural Cell Adhesion Molecule 2 (NCAM2)-Induced c-Src-Dependent Propagation of Submembrane Ca2+ Spikes Along Dendrites Inhibits Synapse 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\"Genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct sequence determination and domain mapping from cloned cDNA\",\n      \"pmids\": [\"9226371\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The crystal structure of NCAM2 Ig1 domain reveals domain swapping of the two N-terminal beta-strands between two molecules, and gel-filtration chromatography confirmed Ig1 forms dimers in solution, suggesting beta-strand swapping underlies homophilic binding.\",\n      \"method\": \"X-ray crystallography at 2.7 Å resolution and gel-filtration chromatography\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with solution-state validation by gel filtration\",\n      \"pmids\": [\"18706912\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Aβ binds directly to NCAM2 at the cell surface of cultured hippocampal neurons, induces removal of NCAM2 from synapses, and promotes cleavage of the membrane-proximal extracellular region of NCAM2 generating soluble extracellular fragments (NCAM2-ED). Knockdown of NCAM2 or addition of NCAM2-ED induces disassembly of GluR1-containing glutamatergic synapses. A cleavage-resistant NCAM2 mutant inhibits Aβ-dependent synapse disassembly.\",\n      \"method\": \"Surface binding assays, live-cell imaging, shRNA knockdown, overexpression of cleavage-resistant mutant, immunofluorescence in cultured hippocampal neurons and AD patient hippocampus\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (binding, KD, mutant rescue) in cultured neurons and human tissue\",\n      \"pmids\": [\"26611261\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The NCAM2 FnIII1-2 double domain forms a rigid, low-flexibility structure (by SAXS), does not bind ATP via its Walker A motif (unlike NCAM1, shown by NMR titration), binds FGFR in vitro, and induces neurite outgrowth in a concentration-dependent manner through FGFR activation and downstream Ras-MAPK signaling.\",\n      \"method\": \"NMR spectroscopy, SAXS, in vitro FGFR binding assay, neurite outgrowth assay with FGFR inhibitors and Ras-MAPK pathway inhibitors\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — structure by NMR/SAXS plus in vitro binding and functional assay with pathway inhibition\",\n      \"pmids\": [\"29895898\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"NCAM2 overexpression induces L-type voltage-gated Ca2+ channel-dependent submembrane Ca2+ spikes in individual dendritic protrusions, propagates these spikes along dendrites via c-Src kinase, increases instability of dendritic protrusions, reduces their conversion to mature spines, and results in synaptic boutons enriched in immature marker GAP43 with reduced activity-dependent vesicle recycling.\",\n      \"method\": \"Ca2+ imaging in live mouse cortical neurons, NCAM2 overexpression, L-type Ca2+ channel blockers, c-Src inhibition, synaptic vesicle recycling assay\",\n      \"journal\": \"Cerebral cortex\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — live-cell Ca2+ imaging with pharmacological dissection of pathway, replicated with multiple inhibitors\",\n      \"pmids\": [\"29522129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"NCAM2 forms a protein complex with cytoskeletal-associated proteins MAP2 and 14-3-3γ/ζ. NCAM2 knockdown destabilizes the microtubular network and reduces MAP2 signal, leading to shortened dendritic trees, dendritic retraction, somatic neurite emergence, axonal defects, impaired neuronal polarization, and cortical migration deficits in vivo.\",\n      \"method\": \"Co-immunoprecipitation (proteomic/cell biology validation), shRNA knockdown in hippocampal neurons and in vivo cortical electroporation, immunofluorescence, microtubule stability assays\",\n      \"journal\": \"Cerebral cortex\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal interaction validated by proteomics and Co-IP, combined with in vitro and in vivo KD phenotype\",\n      \"pmids\": [\"32043120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Mass spectrometry-based interactome analysis identified NCAM2 binding partners in mouse cerebral cortex including Neurofilaments (NEFs), MAP2, CaMKIIα, Actin, and Nogo, validated by co-immunoprecipitation; in silico analysis of the NCAM2.1 cytosolic tail revealed phosphorylation site motifs with affinity for these interactors.\",\n      \"method\": \"Mass spectrometry immunoprecipitation, co-immunoprecipitation validation, in silico phosphorylation site analysis\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — MS interactome with Co-IP validation, single lab\",\n      \"pmids\": [\"34299022\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"BACE1 cleaves NCAM2 in cultured hippocampal neurons and transfected CHO cells. The resulting C-terminal fragment of NCAM2 (comprising intracellular domain and small extracellular portion) associates with BACE1 before endocytosis, and co-localizes with BACE1 in Rab11-positive recycling endosomes. Overexpression of full-length NCAM2 or the transmembrane/intracellular fragment increases BACE1 in Rab11+ endosomes; NCAM2 deficiency increases BACE1 at the cell surface and reduces intracellular BACE1, correlating with increased BACE1 shedding and reduced Sez6 cleavage in vivo.\",\n      \"method\": \"Co-immunoprecipitation, confocal co-localization, overexpression and KO in neurons and CHO cells, endocytosis inhibition, BACE1 shedding assay in NCAM2-deficient mice\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Co-IP, co-localization, gain- and loss-of-function) across two cell systems and in vivo\",\n      \"pmids\": [\"36251052\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"NCAM2 increases axonal levels of BACE1 in hippocampal mossy fiber projections; NCAM2-deficient mice have reduced BACE1 in mossy fiber axons, a shortened infrapyramidal bundle, and behavioral deficits including impaired short-term spatial memory, reduced cognitive flexibility, and increased self-grooming.\",\n      \"method\": \"NCAM2-deficient mouse model, immunofluorescence quantification of BACE1 in axonal projections, behavioral tests (spatial memory, cognitive flexibility, grooming)\",\n      \"journal\": \"Cerebral cortex\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined axonal and behavioral phenotypes, single lab\",\n      \"pmids\": [\"37522285\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"NCAM2 overexpression in adult mice arrests radial glial progenitors (RGPs) in an RGP-like state in the dentate gyrus, disrupting normal young-adult neurogenesis progression, while changes in NCAM2 levels during corticogenesis cause transient migratory deficits without affecting RGP survival or proliferation.\",\n      \"method\": \"In vivo NCAM2 overexpression in adult mice via viral vectors, immunofluorescence characterization of neurogenic cell types, BrdU/EdU proliferation assays, cortical electroporation\",\n      \"journal\": \"Cerebral cortex\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo gain-of-function with defined cellular phenotype, single lab\",\n      \"pmids\": [\"37724425\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"APP binds to the extracellular domain of NCAM2; the intracellular domain of NCAM2 binds the Rab11 adaptor protein Rab11-FIP5. The NCAM2/APP complex is endocytosed from the cell surface and targeted to BACE1-containing Rab11-positive recycling endosomes where APP is processed. NCAM2 expression increases amyloidogenic APP cleavage products; NCAM2 deficiency causes APP accumulation at the cell surface and in early endosomes with reduced APP in recycling endosomes. Aβ oligomers and synaptic NMDA receptor activation increase NCAM2-APP binding.\",\n      \"method\": \"Co-immunoprecipitation (extracellular and intracellular domain interactions), confocal co-localization, overexpression in CHO cells and neurons, NCAM2-deficient neurons, endocytosis assays, Aβ oligomer and NMDA receptor stimulation experiments\",\n      \"journal\": \"Progress in neurobiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Co-IP of distinct domains, gain- and loss-of-function, two cell systems), single lab with comprehensive mechanistic dissection\",\n      \"pmids\": [\"40721030\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"NCAM2 is a synaptic cell adhesion molecule that mediates homophilic binding via Ig-domain swapping, activates FGFR/Ras-MAPK signaling through its rigid FnIII domains to promote neurite outgrowth, organizes the dendritic cytoskeleton by complexing with MAP2 and 14-3-3 proteins, regulates synapse maturation by triggering c-Src-dependent propagation of L-type Ca2+-channel-mediated submembrane Ca2+ spikes, and controls amyloidogenic processing by binding APP extracellularly and Rab11-FIP5 intracellularly to co-traffic APP with BACE1 into Rab11-positive recycling endosomes, while its BACE1-generated C-terminal fragment reciprocally promotes BACE1 targeting to those same endosomes.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"NCAM2 is a brain-enriched immunoglobulin superfamily cell adhesion molecule that mediates homophilic trans-interactions, organizes dendritic and axonal cytoskeletal architecture, regulates synapse maturation, and controls the intracellular trafficking and amyloidogenic processing of APP and BACE1. Its Ig1 domain undergoes beta-strand swapping to form homophilic dimers [PMID:18706912], while its rigid FnIII domains bind FGFR and activate Ras-MAPK signaling to promote neurite outgrowth [PMID:29895898]. NCAM2 complexes with MAP2 and 14-3-3 proteins to stabilize dendritic microtubules and support neuronal polarization and cortical migration [PMID:32043120], and triggers c-Src-dependent propagation of L-type Ca²⁺ channel-mediated submembrane Ca²⁺ spikes that regulate dendritic protrusion dynamics and synaptic vesicle maturation [PMID:29522129]. NCAM2 binds APP extracellularly and Rab11-FIP5 intracellularly to direct APP into BACE1-containing Rab11-positive recycling endosomes for amyloidogenic processing, while BACE1-generated NCAM2 C-terminal fragments reciprocally promote BACE1 targeting to those endosomes; Aβ oligomers in turn bind NCAM2 and induce its cleavage and removal from synapses, driving disassembly of GluR1-containing glutamatergic synapses [PMID:40721030, PMID:36251052, PMID:26611261].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Cloning of NCAM2 established it as a brain-enriched Ig-superfamily member structurally related to NCAM1, defining the domain architecture (five Ig, two FnIII, TM, cytoplasmic tail) that subsequent work would parse for discrete functions.\",\n      \"evidence\": \"cDNA cloning and sequence analysis from human fetal brain library\",\n      \"pmids\": [\"9226371\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No functional data at this stage\", \"Expression pattern limited to Northern blot survey\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Crystal structure of the Ig1 domain revealed that homophilic binding is mediated by reciprocal beta-strand swapping, providing the first molecular mechanism for NCAM2 trans-adhesion.\",\n      \"evidence\": \"X-ray crystallography at 2.7 Å resolution with gel-filtration confirmation of Ig1 dimerization\",\n      \"pmids\": [\"18706912\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length extracellular domain structure not determined\", \"Contribution of other Ig domains to binding affinity unknown\", \"No cell-based validation of the swapping interface\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Discovery that Aβ binds NCAM2 at the neuronal surface, induces its proteolytic cleavage and synaptic removal, and thereby triggers GluR1-positive glutamatergic synapse disassembly provided the first link between NCAM2 and Alzheimer's disease-related synaptotoxicity.\",\n      \"evidence\": \"Surface binding assays, shRNA knockdown, cleavage-resistant mutant rescue in cultured hippocampal neurons; confirmation in AD patient hippocampus\",\n      \"pmids\": [\"26611261\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the protease cleaving NCAM2 in this context was not established\", \"Whether NCAM2 cleavage is necessary or sufficient for synapse loss in vivo was not resolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Structural and functional dissection of the FnIII domains showed they form a rigid unit that binds FGFR and activates Ras-MAPK signaling to drive neurite outgrowth, assigning a signaling output to a specific extracellular region distinct from the homophilic Ig1 domain.\",\n      \"evidence\": \"NMR and SAXS structural analysis; in vitro FGFR binding; neurite outgrowth with FGFR and MAPK inhibitors\",\n      \"pmids\": [\"29895898\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct FnIII–FGFR binding interface not mapped at residue level\", \"Relevance to in vivo neurite outgrowth not tested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"NCAM2 overexpression was shown to induce L-type Ca²⁺ channel-dependent submembrane Ca²⁺ spikes in dendritic protrusions, propagated by c-Src, that increase protrusion instability and impair spine maturation, linking NCAM2 levels to calcium-dependent control of synapse development.\",\n      \"evidence\": \"Live Ca²⁺ imaging in mouse cortical neurons with pharmacological dissection (L-type Ca²⁺ channel blockers, c-Src inhibitors)\",\n      \"pmids\": [\"29522129\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether endogenous NCAM2 loss-of-function has reciprocal effects on Ca²⁺ dynamics not shown\", \"Direct physical interaction between NCAM2 and L-type channels or c-Src not demonstrated\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identification of a NCAM2–MAP2–14-3-3γ/ζ complex and demonstration that NCAM2 knockdown destabilizes microtubules, shortens dendrites, and impairs neuronal polarization and cortical migration established a cytoskeletal organizing function for NCAM2.\",\n      \"evidence\": \"Co-immunoprecipitation with proteomic validation; shRNA knockdown in hippocampal neurons and in vivo cortical electroporation\",\n      \"pmids\": [\"32043120\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether NCAM2 directly binds MAP2 or the interaction is bridged by 14-3-3 unknown\", \"Phosphorylation-dependence of complex formation not functionally tested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"A broader interactome (neurofilaments, CaMKIIα, actin, Nogo) was identified for NCAM2 in cerebral cortex, expanding the scope of cytoskeletal and signaling partners beyond the MAP2/14-3-3 complex.\",\n      \"evidence\": \"Mass spectrometry immunoprecipitation with co-IP validation from mouse cortex\",\n      \"pmids\": [\"34299022\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab MS interactome; independent validation in other systems needed\", \"Functional significance of individual interactions not tested\", \"In silico phosphorylation site predictions not experimentally confirmed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"BACE1 was identified as the protease that cleaves NCAM2, and the resulting C-terminal fragment was shown to associate with BACE1 and promote its targeting to Rab11-positive recycling endosomes, revealing a reciprocal trafficking relationship.\",\n      \"evidence\": \"Co-IP, confocal co-localization, gain- and loss-of-function in neurons and CHO cells; NCAM2-KO mice show increased surface BACE1 and altered Sez6 cleavage\",\n      \"pmids\": [\"36251052\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Exact BACE1 cleavage site on NCAM2 not mapped\", \"Whether NCAM2 CTF has signaling activity beyond BACE1 trafficking unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"In vivo loss of NCAM2 reduces axonal BACE1 in hippocampal mossy fibers, shortens the infrapyramidal bundle, and causes behavioral deficits in spatial memory and cognitive flexibility, demonstrating a physiological role for the NCAM2–BACE1 trafficking axis in circuit function.\",\n      \"evidence\": \"NCAM2-deficient mouse model with immunofluorescence quantification and behavioral testing\",\n      \"pmids\": [\"37522285\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab KO model; replication in independent cohorts needed\", \"Whether behavioral phenotypes are BACE1-dependent or reflect other NCAM2 functions not dissected\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"NCAM2 overexpression in the adult dentate gyrus arrests radial glial progenitors in an undifferentiated state, revealing a role in regulating adult neurogenesis progression beyond its known synaptogenic and cytoskeletal functions.\",\n      \"evidence\": \"In vivo viral overexpression in adult mice with immunofluorescence characterization of neurogenic stages\",\n      \"pmids\": [\"37724425\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which NCAM2 maintains RGP-like state not identified\", \"Whether NCAM2 loss-of-function accelerates RGP differentiation not tested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A complete trafficking model was established: NCAM2 binds APP extracellularly and Rab11-FIP5 intracellularly, internalizes APP from the surface into BACE1-containing Rab11+ recycling endosomes for amyloidogenic processing, with Aβ oligomers and synaptic NMDA receptor activation enhancing NCAM2–APP association, creating a potential pathogenic feed-forward loop.\",\n      \"evidence\": \"Domain-specific co-IP, confocal co-localization, gain- and loss-of-function in CHO cells and neurons, Aβ oligomer and NMDA receptor stimulation\",\n      \"pmids\": [\"40721030\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the NCAM2–APP–BACE1 axis operates identically in vivo in AD models not shown\", \"Stoichiometry and structural basis of the NCAM2–APP and NCAM2–Rab11-FIP5 interactions not determined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: the structural basis of full-length NCAM2 extracellular domain interactions (only Ig1 and FnIII structures are known), the identity and regulation of proteases other than BACE1 that cleave NCAM2 in synaptic contexts, whether the NCAM2–APP–BACE1 trafficking axis is a viable therapeutic target in Alzheimer's disease in vivo, and how the cytoskeletal, signaling, and trafficking functions of NCAM2 are coordinated through its phosphorylation state.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Full-length ectodomain structure unavailable\", \"Non-BACE1 proteases responsible for Aβ-induced cleavage unidentified\", \"In vivo AD model validation of the trafficking axis lacking\", \"Phosphorylation-dependent regulation of NCAM2 complexes unexplored\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098631\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3, 4, 10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2, 7, 10]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [10]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [7, 10]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [5, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 4]},\n      {\"term_id\": \"R-HSA-1500931\", \"supporting_discovery_ids\": [1, 2, 5]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [4, 5, 8]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [5, 9]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [7, 10]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"MAP2\", \"FGFR1\", \"BACE1\", \"APP\", \"RAB11FIP5\", \"YWHAG\", \"YWHAZ\", \"CAMK2A\"],\n    \"other_free_text\": []\n  }\n}\n```"}