{"gene":"NCAM2","run_date":"2026-06-10T05:19:52","timeline":{"discoveries":[{"year":1997,"finding":"NCAM2 encodes a 837-amino acid protein containing five immunoglobulin-like domains, two fibronectin type III domains, a transmembrane domain, and a cytoplasmic domain, establishing its structural classification as a member of the immunoglobulin superfamily of cell adhesion molecules.","method":"cDNA cloning from human fetal brain library, sequence analysis, chromosomal mapping via somatic cell hybrids and radiation hybrid mapping","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — direct molecular cloning and sequence determination in a single study; no functional validation beyond structural prediction","pmids":["9226371"],"is_preprint":false},{"year":2008,"finding":"The crystal structure of NCAM2 Ig1 domain at 2.7 Å resolution revealed domain swapping of the two N-terminal beta-strands between two Ig1 monomers, and gel-filtration chromatography confirmed that NCAM2 Ig1 forms dimers in solution, suggesting beta-strand swapping as the molecular mechanism of NCAM2 homophilic binding.","method":"X-ray crystallography (2.7 Å resolution) and gel-filtration chromatography","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure plus solution biochemistry (gel filtration) using two orthogonal methods in one study","pmids":["18706912"],"is_preprint":false},{"year":2015,"finding":"Aβ binds directly to NCAM2 at the cell surface of hippocampal neurons and induces removal of NCAM2 from synapses. BACE1-mediated cleavage of the membrane-proximal external region of NCAM2 is increased in AD hippocampus, generating soluble extracellular fragments (NCAM2-ED). Knockdown of NCAM2 or incubation with NCAM2-ED causes disassembly of GluR1-containing glutamatergic synapses. A cleavage-resistant NCAM2 mutant inhibits Aβ-dependent synapse disassembly.","method":"Co-incubation binding assay (Aβ–NCAM2 at cell surface), NCAM2 knockdown in cultured hippocampal neurons, overexpression of cleavage-resistant NCAM2 mutant, immunofluorescence of synaptic markers, human AD hippocampus tissue analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (loss-of-function, gain-of-function with cleavage-resistant mutant, human tissue validation) in a single study with clear mechanistic readout","pmids":["26611261"],"is_preprint":false},{"year":2018,"finding":"The NCAM2 FnIII1-2 double domain adopts a rigid structure (low flexibility by SAXS), does not bind ATP (unlike NCAM1, whose Walker A motif in FnIII2 binds ATP), and binds FGFR in vitro. The FnIII1-2 double domain induces neurite outgrowth in a concentration-dependent manner through activation of FGFR, and the most potent NCAM2-derived peptide stimulates neurite outgrowth via FGFR-dependent activation of the Ras-MAPK pathway.","method":"NMR spectroscopy (structural model of FnIII2), SAXS (domain flexibility), ATP analogue titration, in vitro FGFR binding assay, neurite outgrowth assay with FGFR inhibitors, Ras-MAPK pathway readout","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1 / Moderate — NMR structure, SAXS, in vitro binding, and functional neurite outgrowth assays with pathway inhibition, multiple orthogonal methods in one study","pmids":["29895898"],"is_preprint":false},{"year":2019,"finding":"Elevated NCAM2 levels in cortical neurons increase the frequency of L-type voltage-gated Ca2+ channel-dependent submembrane Ca2+ spikes in dendritic protrusions and promote their propagation along dendrites via c-Src protein tyrosine kinase. This Ca2+ spike propagation increases instability of dendritic protrusions, reduces conversion to dendritic spines, and inhibits synapse maturation (increased GAP43, reduced activity-dependent synaptic vesicle recycling).","method":"NCAM2 overexpression in mouse cortical neurons, live Ca2+ imaging, pharmacological inhibition of L-type VGCCs and c-Src, dendritic protrusion dynamics tracking, synaptic vesicle recycling assay","journal":"Cerebral cortex","confidence":"High","confidence_rationale":"Tier 2 / Moderate — live imaging with pharmacological dissection of pathway components (VGCC, c-Src), multiple functional readouts in a single study","pmids":["29522129"],"is_preprint":false},{"year":2020,"finding":"NCAM2 interacts physically with the cytoskeletal-associated proteins MAP2 and 14-3-3γ and ζ, forming a protein complex. NCAM2 depletion destabilizes the microtubular network and reduces MAP2 signal, compromising dendritic architecture (shorter trees, retraction, somatic neurites) and causing deficits in neuronal polarization and cortical migration in vivo.","method":"Proteomic/cell biology experiments (protein complex identification), NCAM2 knockdown in hippocampal neurons and in vivo, immunofluorescence for MAP2, dendritic morphology analysis, in utero electroporation for cortical migration","journal":"Cerebral cortex","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal protein interaction experiments plus loss-of-function in vitro and in vivo with multiple orthogonal phenotypic readouts","pmids":["32043120"],"is_preprint":false},{"year":2021,"finding":"Mass spectrometry-based interactome analysis of NCAM2 in mouse postnatal cerebral cortex identified >100 interacting proteins; validated partners include Neurofilaments (NEFs), MAP2, CaMKIIα, Actin, and Nogo. In silico analysis of the NCAM2.1 cytosolic tail revealed phosphorylation site motifs with predicted affinity for these interactors.","method":"Co-immunoprecipitation followed by mass spectrometry (MS), validation by additional co-IP/pulldown, in silico phosphorylation site analysis","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — MS-based interactome with validated subset by Co-IP; functional consequences for most partners not individually established in this study","pmids":["34299022"],"is_preprint":false},{"year":2022,"finding":"BACE1 cleaves NCAM2 in cultured hippocampal neurons and NCAM2-transfected CHO cells, generating a C-terminal fragment (CTF) comprising the intracellular domain and a small portion of the extracellular domain. This NCAM2-CTF associates with BACE1 (interaction that precedes endocytosis) and both co-localize in Rab11-positive recycling endosomes. Overexpression of full-length NCAM2 or the transmembrane/intracellular fragment increases BACE1 in recycling endosomes; in NCAM2-deficient neurons, BACE1 accumulates at the cell surface and is reduced intracellularly, correlating with increased BACE1 shedding and reduced cleavage of the BACE1-exclusive substrate Sez6.","method":"Overexpression and knockdown in hippocampal neurons and CHO cells, co-localization imaging with Rab11 marker, BACE1 inhibition experiments, NCAM2-deficient mouse brains (ELISA for shed BACE1), Sez6 cleavage assay","journal":"Cellular and molecular life sciences","confidence":"High","confidence_rationale":"Tier 2 / Moderate — loss-of-function (KO mouse) and gain-of-function (overexpression), multiple cell types, endogenous substrate cleavage readout, multiple orthogonal methods","pmids":["36251052"],"is_preprint":false},{"year":2023,"finding":"NCAM2 deficiency in mice reduces axonal BACE1 levels in hippocampal mossy fiber projections and shortens the infrapyramidal bundle, demonstrating that NCAM2 regulates axonal BACE1 levels and hippocampal axonal organization. This is associated with impaired short-term spatial memory and cognitive flexibility, and sex-differential behavioral phenotypes including increased self-grooming.","method":"NCAM2-deficient mouse analysis, immunofluorescence of BACE1 in mossy fibers, morphometric measurement of infrapyramidal bundle, behavioral testing (Morris water maze, Y-maze, self-grooming, rearing, digging)","journal":"Cerebral cortex","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — clean KO with defined cellular (axonal BACE1 levels, bundle morphometry) 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, impairing normal progression of young-adult neurogenesis in the hippocampal dentate gyrus. Changes in NCAM2 levels during corticogenesis cause transient migratory deficits without affecting RGP survival or proliferation, indicating a stage-specific role.","method":"Ncam2 overexpression by viral vector in adult mice, BrdU/EdU lineage tracing, immunofluorescence of RGP markers, in utero electroporation for corticogenesis studies","journal":"Cerebral cortex","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — gain-of-function in vivo with defined cellular phenotype (RGP arrest), single lab","pmids":["37724425"],"is_preprint":false},{"year":2025,"finding":"APP binds to the extracellular domain of NCAM2, and 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 convergence of APP with BACE1 and elevates amyloidogenic APP cleavage products. In NCAM2-deficient neurons, APP accumulates at the cell surface and in early endosomes, with reduced APP in recycling endosomes. Binding of NCAM2 to APP is increased by Aβ oligomers and activation of synaptic NMDA receptors.","method":"Co-immunoprecipitation (NCAM2-APP and NCAM2-Rab11-FIP5), overexpression in CHO cells and neurons, NCAM2-deficient neurons (loss-of-function), endosome fractionation/imaging, BACE1 cleavage product quantification, Aβ oligomer treatment, NMDA receptor activation","journal":"Progress in neurobiology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP for multiple binding partners, loss-of-function (KO neurons) and gain-of-function (overexpression), multiple orthogonal readouts in a single rigorous study","pmids":["40721030"],"is_preprint":false}],"current_model":"NCAM2 is a GPI-anchored and transmembrane immunoglobulin superfamily cell adhesion molecule that mediates homophilic adhesion via Ig1 domain beta-strand swapping and engages FGFR through its rigid FnIII1-2 domains to activate Ras-MAPK and promote neurite outgrowth; at synapses, it stabilizes GluR1-containing glutamatergic synapses through interactions with MAP2 and 14-3-3 proteins to maintain microtubule stability, while also forming a complex with APP via its extracellular domain and with Rab11-FIP5 via its intracellular domain to traffic APP into BACE1-containing Rab11-positive recycling endosomes, thereby regulating amyloidogenic processing; BACE1-mediated cleavage of NCAM2 generates a CTF that in turn promotes BACE1 targeting to recycling endosomes, and Aβ-induced cleavage of NCAM2 disrupts its synaptic adhesion function, contributing to synapse loss in Alzheimer's disease."},"narrative":{"mechanistic_narrative":"NCAM2 is an immunoglobulin superfamily cell adhesion molecule of the neuronal surface that organizes dendritic and axonal architecture, glutamatergic synapse stability, and amyloidogenic trafficking [PMID:9226371, PMID:26611261, PMID:32043120]. Its N-terminal Ig1 domain mediates homophilic binding through reciprocal swapping of two N-terminal beta-strands between monomers, while its rigid FnIII1-2 double domain binds and activates FGFR to drive Ras-MAPK-dependent neurite outgrowth [PMID:18706912, PMID:29895898]. At the cytoskeletal interface, NCAM2 forms a complex with MAP2 and 14-3-3 proteins that stabilizes the microtubule network and supports dendritic arborization, neuronal polarization, and cortical migration; its loss destabilizes microtubules and disrupts these processes in vivo [PMID:32043120, PMID:34299022]. NCAM2 couples surface adhesion to endosomal trafficking: it forms a complex with APP through its extracellular domain and with the Rab11 adaptor Rab11-FIP5 through its intracellular domain, channeling APP into BACE1-containing Rab11-positive recycling endosomes and thereby promoting amyloidogenic APP processing, an interaction enhanced by Abeta oligomers and synaptic NMDA receptor activation [PMID:40721030]. NCAM2 is itself a BACE1 substrate; cleavage liberates a C-terminal fragment that associates with BACE1 and helps target the protease to recycling endosomes, so that NCAM2 deficiency redistributes BACE1 to the cell surface and lowers axonal BACE1 levels [PMID:36251052, PMID:37522285]. In Alzheimer-relevant settings, Abeta binds NCAM2 directly and triggers its BACE1-mediated removal from synapses, and the resulting extracellular fragment drives disassembly of GluR1-containing glutamatergic synapses, linking NCAM2 cleavage to synapse loss [PMID:26611261].","teleology":[{"year":1997,"claim":"Established NCAM2's molecular identity, defining it as an Ig-superfamily cell adhesion molecule with a defined domain architecture and chromosomal locus.","evidence":"cDNA cloning from human fetal brain and sequence/chromosomal mapping","pmids":["9226371"],"confidence":"Medium","gaps":["No functional assay beyond structural prediction","Binding partners and adhesion mode unknown at this stage"]},{"year":2008,"claim":"Resolved the molecular basis of NCAM2 homophilic adhesion by showing the Ig1 domain dimerizes via N-terminal beta-strand swapping.","evidence":"X-ray crystallography at 2.7 A and gel-filtration chromatography of the Ig1 domain","pmids":["18706912"],"confidence":"High","gaps":["Adhesion demonstrated for an isolated domain, not full-length cell-cell contacts","Functional consequence of homophilic binding not tested"]},{"year":2015,"claim":"Connected NCAM2 cleavage to synapse loss, showing Abeta binds NCAM2 and BACE1 cleavage of its extracellular region disassembles glutamatergic synapses.","evidence":"Abeta-NCAM2 binding assays, knockdown and cleavage-resistant mutant in hippocampal neurons, AD hippocampus tissue analysis","pmids":["26611261"],"confidence":"High","gaps":["Synaptic adhesion partners of NCAM2 not fully defined","Intracellular signaling downstream of NCAM2 loss at synapses unresolved"]},{"year":2018,"claim":"Identified an FGFR-activating, growth-promoting function distinct from NCAM1, defining the rigid FnIII1-2 domains as the FGFR-binding module driving neurite outgrowth.","evidence":"NMR and SAXS structural analysis, ATP-binding test, in vitro FGFR binding, neurite outgrowth with FGFR/Ras-MAPK inhibitors","pmids":["29895898"],"confidence":"High","gaps":["Direct FGFR contact residues not mapped","In vivo relevance of FGFR activation not established"]},{"year":2019,"claim":"Revealed a signaling role in dendritic maturation, where NCAM2 modulates L-type VGCC Ca2+ spikes via c-Src to control spine conversion and synapse maturation.","evidence":"Overexpression in mouse cortical neurons, live Ca2+ imaging, VGCC and c-Src pharmacological inhibition, synaptic vesicle recycling assays","pmids":["29522129"],"confidence":"High","gaps":["Mechanism linking NCAM2 to VGCC/c-Src activation unclear","Loss-of-function effect on Ca2+ spikes not tested"]},{"year":2020,"claim":"Linked NCAM2 to the cytoskeleton, showing a MAP2/14-3-3 complex through which NCAM2 stabilizes microtubules and supports dendritic and migratory architecture.","evidence":"Protein complex identification, NCAM2 knockdown in neurons and in vivo, MAP2 immunofluorescence, in utero electroporation for cortical migration","pmids":["32043120"],"confidence":"High","gaps":["Direct versus indirect MAP2/14-3-3 binding not fully resolved","How surface NCAM2 transmits signals to microtubules unknown"]},{"year":2021,"claim":"Expanded the NCAM2 interactome, identifying >100 candidate partners including neurofilaments, CaMKIIalpha, actin, and Nogo with predicted phospho-regulated binding.","evidence":"Co-IP mass spectrometry from mouse cerebral cortex, validation co-IP, in silico phosphosite analysis","pmids":["34299022"],"confidence":"Medium","gaps":["Functional consequences of most interactions not established","Phosphorylation sites predicted, not experimentally mapped"]},{"year":2022,"claim":"Showed NCAM2 controls BACE1 subcellular distribution: a BACE1-generated NCAM2 CTF associates with BACE1 and targets it to Rab11 recycling endosomes.","evidence":"Overexpression/knockdown in neurons and CHO cells, Rab11 co-localization, BACE1 shedding ELISA in KO mice, Sez6 cleavage assay","pmids":["36251052"],"confidence":"High","gaps":["Motifs in the NCAM2 CTF mediating BACE1 targeting not defined","Direct versus adaptor-mediated NCAM2-BACE1 association unresolved"]},{"year":2023,"claim":"Established an in vivo axonal role, with NCAM2 deficiency lowering axonal BACE1, shortening the mossy fiber infrapyramidal bundle, and impairing spatial memory.","evidence":"NCAM2-deficient mice, BACE1 immunofluorescence in mossy fibers, bundle morphometry, behavioral testing","pmids":["37522285"],"confidence":"Medium","gaps":["Causal link between axonal BACE1 changes and behavior not isolated","Sex-differential phenotype mechanism unexplained"]},{"year":2023,"claim":"Demonstrated a stage-specific developmental role, where elevated NCAM2 arrests radial glial progenitors and causes transient migratory deficits.","evidence":"Viral Ncam2 overexpression in adult mice, BrdU/EdU lineage tracing, RGP marker immunofluorescence, in utero electroporation","pmids":["37724425"],"confidence":"Medium","gaps":["Molecular pathway driving RGP arrest not defined","Loss-of-function effect on adult neurogenesis not reported"]},{"year":2025,"claim":"Defined NCAM2 as a trafficking scaffold for amyloidogenesis, bridging APP (extracellular) to Rab11-FIP5 (intracellular) to deliver APP into BACE1-positive recycling endosomes.","evidence":"Reciprocal Co-IP for NCAM2-APP and NCAM2-Rab11-FIP5, overexpression and KO neurons, endosome fractionation/imaging, BACE1 product quantification, Abeta oligomer and NMDA receptor activation","pmids":["40721030"],"confidence":"High","gaps":["Structural basis of NCAM2-APP and NCAM2-Rab11-FIP5 binding unknown","Whether this pathway is therapeutically targetable not addressed"]},{"year":null,"claim":"How NCAM2's adhesion, FGFR-signaling, cytoskeletal, and APP/BACE1 trafficking functions are integrated and differentially deployed across neuronal compartments remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking surface adhesion to endosomal trafficking control","Splice-isoform-specific functions not dissected","No human disease-causing mutation defined in the corpus"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098631","term_label":"cell adhesion mediator activity","supporting_discovery_ids":[1,2]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[3,4]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[5,10]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[5,6]}],"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":[7,10]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,4]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[7,10]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[5,9]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[2,10]}],"complexes":["NCAM2-MAP2-14-3-3 complex","NCAM2-APP-Rab11-FIP5 complex"],"partners":["MAP2","YWHAG","YWHAZ","FGFR","APP","RAB11FIP5","BACE1","CAMK2A"],"other_free_text":[]}},"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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from human fetal brain library, sequence analysis, chromosomal mapping via somatic cell hybrids and radiation hybrid mapping\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — direct molecular cloning and sequence determination in a single study; no functional validation beyond structural prediction\",\n      \"pmids\": [\"9226371\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The crystal structure of NCAM2 Ig1 domain at 2.7 Å resolution revealed domain swapping of the two N-terminal beta-strands between two Ig1 monomers, and gel-filtration chromatography confirmed that NCAM2 Ig1 forms dimers in solution, suggesting beta-strand swapping as the molecular mechanism of NCAM2 homophilic binding.\",\n      \"method\": \"X-ray crystallography (2.7 Å resolution) and gel-filtration chromatography\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure plus solution biochemistry (gel filtration) using two orthogonal methods in one study\",\n      \"pmids\": [\"18706912\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Aβ binds directly to NCAM2 at the cell surface of hippocampal neurons and induces removal of NCAM2 from synapses. BACE1-mediated cleavage of the membrane-proximal external region of NCAM2 is increased in AD hippocampus, generating soluble extracellular fragments (NCAM2-ED). Knockdown of NCAM2 or incubation with NCAM2-ED causes disassembly of GluR1-containing glutamatergic synapses. A cleavage-resistant NCAM2 mutant inhibits Aβ-dependent synapse disassembly.\",\n      \"method\": \"Co-incubation binding assay (Aβ–NCAM2 at cell surface), NCAM2 knockdown in cultured hippocampal neurons, overexpression of cleavage-resistant NCAM2 mutant, immunofluorescence of synaptic markers, human AD hippocampus tissue analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (loss-of-function, gain-of-function with cleavage-resistant mutant, human tissue validation) in a single study with clear mechanistic readout\",\n      \"pmids\": [\"26611261\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The NCAM2 FnIII1-2 double domain adopts a rigid structure (low flexibility by SAXS), does not bind ATP (unlike NCAM1, whose Walker A motif in FnIII2 binds ATP), and binds FGFR in vitro. The FnIII1-2 double domain induces neurite outgrowth in a concentration-dependent manner through activation of FGFR, and the most potent NCAM2-derived peptide stimulates neurite outgrowth via FGFR-dependent activation of the Ras-MAPK pathway.\",\n      \"method\": \"NMR spectroscopy (structural model of FnIII2), SAXS (domain flexibility), ATP analogue titration, in vitro FGFR binding assay, neurite outgrowth assay with FGFR inhibitors, Ras-MAPK pathway readout\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR structure, SAXS, in vitro binding, and functional neurite outgrowth assays with pathway inhibition, multiple orthogonal methods in one study\",\n      \"pmids\": [\"29895898\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Elevated NCAM2 levels in cortical neurons increase the frequency of L-type voltage-gated Ca2+ channel-dependent submembrane Ca2+ spikes in dendritic protrusions and promote their propagation along dendrites via c-Src protein tyrosine kinase. This Ca2+ spike propagation increases instability of dendritic protrusions, reduces conversion to dendritic spines, and inhibits synapse maturation (increased GAP43, reduced activity-dependent synaptic vesicle recycling).\",\n      \"method\": \"NCAM2 overexpression in mouse cortical neurons, live Ca2+ imaging, pharmacological inhibition of L-type VGCCs and c-Src, dendritic protrusion dynamics tracking, synaptic vesicle recycling assay\",\n      \"journal\": \"Cerebral cortex\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — live imaging with pharmacological dissection of pathway components (VGCC, c-Src), multiple functional readouts in a single study\",\n      \"pmids\": [\"29522129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"NCAM2 interacts physically with the cytoskeletal-associated proteins MAP2 and 14-3-3γ and ζ, forming a protein complex. NCAM2 depletion destabilizes the microtubular network and reduces MAP2 signal, compromising dendritic architecture (shorter trees, retraction, somatic neurites) and causing deficits in neuronal polarization and cortical migration in vivo.\",\n      \"method\": \"Proteomic/cell biology experiments (protein complex identification), NCAM2 knockdown in hippocampal neurons and in vivo, immunofluorescence for MAP2, dendritic morphology analysis, in utero electroporation for cortical migration\",\n      \"journal\": \"Cerebral cortex\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal protein interaction experiments plus loss-of-function in vitro and in vivo with multiple orthogonal phenotypic readouts\",\n      \"pmids\": [\"32043120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Mass spectrometry-based interactome analysis of NCAM2 in mouse postnatal cerebral cortex identified >100 interacting proteins; validated partners include Neurofilaments (NEFs), MAP2, CaMKIIα, Actin, and Nogo. In silico analysis of the NCAM2.1 cytosolic tail revealed phosphorylation site motifs with predicted affinity for these interactors.\",\n      \"method\": \"Co-immunoprecipitation followed by mass spectrometry (MS), validation by additional co-IP/pulldown, in silico phosphorylation site analysis\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — MS-based interactome with validated subset by Co-IP; functional consequences for most partners not individually established in this study\",\n      \"pmids\": [\"34299022\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"BACE1 cleaves NCAM2 in cultured hippocampal neurons and NCAM2-transfected CHO cells, generating a C-terminal fragment (CTF) comprising the intracellular domain and a small portion of the extracellular domain. This NCAM2-CTF associates with BACE1 (interaction that precedes endocytosis) and both co-localize in Rab11-positive recycling endosomes. Overexpression of full-length NCAM2 or the transmembrane/intracellular fragment increases BACE1 in recycling endosomes; in NCAM2-deficient neurons, BACE1 accumulates at the cell surface and is reduced intracellularly, correlating with increased BACE1 shedding and reduced cleavage of the BACE1-exclusive substrate Sez6.\",\n      \"method\": \"Overexpression and knockdown in hippocampal neurons and CHO cells, co-localization imaging with Rab11 marker, BACE1 inhibition experiments, NCAM2-deficient mouse brains (ELISA for shed BACE1), Sez6 cleavage assay\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function (KO mouse) and gain-of-function (overexpression), multiple cell types, endogenous substrate cleavage readout, multiple orthogonal methods\",\n      \"pmids\": [\"36251052\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"NCAM2 deficiency in mice reduces axonal BACE1 levels in hippocampal mossy fiber projections and shortens the infrapyramidal bundle, demonstrating that NCAM2 regulates axonal BACE1 levels and hippocampal axonal organization. This is associated with impaired short-term spatial memory and cognitive flexibility, and sex-differential behavioral phenotypes including increased self-grooming.\",\n      \"method\": \"NCAM2-deficient mouse analysis, immunofluorescence of BACE1 in mossy fibers, morphometric measurement of infrapyramidal bundle, behavioral testing (Morris water maze, Y-maze, self-grooming, rearing, digging)\",\n      \"journal\": \"Cerebral cortex\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — clean KO with defined cellular (axonal BACE1 levels, bundle morphometry) 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, impairing normal progression of young-adult neurogenesis in the hippocampal dentate gyrus. Changes in NCAM2 levels during corticogenesis cause transient migratory deficits without affecting RGP survival or proliferation, indicating a stage-specific role.\",\n      \"method\": \"Ncam2 overexpression by viral vector in adult mice, BrdU/EdU lineage tracing, immunofluorescence of RGP markers, in utero electroporation for corticogenesis studies\",\n      \"journal\": \"Cerebral cortex\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — gain-of-function in vivo with defined cellular phenotype (RGP arrest), single lab\",\n      \"pmids\": [\"37724425\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"APP binds to the extracellular domain of NCAM2, and 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 convergence of APP with BACE1 and elevates amyloidogenic APP cleavage products. In NCAM2-deficient neurons, APP accumulates at the cell surface and in early endosomes, with reduced APP in recycling endosomes. Binding of NCAM2 to APP is increased by Aβ oligomers and activation of synaptic NMDA receptors.\",\n      \"method\": \"Co-immunoprecipitation (NCAM2-APP and NCAM2-Rab11-FIP5), overexpression in CHO cells and neurons, NCAM2-deficient neurons (loss-of-function), endosome fractionation/imaging, BACE1 cleavage product quantification, Aβ oligomer treatment, NMDA receptor activation\",\n      \"journal\": \"Progress in neurobiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP for multiple binding partners, loss-of-function (KO neurons) and gain-of-function (overexpression), multiple orthogonal readouts in a single rigorous study\",\n      \"pmids\": [\"40721030\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"NCAM2 is a GPI-anchored and transmembrane immunoglobulin superfamily cell adhesion molecule that mediates homophilic adhesion via Ig1 domain beta-strand swapping and engages FGFR through its rigid FnIII1-2 domains to activate Ras-MAPK and promote neurite outgrowth; at synapses, it stabilizes GluR1-containing glutamatergic synapses through interactions with MAP2 and 14-3-3 proteins to maintain microtubule stability, while also forming a complex with APP via its extracellular domain and with Rab11-FIP5 via its intracellular domain to traffic APP into BACE1-containing Rab11-positive recycling endosomes, thereby regulating amyloidogenic processing; BACE1-mediated cleavage of NCAM2 generates a CTF that in turn promotes BACE1 targeting to recycling endosomes, and Aβ-induced cleavage of NCAM2 disrupts its synaptic adhesion function, contributing to synapse loss in Alzheimer's disease.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"NCAM2 is an immunoglobulin superfamily cell adhesion molecule of the neuronal surface that organizes dendritic and axonal architecture, glutamatergic synapse stability, and amyloidogenic trafficking [#0, #2, #5]. Its N-terminal Ig1 domain mediates homophilic binding through reciprocal swapping of two N-terminal beta-strands between monomers, while its rigid FnIII1-2 double domain binds and activates FGFR to drive Ras-MAPK-dependent neurite outgrowth [#1, #3]. At the cytoskeletal interface, NCAM2 forms a complex with MAP2 and 14-3-3 proteins that stabilizes the microtubule network and supports dendritic arborization, neuronal polarization, and cortical migration; its loss destabilizes microtubules and disrupts these processes in vivo [#5, #6]. NCAM2 couples surface adhesion to endosomal trafficking: it forms a complex with APP through its extracellular domain and with the Rab11 adaptor Rab11-FIP5 through its intracellular domain, channeling APP into BACE1-containing Rab11-positive recycling endosomes and thereby promoting amyloidogenic APP processing, an interaction enhanced by Abeta oligomers and synaptic NMDA receptor activation [#10]. NCAM2 is itself a BACE1 substrate; cleavage liberates a C-terminal fragment that associates with BACE1 and helps target the protease to recycling endosomes, so that NCAM2 deficiency redistributes BACE1 to the cell surface and lowers axonal BACE1 levels [#7, #8]. In Alzheimer-relevant settings, Abeta binds NCAM2 directly and triggers its BACE1-mediated removal from synapses, and the resulting extracellular fragment drives disassembly of GluR1-containing glutamatergic synapses, linking NCAM2 cleavage to synapse loss [#2].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Established NCAM2's molecular identity, defining it as an Ig-superfamily cell adhesion molecule with a defined domain architecture and chromosomal locus.\",\n      \"evidence\": \"cDNA cloning from human fetal brain and sequence/chromosomal mapping\",\n      \"pmids\": [\"9226371\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional assay beyond structural prediction\", \"Binding partners and adhesion mode unknown at this stage\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Resolved the molecular basis of NCAM2 homophilic adhesion by showing the Ig1 domain dimerizes via N-terminal beta-strand swapping.\",\n      \"evidence\": \"X-ray crystallography at 2.7 A and gel-filtration chromatography of the Ig1 domain\",\n      \"pmids\": [\"18706912\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Adhesion demonstrated for an isolated domain, not full-length cell-cell contacts\", \"Functional consequence of homophilic binding not tested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Connected NCAM2 cleavage to synapse loss, showing Abeta binds NCAM2 and BACE1 cleavage of its extracellular region disassembles glutamatergic synapses.\",\n      \"evidence\": \"Abeta-NCAM2 binding assays, knockdown and cleavage-resistant mutant in hippocampal neurons, AD hippocampus tissue analysis\",\n      \"pmids\": [\"26611261\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Synaptic adhesion partners of NCAM2 not fully defined\", \"Intracellular signaling downstream of NCAM2 loss at synapses unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified an FGFR-activating, growth-promoting function distinct from NCAM1, defining the rigid FnIII1-2 domains as the FGFR-binding module driving neurite outgrowth.\",\n      \"evidence\": \"NMR and SAXS structural analysis, ATP-binding test, in vitro FGFR binding, neurite outgrowth with FGFR/Ras-MAPK inhibitors\",\n      \"pmids\": [\"29895898\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct FGFR contact residues not mapped\", \"In vivo relevance of FGFR activation not established\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Revealed a signaling role in dendritic maturation, where NCAM2 modulates L-type VGCC Ca2+ spikes via c-Src to control spine conversion and synapse maturation.\",\n      \"evidence\": \"Overexpression in mouse cortical neurons, live Ca2+ imaging, VGCC and c-Src pharmacological inhibition, synaptic vesicle recycling assays\",\n      \"pmids\": [\"29522129\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking NCAM2 to VGCC/c-Src activation unclear\", \"Loss-of-function effect on Ca2+ spikes not tested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Linked NCAM2 to the cytoskeleton, showing a MAP2/14-3-3 complex through which NCAM2 stabilizes microtubules and supports dendritic and migratory architecture.\",\n      \"evidence\": \"Protein complex identification, NCAM2 knockdown in neurons and in vivo, MAP2 immunofluorescence, in utero electroporation for cortical migration\",\n      \"pmids\": [\"32043120\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct versus indirect MAP2/14-3-3 binding not fully resolved\", \"How surface NCAM2 transmits signals to microtubules unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Expanded the NCAM2 interactome, identifying >100 candidate partners including neurofilaments, CaMKIIalpha, actin, and Nogo with predicted phospho-regulated binding.\",\n      \"evidence\": \"Co-IP mass spectrometry from mouse cerebral cortex, validation co-IP, in silico phosphosite analysis\",\n      \"pmids\": [\"34299022\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequences of most interactions not established\", \"Phosphorylation sites predicted, not experimentally mapped\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showed NCAM2 controls BACE1 subcellular distribution: a BACE1-generated NCAM2 CTF associates with BACE1 and targets it to Rab11 recycling endosomes.\",\n      \"evidence\": \"Overexpression/knockdown in neurons and CHO cells, Rab11 co-localization, BACE1 shedding ELISA in KO mice, Sez6 cleavage assay\",\n      \"pmids\": [\"36251052\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Motifs in the NCAM2 CTF mediating BACE1 targeting not defined\", \"Direct versus adaptor-mediated NCAM2-BACE1 association unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Established an in vivo axonal role, with NCAM2 deficiency lowering axonal BACE1, shortening the mossy fiber infrapyramidal bundle, and impairing spatial memory.\",\n      \"evidence\": \"NCAM2-deficient mice, BACE1 immunofluorescence in mossy fibers, bundle morphometry, behavioral testing\",\n      \"pmids\": [\"37522285\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal link between axonal BACE1 changes and behavior not isolated\", \"Sex-differential phenotype mechanism unexplained\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Demonstrated a stage-specific developmental role, where elevated NCAM2 arrests radial glial progenitors and causes transient migratory deficits.\",\n      \"evidence\": \"Viral Ncam2 overexpression in adult mice, BrdU/EdU lineage tracing, RGP marker immunofluorescence, in utero electroporation\",\n      \"pmids\": [\"37724425\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular pathway driving RGP arrest not defined\", \"Loss-of-function effect on adult neurogenesis not reported\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined NCAM2 as a trafficking scaffold for amyloidogenesis, bridging APP (extracellular) to Rab11-FIP5 (intracellular) to deliver APP into BACE1-positive recycling endosomes.\",\n      \"evidence\": \"Reciprocal Co-IP for NCAM2-APP and NCAM2-Rab11-FIP5, overexpression and KO neurons, endosome fractionation/imaging, BACE1 product quantification, Abeta oligomer and NMDA receptor activation\",\n      \"pmids\": [\"40721030\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of NCAM2-APP and NCAM2-Rab11-FIP5 binding unknown\", \"Whether this pathway is therapeutically targetable not addressed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How NCAM2's adhesion, FGFR-signaling, cytoskeletal, and APP/BACE1 trafficking functions are integrated and differentially deployed across neuronal compartments remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking surface adhesion to endosomal trafficking control\", \"Splice-isoform-specific functions not dissected\", \"No human disease-causing mutation defined in the corpus\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098631\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [3, 4]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [5, 10]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [5, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2, 7, 10]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [7, 10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": []},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 4]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [7, 10]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [5, 9]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [2, 10]}\n    ],\n    \"complexes\": [\n      \"NCAM2-MAP2-14-3-3 complex\",\n      \"NCAM2-APP-Rab11-FIP5 complex\"\n    ],\n    \"partners\": [\n      \"MAP2\",\n      \"YWHAG\",\n      \"YWHAZ\",\n      \"FGFR\",\n      \"APP\",\n      \"RAB11FIP5\",\n      \"BACE1\",\n      \"CAMK2A\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}