{"gene":"CSPG5","run_date":"2026-06-09T22:57:19","timeline":{"discoveries":[{"year":1998,"finding":"Human CSPG5 (NGC/neuroglycan C) encodes a 539-amino acid transmembrane chondroitin sulfate proteoglycan with a domain structure consisting of an N-terminal signal sequence, a chondroitin sulfate-attachment domain, an acidic amino acid cluster, an EGF-like domain, a transmembrane domain, and a cytoplasmic tail; brain-specific expression (2.4 kb transcript) was confirmed by Northern blot, and the gene was mapped to chromosomal band 3p21.3 by FISH.","method":"cDNA cloning from human brain library, Northern blot analysis, FISH chromosomal mapping","journal":"Neuroscience research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cDNA cloning with domain characterization and chromosomal mapping, single lab, two orthogonal methods","pmids":["9950058"],"is_preprint":false},{"year":2003,"finding":"CALEB/NGC interacts with the Golgi-associated protein PIST via its juxtamembrane cytoplasmic peptide segment (highly conserved during evolution); this interaction was confirmed by yeast two-hybrid, co-immunoprecipitation, and co-localization in the Golgi apparatus of transfected COS7 cells and primary hippocampal neurons. CALEB/NGC co-localizes with PIST in Golgi-derived vesicles after brefeldin A or nocodazole treatment, implicating PIST in intracellular transport of CALEB/NGC.","method":"Yeast two-hybrid screen, co-immunoprecipitation, co-localization immunofluorescence, brefeldin A/nocodazole treatment in COS7 cells and primary neurons","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP confirmed by multiple orthogonal methods (Y2H, Co-IP, co-localization) with domain mapping, single lab","pmids":["12885772"],"is_preprint":false},{"year":2007,"finding":"CALEB/NGC mediates dendritic tree complexity and spine formation: overexpression enhances dendritic branching and spine/filopodia complexity, while genetic and functional inactivation impairs arborization and spine formation in cortical neurons (confirmed by in utero electroporation). The EGF-like domain drives both processes. PI3K-Akt-mTOR signaling and PKC are required for CALEB/NGC-induced dendritic branching; spine morphogenesis is PI3K-independent but PKC-dependent.","method":"Overexpression and loss-of-function (knockdown/knockout) in primary neurons, in utero electroporation in mouse cortex, pharmacological inhibition of PI3K/Akt/mTOR/PKC pathways","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — gain- and loss-of-function with specific phenotypic readouts, in vivo validation by in utero electroporation, pathway dissection with pharmacological inhibitors, replicated across multiple experimental systems","pmids":["17431398"],"is_preprint":false},{"year":2008,"finding":"B56beta, a regulatory subunit of protein phosphatase 2A (PP2A), interacts with CALEB/NGC and inhibits CALEB/NGC-mediated dendritic branching but not spine formation. The entire PP2A trimer (structural and catalytic subunits) binds to CALEB/NGC via B56beta (confirmed by affinity chromatography and mass spectrometry). CALEB/NGC induces Akt phosphorylation in dendrites; B56beta inhibits this Akt phosphorylation and thereby inhibits Akt-dependent dendritic branching.","method":"Yeast two-hybrid screen, co-immunoprecipitation, affinity chromatography, mass spectrometry, immunocytochemistry, Akt phosphorylation assays in primary neurons","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — interaction confirmed by multiple orthogonal methods (Y2H, Co-IP, affinity chromatography/MS), functional consequence established by phosphorylation assay and dendritic branching readout, single lab","pmids":["18385213"],"is_preprint":false},{"year":2013,"finding":"CALEB/CSPG5-deficient mice show impaired presynaptic maturation of inhibitory GABAergic synapses on cerebellar Purkinje cells (decreased evoked amplitudes, altered paired-pulse facilitation, reduced depression after repetitive stimulation at early postnatal stages) and premature elimination of supernumerary climbing fiber synapses. CALEB expression is dynamically regulated during development from a high chondroitin sulfate-containing form to a non-chondroitin sulfate-containing form in Purkinje cells.","method":"CALEB-knockout mice, patch-clamp electrophysiology of Purkinje cells, Rota-Rod motor coordination test, Sholl analysis of dye-injected Purkinje cells","journal":"The European journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — constitutive knockout with multiple specific electrophysiological readouts and developmental analysis, single lab but orthogonal methods","pmids":["23889129"],"is_preprint":false},{"year":2016,"finding":"CALEB/NGC activates Rac1 at the plasma membrane to drive dendritic branching; Rac1 is essential for CALEB/NGC-mediated dendritic branching. RhoG reduces dendritic complexity by acting upstream of CALEB/NGC, decreasing the amount of CALEB/NGC at the plasma membrane. The palmitoylated (but not prenylated) isoform of Cdc42 adversely affects dendritic outgrowth independently of CALEB/NGC (they are not directly interconnected).","method":"Gain- and loss-of-function of Rac1, Cdc42 isoforms, and RhoG in primary hippocampal neurons; Rac1 activity assays; subcellular localization analysis of CALEB/NGC","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal gain/loss-of-function with GTPase activity assays and plasma membrane localization readouts, epistasis established, single lab with multiple orthogonal approaches","pmids":["27412363"],"is_preprint":false}],"current_model":"CSPG5 (CALEB/NGC/neuroglycan C) is a transmembrane EGF-domain-containing chondroitin sulfate proteoglycan expressed exclusively in the brain that promotes dendritic arborization and spine formation through its EGF-like domain by activating Rac1 at the plasma membrane via PI3K-Akt-mTOR and PKC signaling; its cytoplasmic tail binds the Golgi protein PIST (regulating intracellular trafficking) and recruits the PP2A trimer via B56beta (which antagonizes Akt-dependent dendritic branching), while RhoG acts upstream to limit plasma membrane localization of CALEB/NGC, and loss of CALEB/NGC in mice impairs presynaptic GABAergic maturation and perturbs climbing fiber synapse elimination in the developing cerebellum."},"narrative":{"mechanistic_narrative":"CSPG5 (CALEB/NGC/neuroglycan C) is a brain-specific transmembrane EGF-domain chondroitin sulfate proteoglycan that promotes dendritic arborization and dendritic spine formation during neuronal development [PMID:9950058, PMID:17431398]. Its EGF-like domain drives both processes, with dendritic branching requiring PI3K-Akt-mTOR and PKC signaling while spine morphogenesis is PI3K-independent but PKC-dependent [PMID:17431398]. Mechanistically, CALEB/NGC activates Rac1 at the plasma membrane to drive branching, and RhoG acts upstream to limit its plasma membrane abundance and thereby reduce dendritic complexity [PMID:27412363]. Signaling output is tuned by two cytoplasmic-tail interactions: the Golgi protein PIST binds the juxtamembrane segment and regulates intracellular trafficking through Golgi-derived vesicles [PMID:12885772], while the PP2A regulatory subunit B56beta recruits the PP2A trimer to suppress CALEB/NGC-induced Akt phosphorylation and selectively antagonize Akt-dependent dendritic branching [PMID:18385213]. In vivo, loss of CALEB/NGC impairs presynaptic maturation of inhibitory GABAergic synapses on cerebellar Purkinje cells and causes premature elimination of supernumerary climbing fiber synapses [PMID:23889129].","teleology":[{"year":1998,"claim":"Defined CSPG5 as a brain-specific transmembrane chondroitin sulfate proteoglycan with a modular domain architecture, establishing the molecular substrate for all later functional work.","evidence":"cDNA cloning from human brain library, Northern blot, and FISH chromosomal mapping","pmids":["9950058"],"confidence":"Medium","gaps":["No function assigned to any domain at this stage","Cytoplasmic-tail binding partners unidentified","Tissue distribution within brain not resolved"]},{"year":2003,"claim":"Identified the first cytoplasmic-tail partner, linking CALEB/NGC to intracellular trafficking machinery and assigning a function to its conserved juxtamembrane segment.","evidence":"Yeast two-hybrid, reciprocal co-immunoprecipitation, and Golgi co-localization (with brefeldin A/nocodazole) in COS7 cells and primary neurons","pmids":["12885772"],"confidence":"High","gaps":["Functional consequence of PIST binding for trafficking not quantified at the cell-surface level","Whether PIST regulates CALEB/NGC signaling output unknown"]},{"year":2007,"claim":"Established the core developmental function of CALEB/NGC — driving dendritic branching and spine formation via its EGF-like domain — and dissected the divergent signaling pathways underlying each process.","evidence":"Gain/loss-of-function in primary neurons, in utero electroporation in mouse cortex, and pharmacological inhibition of PI3K/Akt/mTOR/PKC","pmids":["17431398"],"confidence":"High","gaps":["Upstream activator/ligand of the EGF-like domain not identified","Direct effector linking signaling to cytoskeletal remodeling not yet defined"]},{"year":2008,"claim":"Showed how CALEB/NGC signaling is negatively regulated, identifying PP2A recruitment via B56beta as a brake on Akt-dependent branching but not spine formation.","evidence":"Yeast two-hybrid, Co-IP, affinity chromatography/mass spectrometry, and Akt phosphorylation assays in primary neurons","pmids":["18385213"],"confidence":"High","gaps":["Direct PP2A dephosphorylation target on the Akt axis not pinpointed","Whether B56beta recruitment is regulated dynamically during development unknown"]},{"year":2013,"claim":"Provided in vivo developmental relevance by showing CALEB/NGC is required for presynaptic GABAergic maturation and proper climbing fiber synapse refinement in the cerebellum.","evidence":"Constitutive knockout mice with Purkinje cell patch-clamp electrophysiology, Sholl analysis, and Rota-Rod testing","pmids":["23889129"],"confidence":"High","gaps":["Cell-autonomous versus non-autonomous basis of the presynaptic phenotype not resolved","Link between CALEB chondroitin sulfate state and synaptic phenotype not mechanistically established"]},{"year":2016,"claim":"Placed Rac1 as the essential effector of CALEB/NGC-driven branching and defined RhoG as an upstream regulator controlling its plasma membrane localization.","evidence":"Gain/loss-of-function of Rac1, Cdc42 isoforms, and RhoG in hippocampal neurons with Rac1 activity assays and subcellular localization analysis","pmids":["27412363"],"confidence":"High","gaps":["Molecular step linking CALEB/NGC to Rac1 GEF activation not identified","Mechanism by which RhoG reduces CALEB/NGC surface levels unknown"]},{"year":null,"claim":"The extracellular ligand or activating partner engaging the CALEB/NGC EGF-like domain to initiate intracellular signaling remains unidentified.","evidence":"","pmids":[],"confidence":"High","gaps":["No receptor or ligand for the EGF-like domain characterized in the corpus","Direct biochemical coupling between the cytoplasmic tail and the Rac1/Akt machinery undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[2,5]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[5]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[1]}],"pathway":[],"complexes":["PP2A"],"partners":["GOPC","PPP2R5B","RAC1","RHOG"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O95196","full_name":"Chondroitin sulfate proteoglycan 5","aliases":["Acidic leucine-rich EGF-like domain-containing brain protein","Neuroglycan C"],"length_aa":566,"mass_kda":60.0,"function":"May function as a growth and differentiation factor involved in neuritogenesis. May induce ERBB3 activation","subcellular_location":"Cell membrane; Synaptic cell membrane; Endoplasmic reticulum membrane; Golgi apparatus membrane; Cell surface; Secreted","url":"https://www.uniprot.org/uniprotkb/O95196/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CSPG5","classification":"Not Classified","n_dependent_lines":7,"n_total_lines":1208,"dependency_fraction":0.005794701986754967},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CAPZB","stoichiometry":0.2},{"gene":"DIAPH1","stoichiometry":0.2},{"gene":"SRP14","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/CSPG5","total_profiled":1310},"omim":[{"mim_id":"606775","title":"CHONDROITIN SULFATE PROTEOGLYCAN 5; CSPG5","url":"https://www.omim.org/entry/606775"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Golgi apparatus","reliability":"Approved"},{"location":"Vesicles","reliability":"Approved"},{"location":"Plasma membrane","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"brain","ntpm":103.3},{"tissue":"choroid plexus","ntpm":53.4},{"tissue":"retina","ntpm":26.3}],"url":"https://www.proteinatlas.org/search/CSPG5"},"hgnc":{"alias_symbol":["NGC"],"prev_symbol":[]},"alphafold":{"accession":"O95196","domains":[{"cath_id":"2.10.25","chopping":"364-413","consensus_level":"high","plddt":89.1874,"start":364,"end":413},{"cath_id":"1.20.5","chopping":"419-460","consensus_level":"medium","plddt":90.4776,"start":419,"end":460}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O95196","model_url":"https://alphafold.ebi.ac.uk/files/AF-O95196-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O95196-F1-predicted_aligned_error_v6.png","plddt_mean":51.84},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CSPG5","jax_strain_url":"https://www.jax.org/strain/search?query=CSPG5"},"sequence":{"accession":"O95196","fasta_url":"https://rest.uniprot.org/uniprotkb/O95196.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O95196/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O95196"}},"corpus_meta":[{"pmid":"12111550","id":"PMC_12111550","title":"The novel Streptomyces olivaceoviridis ABC transporter Ngc mediates uptake of N-acetylglucosamine and N,N'-diacetylchitobiose.","date":"2002","source":"Molecular genetics and genomics : MGG","url":"https://pubmed.ncbi.nlm.nih.gov/12111550","citation_count":49,"is_preprint":false},{"pmid":"17431398","id":"PMC_17431398","title":"The neural EGF family member CALEB/NGC mediates dendritic tree and spine complexity.","date":"2007","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/17431398","citation_count":38,"is_preprint":false},{"pmid":"9950058","id":"PMC_9950058","title":"Cloning and chromosomal mapping of the human gene of neuroglycan C (NGC), a neural transmembrane chondroitin sulfate proteoglycan with an EGF module.","date":"1998","source":"Neuroscience research","url":"https://pubmed.ncbi.nlm.nih.gov/9950058","citation_count":33,"is_preprint":false},{"pmid":"15148605","id":"PMC_15148605","title":"Mutational analysis of the binding affinity and transport activity for N-acetylglucosamine of the novel ABC transporter Ngc in the chitin-degrader Streptomyces olivaceoviridis.","date":"2004","source":"Molecular genetics and genomics : MGG","url":"https://pubmed.ncbi.nlm.nih.gov/15148605","citation_count":22,"is_preprint":false},{"pmid":"12885772","id":"PMC_12885772","title":"CALEB/NGC interacts with the Golgi-associated protein PIST.","date":"2003","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12885772","citation_count":19,"is_preprint":false},{"pmid":"22374315","id":"PMC_22374315","title":"Flavone enhances dengue virus type-2 (NGC strain) infectivity and replication in vero cells.","date":"2012","source":"Molecules (Basel, Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/22374315","citation_count":18,"is_preprint":false},{"pmid":"30102973","id":"PMC_30102973","title":"A fully automated three-step protein purification procedure for up to five samples using the NGC chromatography system.","date":"2018","source":"Protein expression and purification","url":"https://pubmed.ncbi.nlm.nih.gov/30102973","citation_count":15,"is_preprint":false},{"pmid":"27412363","id":"PMC_27412363","title":"Different roles of the small GTPases Rac1, Cdc42, and RhoG in CALEB/NGC-induced dendritic tree complexity.","date":"2016","source":"Journal of neurochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/27412363","citation_count":14,"is_preprint":false},{"pmid":"23889129","id":"PMC_23889129","title":"Impaired presynaptic function and elimination of synapses at premature stages during postnatal development of the cerebellum in the absence of CALEB (CSPG5/neuroglycan C).","date":"2013","source":"The European journal of neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/23889129","citation_count":14,"is_preprint":false},{"pmid":"18355889","id":"PMC_18355889","title":"Immunization with Toscana virus N-Gc proteins protects mice against virus challenge.","date":"2008","source":"Virology","url":"https://pubmed.ncbi.nlm.nih.gov/18355889","citation_count":14,"is_preprint":false},{"pmid":"18385213","id":"PMC_18385213","title":"B56beta, a regulatory subunit of protein phosphatase 2A, interacts with CALEB/NGC and inhibits CALEB/NGC-mediated dendritic branching.","date":"2008","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/18385213","citation_count":12,"is_preprint":false},{"pmid":"31499166","id":"PMC_31499166","title":"Development of BioRad NGC and GE ÄKTA pure systems for highly automated three column protein purification employing tandem affinity, buffer exchange and size exclusion chromatography.","date":"2019","source":"Protein expression and purification","url":"https://pubmed.ncbi.nlm.nih.gov/31499166","citation_count":6,"is_preprint":false},{"pmid":"26924856","id":"PMC_26924856","title":"Polycyclic aromatic hydrocarbons and molecular hydrogen in oxygen-rich planetary nebulae: the case of NGC 6720.","date":"2016","source":"Monthly notices of the Royal Astronomical Society","url":"https://pubmed.ncbi.nlm.nih.gov/26924856","citation_count":3,"is_preprint":false},{"pmid":"8299969","id":"PMC_8299969","title":"Purification and characterisation of the restriction endonuclease ItaI from Ilyobacter tartaricus recognizing 5'-GC decreases NGC-3'.","date":"1993","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/8299969","citation_count":1,"is_preprint":false},{"pmid":"16624755","id":"PMC_16624755","title":"[Construction and identification of genomic cDNA subclones of dengue 2 virus NGC strain].","date":"2006","source":"Nan fang yi ke da xue xue bao = Journal of Southern Medical University","url":"https://pubmed.ncbi.nlm.nih.gov/16624755","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.12.24.630138","title":"Effect of Stroma-directed Drugs in Combination with Chemotherapy Against 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CSPG5 (NGC/neuroglycan C) encodes a 539-amino acid transmembrane chondroitin sulfate proteoglycan with a domain structure consisting of an N-terminal signal sequence, a chondroitin sulfate-attachment domain, an acidic amino acid cluster, an EGF-like domain, a transmembrane domain, and a cytoplasmic tail; brain-specific expression (2.4 kb transcript) was confirmed by Northern blot, and the gene was mapped to chromosomal band 3p21.3 by FISH.\",\n      \"method\": \"cDNA cloning from human brain library, Northern blot analysis, FISH chromosomal mapping\",\n      \"journal\": \"Neuroscience research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cDNA cloning with domain characterization and chromosomal mapping, single lab, two orthogonal methods\",\n      \"pmids\": [\"9950058\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"CALEB/NGC interacts with the Golgi-associated protein PIST via its juxtamembrane cytoplasmic peptide segment (highly conserved during evolution); this interaction was confirmed by yeast two-hybrid, co-immunoprecipitation, and co-localization in the Golgi apparatus of transfected COS7 cells and primary hippocampal neurons. CALEB/NGC co-localizes with PIST in Golgi-derived vesicles after brefeldin A or nocodazole treatment, implicating PIST in intracellular transport of CALEB/NGC.\",\n      \"method\": \"Yeast two-hybrid screen, co-immunoprecipitation, co-localization immunofluorescence, brefeldin A/nocodazole treatment in COS7 cells and primary neurons\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP confirmed by multiple orthogonal methods (Y2H, Co-IP, co-localization) with domain mapping, single lab\",\n      \"pmids\": [\"12885772\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"CALEB/NGC mediates dendritic tree complexity and spine formation: overexpression enhances dendritic branching and spine/filopodia complexity, while genetic and functional inactivation impairs arborization and spine formation in cortical neurons (confirmed by in utero electroporation). The EGF-like domain drives both processes. PI3K-Akt-mTOR signaling and PKC are required for CALEB/NGC-induced dendritic branching; spine morphogenesis is PI3K-independent but PKC-dependent.\",\n      \"method\": \"Overexpression and loss-of-function (knockdown/knockout) in primary neurons, in utero electroporation in mouse cortex, pharmacological inhibition of PI3K/Akt/mTOR/PKC pathways\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — gain- and loss-of-function with specific phenotypic readouts, in vivo validation by in utero electroporation, pathway dissection with pharmacological inhibitors, replicated across multiple experimental systems\",\n      \"pmids\": [\"17431398\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"B56beta, a regulatory subunit of protein phosphatase 2A (PP2A), interacts with CALEB/NGC and inhibits CALEB/NGC-mediated dendritic branching but not spine formation. The entire PP2A trimer (structural and catalytic subunits) binds to CALEB/NGC via B56beta (confirmed by affinity chromatography and mass spectrometry). CALEB/NGC induces Akt phosphorylation in dendrites; B56beta inhibits this Akt phosphorylation and thereby inhibits Akt-dependent dendritic branching.\",\n      \"method\": \"Yeast two-hybrid screen, co-immunoprecipitation, affinity chromatography, mass spectrometry, immunocytochemistry, Akt phosphorylation assays in primary neurons\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — interaction confirmed by multiple orthogonal methods (Y2H, Co-IP, affinity chromatography/MS), functional consequence established by phosphorylation assay and dendritic branching readout, single lab\",\n      \"pmids\": [\"18385213\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"CALEB/CSPG5-deficient mice show impaired presynaptic maturation of inhibitory GABAergic synapses on cerebellar Purkinje cells (decreased evoked amplitudes, altered paired-pulse facilitation, reduced depression after repetitive stimulation at early postnatal stages) and premature elimination of supernumerary climbing fiber synapses. CALEB expression is dynamically regulated during development from a high chondroitin sulfate-containing form to a non-chondroitin sulfate-containing form in Purkinje cells.\",\n      \"method\": \"CALEB-knockout mice, patch-clamp electrophysiology of Purkinje cells, Rota-Rod motor coordination test, Sholl analysis of dye-injected Purkinje cells\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — constitutive knockout with multiple specific electrophysiological readouts and developmental analysis, single lab but orthogonal methods\",\n      \"pmids\": [\"23889129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CALEB/NGC activates Rac1 at the plasma membrane to drive dendritic branching; Rac1 is essential for CALEB/NGC-mediated dendritic branching. RhoG reduces dendritic complexity by acting upstream of CALEB/NGC, decreasing the amount of CALEB/NGC at the plasma membrane. The palmitoylated (but not prenylated) isoform of Cdc42 adversely affects dendritic outgrowth independently of CALEB/NGC (they are not directly interconnected).\",\n      \"method\": \"Gain- and loss-of-function of Rac1, Cdc42 isoforms, and RhoG in primary hippocampal neurons; Rac1 activity assays; subcellular localization analysis of CALEB/NGC\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal gain/loss-of-function with GTPase activity assays and plasma membrane localization readouts, epistasis established, single lab with multiple orthogonal approaches\",\n      \"pmids\": [\"27412363\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CSPG5 (CALEB/NGC/neuroglycan C) is a transmembrane EGF-domain-containing chondroitin sulfate proteoglycan expressed exclusively in the brain that promotes dendritic arborization and spine formation through its EGF-like domain by activating Rac1 at the plasma membrane via PI3K-Akt-mTOR and PKC signaling; its cytoplasmic tail binds the Golgi protein PIST (regulating intracellular trafficking) and recruits the PP2A trimer via B56beta (which antagonizes Akt-dependent dendritic branching), while RhoG acts upstream to limit plasma membrane localization of CALEB/NGC, and loss of CALEB/NGC in mice impairs presynaptic GABAergic maturation and perturbs climbing fiber synapse elimination in the developing cerebellum.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CSPG5 (CALEB/NGC/neuroglycan C) is a brain-specific transmembrane EGF-domain chondroitin sulfate proteoglycan that promotes dendritic arborization and dendritic spine formation during neuronal development [#0, #2]. Its EGF-like domain drives both processes, with dendritic branching requiring PI3K-Akt-mTOR and PKC signaling while spine morphogenesis is PI3K-independent but PKC-dependent [#2]. Mechanistically, CALEB/NGC activates Rac1 at the plasma membrane to drive branching, and RhoG acts upstream to limit its plasma membrane abundance and thereby reduce dendritic complexity [#5]. Signaling output is tuned by two cytoplasmic-tail interactions: the Golgi protein PIST binds the juxtamembrane segment and regulates intracellular trafficking through Golgi-derived vesicles [#1], while the PP2A regulatory subunit B56beta recruits the PP2A trimer to suppress CALEB/NGC-induced Akt phosphorylation and selectively antagonize Akt-dependent dendritic branching [#3]. In vivo, loss of CALEB/NGC impairs presynaptic maturation of inhibitory GABAergic synapses on cerebellar Purkinje cells and causes premature elimination of supernumerary climbing fiber synapses [#4].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Defined CSPG5 as a brain-specific transmembrane chondroitin sulfate proteoglycan with a modular domain architecture, establishing the molecular substrate for all later functional work.\",\n      \"evidence\": \"cDNA cloning from human brain library, Northern blot, and FISH chromosomal mapping\",\n      \"pmids\": [\"9950058\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No function assigned to any domain at this stage\",\n        \"Cytoplasmic-tail binding partners unidentified\",\n        \"Tissue distribution within brain not resolved\"\n      ]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Identified the first cytoplasmic-tail partner, linking CALEB/NGC to intracellular trafficking machinery and assigning a function to its conserved juxtamembrane segment.\",\n      \"evidence\": \"Yeast two-hybrid, reciprocal co-immunoprecipitation, and Golgi co-localization (with brefeldin A/nocodazole) in COS7 cells and primary neurons\",\n      \"pmids\": [\"12885772\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Functional consequence of PIST binding for trafficking not quantified at the cell-surface level\",\n        \"Whether PIST regulates CALEB/NGC signaling output unknown\"\n      ]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Established the core developmental function of CALEB/NGC — driving dendritic branching and spine formation via its EGF-like domain — and dissected the divergent signaling pathways underlying each process.\",\n      \"evidence\": \"Gain/loss-of-function in primary neurons, in utero electroporation in mouse cortex, and pharmacological inhibition of PI3K/Akt/mTOR/PKC\",\n      \"pmids\": [\"17431398\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Upstream activator/ligand of the EGF-like domain not identified\",\n        \"Direct effector linking signaling to cytoskeletal remodeling not yet defined\"\n      ]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Showed how CALEB/NGC signaling is negatively regulated, identifying PP2A recruitment via B56beta as a brake on Akt-dependent branching but not spine formation.\",\n      \"evidence\": \"Yeast two-hybrid, Co-IP, affinity chromatography/mass spectrometry, and Akt phosphorylation assays in primary neurons\",\n      \"pmids\": [\"18385213\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Direct PP2A dephosphorylation target on the Akt axis not pinpointed\",\n        \"Whether B56beta recruitment is regulated dynamically during development unknown\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Provided in vivo developmental relevance by showing CALEB/NGC is required for presynaptic GABAergic maturation and proper climbing fiber synapse refinement in the cerebellum.\",\n      \"evidence\": \"Constitutive knockout mice with Purkinje cell patch-clamp electrophysiology, Sholl analysis, and Rota-Rod testing\",\n      \"pmids\": [\"23889129\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Cell-autonomous versus non-autonomous basis of the presynaptic phenotype not resolved\",\n        \"Link between CALEB chondroitin sulfate state and synaptic phenotype not mechanistically established\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Placed Rac1 as the essential effector of CALEB/NGC-driven branching and defined RhoG as an upstream regulator controlling its plasma membrane localization.\",\n      \"evidence\": \"Gain/loss-of-function of Rac1, Cdc42 isoforms, and RhoG in hippocampal neurons with Rac1 activity assays and subcellular localization analysis\",\n      \"pmids\": [\"27412363\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Molecular step linking CALEB/NGC to Rac1 GEF activation not identified\",\n        \"Mechanism by which RhoG reduces CALEB/NGC surface levels unknown\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The extracellular ligand or activating partner engaging the CALEB/NGC EGF-like domain to initiate intracellular signaling remains unidentified.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No receptor or ligand for the EGF-like domain characterized in the corpus\",\n        \"Direct biochemical coupling between the cytoplasmic tail and the Rac1/Akt machinery undefined\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [2, 5]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0162582\", \"supporting_discovery_ids\": [2, 5]}\n    ],\n    \"complexes\": [\"PP2A\"],\n    \"partners\": [\"GOPC\", \"PPP2R5B\", \"RAC1\", \"RHOG\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}