{"gene":"CTTNBP2","run_date":"2026-06-09T22:57:19","timeline":{"discoveries":[{"year":2012,"finding":"CTTNBP2 interacts with cortactin and regulates cortactin mobility and distribution in neurons, controlling dendritic spine formation. CTTNBP2 also interacts with striatin and zinedin (regulatory B subunits of PP2A), targeting the PP2A complex to dendritic spines. CTTNBP2NL, despite also binding cortactin, does not regulate dendritic spinogenesis and is associated with stress fibers rather than dendritic spines.","method":"Co-immunoprecipitation, subcellular fractionation/localization, overexpression and knockdown in neurons, HEK293 cell binding assays","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP and direct localization experiments with functional dendritic spine readout in primary neurons, single lab but multiple orthogonal methods","pmids":["23015759"],"is_preprint":false},{"year":2012,"finding":"CTTNBP2 is a neuron-specific protein that regulates F-actin cytoskeletal organization by controlling the mobility and distribution of cortactin, thereby influencing dendritic spine density and morphology.","method":"Live imaging, fluorescence recovery after photobleaching (FRAP), overexpression and knockdown in cultured neurons","journal":"Communicative & integrative biology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — single lab review/commentary summarizing primary data from same group, no new orthogonal methods described in abstract","pmids":["23060955"],"is_preprint":false},{"year":2020,"finding":"CTTNBP2 deficiency reduces zinc levels in the brain, impairs synaptic targeting of zinc-related autism-associated proteins (including NMDAR-SHANK pathway components), and disrupts dendritic spine formation and postsynaptic density ultrastructure. Zinc supplementation rescues synaptic expression of CTTNBP2-regulated proteins. Administration of D-cycloserine (NMDAR co-agonist) and zinc supplementation improve social behaviors in Cttnbp2-deficient mice.","method":"Cttnbp2 knockout and ASD-linked knockin mice, zinc measurement, synaptic fractionation, electron microscopy of postsynaptic density, behavioral assays, pharmacological rescue","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (KO mice, EM, zinc measurement, behavioral rescue) in a single study establishing zinc regulation as a mechanistic link","pmids":["32492416"],"is_preprint":false},{"year":2022,"finding":"CTTNBP2 undergoes liquid-liquid phase separation (LLPS) via its C-terminal intrinsically disordered region, forming self-assembled condensates that facilitate SHANK3 co-condensation at dendritic spines. Zinc binds the N-terminal coiled-coil region of CTTNBP2, promoting higher-order assemblies and a liquid-to-gel phase transition that reduces CTTNBP2 mobility and enhances synaptic retention of CTTNBP2 condensates. ASD-linked mutations alter condensate formation and synaptic retention, and these defects are ameliorated by zinc supplementation.","method":"Live imaging of phase separation in neurons, FRAP, deletion/domain mutant analysis, ASD knockin mouse behavioral assays, zinc supplementation rescue","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — direct reconstitution of LLPS, FRAP-based mobility measurements, domain mutagenesis, and in vivo behavioral rescue with zinc, multiple orthogonal methods","pmids":["35562389"],"is_preprint":false},{"year":2020,"finding":"Three ASD-linked mutations in CTTNBP2 (M120I, R533*, D570Y) impair dendritic spine density through divergent molecular mechanisms: R533* lacks the C-terminal proline-rich domain required for cortactin interaction; M120I disrupts cortactin interaction via an N-C terminal intramolecular interaction; D570Y increases microtubule association, causing dendritic (non-spine) localization of CTTNBP2 and reducing its synaptic function. Heterozygous M120I knockin mice exhibit reduced social interaction.","method":"Co-immunoprecipitation of CTTNBP2 with cortactin and microtubule, subcellular localization in hippocampal neurons, knockin mouse behavioral assays, domain deletion constructs","journal":"Acta neuropathologica communications","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple mutations tested with Co-IP, localization, and in vivo behavioral readout; multiple orthogonal methods in single study","pmids":["33168105"],"is_preprint":false},{"year":2023,"finding":"Cttnbp2 mutation results in male-biased social deficits associated with reduced neural activity in seven brain regions including the infralimbic area (ILA) of the medial prefrontal cortex upon social stimulation. Chemogenetic activation of ILA rescues social deficits in male mutant mice. Male-specific downregulation of synaptic zinc-binding proteins (SHANK2, PSD-95) and female-specific upregulation of RRAGC (mTOR upstream regulator) are identified. Increased BCAA intake activates mTOR and rescues neuronal responses and social behaviors in male Cttnbp2 mutant mice.","method":"C-FOS staining, chemogenetic (DREADD) manipulation, proteomics, behavioral assays, dietary BCAA supplementation","journal":"Brain : a journal of neurology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — chemogenetic circuit manipulation combined with proteomics and behavioral rescue establishes mechanistic pathway positions; multiple orthogonal methods","pmids":["36385662"],"is_preprint":false},{"year":2013,"finding":"In Brown Swiss cattle, non-synonymous mutations (lysine to glutamic acid, and synonymous) in CTTNBP2 are among 41 concordant diagnostic SNPs for Weaver Syndrome (Bovine Progressive Degenerative Myeloencephalopathy), implicating CTTNBP2 in neurological disease in this breed.","method":"Genome-wide SNP association mapping, whole genome sequencing, haplotype analysis across 841 animals","journal":"PloS one","confidence":"Low","confidence_rationale":"Tier 4 / Weak — genetic mapping only, no direct functional/mechanistic experiment on the CTTNBP2 protein itself","pmids":["23527149"],"is_preprint":false},{"year":2025,"finding":"In male Cttnbp2 ASD mutant mice, zinc supplementation enhances ribosome biogenesis and increases dendritic spine density and size, alleviating male-biased social deficits. Neurons (not astrocytes) respond to zinc to enhance protein synthesis. Female Cttnbp2 mutants are resilient to differential zinc intake, associated with elevated mTOR phosphorylation and increased translational initiation factor levels in female brains.","method":"Puromycin pulse labeling for protein synthesis, proteomic/bioinformatic analysis, dendritic spine morphometry, behavioral assays, zinc dietary manipulation in sex-stratified cohorts","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — multiple orthogonal methods but preprint, single lab, not yet peer-reviewed","pmids":[],"is_preprint":true},{"year":2025,"finding":"Supplement cocktails containing zinc, branched-chain amino acids (BCAA), and serine improve social behaviors in Cttnbp2+/M120I ASD mouse models, altering synaptic and metabolic proteomes, consistent with a role for CTTNBP2 in nutrient-sensitive synaptic regulation.","method":"Behavioral assays, synaptic proteomics, dietary supplementation in Cttnbp2+/M120I knockin mice","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — preprint, dietary supplementation experiment with behavioral readout, no direct mechanistic dissection of CTTNBP2 protein function","pmids":[],"is_preprint":true}],"current_model":"CTTNBP2 is a neuron-specific cytoskeletal regulator that binds cortactin via its C-terminal proline-rich domain to control cortactin mobility and distribution, recruits the PP2A complex (via striatin/zinedin) to dendritic spines, undergoes zinc-regulated liquid-liquid phase separation through its intrinsically disordered C-terminal region and coiled-coil N-terminal domain to form synaptic condensates that retain SHANK3, and controls the synaptic expression of a set of zinc-sensitive autism-associated proteins (including NMDAR-SHANK pathway components); loss of CTTNBP2 reduces brain zinc, impairs dendritic spine formation and postsynaptic density ultrastructure, and causes autism-like social deficits that can be rescued by zinc supplementation or NMDAR co-agonism."},"narrative":{"mechanistic_narrative":"CTTNBP2 is a neuron-specific cytoskeletal regulator that controls dendritic spine formation and the molecular organization of the postsynaptic compartment [PMID:23015759, PMID:32492416]. It binds cortactin through its C-terminal proline-rich domain and governs cortactin mobility and distribution to shape F-actin organization and spine density and morphology [PMID:23015759]; in parallel it recruits the PP2A regulatory subunits striatin and zinedin to dendritic spines [PMID:23015759]. CTTNBP2 undergoes liquid-liquid phase separation via its C-terminal intrinsically disordered region to form synaptic condensates that co-recruit and retain SHANK3, while zinc binding to its N-terminal coiled-coil drives higher-order assembly and a liquid-to-gel transition that lowers CTTNBP2 mobility and enhances synaptic retention [PMID:35562389]. Through this activity CTTNBP2 sustains brain zinc levels and the synaptic targeting of zinc-sensitive, autism-associated proteins of the NMDAR–SHANK pathway; its loss reduces brain zinc, disrupts postsynaptic density ultrastructure, and produces autism-like social deficits that are rescued by zinc supplementation or NMDAR co-agonism [PMID:32492416]. Autism-linked mutations impair spine density through distinct mechanisms — loss of the cortactin-binding domain, disruption of an N-to-C intramolecular interaction, or aberrant microtubule association that mislocalizes the protein away from spines — and the corresponding knockin mice show reduced social interaction [PMID:33168105]. The resulting social deficits are male-biased and map onto reduced activity in defined cortical circuits including the infralimbic prefrontal cortex, and can be rescued by chemogenetic circuit activation or by nutrient-sensitive (zinc, BCAA/mTOR) manipulations [PMID:36385662].","teleology":[{"year":2012,"claim":"Established the founding molecular activity of CTTNBP2: how a neuron-specific protein could control dendritic spine formation by acting on the actin cytoskeleton and a phosphatase complex.","evidence":"Reciprocal Co-IP, subcellular fractionation, FRAP, and overexpression/knockdown in primary neurons","pmids":["23015759","23060955"],"confidence":"High","gaps":["Did not define structural basis of cortactin binding","Functional role of PP2A/striatin recruitment to spines left mechanistically open","Distinction from paralog CTTNBP2NL noted but not fully resolved"]},{"year":2020,"claim":"Connected CTTNBP2 to brain zinc homeostasis and the NMDAR–SHANK synaptic pathway, providing a mechanistic and therapeutic link to autism phenotypes.","evidence":"Cttnbp2 knockout and ASD knockin mice, zinc measurement, synaptic fractionation, EM of PSD, and pharmacological rescue (zinc, D-cycloserine)","pmids":["32492416"],"confidence":"High","gaps":["Did not establish how CTTNBP2 loss lowers brain zinc","Molecular mechanism linking zinc to synaptic protein retention not yet defined"]},{"year":2020,"claim":"Showed that distinct ASD-linked mutations converge on reduced spine density through divergent molecular defects, distinguishing cortactin-binding from microtubule-localization mechanisms.","evidence":"Co-IP with cortactin and microtubules, localization in hippocampal neurons, domain-deletion constructs, and M120I knockin behavioral assays","pmids":["33168105"],"confidence":"High","gaps":["Did not resolve the intramolecular N–C interaction structurally","Behavioral testing limited to one knockin allele"]},{"year":2022,"claim":"Defined the physical basis for synaptic CTTNBP2 organization: zinc-regulated liquid-liquid phase separation that builds SHANK3-containing condensates and tunes their stability.","evidence":"Live imaging of phase separation, FRAP, domain mutagenesis, and zinc-supplementation rescue in ASD knockin mice","pmids":["35562389"],"confidence":"High","gaps":["Stoichiometry of zinc binding to the coiled-coil not quantified","In vivo evidence that condensate state controls behavior remains indirect"]},{"year":2023,"claim":"Placed CTTNBP2 deficits within specific brain circuits and revealed sex-biased molecular consequences, linking the protein to nutrient/mTOR signaling.","evidence":"c-Fos mapping, chemogenetic (DREADD) ILA activation, proteomics, and dietary BCAA rescue in male mutant mice","pmids":["36385662"],"confidence":"High","gaps":["Mechanistic basis of sex bias not fully resolved","How CTTNBP2 loss alters RRAGC/mTOR signaling not established"]},{"year":2025,"claim":"Extended the zinc rescue mechanism to protein synthesis, proposing that neuronal ribosome biogenesis underlies zinc-dependent spine and behavioral improvement in a sex-specific manner.","evidence":"Puromycin pulse labeling, proteomics, spine morphometry, and sex-stratified zinc dietary manipulation (preprint)","pmids":[],"confidence":"Medium","gaps":["Preprint, single lab, not peer-reviewed","Direct link from CTTNBP2 protein activity to translation machinery not biochemically demonstrated"]},{"year":null,"claim":"How the cytoskeletal/condensate functions of CTTNBP2 mechanistically feed into zinc homeostasis, mTOR/translation, and the male-biased circuit phenotype remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No molecular mechanism linking CTTNBP2 loss to reduced brain zinc","Structural model of zinc binding and phase transition lacking","Causal chain from condensate state to circuit-level social behavior not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0,1,4]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0]},{"term_id":"GO:0140313","term_label":"molecular sequestering activity","supporting_discovery_ids":[3]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,1]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,2,3]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[2,3,5]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[0,2]}],"complexes":["CTTNBP2-SHANK3 synaptic condensate","PP2A complex"],"partners":["CTTN","STRN","STRN4","SHANK3"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8WZ74","full_name":"Cortactin-binding protein 2","aliases":[],"length_aa":1663,"mass_kda":181.1,"function":"Regulates the dendritic spine distribution of CTTN/cortactin in hippocampal neurons, and thus controls dendritic spinogenesis and dendritic spine maintenance. Associates with the striatin-interacting phosphatase and kinase (STRIPAK) core complex to regulate dendritic spine distribution of the STRIPAK complex in hippocampal neurons","subcellular_location":"Cytoplasm, cell cortex; Cell projection, dendritic spine","url":"https://www.uniprot.org/uniprotkb/Q8WZ74/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CTTNBP2","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CTTN","stoichiometry":0.2},{"gene":"DYNLL1","stoichiometry":0.2},{"gene":"DYNLL2","stoichiometry":0.2},{"gene":"STK26","stoichiometry":0.2},{"gene":"STRN3","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/CTTNBP2","total_profiled":1310},"omim":[{"mim_id":"615100","title":"CTTNBP2 N TERMINUS-LIKE PROTEIN; CTTNBP2NL","url":"https://www.omim.org/entry/615100"},{"mim_id":"609772","title":"CORTACTIN-BINDING PROTEIN 2; CTTNBP2","url":"https://www.omim.org/entry/609772"},{"mim_id":"608532","title":"NON-SMC CONDENSIN II COMPLEX SUBUNIT G2; NCAPG2","url":"https://www.omim.org/entry/608532"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Midbody ring","reliability":"Approved"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/CTTNBP2"},"hgnc":{"alias_symbol":["KIAA1758","Orf4"],"prev_symbol":["CORTBP2","C7orf8"]},"alphafold":{"accession":"Q8WZ74","domains":[{"cath_id":"3.40.50.300","chopping":"973-1032_1046-1283","consensus_level":"medium","plddt":78.0426,"start":973,"end":1283},{"cath_id":"-","chopping":"1299-1376_1394-1435","consensus_level":"medium","plddt":79.4423,"start":1299,"end":1435},{"cath_id":"1.20.5","chopping":"79-93_108-205","consensus_level":"medium","plddt":82.0763,"start":79,"end":205}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8WZ74","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8WZ74-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8WZ74-F1-predicted_aligned_error_v6.png","plddt_mean":58.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CTTNBP2","jax_strain_url":"https://www.jax.org/strain/search?query=CTTNBP2"},"sequence":{"accession":"Q8WZ74","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8WZ74.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8WZ74/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8WZ74"}},"corpus_meta":[{"pmid":"1316677","id":"PMC_1316677","title":"TGEV 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CTTNBP2 also interacts with striatin and zinedin (regulatory B subunits of PP2A), targeting the PP2A complex to dendritic spines. CTTNBP2NL, despite also binding cortactin, does not regulate dendritic spinogenesis and is associated with stress fibers rather than dendritic spines.\",\n      \"method\": \"Co-immunoprecipitation, subcellular fractionation/localization, overexpression and knockdown in neurons, HEK293 cell binding assays\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP and direct localization experiments with functional dendritic spine readout in primary neurons, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"23015759\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CTTNBP2 is a neuron-specific protein that regulates F-actin cytoskeletal organization by controlling the mobility and distribution of cortactin, thereby influencing dendritic spine density and morphology.\",\n      \"method\": \"Live imaging, fluorescence recovery after photobleaching (FRAP), overexpression and knockdown in cultured neurons\",\n      \"journal\": \"Communicative & integrative biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — single lab review/commentary summarizing primary data from same group, no new orthogonal methods described in abstract\",\n      \"pmids\": [\"23060955\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CTTNBP2 deficiency reduces zinc levels in the brain, impairs synaptic targeting of zinc-related autism-associated proteins (including NMDAR-SHANK pathway components), and disrupts dendritic spine formation and postsynaptic density ultrastructure. Zinc supplementation rescues synaptic expression of CTTNBP2-regulated proteins. Administration of D-cycloserine (NMDAR co-agonist) and zinc supplementation improve social behaviors in Cttnbp2-deficient mice.\",\n      \"method\": \"Cttnbp2 knockout and ASD-linked knockin mice, zinc measurement, synaptic fractionation, electron microscopy of postsynaptic density, behavioral assays, pharmacological rescue\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (KO mice, EM, zinc measurement, behavioral rescue) in a single study establishing zinc regulation as a mechanistic link\",\n      \"pmids\": [\"32492416\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CTTNBP2 undergoes liquid-liquid phase separation (LLPS) via its C-terminal intrinsically disordered region, forming self-assembled condensates that facilitate SHANK3 co-condensation at dendritic spines. Zinc binds the N-terminal coiled-coil region of CTTNBP2, promoting higher-order assemblies and a liquid-to-gel phase transition that reduces CTTNBP2 mobility and enhances synaptic retention of CTTNBP2 condensates. ASD-linked mutations alter condensate formation and synaptic retention, and these defects are ameliorated by zinc supplementation.\",\n      \"method\": \"Live imaging of phase separation in neurons, FRAP, deletion/domain mutant analysis, ASD knockin mouse behavioral assays, zinc supplementation rescue\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — direct reconstitution of LLPS, FRAP-based mobility measurements, domain mutagenesis, and in vivo behavioral rescue with zinc, multiple orthogonal methods\",\n      \"pmids\": [\"35562389\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Three ASD-linked mutations in CTTNBP2 (M120I, R533*, D570Y) impair dendritic spine density through divergent molecular mechanisms: R533* lacks the C-terminal proline-rich domain required for cortactin interaction; M120I disrupts cortactin interaction via an N-C terminal intramolecular interaction; D570Y increases microtubule association, causing dendritic (non-spine) localization of CTTNBP2 and reducing its synaptic function. Heterozygous M120I knockin mice exhibit reduced social interaction.\",\n      \"method\": \"Co-immunoprecipitation of CTTNBP2 with cortactin and microtubule, subcellular localization in hippocampal neurons, knockin mouse behavioral assays, domain deletion constructs\",\n      \"journal\": \"Acta neuropathologica communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple mutations tested with Co-IP, localization, and in vivo behavioral readout; multiple orthogonal methods in single study\",\n      \"pmids\": [\"33168105\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Cttnbp2 mutation results in male-biased social deficits associated with reduced neural activity in seven brain regions including the infralimbic area (ILA) of the medial prefrontal cortex upon social stimulation. Chemogenetic activation of ILA rescues social deficits in male mutant mice. Male-specific downregulation of synaptic zinc-binding proteins (SHANK2, PSD-95) and female-specific upregulation of RRAGC (mTOR upstream regulator) are identified. Increased BCAA intake activates mTOR and rescues neuronal responses and social behaviors in male Cttnbp2 mutant mice.\",\n      \"method\": \"C-FOS staining, chemogenetic (DREADD) manipulation, proteomics, behavioral assays, dietary BCAA supplementation\",\n      \"journal\": \"Brain : a journal of neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — chemogenetic circuit manipulation combined with proteomics and behavioral rescue establishes mechanistic pathway positions; multiple orthogonal methods\",\n      \"pmids\": [\"36385662\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"In Brown Swiss cattle, non-synonymous mutations (lysine to glutamic acid, and synonymous) in CTTNBP2 are among 41 concordant diagnostic SNPs for Weaver Syndrome (Bovine Progressive Degenerative Myeloencephalopathy), implicating CTTNBP2 in neurological disease in this breed.\",\n      \"method\": \"Genome-wide SNP association mapping, whole genome sequencing, haplotype analysis across 841 animals\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — genetic mapping only, no direct functional/mechanistic experiment on the CTTNBP2 protein itself\",\n      \"pmids\": [\"23527149\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In male Cttnbp2 ASD mutant mice, zinc supplementation enhances ribosome biogenesis and increases dendritic spine density and size, alleviating male-biased social deficits. Neurons (not astrocytes) respond to zinc to enhance protein synthesis. Female Cttnbp2 mutants are resilient to differential zinc intake, associated with elevated mTOR phosphorylation and increased translational initiation factor levels in female brains.\",\n      \"method\": \"Puromycin pulse labeling for protein synthesis, proteomic/bioinformatic analysis, dendritic spine morphometry, behavioral assays, zinc dietary manipulation in sex-stratified cohorts\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — multiple orthogonal methods but preprint, single lab, not yet peer-reviewed\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Supplement cocktails containing zinc, branched-chain amino acids (BCAA), and serine improve social behaviors in Cttnbp2+/M120I ASD mouse models, altering synaptic and metabolic proteomes, consistent with a role for CTTNBP2 in nutrient-sensitive synaptic regulation.\",\n      \"method\": \"Behavioral assays, synaptic proteomics, dietary supplementation in Cttnbp2+/M120I knockin mice\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — preprint, dietary supplementation experiment with behavioral readout, no direct mechanistic dissection of CTTNBP2 protein function\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"CTTNBP2 is a neuron-specific cytoskeletal regulator that binds cortactin via its C-terminal proline-rich domain to control cortactin mobility and distribution, recruits the PP2A complex (via striatin/zinedin) to dendritic spines, undergoes zinc-regulated liquid-liquid phase separation through its intrinsically disordered C-terminal region and coiled-coil N-terminal domain to form synaptic condensates that retain SHANK3, and controls the synaptic expression of a set of zinc-sensitive autism-associated proteins (including NMDAR-SHANK pathway components); loss of CTTNBP2 reduces brain zinc, impairs dendritic spine formation and postsynaptic density ultrastructure, and causes autism-like social deficits that can be rescued by zinc supplementation or NMDAR co-agonism.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CTTNBP2 is a neuron-specific cytoskeletal regulator that controls dendritic spine formation and the molecular organization of the postsynaptic compartment [#0, #2]. It binds cortactin through its C-terminal proline-rich domain and governs cortactin mobility and distribution to shape F-actin organization and spine density and morphology [#0]; in parallel it recruits the PP2A regulatory subunits striatin and zinedin to dendritic spines [#0]. CTTNBP2 undergoes liquid-liquid phase separation via its C-terminal intrinsically disordered region to form synaptic condensates that co-recruit and retain SHANK3, while zinc binding to its N-terminal coiled-coil drives higher-order assembly and a liquid-to-gel transition that lowers CTTNBP2 mobility and enhances synaptic retention [#3]. Through this activity CTTNBP2 sustains brain zinc levels and the synaptic targeting of zinc-sensitive, autism-associated proteins of the NMDAR–SHANK pathway; its loss reduces brain zinc, disrupts postsynaptic density ultrastructure, and produces autism-like social deficits that are rescued by zinc supplementation or NMDAR co-agonism [#2]. Autism-linked mutations impair spine density through distinct mechanisms — loss of the cortactin-binding domain, disruption of an N-to-C intramolecular interaction, or aberrant microtubule association that mislocalizes the protein away from spines — and the corresponding knockin mice show reduced social interaction [#4]. The resulting social deficits are male-biased and map onto reduced activity in defined cortical circuits including the infralimbic prefrontal cortex, and can be rescued by chemogenetic circuit activation or by nutrient-sensitive (zinc, BCAA/mTOR) manipulations [#5].\"\n,\n  \"teleology\": [\n    {\n      \"year\": 2012,\n      \"claim\": \"Established the founding molecular activity of CTTNBP2: how a neuron-specific protein could control dendritic spine formation by acting on the actin cytoskeleton and a phosphatase complex.\",\n      \"evidence\": \"Reciprocal Co-IP, subcellular fractionation, FRAP, and overexpression/knockdown in primary neurons\",\n      \"pmids\": [\"23015759\", \"23060955\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define structural basis of cortactin binding\", \"Functional role of PP2A/striatin recruitment to spines left mechanistically open\", \"Distinction from paralog CTTNBP2NL noted but not fully resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Connected CTTNBP2 to brain zinc homeostasis and the NMDAR–SHANK synaptic pathway, providing a mechanistic and therapeutic link to autism phenotypes.\",\n      \"evidence\": \"Cttnbp2 knockout and ASD knockin mice, zinc measurement, synaptic fractionation, EM of PSD, and pharmacological rescue (zinc, D-cycloserine)\",\n      \"pmids\": [\"32492416\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish how CTTNBP2 loss lowers brain zinc\", \"Molecular mechanism linking zinc to synaptic protein retention not yet defined\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showed that distinct ASD-linked mutations converge on reduced spine density through divergent molecular defects, distinguishing cortactin-binding from microtubule-localization mechanisms.\",\n      \"evidence\": \"Co-IP with cortactin and microtubules, localization in hippocampal neurons, domain-deletion constructs, and M120I knockin behavioral assays\",\n      \"pmids\": [\"33168105\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve the intramolecular N–C interaction structurally\", \"Behavioral testing limited to one knockin allele\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined the physical basis for synaptic CTTNBP2 organization: zinc-regulated liquid-liquid phase separation that builds SHANK3-containing condensates and tunes their stability.\",\n      \"evidence\": \"Live imaging of phase separation, FRAP, domain mutagenesis, and zinc-supplementation rescue in ASD knockin mice\",\n      \"pmids\": [\"35562389\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of zinc binding to the coiled-coil not quantified\", \"In vivo evidence that condensate state controls behavior remains indirect\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Placed CTTNBP2 deficits within specific brain circuits and revealed sex-biased molecular consequences, linking the protein to nutrient/mTOR signaling.\",\n      \"evidence\": \"c-Fos mapping, chemogenetic (DREADD) ILA activation, proteomics, and dietary BCAA rescue in male mutant mice\",\n      \"pmids\": [\"36385662\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanistic basis of sex bias not fully resolved\", \"How CTTNBP2 loss alters RRAGC/mTOR signaling not established\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Extended the zinc rescue mechanism to protein synthesis, proposing that neuronal ribosome biogenesis underlies zinc-dependent spine and behavioral improvement in a sex-specific manner.\",\n      \"evidence\": \"Puromycin pulse labeling, proteomics, spine morphometry, and sex-stratified zinc dietary manipulation (preprint)\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, single lab, not peer-reviewed\", \"Direct link from CTTNBP2 protein activity to translation machinery not biochemically demonstrated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the cytoskeletal/condensate functions of CTTNBP2 mechanistically feed into zinc homeostasis, mTOR/translation, and the male-biased circuit phenotype remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No molecular mechanism linking CTTNBP2 loss to reduced brain zinc\", \"Structural model of zinc binding and phase transition lacking\", \"Causal chain from condensate state to circuit-level social behavior not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 1, 4]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0140313\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 2, 3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [2, 3, 5]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"complexes\": [\"CTTNBP2-SHANK3 synaptic condensate\", \"PP2A complex\"],\n    \"partners\": [\"CTTN\", \"STRN\", \"STRN4\", \"SHANK3\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}