{"gene":"CHN1","run_date":"2026-06-09T22:57:18","timeline":{"discoveries":[{"year":1993,"finding":"Alpha2-chimaerin (CHN1) is an alternatively spliced product of the n-chimerin gene that contains an N-terminal SH2 domain in addition to phorbol ester receptor (C1) and GAP domains. The purified protein exhibits RacGAP activity that is stimulated by phosphatidylserine, and the SH2 domain binds phosphoproteins of PC12 cells whose phosphorylation increases in response to trophic factors including NGF.","method":"Protein purification from rat brain, in vitro RacGAP activity assay, recombinant E. coli protein assay, SH2 domain binding assay with 32P-labelled phosphoproteins","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct biochemical reconstitution of enzymatic activity with purified native and recombinant protein, multiple orthogonal methods (GAP assay, lipid stimulation, SH2 binding)","pmids":["8336731"],"is_preprint":false},{"year":2008,"finding":"Missense mutations in CHN1 cause Duane's retraction syndrome (DURS2) via gain-of-function hyperactivation of alpha2-chimaerin RacGAP activity. Multiple mutations enhance alpha2-chimaerin translocation to the cell membrane and/or enhance self-association (dimerization). Expression of mutant alpha2-chimaerin in chick embryos causes failure of oculomotor axons to innervate target extraocular muscles.","method":"In vitro RacGAP activity assay, cell membrane translocation assay, self-association assay, in ovo chick embryo expression of mutant constructs, genetic linkage and mutation analysis in human families","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple orthogonal functional assays (GAP activity, translocation, dimerization) plus in vivo chick model, replicated across multiple mutations","pmids":["18653847"],"is_preprint":false},{"year":2011,"finding":"A novel CHN1 mutation (Y148F) hyperactivates alpha2-chimaerin by enhancing its dimerization and membrane association, and lowers total intracellular Rac-GTP levels. This mutation causes vertical strabismus and supraduction deficits in addition to Duane retraction syndrome.","method":"Rac-GTP activation assay, alpha2-chimaerin translocation quantification, co-immunoprecipitation for dimerization, genetic linkage analysis","journal":"Investigative ophthalmology & visual science","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP for dimerization, translocation assay, and Rac-GTP assay in single lab with multiple orthogonal methods","pmids":["21715346"],"is_preprint":false},{"year":2011,"finding":"Two novel CHN1 mutations (P141L and P252S) alter residues that participate in intramolecular interactions stabilizing the inactive, closed conformation of alpha2-chimaerin, predicted to result in hyperactivation by disrupting autoinhibition. The same residue P252 was previously found mutated in another DRS pedigree, supporting a gain-of-function mechanism.","method":"DNA sequencing and mutation analysis, structural modeling of intramolecular interactions","journal":"Archives of ophthalmology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — sequencing with structural interpretation, consistent with prior functional data but no direct enzymatic assay in this paper","pmids":["21555619"],"is_preprint":false},{"year":2020,"finding":"A CHN1 variant (p.Phe213Val) in the C1 domain reduces Rac-GTP activity while enhancing membrane translocation in response to phorbol-myristoyl acetate (PMA), demonstrating that the C1 domain is critical for regulating both catalytic activity and subcellular localization of alpha2-chimaerin.","method":"Rac-GTP activation assay, alpha2-chimaerin translocation assay (PMA stimulation), co-immunoprecipitation, exome sequencing","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct functional assays (Rac-GTP, translocation) in transfected 293T cells, single lab with multiple orthogonal methods","pmids":["33004823"],"is_preprint":false},{"year":2023,"finding":"TBX18 binds to the CHN1 promoter region to transcriptionally activate CHN1 expression, and elevated CHN1 increases RhoA activity (demonstrated by GST pull-down). This TBX18/CHN1/RhoA axis promotes radioresistance in esophageal squamous cell carcinoma cells.","method":"Dual-luciferase reporter assay, ChIP assay, GST pull-down for CHN1-RhoA interaction, ectopic expression/knockdown experiments in cells and xenograft mouse model","journal":"Radiotherapy and oncology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP confirms TBX18 binding to CHN1 promoter, GST pull-down confirms CHN1-RhoA interaction, single lab with multiple orthogonal methods","pmids":["37399907"],"is_preprint":false},{"year":2021,"finding":"CHN1 overexpression activates the Akt/GSK-3β/Snail signaling pathway to promote epithelial-mesenchymal transition (EMT) in cervical carcinoma cells, as demonstrated by increased phospho-Akt/phospho-GSK-3β, decreased epithelial markers, and increased mesenchymal markers; inhibition with LY294002 (PI3K inhibitor) blocked these effects.","method":"Overexpression and knockdown in cervical carcinoma cell lines, western blotting for EMT markers and pathway proteins, CCK-8/scratch/transwell assays, xenograft mouse model, pharmacological inhibition with LY294002","journal":"Journal of translational medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological validation combined with OE/KD and in vivo xenograft, single lab","pmids":["34238315"],"is_preprint":false},{"year":2023,"finding":"Two novel CHN1 variants (p.His217Arg and p.Phe213Leu) cause dysplasia of ocular motor nerves when expressed as mutant mRNAs injected into zebrafish embryos, confirming a role for CHN1 in ocular motor nerve development in a vertebrate in vivo model.","method":"Whole exome sequencing, zebrafish embryo mRNA injection with mutant CHN1 constructs, imaging of ocular motor nerve development","journal":"Journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo zebrafish functional assay with defined morphological readout, single lab","pmids":["37853116"],"is_preprint":false}],"current_model":"CHN1 encodes alpha2-chimaerin, an SH2-domain-containing RacGAP that is normally held in an autoinhibited, closed conformation; phorbol ester/diacylglycerol engages its C1 domain to drive membrane translocation and activation, whereupon it stimulates Rac-GTP hydrolysis (stimulated by phosphatidylserine) to suppress Rac signaling; gain-of-function missense mutations that disrupt intramolecular autoinhibitory contacts hyperactivate RacGAP activity, enhance membrane translocation and dimerization, reduce cellular Rac-GTP, and cause aberrant ocular motor axon pathfinding leading to Duane retraction syndrome and related congenital cranial dysinnervation disorders; in cancer contexts, CHN1 is transcriptionally activated by TBX18 and can signal through RhoA and Akt/GSK-3β/Snail to promote EMT and radioresistance."},"narrative":{"mechanistic_narrative":"CHN1 encodes alpha2-chimaerin, an SH2-domain-containing RacGAP that suppresses Rac signaling and governs ocular motor axon pathfinding [PMID:8336731, PMID:18653847]. The purified protein hydrolyzes Rac-GTP in a reaction stimulated by phosphatidylserine, and its N-terminal SH2 domain binds phosphoproteins whose phosphorylation rises in response to trophic factors including NGF [PMID:8336731]. Its C1 (phorbol ester/diacylglycerol) domain couples catalytic activity to subcellular localization, with C1 variants altering both Rac-GTP turnover and PMA-driven membrane translocation [PMID:33004823]. Gain-of-function missense mutations that disrupt intramolecular contacts stabilizing the closed, autoinhibited conformation hyperactivate RacGAP activity, enhance membrane translocation and self-association/dimerization, and lower intracellular Rac-GTP, causing Duane retraction syndrome and related ocular motor nerve dysinnervation in human families and in chick and zebrafish models [PMID:18653847, PMID:21715346, PMID:21555619, PMID:37853116]. In cancer, CHN1 is transcriptionally activated by TBX18 and increases RhoA activity to drive radioresistance, and its overexpression engages Akt/GSK-3β/Snail signaling to promote epithelial-mesenchymal transition [PMID:37399907, PMID:34238315].","teleology":[{"year":1993,"claim":"Established alpha2-chimaerin's core biochemical identity: that the CHN1 splice product is a phosphatidylserine-stimulated RacGAP bearing an SH2 domain that reads trophic-factor-induced phosphorylation, linking it to Rac regulation downstream of signaling.","evidence":"Protein purification from rat brain plus recombinant assays for RacGAP activity, lipid stimulation, and SH2 phosphoprotein binding","pmids":["8336731"],"confidence":"High","gaps":["Physiological SH2 ligands not molecularly identified","In vivo role of GAP activity not yet established"]},{"year":2008,"claim":"Connected CHN1 to human disease and defined the mechanism as gain-of-function: hyperactivating missense mutations enhance RacGAP activity, membrane translocation, and dimerization, and disrupt ocular motor axon innervation in vivo.","evidence":"In vitro RacGAP, translocation and self-association assays, in ovo chick mutant expression, and family genetic linkage","pmids":["18653847"],"confidence":"High","gaps":["How excess RacGAP activity misroutes specific axons not resolved","Endogenous activators in motor neurons unknown"]},{"year":2011,"claim":"Extended the gain-of-function model by tying dimerization and membrane association directly to reduced cellular Rac-GTP, and broadened the clinical phenotype beyond classic Duane syndrome.","evidence":"Rac-GTP assay, translocation quantification, reciprocal co-IP for dimerization, and linkage analysis for the Y148F variant","pmids":["21715346"],"confidence":"High","gaps":["Structural basis of dimer interface not determined","Phenotype-genotype correlation across variants unexplained"]},{"year":2011,"claim":"Identified the structural logic of hyperactivation, mapping mutations to residues stabilizing the inactive closed conformation, implying disruption of autoinhibition.","evidence":"Sequencing and structural modeling of intramolecular interactions for P141L and P252S","pmids":["21555619"],"confidence":"Medium","gaps":["No direct enzymatic assay in this study","Closed-to-open transition not visualized structurally"]},{"year":2020,"claim":"Defined the C1 domain as a regulatory node controlling both catalysis and localization, showing a C1 variant can lower Rac-GTP yet still enhance PMA-induced translocation.","evidence":"Rac-GTP and PMA translocation assays plus co-IP in 293T cells with exome-identified p.Phe213Val","pmids":["33004823"],"confidence":"Medium","gaps":["Single cell-line context","Relationship between C1 lipid sensing and SH2 input not integrated"]},{"year":2021,"claim":"Opened a cancer-relevant role distinct from neurodevelopment, showing CHN1 overexpression drives EMT via Akt/GSK-3β/Snail signaling.","evidence":"Overexpression/knockdown, EMT marker western blots, migration assays, xenograft, and PI3K inhibition with LY294002 in cervical carcinoma cells","pmids":["34238315"],"confidence":"Medium","gaps":["Mechanistic link between RacGAP activity and Akt activation unresolved","Single tumor-type context"]},{"year":2023,"claim":"Placed CHN1 in a transcriptional axis promoting radioresistance, with TBX18 activating CHN1 and CHN1 increasing RhoA activity.","evidence":"Luciferase and ChIP for TBX18-promoter binding, GST pull-down for CHN1-RhoA, and knockdown/xenograft in esophageal squamous cell carcinoma","pmids":["37399907"],"confidence":"Medium","gaps":["How a RacGAP elevates RhoA activity mechanistically not explained","Whether RhoA effect requires GAP catalysis untested"]},{"year":2023,"claim":"Confirmed in a second vertebrate model that disease variants impair ocular motor nerve development, strengthening the in vivo neurodevelopmental link.","evidence":"Whole exome sequencing and zebrafish mutant-mRNA injection imaging for p.His217Arg and p.Phe213Leu","pmids":["37853116"],"confidence":"Medium","gaps":["Functional RacGAP consequences of these variants not assayed biochemically","Cellular target of axon misrouting not identified"]},{"year":null,"claim":"How the same RacGAP reconciles its neurodevelopmental Rac-suppressing role with cancer-context RhoA activation and Akt signaling, and what its endogenous SH2 ligands and upstream activators are, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of the autoinhibited or active state","Endogenous SH2-binding phosphoproteins unidentified","Mechanistic basis for RhoA activation by a RacGAP unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,2]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,4]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,2,4]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,5]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[1,7]}],"complexes":[],"partners":["RAC1","RHOA","TBX18"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P15882","full_name":"N-chimaerin","aliases":["A-chimaerin","Alpha-chimerin","N-chimerin","NC","Rho GTPase-activating protein 2"],"length_aa":459,"mass_kda":53.2,"function":"GTPase-activating protein for p21-rac and a phorbol ester receptor. Involved in the assembly of neuronal locomotor circuits as a direct effector of EPHA4 in axon guidance","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/P15882/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CHN1","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000128656","cell_line_id":"CID000561","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"nucleoplasm","grade":3},{"compartment":"big_aggregates","grade":1}],"interactors":[{"gene":"ALDH1A1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000561","total_profiled":1310},"omim":[{"mim_id":"618186","title":"NEUROPATHY, CONGENITAL HYPOMYELINATING, 3; CHN3","url":"https://www.omim.org/entry/618186"},{"mim_id":"618184","title":"NEUROPATHY, CONGENITAL HYPOMYELINATING, 2; CHN2","url":"https://www.omim.org/entry/618184"},{"mim_id":"617368","title":"SH3 DOMAIN-BINDING PROTEIN 1; SH3BP1","url":"https://www.omim.org/entry/617368"},{"mim_id":"616407","title":"BROWN SYNDROME; BRWNS","url":"https://www.omim.org/entry/616407"},{"mim_id":"605253","title":"NEUROPATHY, CONGENITAL HYPOMYELINATING, 1, AUTOSOMAL RECESSIVE; CHN1","url":"https://www.omim.org/entry/605253"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":842.8}],"url":"https://www.proteinatlas.org/search/CHN1"},"hgnc":{"alias_symbol":["RhoGAP2","ARHGAP2","n-chimerin"],"prev_symbol":["CHN","DURS2"]},"alphafold":{"accession":"P15882","domains":[{"cath_id":"3.30.505.10","chopping":"17-135","consensus_level":"high","plddt":95.6867,"start":17,"end":135},{"cath_id":"3.30.60.20","chopping":"207-261","consensus_level":"high","plddt":94.3215,"start":207,"end":261},{"cath_id":"1.10.555.10","chopping":"276-453","consensus_level":"high","plddt":96.0118,"start":276,"end":453}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P15882","model_url":"https://alphafold.ebi.ac.uk/files/AF-P15882-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P15882-F1-predicted_aligned_error_v6.png","plddt_mean":86.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CHN1","jax_strain_url":"https://www.jax.org/strain/search?query=CHN1"},"sequence":{"accession":"P15882","fasta_url":"https://rest.uniprot.org/uniprotkb/P15882.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P15882/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P15882"}},"corpus_meta":[{"pmid":"18653847","id":"PMC_18653847","title":"Human CHN1 mutations hyperactivate alpha2-chimaerin and cause Duane's retraction syndrome.","date":"2008","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/18653847","citation_count":128,"is_preprint":false},{"pmid":"8336731","id":"PMC_8336731","title":"Alpha 2-chimerin, an SH2-containing GTPase-activating protein for the ras-related protein p21rac derived by alternate splicing of the human n-chimerin gene, is selectively expressed in brain regions and testes.","date":"1993","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/8336731","citation_count":81,"is_preprint":false},{"pmid":"17197533","id":"PMC_17197533","title":"Magnetic resonance imaging evidence for widespread orbital dysinnervation in dominant Duane's retraction syndrome linked to the DURS2 locus.","date":"2007","source":"Investigative ophthalmology & visual science","url":"https://pubmed.ncbi.nlm.nih.gov/17197533","citation_count":80,"is_preprint":false},{"pmid":"34724818","id":"PMC_34724818","title":"Candida albicans Isolates 529L and CHN1 Exhibit Stable Colonization of the Murine Gastrointestinal Tract.","date":"2021","source":"mBio","url":"https://pubmed.ncbi.nlm.nih.gov/34724818","citation_count":56,"is_preprint":false},{"pmid":"21715346","id":"PMC_21715346","title":"Expansion of the CHN1 strabismus phenotype.","date":"2011","source":"Investigative ophthalmology & visual science","url":"https://pubmed.ncbi.nlm.nih.gov/21715346","citation_count":39,"is_preprint":false},{"pmid":"33109127","id":"PMC_33109127","title":"Upregulation of miR-205 induces CHN1 expression, which is associated with the aggressive behaviour of cervical cancer cells and correlated with lymph node metastasis.","date":"2020","source":"BMC cancer","url":"https://pubmed.ncbi.nlm.nih.gov/33109127","citation_count":24,"is_preprint":false},{"pmid":"21555619","id":"PMC_21555619","title":"Two novel CHN1 mutations in 2 families with Duane retraction syndrome.","date":"2011","source":"Archives of ophthalmology (Chicago, Ill. : 1960)","url":"https://pubmed.ncbi.nlm.nih.gov/21555619","citation_count":24,"is_preprint":false},{"pmid":"17197532","id":"PMC_17197532","title":"Two pedigrees segregating Duane's retraction syndrome as a dominant trait map to the DURS2 genetic locus.","date":"2007","source":"Investigative ophthalmology & visual science","url":"https://pubmed.ncbi.nlm.nih.gov/17197532","citation_count":20,"is_preprint":false},{"pmid":"34238315","id":"PMC_34238315","title":"CHN1 promotes epithelial-mesenchymal transition via the Akt/GSK-3β/Snail pathway in cervical carcinoma.","date":"2021","source":"Journal of translational medicine","url":"https://pubmed.ncbi.nlm.nih.gov/34238315","citation_count":15,"is_preprint":false},{"pmid":"20535495","id":"PMC_20535495","title":"Analysis of the CHN1 gene in patients with various types of congenital ocular motility disorders.","date":"2010","source":"Graefe's archive for clinical and experimental ophthalmology = Albrecht von Graefes Archiv fur klinische und experimentelle Ophthalmologie","url":"https://pubmed.ncbi.nlm.nih.gov/20535495","citation_count":12,"is_preprint":false},{"pmid":"33667650","id":"PMC_33667650","title":"CHN1 and duane retraction syndrome: Expanding the phenotype to cranial nerves development disease.","date":"2021","source":"European journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/33667650","citation_count":6,"is_preprint":false},{"pmid":"29031989","id":"PMC_29031989","title":"CHN1 gene mutation analysis in patients with Duane retraction syndrome.","date":"2017","source":"Journal of AAPOS : the official publication of the American Association for Pediatric Ophthalmology and Strabismus","url":"https://pubmed.ncbi.nlm.nih.gov/29031989","citation_count":4,"is_preprint":false},{"pmid":"34152250","id":"PMC_34152250","title":"Bioinformatics-based analysis of the association between the A1-chimaerin (CHN1) gene and gastric cancer.","date":"2021","source":"Bioengineered","url":"https://pubmed.ncbi.nlm.nih.gov/34152250","citation_count":4,"is_preprint":false},{"pmid":"33004823","id":"PMC_33004823","title":"Identification of a novel CHN1 p.(Phe213Val) variant in a large Han Chinese family with congenital Duane retraction syndrome.","date":"2020","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/33004823","citation_count":4,"is_preprint":false},{"pmid":"32219675","id":"PMC_32219675","title":"Efficacy and Safety of Dulaglutide Monotherapy Compared to Glimepiride in Oral Antihyperglycemic Medication-Naïve Chinese patients with Type 2 Diabetes: A Post Hoc Analysis of AWARD-CHN1.","date":"2020","source":"Diabetes therapy : research, treatment and education of diabetes and related disorders","url":"https://pubmed.ncbi.nlm.nih.gov/32219675","citation_count":4,"is_preprint":false},{"pmid":"39812067","id":"PMC_39812067","title":"COL1A1, COL1A2, CHN1, and FN1 Promote Tumorogenesis and Act as Markers of Diagnosis and Survival in Gastric Cancer Patients.","date":"2025","source":"Current pharmaceutical biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/39812067","citation_count":3,"is_preprint":false},{"pmid":"38356699","id":"PMC_38356699","title":"Case report: Identification of a novel variant p.Gly215Arg in the CHN1 gene causing Moebius syndrome.","date":"2024","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/38356699","citation_count":2,"is_preprint":false},{"pmid":"37399907","id":"PMC_37399907","title":"TBX18 knockdown sensitizes esophageal squamous cell carcinoma to radiotherapy by blocking the CHN1/RhoA axis.","date":"2023","source":"Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology","url":"https://pubmed.ncbi.nlm.nih.gov/37399907","citation_count":1,"is_preprint":false},{"pmid":"41333466","id":"PMC_41333466","title":"CHN1 as a potential predictive genetic biomarker for atopic dermatitis-related depression.","date":"2025","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/41333466","citation_count":0,"is_preprint":false},{"pmid":"38509018","id":"PMC_38509018","title":"Special clinical features with a novel mutation site of CHN1 gene in a Chinese family with Duane retraction syndrome.","date":"2024","source":"Strabismus","url":"https://pubmed.ncbi.nlm.nih.gov/38509018","citation_count":0,"is_preprint":false},{"pmid":"37853116","id":"PMC_37853116","title":"Two novel CHN1 variants identified in Duane retraction syndrome pedigrees disrupt development of ocular motor nerves in zebrafish.","date":"2023","source":"Journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/37853116","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":13851,"output_tokens":2248,"usd":0.037637,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9292,"output_tokens":2772,"usd":0.05788,"stage2_stop_reason":"end_turn"},"total_usd":0.095517,"stage1_batch_id":"msgbatch_01ACAxJQabDsht39JXeWG22d","stage2_batch_id":"msgbatch_01QEU22A9U5sbPTgsMzTmvSf","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1993,\n      \"finding\": \"Alpha2-chimaerin (CHN1) is an alternatively spliced product of the n-chimerin gene that contains an N-terminal SH2 domain in addition to phorbol ester receptor (C1) and GAP domains. The purified protein exhibits RacGAP activity that is stimulated by phosphatidylserine, and the SH2 domain binds phosphoproteins of PC12 cells whose phosphorylation increases in response to trophic factors including NGF.\",\n      \"method\": \"Protein purification from rat brain, in vitro RacGAP activity assay, recombinant E. coli protein assay, SH2 domain binding assay with 32P-labelled phosphoproteins\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct biochemical reconstitution of enzymatic activity with purified native and recombinant protein, multiple orthogonal methods (GAP assay, lipid stimulation, SH2 binding)\",\n      \"pmids\": [\"8336731\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Missense mutations in CHN1 cause Duane's retraction syndrome (DURS2) via gain-of-function hyperactivation of alpha2-chimaerin RacGAP activity. Multiple mutations enhance alpha2-chimaerin translocation to the cell membrane and/or enhance self-association (dimerization). Expression of mutant alpha2-chimaerin in chick embryos causes failure of oculomotor axons to innervate target extraocular muscles.\",\n      \"method\": \"In vitro RacGAP activity assay, cell membrane translocation assay, self-association assay, in ovo chick embryo expression of mutant constructs, genetic linkage and mutation analysis in human families\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple orthogonal functional assays (GAP activity, translocation, dimerization) plus in vivo chick model, replicated across multiple mutations\",\n      \"pmids\": [\"18653847\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"A novel CHN1 mutation (Y148F) hyperactivates alpha2-chimaerin by enhancing its dimerization and membrane association, and lowers total intracellular Rac-GTP levels. This mutation causes vertical strabismus and supraduction deficits in addition to Duane retraction syndrome.\",\n      \"method\": \"Rac-GTP activation assay, alpha2-chimaerin translocation quantification, co-immunoprecipitation for dimerization, genetic linkage analysis\",\n      \"journal\": \"Investigative ophthalmology & visual science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP for dimerization, translocation assay, and Rac-GTP assay in single lab with multiple orthogonal methods\",\n      \"pmids\": [\"21715346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Two novel CHN1 mutations (P141L and P252S) alter residues that participate in intramolecular interactions stabilizing the inactive, closed conformation of alpha2-chimaerin, predicted to result in hyperactivation by disrupting autoinhibition. The same residue P252 was previously found mutated in another DRS pedigree, supporting a gain-of-function mechanism.\",\n      \"method\": \"DNA sequencing and mutation analysis, structural modeling of intramolecular interactions\",\n      \"journal\": \"Archives of ophthalmology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — sequencing with structural interpretation, consistent with prior functional data but no direct enzymatic assay in this paper\",\n      \"pmids\": [\"21555619\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"A CHN1 variant (p.Phe213Val) in the C1 domain reduces Rac-GTP activity while enhancing membrane translocation in response to phorbol-myristoyl acetate (PMA), demonstrating that the C1 domain is critical for regulating both catalytic activity and subcellular localization of alpha2-chimaerin.\",\n      \"method\": \"Rac-GTP activation assay, alpha2-chimaerin translocation assay (PMA stimulation), co-immunoprecipitation, exome sequencing\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct functional assays (Rac-GTP, translocation) in transfected 293T cells, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"33004823\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"TBX18 binds to the CHN1 promoter region to transcriptionally activate CHN1 expression, and elevated CHN1 increases RhoA activity (demonstrated by GST pull-down). This TBX18/CHN1/RhoA axis promotes radioresistance in esophageal squamous cell carcinoma cells.\",\n      \"method\": \"Dual-luciferase reporter assay, ChIP assay, GST pull-down for CHN1-RhoA interaction, ectopic expression/knockdown experiments in cells and xenograft mouse model\",\n      \"journal\": \"Radiotherapy and oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP confirms TBX18 binding to CHN1 promoter, GST pull-down confirms CHN1-RhoA interaction, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"37399907\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CHN1 overexpression activates the Akt/GSK-3β/Snail signaling pathway to promote epithelial-mesenchymal transition (EMT) in cervical carcinoma cells, as demonstrated by increased phospho-Akt/phospho-GSK-3β, decreased epithelial markers, and increased mesenchymal markers; inhibition with LY294002 (PI3K inhibitor) blocked these effects.\",\n      \"method\": \"Overexpression and knockdown in cervical carcinoma cell lines, western blotting for EMT markers and pathway proteins, CCK-8/scratch/transwell assays, xenograft mouse model, pharmacological inhibition with LY294002\",\n      \"journal\": \"Journal of translational medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological validation combined with OE/KD and in vivo xenograft, single lab\",\n      \"pmids\": [\"34238315\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Two novel CHN1 variants (p.His217Arg and p.Phe213Leu) cause dysplasia of ocular motor nerves when expressed as mutant mRNAs injected into zebrafish embryos, confirming a role for CHN1 in ocular motor nerve development in a vertebrate in vivo model.\",\n      \"method\": \"Whole exome sequencing, zebrafish embryo mRNA injection with mutant CHN1 constructs, imaging of ocular motor nerve development\",\n      \"journal\": \"Journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo zebrafish functional assay with defined morphological readout, single lab\",\n      \"pmids\": [\"37853116\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CHN1 encodes alpha2-chimaerin, an SH2-domain-containing RacGAP that is normally held in an autoinhibited, closed conformation; phorbol ester/diacylglycerol engages its C1 domain to drive membrane translocation and activation, whereupon it stimulates Rac-GTP hydrolysis (stimulated by phosphatidylserine) to suppress Rac signaling; gain-of-function missense mutations that disrupt intramolecular autoinhibitory contacts hyperactivate RacGAP activity, enhance membrane translocation and dimerization, reduce cellular Rac-GTP, and cause aberrant ocular motor axon pathfinding leading to Duane retraction syndrome and related congenital cranial dysinnervation disorders; in cancer contexts, CHN1 is transcriptionally activated by TBX18 and can signal through RhoA and Akt/GSK-3β/Snail to promote EMT and radioresistance.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CHN1 encodes alpha2-chimaerin, an SH2-domain-containing RacGAP that suppresses Rac signaling and governs ocular motor axon pathfinding [#0, #1]. The purified protein hydrolyzes Rac-GTP in a reaction stimulated by phosphatidylserine, and its N-terminal SH2 domain binds phosphoproteins whose phosphorylation rises in response to trophic factors including NGF [#0]. Its C1 (phorbol ester/diacylglycerol) domain couples catalytic activity to subcellular localization, with C1 variants altering both Rac-GTP turnover and PMA-driven membrane translocation [#4]. Gain-of-function missense mutations that disrupt intramolecular contacts stabilizing the closed, autoinhibited conformation hyperactivate RacGAP activity, enhance membrane translocation and self-association/dimerization, and lower intracellular Rac-GTP, causing Duane retraction syndrome and related ocular motor nerve dysinnervation in human families and in chick and zebrafish models [#1, #2, #3, #7]. In cancer, CHN1 is transcriptionally activated by TBX18 and increases RhoA activity to drive radioresistance, and its overexpression engages Akt/GSK-3\\u03b2/Snail signaling to promote epithelial-mesenchymal transition [#5, #6].\",\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"Established alpha2-chimaerin's core biochemical identity: that the CHN1 splice product is a phosphatidylserine-stimulated RacGAP bearing an SH2 domain that reads trophic-factor-induced phosphorylation, linking it to Rac regulation downstream of signaling.\",\n      \"evidence\": \"Protein purification from rat brain plus recombinant assays for RacGAP activity, lipid stimulation, and SH2 phosphoprotein binding\",\n      \"pmids\": [\"8336731\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological SH2 ligands not molecularly identified\", \"In vivo role of GAP activity not yet established\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Connected CHN1 to human disease and defined the mechanism as gain-of-function: hyperactivating missense mutations enhance RacGAP activity, membrane translocation, and dimerization, and disrupt ocular motor axon innervation in vivo.\",\n      \"evidence\": \"In vitro RacGAP, translocation and self-association assays, in ovo chick mutant expression, and family genetic linkage\",\n      \"pmids\": [\"18653847\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How excess RacGAP activity misroutes specific axons not resolved\", \"Endogenous activators in motor neurons unknown\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Extended the gain-of-function model by tying dimerization and membrane association directly to reduced cellular Rac-GTP, and broadened the clinical phenotype beyond classic Duane syndrome.\",\n      \"evidence\": \"Rac-GTP assay, translocation quantification, reciprocal co-IP for dimerization, and linkage analysis for the Y148F variant\",\n      \"pmids\": [\"21715346\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of dimer interface not determined\", \"Phenotype-genotype correlation across variants unexplained\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identified the structural logic of hyperactivation, mapping mutations to residues stabilizing the inactive closed conformation, implying disruption of autoinhibition.\",\n      \"evidence\": \"Sequencing and structural modeling of intramolecular interactions for P141L and P252S\",\n      \"pmids\": [\"21555619\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No direct enzymatic assay in this study\", \"Closed-to-open transition not visualized structurally\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Defined the C1 domain as a regulatory node controlling both catalysis and localization, showing a C1 variant can lower Rac-GTP yet still enhance PMA-induced translocation.\",\n      \"evidence\": \"Rac-GTP and PMA translocation assays plus co-IP in 293T cells with exome-identified p.Phe213Val\",\n      \"pmids\": [\"33004823\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single cell-line context\", \"Relationship between C1 lipid sensing and SH2 input not integrated\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Opened a cancer-relevant role distinct from neurodevelopment, showing CHN1 overexpression drives EMT via Akt/GSK-3\\u03b2/Snail signaling.\",\n      \"evidence\": \"Overexpression/knockdown, EMT marker western blots, migration assays, xenograft, and PI3K inhibition with LY294002 in cervical carcinoma cells\",\n      \"pmids\": [\"34238315\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanistic link between RacGAP activity and Akt activation unresolved\", \"Single tumor-type context\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Placed CHN1 in a transcriptional axis promoting radioresistance, with TBX18 activating CHN1 and CHN1 increasing RhoA activity.\",\n      \"evidence\": \"Luciferase and ChIP for TBX18-promoter binding, GST pull-down for CHN1-RhoA, and knockdown/xenograft in esophageal squamous cell carcinoma\",\n      \"pmids\": [\"37399907\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How a RacGAP elevates RhoA activity mechanistically not explained\", \"Whether RhoA effect requires GAP catalysis untested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Confirmed in a second vertebrate model that disease variants impair ocular motor nerve development, strengthening the in vivo neurodevelopmental link.\",\n      \"evidence\": \"Whole exome sequencing and zebrafish mutant-mRNA injection imaging for p.His217Arg and p.Phe213Leu\",\n      \"pmids\": [\"37853116\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional RacGAP consequences of these variants not assayed biochemically\", \"Cellular target of axon misrouting not identified\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the same RacGAP reconciles its neurodevelopmental Rac-suppressing role with cancer-context RhoA activation and Akt signaling, and what its endogenous SH2 ligands and upstream activators are, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of the autoinhibited or active state\", \"Endogenous SH2-binding phosphoproteins unidentified\", \"Mechanistic basis for RhoA activation by a RacGAP unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 2, 4]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 5]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [1, 7]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"RAC1\", \"RHOA\", \"TBX18\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}