{"gene":"C2CD3","run_date":"2026-06-09T22:02:45","timeline":{"discoveries":[{"year":2008,"finding":"C2cd3 is required for ciliogenesis and intracellular Hedgehog signal transduction in mouse embryos; loss of C2cd3 disrupts cilia formation, impairs proteolytic processing of Gli3, and C2cd3 protein localizes to the basal body consistent with its function in ciliogenesis. Double-mutant analyses placed C2cd3 as an essential regulator of Hedgehog signal transduction.","method":"Forward genetic screen (ENU mutagenesis), genetic mapping, sequence analysis, double-mutant epistasis analysis, immunolocalization, Gli3 processing assay","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (genetic epistasis, immunolocalization, Gli3 processing assay) in a focused study; foundational mechanism paper replicated by subsequent work","pmids":["19004860"],"is_preprint":false},{"year":2014,"finding":"C2CD3 localizes to the distal end of centrioles, physically associates with OFD1, and positively promotes centriole elongation; overexpression of C2CD3 triggers centriole hyperelongation, whereas loss of C2CD3 results in short centrioles lacking subdistal and distal appendages. OFD1 acts as a negative regulator of C2CD3's elongation-promoting activity.","method":"Immunofluorescence co-localization, co-immunoprecipitation (physical association with OFD1), overexpression and loss-of-function centriole length measurements, genetic epistasis with OFD1 deletion","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal functional assays (OE + KD), co-IP, precise subcellular localization with functional consequence, replicated across two affected families and model systems","pmids":["24997988"],"is_preprint":false},{"year":2016,"finding":"Loss of C2CD3 in patient-derived fibroblasts reduces cilia formation and impairs basal body maturation; however, the distal appendage protein CEP164 is still recruited to the basal body in C2CD3-defective cells, indicating CEP164 recruitment alone is not sufficient for efficient axonemal extension.","method":"Patient-derived fibroblast cultures, immunofluorescence for ciliogenesis markers including CEP164 localization","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — single lab, cell-based functional assay with specific mechanistic conclusion about CEP164 sufficiency, single method","pmids":["27094867"],"is_preprint":false},{"year":2019,"finding":"CEP120 interacts with C2CD3 (and Talpid3) at the distal ends of centrioles; loss of CEP120 impairs recruitment of C2CD3 to the distal centriole, disrupting centriole appendage assembly and ciliogenesis. A disease-associated CEP120 mutant (I975S) has reduced affinity for C2CD3 and perturbs cilia assembly.","method":"CRISPR/Cas9 knockout of CEP120 in RPE1 cells, co-immunoprecipitation (CEP120–C2CD3 interaction), immunofluorescence for C2CD3/Talpid3 localization, mutant affinity comparison","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, CRISPR KO with defined cellular phenotype and localization readout, disease-mutant mechanistic validation, single lab","pmids":["30988386"],"is_preprint":false},{"year":2021,"finding":"Conditional deletion of C2cd3 in cranial neural crest cells causes craniofacial-specific defects; analysis of N-terminal C2CD3N-C2 domain deletion versus C-terminal PKC-C2 domain deletion reveals that the N-terminal C2CD3N-C2 domain is critical for early embryonic development and has a craniofacial-specific function.","method":"Conditional allelic series (tissue-specific Cre-lox), phenotypic analysis of domain-specific deletions in mouse, isoform characterization","journal":"Frontiers in cell and developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — domain-specific conditional KO with defined craniofacial phenotype, single lab, no biochemical assays","pmids":["34211969"],"is_preprint":false},{"year":2025,"finding":"C2CD3 adopts a radially symmetric 9-fold organization within the centriole's distal lumen, forming a ~100 nm luminal ring (~27 nodes). Its C-terminal region is close to this luminal ring and its N-terminal region is close to a hook-like structure attaching to the A-microtubule. C2CD3 directly interacts with MNR of the DISCO complex (MNR/CEP90/OFD1) to recruit it to future appendage sites. C2CD3 depletion destabilizes the luminal ring network (C2CD3/SFI1/centrin-2/CEP135/NA14) and the distal tip protein CEP162, but key structural elements remain intact permitting centriole duplication. C2CD3 thus functions as an architectural hub scaffolding the distal centriole and directing appendage formation.","method":"Ultrastructure Expansion Microscopy (U-ExM), iterative U-ExM, in situ cryo-electron tomography (cryo-ET), C2CD3 depletion/KO with quantitative protein recruitment assays, direct interaction assay (C2CD3–MNR), domain localization mapping","journal":"PLoS biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-ET structural analysis combined with U-ExM and functional depletion studies across multiple orthogonal methods; peer-reviewed study with mechanistic detail","pmids":["41364719"],"is_preprint":false},{"year":2025,"finding":"Biallelic hypomorphic missense C2CD3 variants reduce C2CD3 localization to the basal body, shorten cilia, reduce ciliation frequency in kidney epithelial cells, and dysregulate SHH signaling (reduced GLI3 activator and GLI1 mRNA). Rescue experiments in C2CD3 KO RPE-1 cells confirmed each variant's reduced capacity to restore ciliogenesis.","method":"Patient-derived fibroblasts and urinary renal epithelial cells, C2CD3 KO RPE-1 rescue assay, immunofluorescence for C2CD3 basal body localization, cilia length and frequency measurements, GLI1/GLI3 expression assays","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple cell models, KO rescue experiments, SHH pathway readouts, single lab","pmids":["39690811"],"is_preprint":false},{"year":2025,"finding":"A hierarchical targeting axis exists in the distal centriolar lumen where C2CD3 is required upstream for SSNA1 localization; C2CD3 KO results in loss of SSNA1 from the distal lumen (C2CD3–SSNA1–LRRCC1 axis).","method":"KO-validated antibody, super-resolution imaging with expansion microscopy, KO analysis of targeting hierarchy","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — super-resolution localization and KO hierarchy study, preprint, single lab","pmids":[],"is_preprint":true}],"current_model":"C2CD3 is a centriolar protein that localizes to the distal lumen of centrioles in a 9-fold radially symmetric arrangement, where it forms a luminal ring structure and extends a hook-like projection to the A-microtubule; it promotes centriole elongation, scaffolds the distal centriole end by stabilizing the luminal ring network (with SFI1/centrin-2/CEP135/NA14) and directly recruits the DISCO complex (via MNR interaction) to future appendage sites, thereby orchestrating distal appendage assembly and ciliogenesis, and its loss disrupts Hedgehog signal transduction by impairing Gli3 processing."},"narrative":{"mechanistic_narrative":"C2CD3 is a centriolar architectural protein that scaffolds the distal centriole and directs the assembly of centriolar appendages required for ciliogenesis and Hedgehog signal transduction [PMID:19004860, PMID:41364719]. Within the distal centriolar lumen it adopts a 9-fold radially symmetric organization, forming a ~100 nm luminal ring whose C-terminal region lies near the ring and whose N-terminal region projects toward a hook-like structure attaching to the A-microtubule; its depletion destabilizes the luminal ring network (with SFI1, centrin-2, CEP135 and NA14) and the distal tip protein CEP162 [PMID:41364719]. C2CD3 directly engages MNR of the DISCO complex (MNR/CEP90/OFD1) to recruit it to future appendage sites, and acts upstream in a hierarchical targeting axis required for SSNA1 localization to the distal lumen [PMID:41364719]. Functionally, C2CD3 promotes centriole elongation — overexpression drives hyperelongation while loss yields short centrioles lacking subdistal and distal appendages — an activity negatively regulated by its binding partner OFD1 [PMID:24997988]. Its recruitment to the distal centriole depends on CEP120, and a disease-associated CEP120 mutant with reduced C2CD3 affinity perturbs cilia assembly [PMID:30988386]. Loss or hypomorphic mutation of C2CD3 impairs basal body maturation, shortens and reduces cilia, and disrupts Hedgehog/SHH signaling through defective GLI3 processing and reduced GLI activator output, with biallelic hypomorphic missense variants causing a human ciliopathy phenotype [PMID:19004860, PMID:39690811].","teleology":[{"year":2008,"claim":"Established C2CD3 as an essential basal-body regulator of ciliogenesis and a required component of intracellular Hedgehog signal transduction, answering whether the gene functions in cilia-dependent signaling.","evidence":"ENU forward genetic screen in mouse with epistasis, immunolocalization, and Gli3 processing assays","pmids":["19004860"],"confidence":"High","gaps":["Did not define the molecular partners or structural role of C2CD3 at the centriole","Mechanism linking basal body localization to Gli3 processing unresolved"]},{"year":2014,"claim":"Localized C2CD3 to the distal centriole and assigned it a centriole-elongation function counterbalanced by OFD1, defining its first direct physical partner and its role in appendage formation.","evidence":"Immunofluorescence, co-IP with OFD1, overexpression/knockdown length measurements, and OFD1-deletion epistasis","pmids":["24997988"],"confidence":"High","gaps":["Did not resolve how C2CD3 organizes appendage assembly structurally","Direct substrates or scaffold architecture unknown"]},{"year":2016,"claim":"Showed in patient fibroblasts that C2CD3 loss impairs basal body maturation and ciliogenesis even when the distal appendage protein CEP164 is recruited, establishing that CEP164 recruitment is insufficient for axonemal extension.","evidence":"Patient-derived fibroblast immunofluorescence for ciliogenesis and CEP164 markers","pmids":["27094867"],"confidence":"Medium","gaps":["Single method, single lab","Did not identify the missing step downstream of CEP164 recruitment"]},{"year":2019,"claim":"Identified CEP120 as required for recruiting C2CD3 to the distal centriole, placing C2CD3 within a targeting hierarchy for appendage assembly and linking a disease mutation to reduced C2CD3 binding.","evidence":"CRISPR KO of CEP120 in RPE1 cells, reciprocal co-IP, localization imaging, and disease-mutant affinity comparison","pmids":["30988386"],"confidence":"High","gaps":["Did not define the C2CD3 binding interface on CEP120","Order of recruitment relative to other distal proteins unresolved"]},{"year":2021,"claim":"Dissected domain-specific requirements in vivo, showing the N-terminal C2CD3N-C2 domain is critical for early development and craniofacial morphogenesis, distinguishing functions of the two C2 domains.","evidence":"Tissue-specific conditional Cre-lox allelic series with domain-specific deletions in mouse","pmids":["34211969"],"confidence":"Medium","gaps":["No biochemical assignment of molecular activity to either domain","Mechanism of craniofacial specificity unknown"]},{"year":2025,"claim":"Resolved the structural role of C2CD3 as a 9-fold symmetric luminal-ring scaffold that stabilizes the distal centriole network and directly recruits the DISCO complex via MNR to direct appendage formation.","evidence":"U-ExM, iterative U-ExM, in situ cryo-ET, depletion/KO recruitment assays, and direct C2CD3–MNR interaction and domain mapping","pmids":["41364719"],"confidence":"High","gaps":["Atomic-resolution structure of the C2CD3 ring not determined","How C2CD3 elongation activity integrates with its scaffold function unresolved"]},{"year":2025,"claim":"Confirmed the human disease relevance of C2CD3 by showing biallelic hypomorphic missense variants reduce basal body localization, impair ciliation, and dysregulate SHH/GLI output, with KO-rescue validation of each variant.","evidence":"Patient fibroblasts and urinary renal epithelial cells, C2CD3 KO RPE-1 rescue, ciliogenesis quantification, and GLI1/GLI3 expression assays","pmids":["39690811"],"confidence":"Medium","gaps":["Single lab","Genotype-phenotype correlation across the variant spectrum not established"]},{"year":2025,"claim":"Placed C2CD3 upstream of SSNA1 in a distal-lumen targeting axis, extending the hierarchy of proteins it organizes.","evidence":"KO-validated antibody and super-resolution expansion microscopy of targeting hierarchy (preprint)","pmids":[],"confidence":"Medium","gaps":["Preprint, single lab, not peer-reviewed","Whether C2CD3–SSNA1 dependency is direct or indirect unresolved"]},{"year":null,"claim":"How C2CD3's distinct activities — centriole elongation, luminal ring scaffolding, and hierarchical appendage-protein recruitment — are mechanistically coordinated, and how these translate into the precise control of Gli3 processing, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking scaffold architecture to elongation control","Molecular link between distal appendage assembly and Hedgehog/Gli3 processing undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[5]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[5,3]}],"localization":[{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[1,5]}],"pathway":[{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[1,5]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,6]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[0,4]}],"complexes":[],"partners":["OFD1","CEP120","MNR","SFI1","CETN2","CEP135","SSNA1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q4AC94","full_name":"C2 domain-containing protein 3","aliases":[],"length_aa":2353,"mass_kda":260.4,"function":"Component of the centrioles that acts as a positive regulator of centriole elongation (PubMed:24997988). Promotes assembly of centriolar distal appendage, a structure at the distal end of the mother centriole that acts as an anchor of the cilium, and is required for recruitment of centriolar distal appendages proteins CEP83, SCLT1, CEP89, FBF1 and CEP164. Not required for centriolar satellite integrity or RAB8 activation. Required for primary cilium formation (PubMed:23769972). Required for sonic hedgehog/SHH signaling and for proteolytic processing of GLI3","subcellular_location":"Cytoplasm, cytoskeleton, cilium basal body; Cytoplasm, cytoskeleton, microtubule organizing center, centrosome, centriole","url":"https://www.uniprot.org/uniprotkb/Q4AC94/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/C2CD3","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/C2CD3","total_profiled":1310},"omim":[{"mim_id":"615948","title":"OROFACIODIGITAL SYNDROME XIV; OFD14","url":"https://www.omim.org/entry/615948"},{"mim_id":"615944","title":"C2 CALCIUM-DEPENDENT DOMAIN-CONTAINING PROTEIN 3; C2CD3","url":"https://www.omim.org/entry/615944"},{"mim_id":"300170","title":"OFD1 CENTRIOLE AND CENTRIOLAR SATELLITE PROTEIN; OFD1","url":"https://www.omim.org/entry/300170"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Centrosome","reliability":"Supported"},{"location":"Basal body","reliability":"Supported"},{"location":"Acrosome","reliability":"Additional"},{"location":"Equatorial segment","reliability":"Additional"},{"location":"Principal piece","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/C2CD3"},"hgnc":{"alias_symbol":["DKFZP586P0123"],"prev_symbol":[]},"alphafold":{"accession":"Q4AC94","domains":[{"cath_id":"2.60.40.150","chopping":"29-169","consensus_level":"high","plddt":80.5744,"start":29,"end":169},{"cath_id":"2.60.40.150","chopping":"533-551_576-702","consensus_level":"high","plddt":80.2621,"start":533,"end":702},{"cath_id":"2.60.40.150","chopping":"804-969","consensus_level":"medium","plddt":80.0045,"start":804,"end":969},{"cath_id":"2.60.40","chopping":"1023-1041_1054-1162_1171-1187","consensus_level":"medium","plddt":76.7797,"start":1023,"end":1187},{"cath_id":"2.60.40.150","chopping":"1191-1303_1315-1347_1363-1389","consensus_level":"medium","plddt":82.2339,"start":1191,"end":1389},{"cath_id":"2.60.40.150","chopping":"1404-1562","consensus_level":"medium","plddt":79.6753,"start":1404,"end":1562},{"cath_id":"2.60.40.150","chopping":"1634-1652_1660-1777","consensus_level":"high","plddt":79.1327,"start":1634,"end":1777}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q4AC94","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q4AC94-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q4AC94-F1-predicted_aligned_error_v6.png","plddt_mean":55.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=C2CD3","jax_strain_url":"https://www.jax.org/strain/search?query=C2CD3"},"sequence":{"accession":"Q4AC94","fasta_url":"https://rest.uniprot.org/uniprotkb/Q4AC94.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q4AC94/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q4AC94"}},"corpus_meta":[{"pmid":"24997988","id":"PMC_24997988","title":"The oral-facial-digital syndrome gene C2CD3 encodes a positive regulator of centriole elongation.","date":"2014","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/24997988","citation_count":116,"is_preprint":false},{"pmid":"19004860","id":"PMC_19004860","title":"C2cd3 is required for cilia formation and Hedgehog signaling in mouse.","date":"2008","source":"Development (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/19004860","citation_count":85,"is_preprint":false},{"pmid":"30988386","id":"PMC_30988386","title":"CEP120 interacts with C2CD3 and Talpid3 and is required for centriole appendage assembly and ciliogenesis.","date":"2019","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/30988386","citation_count":37,"is_preprint":false},{"pmid":"27094867","id":"PMC_27094867","title":"Mutations in human C2CD3 cause skeletal dysplasia and provide new insights into phenotypic and cellular consequences of altered C2CD3 function.","date":"2016","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/27094867","citation_count":30,"is_preprint":false},{"pmid":"30097616","id":"PMC_30097616","title":"Characterization of three ciliopathy pedigrees expands the phenotype associated with biallelic C2CD3 variants.","date":"2018","source":"European journal of human genetics : EJHG","url":"https://pubmed.ncbi.nlm.nih.gov/30097616","citation_count":22,"is_preprint":false},{"pmid":"34211969","id":"PMC_34211969","title":"Centriolar Protein C2cd3 Is Required for Craniofacial Development.","date":"2021","source":"Frontiers in cell and developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/34211969","citation_count":6,"is_preprint":false},{"pmid":"33805906","id":"PMC_33805906","title":"Mutation in the Ciliary Protein C2CD3 Reveals Organ-Specific Mechanisms of Hedgehog Signal Transduction in Avian Embryos.","date":"2021","source":"Journal of developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/33805906","citation_count":6,"is_preprint":false},{"pmid":"40667239","id":"PMC_40667239","title":"The Luminal Ring Protein C2CD3 Acts as a Radial In-to-Out Organizer of the Distal Centriole and Appendages.","date":"2025","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/40667239","citation_count":5,"is_preprint":false},{"pmid":"38810379","id":"PMC_38810379","title":"The ciliary protein C2cd3 is required for mandibular musculoskeletal tissue patterning.","date":"2024","source":"Differentiation; research in biological diversity","url":"https://pubmed.ncbi.nlm.nih.gov/38810379","citation_count":1,"is_preprint":false},{"pmid":"41364719","id":"PMC_41364719","title":"The luminal ring protein C2CD3 acts as a radial in-to-out organizer of the distal centriole and appendages.","date":"2025","source":"PLoS biology","url":"https://pubmed.ncbi.nlm.nih.gov/41364719","citation_count":1,"is_preprint":false},{"pmid":"39734585","id":"PMC_39734585","title":"Multiple Fibrolipomas of the Tongue: A Rare Case Report of a Pediatric Patient With Whole Exome Sequencing of the C2CD3 Gene.","date":"2024","source":"Case reports in dentistry","url":"https://pubmed.ncbi.nlm.nih.gov/39734585","citation_count":1,"is_preprint":false},{"pmid":"39690811","id":"PMC_39690811","title":"Use of patient-derived cell models for characterization of compound heterozygous hypomorphic C2CD3 variants in a patient with isolated nephronophthisis.","date":"2025","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/39690811","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.04.28.648957","title":"SSNA1 organizes the distal luminal centriolar network and promotes ciliogenesis without microtubule association","date":"2025-04-28","source":"bioRxiv","url":"https://doi.org/10.1101/2025.04.28.648957","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.04.22.650004","title":"<i>C. elegans</i>  SAS-1 ensures centriole integrity and ciliary function, and operates with SSNA-1","date":"2025-04-24","source":"bioRxiv","url":"https://doi.org/10.1101/2025.04.22.650004","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":9266,"output_tokens":2314,"usd":0.031254,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9368,"output_tokens":3002,"usd":0.060945,"stage2_stop_reason":"end_turn"},"total_usd":0.092199,"stage1_batch_id":"msgbatch_0179Z2pxRYBsXi2xADneafRw","stage2_batch_id":"msgbatch_01LaY9ZaVdgjWArcZo9eqQE5","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2008,\n      \"finding\": \"C2cd3 is required for ciliogenesis and intracellular Hedgehog signal transduction in mouse embryos; loss of C2cd3 disrupts cilia formation, impairs proteolytic processing of Gli3, and C2cd3 protein localizes to the basal body consistent with its function in ciliogenesis. Double-mutant analyses placed C2cd3 as an essential regulator of Hedgehog signal transduction.\",\n      \"method\": \"Forward genetic screen (ENU mutagenesis), genetic mapping, sequence analysis, double-mutant epistasis analysis, immunolocalization, Gli3 processing assay\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (genetic epistasis, immunolocalization, Gli3 processing assay) in a focused study; foundational mechanism paper replicated by subsequent work\",\n      \"pmids\": [\"19004860\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"C2CD3 localizes to the distal end of centrioles, physically associates with OFD1, and positively promotes centriole elongation; overexpression of C2CD3 triggers centriole hyperelongation, whereas loss of C2CD3 results in short centrioles lacking subdistal and distal appendages. OFD1 acts as a negative regulator of C2CD3's elongation-promoting activity.\",\n      \"method\": \"Immunofluorescence co-localization, co-immunoprecipitation (physical association with OFD1), overexpression and loss-of-function centriole length measurements, genetic epistasis with OFD1 deletion\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal functional assays (OE + KD), co-IP, precise subcellular localization with functional consequence, replicated across two affected families and model systems\",\n      \"pmids\": [\"24997988\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Loss of C2CD3 in patient-derived fibroblasts reduces cilia formation and impairs basal body maturation; however, the distal appendage protein CEP164 is still recruited to the basal body in C2CD3-defective cells, indicating CEP164 recruitment alone is not sufficient for efficient axonemal extension.\",\n      \"method\": \"Patient-derived fibroblast cultures, immunofluorescence for ciliogenesis markers including CEP164 localization\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — single lab, cell-based functional assay with specific mechanistic conclusion about CEP164 sufficiency, single method\",\n      \"pmids\": [\"27094867\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CEP120 interacts with C2CD3 (and Talpid3) at the distal ends of centrioles; loss of CEP120 impairs recruitment of C2CD3 to the distal centriole, disrupting centriole appendage assembly and ciliogenesis. A disease-associated CEP120 mutant (I975S) has reduced affinity for C2CD3 and perturbs cilia assembly.\",\n      \"method\": \"CRISPR/Cas9 knockout of CEP120 in RPE1 cells, co-immunoprecipitation (CEP120–C2CD3 interaction), immunofluorescence for C2CD3/Talpid3 localization, mutant affinity comparison\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, CRISPR KO with defined cellular phenotype and localization readout, disease-mutant mechanistic validation, single lab\",\n      \"pmids\": [\"30988386\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Conditional deletion of C2cd3 in cranial neural crest cells causes craniofacial-specific defects; analysis of N-terminal C2CD3N-C2 domain deletion versus C-terminal PKC-C2 domain deletion reveals that the N-terminal C2CD3N-C2 domain is critical for early embryonic development and has a craniofacial-specific function.\",\n      \"method\": \"Conditional allelic series (tissue-specific Cre-lox), phenotypic analysis of domain-specific deletions in mouse, isoform characterization\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — domain-specific conditional KO with defined craniofacial phenotype, single lab, no biochemical assays\",\n      \"pmids\": [\"34211969\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"C2CD3 adopts a radially symmetric 9-fold organization within the centriole's distal lumen, forming a ~100 nm luminal ring (~27 nodes). Its C-terminal region is close to this luminal ring and its N-terminal region is close to a hook-like structure attaching to the A-microtubule. C2CD3 directly interacts with MNR of the DISCO complex (MNR/CEP90/OFD1) to recruit it to future appendage sites. C2CD3 depletion destabilizes the luminal ring network (C2CD3/SFI1/centrin-2/CEP135/NA14) and the distal tip protein CEP162, but key structural elements remain intact permitting centriole duplication. C2CD3 thus functions as an architectural hub scaffolding the distal centriole and directing appendage formation.\",\n      \"method\": \"Ultrastructure Expansion Microscopy (U-ExM), iterative U-ExM, in situ cryo-electron tomography (cryo-ET), C2CD3 depletion/KO with quantitative protein recruitment assays, direct interaction assay (C2CD3–MNR), domain localization mapping\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-ET structural analysis combined with U-ExM and functional depletion studies across multiple orthogonal methods; peer-reviewed study with mechanistic detail\",\n      \"pmids\": [\"41364719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Biallelic hypomorphic missense C2CD3 variants reduce C2CD3 localization to the basal body, shorten cilia, reduce ciliation frequency in kidney epithelial cells, and dysregulate SHH signaling (reduced GLI3 activator and GLI1 mRNA). Rescue experiments in C2CD3 KO RPE-1 cells confirmed each variant's reduced capacity to restore ciliogenesis.\",\n      \"method\": \"Patient-derived fibroblasts and urinary renal epithelial cells, C2CD3 KO RPE-1 rescue assay, immunofluorescence for C2CD3 basal body localization, cilia length and frequency measurements, GLI1/GLI3 expression assays\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple cell models, KO rescue experiments, SHH pathway readouts, single lab\",\n      \"pmids\": [\"39690811\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A hierarchical targeting axis exists in the distal centriolar lumen where C2CD3 is required upstream for SSNA1 localization; C2CD3 KO results in loss of SSNA1 from the distal lumen (C2CD3–SSNA1–LRRCC1 axis).\",\n      \"method\": \"KO-validated antibody, super-resolution imaging with expansion microscopy, KO analysis of targeting hierarchy\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — super-resolution localization and KO hierarchy study, preprint, single lab\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"C2CD3 is a centriolar protein that localizes to the distal lumen of centrioles in a 9-fold radially symmetric arrangement, where it forms a luminal ring structure and extends a hook-like projection to the A-microtubule; it promotes centriole elongation, scaffolds the distal centriole end by stabilizing the luminal ring network (with SFI1/centrin-2/CEP135/NA14) and directly recruits the DISCO complex (via MNR interaction) to future appendage sites, thereby orchestrating distal appendage assembly and ciliogenesis, and its loss disrupts Hedgehog signal transduction by impairing Gli3 processing.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"C2CD3 is a centriolar architectural protein that scaffolds the distal centriole and directs the assembly of centriolar appendages required for ciliogenesis and Hedgehog signal transduction [#0, #5]. Within the distal centriolar lumen it adopts a 9-fold radially symmetric organization, forming a ~100 nm luminal ring whose C-terminal region lies near the ring and whose N-terminal region projects toward a hook-like structure attaching to the A-microtubule; its depletion destabilizes the luminal ring network (with SFI1, centrin-2, CEP135 and NA14) and the distal tip protein CEP162 [#5]. C2CD3 directly engages MNR of the DISCO complex (MNR/CEP90/OFD1) to recruit it to future appendage sites, and acts upstream in a hierarchical targeting axis required for SSNA1 localization to the distal lumen [#5, #7]. Functionally, C2CD3 promotes centriole elongation \\u2014 overexpression drives hyperelongation while loss yields short centrioles lacking subdistal and distal appendages \\u2014 an activity negatively regulated by its binding partner OFD1 [#1]. Its recruitment to the distal centriole depends on CEP120, and a disease-associated CEP120 mutant with reduced C2CD3 affinity perturbs cilia assembly [#3]. Loss or hypomorphic mutation of C2CD3 impairs basal body maturation, shortens and reduces cilia, and disrupts Hedgehog/SHH signaling through defective GLI3 processing and reduced GLI activator output, with biallelic hypomorphic missense variants causing a human ciliopathy phenotype [#0, #6].\",\n  \"teleology\": [\n    {\n      \"year\": 2008,\n      \"claim\": \"Established C2CD3 as an essential basal-body regulator of ciliogenesis and a required component of intracellular Hedgehog signal transduction, answering whether the gene functions in cilia-dependent signaling.\",\n      \"evidence\": \"ENU forward genetic screen in mouse with epistasis, immunolocalization, and Gli3 processing assays\",\n      \"pmids\": [\"19004860\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the molecular partners or structural role of C2CD3 at the centriole\", \"Mechanism linking basal body localization to Gli3 processing unresolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Localized C2CD3 to the distal centriole and assigned it a centriole-elongation function counterbalanced by OFD1, defining its first direct physical partner and its role in appendage formation.\",\n      \"evidence\": \"Immunofluorescence, co-IP with OFD1, overexpression/knockdown length measurements, and OFD1-deletion epistasis\",\n      \"pmids\": [\"24997988\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve how C2CD3 organizes appendage assembly structurally\", \"Direct substrates or scaffold architecture unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showed in patient fibroblasts that C2CD3 loss impairs basal body maturation and ciliogenesis even when the distal appendage protein CEP164 is recruited, establishing that CEP164 recruitment is insufficient for axonemal extension.\",\n      \"evidence\": \"Patient-derived fibroblast immunofluorescence for ciliogenesis and CEP164 markers\",\n      \"pmids\": [\"27094867\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single method, single lab\", \"Did not identify the missing step downstream of CEP164 recruitment\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified CEP120 as required for recruiting C2CD3 to the distal centriole, placing C2CD3 within a targeting hierarchy for appendage assembly and linking a disease mutation to reduced C2CD3 binding.\",\n      \"evidence\": \"CRISPR KO of CEP120 in RPE1 cells, reciprocal co-IP, localization imaging, and disease-mutant affinity comparison\",\n      \"pmids\": [\"30988386\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the C2CD3 binding interface on CEP120\", \"Order of recruitment relative to other distal proteins unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Dissected domain-specific requirements in vivo, showing the N-terminal C2CD3N-C2 domain is critical for early development and craniofacial morphogenesis, distinguishing functions of the two C2 domains.\",\n      \"evidence\": \"Tissue-specific conditional Cre-lox allelic series with domain-specific deletions in mouse\",\n      \"pmids\": [\"34211969\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No biochemical assignment of molecular activity to either domain\", \"Mechanism of craniofacial specificity unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Resolved the structural role of C2CD3 as a 9-fold symmetric luminal-ring scaffold that stabilizes the distal centriole network and directly recruits the DISCO complex via MNR to direct appendage formation.\",\n      \"evidence\": \"U-ExM, iterative U-ExM, in situ cryo-ET, depletion/KO recruitment assays, and direct C2CD3\\u2013MNR interaction and domain mapping\",\n      \"pmids\": [\"41364719\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-resolution structure of the C2CD3 ring not determined\", \"How C2CD3 elongation activity integrates with its scaffold function unresolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Confirmed the human disease relevance of C2CD3 by showing biallelic hypomorphic missense variants reduce basal body localization, impair ciliation, and dysregulate SHH/GLI output, with KO-rescue validation of each variant.\",\n      \"evidence\": \"Patient fibroblasts and urinary renal epithelial cells, C2CD3 KO RPE-1 rescue, ciliogenesis quantification, and GLI1/GLI3 expression assays\",\n      \"pmids\": [\"39690811\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Genotype-phenotype correlation across the variant spectrum not established\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Placed C2CD3 upstream of SSNA1 in a distal-lumen targeting axis, extending the hierarchy of proteins it organizes.\",\n      \"evidence\": \"KO-validated antibody and super-resolution expansion microscopy of targeting hierarchy (preprint)\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, single lab, not peer-reviewed\", \"Whether C2CD3\\u2013SSNA1 dependency is direct or indirect unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How C2CD3's distinct activities \\u2014 centriole elongation, luminal ring scaffolding, and hierarchical appendage-protein recruitment \\u2014 are mechanistically coordinated, and how these translate into the precise control of Gli3 processing, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking scaffold architecture to elongation control\", \"Molecular link between distal appendage assembly and Hedgehog/Gli3 processing undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [5, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005814\", \"supporting_discovery_ids\": [1, 5]},\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [1, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [1, 5]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 6]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [0, 4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"OFD1\", \"CEP120\", \"MNR\", \"SFI1\", \"CETN2\", \"CEP135\", \"SSNA1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}