{"gene":"CEP19","run_date":"2026-04-28T17:28:52","timeline":{"discoveries":[{"year":2017,"finding":"CEP19 is recruited to the ciliary base by the centriolar CEP350/FOP complex, where it specifically captures GTP-bound RABL2B (activated via its intrinsic nucleotide exchange). Activated RABL2B then captures and releases the IFT-B holocomplex from pre-docked IFT-B complexes, initiating ciliary entry of IFT.","method":"Affinity-purification/mass spectrometry, Co-IP, GTPase binding assays, functional cell-based assays","journal":"Developmental Cell","confidence":"High","confidence_rationale":"Tier 1-2 — AP-MS + multiple binding assays + functional reconstitution + mechanistic dissection in single rigorous study","pmids":["28625565"],"is_preprint":false},{"year":2017,"finding":"CEP19 is recruited to the centriole via binding to FGFR1OP (FOP), and RABL2 recruitment to the mother centriole/basal body is dependent on CEP19. RABL2 binds CEP19 and the IFT74-IFT81 heterodimer in a mutually exclusive manner, and GTP-bound RABL2 interacts with the IFT-B complex via IFT74-IFT81.","method":"Co-immunoprecipitation, RABL2 gene disruption in Chlamydomonas, exogenous expression of RABL2 mutants in human cells, fluorescence microscopy","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, genetic disruption, mutagenesis, replicated across two independent labs","pmids":["28428259"],"is_preprint":false},{"year":2013,"finding":"CEP19 localizes to the centrosome and primary cilia; homozygous loss-of-function in humans and mice causes morbid obesity, hyperphagia, glucose intolerance, and insulin resistance, establishing CEP19 as a ciliary protein required for energy balance regulation.","method":"Homozygosity mapping, sequencing, Cep19-knockout mouse model with metabolic phenotyping, immunolocalization","journal":"American Journal of Human Genetics","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with defined metabolic phenotype replicated in human family and mouse model","pmids":["24268657"],"is_preprint":false},{"year":2018,"finding":"The CEP350/FOP/CEP19 module at the distal centriole is regulated by Talpid3 and C2CD3; Talpid3, C2CD3, and OFD1 differentially control assembly of sub-distal appendages, the CEP350/FOP/CEP19 module, centriolar satellites, and actin networks during centriole maturation.","method":"RNAi knockdown, rescue experiments, fluorescence microscopy, epistasis analysis in human cells","journal":"Nature Communications","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis with multiple knockdowns and phenotypic readouts, single lab","pmids":["30258116"],"is_preprint":false},{"year":2019,"finding":"Ablation of CEP19 leads to mis-localization of ciliary GPCRs (GPR161), placing CEP19 upstream of RABL2-mediated GPCR ciliary trafficking at the ciliary base.","method":"siRNA knockdown, fluorescence microscopy, GPCR localization assays in mammalian cells","journal":"Journal of Cell Science","confidence":"Medium","confidence_rationale":"Tier 2 — clean KD with defined ciliary localization phenotype, single lab","pmids":["30578315"],"is_preprint":false},{"year":2022,"finding":"GTP-bound RABL2 and IFT25-IFT27 bind the IFT74-IFT81 dimer of IFT-B in a mutually exclusive manner. GTP-locked RABL2(Q80L) phenocopies IFT27-KO cells (BBSome accumulation in cilia, failure to export ciliary GPCRs), and RABL2(Q80L) enters cilia in a CEP19-dependent manner.","method":"RABL2 GTP-locked mutant expression, IFT27-KO cells, fluorescence microscopy, Co-IP, functional ciliary export assays","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 — KO/mutant expression with defined pathway phenotype, single lab, multiple orthogonal methods","pmids":["36074075"],"is_preprint":false},{"year":2023,"finding":"The IFT81/74 coiled-coil region acts as an unconventional GAP for RabL2, enhancing its GTP hydrolysis rate. CEP19 binds RabL2 at the basal body prior to IFT complex association; structural models for the RabL2-IFT complex were validated in vitro and in cellulo, explaining how RabL2 dissociates from anterograde IFT trains after departure from the ciliary base.","method":"In vitro reconstitution of pentameric IFT complex, GTPase activity assay, structural modeling, mutagenesis, functional cell-based validation","journal":"The EMBO Journal","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution + GTPase assay + mutagenesis + structural validation, single rigorous study","pmids":["37606072"],"is_preprint":false}],"current_model":"CEP19 is a centrosomal/ciliary base protein recruited by the CEP350/FOP complex that acts as a GTP-state sensor for RABL2/RabL2: CEP19 captures GTP-bound RABL2 at the basal body, enabling RABL2 to release the IFT-B holocomplex from a pre-docked pool to initiate intraflagellar transport entry into cilia, after which the IFT81/74 coiled-coil region acts as a GAP to hydrolyze RABL2's GTP and dissociate it from anterograde IFT trains; this CEP19-RABL2-IFT-B axis also controls BBSome-mediated ciliary GPCR export, and its loss causes morbid obesity and ciliopathy features in humans and mice."},"narrative":{"teleology":[{"year":2013,"claim":"Before CEP19's molecular function was known, genetic evidence established that it is a centrosome/cilium-associated protein whose loss causes a morbid obesity ciliopathy, demonstrating a previously unrecognized link between this uncharacterized centriolar protein and systemic energy balance.","evidence":"Homozygosity mapping in a consanguineous family plus Cep19-knockout mouse with metabolic phenotyping and immunolocalization","pmids":["24268657"],"confidence":"High","gaps":["Molecular mechanism by which CEP19 loss leads to obesity was unknown","No binding partners or pathway placement identified"]},{"year":2017,"claim":"Two concurrent studies revealed that CEP19 is recruited to the centriole by CEP350/FOP and functions as a receptor for GTP-bound RABL2 at the basal body, establishing the CEP19–RABL2–IFT-B axis as the mechanism for initiating IFT ciliary entry.","evidence":"AP-MS, reciprocal Co-IP, GTPase binding assays, RABL2 gene disruption in Chlamydomonas, mutant expression in human cells, fluorescence microscopy (two independent labs)","pmids":["28625565","28428259"],"confidence":"High","gaps":["Structural basis for CEP19–RABL2 and RABL2–IFT-B interactions not resolved","Mechanism of RABL2 GTP hydrolysis and train dissociation unknown","Connection between IFT initiation defect and obesity phenotype not mechanistically established"]},{"year":2018,"claim":"Epistasis analysis placed the CEP350/FOP/CEP19 module downstream of Talpid3 and C2CD3 during centriole maturation, establishing the hierarchical assembly pathway that positions CEP19 at the distal centriole.","evidence":"RNAi knockdown with rescue experiments and fluorescence microscopy epistasis in human cells","pmids":["30258116"],"confidence":"Medium","gaps":["Direct biochemical interactions between Talpid3/C2CD3 and CEP19 module not demonstrated","Whether this hierarchy operates identically in vivo remains untested"]},{"year":2019,"claim":"Functional studies showed that CEP19 loss causes mis-localization of ciliary GPCRs (GPR161), extending the CEP19–RABL2 pathway beyond IFT initiation to ciliary receptor trafficking.","evidence":"siRNA knockdown with GPCR ciliary localization assays in mammalian cells","pmids":["30578315"],"confidence":"Medium","gaps":["Whether CEP19 affects GPCR export directly through BBSome regulation or indirectly via general IFT defects was unresolved","Range of affected ciliary cargoes not systematically surveyed"]},{"year":2022,"claim":"Demonstration that GTP-locked RABL2(Q80L) phenocopies IFT27-KO (BBSome accumulation, GPCR export failure) and enters cilia in a CEP19-dependent manner revealed that RABL2 and IFT25–IFT27 compete for the same IFT74–IFT81 binding site, mechanistically coupling IFT initiation to BBSome-mediated ciliary export.","evidence":"RABL2 GTP-locked mutant expression, IFT27-KO cells, Co-IP, functional ciliary export assays","pmids":["36074075"],"confidence":"Medium","gaps":["GAP identity for RABL2 GTP hydrolysis on IFT trains was still unknown","Structural basis for mutual exclusivity of RABL2 and IFT25–IFT27 binding not resolved"]},{"year":2023,"claim":"Reconstitution of the pentameric IFT complex identified the IFT81/74 coiled-coil as an unconventional GAP for RABL2, explaining how RABL2 dissociates from anterograde IFT trains after CEP19-dependent loading at the ciliary base and completing the GTPase cycle model.","evidence":"In vitro reconstitution, GTPase activity assay, structural modeling, mutagenesis, cell-based functional validation","pmids":["37606072"],"confidence":"High","gaps":["High-resolution atomic structure of the CEP19–RABL2 complex remains unavailable","How CEP19–RABL2 pathway defects mechanistically drive obesity (neuronal vs. systemic ciliary dysfunction) is unresolved"]},{"year":null,"claim":"The precise mechanism by which CEP19/RABL2/IFT-B pathway disruption leads to morbid obesity — whether through defective ciliary signaling in hypothalamic neurons, adipocytes, or other cell types — remains an open question.","evidence":"","pmids":[],"confidence":"High","gaps":["Cell-type-specific contributions to the obesity phenotype are not delineated","Atomic-resolution structures for CEP19 and its complexes are lacking","Whether CEP19 has functions independent of RABL2 and IFT is unexplored"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1]}],"localization":[{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[0,1,2,3]},{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[2]}],"pathway":[{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[0,1,3,6]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,1,5,6]}],"complexes":["CEP350/FOP/CEP19"],"partners":["RABL2B","FGFR1OP","CEP350","IFT74","IFT81"],"other_free_text":[]},"mechanistic_narrative":"CEP19 is a centrosomal and ciliary base protein that functions as a critical gating factor for intraflagellar transport (IFT) initiation by capturing GTP-bound RABL2 at the basal body. CEP19 is recruited to the distal centriole through the CEP350/FOP complex, and its binding to activated RABL2 enables RABL2 to engage and release the pre-docked IFT-B holocomplex via IFT74–IFT81, thereby licensing ciliary entry of IFT trains; after departure, the IFT81/74 coiled-coil acts as a GAP to hydrolyze RABL2-GTP and dissociate RABL2 from anterograde trains [PMID:28625565, PMID:28428259, PMID:37606072]. This CEP19–RABL2–IFT-B axis also governs BBSome-mediated export of ciliary GPCRs such as GPR161, linking it to ciliary signaling homeostasis [PMID:30578315, PMID:36074075]. Homozygous loss-of-function mutations in CEP19 cause morbid obesity with hyperphagia, glucose intolerance, and insulin resistance in both humans and mice [PMID:24268657]."},"prefetch_data":{"uniprot":{"accession":"Q96LK0","full_name":"Centrosomal protein of 19 kDa","aliases":[],"length_aa":163,"mass_kda":19.2,"function":"Required for ciliation (PubMed:28428259, PubMed:28625565, PubMed:28659385). Recruits the RABL2B GTPase to the ciliary base to initiate ciliation. After specifically capturing the activated GTP-bound RABL2B, the CEP19-RABL2B complex binds intraflagellar transport (IFT) complex B from the large pool pre-docked at the base of the cilium and thus triggers its entry into the cilia (PubMed:28428259, PubMed:28625565). Involved in the early steps in cilia formation by recruiting the ciliary vesicles (CVs) to the distal end of the mother centriole where they fuse to initiate cilium assembly. Involved in microtubule (MT) anchoring to the centrosomes (PubMed:28659385)","subcellular_location":"Cytoplasm, cytoskeleton, microtubule organizing center, centrosome, centriole; Cytoplasm, cytoskeleton, spindle pole; Cytoplasm, cytoskeleton, cilium basal body","url":"https://www.uniprot.org/uniprotkb/Q96LK0/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CEP19","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":[],"url":"https://opencell.sf.czbiohub.org/search/CEP19","total_profiled":1310},"omim":[{"mim_id":"617870","title":"CENTROSOMAL PROTEIN 350; CEP350","url":"https://www.omim.org/entry/617870"},{"mim_id":"615703","title":"MORBID OBESITY AND SPERMATOGENIC FAILURE; MOSPGF","url":"https://www.omim.org/entry/615703"},{"mim_id":"615586","title":"CENTROSOMAL PROTEIN, 19-KD; CEP19","url":"https://www.omim.org/entry/615586"},{"mim_id":"605413","title":"RAB, MEMBER OF RAS ONCOGENE FAMILY-LIKE 2B; RABL2B","url":"https://www.omim.org/entry/605413"},{"mim_id":"605412","title":"RAB, MEMBER OF RAS ONCOGENE FAMILY-LIKE 2A; RABL2A","url":"https://www.omim.org/entry/605412"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Centrosome","reliability":"Supported"},{"location":"Basal body","reliability":"Supported"},{"location":"Nucleoplasm","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/CEP19"},"hgnc":{"alias_symbol":["MGC14126"],"prev_symbol":["C3orf34"]},"alphafold":{"accession":"Q96LK0","domains":[{"cath_id":"-","chopping":"4-99","consensus_level":"high","plddt":89.4672,"start":4,"end":99},{"cath_id":"1.20.5","chopping":"106-131","consensus_level":"medium","plddt":82.7669,"start":106,"end":131}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96LK0","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96LK0-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96LK0-F1-predicted_aligned_error_v6.png","plddt_mean":82.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CEP19","jax_strain_url":"https://www.jax.org/strain/search?query=CEP19"},"sequence":{"accession":"Q96LK0","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96LK0.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96LK0/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96LK0"}},"corpus_meta":[{"pmid":"28625565","id":"PMC_28625565","title":"The CEP19-RABL2 GTPase Complex Binds IFT-B to Initiate Intraflagellar Transport at the Ciliary Base.","date":"2017","source":"Developmental cell","url":"https://pubmed.ncbi.nlm.nih.gov/28625565","citation_count":94,"is_preprint":false},{"pmid":"28428259","id":"PMC_28428259","title":"RABL2 interacts with the intraflagellar transport-B complex and CEP19 and participates in ciliary assembly.","date":"2017","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/28428259","citation_count":75,"is_preprint":false},{"pmid":"24268657","id":"PMC_24268657","title":"Morbid obesity resulting from inactivation of the ciliary protein CEP19 in humans and mice.","date":"2013","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/24268657","citation_count":52,"is_preprint":false},{"pmid":"30258116","id":"PMC_30258116","title":"A distal centriolar protein network controls organelle maturation and asymmetry.","date":"2018","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/30258116","citation_count":41,"is_preprint":false},{"pmid":"30578315","id":"PMC_30578315","title":"RABL2 positively controls localization of GPCRs in mammalian primary cilia.","date":"2019","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/30578315","citation_count":25,"is_preprint":false},{"pmid":"29127258","id":"PMC_29127258","title":"Homozygous mutation in CEP19, a gene mutated in morbid obesity, in Bardet-Biedl syndrome with predominant postaxial polydactyly.","date":"2017","source":"Journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/29127258","citation_count":24,"is_preprint":false},{"pmid":"32681070","id":"PMC_32681070","title":"Analysis of the \"centrosome-ome\" identifies MCPH1 deletion as a cause of centrosome amplification in human cancer.","date":"2020","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/32681070","citation_count":13,"is_preprint":false},{"pmid":"36474803","id":"PMC_36474803","title":"Genetic and epigenetic interplay allows rapid transgenerational adaptation to metal pollution in zebrafish.","date":"2022","source":"Environmental epigenetics","url":"https://pubmed.ncbi.nlm.nih.gov/36474803","citation_count":10,"is_preprint":false},{"pmid":"36074075","id":"PMC_36074075","title":"CEP19-RABL2-IFT-B axis controls BBSome-mediated ciliary GPCR export.","date":"2022","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/36074075","citation_count":9,"is_preprint":false},{"pmid":"37606072","id":"PMC_37606072","title":"The IFT81-IFT74 complex acts as an unconventional RabL2 GTPase-activating protein during intraflagellar transport.","date":"2023","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/37606072","citation_count":9,"is_preprint":false},{"pmid":"34646484","id":"PMC_34646484","title":"Comparative transcriptome provides insights into the selection adaptation between wild and farmed foxes.","date":"2021","source":"Ecology and evolution","url":"https://pubmed.ncbi.nlm.nih.gov/34646484","citation_count":6,"is_preprint":false},{"pmid":"37540954","id":"PMC_37540954","title":"Comparison of symmetrical and asymmetrical cleavage 2-cell embryos of porcine by Smart-seq2.","date":"2023","source":"Theriogenology","url":"https://pubmed.ncbi.nlm.nih.gov/37540954","citation_count":3,"is_preprint":false},{"pmid":"38585545","id":"PMC_38585545","title":"Severe Early-Onset Obesity and Diabetic Ketoacidosis due to a Novel Homozygous c.169C>T p.Arg57* Variant in CEP19 Gene.","date":"2023","source":"Molecular syndromology","url":"https://pubmed.ncbi.nlm.nih.gov/38585545","citation_count":0,"is_preprint":false},{"pmid":"28697332","id":"PMC_28697332","title":"Gating Ciliary Transport.","date":"2017","source":"Developmental cell","url":"https://pubmed.ncbi.nlm.nih.gov/28697332","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7899,"output_tokens":1813,"usd":0.025446},"stage2":{"model":"claude-opus-4-6","input_tokens":5065,"output_tokens":2079,"usd":0.11595},"total_usd":0.141396,"stage1_batch_id":"msgbatch_011kfMfE81o6CTcyhVUqumuW","stage2_batch_id":"msgbatch_01DTputS6WNkH745x1nVSoBo","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2017,\n      \"finding\": \"CEP19 is recruited to the ciliary base by the centriolar CEP350/FOP complex, where it specifically captures GTP-bound RABL2B (activated via its intrinsic nucleotide exchange). Activated RABL2B then captures and releases the IFT-B holocomplex from pre-docked IFT-B complexes, initiating ciliary entry of IFT.\",\n      \"method\": \"Affinity-purification/mass spectrometry, Co-IP, GTPase binding assays, functional cell-based assays\",\n      \"journal\": \"Developmental Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — AP-MS + multiple binding assays + functional reconstitution + mechanistic dissection in single rigorous study\",\n      \"pmids\": [\"28625565\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CEP19 is recruited to the centriole via binding to FGFR1OP (FOP), and RABL2 recruitment to the mother centriole/basal body is dependent on CEP19. RABL2 binds CEP19 and the IFT74-IFT81 heterodimer in a mutually exclusive manner, and GTP-bound RABL2 interacts with the IFT-B complex via IFT74-IFT81.\",\n      \"method\": \"Co-immunoprecipitation, RABL2 gene disruption in Chlamydomonas, exogenous expression of RABL2 mutants in human cells, fluorescence microscopy\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, genetic disruption, mutagenesis, replicated across two independent labs\",\n      \"pmids\": [\"28428259\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"CEP19 localizes to the centrosome and primary cilia; homozygous loss-of-function in humans and mice causes morbid obesity, hyperphagia, glucose intolerance, and insulin resistance, establishing CEP19 as a ciliary protein required for energy balance regulation.\",\n      \"method\": \"Homozygosity mapping, sequencing, Cep19-knockout mouse model with metabolic phenotyping, immunolocalization\",\n      \"journal\": \"American Journal of Human Genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with defined metabolic phenotype replicated in human family and mouse model\",\n      \"pmids\": [\"24268657\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The CEP350/FOP/CEP19 module at the distal centriole is regulated by Talpid3 and C2CD3; Talpid3, C2CD3, and OFD1 differentially control assembly of sub-distal appendages, the CEP350/FOP/CEP19 module, centriolar satellites, and actin networks during centriole maturation.\",\n      \"method\": \"RNAi knockdown, rescue experiments, fluorescence microscopy, epistasis analysis in human cells\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with multiple knockdowns and phenotypic readouts, single lab\",\n      \"pmids\": [\"30258116\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Ablation of CEP19 leads to mis-localization of ciliary GPCRs (GPR161), placing CEP19 upstream of RABL2-mediated GPCR ciliary trafficking at the ciliary base.\",\n      \"method\": \"siRNA knockdown, fluorescence microscopy, GPCR localization assays in mammalian cells\",\n      \"journal\": \"Journal of Cell Science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with defined ciliary localization phenotype, single lab\",\n      \"pmids\": [\"30578315\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GTP-bound RABL2 and IFT25-IFT27 bind the IFT74-IFT81 dimer of IFT-B in a mutually exclusive manner. GTP-locked RABL2(Q80L) phenocopies IFT27-KO cells (BBSome accumulation in cilia, failure to export ciliary GPCRs), and RABL2(Q80L) enters cilia in a CEP19-dependent manner.\",\n      \"method\": \"RABL2 GTP-locked mutant expression, IFT27-KO cells, fluorescence microscopy, Co-IP, functional ciliary export assays\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO/mutant expression with defined pathway phenotype, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"36074075\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"The IFT81/74 coiled-coil region acts as an unconventional GAP for RabL2, enhancing its GTP hydrolysis rate. CEP19 binds RabL2 at the basal body prior to IFT complex association; structural models for the RabL2-IFT complex were validated in vitro and in cellulo, explaining how RabL2 dissociates from anterograde IFT trains after departure from the ciliary base.\",\n      \"method\": \"In vitro reconstitution of pentameric IFT complex, GTPase activity assay, structural modeling, mutagenesis, functional cell-based validation\",\n      \"journal\": \"The EMBO Journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution + GTPase assay + mutagenesis + structural validation, single rigorous study\",\n      \"pmids\": [\"37606072\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CEP19 is a centrosomal/ciliary base protein recruited by the CEP350/FOP complex that acts as a GTP-state sensor for RABL2/RabL2: CEP19 captures GTP-bound RABL2 at the basal body, enabling RABL2 to release the IFT-B holocomplex from a pre-docked pool to initiate intraflagellar transport entry into cilia, after which the IFT81/74 coiled-coil region acts as a GAP to hydrolyze RABL2's GTP and dissociate it from anterograde IFT trains; this CEP19-RABL2-IFT-B axis also controls BBSome-mediated ciliary GPCR export, and its loss causes morbid obesity and ciliopathy features in humans and mice.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CEP19 is a centrosomal and ciliary base protein that functions as a critical gating factor for intraflagellar transport (IFT) initiation by capturing GTP-bound RABL2 at the basal body. CEP19 is recruited to the distal centriole through the CEP350/FOP complex, and its binding to activated RABL2 enables RABL2 to engage and release the pre-docked IFT-B holocomplex via IFT74–IFT81, thereby licensing ciliary entry of IFT trains; after departure, the IFT81/74 coiled-coil acts as a GAP to hydrolyze RABL2-GTP and dissociate RABL2 from anterograde trains [PMID:28625565, PMID:28428259, PMID:37606072]. This CEP19–RABL2–IFT-B axis also governs BBSome-mediated export of ciliary GPCRs such as GPR161, linking it to ciliary signaling homeostasis [PMID:30578315, PMID:36074075]. Homozygous loss-of-function mutations in CEP19 cause morbid obesity with hyperphagia, glucose intolerance, and insulin resistance in both humans and mice [PMID:24268657].\",\n  \"teleology\": [\n    {\n      \"year\": 2013,\n      \"claim\": \"Before CEP19's molecular function was known, genetic evidence established that it is a centrosome/cilium-associated protein whose loss causes a morbid obesity ciliopathy, demonstrating a previously unrecognized link between this uncharacterized centriolar protein and systemic energy balance.\",\n      \"evidence\": \"Homozygosity mapping in a consanguineous family plus Cep19-knockout mouse with metabolic phenotyping and immunolocalization\",\n      \"pmids\": [\"24268657\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Molecular mechanism by which CEP19 loss leads to obesity was unknown\",\n        \"No binding partners or pathway placement identified\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Two concurrent studies revealed that CEP19 is recruited to the centriole by CEP350/FOP and functions as a receptor for GTP-bound RABL2 at the basal body, establishing the CEP19–RABL2–IFT-B axis as the mechanism for initiating IFT ciliary entry.\",\n      \"evidence\": \"AP-MS, reciprocal Co-IP, GTPase binding assays, RABL2 gene disruption in Chlamydomonas, mutant expression in human cells, fluorescence microscopy (two independent labs)\",\n      \"pmids\": [\"28625565\", \"28428259\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis for CEP19–RABL2 and RABL2–IFT-B interactions not resolved\",\n        \"Mechanism of RABL2 GTP hydrolysis and train dissociation unknown\",\n        \"Connection between IFT initiation defect and obesity phenotype not mechanistically established\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Epistasis analysis placed the CEP350/FOP/CEP19 module downstream of Talpid3 and C2CD3 during centriole maturation, establishing the hierarchical assembly pathway that positions CEP19 at the distal centriole.\",\n      \"evidence\": \"RNAi knockdown with rescue experiments and fluorescence microscopy epistasis in human cells\",\n      \"pmids\": [\"30258116\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct biochemical interactions between Talpid3/C2CD3 and CEP19 module not demonstrated\",\n        \"Whether this hierarchy operates identically in vivo remains untested\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Functional studies showed that CEP19 loss causes mis-localization of ciliary GPCRs (GPR161), extending the CEP19–RABL2 pathway beyond IFT initiation to ciliary receptor trafficking.\",\n      \"evidence\": \"siRNA knockdown with GPCR ciliary localization assays in mammalian cells\",\n      \"pmids\": [\"30578315\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether CEP19 affects GPCR export directly through BBSome regulation or indirectly via general IFT defects was unresolved\",\n        \"Range of affected ciliary cargoes not systematically surveyed\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstration that GTP-locked RABL2(Q80L) phenocopies IFT27-KO (BBSome accumulation, GPCR export failure) and enters cilia in a CEP19-dependent manner revealed that RABL2 and IFT25–IFT27 compete for the same IFT74–IFT81 binding site, mechanistically coupling IFT initiation to BBSome-mediated ciliary export.\",\n      \"evidence\": \"RABL2 GTP-locked mutant expression, IFT27-KO cells, Co-IP, functional ciliary export assays\",\n      \"pmids\": [\"36074075\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"GAP identity for RABL2 GTP hydrolysis on IFT trains was still unknown\",\n        \"Structural basis for mutual exclusivity of RABL2 and IFT25–IFT27 binding not resolved\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Reconstitution of the pentameric IFT complex identified the IFT81/74 coiled-coil as an unconventional GAP for RABL2, explaining how RABL2 dissociates from anterograde IFT trains after CEP19-dependent loading at the ciliary base and completing the GTPase cycle model.\",\n      \"evidence\": \"In vitro reconstitution, GTPase activity assay, structural modeling, mutagenesis, cell-based functional validation\",\n      \"pmids\": [\"37606072\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"High-resolution atomic structure of the CEP19–RABL2 complex remains unavailable\",\n        \"How CEP19–RABL2 pathway defects mechanistically drive obesity (neuronal vs. systemic ciliary dysfunction) is unresolved\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The precise mechanism by which CEP19/RABL2/IFT-B pathway disruption leads to morbid obesity — whether through defective ciliary signaling in hypothalamic neurons, adipocytes, or other cell types — remains an open question.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Cell-type-specific contributions to the obesity phenotype are not delineated\",\n        \"Atomic-resolution structures for CEP19 and its complexes are lacking\",\n        \"Whether CEP19 has functions independent of RABL2 and IFT is unexplored\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [0, 1, 2, 3]},\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [0, 1, 3, 6]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 1, 5, 6]}\n    ],\n    \"complexes\": [\n      \"CEP350/FOP/CEP19\"\n    ],\n    \"partners\": [\n      \"RABL2B\",\n      \"FGFR1OP\",\n      \"CEP350\",\n      \"IFT74\",\n      \"IFT81\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}