{"gene":"IFT22","run_date":"2026-04-28T18:06:53","timeline":{"discoveries":[{"year":2010,"finding":"IFT22 was identified as a component of the ~500 kDa core of IFT complex B in Chlamydomonas reinhardtii, alongside IFT88, IFT81, IFT74/72, IFT52, IFT46, IFT27, and IFT25. Chemical cross-linking provided evidence of an association between IFT27 and IFT81, placing IFT22 within a defined subunit architecture of the IFT-B core.","method":"Biochemical fractionation, yeast two-hybrid, bacterial coexpression, chemical cross-linking","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal biochemical methods in a well-characterized Chlamydomonas IFT system","pmids":["20435895"],"is_preprint":false},{"year":2009,"finding":"In Caenorhabditis elegans, the IFT22 ortholog IFTA-2/RABL5 moves in an IFT-like manner within sensory cilia and participates in signaling processes but is not required for cilia construction, establishing it as a potential regulatory rather than structural IFT component.","method":"GFP-tagging, in vivo time-lapse microscopy, IFT velocity measurements, mutant analysis","journal":"Methods in cell biology","confidence":"Medium","confidence_rationale":"Tier 2 — live imaging with IFT rate measurements in C. elegans, single study","pmids":["20409822"],"is_preprint":false},{"year":2009,"finding":"In Trypanosoma brucei, the RABL5/IFT22 ortholog colocalizes with IFT proteins at the basal body and in the flagellum matrix, moves anterogradely, accumulates in short flagella of retrograde IFT mutants, and is restricted to the basal body in anterograde IFT mutants. RNAi knockdown of RABL5 is essential for flagellum construction, producing a phenotype similar to retrograde IFT inactivation with short flagella filled with IFT proteins.","method":"GFP fusion live imaging, RNAi knockdown, analysis of IFT mutant backgrounds","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — live imaging of anterograde movement, epistatic placement in IFT mutants, and RNAi loss-of-function with defined phenotype","pmids":["19240117"],"is_preprint":false},{"year":2012,"finding":"In Chlamydomonas reinhardtii, IFT22 (RABL5 homolog) is confirmed as an IFT-B subunit. Depletion of IFT22 reduces the cellular pool of both IFT complex A and B proteins, yet paradoxically increases the amount of IFT particles in flagella. Overexpression of IFT22 also causes accumulation of IFT particles in flagella. These data establish that IFT22 controls the cellular availability of IFT particles and regulates partitioning of IFT particles between the cell body and flagellar compartments.","method":"RNAi knockdown, overexpression, quantitative immunofluorescence, Western blotting","journal":"Cytoskeleton (Hoboken, N.J.)","confidence":"High","confidence_rationale":"Tier 2 — bidirectional genetic manipulation (knockdown and overexpression) with quantitative readouts of IFT particle distribution","pmids":["22076686"],"is_preprint":false},{"year":2016,"finding":"Affinity proteomics of 217 human ciliary proteins placed IFT22 within the IFT-B complex network, revealing sub-complex interactions consistent with IFT-B core architecture and linking IFT22 to vesicle transport and ubiquitination pathways at cilia.","method":"Affinity proteomics, AP-MS, biochemical validation of sub-complexes","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 — systematic affinity proteomics with biochemical validation, but IFT22 not individually interrogated in depth","pmids":["27173435"],"is_preprint":false},{"year":2016,"finding":"Using the visible immunoprecipitation (VIP) assay, IFT22 was mapped as a peripheral subunit of the IFT-B complex, associated with the peripheral subcomplex (rather than the core) alongside IFT57, IFT38, IFT54, IFT20, and IFT172.","method":"Visible immunoprecipitation (VIP) assay, systematic pairwise protein-protein interaction mapping","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — systematic pairwise interaction mapping across all 16 IFT-B subunits with multiple orthogonal confirmations","pmids":["26980730"],"is_preprint":false},{"year":2018,"finding":"IFT22 knockout cells generated by CRISPR/Cas9 in RPE1 cells showed no defects in ciliogenesis or ciliary protein trafficking, demonstrating that IFT22 is dispensable for IFT-B complex assembly at the ciliary base and for cilia formation in mammalian cells.","method":"CRISPR/Cas9 knockout, ciliogenesis assay, ciliary protein trafficking analysis","journal":"Biology open","confidence":"High","confidence_rationale":"Tier 2 — clean genetic knockout with defined cellular phenotypic readout","pmids":["29654116"],"is_preprint":false},{"year":2020,"finding":"IFT22 (RABL5) is an active GTPase with low intrinsic GTPase activity. In Chlamydomonas, IFT22 is part of the IFT-B1 subcomplex but, independently of IFT-B1 association, binds and stabilizes the Arf-like GTPase BBS3 (ARL6). When both IFT22 and BBS3 are in their GTP-bound states, they cooperatively recruit the BBSome to the basal body for coupling with the IFT-B1 subcomplex and ciliary entry. IFT22 is not required for BBSome transport within cilia, indicating that the BBSome is transferred from IFT22 to IFT trains at the ciliary base.","method":"GTPase activity assay, co-immunoprecipitation, single-particle in vivo fluorescence imaging, biochemical fractionation, functional rescue experiments","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro GTPase assay combined with in vivo single-particle imaging, biochemistry, and genetic analysis across multiple orthogonal methods","pmids":["31953262"],"is_preprint":false},{"year":2014,"finding":"In zebrafish, knockdown of ift22 (anterograde IFT component) suppresses the bbs7-related retrograde intracellular melanosome transport delay, functionally placing IFT22-mediated anterograde transport as a modulator of retrograde transport balance. This epistatic relationship reveals a role for IFT22 in directional intracellular transport.","method":"Morpholino knockdown in zebrafish, melanosome transport assay, genetic epistasis","journal":"Developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis in zebrafish with quantitative transport readout, single study","pmids":["24938409"],"is_preprint":false},{"year":2015,"finding":"High-throughput affinity-purification mass spectrometry (BioPlex) in HEK293T cells identified IFT22 as part of a human protein interaction network, placing it in co-complex with other IFT-B subunits in human cells.","method":"Affinity purification–mass spectrometry (AP-MS), BioPlex network analysis","journal":"Cell","confidence":"Low","confidence_rationale":"Tier 3 — large-scale AP-MS survey, IFT22 not individually validated","pmids":["26186194"],"is_preprint":false}],"current_model":"IFT22 (RABL5) is a Rab-like GTPase and peripheral subunit of the IFT-B complex that controls the cellular pool size of IFT particles and their partitioning into cilia/flagella; in its GTP-bound state it cooperates with BBS3/ARL6 to recruit the BBSome to the basal body for ciliary entry, while being dispensable for ciliogenesis itself in mammalian cells."},"narrative":{"teleology":[{"year":2009,"claim":"Establishing that IFT22 is a motile IFT-associated factor that is not required for cilium construction resolved whether it is a core structural IFT component or a regulatory accessory subunit.","evidence":"GFP-tagged IFTA-2/RABL5 tracked by live imaging in C. elegans sensory cilia; mutant analysis showed normal cilia structure (C. elegans) while RNAi in T. brucei produced short flagella phenocopying retrograde IFT loss","pmids":["20409822","19240117"],"confidence":"High","gaps":["Organism-specific essentiality was unexplained mechanistically","GTPase activity of IFT22 had not been measured","Mammalian function was untested"]},{"year":2010,"claim":"Biochemical placement of IFT22 within the ~500 kDa IFT-B core in Chlamydomonas established it as a bona fide complex subunit rather than a transient IFT cargo.","evidence":"Biochemical fractionation, yeast two-hybrid, bacterial coexpression, and chemical cross-linking in Chlamydomonas reinhardtii","pmids":["20435895"],"confidence":"High","gaps":["Precise position within IFT-B subcomplex hierarchy was unresolved","Interaction topology in human IFT-B was unknown"]},{"year":2012,"claim":"Bidirectional genetic manipulation in Chlamydomonas demonstrated that IFT22 controls the total cellular pool of IFT particles and governs their partitioning between cell body and flagella, defining a unique regulatory function.","evidence":"RNAi knockdown and overexpression with quantitative immunofluorescence and Western blotting in Chlamydomonas","pmids":["22076686"],"confidence":"High","gaps":["Whether pool-size regulation depends on GTPase cycling was unknown","Downstream effectors of IFT22-mediated partitioning were unidentified"]},{"year":2016,"claim":"Systematic pairwise mapping of all 16 IFT-B subunits reclassified IFT22 as a peripheral rather than core subunit, refining its architectural position within IFT-B and explaining its dispensability for complex integrity.","evidence":"Visible immunoprecipitation (VIP) assay and affinity proteomics of human ciliary proteins","pmids":["26980730","27173435"],"confidence":"High","gaps":["Direct binding partner within the peripheral subcomplex was not narrowed to a single subunit","Structural basis for peripheral attachment was lacking"]},{"year":2018,"claim":"CRISPR knockout of IFT22 in mammalian RPE1 cells showed no ciliogenesis or ciliary trafficking defects, definitively demonstrating dispensability in mammals and focusing its role on regulatory rather than structural IFT functions.","evidence":"CRISPR/Cas9 knockout in human RPE1 cells with ciliogenesis and ciliary protein trafficking assays","pmids":["29654116"],"confidence":"High","gaps":["BBSome recruitment and signaling-dependent phenotypes were not assessed in these knockout cells","Possible redundancy with IFT27 was not tested"]},{"year":2020,"claim":"Demonstration that GTP-bound IFT22 binds and stabilizes GTP-bound BBS3/ARL6 to cooperatively recruit the BBSome to the basal body provided the first mechanistic explanation for IFT22's regulatory role, linking its GTPase cycle to BBSome-IFT coupling.","evidence":"In vitro GTPase activity assay, co-immunoprecipitation, single-particle in vivo fluorescence imaging, and functional rescue experiments in Chlamydomonas","pmids":["31953262"],"confidence":"High","gaps":["GTPase-activating protein (GAP) and guanine-nucleotide exchange factor (GEF) for IFT22 are unidentified","Structural basis of the IFT22–BBS3 interaction is unresolved","Whether IFT22 GTPase cycling explains the IFT particle pool-size regulation phenotype remains untested"]},{"year":null,"claim":"Key open questions include the identity of IFT22's GAP and GEF, the structural basis for IFT22–BBS3 cooperative BBSome recruitment, and whether IFT22 GTPase cycling underlies the organism-specific differences in its essentiality for ciliogenesis.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No GAP or GEF identified for IFT22","No high-resolution structure of IFT22 in complex with BBS3 or the BBSome","Mechanism underlying organism-specific essentiality (T. brucei vs mammals) is unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003924","term_label":"GTPase activity","supporting_discovery_ids":[7]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3,7]}],"localization":[{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[1,2,3,7]},{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[2,7]}],"pathway":[{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[1,2,3,7]}],"complexes":["IFT-B complex"],"partners":["IFT88","IFT81","IFT52","IFT46","IFT27","IFT25","BBS3"],"other_free_text":[]},"mechanistic_narrative":"IFT22 (RABL5) is a Rab-like GTPase and peripheral subunit of the intraflagellar transport complex B (IFT-B) that regulates the cellular pool size and ciliary partitioning of IFT particles rather than serving as a structural scaffold for ciliogenesis [PMID:22076686, PMID:29654116]. IFT22 possesses low intrinsic GTPase activity; in its GTP-bound state it binds and stabilizes the Arf-like GTPase BBS3/ARL6, and the two GTPases cooperatively recruit the BBSome to the basal body for coupling with the IFT-B1 subcomplex and ciliary entry [PMID:31953262]. IFT22 is dispensable for IFT-B complex assembly and cilia formation in mammalian cells, consistent with a regulatory rather than core-structural role in IFT [PMID:29654116, PMID:20409822]. The requirement for IFT22 in flagellum construction varies across organisms: it is essential in Trypanosoma brucei, where its depletion phenocopies retrograde IFT loss, but dispensable in mammalian RPE1 cells and C. elegans sensory cilia [PMID:19240117, PMID:29654116]."},"prefetch_data":{"uniprot":{"accession":"Q9H7X7","full_name":"Intraflagellar transport protein 22 homolog","aliases":["Rab-like protein 5"],"length_aa":185,"mass_kda":20.8,"function":"Small GTPase-like component of the intraflagellar transport (IFT) complex B","subcellular_location":"Cell projection, cilium","url":"https://www.uniprot.org/uniprotkb/Q9H7X7/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/IFT22","classification":"Not 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piece","reliability":"Additional"},{"location":"Principal piece","reliability":"Additional"},{"location":"End piece","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"choroid plexus","ntpm":69.9}],"url":"https://www.proteinatlas.org/search/IFT22"},"hgnc":{"alias_symbol":["FLJ14117","FLJ13225","DKFZp761N0823","FAP9","CFAP9"],"prev_symbol":["RABL5"]},"alphafold":{"accession":"Q9H7X7","domains":[{"cath_id":"3.40.50.300","chopping":"1-183","consensus_level":"high","plddt":91.8236,"start":1,"end":183}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H7X7","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H7X7-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H7X7-F1-predicted_aligned_error_v6.png","plddt_mean":91.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=IFT22","jax_strain_url":"https://www.jax.org/strain/search?query=IFT22"},"sequence":{"accession":"Q9H7X7","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9H7X7.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9H7X7/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H7X7"}},"corpus_meta":[{"pmid":"20435895","id":"PMC_20435895","title":"Direct 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\"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"IFT22 (RABL5 homolog) controls the cellular pool size of both IFT complex A and B particles in Chlamydomonas; depletion of IFT22 reduces the cellular IFT particle pool and paradoxically increases the amount of IFT particles in flagella, while overexpression also causes flagellar accumulation of IFT particles, indicating IFT22 regulates the partitioning of IFT particles between the cell body and flagellar compartments.\",\n      \"method\": \"RNAi-mediated depletion, overexpression, quantitative immunofluorescence, and flagellar protein analysis in Chlamydomonas\",\n      \"journal\": \"Cytoskeleton (Hoboken, N.J.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KD/OE with specific quantitative phenotypic readouts; single lab\",\n      \"pmids\": [\"22076686\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IFT22 knockout cells show no defects in ciliogenesis or ciliary protein trafficking, establishing that IFT22 is a peripheral (dispensable) subunit of the IFT-B complex for ciliogenesis, in contrast to core subunits.\",\n      \"method\": \"CRISPR/Cas9 knockout of IFT22, ciliogenesis assays, ciliary protein trafficking assays\",\n      \"journal\": \"Biology open\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with specific phenotypic readout; single lab\",\n      \"pmids\": [\"29654116\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"IFT22 (RABL5) is an active GTPase with low intrinsic GTPase activity that, independent of its IFT-B1 association, binds and stabilizes the Arf-like GTPase BBS3/ARL6; when both IFT22 and BBS3 are in their GTP-bound states, they recruit the BBSome to the basal body for coupling with the IFT-B1 subcomplex and ciliary entry, after which IFT22 is not required for BBSome transport within cilia.\",\n      \"method\": \"GTPase activity assays, biochemical binding/co-immunoprecipitation, single-particle in vivo fluorescence imaging in Chlamydomonas, genetic mutant analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (in vitro GTPase assay, biochemistry, live imaging, genetics) in a single rigorous study\",\n      \"pmids\": [\"31953262\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Knockdown of ift22 in zebrafish suppresses the bbs7 knockdown-related retrograde intracellular (melanosome) transport delay, placing IFT22 (anterograde IFT component) in a pathway that influences the balance between anterograde and retrograde intracellular transport.\",\n      \"method\": \"Morpholino knockdown in zebrafish, intracellular melanosome transport assay\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, single method (morpholino knockdown with transport assay), limited mechanistic depth\",\n      \"pmids\": [\"24938409\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The C. elegans ortholog of IFT22 (RABL5), called IFTA-2, was identified as a potential regulatory protein of the IFT machinery and shown to move with IFT-like dynamics in cilia by in vivo GFP imaging, associating with the IFT-B subcomplex.\",\n      \"method\": \"GFP transgenic reporter strains, in vivo time-lapse microscopy, IFT velocity measurements in C. elegans\",\n      \"journal\": \"Methods in cell biology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — localization and dynamics data without direct functional mutagenesis or biochemical reconstitution\",\n      \"pmids\": [\"20409822\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IFT22 (RABL5) is a Rab-like GTPase and peripheral subunit of the IFT-B1 complex that is dispensable for ciliogenesis per se but plays a critical regulatory role: in its GTP-bound state it binds and stabilizes BBS3/ARL6, and together they recruit the BBSome to the basal body for entry into cilia via IFT trains, while also controlling the cellular pool size and flagellar partitioning of IFT particles.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper first, then extract discoveries only from KEPT papers.\n\n**Classification:**\n\nRetrieved papers:\n1. PMID:20435895 — IFT complex B interactions, includes IFT22 in core B. KEEP\n2. PMID:29654116 — IFT22-KO cells, IFT-B complex. KEEP\n3. PMID:31953262 — IFT22/RABL5 recruits BBSome. KEEP\n4. PMID:22076686 — IFT22 in Chlamydomonas, IFT particle pool. KEEP\n5. PMID:34224160 — GWAS chicken plumage color; IFT22 mentioned as candidate gene for black plumage with no mechanism. EXCLUDE (expression/GWAS association only)\n6. PMID:20409822 — C. elegans IFT, mentions IFTA-2/RABL5/IFT22 as potential regulatory protein. KEEP (ortholog, functional genomics)\n7. PMID:24938409 — Zebrafish knockdown of ift22 suppresses bbs7-related retrograde transport delay. KEEP\n8. PMID:38641568 — Marine worm larval settlement; IFT22 mentioned as down-regulated gene. EXCLUDE (expression correlation, no mechanism for IFT22)\n9. PMID:39417279 — ASD bioinformatics; IFT22 identified computationally. EXCLUDE (Tier 4 computational)\n10. PMID:41412973 — Fluorescence-guided surgery. EXCLUDE (unrelated)\n\nGene2pubmed papers:\n- PMID:12477932 — MGC cDNA sequencing. EXCLUDE (no mechanism)\n- PMID:26186194 — BioPlex interactome. KEEP (IFT22 interactions in human cells)\n- PMID:28514442 — BioPlex 2.0. KEEP (IFT22 interactions)\n- PMID:26496610 — Human interactome stoichiometries. KEEP if IFT22 specifically discussed — general proteomics resource, no IFT22-specific mechanism. EXCLUDE\n- PMID:14702039 — FLJ cDNA sequencing. EXCLUDE\n- PMID:33961781 — BioPlex 3.0. KEEP (IFT22 interactions)\n- PMID:22939629 — Census of human complexes. EXCLUDE (no IFT22-specific mechanism)\n- PMID:21873635 — GO annotation. EXCLUDE\n- PMID:15489334 — MGC project. EXCLUDE\n- PMID:26638075 — BioID centrosome-cilium interface, likely includes IFT22. KEEP\n- PMID:35271311 — OpenCell, IFT22 localization data. KEEP\n- PMID:16344560 — Alternative promoters. EXCLUDE\n- PMID:17207965 — hORFeome. EXCLUDE\n- PMID:27173435 — Ciliary organelle proteomics, IFT-B subcomplexes. KEEP\n- PMID:28718761 — Dynein interactome. EXCLUDE (IFT22 not specifically studied)\n- PMID:29229926 — RECQL4/DNA repair. EXCLUDE (alias collision — different gene)\n- PMID:26389662 — UBXN10/IFT-B complex, includes IFT22. KEEP\n- PMID:26972000 — PHD3/FIH hydroxylation. EXCLUDE\n- PMID:12107410 — RPE EST analysis. EXCLUDE\n- PMID:19240117 — Trypanosome RABL5/IFT22 ortholog. KEEP\n- PMID:29615496 — Cluap1/IFT38 CRISPR, IFT-B complex context. EXCLUDE (about IFT38, not IFT22 specifically)\n- PMID:36897256 — XPO7/senescence. EXCLUDE\n- PMID:40205054 — Multimodal cell maps. EXCLUDE (no IFT22-specific mechanism)\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2010,\n      \"finding\": \"IFT22 was identified as a component of the ~500 kDa core of IFT complex B in Chlamydomonas reinhardtii, alongside IFT88, IFT81, IFT74/72, IFT52, IFT46, IFT27, and IFT25. Chemical cross-linking provided evidence of an association between IFT27 and IFT81, placing IFT22 within a defined subunit architecture of the IFT-B core.\",\n      \"method\": \"Biochemical fractionation, yeast two-hybrid, bacterial coexpression, chemical cross-linking\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal biochemical methods in a well-characterized Chlamydomonas IFT system\",\n      \"pmids\": [\"20435895\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In Caenorhabditis elegans, the IFT22 ortholog IFTA-2/RABL5 moves in an IFT-like manner within sensory cilia and participates in signaling processes but is not required for cilia construction, establishing it as a potential regulatory rather than structural IFT component.\",\n      \"method\": \"GFP-tagging, in vivo time-lapse microscopy, IFT velocity measurements, mutant analysis\",\n      \"journal\": \"Methods in cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — live imaging with IFT rate measurements in C. elegans, single study\",\n      \"pmids\": [\"20409822\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In Trypanosoma brucei, the RABL5/IFT22 ortholog colocalizes with IFT proteins at the basal body and in the flagellum matrix, moves anterogradely, accumulates in short flagella of retrograde IFT mutants, and is restricted to the basal body in anterograde IFT mutants. RNAi knockdown of RABL5 is essential for flagellum construction, producing a phenotype similar to retrograde IFT inactivation with short flagella filled with IFT proteins.\",\n      \"method\": \"GFP fusion live imaging, RNAi knockdown, analysis of IFT mutant backgrounds\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — live imaging of anterograde movement, epistatic placement in IFT mutants, and RNAi loss-of-function with defined phenotype\",\n      \"pmids\": [\"19240117\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In Chlamydomonas reinhardtii, IFT22 (RABL5 homolog) is confirmed as an IFT-B subunit. Depletion of IFT22 reduces the cellular pool of both IFT complex A and B proteins, yet paradoxically increases the amount of IFT particles in flagella. Overexpression of IFT22 also causes accumulation of IFT particles in flagella. These data establish that IFT22 controls the cellular availability of IFT particles and regulates partitioning of IFT particles between the cell body and flagellar compartments.\",\n      \"method\": \"RNAi knockdown, overexpression, quantitative immunofluorescence, Western blotting\",\n      \"journal\": \"Cytoskeleton (Hoboken, N.J.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — bidirectional genetic manipulation (knockdown and overexpression) with quantitative readouts of IFT particle distribution\",\n      \"pmids\": [\"22076686\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Affinity proteomics of 217 human ciliary proteins placed IFT22 within the IFT-B complex network, revealing sub-complex interactions consistent with IFT-B core architecture and linking IFT22 to vesicle transport and ubiquitination pathways at cilia.\",\n      \"method\": \"Affinity proteomics, AP-MS, biochemical validation of sub-complexes\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic affinity proteomics with biochemical validation, but IFT22 not individually interrogated in depth\",\n      \"pmids\": [\"27173435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Using the visible immunoprecipitation (VIP) assay, IFT22 was mapped as a peripheral subunit of the IFT-B complex, associated with the peripheral subcomplex (rather than the core) alongside IFT57, IFT38, IFT54, IFT20, and IFT172.\",\n      \"method\": \"Visible immunoprecipitation (VIP) assay, systematic pairwise protein-protein interaction mapping\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic pairwise interaction mapping across all 16 IFT-B subunits with multiple orthogonal confirmations\",\n      \"pmids\": [\"26980730\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IFT22 knockout cells generated by CRISPR/Cas9 in RPE1 cells showed no defects in ciliogenesis or ciliary protein trafficking, demonstrating that IFT22 is dispensable for IFT-B complex assembly at the ciliary base and for cilia formation in mammalian cells.\",\n      \"method\": \"CRISPR/Cas9 knockout, ciliogenesis assay, ciliary protein trafficking analysis\",\n      \"journal\": \"Biology open\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic knockout with defined cellular phenotypic readout\",\n      \"pmids\": [\"29654116\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"IFT22 (RABL5) is an active GTPase with low intrinsic GTPase activity. In Chlamydomonas, IFT22 is part of the IFT-B1 subcomplex but, independently of IFT-B1 association, binds and stabilizes the Arf-like GTPase BBS3 (ARL6). When both IFT22 and BBS3 are in their GTP-bound states, they cooperatively recruit the BBSome to the basal body for coupling with the IFT-B1 subcomplex and ciliary entry. IFT22 is not required for BBSome transport within cilia, indicating that the BBSome is transferred from IFT22 to IFT trains at the ciliary base.\",\n      \"method\": \"GTPase activity assay, co-immunoprecipitation, single-particle in vivo fluorescence imaging, biochemical fractionation, functional rescue experiments\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro GTPase assay combined with in vivo single-particle imaging, biochemistry, and genetic analysis across multiple orthogonal methods\",\n      \"pmids\": [\"31953262\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In zebrafish, knockdown of ift22 (anterograde IFT component) suppresses the bbs7-related retrograde intracellular melanosome transport delay, functionally placing IFT22-mediated anterograde transport as a modulator of retrograde transport balance. This epistatic relationship reveals a role for IFT22 in directional intracellular transport.\",\n      \"method\": \"Morpholino knockdown in zebrafish, melanosome transport assay, genetic epistasis\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis in zebrafish with quantitative transport readout, single study\",\n      \"pmids\": [\"24938409\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"High-throughput affinity-purification mass spectrometry (BioPlex) in HEK293T cells identified IFT22 as part of a human protein interaction network, placing it in co-complex with other IFT-B subunits in human cells.\",\n      \"method\": \"Affinity purification–mass spectrometry (AP-MS), BioPlex network analysis\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — large-scale AP-MS survey, IFT22 not individually validated\",\n      \"pmids\": [\"26186194\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IFT22 (RABL5) is a Rab-like GTPase and peripheral subunit of the IFT-B complex that controls the cellular pool size of IFT particles and their partitioning into cilia/flagella; in its GTP-bound state it cooperates with BBS3/ARL6 to recruit the BBSome to the basal body for ciliary entry, while being dispensable for ciliogenesis itself in mammalian cells.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"IFT22 (RABL5) is a Rab-like GTPase and peripheral subunit of the intraflagellar transport complex B (IFT-B1) that regulates BBSome recruitment to cilia rather than ciliogenesis itself [PMID:29654116, PMID:20435895]. IFT22 possesses low intrinsic GTPase activity and, in its GTP-bound state, directly binds and stabilizes the Arf-like GTPase BBS3/ARL6; when both GTPases are GTP-loaded, they recruit the BBSome to the basal body for coupling with IFT-B1 and ciliary entry, after which IFT22 is dispensable for intra-ciliary BBSome transport [PMID:31953262]. IFT22 also controls the cellular pool size and flagellar partitioning of IFT-A and IFT-B particles, with both its depletion and overexpression leading to abnormal flagellar accumulation of IFT components [PMID:22076686].\",\n  \"teleology\": [\n    {\n      \"year\": 2009,\n      \"claim\": \"Initial live imaging established that IFT22 (IFTA-2 in C. elegans) moves with IFT-like dynamics along cilia and associates with the IFT-B subcomplex, positioning it as a candidate IFT regulatory factor rather than a structural cargo.\",\n      \"evidence\": \"GFP transgenic reporters and time-lapse microscopy in C. elegans cilia\",\n      \"pmids\": [\"20409822\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No functional mutagenesis or biochemical reconstitution to confirm regulatory role\",\n        \"Dynamics alone do not distinguish a core structural subunit from a regulatory peripheral factor\",\n        \"No GTPase activity data\"\n      ]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Biochemical fractionation placed IFT22 as a defined subunit of the ~500 kDa IFT-B core alongside IFT88, IFT81, IFT74, IFT52, IFT46, IFT27, and IFT25, establishing its precise position within the IFT-B architecture.\",\n      \"evidence\": \"Biochemical isolation from Chlamydomonas flagella, yeast two-hybrid, bacterial coexpression, and chemical cross-linking\",\n      \"pmids\": [\"20435895\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether IFT22 is essential for IFT-B assembly or is a peripheral component was not resolved\",\n        \"GTPase activity and nucleotide state not characterized\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"RNAi and overexpression experiments revealed that IFT22 controls the partitioning of both IFT-A and IFT-B particles between the cell body and flagella, shifting the understanding of IFT22 from a simple structural subunit to a regulator of IFT pool homeostasis.\",\n      \"evidence\": \"RNAi depletion and overexpression with quantitative immunofluorescence and flagellar protein analysis in Chlamydomonas\",\n      \"pmids\": [\"22076686\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism by which IFT22 controls pool size (e.g., via GTPase cycling or protein stability) was unknown\",\n        \"Single-laboratory finding without independent replication at the time\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"CRISPR knockout of IFT22 in mammalian cells demonstrated that IFT22 is dispensable for ciliogenesis and ciliary protein trafficking, reclassifying it as a peripheral rather than core IFT-B subunit and focusing attention on its non-structural regulatory functions.\",\n      \"evidence\": \"CRISPR/Cas9 knockout with ciliogenesis and ciliary trafficking assays\",\n      \"pmids\": [\"29654116\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"What specific regulatory process IFT22 controls remained undefined\",\n        \"Only tested in one cell line; tissue-specific requirements not excluded\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"A comprehensive mechanistic study demonstrated that IFT22 is an active GTPase that, in its GTP-bound state, directly binds and stabilizes BBS3/ARL6 to recruit the BBSome to the basal body for IFT-coupled ciliary entry, unifying the dispensability for ciliogenesis with a specific role in BBSome trafficking.\",\n      \"evidence\": \"In vitro GTPase assays, co-immunoprecipitation, single-particle in vivo fluorescence imaging, and genetic mutant analysis in Chlamydomonas\",\n      \"pmids\": [\"31953262\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"GAP and GEF for IFT22 GTPase cycle are not identified\",\n        \"Structural basis of the IFT22–BBS3 interaction is not resolved\",\n        \"Whether the IFT particle pool-size phenotype is mechanistically linked to BBSome recruitment is unclear\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The identity of the GEF and GAP that regulate IFT22's GTPase cycle, the structural details of the IFT22–BBS3 interaction, and whether IFT22's control of IFT particle pool size operates through the same BBSome-recruitment mechanism remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No GEF or GAP identified for IFT22\",\n        \"No high-resolution structure of IFT22–BBS3 complex\",\n        \"Relationship between IFT pool-size regulation and BBSome recruitment not tested\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003924\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [0, 1, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [0, 1, 3]}\n    ],\n    \"complexes\": [\n      \"IFT-B1 complex\"\n    ],\n    \"partners\": [\n      \"BBS3\",\n      \"IFT88\",\n      \"IFT81\",\n      \"IFT74\",\n      \"IFT52\",\n      \"IFT46\",\n      \"IFT27\",\n      \"IFT25\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"IFT22 (RABL5) is a Rab-like GTPase and peripheral subunit of the intraflagellar transport complex B (IFT-B) that regulates the cellular pool size and ciliary partitioning of IFT particles rather than serving as a structural scaffold for ciliogenesis [PMID:22076686, PMID:29654116]. IFT22 possesses low intrinsic GTPase activity; in its GTP-bound state it binds and stabilizes the Arf-like GTPase BBS3/ARL6, and the two GTPases cooperatively recruit the BBSome to the basal body for coupling with the IFT-B1 subcomplex and ciliary entry [PMID:31953262]. IFT22 is dispensable for IFT-B complex assembly and cilia formation in mammalian cells, consistent with a regulatory rather than core-structural role in IFT [PMID:29654116, PMID:20409822]. The requirement for IFT22 in flagellum construction varies across organisms: it is essential in Trypanosoma brucei, where its depletion phenocopies retrograde IFT loss, but dispensable in mammalian RPE1 cells and C. elegans sensory cilia [PMID:19240117, PMID:29654116].\",\n  \"teleology\": [\n    {\n      \"year\": 2009,\n      \"claim\": \"Establishing that IFT22 is a motile IFT-associated factor that is not required for cilium construction resolved whether it is a core structural IFT component or a regulatory accessory subunit.\",\n      \"evidence\": \"GFP-tagged IFTA-2/RABL5 tracked by live imaging in C. elegans sensory cilia; mutant analysis showed normal cilia structure (C. elegans) while RNAi in T. brucei produced short flagella phenocopying retrograde IFT loss\",\n      \"pmids\": [\"20409822\", \"19240117\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Organism-specific essentiality was unexplained mechanistically\",\n        \"GTPase activity of IFT22 had not been measured\",\n        \"Mammalian function was untested\"\n      ]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Biochemical placement of IFT22 within the ~500 kDa IFT-B core in Chlamydomonas established it as a bona fide complex subunit rather than a transient IFT cargo.\",\n      \"evidence\": \"Biochemical fractionation, yeast two-hybrid, bacterial coexpression, and chemical cross-linking in Chlamydomonas reinhardtii\",\n      \"pmids\": [\"20435895\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Precise position within IFT-B subcomplex hierarchy was unresolved\",\n        \"Interaction topology in human IFT-B was unknown\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Bidirectional genetic manipulation in Chlamydomonas demonstrated that IFT22 controls the total cellular pool of IFT particles and governs their partitioning between cell body and flagella, defining a unique regulatory function.\",\n      \"evidence\": \"RNAi knockdown and overexpression with quantitative immunofluorescence and Western blotting in Chlamydomonas\",\n      \"pmids\": [\"22076686\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether pool-size regulation depends on GTPase cycling was unknown\",\n        \"Downstream effectors of IFT22-mediated partitioning were unidentified\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Systematic pairwise mapping of all 16 IFT-B subunits reclassified IFT22 as a peripheral rather than core subunit, refining its architectural position within IFT-B and explaining its dispensability for complex integrity.\",\n      \"evidence\": \"Visible immunoprecipitation (VIP) assay and affinity proteomics of human ciliary proteins\",\n      \"pmids\": [\"26980730\", \"27173435\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Direct binding partner within the peripheral subcomplex was not narrowed to a single subunit\",\n        \"Structural basis for peripheral attachment was lacking\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"CRISPR knockout of IFT22 in mammalian RPE1 cells showed no ciliogenesis or ciliary trafficking defects, definitively demonstrating dispensability in mammals and focusing its role on regulatory rather than structural IFT functions.\",\n      \"evidence\": \"CRISPR/Cas9 knockout in human RPE1 cells with ciliogenesis and ciliary protein trafficking assays\",\n      \"pmids\": [\"29654116\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"BBSome recruitment and signaling-dependent phenotypes were not assessed in these knockout cells\",\n        \"Possible redundancy with IFT27 was not tested\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstration that GTP-bound IFT22 binds and stabilizes GTP-bound BBS3/ARL6 to cooperatively recruit the BBSome to the basal body provided the first mechanistic explanation for IFT22's regulatory role, linking its GTPase cycle to BBSome-IFT coupling.\",\n      \"evidence\": \"In vitro GTPase activity assay, co-immunoprecipitation, single-particle in vivo fluorescence imaging, and functional rescue experiments in Chlamydomonas\",\n      \"pmids\": [\"31953262\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"GTPase-activating protein (GAP) and guanine-nucleotide exchange factor (GEF) for IFT22 are unidentified\",\n        \"Structural basis of the IFT22–BBS3 interaction is unresolved\",\n        \"Whether IFT22 GTPase cycling explains the IFT particle pool-size regulation phenotype remains untested\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include the identity of IFT22's GAP and GEF, the structural basis for IFT22–BBS3 cooperative BBSome recruitment, and whether IFT22 GTPase cycling underlies the organism-specific differences in its essentiality for ciliogenesis.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No GAP or GEF identified for IFT22\",\n        \"No high-resolution structure of IFT22 in complex with BBS3 or the BBSome\",\n        \"Mechanism underlying organism-specific essentiality (T. brucei vs mammals) is unknown\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003924\", \"supporting_discovery_ids\": [7]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [1, 2, 3, 7]},\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [2, 7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [1, 2, 3, 7]}\n    ],\n    \"complexes\": [\n      \"IFT-B complex\"\n    ],\n    \"partners\": [\n      \"IFT88\",\n      \"IFT81\",\n      \"IFT52\",\n      \"IFT46\",\n      \"IFT27\",\n      \"IFT25\",\n      \"BBS3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}