{"gene":"WDR35","run_date":"2026-04-28T23:00:23","timeline":{"discoveries":[{"year":2006,"finding":"C. elegans IFTA-1 (ortholog of WDR35/IFT121) localizes to the base of cilia and undergoes intraflagellar transport; it is required for retrograde IFT, as ifta-1 mutants display shortened cilia with accumulations of core IFT machinery indicative of retrograde transport defects. IFTA-1 co-localizes with the IFT-A subcomplex in bbs and che-11 mutant backgrounds.","method":"C. elegans genetics, fluorescence localization, IFT motility analysis, epistasis with bbs and che-11 mutants","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — reciprocal genetic epistasis, direct localization, motility assays, replicated across multiple mutant backgrounds","pmids":["17021254"],"is_preprint":false},{"year":2011,"finding":"WDR35 localizes to cilia and centrosomes throughout the developing mouse embryo; human and mouse fibroblasts lacking WDR35 fail to produce cilia, and Wdr35 mouse mutants display Hedgehog signaling defects (midgestation lethality with Hh pathway abnormalities). Structural modeling shows WDR35 has strong homology to COPI coatamer subunits involved in vesicular trafficking.","method":"Immunofluorescence localization in embryo, loss-of-function fibroblasts, mouse knockout phenotyping, structural homology modeling","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 — direct localization, KO fibroblasts with ciliogenesis readout, in vivo mouse model with Hh pathway phenotype, structural modeling","pmids":["21473986"],"is_preprint":false},{"year":2015,"finding":"WDR35/IFT121 is specifically required for entry of EVC, EVC2, and Smoothened (SMO) into the ciliary compartment; in Wdr35-/- cilia these three proteins fail to localize, but they do localize in Dync2h1-/- (retrograde motor mutant) cilia, indicating IFT121 has a specific role beyond retrograde motor activity in targeting the EvC complex and SMO to cilia, with consequent Hedgehog signaling defects.","method":"Immunofluorescence of EVC/EVC2/SMO in Wdr35-/- vs Dync2h1-/- fibroblasts; rescue experiments with disease cDNAs; Hh signaling assays","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis between Wdr35 and Dync2h1, direct localization of multiple cargo proteins, functional rescue, multiple orthogonal methods","pmids":["25908617"],"is_preprint":false},{"year":2018,"finding":"Drosophila Oseg4 (WDR35 ortholog) is required for both retrograde IFT and anterograde movement specifically in the distal ciliary segment, as revealed by time-lapse live-cell imaging of IFT88-GFP in oseg4 mutant cilia.","method":"Time-lapse live-cell imaging of IFT88-GFP in Drosophila cilia, genetic loss-of-function","journal":"Molecules and cells","confidence":"Medium","confidence_rationale":"Tier 2 — direct live imaging in vivo, but single lab and single model organism","pmids":["29983040"],"is_preprint":false},{"year":2019,"finding":"WDR35 physically interacts with RagA, RagB, and RagC (mTORC1 regulatory GTPases), and overexpression of WDR35 decreases phosphorylation of ribosomal S6 protein in a RagA/RagB/RagC-dependent manner, indicating WDR35 negatively influences mTORC1 activity.","method":"Co-immunoprecipitation, overexpression/knockdown, phospho-S6 western blot","journal":"Genes to cells","confidence":"Low","confidence_rationale":"Tier 3 — single Co-IP with partial functional follow-up, single lab","pmids":["30570184"],"is_preprint":false},{"year":2019,"finding":"WDR35 overexpression or Gli2 overexpression enhances osteogenic differentiation marker gene expression and ALP activity, while WDR35 silencing in C3H10T1/2 cells inhibits cilia formation and osteogenic differentiation; this inhibitory effect is rescued by Gli2 overexpression, placing WDR35 upstream of Gli2/Hedgehog signaling in osteogenic differentiation.","method":"siRNA knockdown, overexpression, ALP activity assay, immunofluorescence of cilia, gene expression analysis","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 2 — epistasis via Gli2 rescue, multiple functional readouts; single lab","pmids":["30790652"],"is_preprint":false},{"year":2021,"finding":"WDR35 associates with CCT complex proteins (TCP1/CCT1 chaperonins for α-tubulin folding), identified by mass spectrometry; partial knockout of WDR35 disperses acetylated α-tubulin from the peri-ciliary region, and RagA (GDP-bound form) binds WDR35 and negatively regulates primary cilium formation.","method":"Mass spectrometry interactome, immunostaining in WDR35 partial KO and RagA KO 293T cells, co-immunoprecipitation","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2–3 — MS interactome plus localization phenotype in KO cells; single lab, moderate follow-up","pmids":["33610917"],"is_preprint":false},{"year":2021,"finding":"In the absence of WDR35, small mutant cilia form but fail to enrich diverse classes of ciliary membrane proteins; non-core IFT-A components are degraded and core components accumulate at the ciliary base in Wdr35 mouse mutants. WDR35 and other IFT-A subunits share deep sequence homology with α and β' COPI coatomer subunits. Coat-less vesicles accumulate and fail to fuse with Wdr35 mutant cilia. Recombinant non-core IFT-A proteins bind directly to lipids, providing in situ evidence that WDR35, likely with other IFT-A proteins, forms a coat on vesicles that delivers ciliary membrane cargo.","method":"Mouse genetics (Wdr35 mutant), in situ electron tomography, biochemical fractionation, recombinant protein-lipid binding assay, sequence homology analysis","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 — reconstitution of lipid binding, in situ structural evidence of coat-less vesicles, multiple orthogonal methods including mouse genetics, electron tomography, and biochemistry","pmids":["34734804"],"is_preprint":false},{"year":2017,"finding":"WDR35/IFT121 directly interacts with IFT43 as a satellite component of the IFT-A complex; mutations in IFT43 that disrupt ciliogenesis produce a phenotype similar to WDR35/IFT121 mutations, supporting their direct functional interaction in retrograde IFT and endochondral ossification.","method":"Patient genetics, ciliogenesis assays in patient-derived cells, phenotypic comparison of IFT43 and WDR35 mutants","journal":"Cilia","confidence":"Medium","confidence_rationale":"Tier 3 — phenotypic epistasis and inferred interaction, no direct biochemical reconstitution of interaction in this paper","pmids":["28400947"],"is_preprint":false}],"current_model":"WDR35/IFT121 is a component of the IFT-A complex that functions as a COPI-like coat protein on vesicles to deliver ciliary membrane cargo to cilia, is required for retrograde IFT and specifically for the entry of the EvC complex (EVC/EVC2) and Smoothened into the ciliary compartment to support Hedgehog signaling, interacts with IFT43 and CCT chaperonins, and negatively regulates mTORC1 activity through physical association with RagA/B/C GTPases."},"narrative":{"teleology":[{"year":2006,"claim":"The first functional assignment of WDR35/IFTA-1 established it as an IFT-A subcomplex component required for retrograde intraflagellar transport, resolving the question of whether this WD40-repeat protein participates in ciliary trafficking.","evidence":"C. elegans ifta-1 mutant analysis with fluorescence localization and IFT motility assays","pmids":["17021254"],"confidence":"High","gaps":["Mammalian function not yet tested","Mechanism of retrograde IFT contribution (motor vs. cargo adapter) unresolved","Direct protein–protein interactions within IFT-A not mapped"]},{"year":2011,"claim":"Demonstration that mammalian WDR35 localizes to cilia and centrosomes and is absolutely required for ciliogenesis and Hedgehog signaling in vivo established WDR35 as essential for both cilium formation and developmental signaling in vertebrates.","evidence":"Mouse Wdr35 knockout, immunofluorescence in embryos and fibroblasts, structural homology modeling to COPI coatomer","pmids":["21473986"],"confidence":"High","gaps":["Specific ciliary cargoes dependent on WDR35 not identified","COPI homology functional significance not experimentally tested","Distinction from retrograde dynein motor function unknown"]},{"year":2015,"claim":"Genetic epistasis between Wdr35 and the retrograde dynein motor Dync2h1 revealed that WDR35 has a specific, motor-independent role in delivering Smoothened and the EVC/EVC2 complex to cilia, explaining the Hedgehog signaling defects in WDR35 mutants.","evidence":"Immunofluorescence of EVC, EVC2, and SMO in Wdr35−/− versus Dync2h1−/− fibroblasts with functional rescue","pmids":["25908617"],"confidence":"High","gaps":["Direct physical interaction between WDR35 and SMO/EVC not shown","Whether other IFT-A subunits share this cargo-specific function unclear","Mechanism of cargo selectivity not defined"]},{"year":2017,"claim":"Identification of IFT43 as a direct functional partner of WDR35 within the IFT-A peripheral subcomplex clarified the subunit organization and showed that mutations in either gene produce overlapping ciliopathy phenotypes.","evidence":"Patient genetics and ciliogenesis assays comparing IFT43 and WDR35 mutant cells","pmids":["28400947"],"confidence":"Medium","gaps":["Direct biochemical reconstitution of WDR35–IFT43 interaction not performed in this study","Stoichiometry and binding interface unknown","Whether IFT43 mediates the same cargo specificity as WDR35 untested"]},{"year":2018,"claim":"Live imaging in Drosophila cilia demonstrated that WDR35/Oseg4 is required not only for retrograde IFT but also for anterograde movement in the distal ciliary segment, extending its transport role beyond simple retrograde function.","evidence":"Time-lapse imaging of IFT88-GFP in Drosophila oseg4 mutant cilia","pmids":["29983040"],"confidence":"Medium","gaps":["Distal-segment-specific role not confirmed in mammalian systems","Mechanism of anterograde involvement unknown","Single lab observation"]},{"year":2019,"claim":"Discovery that WDR35 physically binds Rag GTPases (RagA/B/C) and suppresses mTORC1-dependent S6 phosphorylation identified a non-ciliary signaling role, raising the question of whether WDR35 integrates nutrient sensing with ciliogenesis.","evidence":"Co-immunoprecipitation and phospho-S6 western blot upon WDR35 overexpression/knockdown","pmids":["30570184"],"confidence":"Low","gaps":["Single Co-IP without reciprocal validation or endogenous-level confirmation","Mechanism by which WDR35 inhibits mTORC1 not defined","Relevance to ciliary vs. cytoplasmic pools of WDR35 unclear"]},{"year":2021,"claim":"In situ electron tomography and lipid-binding reconstitution established that WDR35 and the IFT-A complex function as a bona fide vesicle coat — analogous to COPI — that directly coats and delivers membrane-protein-laden vesicles to cilia, providing the structural and biochemical basis for how ciliary membrane composition is maintained.","evidence":"Mouse Wdr35 mutant electron tomography, recombinant non-core IFT-A lipid binding, biochemical fractionation","pmids":["34734804"],"confidence":"High","gaps":["Full reconstitution of IFT-A coat assembly on liposomes not achieved","High-resolution structure of the WDR35-containing coat not available","Cargo-sorting signals recognized by the coat not identified"]},{"year":2021,"claim":"Mass spectrometry interactome analysis linked WDR35 to CCT/TRiC chaperonins involved in tubulin folding and showed that partial WDR35 loss disperses acetylated α-tubulin, connecting WDR35 to cytoskeletal quality control at the ciliary base.","evidence":"Mass spectrometry, immunostaining in WDR35 partial-KO 293T cells, co-immunoprecipitation","pmids":["33610917"],"confidence":"Medium","gaps":["Direct binding between WDR35 and CCT subunits not biochemically validated","Functional consequence of CCT interaction for ciliogenesis not tested by reconstitution","Relationship between tubulin folding and vesicle coat function unclear"]},{"year":null,"claim":"The molecular logic by which WDR35/IFT-A coat selects specific membrane cargoes (e.g., SMO, EVC) for ciliary delivery, the high-resolution structure of the assembled coat on vesicles, and the physiological significance of the WDR35–Rag GTPase interaction remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["Cargo-sorting motifs or adaptors for IFT-A coat not identified","Cryo-EM or crystal structure of WDR35 within the coat complex absent","Endogenous role of WDR35 in mTORC1 regulation not confirmed in vivo"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[7]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[1,7]}],"localization":[{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[0,1,2,7]},{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[1]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[7]}],"pathway":[{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[0,1,2,7]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,5]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[7]}],"complexes":["IFT-A complex"],"partners":["IFT43","EVC","EVC2","SMO","RAGA","RAGB","RAGC","TCP1"],"other_free_text":[]},"mechanistic_narrative":"WDR35 (IFT121) is a subunit of the IFT-A complex that functions as a COPI-like vesicle coat protein essential for ciliogenesis, retrograde intraflagellar transport, and delivery of membrane cargo to cilia. WDR35 shares deep structural homology with COPI coatomer subunits; in its absence, coat-less vesicles accumulate at the ciliary base and fail to fuse, and recombinant non-core IFT-A proteins including WDR35 bind lipids directly, establishing a vesicular coat mechanism for ciliary membrane protein delivery [PMID:34734804, PMID:21473986]. Beyond general retrograde IFT, WDR35 is specifically required for ciliary entry of Smoothened and the EVC/EVC2 complex, distinguishing its function from that of the retrograde dynein motor and linking it to Hedgehog signaling during embryonic development and osteogenic differentiation [PMID:25908617, PMID:30790652]. WDR35 also interacts with IFT43 within the IFT-A peripheral subcomplex, associates with CCT chaperonins involved in tubulin folding, and physically binds Rag GTPases to negatively regulate mTORC1 signaling [PMID:28400947, PMID:33610917, PMID:30570184]."},"prefetch_data":{"uniprot":{"accession":"Q9P2L0","full_name":"WD repeat-containing protein 35","aliases":["Intraflagellar transport protein 121 homolog"],"length_aa":1181,"mass_kda":133.5,"function":"As a component of the IFT complex A (IFT-A), a complex required for retrograde ciliary transport and entry into cilia of G protein-coupled receptors (GPCRs), it is involved in ciliogenesis and ciliary protein trafficking (PubMed:21473986, PubMed:28400947, PubMed:29220510). May promote CASP3 activation and TNF-stimulated apoptosis","subcellular_location":"Cytoplasm, cytoskeleton, microtubule organizing center, centrosome; Cytoplasm, cytoskeleton, cilium axoneme; Cytoplasm, cytoskeleton, cilium basal body","url":"https://www.uniprot.org/uniprotkb/Q9P2L0/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/WDR35","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/WDR35","total_profiled":1310},"omim":[{"mim_id":"618123","title":"POLYDACTYLY, POSTAXIAL, TYPE A8; PAPA8","url":"https://www.omim.org/entry/618123"},{"mim_id":"617925","title":"SHORT-RIB THORACIC DYSPLASIA 20 WITH POLYDACTYLY; SRTD20","url":"https://www.omim.org/entry/617925"},{"mim_id":"617088","title":"SHORT-RIB THORACIC DYSPLASIA 15 WITH POLYDACTYLY; SRTD15","url":"https://www.omim.org/entry/617088"},{"mim_id":"614099","title":"CRANIOECTODERMAL DYSPLASIA 3; CED3","url":"https://www.omim.org/entry/614099"},{"mim_id":"614091","title":"SHORT-RIB THORACIC DYSPLASIA 7 WITH OR WITHOUT POLYDACTYLY; SRTD7","url":"https://www.omim.org/entry/614091"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/WDR35"},"hgnc":{"alias_symbol":["MGC33196","KIAA1336","IFT121","IFTA1","FAP118","CFAP118"],"prev_symbol":[]},"alphafold":{"accession":"Q9P2L0","domains":[{"cath_id":"2.130.10.10","chopping":"3-333","consensus_level":"medium","plddt":90.5522,"start":3,"end":333},{"cath_id":"3.30.40,3.30.40","chopping":"1136-1181","consensus_level":"medium","plddt":82.9211,"start":1136,"end":1181}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9P2L0","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9P2L0-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9P2L0-F1-predicted_aligned_error_v6.png","plddt_mean":85.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=WDR35","jax_strain_url":"https://www.jax.org/strain/search?query=WDR35"},"sequence":{"accession":"Q9P2L0","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9P2L0.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9P2L0/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9P2L0"}},"corpus_meta":[{"pmid":"20817137","id":"PMC_20817137","title":"Exome sequencing identifies WDR35 variants involved in Sensenbrenner syndrome.","date":"2010","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/20817137","citation_count":231,"is_preprint":false},{"pmid":"21473986","id":"PMC_21473986","title":"Human and mouse mutations in WDR35 cause short-rib polydactyly syndromes due to abnormal ciliogenesis.","date":"2011","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/21473986","citation_count":110,"is_preprint":false},{"pmid":"17021254","id":"PMC_17021254","title":"The WD repeat-containing protein IFTA-1 is required for retrograde intraflagellar transport.","date":"2006","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/17021254","citation_count":90,"is_preprint":false},{"pmid":"25908617","id":"PMC_25908617","title":"Specific variants in WDR35 cause a distinctive form of Ellis-van Creveld syndrome by disrupting the recruitment of the EvC complex and SMO into the cilium.","date":"2015","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/25908617","citation_count":48,"is_preprint":false},{"pmid":"22987818","id":"PMC_22987818","title":"WDR35 mutation in siblings with Sensenbrenner syndrome: a ciliopathy with variable phenotype.","date":"2012","source":"American journal of medical genetics. 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IFTA-1 co-localizes with the IFT-A subcomplex in bbs and che-11 mutant backgrounds.\",\n      \"method\": \"C. elegans genetics, fluorescence localization, IFT motility analysis, epistasis with bbs and che-11 mutants\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal genetic epistasis, direct localization, motility assays, replicated across multiple mutant backgrounds\",\n      \"pmids\": [\"17021254\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"WDR35 localizes to cilia and centrosomes throughout the developing mouse embryo; human and mouse fibroblasts lacking WDR35 fail to produce cilia, and Wdr35 mouse mutants display Hedgehog signaling defects (midgestation lethality with Hh pathway abnormalities). Structural modeling shows WDR35 has strong homology to COPI coatamer subunits involved in vesicular trafficking.\",\n      \"method\": \"Immunofluorescence localization in embryo, loss-of-function fibroblasts, mouse knockout phenotyping, structural homology modeling\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization, KO fibroblasts with ciliogenesis readout, in vivo mouse model with Hh pathway phenotype, structural modeling\",\n      \"pmids\": [\"21473986\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"WDR35/IFT121 is specifically required for entry of EVC, EVC2, and Smoothened (SMO) into the ciliary compartment; in Wdr35-/- cilia these three proteins fail to localize, but they do localize in Dync2h1-/- (retrograde motor mutant) cilia, indicating IFT121 has a specific role beyond retrograde motor activity in targeting the EvC complex and SMO to cilia, with consequent Hedgehog signaling defects.\",\n      \"method\": \"Immunofluorescence of EVC/EVC2/SMO in Wdr35-/- vs Dync2h1-/- fibroblasts; rescue experiments with disease cDNAs; Hh signaling assays\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis between Wdr35 and Dync2h1, direct localization of multiple cargo proteins, functional rescue, multiple orthogonal methods\",\n      \"pmids\": [\"25908617\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Drosophila Oseg4 (WDR35 ortholog) is required for both retrograde IFT and anterograde movement specifically in the distal ciliary segment, as revealed by time-lapse live-cell imaging of IFT88-GFP in oseg4 mutant cilia.\",\n      \"method\": \"Time-lapse live-cell imaging of IFT88-GFP in Drosophila cilia, genetic loss-of-function\",\n      \"journal\": \"Molecules and cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct live imaging in vivo, but single lab and single model organism\",\n      \"pmids\": [\"29983040\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"WDR35 physically interacts with RagA, RagB, and RagC (mTORC1 regulatory GTPases), and overexpression of WDR35 decreases phosphorylation of ribosomal S6 protein in a RagA/RagB/RagC-dependent manner, indicating WDR35 negatively influences mTORC1 activity.\",\n      \"method\": \"Co-immunoprecipitation, overexpression/knockdown, phospho-S6 western blot\",\n      \"journal\": \"Genes to cells\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single Co-IP with partial functional follow-up, single lab\",\n      \"pmids\": [\"30570184\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"WDR35 overexpression or Gli2 overexpression enhances osteogenic differentiation marker gene expression and ALP activity, while WDR35 silencing in C3H10T1/2 cells inhibits cilia formation and osteogenic differentiation; this inhibitory effect is rescued by Gli2 overexpression, placing WDR35 upstream of Gli2/Hedgehog signaling in osteogenic differentiation.\",\n      \"method\": \"siRNA knockdown, overexpression, ALP activity assay, immunofluorescence of cilia, gene expression analysis\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epistasis via Gli2 rescue, multiple functional readouts; single lab\",\n      \"pmids\": [\"30790652\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"WDR35 associates with CCT complex proteins (TCP1/CCT1 chaperonins for α-tubulin folding), identified by mass spectrometry; partial knockout of WDR35 disperses acetylated α-tubulin from the peri-ciliary region, and RagA (GDP-bound form) binds WDR35 and negatively regulates primary cilium formation.\",\n      \"method\": \"Mass spectrometry interactome, immunostaining in WDR35 partial KO and RagA KO 293T cells, co-immunoprecipitation\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — MS interactome plus localization phenotype in KO cells; single lab, moderate follow-up\",\n      \"pmids\": [\"33610917\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In the absence of WDR35, small mutant cilia form but fail to enrich diverse classes of ciliary membrane proteins; non-core IFT-A components are degraded and core components accumulate at the ciliary base in Wdr35 mouse mutants. WDR35 and other IFT-A subunits share deep sequence homology with α and β' COPI coatomer subunits. Coat-less vesicles accumulate and fail to fuse with Wdr35 mutant cilia. Recombinant non-core IFT-A proteins bind directly to lipids, providing in situ evidence that WDR35, likely with other IFT-A proteins, forms a coat on vesicles that delivers ciliary membrane cargo.\",\n      \"method\": \"Mouse genetics (Wdr35 mutant), in situ electron tomography, biochemical fractionation, recombinant protein-lipid binding assay, sequence homology analysis\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution of lipid binding, in situ structural evidence of coat-less vesicles, multiple orthogonal methods including mouse genetics, electron tomography, and biochemistry\",\n      \"pmids\": [\"34734804\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"WDR35/IFT121 directly interacts with IFT43 as a satellite component of the IFT-A complex; mutations in IFT43 that disrupt ciliogenesis produce a phenotype similar to WDR35/IFT121 mutations, supporting their direct functional interaction in retrograde IFT and endochondral ossification.\",\n      \"method\": \"Patient genetics, ciliogenesis assays in patient-derived cells, phenotypic comparison of IFT43 and WDR35 mutants\",\n      \"journal\": \"Cilia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — phenotypic epistasis and inferred interaction, no direct biochemical reconstitution of interaction in this paper\",\n      \"pmids\": [\"28400947\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"WDR35/IFT121 is a component of the IFT-A complex that functions as a COPI-like coat protein on vesicles to deliver ciliary membrane cargo to cilia, is required for retrograde IFT and specifically for the entry of the EvC complex (EVC/EVC2) and Smoothened into the ciliary compartment to support Hedgehog signaling, interacts with IFT43 and CCT chaperonins, and negatively regulates mTORC1 activity through physical association with RagA/B/C GTPases.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"WDR35 (IFT121) is a subunit of the IFT-A complex that functions as a COPI-like vesicle coat protein essential for ciliogenesis, retrograde intraflagellar transport, and delivery of membrane cargo to cilia. WDR35 shares deep structural homology with COPI coatomer subunits; in its absence, coat-less vesicles accumulate at the ciliary base and fail to fuse, and recombinant non-core IFT-A proteins including WDR35 bind lipids directly, establishing a vesicular coat mechanism for ciliary membrane protein delivery [PMID:34734804, PMID:21473986]. Beyond general retrograde IFT, WDR35 is specifically required for ciliary entry of Smoothened and the EVC/EVC2 complex, distinguishing its function from that of the retrograde dynein motor and linking it to Hedgehog signaling during embryonic development and osteogenic differentiation [PMID:25908617, PMID:30790652]. WDR35 also interacts with IFT43 within the IFT-A peripheral subcomplex, associates with CCT chaperonins involved in tubulin folding, and physically binds Rag GTPases to negatively regulate mTORC1 signaling [PMID:28400947, PMID:33610917, PMID:30570184].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"The first functional assignment of WDR35/IFTA-1 established it as an IFT-A subcomplex component required for retrograde intraflagellar transport, resolving the question of whether this WD40-repeat protein participates in ciliary trafficking.\",\n      \"evidence\": \"C. elegans ifta-1 mutant analysis with fluorescence localization and IFT motility assays\",\n      \"pmids\": [\"17021254\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mammalian function not yet tested\", \"Mechanism of retrograde IFT contribution (motor vs. cargo adapter) unresolved\", \"Direct protein–protein interactions within IFT-A not mapped\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Demonstration that mammalian WDR35 localizes to cilia and centrosomes and is absolutely required for ciliogenesis and Hedgehog signaling in vivo established WDR35 as essential for both cilium formation and developmental signaling in vertebrates.\",\n      \"evidence\": \"Mouse Wdr35 knockout, immunofluorescence in embryos and fibroblasts, structural homology modeling to COPI coatomer\",\n      \"pmids\": [\"21473986\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific ciliary cargoes dependent on WDR35 not identified\", \"COPI homology functional significance not experimentally tested\", \"Distinction from retrograde dynein motor function unknown\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Genetic epistasis between Wdr35 and the retrograde dynein motor Dync2h1 revealed that WDR35 has a specific, motor-independent role in delivering Smoothened and the EVC/EVC2 complex to cilia, explaining the Hedgehog signaling defects in WDR35 mutants.\",\n      \"evidence\": \"Immunofluorescence of EVC, EVC2, and SMO in Wdr35−/− versus Dync2h1−/− fibroblasts with functional rescue\",\n      \"pmids\": [\"25908617\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct physical interaction between WDR35 and SMO/EVC not shown\", \"Whether other IFT-A subunits share this cargo-specific function unclear\", \"Mechanism of cargo selectivity not defined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identification of IFT43 as a direct functional partner of WDR35 within the IFT-A peripheral subcomplex clarified the subunit organization and showed that mutations in either gene produce overlapping ciliopathy phenotypes.\",\n      \"evidence\": \"Patient genetics and ciliogenesis assays comparing IFT43 and WDR35 mutant cells\",\n      \"pmids\": [\"28400947\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct biochemical reconstitution of WDR35–IFT43 interaction not performed in this study\", \"Stoichiometry and binding interface unknown\", \"Whether IFT43 mediates the same cargo specificity as WDR35 untested\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Live imaging in Drosophila cilia demonstrated that WDR35/Oseg4 is required not only for retrograde IFT but also for anterograde movement in the distal ciliary segment, extending its transport role beyond simple retrograde function.\",\n      \"evidence\": \"Time-lapse imaging of IFT88-GFP in Drosophila oseg4 mutant cilia\",\n      \"pmids\": [\"29983040\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Distal-segment-specific role not confirmed in mammalian systems\", \"Mechanism of anterograde involvement unknown\", \"Single lab observation\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Discovery that WDR35 physically binds Rag GTPases (RagA/B/C) and suppresses mTORC1-dependent S6 phosphorylation identified a non-ciliary signaling role, raising the question of whether WDR35 integrates nutrient sensing with ciliogenesis.\",\n      \"evidence\": \"Co-immunoprecipitation and phospho-S6 western blot upon WDR35 overexpression/knockdown\",\n      \"pmids\": [\"30570184\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single Co-IP without reciprocal validation or endogenous-level confirmation\", \"Mechanism by which WDR35 inhibits mTORC1 not defined\", \"Relevance to ciliary vs. cytoplasmic pools of WDR35 unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"In situ electron tomography and lipid-binding reconstitution established that WDR35 and the IFT-A complex function as a bona fide vesicle coat — analogous to COPI — that directly coats and delivers membrane-protein-laden vesicles to cilia, providing the structural and biochemical basis for how ciliary membrane composition is maintained.\",\n      \"evidence\": \"Mouse Wdr35 mutant electron tomography, recombinant non-core IFT-A lipid binding, biochemical fractionation\",\n      \"pmids\": [\"34734804\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full reconstitution of IFT-A coat assembly on liposomes not achieved\", \"High-resolution structure of the WDR35-containing coat not available\", \"Cargo-sorting signals recognized by the coat not identified\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Mass spectrometry interactome analysis linked WDR35 to CCT/TRiC chaperonins involved in tubulin folding and showed that partial WDR35 loss disperses acetylated α-tubulin, connecting WDR35 to cytoskeletal quality control at the ciliary base.\",\n      \"evidence\": \"Mass spectrometry, immunostaining in WDR35 partial-KO 293T cells, co-immunoprecipitation\",\n      \"pmids\": [\"33610917\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct binding between WDR35 and CCT subunits not biochemically validated\", \"Functional consequence of CCT interaction for ciliogenesis not tested by reconstitution\", \"Relationship between tubulin folding and vesicle coat function unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The molecular logic by which WDR35/IFT-A coat selects specific membrane cargoes (e.g., SMO, EVC) for ciliary delivery, the high-resolution structure of the assembled coat on vesicles, and the physiological significance of the WDR35–Rag GTPase interaction remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cargo-sorting motifs or adaptors for IFT-A coat not identified\", \"Cryo-EM or crystal structure of WDR35 within the coat complex absent\", \"Endogenous role of WDR35 in mTORC1 regulation not confirmed in vivo\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [7]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [1, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [0, 1, 2, 7]},\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [0, 1, 2, 7]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 5]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"complexes\": [\n      \"IFT-A complex\"\n    ],\n    \"partners\": [\n      \"IFT43\",\n      \"EVC\",\n      \"EVC2\",\n      \"SMO\",\n      \"RAGA\",\n      \"RAGB\",\n      \"RAGC\",\n      \"TCP1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}