{"gene":"IFT25","run_date":"2026-06-10T01:55:22","timeline":{"discoveries":[{"year":2009,"finding":"IFT25 is a phosphoprotein component of IFT complex B in Chlamydomonas; it directly binds IFT27 (a Rab-like GTPase) in vitro, and the two proteins form a subcomplex. In the cell body, only a fraction of IFT25/IFT27 is integrated into pre-assembled complex B, and cell-body IFT25 found in complex B is preferentially phosphorylated, suggesting phosphorylation-dependent regulation of subcomplex association with IFT-B.","method":"Biochemical fractionation of IFT mutants, in vitro binding assay, dephosphorylation assay, sucrose density gradient centrifugation, immunofluorescence","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro binding assay plus orthogonal biochemical methods (dephosphorylation, sucrose gradient, immunofluorescence) in a single focused study","pmids":["19412537"],"is_preprint":false},{"year":2012,"finding":"IFT25 is not required for ciliary assembly in mice but is required for signal-dependent transport of Hedgehog pathway components (Patched-1, Smoothened, Gli2) within cilia; Ift25-null mice fail to activate Hedgehog signaling, demonstrating a separable IFT role in signal transduction distinct from ciliogenesis.","method":"Ift25 null mouse generation, immunofluorescence for Hedgehog components in cilia, pathway activation assays, phenotypic analysis of mutant mice","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic loss-of-function (null mouse) with multiple orthogonal readouts (subcellular localization of multiple pathway components, signaling assays, developmental phenotypes); widely replicated concept","pmids":["22595669"],"is_preprint":false},{"year":2017,"finding":"IFT25 is dispensable for somatic ciliogenesis but essential for sperm flagella formation and male fertility in mice; in Ift25-knockout testes, IFT27 (its direct binding partner) was absent, and IFT20 and IFT81 levels were reduced, indicating IFT25 stabilizes IFT27 and influences broader IFT-B complex integrity in the testis.","method":"Conditional male-germ-cell-specific Ift25 knockout mouse, Western blotting, TEM, light microscopy, SEM, fertility assays","journal":"Biology of reproduction","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean conditional KO with multiple orthogonal methods (Western blot, TEM, SEM, fertility assay) establishing mechanistic dependency of IFT27 stability on IFT25","pmids":["28430876"],"is_preprint":false},{"year":2017,"finding":"IFT27 (an IFT25-binding partner) is also essential for sperm flagella formation and male fertility in mice; conditional Ift27 knockout causes loss of IFT25 and IFT81 in the testis but not IFT20, IFT74, or IFT140, indicating IFT25 and IFT27 form a mutually stabilizing subcomplex that is specifically required for sperm flagella but not somatic cilia. Unlike Ift25 KO, sperm lipid rafts were normal in Ift27 KO, indicating IFT25 has additional roles beyond IFT27.","method":"Conditional Ift27 knockout (Stra8-iCre), Western blotting, TEM, SEM, fertility assays, comparison with Ift25 KO","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with multiple orthogonal methods, direct mechanistic comparison with Ift25 KO establishing shared and distinct roles","pmids":["28964737"],"is_preprint":false},{"year":2017,"finding":"In Chlamydomonas, IFT25 depletion does not impair flagellar assembly or BBSome entry into flagella, but specifically impairs BBSome movement out of (export from) the flagellum; IFT25 depletion causes dramatic reduction of IFT27, consistent with IFT25-IFT27 mutual stabilization.","method":"IFT25 RNAi depletion in Chlamydomonas, immunofluorescence, BBSome trafficking analysis","journal":"Biology open","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — single lab, RNAi knockdown with BBSome localization/trafficking readout, consistent with vertebrate data","pmids":["28838966"],"is_preprint":false},{"year":2019,"finding":"In Trypanosoma brucei, IFT25 is a component of the IFT-B complex and interacts with IFT27 within the flagellum during active IFT (shown by bimolecular fluorescence complementation in live cells); IFT25 depletion results in tiny disorganized flagella with accumulation of IFT-B proteins (except IFT27) but not IFT-A proteins, demonstrating that the IFT25–IFT27 module is required for proper IFT and flagellum construction in trypanosomes.","method":"Bimolecular fluorescence complementation in live cells, RNAi depletion, immunofluorescence, flagella phenotype analysis","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — live-cell BiFC for interaction, RNAi with IFT-B/A protein accumulation readout, single lab","pmids":["30709917"],"is_preprint":false},{"year":2022,"finding":"The IFT25–IFT27 heterodimer binds the C-terminal region of the IFT74–IFT81 heterodimer within IFT-B; BBS variants of IFT27 are impaired in IFT74–IFT81 binding and cannot rescue BBS-like phenotypes of IFT27-KO cells; BBS variants of IFT74 (which delete the IFT25–IFT27-binding region) rescue ciliogenesis but produce BBS-like ciliary export defects, establishing that impaired IFT25–IFT27 / IFT74–IFT81 interaction underlies BBS-associated ciliary defects.","method":"Knockout cell lines, rescue experiments with BBS variant constructs, co-immunoprecipitation, phenotypic readout (ciliogenesis, BBSome export)","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO rescue with separation-of-function BBS variants, reciprocal binding assays, multiple orthogonal phenotypic readouts in a single rigorous study","pmids":["34888642"],"is_preprint":false},{"year":2025,"finding":"In developing mouse sperm flagella, IFT25-GFP (knock-in) traffics bidirectionally without apparent preference toward or away from the cell body; FRAP and kymograph analyses show mobile and immobile fractions, with trafficking speed depending on spermatogenic stage: unrestricted diffusion early, mobile puncta in developing sperm, and immobile puncta in mature sperm. IFT25-GFP is highly abundant only in testis, consistent with its germ-cell-specific functional requirement.","method":"CRISPR/Cas9 IFT25-GFP knock-in mouse, FRAP, kymograph analysis, Western blotting, live imaging of isolated germ cells","journal":"Biology of reproduction","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct live imaging with FRAP and kymography in a validated knock-in model; single lab, single study","pmids":["39561113"],"is_preprint":false},{"year":2018,"finding":"Loss of Ift25 in mice causes duplex kidneys (from defects in ureteric bud initiation at earliest metanephric kidney development) and smaller kidneys with reduced branching, but does not cause rapid cyst growth typical of other IFT gene deletions, establishing a role for IFT25 (together with IFT27) in early kidney development distinct from cystogenesis.","method":"Ift25 null mouse, histological and morphological analysis of kidney development, comparison with Ift27 mutants","journal":"Mechanisms of development","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with specific developmental phenotype readout; single lab, primarily morphological analysis","pmids":["29626631"],"is_preprint":false}],"current_model":"IFT25 is a phosphoprotein component of IFT-B complex that forms a mutually stabilizing heterodimer with IFT27, which in turn docks onto the IFT74–IFT81 dimer; this IFT25–IFT27 module is dispensable for somatic ciliogenesis but is specifically required for signal-dependent transport of Hedgehog pathway components (Patched-1, Smoothened, Gli2) within cilia, for BBSome export from cilia, for sperm flagella assembly and male fertility, and for early kidney development, with disruption of the IFT25–IFT27/IFT74–IFT81 interface causing Bardet-Biedl syndrome phenotypes."},"narrative":{"mechanistic_narrative":"IFT25 is a phosphoprotein subunit of the intraflagellar transport complex B (IFT-B) that governs signal-dependent ciliary trafficking and flagellum assembly rather than core ciliogenesis [PMID:19412537, PMID:22595669]. It directly binds the Rab-like GTPase IFT27 to form a mutually stabilizing heterodimer, such that loss of either partner destabilizes the other and reduces broader IFT-B integrity [PMID:19412537, PMID:28430876, PMID:28964737]. This IFT25–IFT27 module docks onto the C-terminal region of the IFT74–IFT81 heterodimer within IFT-B; disruption of this interface, including by Bardet-Biedl syndrome variants of IFT27 and IFT74, produces BBS-like ciliary export defects while leaving ciliogenesis intact [PMID:34888642]. Functionally, IFT25 is dispensable for somatic ciliary assembly but is specifically required for signal-dependent intraciliary transport of Hedgehog pathway components (Patched-1, Smoothened, Gli2) and for BBSome export from the cilium [PMID:22595669, PMID:28838966]. Beyond cilia, IFT25 is essential for sperm flagella formation and male fertility, with germ-cell-restricted abundance and bidirectional intraflagellar mobility that varies across spermatogenic stages, and it contributes to early kidney development through ureteric bud initiation and branching [PMID:28430876, PMID:39561113, PMID:29626631].","teleology":[{"year":2009,"claim":"Established that IFT25 is a bona fide IFT-B component and identified its direct binding partner, defining the molecular core of its function.","evidence":"In vitro binding, dephosphorylation, sucrose gradient and immunofluorescence in Chlamydomonas IFT mutants","pmids":["19412537"],"confidence":"High","gaps":["Functional consequence of phosphorylation-dependent subcomplex association not resolved","Role within intact IFT-B during transport not addressed in vivo"]},{"year":2012,"claim":"Separated IFT25's role in ciliary signaling from ciliogenesis, showing it is required for Hedgehog component transport but not cilium assembly.","evidence":"Ift25-null mouse with immunofluorescence of Hedgehog components and pathway activation assays","pmids":["22595669"],"confidence":"High","gaps":["Mechanism by which IFT25 selectively transports Hedgehog cargo unknown","Whether transport defect is direct or via IFT-B destabilization not distinguished"]},{"year":2017,"claim":"Demonstrated tissue-specific essentiality in male germ cells and mutual stabilization between IFT25 and IFT27, with effects on broader IFT-B integrity.","evidence":"Germ-cell-specific conditional Ift25 and Ift27 knockouts with Western blot, TEM/SEM and fertility assays","pmids":["28430876","28964737"],"confidence":"High","gaps":["IFT25-specific functions beyond IFT27 (e.g. sperm lipid rafts) not mechanistically defined","How flagellar requirement differs from dispensable somatic cilia unexplained"]},{"year":2017,"claim":"Defined the trafficking step IFT25 controls, showing it is required for BBSome export from rather than entry into the cilium.","evidence":"IFT25 RNAi in Chlamydomonas with BBSome trafficking analysis by immunofluorescence","pmids":["28838966"],"confidence":"Medium","gaps":["Single-lab RNAi knockdown without rescue","Molecular basis of BBSome export coupling to IFT25 unresolved"]},{"year":2019,"claim":"Confirmed the IFT25–IFT27 interaction occurs within the flagellum during active transport and is needed for proper IFT and flagellum construction across species.","evidence":"Bimolecular fluorescence complementation and RNAi depletion in live Trypanosoma brucei","pmids":["30709917"],"confidence":"Medium","gaps":["Single-lab study","Whether trypanosome IFT requirement maps to the same Hedgehog/BBSome roles in vertebrates unclear"]},{"year":2022,"claim":"Pinpointed the IFT25–IFT27 / IFT74–IFT81 docking interface as the structural basis of Bardet-Biedl syndrome ciliary export defects.","evidence":"Knockout cell rescue with separation-of-function BBS variants, co-immunoprecipitation and ciliary phenotype readouts","pmids":["34888642"],"confidence":"High","gaps":["No high-resolution structure of the assembled module reported here","How export cargo is selected at this interface not defined"]},{"year":2025,"claim":"Characterized IFT25 dynamics in sperm flagella, revealing stage-dependent mobility and germ-cell-restricted abundance underlying its fertility role.","evidence":"CRISPR IFT25-GFP knock-in mouse with FRAP, kymography and live imaging of germ cells","pmids":["39561113"],"confidence":"Medium","gaps":["Single-lab single-study imaging model","Functional meaning of immobile fractions in mature sperm unresolved"]},{"year":null,"claim":"How IFT25-IFT27 selectively recognizes and exports specific cargo (Hedgehog components, BBSome) remains the central open mechanistic question.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of cargo engagement","Role of IFT25 phosphorylation in cargo selection untested","IFT27-independent functions of IFT25 uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,6]}],"localization":[{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[1,4,5,7]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[4,6]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[2,8]}],"complexes":["IFT-B"],"partners":["IFT27","IFT74","IFT81"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9Y547","full_name":"Intraflagellar transport protein 25 homolog","aliases":["Heat shock protein beta-11","Hspb11","Heat shock protein family B member 11","Placental protein 25","PP25"],"length_aa":144,"mass_kda":16.3,"function":"Component of the IFT complex B required for sonic hedgehog/SHH signaling. May mediate transport of SHH components: required for the export of SMO and PTCH1 receptors out of the cilium and the accumulation of GLI2 at the ciliary tip in response to activation of the SHH pathway, suggesting it is involved in the dynamic transport of SHH signaling molecules within the cilium. Not required for ciliary assembly. Its role in intraflagellar transport is mainly seen in tissues rich in ciliated cells such as kidney and testis. Essential for male fertility, spermiogenesis and sperm flagella formation. Plays a role in the early development of the kidney. May be involved in the regulation of ureteric bud initiation (By similarity)","subcellular_location":"Cell projection, cilium","url":"https://www.uniprot.org/uniprotkb/Q9Y547/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/IFT25","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":true,"resolved_as":"HSPB11","ensg_id":"ENSG00000081870","cell_line_id":"CID000051","localizations":[{"compartment":"cytoplasmic","grade":2},{"compartment":"nucleoplasm","grade":1}],"interactors":[{"gene":"TTC26","stoichiometry":10.0},{"gene":"IFT81","stoichiometry":10.0},{"gene":"IFT27","stoichiometry":10.0},{"gene":"IFT22","stoichiometry":10.0},{"gene":"IFT74","stoichiometry":10.0},{"gene":"IFT52","stoichiometry":10.0},{"gene":"IFT172","stoichiometry":10.0},{"gene":"TTC30A;TTC30B","stoichiometry":10.0},{"gene":"IFT20","stoichiometry":10.0},{"gene":"TRAF3IP1","stoichiometry":4.0}],"url":"https://opencell.sf.czbiohub.org/target/CID000051","total_profiled":1310},"omim":[{"mim_id":"620841","title":"INTRAFLAGELLAR TRANSPORT 25; IFT25","url":"https://www.omim.org/entry/620841"},{"mim_id":"615996","title":"BARDET-BIEDL SYNDROME 19; BBS19","url":"https://www.omim.org/entry/615996"},{"mim_id":"615870","title":"INTRAFLAGELLAR TRANSPORT 27; IFT27","url":"https://www.omim.org/entry/615870"},{"mim_id":"608040","title":"INTRAFLAGELLAR TRANSPORT 74; IFT74","url":"https://www.omim.org/entry/608040"},{"mim_id":"605489","title":"INTRAFLAGELLAR TRANSPORT 81; IFT81","url":"https://www.omim.org/entry/605489"}],"hpa":{"profiled":true,"resolved_as":"HSPB11","reliability":"Approved","locations":[{"location":"Mid piece","reliability":"Approved"},{"location":"Principal piece","reliability":"Approved"},{"location":"End piece","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/HSPB11"},"hgnc":{"alias_symbol":["HSPCO34","PP25","FAP232","CFAP232"],"prev_symbol":["C1orf41","HSPB11"]},"alphafold":{"accession":"Q9Y547","domains":[{"cath_id":"2.60.120.260","chopping":"5-142","consensus_level":"high","plddt":95.6217,"start":5,"end":142}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y547","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y547-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y547-F1-predicted_aligned_error_v6.png","plddt_mean":94.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=IFT25","jax_strain_url":"https://www.jax.org/strain/search?query=IFT25"},"sequence":{"accession":"Q9Y547","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y547.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y547/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y547"}},"corpus_meta":[{"pmid":"22595669","id":"PMC_22595669","title":"IFT25 links the signal-dependent movement of Hedgehog components to intraflagellar transport.","date":"2012","source":"Developmental cell","url":"https://pubmed.ncbi.nlm.nih.gov/22595669","citation_count":183,"is_preprint":false},{"pmid":"19412537","id":"PMC_19412537","title":"Intraflagellar transport (IFT) protein IFT25 is a phosphoprotein component of IFT complex B and physically interacts with IFT27 in Chlamydomonas.","date":"2009","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/19412537","citation_count":79,"is_preprint":false},{"pmid":"28964737","id":"PMC_28964737","title":"Intraflagellar transporter protein (IFT27), an IFT25 binding partner, is essential for male fertility and spermiogenesis in mice.","date":"2017","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/28964737","citation_count":69,"is_preprint":false},{"pmid":"28430876","id":"PMC_28430876","title":"IFT25, an intraflagellar transporter protein dispensable for ciliogenesis in somatic cells, is essential for sperm flagella formation.","date":"2017","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/28430876","citation_count":58,"is_preprint":false},{"pmid":"34888642","id":"PMC_34888642","title":"Impaired cooperation between IFT74/BBS22-IFT81 and IFT25-IFT27/BBS19 causes Bardet-Biedl syndrome.","date":"2022","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/34888642","citation_count":31,"is_preprint":false},{"pmid":"28838966","id":"PMC_28838966","title":"Chlamydomonas IFT25 is dispensable for flagellar assembly but required to export the BBSome from flagella.","date":"2017","source":"Biology open","url":"https://pubmed.ncbi.nlm.nih.gov/28838966","citation_count":23,"is_preprint":false},{"pmid":"30709917","id":"PMC_30709917","title":"IFT25 is required for the construction of the trypanosome flagellum.","date":"2019","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/30709917","citation_count":10,"is_preprint":false},{"pmid":"29626631","id":"PMC_29626631","title":"Ift25 is not a cystic kidney disease gene but is required for early steps of kidney development.","date":"2018","source":"Mechanisms of development","url":"https://pubmed.ncbi.nlm.nih.gov/29626631","citation_count":10,"is_preprint":false},{"pmid":"39561113","id":"PMC_39561113","title":"Two-directional trafficking of the IFT25 protein in the developing mouse sperm flagella.","date":"2025","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/39561113","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7020,"output_tokens":2630,"usd":0.030255,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9739,"output_tokens":2455,"usd":0.055035,"stage2_stop_reason":"end_turn"},"total_usd":0.08529,"stage1_batch_id":"msgbatch_01DUPACZi7AAWwuZiUjseQF4","stage2_batch_id":"msgbatch_018yt7chE3f48PEFtDwtj6AE","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2009,\n      \"finding\": \"IFT25 is a phosphoprotein component of IFT complex B in Chlamydomonas; it directly binds IFT27 (a Rab-like GTPase) in vitro, and the two proteins form a subcomplex. In the cell body, only a fraction of IFT25/IFT27 is integrated into pre-assembled complex B, and cell-body IFT25 found in complex B is preferentially phosphorylated, suggesting phosphorylation-dependent regulation of subcomplex association with IFT-B.\",\n      \"method\": \"Biochemical fractionation of IFT mutants, in vitro binding assay, dephosphorylation assay, sucrose density gradient centrifugation, immunofluorescence\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro binding assay plus orthogonal biochemical methods (dephosphorylation, sucrose gradient, immunofluorescence) in a single focused study\",\n      \"pmids\": [\"19412537\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"IFT25 is not required for ciliary assembly in mice but is required for signal-dependent transport of Hedgehog pathway components (Patched-1, Smoothened, Gli2) within cilia; Ift25-null mice fail to activate Hedgehog signaling, demonstrating a separable IFT role in signal transduction distinct from ciliogenesis.\",\n      \"method\": \"Ift25 null mouse generation, immunofluorescence for Hedgehog components in cilia, pathway activation assays, phenotypic analysis of mutant mice\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic loss-of-function (null mouse) with multiple orthogonal readouts (subcellular localization of multiple pathway components, signaling assays, developmental phenotypes); widely replicated concept\",\n      \"pmids\": [\"22595669\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"IFT25 is dispensable for somatic ciliogenesis but essential for sperm flagella formation and male fertility in mice; in Ift25-knockout testes, IFT27 (its direct binding partner) was absent, and IFT20 and IFT81 levels were reduced, indicating IFT25 stabilizes IFT27 and influences broader IFT-B complex integrity in the testis.\",\n      \"method\": \"Conditional male-germ-cell-specific Ift25 knockout mouse, Western blotting, TEM, light microscopy, SEM, fertility assays\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean conditional KO with multiple orthogonal methods (Western blot, TEM, SEM, fertility assay) establishing mechanistic dependency of IFT27 stability on IFT25\",\n      \"pmids\": [\"28430876\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"IFT27 (an IFT25-binding partner) is also essential for sperm flagella formation and male fertility in mice; conditional Ift27 knockout causes loss of IFT25 and IFT81 in the testis but not IFT20, IFT74, or IFT140, indicating IFT25 and IFT27 form a mutually stabilizing subcomplex that is specifically required for sperm flagella but not somatic cilia. Unlike Ift25 KO, sperm lipid rafts were normal in Ift27 KO, indicating IFT25 has additional roles beyond IFT27.\",\n      \"method\": \"Conditional Ift27 knockout (Stra8-iCre), Western blotting, TEM, SEM, fertility assays, comparison with Ift25 KO\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with multiple orthogonal methods, direct mechanistic comparison with Ift25 KO establishing shared and distinct roles\",\n      \"pmids\": [\"28964737\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In Chlamydomonas, IFT25 depletion does not impair flagellar assembly or BBSome entry into flagella, but specifically impairs BBSome movement out of (export from) the flagellum; IFT25 depletion causes dramatic reduction of IFT27, consistent with IFT25-IFT27 mutual stabilization.\",\n      \"method\": \"IFT25 RNAi depletion in Chlamydomonas, immunofluorescence, BBSome trafficking analysis\",\n      \"journal\": \"Biology open\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — single lab, RNAi knockdown with BBSome localization/trafficking readout, consistent with vertebrate data\",\n      \"pmids\": [\"28838966\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In Trypanosoma brucei, IFT25 is a component of the IFT-B complex and interacts with IFT27 within the flagellum during active IFT (shown by bimolecular fluorescence complementation in live cells); IFT25 depletion results in tiny disorganized flagella with accumulation of IFT-B proteins (except IFT27) but not IFT-A proteins, demonstrating that the IFT25–IFT27 module is required for proper IFT and flagellum construction in trypanosomes.\",\n      \"method\": \"Bimolecular fluorescence complementation in live cells, RNAi depletion, immunofluorescence, flagella phenotype analysis\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — live-cell BiFC for interaction, RNAi with IFT-B/A protein accumulation readout, single lab\",\n      \"pmids\": [\"30709917\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The IFT25–IFT27 heterodimer binds the C-terminal region of the IFT74–IFT81 heterodimer within IFT-B; BBS variants of IFT27 are impaired in IFT74–IFT81 binding and cannot rescue BBS-like phenotypes of IFT27-KO cells; BBS variants of IFT74 (which delete the IFT25–IFT27-binding region) rescue ciliogenesis but produce BBS-like ciliary export defects, establishing that impaired IFT25–IFT27 / IFT74–IFT81 interaction underlies BBS-associated ciliary defects.\",\n      \"method\": \"Knockout cell lines, rescue experiments with BBS variant constructs, co-immunoprecipitation, phenotypic readout (ciliogenesis, BBSome export)\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO rescue with separation-of-function BBS variants, reciprocal binding assays, multiple orthogonal phenotypic readouts in a single rigorous study\",\n      \"pmids\": [\"34888642\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In developing mouse sperm flagella, IFT25-GFP (knock-in) traffics bidirectionally without apparent preference toward or away from the cell body; FRAP and kymograph analyses show mobile and immobile fractions, with trafficking speed depending on spermatogenic stage: unrestricted diffusion early, mobile puncta in developing sperm, and immobile puncta in mature sperm. IFT25-GFP is highly abundant only in testis, consistent with its germ-cell-specific functional requirement.\",\n      \"method\": \"CRISPR/Cas9 IFT25-GFP knock-in mouse, FRAP, kymograph analysis, Western blotting, live imaging of isolated germ cells\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct live imaging with FRAP and kymography in a validated knock-in model; single lab, single study\",\n      \"pmids\": [\"39561113\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Loss of Ift25 in mice causes duplex kidneys (from defects in ureteric bud initiation at earliest metanephric kidney development) and smaller kidneys with reduced branching, but does not cause rapid cyst growth typical of other IFT gene deletions, establishing a role for IFT25 (together with IFT27) in early kidney development distinct from cystogenesis.\",\n      \"method\": \"Ift25 null mouse, histological and morphological analysis of kidney development, comparison with Ift27 mutants\",\n      \"journal\": \"Mechanisms of development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with specific developmental phenotype readout; single lab, primarily morphological analysis\",\n      \"pmids\": [\"29626631\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IFT25 is a phosphoprotein component of IFT-B complex that forms a mutually stabilizing heterodimer with IFT27, which in turn docks onto the IFT74–IFT81 dimer; this IFT25–IFT27 module is dispensable for somatic ciliogenesis but is specifically required for signal-dependent transport of Hedgehog pathway components (Patched-1, Smoothened, Gli2) within cilia, for BBSome export from cilia, for sperm flagella assembly and male fertility, and for early kidney development, with disruption of the IFT25–IFT27/IFT74–IFT81 interface causing Bardet-Biedl syndrome phenotypes.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"IFT25 is a phosphoprotein subunit of the intraflagellar transport complex B (IFT-B) that governs signal-dependent ciliary trafficking and flagellum assembly rather than core ciliogenesis [#0, #1]. It directly binds the Rab-like GTPase IFT27 to form a mutually stabilizing heterodimer, such that loss of either partner destabilizes the other and reduces broader IFT-B integrity [#0, #2, #3]. This IFT25–IFT27 module docks onto the C-terminal region of the IFT74–IFT81 heterodimer within IFT-B; disruption of this interface, including by Bardet-Biedl syndrome variants of IFT27 and IFT74, produces BBS-like ciliary export defects while leaving ciliogenesis intact [#6]. Functionally, IFT25 is dispensable for somatic ciliary assembly but is specifically required for signal-dependent intraciliary transport of Hedgehog pathway components (Patched-1, Smoothened, Gli2) and for BBSome export from the cilium [#1, #4]. Beyond cilia, IFT25 is essential for sperm flagella formation and male fertility, with germ-cell-restricted abundance and bidirectional intraflagellar mobility that varies across spermatogenic stages, and it contributes to early kidney development through ureteric bud initiation and branching [#2, #7, #8].\",\n  \"teleology\": [\n    {\n      \"year\": 2009,\n      \"claim\": \"Established that IFT25 is a bona fide IFT-B component and identified its direct binding partner, defining the molecular core of its function.\",\n      \"evidence\": \"In vitro binding, dephosphorylation, sucrose gradient and immunofluorescence in Chlamydomonas IFT mutants\",\n      \"pmids\": [\"19412537\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of phosphorylation-dependent subcomplex association not resolved\", \"Role within intact IFT-B during transport not addressed in vivo\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Separated IFT25's role in ciliary signaling from ciliogenesis, showing it is required for Hedgehog component transport but not cilium assembly.\",\n      \"evidence\": \"Ift25-null mouse with immunofluorescence of Hedgehog components and pathway activation assays\",\n      \"pmids\": [\"22595669\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which IFT25 selectively transports Hedgehog cargo unknown\", \"Whether transport defect is direct or via IFT-B destabilization not distinguished\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrated tissue-specific essentiality in male germ cells and mutual stabilization between IFT25 and IFT27, with effects on broader IFT-B integrity.\",\n      \"evidence\": \"Germ-cell-specific conditional Ift25 and Ift27 knockouts with Western blot, TEM/SEM and fertility assays\",\n      \"pmids\": [\"28430876\", \"28964737\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"IFT25-specific functions beyond IFT27 (e.g. sperm lipid rafts) not mechanistically defined\", \"How flagellar requirement differs from dispensable somatic cilia unexplained\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Defined the trafficking step IFT25 controls, showing it is required for BBSome export from rather than entry into the cilium.\",\n      \"evidence\": \"IFT25 RNAi in Chlamydomonas with BBSome trafficking analysis by immunofluorescence\",\n      \"pmids\": [\"28838966\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab RNAi knockdown without rescue\", \"Molecular basis of BBSome export coupling to IFT25 unresolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Confirmed the IFT25–IFT27 interaction occurs within the flagellum during active transport and is needed for proper IFT and flagellum construction across species.\",\n      \"evidence\": \"Bimolecular fluorescence complementation and RNAi depletion in live Trypanosoma brucei\",\n      \"pmids\": [\"30709917\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab study\", \"Whether trypanosome IFT requirement maps to the same Hedgehog/BBSome roles in vertebrates unclear\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Pinpointed the IFT25–IFT27 / IFT74–IFT81 docking interface as the structural basis of Bardet-Biedl syndrome ciliary export defects.\",\n      \"evidence\": \"Knockout cell rescue with separation-of-function BBS variants, co-immunoprecipitation and ciliary phenotype readouts\",\n      \"pmids\": [\"34888642\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No high-resolution structure of the assembled module reported here\", \"How export cargo is selected at this interface not defined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Characterized IFT25 dynamics in sperm flagella, revealing stage-dependent mobility and germ-cell-restricted abundance underlying its fertility role.\",\n      \"evidence\": \"CRISPR IFT25-GFP knock-in mouse with FRAP, kymography and live imaging of germ cells\",\n      \"pmids\": [\"39561113\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab single-study imaging model\", \"Functional meaning of immobile fractions in mature sperm unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How IFT25-IFT27 selectively recognizes and exports specific cargo (Hedgehog components, BBSome) remains the central open mechanistic question.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of cargo engagement\", \"Role of IFT25 phosphorylation in cargo selection untested\", \"IFT27-independent functions of IFT25 uncharacterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [1, 4, 5, 7]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [4, 6]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [2, 8]}\n    ],\n    \"complexes\": [\"IFT-B\"],\n    \"partners\": [\"IFT27\", \"IFT74\", \"IFT81\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}