{"gene":"HYDIN","run_date":"2026-06-10T01:55:22","timeline":{"discoveries":[{"year":2007,"finding":"Chlamydomonas reinhardtii HYDIN is a central pair (CP) protein located specifically on the C2 microtubule of the CP apparatus. An ~80% knockdown results in loss of the C2b projection and flagellar arrest at switch points between effective and recovery strokes. HYDIN interacts biochemically with CP proteins CPC1 and kinesin-like protein 1 (KLP1), placing it in the CP-radial spoke control pathway that regulates dynein arm activity.","method":"Antibody localization to C2 microtubule; RNAi knockdown; biochemical interaction analyses (co-purification with CPC1 and KLP1); electron microscopy of axoneme ultrastructure","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal biochemical interaction, precise subcellular localization, loss-of-function with defined structural and motility phenotype, multiple orthogonal methods in one rigorous study","pmids":["17296796"],"is_preprint":false},{"year":2008,"finding":"In mice, Hydin mutations cause loss of a specific projection on one of the two central pair microtubules of the ciliary axoneme; outer dynein arms and radial spokes are normal. This structural defect impairs ciliary bending and beat frequency in both brain ependymal cilia and tracheal cilia, abolishing fluid flow and causing hydrocephalus.","method":"Electron microscopy of axoneme ultrastructure; high-speed videomicroscopy of ciliary beat; comparison of wild-type vs. Hydin mutant mice","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (EM ultrastructure, videomicroscopy, fluid flow measurement) in genetically defined mouse mutant, replicated across two tissue types","pmids":["18250199"],"is_preprint":false},{"year":2003,"finding":"Hydin encodes a large ~5099 amino acid protein whose loss-of-function (frameshift deletion in exon 15 causing premature termination) causes lethal communicating hydrocephalus. Expression is restricted to ciliated ependymal cells lining brain ventricles, bronchial epithelium, oviduct, and developing spermatocytes. The protein contains a domain homologous to caldesmon, an actin-binding protein.","method":"cDNA selection and sequencing; Northern blot analysis; in situ hybridization/expression analysis in neonatal brain; identification of hy3 frameshift mutation","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function with defined phenotype and tissue-specific expression, but caldesmon homology domain is sequence-based inference only, single lab","pmids":["12719380"],"is_preprint":false},{"year":2007,"finding":"In Trypanosoma brucei, RNAi knockdown of HYDIN causes loss of cell motility accompanied by two sequential central pair microtubule defects: early mispositioning of the central pair and later complete loss of the central pair, both originating at the basal plate. This demonstrates HYDIN's role in positioning and maintaining the central pair along the entire axoneme length.","method":"RNAi in Trypanosoma brucei; electron microscopy of flagellar ultrastructure; cell motility assays","journal":"BMC biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean genetic knockdown with defined ultrastructural phenotype in orthologous organism, single lab","pmids":["17683645"],"is_preprint":false},{"year":2012,"finding":"Human HYDIN mutations (splice-site and nonsense) cause primary ciliary dyskinesia characterized by loss of the C2b projection of the central pair apparatus in respiratory cilia (demonstrated by electron microscopy tomography), markedly reduced ciliary beating amplitude, and stiff sperm flagella, without affecting nodal cilia function or left-right body asymmetry.","method":"Homozygosity mapping; whole-exome sequencing; electron microscopy tomography of respiratory cilia; high-speed videomicroscopy of cilia and sperm","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple independent families with biallelic loss-of-function mutations, electron tomography confirming C2b projection loss consistent with model organism findings, multiple orthogonal phenotypic methods","pmids":["23022101"],"is_preprint":false},{"year":2020,"finding":"SPEF2 protein is absent from HYDIN-mutant respiratory cilia as detected by immunofluorescence microscopy, revealing that SPEF2 localization to the central pair apparatus is dependent on functional HYDIN. This dependence is used diagnostically to detect HYDIN-related PCD.","method":"Immunofluorescence microscopy of respiratory cells from HYDIN-mutant individuals; genetic analysis confirming HYDIN mutations","journal":"American journal of respiratory cell and molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct IF localization showing SPEF2 dependence on HYDIN in human patient cells, replicated across multiple individuals but single lab","pmids":["31545650"],"is_preprint":false},{"year":2018,"finding":"HYDIN is essential for spermiogenesis in mice: chimeric mice with Hydin-disrupted spermatogonial stem cells produce spermatozoa with short tails that are completely immotile, establishing a direct requirement for HYDIN in sperm flagella assembly and motility.","method":"CRISPR/Cas9 disruption of Hydin in ESCs; chimeric mouse generation; morphological analysis of sperm tail length; motility assays; ICSI rescue experiment","journal":"Experimental animals","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function with defined cellular phenotype (short tails, immotility), functional rescue via ICSI confirming genome viability, single lab","pmids":["30089752"],"is_preprint":false},{"year":2023,"finding":"In HYDIN-deficient infertile men, immunofluorescence shows reduction of SPEF2 in sperm flagella, revealing a HYDIN–SPEF2 interaction in sperm analogous to that in respiratory cilia. Additionally, loss of HYDIN causes reduction of multiple flagellar components including acrosome markers (ACTL7A, ACROSIN, PLCζ1), centrosome marker (Centrin1), and axonemal proteins (TOMM20, SEPT4, SPAG6, RSPHs), and results in multiple morphological abnormalities of the sperm flagella (MMAF).","method":"Whole-exome sequencing; immunofluorescence microscopy of sperm; western blot; transmission electron microscopy; high-speed video microscopy","journal":"Frontiers in genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods in human patient samples, consistent with prior data, single lab","pmids":["36873931"],"is_preprint":false},{"year":2023,"finding":"HYDIN-deficient patient sperm show loss of HYDIN protein along with disassembly of acrosome components and the neck/centrosome region in addition to flagellar structural defects, providing first evidence that HYDIN function extends to acrosome and neck integrity in sperm.","method":"Whole-exome sequencing identifying compound heterozygous HYDIN splice variants; western blot and immunostaining for HYDIN, acrosome markers, centrosome markers, and flagellar components in patient sperm; SEM and TEM","journal":"Frontiers in endocrinology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single patient, single lab; acrosome/neck disassembly is novel and not yet replicated","pmids":["36742411"],"is_preprint":false},{"year":2020,"finding":"HYDIN loss-of-function in human embryonic stem cells reduces GATA4 expression and impairs cardiomyocyte differentiation; shRNA-mediated Hydin knockdown in mice leads to Gata4 downregulation and increased atrial septal defect risk. A human HYDIN variant (c.A2207C) reduces GATA4 expression in differentiating hESCs, and GATA4 overexpression rescues the differentiation defect caused by HYDIN knockdown.","method":"siRNA/shRNA knockdown and overexpression in hESC cardiac differentiation; transgenic Hydin knockdown mice; GATA4 rescue construct; characterization of cardiac-specific phenotype","journal":"Mechanisms of development","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, mechanistic link between ciliary HYDIN and GATA4 transcriptional regulation is novel and mechanistically unclear; no replication","pmids":["32376282"],"is_preprint":false},{"year":2024,"finding":"In situ cryo-electron tomography of intact mouse sperm axoneme at sub-nanometer resolution reveals that HYDIN is a long chain-like ASH-domain-containing protein responsible for connecting the C1 and C2 central pair microtubules. Cfap47 knockout mice show a hollowing of the C1-C2 bridge structure, demonstrating HYDIN's structural role in the bridge connecting the two central microtubules.","method":"In situ cryo-electron tomography; AlphaFold2-aided atomic model building; Cfap47 knockout mouse with structural and motility phenotype analysis","journal":"bioRxiv (preprint)","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in-cell cryo-ET structure with near-complete atomic model provides direct structural assignment of HYDIN to C1-C2 bridge; preprint, single lab, no independent replication yet","pmids":["bio_10.1101_2024.08.06.606614"],"is_preprint":true}],"current_model":"HYDIN encodes a large axonemal central pair (CP) apparatus protein (~5099 aa, containing an ASH domain) that localizes specifically to the C2 microtubule of the 9+2 axoneme, where it forms the C2b projection and, together with CFAP47, bridges the C1 and C2 microtubules; HYDIN interacts with CP proteins CPC1 and KLP1 (in Chlamydomonas) and with SPEF2 (in mammals), and its loss disrupts ciliary/flagellar beat waveform amplitude and switch-point transitions — causing defective mucociliary clearance (primary ciliary dyskinesia), hydrocephalus (from ependymal ciliary failure), and male infertility (from sperm flagella dysmotility and structural abnormalities) — without affecting outer dynein arms, radial spokes, or nodal cilia function."},"narrative":{"mechanistic_narrative":"HYDIN is a large axonemal protein of the central pair (CP) apparatus that is required for the proper waveform and beat regulation of motile cilia and flagella [PMID:17296796, PMID:18250199]. It localizes specifically to the C2 microtubule of the CP, where it forms the C2b projection [PMID:17296796, PMID:23022101], and functions as a chain-like ASH-domain-containing structural element that connects the C1 and C2 central microtubules, a bridge that also depends on CFAP47 [PMID:bio_10.1101_2024.08.06.606614]. Within the CP-radial spoke control pathway that governs dynein arm activity, HYDIN associates biochemically with the CP proteins CPC1 and the kinesin-like protein KLP1 [PMID:17296796], and its presence is required for recruitment of SPEF2 to the central apparatus in both respiratory cilia and sperm flagella [PMID:31545650, PMID:36873931]. HYDIN is also needed to establish and maintain the position of the central pair along the axoneme [PMID:17683645]. Loss of HYDIN disrupts ciliary bending, beat frequency, and switch-point transitions between effective and recovery strokes while leaving outer dynein arms, radial spokes, and nodal cilia function intact [PMID:17296796, PMID:18250199, PMID:23022101]. In humans, biallelic loss-of-function HYDIN mutations cause primary ciliary dyskinesia with loss of the C2b projection and reduced ciliary beating, and HYDIN deficiency underlies lethal communicating hydrocephalus and male infertility through immotile, structurally abnormal sperm flagella [PMID:18250199, PMID:12719380, PMID:23022101, PMID:30089752, PMID:36873931].","teleology":[{"year":2003,"claim":"Established HYDIN as a hydrocephalus-causing gene and defined where it is expressed, framing it as a ciliated-cell protein before its molecular role was known.","evidence":"cDNA cloning, expression analysis, and identification of the hy3 frameshift mutation in mice","pmids":["12719380"],"confidence":"Medium","gaps":["Subcellular localization within the axoneme not determined","Caldesmon-homology domain is sequence inference only, no functional test"]},{"year":2007,"claim":"Placed HYDIN structurally and biochemically within the central pair apparatus, showing it builds the C2b projection and acts in the CP-radial spoke pathway that controls dynein-driven beating.","evidence":"Antibody localization, RNAi knockdown, co-purification with CPC1 and KLP1, and EM in Chlamydomonas","pmids":["17296796"],"confidence":"High","gaps":["Direct vs. indirect nature of CPC1/KLP1 interactions not dissected","Mechanism linking C2b loss to switch-point arrest not resolved"]},{"year":2007,"claim":"Demonstrated that HYDIN is needed to position and maintain the central pair along the full axoneme length, not merely to build a single projection.","evidence":"RNAi, EM, and motility assays in Trypanosoma brucei","pmids":["17683645"],"confidence":"Medium","gaps":["Molecular basis of CP mispositioning at the basal plate unknown","Single organism, single lab"]},{"year":2008,"claim":"Confirmed in a mammalian system that HYDIN loss removes a specific CP projection and impairs cilia-driven fluid flow, mechanistically connecting the structural defect to hydrocephalus.","evidence":"EM ultrastructure, high-speed videomicroscopy, and fluid flow analysis in Hydin mutant mice","pmids":["18250199"],"confidence":"High","gaps":["Does not address how the projection regulates dynein activity","Sperm and reproductive phenotypes not examined"]},{"year":2012,"claim":"Established HYDIN as a human PCD gene and confirmed the C2b projection defect by tomography, while showing nodal cilia and left-right asymmetry are spared.","evidence":"Homozygosity mapping, exome sequencing, EM tomography, and videomicroscopy of cilia and sperm in PCD families","pmids":["23022101"],"confidence":"High","gaps":["Why nodal cilia are unaffected not mechanistically explained","Interacting partners maintaining the C2b projection not identified"]},{"year":2018,"claim":"Provided direct genetic evidence that HYDIN is required for sperm flagellar assembly and motility, extending its role beyond respiratory and ependymal cilia.","evidence":"CRISPR disruption in ESCs, chimeric mice, sperm morphology/motility assays, and ICSI rescue","pmids":["30089752"],"confidence":"Medium","gaps":["Molecular cause of short-tail phenotype not defined","Chimeric, not full knockout, animals"]},{"year":2020,"claim":"Identified SPEF2 as a HYDIN-dependent CP component, revealing a recruitment relationship usable for PCD diagnosis.","evidence":"Immunofluorescence of SPEF2 in HYDIN-mutant patient respiratory cells","pmids":["31545650"],"confidence":"Medium","gaps":["Direct physical HYDIN-SPEF2 interaction not demonstrated","Whether SPEF2 loss contributes to motility defect not separated from C2b loss"]},{"year":2023,"claim":"Showed the HYDIN-SPEF2 dependence operates in sperm and that HYDIN loss broadly destabilizes acrosomal, centrosomal, and axonemal components in MMAF patients.","evidence":"Exome sequencing, immunofluorescence, western blot, TEM, and videomicroscopy of patient sperm","pmids":["36873931","36742411"],"confidence":"Medium","gaps":["Acrosome/neck disassembly is novel and based on single patient (idx 8)","Whether HYDIN acts directly on acrosome/neck or indirectly via flagellar collapse unresolved"]},{"year":2020,"claim":"Proposed a non-canonical role for HYDIN in cardiomyocyte differentiation via GATA4 regulation, distinct from its axonemal function.","evidence":"Knockdown/overexpression in hESC cardiac differentiation, transgenic mice, and GATA4 rescue","pmids":["32376282"],"confidence":"Low","gaps":["Mechanistic link between ciliary HYDIN and GATA4 transcription unclear and not replicated","Inconsistent with HYDIN's established axonemal localization"]},{"year":2024,"claim":"Resolved HYDIN's molecular architecture in situ, assigning it as the chain-like ASH-domain protein forming the C1-C2 bridge together with CFAP47.","evidence":"In situ cryo-electron tomography with AlphaFold2-aided modeling and Cfap47 knockout mouse analysis (preprint)","pmids":["bio_10.1101_2024.08.06.606614"],"confidence":"Medium","gaps":["Preprint, single lab, not independently replicated","Atomic model partly inference from AlphaFold2"]},{"year":null,"claim":"How the HYDIN-built C1-C2 bridge and C2b projection mechanically transduce signals to regulate dynein activity and beat switch-points remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No reconstituted assay of HYDIN-dependent dynein regulation","Direct interaction map among HYDIN, CFAP47, SPEF2, CPC1, KLP1 incomplete"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,1,4,10]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0,2]}],"localization":[{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[0,1,4,10]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,3,10]}],"pathway":[{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[0,1,10]}],"complexes":["central pair apparatus","C1-C2 central pair bridge"],"partners":["CPC1","KLP1","SPEF2","CFAP47"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q4G0P3","full_name":"Hydrocephalus-inducing protein homolog","aliases":[],"length_aa":5121,"mass_kda":575.9,"function":"Required for ciliary motility","subcellular_location":"Cell projection, cilium; Cytoplasm, cytoskeleton, cilium axoneme; Cell projection, cilium, flagellum","url":"https://www.uniprot.org/uniprotkb/Q4G0P3/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/HYDIN","classification":"Not Classified","n_dependent_lines":99,"n_total_lines":1208,"dependency_fraction":0.08195364238410596},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/HYDIN","total_profiled":1310},"omim":[{"mim_id":"615434","title":"RETINITIS PIGMENTOSA 82 WITH OR WITHOUT SITUS INVERSUS; RP82","url":"https://www.omim.org/entry/615434"},{"mim_id":"615407","title":"ADP-RIBOSYLATION FACTOR-LIKE GTPase 2-BINDING PROTEIN; ARL2BP","url":"https://www.omim.org/entry/615407"},{"mim_id":"612475","title":"CHROMOSOME 1q21.1 DUPLICATION SYNDROME","url":"https://www.omim.org/entry/612475"},{"mim_id":"612474","title":"CHROMOSOME 1q21.1 DELETION SYNDROME, 1.35-MB","url":"https://www.omim.org/entry/612474"},{"mim_id":"611679","title":"F-BOX AND WD40 DOMAIN PROTEIN 10; FBXW10","url":"https://www.omim.org/entry/611679"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytokinetic bridge","reliability":"Approved"},{"location":"Primary cilium","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"},{"location":"Equatorial segment","reliability":"Approved"},{"location":"Nucleoplasm","reliability":"Additional"},{"location":"Mitotic spindle","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"fallopian tube","ntpm":5.0},{"tissue":"retina","ntpm":6.3}],"url":"https://www.proteinatlas.org/search/HYDIN"},"hgnc":{"alias_symbol":["DKFZp434D0513","KIAA1864","PPP1R31","CILD5"],"prev_symbol":[]},"alphafold":{"accession":"Q4G0P3","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q4G0P3","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q4G0P3-8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q4G0P3-8-F1-predicted_aligned_error_v6.png","plddt_mean":84.5},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=HYDIN","jax_strain_url":"https://www.jax.org/strain/search?query=HYDIN"},"sequence":{"accession":"Q4G0P3","fasta_url":"https://rest.uniprot.org/uniprotkb/Q4G0P3.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q4G0P3/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q4G0P3"}},"corpus_meta":[{"pmid":"23022101","id":"PMC_23022101","title":"Recessive HYDIN mutations cause primary ciliary dyskinesia without randomization of left-right body asymmetry.","date":"2012","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/23022101","citation_count":231,"is_preprint":false},{"pmid":"18250199","id":"PMC_18250199","title":"Mutations in Hydin impair ciliary motility in mice.","date":"2008","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/18250199","citation_count":207,"is_preprint":false},{"pmid":"12719380","id":"PMC_12719380","title":"Congenital hydrocephalus in hy3 mice is caused by a frameshift mutation in Hydin, a large novel gene.","date":"2003","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/12719380","citation_count":129,"is_preprint":false},{"pmid":"17296796","id":"PMC_17296796","title":"Chlamydomonas reinhardtii hydin is a central pair protein required for flagellar motility.","date":"2007","source":"The Journal of cell 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Society","url":"https://pubmed.ncbi.nlm.nih.gov/24700285","citation_count":47,"is_preprint":false},{"pmid":"16938426","id":"PMC_16938426","title":"A 360-kb interchromosomal duplication of the human HYDIN locus.","date":"2006","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/16938426","citation_count":41,"is_preprint":false},{"pmid":"36873931","id":"PMC_36873931","title":"Pathogenic gene variants in CCDC39, CCDC40, RSPH1, RSPH9, HYDIN, and SPEF2 cause defects of sperm flagella composition and male infertility.","date":"2023","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/36873931","citation_count":25,"is_preprint":false},{"pmid":"30089752","id":"PMC_30089752","title":"Chimeric analysis with newly established EGFP/DsRed2-tagged ES cells identify HYDIN as essential for spermiogenesis in mice.","date":"2018","source":"Experimental animals","url":"https://pubmed.ncbi.nlm.nih.gov/30089752","citation_count":16,"is_preprint":false},{"pmid":"24777681","id":"PMC_24777681","title":"Alternative variants of human HYDIN are novel cancer-associated antigens recognized by adaptive immunity.","date":"2013","source":"Cancer immunology research","url":"https://pubmed.ncbi.nlm.nih.gov/24777681","citation_count":15,"is_preprint":false},{"pmid":"17296793","id":"PMC_17296793","title":"Hydin seek: finding a function in ciliary motility.","date":"2007","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/17296793","citation_count":12,"is_preprint":false},{"pmid":"38605126","id":"PMC_38605126","title":"Combined approaches, including long-read sequencing, address the diagnostic challenge of HYDIN in primary ciliary dyskinesia.","date":"2024","source":"European journal of human genetics : 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associated with male infertility in two Chinese families.","date":"2023","source":"Frontiers in endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/36742411","citation_count":4,"is_preprint":false},{"pmid":"28441829","id":"PMC_28441829","title":"[Primary ciliary dyskinesia with HYDIN gene mutations in a child and literature review].","date":"2017","source":"Zhonghua er ke za zhi = Chinese journal of pediatrics","url":"https://pubmed.ncbi.nlm.nih.gov/28441829","citation_count":3,"is_preprint":false},{"pmid":"39805680","id":"PMC_39805680","title":"Robust detection of pathogenic HYDIN variants that cause primary ciliary dyskinesia using RNA-seq of nasal mucosa.","date":"2025","source":"Journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/39805680","citation_count":3,"is_preprint":false},{"pmid":"39579181","id":"PMC_39579181","title":"Hydin as the Candidate Master Sex Determination Gene in Channel Catfish (Ictalurus punctatus) and Its Epigenetic 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axoneme","date":"2024-08-06","source":"bioRxiv","url":"https://doi.org/10.1101/2024.08.06.606614","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":14157,"output_tokens":3025,"usd":0.043923,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10477,"output_tokens":3154,"usd":0.065617,"stage2_stop_reason":"end_turn"},"total_usd":0.10954,"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\": 2007,\n      \"finding\": \"Chlamydomonas reinhardtii HYDIN is a central pair (CP) protein located specifically on the C2 microtubule of the CP apparatus. An ~80% knockdown results in loss of the C2b projection and flagellar arrest at switch points between effective and recovery strokes. HYDIN interacts biochemically with CP proteins CPC1 and kinesin-like protein 1 (KLP1), placing it in the CP-radial spoke control pathway that regulates dynein arm activity.\",\n      \"method\": \"Antibody localization to C2 microtubule; RNAi knockdown; biochemical interaction analyses (co-purification with CPC1 and KLP1); electron microscopy of axoneme ultrastructure\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal biochemical interaction, precise subcellular localization, loss-of-function with defined structural and motility phenotype, multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"17296796\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"In mice, Hydin mutations cause loss of a specific projection on one of the two central pair microtubules of the ciliary axoneme; outer dynein arms and radial spokes are normal. This structural defect impairs ciliary bending and beat frequency in both brain ependymal cilia and tracheal cilia, abolishing fluid flow and causing hydrocephalus.\",\n      \"method\": \"Electron microscopy of axoneme ultrastructure; high-speed videomicroscopy of ciliary beat; comparison of wild-type vs. Hydin mutant mice\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (EM ultrastructure, videomicroscopy, fluid flow measurement) in genetically defined mouse mutant, replicated across two tissue types\",\n      \"pmids\": [\"18250199\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Hydin encodes a large ~5099 amino acid protein whose loss-of-function (frameshift deletion in exon 15 causing premature termination) causes lethal communicating hydrocephalus. Expression is restricted to ciliated ependymal cells lining brain ventricles, bronchial epithelium, oviduct, and developing spermatocytes. The protein contains a domain homologous to caldesmon, an actin-binding protein.\",\n      \"method\": \"cDNA selection and sequencing; Northern blot analysis; in situ hybridization/expression analysis in neonatal brain; identification of hy3 frameshift mutation\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function with defined phenotype and tissue-specific expression, but caldesmon homology domain is sequence-based inference only, single lab\",\n      \"pmids\": [\"12719380\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In Trypanosoma brucei, RNAi knockdown of HYDIN causes loss of cell motility accompanied by two sequential central pair microtubule defects: early mispositioning of the central pair and later complete loss of the central pair, both originating at the basal plate. This demonstrates HYDIN's role in positioning and maintaining the central pair along the entire axoneme length.\",\n      \"method\": \"RNAi in Trypanosoma brucei; electron microscopy of flagellar ultrastructure; cell motility assays\",\n      \"journal\": \"BMC biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic knockdown with defined ultrastructural phenotype in orthologous organism, single lab\",\n      \"pmids\": [\"17683645\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Human HYDIN mutations (splice-site and nonsense) cause primary ciliary dyskinesia characterized by loss of the C2b projection of the central pair apparatus in respiratory cilia (demonstrated by electron microscopy tomography), markedly reduced ciliary beating amplitude, and stiff sperm flagella, without affecting nodal cilia function or left-right body asymmetry.\",\n      \"method\": \"Homozygosity mapping; whole-exome sequencing; electron microscopy tomography of respiratory cilia; high-speed videomicroscopy of cilia and sperm\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple independent families with biallelic loss-of-function mutations, electron tomography confirming C2b projection loss consistent with model organism findings, multiple orthogonal phenotypic methods\",\n      \"pmids\": [\"23022101\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SPEF2 protein is absent from HYDIN-mutant respiratory cilia as detected by immunofluorescence microscopy, revealing that SPEF2 localization to the central pair apparatus is dependent on functional HYDIN. This dependence is used diagnostically to detect HYDIN-related PCD.\",\n      \"method\": \"Immunofluorescence microscopy of respiratory cells from HYDIN-mutant individuals; genetic analysis confirming HYDIN mutations\",\n      \"journal\": \"American journal of respiratory cell and molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct IF localization showing SPEF2 dependence on HYDIN in human patient cells, replicated across multiple individuals but single lab\",\n      \"pmids\": [\"31545650\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"HYDIN is essential for spermiogenesis in mice: chimeric mice with Hydin-disrupted spermatogonial stem cells produce spermatozoa with short tails that are completely immotile, establishing a direct requirement for HYDIN in sperm flagella assembly and motility.\",\n      \"method\": \"CRISPR/Cas9 disruption of Hydin in ESCs; chimeric mouse generation; morphological analysis of sperm tail length; motility assays; ICSI rescue experiment\",\n      \"journal\": \"Experimental animals\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function with defined cellular phenotype (short tails, immotility), functional rescue via ICSI confirming genome viability, single lab\",\n      \"pmids\": [\"30089752\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In HYDIN-deficient infertile men, immunofluorescence shows reduction of SPEF2 in sperm flagella, revealing a HYDIN–SPEF2 interaction in sperm analogous to that in respiratory cilia. Additionally, loss of HYDIN causes reduction of multiple flagellar components including acrosome markers (ACTL7A, ACROSIN, PLCζ1), centrosome marker (Centrin1), and axonemal proteins (TOMM20, SEPT4, SPAG6, RSPHs), and results in multiple morphological abnormalities of the sperm flagella (MMAF).\",\n      \"method\": \"Whole-exome sequencing; immunofluorescence microscopy of sperm; western blot; transmission electron microscopy; high-speed video microscopy\",\n      \"journal\": \"Frontiers in genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods in human patient samples, consistent with prior data, single lab\",\n      \"pmids\": [\"36873931\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"HYDIN-deficient patient sperm show loss of HYDIN protein along with disassembly of acrosome components and the neck/centrosome region in addition to flagellar structural defects, providing first evidence that HYDIN function extends to acrosome and neck integrity in sperm.\",\n      \"method\": \"Whole-exome sequencing identifying compound heterozygous HYDIN splice variants; western blot and immunostaining for HYDIN, acrosome markers, centrosome markers, and flagellar components in patient sperm; SEM and TEM\",\n      \"journal\": \"Frontiers in endocrinology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single patient, single lab; acrosome/neck disassembly is novel and not yet replicated\",\n      \"pmids\": [\"36742411\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"HYDIN loss-of-function in human embryonic stem cells reduces GATA4 expression and impairs cardiomyocyte differentiation; shRNA-mediated Hydin knockdown in mice leads to Gata4 downregulation and increased atrial septal defect risk. A human HYDIN variant (c.A2207C) reduces GATA4 expression in differentiating hESCs, and GATA4 overexpression rescues the differentiation defect caused by HYDIN knockdown.\",\n      \"method\": \"siRNA/shRNA knockdown and overexpression in hESC cardiac differentiation; transgenic Hydin knockdown mice; GATA4 rescue construct; characterization of cardiac-specific phenotype\",\n      \"journal\": \"Mechanisms of development\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, mechanistic link between ciliary HYDIN and GATA4 transcriptional regulation is novel and mechanistically unclear; no replication\",\n      \"pmids\": [\"32376282\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In situ cryo-electron tomography of intact mouse sperm axoneme at sub-nanometer resolution reveals that HYDIN is a long chain-like ASH-domain-containing protein responsible for connecting the C1 and C2 central pair microtubules. Cfap47 knockout mice show a hollowing of the C1-C2 bridge structure, demonstrating HYDIN's structural role in the bridge connecting the two central microtubules.\",\n      \"method\": \"In situ cryo-electron tomography; AlphaFold2-aided atomic model building; Cfap47 knockout mouse with structural and motility phenotype analysis\",\n      \"journal\": \"bioRxiv (preprint)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in-cell cryo-ET structure with near-complete atomic model provides direct structural assignment of HYDIN to C1-C2 bridge; preprint, single lab, no independent replication yet\",\n      \"pmids\": [\"bio_10.1101_2024.08.06.606614\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"HYDIN encodes a large axonemal central pair (CP) apparatus protein (~5099 aa, containing an ASH domain) that localizes specifically to the C2 microtubule of the 9+2 axoneme, where it forms the C2b projection and, together with CFAP47, bridges the C1 and C2 microtubules; HYDIN interacts with CP proteins CPC1 and KLP1 (in Chlamydomonas) and with SPEF2 (in mammals), and its loss disrupts ciliary/flagellar beat waveform amplitude and switch-point transitions — causing defective mucociliary clearance (primary ciliary dyskinesia), hydrocephalus (from ependymal ciliary failure), and male infertility (from sperm flagella dysmotility and structural abnormalities) — without affecting outer dynein arms, radial spokes, or nodal cilia function.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"HYDIN is a large axonemal protein of the central pair (CP) apparatus that is required for the proper waveform and beat regulation of motile cilia and flagella [#0, #1]. It localizes specifically to the C2 microtubule of the CP, where it forms the C2b projection [#0, #4], and functions as a chain-like ASH-domain-containing structural element that connects the C1 and C2 central microtubules, a bridge that also depends on CFAP47 [#10]. Within the CP-radial spoke control pathway that governs dynein arm activity, HYDIN associates biochemically with the CP proteins CPC1 and the kinesin-like protein KLP1 [#0], and its presence is required for recruitment of SPEF2 to the central apparatus in both respiratory cilia and sperm flagella [#5, #7]. HYDIN is also needed to establish and maintain the position of the central pair along the axoneme [#3]. Loss of HYDIN disrupts ciliary bending, beat frequency, and switch-point transitions between effective and recovery strokes while leaving outer dynein arms, radial spokes, and nodal cilia function intact [#0, #1, #4]. In humans, biallelic loss-of-function HYDIN mutations cause primary ciliary dyskinesia with loss of the C2b projection and reduced ciliary beating, and HYDIN deficiency underlies lethal communicating hydrocephalus and male infertility through immotile, structurally abnormal sperm flagella [#1, #2, #4, #6, #7].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Established HYDIN as a hydrocephalus-causing gene and defined where it is expressed, framing it as a ciliated-cell protein before its molecular role was known.\",\n      \"evidence\": \"cDNA cloning, expression analysis, and identification of the hy3 frameshift mutation in mice\",\n      \"pmids\": [\"12719380\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Subcellular localization within the axoneme not determined\", \"Caldesmon-homology domain is sequence inference only, no functional test\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Placed HYDIN structurally and biochemically within the central pair apparatus, showing it builds the C2b projection and acts in the CP-radial spoke pathway that controls dynein-driven beating.\",\n      \"evidence\": \"Antibody localization, RNAi knockdown, co-purification with CPC1 and KLP1, and EM in Chlamydomonas\",\n      \"pmids\": [\"17296796\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct vs. indirect nature of CPC1/KLP1 interactions not dissected\", \"Mechanism linking C2b loss to switch-point arrest not resolved\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Demonstrated that HYDIN is needed to position and maintain the central pair along the full axoneme length, not merely to build a single projection.\",\n      \"evidence\": \"RNAi, EM, and motility assays in Trypanosoma brucei\",\n      \"pmids\": [\"17683645\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of CP mispositioning at the basal plate unknown\", \"Single organism, single lab\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Confirmed in a mammalian system that HYDIN loss removes a specific CP projection and impairs cilia-driven fluid flow, mechanistically connecting the structural defect to hydrocephalus.\",\n      \"evidence\": \"EM ultrastructure, high-speed videomicroscopy, and fluid flow analysis in Hydin mutant mice\",\n      \"pmids\": [\"18250199\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not address how the projection regulates dynein activity\", \"Sperm and reproductive phenotypes not examined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Established HYDIN as a human PCD gene and confirmed the C2b projection defect by tomography, while showing nodal cilia and left-right asymmetry are spared.\",\n      \"evidence\": \"Homozygosity mapping, exome sequencing, EM tomography, and videomicroscopy of cilia and sperm in PCD families\",\n      \"pmids\": [\"23022101\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why nodal cilia are unaffected not mechanistically explained\", \"Interacting partners maintaining the C2b projection not identified\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Provided direct genetic evidence that HYDIN is required for sperm flagellar assembly and motility, extending its role beyond respiratory and ependymal cilia.\",\n      \"evidence\": \"CRISPR disruption in ESCs, chimeric mice, sperm morphology/motility assays, and ICSI rescue\",\n      \"pmids\": [\"30089752\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular cause of short-tail phenotype not defined\", \"Chimeric, not full knockout, animals\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identified SPEF2 as a HYDIN-dependent CP component, revealing a recruitment relationship usable for PCD diagnosis.\",\n      \"evidence\": \"Immunofluorescence of SPEF2 in HYDIN-mutant patient respiratory cells\",\n      \"pmids\": [\"31545650\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct physical HYDIN-SPEF2 interaction not demonstrated\", \"Whether SPEF2 loss contributes to motility defect not separated from C2b loss\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Showed the HYDIN-SPEF2 dependence operates in sperm and that HYDIN loss broadly destabilizes acrosomal, centrosomal, and axonemal components in MMAF patients.\",\n      \"evidence\": \"Exome sequencing, immunofluorescence, western blot, TEM, and videomicroscopy of patient sperm\",\n      \"pmids\": [\"36873931\", \"36742411\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Acrosome/neck disassembly is novel and based on single patient (idx 8)\", \"Whether HYDIN acts directly on acrosome/neck or indirectly via flagellar collapse unresolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Proposed a non-canonical role for HYDIN in cardiomyocyte differentiation via GATA4 regulation, distinct from its axonemal function.\",\n      \"evidence\": \"Knockdown/overexpression in hESC cardiac differentiation, transgenic mice, and GATA4 rescue\",\n      \"pmids\": [\"32376282\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Mechanistic link between ciliary HYDIN and GATA4 transcription unclear and not replicated\", \"Inconsistent with HYDIN's established axonemal localization\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Resolved HYDIN's molecular architecture in situ, assigning it as the chain-like ASH-domain protein forming the C1-C2 bridge together with CFAP47.\",\n      \"evidence\": \"In situ cryo-electron tomography with AlphaFold2-aided modeling and Cfap47 knockout mouse analysis (preprint)\",\n      \"pmids\": [\"bio_10.1101_2024.08.06.606614\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, single lab, not independently replicated\", \"Atomic model partly inference from AlphaFold2\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the HYDIN-built C1-C2 bridge and C2b projection mechanically transduce signals to regulate dynein activity and beat switch-points remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No reconstituted assay of HYDIN-dependent dynein regulation\", \"Direct interaction map among HYDIN, CFAP47, SPEF2, CPC1, KLP1 incomplete\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 1, 4, 10]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [0, 1, 4, 10]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 3, 10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [0, 1, 10]}\n    ],\n    \"complexes\": [\"central pair apparatus\", \"C1-C2 central pair bridge\"],\n    \"partners\": [\"CPC1\", \"KLP1\", \"SPEF2\", \"CFAP47\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"faith_supported":6,"faith_total":6,"faith_pct":100.0}}