{"gene":"DRC2","run_date":"2026-06-09T23:54:42","timeline":{"discoveries":[{"year":2013,"finding":"CCDC65 (DRC2) is an essential component of the nexin-dynein regulatory complex (N-DRC) in Chlamydomonas flagella; the ida6 mutant identifies CCDC65/FAP250 as required for N-DRC assembly, and ccdc65 knockdown in zebrafish alters cilia beat pattern rather than blocking dynein arm assembly.","method":"Chlamydomonas genetic mutant analysis (ida6), zebrafish morpholino knockdown, biochemical analysis of flagellar components","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic mutant analysis in Chlamydomonas combined with zebrafish in vivo knockdown, replicated across multiple model organisms and validated in human PCD patients","pmids":["24094744"],"is_preprint":false},{"year":2013,"finding":"CCDC65, the human ortholog of Chlamydomonas DRC2, localizes to cilia of nasal epithelial cells; loss of CCDC65 (via patient mutation or shRNA knockdown) causes stiff and dyskinetic cilia beating without detectable ultrastructural axonemal defects, and results in absence of GAS8 (another N-DRC component), demonstrating a structural/functional link between CCDC65 and GAS8 within the N-DRC.","method":"Immunostaining/localization in human airway epithelial cells, shRNA knockdown in human tracheobronchial epithelial cells, video-microscopy of cilia motion, immunoblotting for GAS8","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal loss-of-function (patient mutation + shRNA), multiple orthogonal readouts (localization, motility, co-component stability), single lab","pmids":["23991085"],"is_preprint":false},{"year":2017,"finding":"The C-terminal region of DRC2 is critical for co-assembly of DRC2 and DRC1 to form the base plate of the N-DRC and its attachment to the outer doublet microtubule; loss of DRC2 disrupts assembly of multiple other N-DRC subunits and destabilizes associated structures including inner dynein arms, radial spokes, and the calmodulin- and spoke-associated complex, establishing DRC2 as a central hub for N-DRC assembly.","method":"High-resolution proteomics, cryo-electron tomography structural analysis, and motility phenotyping of Chlamydomonas drc2 mutants","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1 / Moderate — structural (cryo-ET) plus proteomic analysis with defined mutants, multiple orthogonal methods in one rigorous study","pmids":["29167384"],"is_preprint":false},{"year":2013,"finding":"FAP250 (CCDC65/DRC2) undergoes asymmetric dimethylation on arginine residues (aDMA) during flagellar disassembly in Chlamydomonas, catalyzed by PRMT1, a protein arginine methyltransferase present in the flagellar matrix; this methylation is associated with axonemal instability during resorption.","method":"Tandem mass spectrometry identification of aDMA-modified proteins, immunolocalization of PRMT1 during flagellar resorption, gel shift assays","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — mass spectrometry identification with immunolocalization, single lab, no direct functional rescue or mutagenesis of the modification sites","pmids":["24152136"],"is_preprint":false},{"year":2023,"finding":"DRC2 is transported into Chlamydomonas flagella by intraflagellar transport (IFT) independently of DRC4; in vivo imaging showed DRC2 moves on IFT trains in mutants lacking DRC4 (and vice versa), with only occasional co-transport, indicating the N-DRC assembles onto the axoneme by stepwise addition of subunits rather than as a pre-assembled complex.","method":"In vivo fluorescence imaging of tagged DRC2 and DRC4 in Chlamydomonas mutants, simultaneous dual-color IFT imaging","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct in vivo imaging with genetic rescue constructs, multiple mutant backgrounds, two orthogonal tagged proteins imaged simultaneously","pmids":["36598807"],"is_preprint":false},{"year":2023,"finding":"Homozygous truncating variants in CCDC65 cause near-absence of CCDC65 protein in human sperm and result in multiple morphological abnormalities of the sperm flagella (MMAF) and asthenozoospermia; loss of CCDC65 in patient sperm also causes loss of GAS8, confirming a structural/functional link between these two N-DRC components in the sperm flagellar axoneme.","method":"Immunoblotting of patient sperm for CCDC65 and GAS8, genetic variant identification in human patients","journal":"Clinical genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct protein detection by immunoblot in patient material with defined loss-of-function variant, single lab, limited to patient samples","pmids":["37975235"],"is_preprint":false},{"year":2006,"finding":"NYD-SP28 (DRC2) protein localizes to the entire sperm tail in human spermatozoa and is post-translationally modified during sperm capacitation, as shown by 2D gel electrophoresis and immunoblotting.","method":"Immunohistochemistry, EGFP fusion protein localization, 2D gel electrophoresis and immunoblotting of sperm before and after capacitation","journal":"International journal of molecular medicine","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, localization and post-translational modification shown but modification writer/eraser not identified and functional consequence not established","pmids":["17089017"],"is_preprint":false}],"current_model":"DRC2/CCDC65 is a core structural subunit of the nexin-dynein regulatory complex (N-DRC) in motile cilia and sperm flagella; its C-terminal region is required for co-assembly with DRC1 to form the N-DRC base plate and attachment to the outer doublet microtubule, its loss destabilizes multiple N-DRC subunits (including GAS8) and associated axonemal structures (inner dynein arms, radial spokes), it is transported into flagella by IFT independently of DRC4 suggesting stepwise axonemal assembly, and it undergoes PRMT1-mediated arginine methylation during flagellar disassembly; in humans, loss-of-function mutations cause primary ciliary dyskinesia with dyskinetic (but structurally intact) cilia and also asthenozoospermia with flagellar structural defects."},"narrative":{"mechanistic_narrative":"DRC2 (CCDC65) is a core structural subunit of the nexin-dynein regulatory complex (N-DRC), the axonemal structure that links and regulates outer doublet microtubules in motile cilia and sperm flagella [PMID:24094744, PMID:23991085]. Its C-terminal region drives co-assembly with DRC1 to form the N-DRC base plate and its attachment to the outer doublet microtubule, making DRC2 a central hub whose loss disrupts assembly of multiple N-DRC subunits and destabilizes associated axonemal structures including inner dynein arms, radial spokes, and the calmodulin- and spoke-associated complex [PMID:29167384]. The stability of the N-DRC component GAS8 depends on DRC2, as loss of DRC2 in human airway cells and in patient sperm eliminates GAS8 [PMID:23991085, PMID:37975235]. DRC2 is delivered into the flagellum by intraflagellar transport independently of DRC4, indicating that the N-DRC is built by stepwise addition of subunits onto the axoneme rather than as a preassembled complex [PMID:36598807]. Functionally, DRC2 loss produces stiff, dyskinetic ciliary beating without gross ultrastructural defects [PMID:23991085], and in humans loss-of-function mutations cause primary ciliary dyskinesia [PMID:23991085] and asthenozoospermia with multiple morphological abnormalities of the sperm flagella [PMID:37975235].","teleology":[{"year":2013,"claim":"Established DRC2/CCDC65 as an essential N-DRC component and showed its loss alters ciliary beat regulation rather than blocking dynein arm assembly, defining it as a regulatory rather than load-bearing motor element.","evidence":"Chlamydomonas ida6 mutant analysis, zebrafish morpholino knockdown, and biochemical flagellar analysis","pmids":["24094744"],"confidence":"High","gaps":["Molecular position of DRC2 within the N-DRC not resolved","Mechanism by which beat pattern is regulated not defined"]},{"year":2013,"claim":"Linked human CCDC65 loss to dyskinetic cilia with intact ultrastructure and to destabilization of the N-DRC subunit GAS8, connecting the gene to primary ciliary dyskinesia and revealing an interdependence among N-DRC subunits.","evidence":"Localization, shRNA knockdown, and video-microscopy in human airway epithelial cells with GAS8 immunoblotting","pmids":["23991085"],"confidence":"High","gaps":["Direct physical contact between CCDC65 and GAS8 not demonstrated","Reason for absent ultrastructural defect despite functional loss unclear"]},{"year":2013,"claim":"Identified PRMT1-catalyzed asymmetric arginine dimethylation of DRC2 during flagellar disassembly, raising the possibility that a post-translational mark accompanies axonemal resorption.","evidence":"Tandem MS identification of aDMA-modified proteins, PRMT1 immunolocalization, gel shift assays in Chlamydomonas","pmids":["24152136"],"confidence":"Medium","gaps":["No mutagenesis of methylation sites to test function","Causal role of methylation in disassembly not established"]},{"year":2017,"claim":"Mapped DRC2's C-terminal region as essential for co-assembly with DRC1 into the N-DRC base plate and microtubule attachment, establishing DRC2 as a structural hub whose loss collapses multiple subunits and associated axonemal structures.","evidence":"Proteomics, cryo-electron tomography, and motility phenotyping of Chlamydomonas drc2 mutants","pmids":["29167384"],"confidence":"High","gaps":["Atomic-resolution interface with DRC1 not resolved","Order of subunit recruitment during assembly not fully defined"]},{"year":2023,"claim":"Demonstrated DRC2 and DRC4 are transported into flagella independently on IFT trains, establishing that the N-DRC assembles by stepwise subunit addition rather than as a preformed complex.","evidence":"Dual-color in vivo IFT imaging of tagged DRC2 and DRC4 in Chlamydomonas mutants","pmids":["36598807"],"confidence":"High","gaps":["Order and docking sequence of remaining N-DRC subunits unknown","Regulation of IFT loading not characterized"]},{"year":2023,"claim":"Extended the CCDC65 disease spectrum to human male infertility, showing truncating variants abolish CCDC65 and GAS8 in sperm and cause MMAF and asthenozoospermia.","evidence":"Immunoblotting of patient sperm and genetic variant identification","pmids":["37975235"],"confidence":"Medium","gaps":["Single-lab patient-material study","Functional rescue not performed"]},{"year":null,"claim":"How DRC2 mechanically couples N-DRC integrity to the regulation of beat waveform, and whether its arginine methylation actively triggers axonemal disassembly, remain open.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No causal test of methylation in disassembly","Mechanism converting N-DRC structural loss into dyskinetic beating undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,2]}],"localization":[{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[1]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[2]}],"pathway":[{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[2,4]}],"complexes":["nexin-dynein regulatory complex (N-DRC)"],"partners":["DRC1","DRC4","GAS8","PRMT1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8IXS2","full_name":"Dynein regulatory complex subunit 2","aliases":["Coiled-coil domain-containing protein 65","Testis development protein NYD-SP28"],"length_aa":484,"mass_kda":57.3,"function":"Component of the nexin-dynein regulatory complex (N-DRC), a key regulator of ciliary/flagellar motility which maintains the alignment and integrity of the distal axoneme and regulates microtubule sliding in motile axonemes (By similarity). Plays a critical role in the assembly of N-DRC and also stabilizes the assembly of multiple inner dynein arms and radial spokes. Coassembles with DRC1 to form a central scaffold needed for assembly of the N-DRC and its attachment to the outer doublet microtubules (PubMed:24094744)","subcellular_location":"Cytoplasm, cytoskeleton, flagellum basal body; Cell projection, cilium, flagellum; Cytoplasm, cytoskeleton, flagellum axoneme","url":"https://www.uniprot.org/uniprotkb/Q8IXS2/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"CCDC65","url":"https://depmap.org/portal/gene/CCDC65","classification":"Not Classified","n_dependent_lines":4,"n_total_lines":1208,"dependency_fraction":0.0033112582781456954},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/DRC2","total_profiled":1310},"omim":[{"mim_id":"615504","title":"CILIARY DYSKINESIA, PRIMARY, 27; CILD27","url":"https://www.omim.org/entry/615504"},{"mim_id":"611088","title":"DYNEIN REGULATORY COMPLEX, SUBUNIT 2; DRC2","url":"https://www.omim.org/entry/611088"}],"hpa":{"profiled":true,"resolved_as":"CCDC65","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"},{"location":"Primary cilium transition zone","reliability":"Approved"},{"location":"Centriolar satellite","reliability":"Approved"},{"location":"Mid piece","reliability":"Additional"},{"location":"Principal piece","reliability":"Additional"},{"location":"Annulus","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"choroid plexus","ntpm":18.3},{"tissue":"fallopian tube","ntpm":25.0},{"tissue":"testis","ntpm":34.8}],"url":"https://www.proteinatlas.org/search/CCDC65"},"hgnc":{"alias_symbol":["NYD-SP28","FLJ35732","FAP250","CFAP250","CILD27","DRC2"],"prev_symbol":["CCDC65"]},"alphafold":{"accession":"Q8IXS2","domains":[{"cath_id":"1.20.5","chopping":"24-195","consensus_level":"medium","plddt":94.8464,"start":24,"end":195},{"cath_id":"1.20.5","chopping":"246-358","consensus_level":"medium","plddt":91.97,"start":246,"end":358},{"cath_id":"1.20.5","chopping":"391-446","consensus_level":"medium","plddt":81.605,"start":391,"end":446}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8IXS2","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8IXS2-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8IXS2-F1-predicted_aligned_error_v6.png","plddt_mean":82.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=DRC2","jax_strain_url":"https://www.jax.org/strain/search?query=DRC2"},"sequence":{"accession":"Q8IXS2","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8IXS2.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8IXS2/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8IXS2"}},"corpus_meta":[{"pmid":"24094744","id":"PMC_24094744","title":"Zebrafish Ciliopathy Screen Plus Human Mutational Analysis Identifies C21orf59 and CCDC65 Defects as Causing Primary Ciliary Dyskinesia.","date":"2013","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/24094744","citation_count":151,"is_preprint":false},{"pmid":"23991085","id":"PMC_23991085","title":"CCDC65 mutation causes primary ciliary dyskinesia with normal ultrastructure and hyperkinetic cilia.","date":"2013","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/23991085","citation_count":99,"is_preprint":false},{"pmid":"29167384","id":"PMC_29167384","title":"DRC2/CCDC65 is a central hub for assembly of the nexin-dynein regulatory complex and other regulators of ciliary and flagellar motility.","date":"2017","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/29167384","citation_count":40,"is_preprint":false},{"pmid":"12527906","id":"PMC_12527906","title":"Identification of target genes for EWS/ATF-1 chimeric transcription factor.","date":"2003","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/12527906","citation_count":26,"is_preprint":false},{"pmid":"17089017","id":"PMC_17089017","title":"Cloning and characterization of a novel sperm tail protein, NYD-SP28.","date":"2006","source":"International journal of molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/17089017","citation_count":19,"is_preprint":false},{"pmid":"37975235","id":"PMC_37975235","title":"CCDC65, encoding a component of the axonemal Nexin-Dynein regulatory complex, is required for sperm flagellum structure in humans.","date":"2023","source":"Clinical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/37975235","citation_count":13,"is_preprint":false},{"pmid":"6772148","id":"PMC_6772148","title":"Pyruvate dehydrogenase activity in group N streptococci.","date":"1980","source":"Australian journal of biological sciences","url":"https://pubmed.ncbi.nlm.nih.gov/6772148","citation_count":9,"is_preprint":false},{"pmid":"12783187","id":"PMC_12783187","title":"Growth kinetics of Lactococcus lactis ssp diacetylactis harboring different plasmid content.","date":"2003","source":"Current microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/12783187","citation_count":9,"is_preprint":false},{"pmid":"36598807","id":"PMC_36598807","title":"In vivo imaging reveals independent intraflagellar transport of the nexin-dynein regulatory complex subunits DRC2 and DRC4.","date":"2023","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/36598807","citation_count":7,"is_preprint":false},{"pmid":"24152136","id":"PMC_24152136","title":"Methylation of structural components of the axoneme occurs during flagellar disassembly.","date":"2013","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/24152136","citation_count":7,"is_preprint":false},{"pmid":"35439275","id":"PMC_35439275","title":"Gut mycobiome dysbiosis in rats showing retinal changes indicative of diabetic retinopathy.","date":"2022","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/35439275","citation_count":4,"is_preprint":false},{"pmid":"30913672","id":"PMC_30913672","title":"Preliminary Studies on Antimicrobial Activity of Streptococcus lactis subsp. diacetylactis.","date":"1983","source":"Journal of food protection","url":"https://pubmed.ncbi.nlm.nih.gov/30913672","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7349,"output_tokens":1968,"usd":0.025784,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8851,"output_tokens":2255,"usd":0.050315,"stage2_stop_reason":"end_turn"},"total_usd":0.076099,"stage1_batch_id":"msgbatch_01AsR7g8dGTEiEw9U83bJeWn","stage2_batch_id":"msgbatch_01YV5ZyxtFNUZEjxRcpd9jzb","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2013,\n      \"finding\": \"CCDC65 (DRC2) is an essential component of the nexin-dynein regulatory complex (N-DRC) in Chlamydomonas flagella; the ida6 mutant identifies CCDC65/FAP250 as required for N-DRC assembly, and ccdc65 knockdown in zebrafish alters cilia beat pattern rather than blocking dynein arm assembly.\",\n      \"method\": \"Chlamydomonas genetic mutant analysis (ida6), zebrafish morpholino knockdown, biochemical analysis of flagellar components\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic mutant analysis in Chlamydomonas combined with zebrafish in vivo knockdown, replicated across multiple model organisms and validated in human PCD patients\",\n      \"pmids\": [\"24094744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"CCDC65, the human ortholog of Chlamydomonas DRC2, localizes to cilia of nasal epithelial cells; loss of CCDC65 (via patient mutation or shRNA knockdown) causes stiff and dyskinetic cilia beating without detectable ultrastructural axonemal defects, and results in absence of GAS8 (another N-DRC component), demonstrating a structural/functional link between CCDC65 and GAS8 within the N-DRC.\",\n      \"method\": \"Immunostaining/localization in human airway epithelial cells, shRNA knockdown in human tracheobronchial epithelial cells, video-microscopy of cilia motion, immunoblotting for GAS8\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal loss-of-function (patient mutation + shRNA), multiple orthogonal readouts (localization, motility, co-component stability), single lab\",\n      \"pmids\": [\"23991085\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The C-terminal region of DRC2 is critical for co-assembly of DRC2 and DRC1 to form the base plate of the N-DRC and its attachment to the outer doublet microtubule; loss of DRC2 disrupts assembly of multiple other N-DRC subunits and destabilizes associated structures including inner dynein arms, radial spokes, and the calmodulin- and spoke-associated complex, establishing DRC2 as a central hub for N-DRC assembly.\",\n      \"method\": \"High-resolution proteomics, cryo-electron tomography structural analysis, and motility phenotyping of Chlamydomonas drc2 mutants\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — structural (cryo-ET) plus proteomic analysis with defined mutants, multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"29167384\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"FAP250 (CCDC65/DRC2) undergoes asymmetric dimethylation on arginine residues (aDMA) during flagellar disassembly in Chlamydomonas, catalyzed by PRMT1, a protein arginine methyltransferase present in the flagellar matrix; this methylation is associated with axonemal instability during resorption.\",\n      \"method\": \"Tandem mass spectrometry identification of aDMA-modified proteins, immunolocalization of PRMT1 during flagellar resorption, gel shift assays\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — mass spectrometry identification with immunolocalization, single lab, no direct functional rescue or mutagenesis of the modification sites\",\n      \"pmids\": [\"24152136\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"DRC2 is transported into Chlamydomonas flagella by intraflagellar transport (IFT) independently of DRC4; in vivo imaging showed DRC2 moves on IFT trains in mutants lacking DRC4 (and vice versa), with only occasional co-transport, indicating the N-DRC assembles onto the axoneme by stepwise addition of subunits rather than as a pre-assembled complex.\",\n      \"method\": \"In vivo fluorescence imaging of tagged DRC2 and DRC4 in Chlamydomonas mutants, simultaneous dual-color IFT imaging\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct in vivo imaging with genetic rescue constructs, multiple mutant backgrounds, two orthogonal tagged proteins imaged simultaneously\",\n      \"pmids\": [\"36598807\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Homozygous truncating variants in CCDC65 cause near-absence of CCDC65 protein in human sperm and result in multiple morphological abnormalities of the sperm flagella (MMAF) and asthenozoospermia; loss of CCDC65 in patient sperm also causes loss of GAS8, confirming a structural/functional link between these two N-DRC components in the sperm flagellar axoneme.\",\n      \"method\": \"Immunoblotting of patient sperm for CCDC65 and GAS8, genetic variant identification in human patients\",\n      \"journal\": \"Clinical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct protein detection by immunoblot in patient material with defined loss-of-function variant, single lab, limited to patient samples\",\n      \"pmids\": [\"37975235\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"NYD-SP28 (DRC2) protein localizes to the entire sperm tail in human spermatozoa and is post-translationally modified during sperm capacitation, as shown by 2D gel electrophoresis and immunoblotting.\",\n      \"method\": \"Immunohistochemistry, EGFP fusion protein localization, 2D gel electrophoresis and immunoblotting of sperm before and after capacitation\",\n      \"journal\": \"International journal of molecular medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, localization and post-translational modification shown but modification writer/eraser not identified and functional consequence not established\",\n      \"pmids\": [\"17089017\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"DRC2/CCDC65 is a core structural subunit of the nexin-dynein regulatory complex (N-DRC) in motile cilia and sperm flagella; its C-terminal region is required for co-assembly with DRC1 to form the N-DRC base plate and attachment to the outer doublet microtubule, its loss destabilizes multiple N-DRC subunits (including GAS8) and associated axonemal structures (inner dynein arms, radial spokes), it is transported into flagella by IFT independently of DRC4 suggesting stepwise axonemal assembly, and it undergoes PRMT1-mediated arginine methylation during flagellar disassembly; in humans, loss-of-function mutations cause primary ciliary dyskinesia with dyskinetic (but structurally intact) cilia and also asthenozoospermia with flagellar structural defects.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"DRC2 (CCDC65) is a core structural subunit of the nexin-dynein regulatory complex (N-DRC), the axonemal structure that links and regulates outer doublet microtubules in motile cilia and sperm flagella [#0, #1]. Its C-terminal region drives co-assembly with DRC1 to form the N-DRC base plate and its attachment to the outer doublet microtubule, making DRC2 a central hub whose loss disrupts assembly of multiple N-DRC subunits and destabilizes associated axonemal structures including inner dynein arms, radial spokes, and the calmodulin- and spoke-associated complex [#2]. The stability of the N-DRC component GAS8 depends on DRC2, as loss of DRC2 in human airway cells and in patient sperm eliminates GAS8 [#1, #5]. DRC2 is delivered into the flagellum by intraflagellar transport independently of DRC4, indicating that the N-DRC is built by stepwise addition of subunits onto the axoneme rather than as a preassembled complex [#4]. Functionally, DRC2 loss produces stiff, dyskinetic ciliary beating without gross ultrastructural defects [#1], and in humans loss-of-function mutations cause primary ciliary dyskinesia [#1] and asthenozoospermia with multiple morphological abnormalities of the sperm flagella [#5].\",\n  \"teleology\": [\n    {\n      \"year\": 2013,\n      \"claim\": \"Established DRC2/CCDC65 as an essential N-DRC component and showed its loss alters ciliary beat regulation rather than blocking dynein arm assembly, defining it as a regulatory rather than load-bearing motor element.\",\n      \"evidence\": \"Chlamydomonas ida6 mutant analysis, zebrafish morpholino knockdown, and biochemical flagellar analysis\",\n      \"pmids\": [\"24094744\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular position of DRC2 within the N-DRC not resolved\", \"Mechanism by which beat pattern is regulated not defined\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Linked human CCDC65 loss to dyskinetic cilia with intact ultrastructure and to destabilization of the N-DRC subunit GAS8, connecting the gene to primary ciliary dyskinesia and revealing an interdependence among N-DRC subunits.\",\n      \"evidence\": \"Localization, shRNA knockdown, and video-microscopy in human airway epithelial cells with GAS8 immunoblotting\",\n      \"pmids\": [\"23991085\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct physical contact between CCDC65 and GAS8 not demonstrated\", \"Reason for absent ultrastructural defect despite functional loss unclear\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identified PRMT1-catalyzed asymmetric arginine dimethylation of DRC2 during flagellar disassembly, raising the possibility that a post-translational mark accompanies axonemal resorption.\",\n      \"evidence\": \"Tandem MS identification of aDMA-modified proteins, PRMT1 immunolocalization, gel shift assays in Chlamydomonas\",\n      \"pmids\": [\"24152136\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No mutagenesis of methylation sites to test function\", \"Causal role of methylation in disassembly not established\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Mapped DRC2's C-terminal region as essential for co-assembly with DRC1 into the N-DRC base plate and microtubule attachment, establishing DRC2 as a structural hub whose loss collapses multiple subunits and associated axonemal structures.\",\n      \"evidence\": \"Proteomics, cryo-electron tomography, and motility phenotyping of Chlamydomonas drc2 mutants\",\n      \"pmids\": [\"29167384\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-resolution interface with DRC1 not resolved\", \"Order of subunit recruitment during assembly not fully defined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Demonstrated DRC2 and DRC4 are transported into flagella independently on IFT trains, establishing that the N-DRC assembles by stepwise subunit addition rather than as a preformed complex.\",\n      \"evidence\": \"Dual-color in vivo IFT imaging of tagged DRC2 and DRC4 in Chlamydomonas mutants\",\n      \"pmids\": [\"36598807\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Order and docking sequence of remaining N-DRC subunits unknown\", \"Regulation of IFT loading not characterized\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Extended the CCDC65 disease spectrum to human male infertility, showing truncating variants abolish CCDC65 and GAS8 in sperm and cause MMAF and asthenozoospermia.\",\n      \"evidence\": \"Immunoblotting of patient sperm and genetic variant identification\",\n      \"pmids\": [\"37975235\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab patient-material study\", \"Functional rescue not performed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How DRC2 mechanically couples N-DRC integrity to the regulation of beat waveform, and whether its arginine methylation actively triggers axonemal disassembly, remain open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No causal test of methylation in disassembly\", \"Mechanism converting N-DRC structural loss into dyskinetic beating undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [2, 4]}\n    ],\n    \"complexes\": [\"nexin-dynein regulatory complex (N-DRC)\"],\n    \"partners\": [\"DRC1\", \"DRC4\", \"GAS8\", \"PRMT1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}