{"gene":"TEKT4","run_date":"2026-04-28T21:42:58","timeline":{"discoveries":[{"year":2007,"finding":"TEKT4 protein localizes to sperm flagella and is required for coordinated, progressive flagellar beating; loss of TEKT4 in mice causes drastically reduced forward progressive velocity, uncoordinated waveform propagation, and ~10-fold higher intracellular ATP consumption without gross ultrastructural defects in the axoneme, demonstrating TEKT4 regulates flagellar mechanics rather than flagellar assembly.","method":"Knockout mouse model, transmission electron microscopy, sperm motility analysis, intracellular ATP measurement, immunolocalization","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined cellular phenotype, multiple orthogonal methods, replicated in subsequent study","pmids":["17244819"],"is_preprint":false},{"year":2009,"finding":"TEKT4 and TEKT3 play partially non-redundant roles in sperm motility; double-null mice (TEKT3/TEKT4) show greater subfertility than either single knockout, establishing genetic epistasis between the two tektins in sperm physiology.","method":"Double-knockout mouse model, genetic epistasis analysis, sperm motility assays","journal":"Molecular reproduction and development","confidence":"High","confidence_rationale":"Tier 2 — double-KO epistasis with defined phenotypic readout, same rigorous lab as foundational paper","pmids":["18951373"],"is_preprint":false},{"year":2014,"finding":"TEKT4 associates closely with tubulin in doublet microtubules and helps stabilize these structures; germline variants in TEKT4 deregulate microtubule stability, antagonize paclitaxel-induced microtubule stabilization, and increase paclitaxel resistance in breast cancer cells.","method":"Ectopic expression of variant TEKT4 in cancer cells, microtubule stability assays, exome sequencing with functional validation","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2/3 — functional cell-based assay with variant overexpression, single lab, moderate mechanistic depth","pmids":["24823476"],"is_preprint":false},{"year":2018,"finding":"TEKT4 knockdown in papillary thyroid cancer cell lines suppresses cell proliferation, colony formation, migration, and invasion, and silences the PI3K/Akt signaling pathway, placing TEKT4 upstream of PI3K/Akt in cancer cell behavior.","method":"siRNA knockdown, cell proliferation assay, colony formation assay, migration/invasion assay, pathway analysis (PI3K/Akt)","journal":"Endocrine pathology","confidence":"Low","confidence_rationale":"Tier 3 — single lab, single KD approach, no rescue or direct binding evidence for PI3K/Akt pathway placement","pmids":["30251060"],"is_preprint":false},{"year":2023,"finding":"TBX5 transcription factor binds to the TEKT4 promoter region and promotes its transcription, as demonstrated by chromatin immunoprecipitation in HL-1 cardiomyocytes; TBX5 knockdown reduces TEKT4 expression.","method":"Chromatin immunoprecipitation (ChIP), TBX5 knockdown, qPCR","journal":"Frontiers in genetics","confidence":"Medium","confidence_rationale":"Tier 2 — direct ChIP evidence of TBX5 binding to TEKT4 promoter with functional validation by KD, single lab","pmids":["36936432"],"is_preprint":false},{"year":2012,"finding":"TEKT4 protein is expressed in human ejaculated spermatozoa and is significantly reduced at both mRNA and protein levels in sperm from idiopathic asthenozoospermic men compared to normozoospermic controls, implicating TEKT4 deficiency in human asthenozoospermia.","method":"RT-PCR, Western blot, Percoll density gradient sperm separation","journal":"Zhonghua nan ke xue","confidence":"Low","confidence_rationale":"Tier 3 — correlative expression measurement in human samples, no functional intervention","pmids":["22774605"],"is_preprint":false}],"current_model":"TEKT4 is a flagellar/ciliary structural protein that incorporates into axonemal doublet microtubules alongside tubulin to stabilize these structures and coordinate sperm flagellar beat waveform; loss of TEKT4 impairs flagellar mechanics and energy efficiency without disrupting gross axonemal ultrastructure, and its expression is transcriptionally regulated by TBX5; in cancer contexts, TEKT4 variants destabilize microtubules and confer paclitaxel resistance, and TEKT4 loss suppresses PI3K/Akt signaling in thyroid cancer cells."},"narrative":{"teleology":[{"year":2007,"claim":"The fundamental question of whether TEKT4 is needed for flagellar assembly versus flagellar function was resolved: TEKT4 regulates the mechanics and energy efficiency of the flagellar beat without being required for axonemal ultrastructure.","evidence":"Tekt4-knockout mouse with TEM, motility analysis, ATP measurement, and immunolocalization","pmids":["17244819"],"confidence":"High","gaps":["Molecular mechanism by which TEKT4 coordinates dynein-driven sliding or waveform propagation is unknown","Whether TEKT4 directly modulates mechanochemical coupling or acts indirectly through other axonemal components is unresolved"]},{"year":2009,"claim":"It was unknown whether TEKT4 and its paralog TEKT3 serve redundant roles; double-knockout epistasis analysis established that they have partially non-redundant functions in sperm motility.","evidence":"Tekt3/Tekt4 double-knockout mice with genetic epistasis and motility assays","pmids":["18951373"],"confidence":"High","gaps":["Whether TEKT3 and TEKT4 occupy distinct positions within the doublet microtubule or interact directly is unknown","The molecular basis for their functional divergence has not been determined"]},{"year":2012,"claim":"Whether TEKT4 deficiency is relevant to human male infertility was open; reduced TEKT4 mRNA and protein levels were found in sperm from idiopathic asthenozoospermic men, supporting a correlative link.","evidence":"RT-PCR and Western blot in human ejaculated spermatozoa from asthenozoospermic versus normozoospermic men","pmids":["22774605"],"confidence":"Low","gaps":["Correlative association only; no causal or interventional evidence in human samples","Sample sizes and replication across cohorts not established","Whether TEKT4 reduction is cause or consequence of asthenozoospermia is unresolved"]},{"year":2014,"claim":"Beyond flagella, it was unknown whether TEKT4 influences cytoplasmic microtubule stability; germline TEKT4 variants were shown to destabilize microtubules and antagonize paclitaxel-induced stabilization, establishing TEKT4 as a microtubule-stabilizing factor relevant to drug resistance.","evidence":"Ectopic expression of variant TEKT4 in breast cancer cell lines with microtubule stability assays and exome sequencing","pmids":["24823476"],"confidence":"Medium","gaps":["Whether wild-type TEKT4 is endogenously expressed in breast epithelial cells at functional levels is unclear","The structural basis for variant-mediated destabilization has not been defined"]},{"year":2018,"claim":"Whether TEKT4 has signaling roles beyond structural microtubule functions was unexplored; knockdown in thyroid cancer cells suppressed PI3K/Akt signaling, proliferation, and invasion, suggesting a broader oncogenic role.","evidence":"siRNA knockdown in papillary thyroid cancer cell lines with proliferation, colony formation, migration/invasion, and pathway analysis","pmids":["30251060"],"confidence":"Low","gaps":["No rescue experiment or direct binding evidence linking TEKT4 to PI3K/Akt components; single knockdown approach without orthogonal validation","Whether PI3K/Akt effects are indirect consequences of microtubule disruption is unresolved","Not independently confirmed"]},{"year":2023,"claim":"Upstream transcriptional regulation of TEKT4 was unknown; TBX5 was identified as a direct transcriptional activator that binds the TEKT4 promoter, providing the first defined regulatory input for TEKT4 expression.","evidence":"ChIP for TBX5 on TEKT4 promoter in HL-1 cardiomyocytes with TBX5 knockdown and qPCR validation","pmids":["36936432"],"confidence":"Medium","gaps":["Whether TBX5-driven TEKT4 expression has functional significance in cardiomyocytes or is relevant to cilia/flagella contexts is unknown","Other transcription factors controlling TEKT4 in spermatogenic cells have not been identified"]},{"year":null,"claim":"The structural basis for how TEKT4 integrates into doublet microtubules and mechanistically coordinates dynein-driven flagellar waveform remains undefined, and the physiological relevance of TEKT4 in non-ciliary/flagellar tissues lacks robust evidence.","evidence":"","pmids":[],"confidence":"High","gaps":["No cryo-EM or high-resolution structural model of TEKT4 within the axonemal doublet","Direct binding partners within the outer doublet beyond tubulin are not identified","Whether TEKT4 functions outside flagellar/ciliary contexts under normal physiology is unestablished"]}],"mechanism_profile":{"molecular_activity":[{"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]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,2]}],"pathway":[{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[0,1]}],"complexes":[],"partners":["TEKT3"],"other_free_text":[]},"mechanistic_narrative":"TEKT4 is a tektin-family structural protein that incorporates into axonemal doublet microtubules of sperm flagella, where it stabilizes microtubule architecture and coordinates flagellar beat waveform rather than being required for axonemal assembly [PMID:17244819, PMID:24823476]. Loss of TEKT4 in mice causes uncoordinated flagellar waveform propagation, drastically reduced forward progressive velocity, and ~10-fold higher intracellular ATP consumption without gross ultrastructural defects, and TEKT4 functions non-redundantly with TEKT3, as double-null mice exhibit greater subfertility than either single knockout [PMID:17244819, PMID:18951373]. TEKT4 expression is transcriptionally regulated by TBX5, which directly binds the TEKT4 promoter [PMID:36936432]. Germline TEKT4 variants destabilize microtubules and antagonize paclitaxel-induced stabilization in breast cancer cells, conferring drug resistance [PMID:24823476]."},"prefetch_data":{"uniprot":{"accession":"Q8WW24","full_name":"Tektin-4","aliases":[],"length_aa":435,"mass_kda":50.6,"function":"Microtubule inner protein (MIP) part of the dynein-decorated doublet microtubules (DMTs) in cilia and flagellar axoneme (PubMed:36191189). Forms filamentous polymers in the walls of ciliary and flagellar microtubules (By similarity). Contributes to normal sperm motility (By similarity)","subcellular_location":"Cytoplasm, cytoskeleton, cilium axoneme; Cytoplasm, cytoskeleton, flagellum axoneme","url":"https://www.uniprot.org/uniprotkb/Q8WW24/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TEKT4","classification":"Not Classified","n_dependent_lines":76,"n_total_lines":1208,"dependency_fraction":0.06291390728476821},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TEKT4","total_profiled":1310},"omim":[{"mim_id":"620277","title":"SPERMATOGENIC FAILURE 81; SPGF81","url":"https://www.omim.org/entry/620277"},{"mim_id":"612683","title":"TEKTIN 3; TEKT3","url":"https://www.omim.org/entry/612683"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Perinuclear theca","reliability":"Supported"},{"location":"Connecting piece","reliability":"Supported"},{"location":"Flagellar centriole","reliability":"Supported"},{"location":"Principal piece","reliability":"Supported"},{"location":"End piece","reliability":"Supported"},{"location":"Annulus","reliability":"Supported"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"testis","ntpm":12.8}],"url":"https://www.proteinatlas.org/search/TEKT4"},"hgnc":{"alias_symbol":["MGC27019"],"prev_symbol":[]},"alphafold":{"accession":"Q8WW24","domains":[{"cath_id":"1.10.287","chopping":"310-350_357-425","consensus_level":"medium","plddt":97.1285,"start":310,"end":425}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8WW24","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8WW24-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8WW24-F1-predicted_aligned_error_v6.png","plddt_mean":91.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TEKT4","jax_strain_url":"https://www.jax.org/strain/search?query=TEKT4"},"sequence":{"accession":"Q8WW24","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8WW24.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8WW24/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8WW24"}},"corpus_meta":[{"pmid":"17244819","id":"PMC_17244819","title":"Absence of tektin 4 causes asthenozoospermia and subfertility in male mice.","date":"2007","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/17244819","citation_count":99,"is_preprint":false},{"pmid":"18951373","id":"PMC_18951373","title":"Tektin 3 is required for progressive sperm motility in mice.","date":"2009","source":"Molecular reproduction and development","url":"https://pubmed.ncbi.nlm.nih.gov/18951373","citation_count":76,"is_preprint":false},{"pmid":"24823476","id":"PMC_24823476","title":"Enriched variations in TEKT4 and breast cancer resistance to paclitaxel.","date":"2014","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/24823476","citation_count":30,"is_preprint":false},{"pmid":"25761592","id":"PMC_25761592","title":"Comparative analysis of testis transcriptomes from triploid and fertile diploid cyprinid fish.","date":"2015","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/25761592","citation_count":26,"is_preprint":false},{"pmid":"30251060","id":"PMC_30251060","title":"TEKT4 Promotes Papillary Thyroid Cancer Cell Proliferation, Colony Formation, and Metastasis through Activating PI3K/Akt Pathway.","date":"2018","source":"Endocrine pathology","url":"https://pubmed.ncbi.nlm.nih.gov/30251060","citation_count":20,"is_preprint":false},{"pmid":"35547812","id":"PMC_35547812","title":"Hdh-Tektin-4 Regulates Motility of Fresh and Cryopreserved Sperm in Pacific Abalone, Haliotis discus hannai.","date":"2022","source":"Frontiers in cell and developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/35547812","citation_count":17,"is_preprint":false},{"pmid":"32677196","id":"PMC_32677196","title":"A prospective multicenter phase II study on the efficacy and safety of dasatinib in the treatment of metastatic gastrointestinal stromal tumors failed by imatinib and sunitinib and analysis of NGS in peripheral blood.","date":"2020","source":"Cancer medicine","url":"https://pubmed.ncbi.nlm.nih.gov/32677196","citation_count":16,"is_preprint":false},{"pmid":"35447134","id":"PMC_35447134","title":"Cathepsin F genetic mutation is associated with familial papillary thyroid cancer.","date":"2022","source":"The American journal of the medical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/35447134","citation_count":10,"is_preprint":false},{"pmid":"27871913","id":"PMC_27871913","title":"What can time-frequency and phase coherence measures tell us about the genetic basis of P3 amplitude?","date":"2016","source":"International journal of psychophysiology : official journal of the International Organization of Psychophysiology","url":"https://pubmed.ncbi.nlm.nih.gov/27871913","citation_count":9,"is_preprint":false},{"pmid":"38137330","id":"PMC_38137330","title":"Study on Potential Differentially Expressed Genes in Idiopathic Pulmonary Fibrosis by Bioinformatics and Next-Generation Sequencing Data Analysis.","date":"2023","source":"Biomedicines","url":"https://pubmed.ncbi.nlm.nih.gov/38137330","citation_count":8,"is_preprint":false},{"pmid":"36714547","id":"PMC_36714547","title":"High-throughput proteomic characterization of seminal plasma from bulls with contrasting semen quality.","date":"2023","source":"3 Biotech","url":"https://pubmed.ncbi.nlm.nih.gov/36714547","citation_count":8,"is_preprint":false},{"pmid":"26045100","id":"PMC_26045100","title":"Exome Sequencing and Epigenetic Analysis of Twins Who Are Discordant for Congenital Cataract.","date":"2015","source":"Twin research and human genetics : the official journal of the International Society for Twin Studies","url":"https://pubmed.ncbi.nlm.nih.gov/26045100","citation_count":6,"is_preprint":false},{"pmid":"37694353","id":"PMC_37694353","title":"Identification of molecular biomarkers associated with non-small-cell lung carcinoma (NSCLC) using whole-exome sequencing.","date":"2025","source":"Cancer biomarkers : section A of Disease markers","url":"https://pubmed.ncbi.nlm.nih.gov/37694353","citation_count":5,"is_preprint":false},{"pmid":"36936432","id":"PMC_36936432","title":"Case report: Novel TBX5-related pathogenic mechanism of Holt-Oram syndrome.","date":"2023","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/36936432","citation_count":5,"is_preprint":false},{"pmid":"22774605","id":"PMC_22774605","title":"[Expression of TEKT4 protein decreases in the ejaculated spermatozoa of idiopathic asthenozoospermic men].","date":"2012","source":"Zhonghua nan ke xue = National journal of andrology","url":"https://pubmed.ncbi.nlm.nih.gov/22774605","citation_count":3,"is_preprint":false},{"pmid":"29714424","id":"PMC_29714424","title":"[Genetic genes associated with oligospermia, asthenospermia and teratospermia: Advances in studies].","date":"2017","source":"Zhonghua nan ke xue = National journal of andrology","url":"https://pubmed.ncbi.nlm.nih.gov/29714424","citation_count":3,"is_preprint":false},{"pmid":"32975708","id":"PMC_32975708","title":"Randomized phase II clinical trial and biomarker analysis of paclitaxel plus epirubicin versus vinorelbine plus epirubicin as neoadjuvant chemotherapy in locally advanced HER2-negative breast cancer with TEKT4 variations.","date":"2020","source":"Breast cancer research and treatment","url":"https://pubmed.ncbi.nlm.nih.gov/32975708","citation_count":2,"is_preprint":false},{"pmid":"35691366","id":"PMC_35691366","title":"Gamma-oryzanol supplemented in extender enhances the quality of semen cryopreservation and alters proteomic profile in Thai swamp buffalo.","date":"2022","source":"Cryobiology","url":"https://pubmed.ncbi.nlm.nih.gov/35691366","citation_count":2,"is_preprint":false},{"pmid":"40594066","id":"PMC_40594066","title":"Pan-Cancer Exome-wide analysis of germline mutational patterns and pathways.","date":"2025","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/40594066","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10851,"output_tokens":1383,"usd":0.026649},"stage2":{"model":"claude-opus-4-6","input_tokens":4618,"output_tokens":1859,"usd":0.104347},"total_usd":0.130996,"stage1_batch_id":"msgbatch_01RPbVc9PDH9zQmYK5Hs6srm","stage2_batch_id":"msgbatch_01JVbVLzeKN2yVrsGp3zC8aM","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2007,\n      \"finding\": \"TEKT4 protein localizes to sperm flagella and is required for coordinated, progressive flagellar beating; loss of TEKT4 in mice causes drastically reduced forward progressive velocity, uncoordinated waveform propagation, and ~10-fold higher intracellular ATP consumption without gross ultrastructural defects in the axoneme, demonstrating TEKT4 regulates flagellar mechanics rather than flagellar assembly.\",\n      \"method\": \"Knockout mouse model, transmission electron microscopy, sperm motility analysis, intracellular ATP measurement, immunolocalization\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined cellular phenotype, multiple orthogonal methods, replicated in subsequent study\",\n      \"pmids\": [\"17244819\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"TEKT4 and TEKT3 play partially non-redundant roles in sperm motility; double-null mice (TEKT3/TEKT4) show greater subfertility than either single knockout, establishing genetic epistasis between the two tektins in sperm physiology.\",\n      \"method\": \"Double-knockout mouse model, genetic epistasis analysis, sperm motility assays\",\n      \"journal\": \"Molecular reproduction and development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — double-KO epistasis with defined phenotypic readout, same rigorous lab as foundational paper\",\n      \"pmids\": [\"18951373\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TEKT4 associates closely with tubulin in doublet microtubules and helps stabilize these structures; germline variants in TEKT4 deregulate microtubule stability, antagonize paclitaxel-induced microtubule stabilization, and increase paclitaxel resistance in breast cancer cells.\",\n      \"method\": \"Ectopic expression of variant TEKT4 in cancer cells, microtubule stability assays, exome sequencing with functional validation\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — functional cell-based assay with variant overexpression, single lab, moderate mechanistic depth\",\n      \"pmids\": [\"24823476\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"TEKT4 knockdown in papillary thyroid cancer cell lines suppresses cell proliferation, colony formation, migration, and invasion, and silences the PI3K/Akt signaling pathway, placing TEKT4 upstream of PI3K/Akt in cancer cell behavior.\",\n      \"method\": \"siRNA knockdown, cell proliferation assay, colony formation assay, migration/invasion assay, pathway analysis (PI3K/Akt)\",\n      \"journal\": \"Endocrine pathology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, single KD approach, no rescue or direct binding evidence for PI3K/Akt pathway placement\",\n      \"pmids\": [\"30251060\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"TBX5 transcription factor binds to the TEKT4 promoter region and promotes its transcription, as demonstrated by chromatin immunoprecipitation in HL-1 cardiomyocytes; TBX5 knockdown reduces TEKT4 expression.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP), TBX5 knockdown, qPCR\",\n      \"journal\": \"Frontiers in genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct ChIP evidence of TBX5 binding to TEKT4 promoter with functional validation by KD, single lab\",\n      \"pmids\": [\"36936432\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"TEKT4 protein is expressed in human ejaculated spermatozoa and is significantly reduced at both mRNA and protein levels in sperm from idiopathic asthenozoospermic men compared to normozoospermic controls, implicating TEKT4 deficiency in human asthenozoospermia.\",\n      \"method\": \"RT-PCR, Western blot, Percoll density gradient sperm separation\",\n      \"journal\": \"Zhonghua nan ke xue\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — correlative expression measurement in human samples, no functional intervention\",\n      \"pmids\": [\"22774605\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TEKT4 is a flagellar/ciliary structural protein that incorporates into axonemal doublet microtubules alongside tubulin to stabilize these structures and coordinate sperm flagellar beat waveform; loss of TEKT4 impairs flagellar mechanics and energy efficiency without disrupting gross axonemal ultrastructure, and its expression is transcriptionally regulated by TBX5; in cancer contexts, TEKT4 variants destabilize microtubules and confer paclitaxel resistance, and TEKT4 loss suppresses PI3K/Akt signaling in thyroid cancer cells.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"TEKT4 is a tektin-family structural protein that incorporates into axonemal doublet microtubules of sperm flagella, where it stabilizes microtubule architecture and coordinates flagellar beat waveform rather than being required for axonemal assembly [PMID:17244819, PMID:24823476]. Loss of TEKT4 in mice causes uncoordinated flagellar waveform propagation, drastically reduced forward progressive velocity, and ~10-fold higher intracellular ATP consumption without gross ultrastructural defects, and TEKT4 functions non-redundantly with TEKT3, as double-null mice exhibit greater subfertility than either single knockout [PMID:17244819, PMID:18951373]. TEKT4 expression is transcriptionally regulated by TBX5, which directly binds the TEKT4 promoter [PMID:36936432]. Germline TEKT4 variants destabilize microtubules and antagonize paclitaxel-induced stabilization in breast cancer cells, conferring drug resistance [PMID:24823476].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"The fundamental question of whether TEKT4 is needed for flagellar assembly versus flagellar function was resolved: TEKT4 regulates the mechanics and energy efficiency of the flagellar beat without being required for axonemal ultrastructure.\",\n      \"evidence\": \"Tekt4-knockout mouse with TEM, motility analysis, ATP measurement, and immunolocalization\",\n      \"pmids\": [\"17244819\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Molecular mechanism by which TEKT4 coordinates dynein-driven sliding or waveform propagation is unknown\",\n        \"Whether TEKT4 directly modulates mechanochemical coupling or acts indirectly through other axonemal components is unresolved\"\n      ]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"It was unknown whether TEKT4 and its paralog TEKT3 serve redundant roles; double-knockout epistasis analysis established that they have partially non-redundant functions in sperm motility.\",\n      \"evidence\": \"Tekt3/Tekt4 double-knockout mice with genetic epistasis and motility assays\",\n      \"pmids\": [\"18951373\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether TEKT3 and TEKT4 occupy distinct positions within the doublet microtubule or interact directly is unknown\",\n        \"The molecular basis for their functional divergence has not been determined\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Whether TEKT4 deficiency is relevant to human male infertility was open; reduced TEKT4 mRNA and protein levels were found in sperm from idiopathic asthenozoospermic men, supporting a correlative link.\",\n      \"evidence\": \"RT-PCR and Western blot in human ejaculated spermatozoa from asthenozoospermic versus normozoospermic men\",\n      \"pmids\": [\"22774605\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Correlative association only; no causal or interventional evidence in human samples\",\n        \"Sample sizes and replication across cohorts not established\",\n        \"Whether TEKT4 reduction is cause or consequence of asthenozoospermia is unresolved\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Beyond flagella, it was unknown whether TEKT4 influences cytoplasmic microtubule stability; germline TEKT4 variants were shown to destabilize microtubules and antagonize paclitaxel-induced stabilization, establishing TEKT4 as a microtubule-stabilizing factor relevant to drug resistance.\",\n      \"evidence\": \"Ectopic expression of variant TEKT4 in breast cancer cell lines with microtubule stability assays and exome sequencing\",\n      \"pmids\": [\"24823476\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether wild-type TEKT4 is endogenously expressed in breast epithelial cells at functional levels is unclear\",\n        \"The structural basis for variant-mediated destabilization has not been defined\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Whether TEKT4 has signaling roles beyond structural microtubule functions was unexplored; knockdown in thyroid cancer cells suppressed PI3K/Akt signaling, proliferation, and invasion, suggesting a broader oncogenic role.\",\n      \"evidence\": \"siRNA knockdown in papillary thyroid cancer cell lines with proliferation, colony formation, migration/invasion, and pathway analysis\",\n      \"pmids\": [\"30251060\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No rescue experiment or direct binding evidence linking TEKT4 to PI3K/Akt components; single knockdown approach without orthogonal validation\",\n        \"Whether PI3K/Akt effects are indirect consequences of microtubule disruption is unresolved\",\n        \"Not independently confirmed\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Upstream transcriptional regulation of TEKT4 was unknown; TBX5 was identified as a direct transcriptional activator that binds the TEKT4 promoter, providing the first defined regulatory input for TEKT4 expression.\",\n      \"evidence\": \"ChIP for TBX5 on TEKT4 promoter in HL-1 cardiomyocytes with TBX5 knockdown and qPCR validation\",\n      \"pmids\": [\"36936432\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether TBX5-driven TEKT4 expression has functional significance in cardiomyocytes or is relevant to cilia/flagella contexts is unknown\",\n        \"Other transcription factors controlling TEKT4 in spermatogenic cells have not been identified\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The structural basis for how TEKT4 integrates into doublet microtubules and mechanistically coordinates dynein-driven flagellar waveform remains undefined, and the physiological relevance of TEKT4 in non-ciliary/flagellar tissues lacks robust evidence.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No cryo-EM or high-resolution structural model of TEKT4 within the axonemal doublet\",\n        \"Direct binding partners within the outer doublet beyond tubulin are not identified\",\n        \"Whether TEKT4 functions outside flagellar/ciliary contexts under normal physiology is unestablished\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"TEKT3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}