{"gene":"METTL5","run_date":"2026-04-28T18:30:28","timeline":{"discoveries":[{"year":2019,"finding":"METTL5 is the 18S rRNA m6A methyltransferase responsible for N6-methyladenosine modification of human 18S rRNA, and must form a heterodimeric complex with TRMT112 to gain metabolic stability in cells. The first atomic resolution structure of METTL5-TRMT112 was solved, revealing an RNA-binding mode distinct from other m6A methyltransferases, and suggesting an adenosine extrusion mechanism analogous to DNA methyltransferases.","method":"In vitro methyltransferase assay, co-immunoprecipitation, X-ray crystallography, cellular stability assays","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 — reconstitution, crystal structure, and functional validation in single highly-cited study","pmids":["31328227"],"is_preprint":false},{"year":2020,"finding":"METTL5 catalyzes m6A modification at position A1832 of 18S rRNA in vivo and in vitro. Loss of Mettl5 in mouse embryonic stem cells reduces global translation rate, causes spontaneous loss of pluripotency, and compromises differentiation potential.","method":"In vitro methyltransferase assay, Mettl5 knockout mESCs, polysome profiling, translation rate measurement","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro assay confirmed, KO phenotype with multiple orthogonal readouts, independently replicated","pmids":["32217665"],"is_preprint":false},{"year":2020,"finding":"METTL5 shows strong substrate preference for 18S A1832 and promotes p70-S6K activation and proper translation initiation; loss of METTL5 significantly reduces polysome abundance. Structural comparison with unmodified yeast ribosomes indicates the m6A modification may facilitate mRNA binding by inducing conformation changes in the decoding center.","method":"Methyltransferase substrate specificity assay, polysome profiling, p70-S6K activation assay, structural modeling","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including biochemical assays and polysome profiling, replicated across organisms","pmids":["33357433"],"is_preprint":false},{"year":2020,"finding":"Deletion of Mettl5 in mouse embryonic stem cells impairs efficient translation of FBXW7, a key regulator of cell differentiation, leading to c-MYC accumulation and delayed differentiation onset. METTL5 methylates 18S rRNA both in vivo and in vitro.","method":"Mettl5 knockout mESCs, polysome profiling, western blotting for FBXW7 and c-MYC, in vitro methyltransferase assay","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro assay plus KO with defined molecular mechanism linking rRNA modification to translational regulation of specific substrate","pmids":["32783360"],"is_preprint":false},{"year":2020,"finding":"Drosophila CG9666 (ortholog of human METTL5) directly interacts with CG12975 (ortholog of TRMT112) to deposit m6A specifically on 18S rRNA; depletion of CG9666 abolishes 18S rRNA m6A without compromising rRNA maturation, but impairs fly behavior.","method":"RNAi screen, mass spectrometry of RNA modifications, co-immunoprecipitation, behavioral assays","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 — reciprocal interaction confirmed, direct modification detected by MS, functional phenotype established","pmids":["32350990"],"is_preprint":false},{"year":2022,"finding":"The METTL5-TRMT112 complex installs m6A at position A1832 of human 18S rRNA; TRMT112 is required for METTL5 stability; human METTL5 mutations associated with microcephaly and intellectual disability disrupt the METTL5-TRMT112 interaction. Loss of METTL5 in human cancer cell lines and mice regulates gene expression at the translational level.","method":"In vitro methyltransferase assay, co-immunoprecipitation, Mettl5 knockout mice, ribosome profiling","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods, mechanistic link between disease mutations and protein interaction confirmed","pmids":["35033535"],"is_preprint":false},{"year":2019,"finding":"Bi-allelic frameshift variants in METTL5 cause intellectual disability and microcephaly; METTL5 protein is enriched in the nucleus and synapses of hippocampal neurons; truncating variants do not affect localization but alter protein expression levels. Mettl5 knockdown in zebrafish causes microcephaly.","method":"Exome sequencing, transfection of orthologous cells, immunofluorescence localization in hippocampal neurons, zebrafish knockdown","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2-3 — direct localization experiment with functional consequence, zebrafish phenotypic validation","pmids":["31564433"],"is_preprint":false},{"year":2020,"finding":"Mettl5 knockout in mESCs leads to abnormal craniofacial and nervous development; the METTL5 protein complex predominantly interacts with RNA binding proteins and ribosome proteins. Mettl5 knockout mice exhibit intellectual disability and impaired myelination in brain.","method":"Co-immunoprecipitation/mass spectrometry of METTL5 protein complex, Mettl5 knockout mice, behavioral testing, myelin staining","journal":"Genes & diseases","confidence":"Medium","confidence_rationale":"Tier 2-3 — interactome by MS, KO mouse with defined cellular phenotype","pmids":["35005123"],"is_preprint":false},{"year":2021,"finding":"METTL5 promotes pancreatic cancer cell proliferation, migration, and invasion through increased c-Myc translation. m6A modifications at the 5'UTR and CDS (near 5'UTR) of c-Myc mRNA are critical for this specific translational regulation. METTL5 and its cofactor TRMT112 synergistically promote cancer progression.","method":"Polysome profiling, siRNA knockdown/overexpression, m6A quantification, in vitro functional assays","journal":"International journal of oncology","confidence":"Medium","confidence_rationale":"Tier 2-3 — polysome profiling supports translational mechanism, single lab","pmids":["34970694"],"is_preprint":false},{"year":2022,"finding":"METTL5-mediated 18S rRNA m6A modification modulates translation of SUZ12 (a core PRC2 component) to regulate transcriptomic shifts during cardiac hypertrophy. Cardiac-specific METTL5 knockout mice show enhanced pressure overload-induced hypertrophy.","method":"Cardiac-specific Mettl5 conditional knockout mice, polysome profiling, western blotting, cardiomyocyte gain- and loss-of-function assays","journal":"Frontiers in cardiovascular medicine","confidence":"Medium","confidence_rationale":"Tier 2 — conditional KO with defined molecular mechanism linking rRNA methylation to translational control of specific target","pmids":["35295259"],"is_preprint":false},{"year":2023,"finding":"METTL5 controls USP5 translation, which in turn stabilizes c-Myc by inhibiting K48-linked polyubiquitination via USP5 binding to c-Myc. CREB1/P300 acts as a transcriptional regulator promoting METTL5 transcription in HCC.","method":"GST pulldown, co-immunoprecipitation, polysome profiling, RNA sequencing, luciferase reporter assay, ubiquitination assay","journal":"Cancer communications","confidence":"Medium","confidence_rationale":"Tier 2-3 — multiple orthogonal methods from single lab, molecular mechanism established","pmids":["36602428"],"is_preprint":false},{"year":2023,"finding":"METTL5 depletion impairs 18S rRNA m6A modification, hampers ribosome synthesis, and inhibits translation of G-quadruplex-containing mRNAs enriched in TGF-β pathway in intrahepatic cholangiocarcinoma. Liver-specific METTL5 knockout and overexpression ICC mouse models confirmed these effects.","method":"Loss- and gain-of-function in vitro and in vivo assays, ribosome profiling, m6A quantification, G-quadruplex mRNA translation analysis, liver-specific KO mouse models","journal":"Molecular therapy","confidence":"Medium","confidence_rationale":"Tier 2 — multiple mouse models, ribosome profiling identifying specific mRNA class as targets","pmids":["37735874"],"is_preprint":false},{"year":2022,"finding":"METTL5 regulates cranial suture fusion by controlling Wnt signaling; Mettl5 knockout mice show poor ossification, widened cranial sutures, increased proliferation and decreased osteogenic differentiation of suture mesenchymal stem cells.","method":"Mettl5 knockout mice, cell proliferation and differentiation assays, Wnt signaling pathway analysis","journal":"Fundamental research","confidence":"Medium","confidence_rationale":"Tier 2-3 — KO mice with defined cellular phenotype and pathway placement","pmids":["38933773"],"is_preprint":false},{"year":2025,"finding":"METTL5 knockout in ovarian cancer disrupts ATF4 translation by altering 18S rRNA m6A levels, leading to downregulation of SLC7A11 and SLC3A2, thus enhancing ferroptosis sensitivity and tumor susceptibility to T cell-mediated antitumor immunity. ATF4 overexpression or ferroptosis inhibition reverses METTL5-KO immune-sensitive phenotypes.","method":"Genome-wide immune screens, METTL5 KO in cancer cells, rescue experiments with ATF4 overexpression, ferroptosis inhibitor, in vivo tumor models","journal":"Advanced science","confidence":"Medium","confidence_rationale":"Tier 2 — epistasis established via rescue, multiple orthogonal approaches linking rRNA methylation to specific translational target","pmids":["41042068"],"is_preprint":false},{"year":2025,"finding":"TRIM28 mediates Mettl5 ubiquitination and degradation in CD4+ T cells; reduced Mettl5 levels lead to hypomethylation at the Gata3 promoter and increased GATA3 transcription, promoting Th2 polarization. In airway allergy, Mettl5 also recruits USP21 to deubiquitinate GATA3, boosting IL-4 expression in M2 macrophages.","method":"Chromatin immunoprecipitation assay, co-immunoprecipitation, ubiquitination assay, Mettl5 conditional KO in macrophages/T cells, mouse allergy model","journal":"Frontiers in immunology / Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2-3 — identified ubiquitin writer (TRIM28) by ChIP and Co-IP, functional consequence in defined immune cell context","pmids":["40391221","40089091"],"is_preprint":false},{"year":2025,"finding":"METTL5 depletion reduces selenophosphate synthetase 2 (SEPHS2) translation efficiency, leading to diminished selenoprotein synthesis and increased ROS, inducing apoptosis in multiple myeloma. Salvianolic acid C (SAC) was identified as a METTL5 inhibitor.","method":"Mettl5 knockdown, ribosome profiling/translation efficiency measurement, ROS assay, in vitro and in vivo myeloma models, drug inhibitor assay","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2-3 — translation efficiency of specific target measured, functional link to apoptosis established","pmids":["40750759"],"is_preprint":false},{"year":2025,"finding":"METTL5-mediated 18S rRNA m6A modification promotes translation of CXCL16, enabling immune evasion in intrahepatic cholangiocarcinoma by excluding CD8+ T cells. Mettl5 liver-specific KO increases CD8+ T cell infiltration and reduces immunosuppressive tumor-associated macrophages.","method":"Liver-specific Mettl5 conditional KO mice, scRNA-seq, scTCR-seq, adoptive macrophage transfer, lipid nanoparticle siRNA delivery combined with PD-1 blockade","journal":"Advanced science","confidence":"Medium","confidence_rationale":"Tier 2 — multiple in vivo models with defined translational target and immune mechanism","pmids":["41431992"],"is_preprint":false},{"year":2024,"finding":"METTL5 upregulation promotes NRF2 mRNA stability; IGF2BP1 mediates NRF2 mRNA stability via the METTL5/m6A/NRF2 axis, thereby inactivating ferroptosis and repressing anti-tumor immunity in gastric cancer.","method":"mRNA stability assay, RNA immunoprecipitation, loss-of-function experiments, co-culture with PBMCs","journal":"Cell death discovery","confidence":"Low","confidence_rationale":"Tier 3 — single lab, limited mechanistic detail on direct m6A site, functional link inferred","pmids":["39261486"],"is_preprint":false},{"year":2024,"finding":"METTL5 positively regulates TPRKB expression by enhancing TPRKB mRNA stability via m6A modification in hepatocellular carcinoma.","method":"mRNA stability assay, METTL5 knockdown, rescue experiments with TPRKB overexpression","journal":"Experimental cell research","confidence":"Low","confidence_rationale":"Tier 3 — single lab, single method for m6A-stability link","pmids":["39182664"],"is_preprint":false},{"year":2025,"finding":"METTL5-mediated m6A modification enhances UBE3C mRNA stability by enabling YTHDF1 to bind and protect the modified mRNA from degradation; UBE3C then promotes ubiquitination and degradation of AHNAK, suppressing ferroptosis in osteosarcoma.","method":"mRNA stability assay, RIP for YTHDF1 binding, UBE3C knockdown/overexpression, ferroptosis assay, Co-IP","journal":"Journal of molecular histology","confidence":"Low","confidence_rationale":"Tier 3 — single lab, indirect mechanistic chain, limited direct m6A site validation","pmids":["40696164"],"is_preprint":false},{"year":2025,"finding":"METTL5 promotes HCC recurrence after thermal ablation by enhancing PEX16 translation, which promotes peroxisomal biogenesis and β-oxidation of very long-chain fatty acids, thereby facilitating mitochondrial respiration under heat stress.","method":"Insufficient RFA in vitro and in vivo models, translation efficiency analysis, peroxisome biogenesis assay, fatty acid oxidation assay","journal":"Molecular therapy","confidence":"Low","confidence_rationale":"Tier 3 — mechanistic chain proposed with limited direct validation of m6A on PEX16 mRNA","pmids":["41234012"],"is_preprint":false},{"year":2024,"finding":"METTL5 promotes corticospinal tract sprouting after traumatic brain injury by increasing translation efficiency of Cfl1 (cofilin) and Inpp5k, leading to cofilin activation, actin polymerization, and axon outgrowth.","method":"METTL5 overexpression in corticospinal neurons, ribosome profiling (translation efficiency), anterograde axonal tracing, cofilin activity assay","journal":"Experimental neurology","confidence":"Medium","confidence_rationale":"Tier 2-3 — ribosome profiling identifies specific translational targets, in vivo functional outcome established","pmids":["39406306"],"is_preprint":false},{"year":2025,"finding":"Bicyclopyrrolidine acrylamide stereoprobes react covalently with C100 of TRMT112 exclusively within the METTL5-TRMT112 complex (not other TRMT112 complexes). Co-crystal structure revealed a composite binding pocket templated by METTL5 at TRMT112's C100; stereoprobe binding causes allosteric agonism of METTL5 catalytic activity.","method":"Chemical proteomics, co-crystal structure (X-ray crystallography), in vitro methyltransferase activity assay, recombinant protein binding assays","journal":"Nature chemical biology / bioRxiv","confidence":"High","confidence_rationale":"Tier 1 — co-crystal structure plus functional validation of allosteric mechanism, published in peer-reviewed journal","pmids":["41507545","40475643"],"is_preprint":false},{"year":2024,"finding":"Drosophila Mettl5 regulates sleep by controlling translational output of proteasome components and clock genes; loss of Mettl5 or Trmt112 increases PERIOD protein levels, causing sleep phenotypes. Mettl5 functions predominantly within neurons and glia.","method":"Drosophila Mettl5 mutants, rescue experiments with tissue-specific expression, RNA-seq and Ribo-seq, PERIOD protein quantification","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 — Ribo-seq plus genetic rescue in Drosophila ortholog, preprint only","pmids":["bio_10.1101_2024.10.24.620129"],"is_preprint":true},{"year":2025,"finding":"METTL5 deficiency decreases translation fidelity of ribosomes, increases non-canonical translation products, and generates tumor neoantigens that stimulate CD8+ T cell infiltration and TCR repertoire diversity in murine tumor models. This effect depends on intact antigen presentation pathways.","method":"Mettl5 knockout tumor models, antigen presentation pathway epistasis, TCR-seq, CD8+ T cell infiltration analysis","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 — mechanistic epistasis with antigen presentation, in vivo immune phenotype, preprint","pmids":["bio_10.1101_2025.06.06.658288"],"is_preprint":true},{"year":2025,"finding":"METTL5 promotes METTL5-mediated m6A modification of 18S rRNA, which modulates MGST1 protein expression through its N6-methyladenosine catalytic function, suppressing ferroptosis in HCC.","method":"Tandem mass tagging proteomic quantification, METTL5 knockdown, ferroptosis assay, western blotting","journal":"Molecular and cellular biochemistry","confidence":"Low","confidence_rationale":"Tier 3 — single lab, proteomics identifies MGST1 as downstream target but direct m6A mechanism not fully established","pmids":["41557129"],"is_preprint":false},{"year":2025,"finding":"Cortical organoids from METTL5-KO human iPSCs show delayed neural stem cell proliferation and neuronal differentiation timing. CHCHD2, a nuclear-encoded mitochondrial gene, is significantly downregulated; overexpression of CHCHD2 rescues proliferation defects of METTL5-KO neural progenitors, linking METTL5-mediated rRNA modification to mitochondrial metabolism in human neurodevelopment.","method":"Human iPSC-derived cortical organoids, METTL5 KO, transcriptomic analysis, CHCHD2 rescue experiments","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2-3 — genetic rescue in human-specific organoid model establishes pathway placement, preprint","pmids":["40672170"],"is_preprint":true},{"year":2025,"finding":"METTL5 promotes OSCC progression via m6A-mediated 18S rRNA methylation that enhances translation of CCND3 (cyclin D3), as identified by ribosome nascent-chain complex-bound mRNA sequencing (RNC-seq).","method":"METTL5 knockout, RNC-seq (ribosome nascent-chain complex-bound mRNA sequencing), in vitro and in vivo functional assays","journal":"Oncology letters","confidence":"Medium","confidence_rationale":"Tier 2 — RNC-seq directly measures translation efficiency of specific downstream target","pmids":["41743013"],"is_preprint":false},{"year":2025,"finding":"METTL5 deficiency in humans and mice (null mutation of Mettl5) leads to male infertility (oligoasthenoteratozoospermia) by compromising translational efficiency of mRNAs encoding proteins critical for spermiogenesis (Gk2, Akap4, Fsip2, Odf2, Pgk2) without affecting global translation.","method":"Human genetics (variant identification in infertility patients), Mettl5 knockout mice, ribosome profiling for translation efficiency, sperm functional analysis","journal":"Molecular therapy","confidence":"Medium","confidence_rationale":"Tier 2 — ribosome profiling identifies specific translational targets, KO mouse phenotype confirms, human genetics corroborates","pmids":["40783785"],"is_preprint":false},{"year":2024,"finding":"METTL5 interacts with IGF2BP3 in NSCLC cells, and IGF2BP3 expression is regulated downstream of METTL5; IGF2BP3 overexpression rescues METTL5 knockdown-impaired cell proliferation, placing IGF2BP3 in the METTL5 pathway.","method":"Co-immunoprecipitation, knockdown/overexpression rescue experiments, in vivo tumor model","journal":"Genetic testing and molecular biomarkers","confidence":"Low","confidence_rationale":"Tier 3 — single Co-IP, pathway placement inferred from rescue, limited mechanistic detail","pmids":["39023781"],"is_preprint":false}],"current_model":"METTL5 forms an obligate heterodimeric complex with the adaptor protein TRMT112 (which stabilizes METTL5) and functions as the dedicated N6-methyladenosine (m6A) methyltransferase at position A1832 of 18S rRNA within the ribosomal decoding center; this modification modulates ribosome conformation to regulate translation initiation and the selective translational efficiency of specific mRNAs (including FBXW7, c-Myc/USP5, SUZ12, ATF4, CXCL16, and spermiogenesis factors), thereby controlling stem cell pluripotency, differentiation, neuronal development, cardiac remodeling, spermatogenesis, and immune evasion in cancer, while loss of METTL5 reduces translation fidelity and can generate neoantigens from non-canonical translation."},"narrative":{"teleology":[{"year":2019,"claim":"Establishing METTL5 as the 18S rRNA m6A methyltransferase and defining its obligate partnership with TRMT112 resolved the long-standing question of which enzyme installs m6A on eukaryotic ribosomal RNA.","evidence":"X-ray crystallography of METTL5–TRMT112, in vitro methyltransferase assays, and cellular stability assays","pmids":["31328227"],"confidence":"High","gaps":["No substrate RNA-bound co-crystal structure","Mechanism of substrate recognition on intact ribosomal subunits not resolved","Regulation of METTL5 expression or activity unknown"]},{"year":2019,"claim":"Identification of bi-allelic METTL5 loss-of-function variants in families with intellectual disability and microcephaly established the first human disease link for this rRNA methyltransferase, and localization studies placed METTL5 in both nuclear and synaptic compartments of hippocampal neurons.","evidence":"Exome sequencing of affected families, immunofluorescence in hippocampal neurons, zebrafish morpholino knockdown recapitulating microcephaly","pmids":["31564433"],"confidence":"Medium","gaps":["Zebrafish knockdown does not prove causality in humans without rescue","Precise neural cell-type requirement unresolved","How rRNA m6A loss leads to microcephaly mechanistically unclear"]},{"year":2020,"claim":"Demonstrating that Mettl5 knockout in mouse ESCs reduces global translation, causes spontaneous loss of pluripotency, and impairs differentiation — with FBXW7 identified as a translationally regulated target whose reduced expression leads to c-MYC accumulation — connected the rRNA modification to specific mRNA translational control and stem cell biology.","evidence":"Mettl5 KO mESCs, polysome profiling, FBXW7/c-MYC western blots, translation rate measurements across multiple labs","pmids":["32217665","32783360"],"confidence":"High","gaps":["Whether translational selectivity is direct (codon usage, mRNA structure) or indirect not distinguished","Genome-wide ribosome profiling in mESCs not performed at this stage"]},{"year":2020,"claim":"Biochemical substrate specificity assays and polysome profiling showed METTL5 has strong preference for 18S A1832 and that this modification facilitates translation initiation, likely through conformational changes in the decoding center — providing the first mechanistic link between the specific modification site and ribosome function.","evidence":"Methyltransferase substrate specificity assays, p70-S6K phosphorylation, polysome profiling, structural modeling with yeast ribosome","pmids":["33357433"],"confidence":"High","gaps":["No direct cryo-EM structure of m6A1832-containing human ribosome","Whether p70-S6K activation is a direct or indirect consequence remains uncertain"]},{"year":2020,"claim":"Conservation of the METTL5–TRMT112 partnership and its specific role in 18S rRNA m6A deposition was confirmed in Drosophila, where loss causes behavioral deficits without affecting rRNA maturation, demonstrating an evolutionarily conserved post-transcriptional role in neuronal function.","evidence":"Drosophila RNAi, mass spectrometry of RNA modifications, co-IP, behavioral assays","pmids":["32350990"],"confidence":"High","gaps":["Specific neuronal mRNA targets in Drosophila not identified","Whether behavioral phenotype maps to specific brain regions unknown"]},{"year":2022,"claim":"Disease-associated METTL5 mutations were shown to disrupt the METTL5–TRMT112 interaction, providing a direct molecular mechanism linking human microcephaly/intellectual disability variants to loss of rRNA methyltransferase function.","evidence":"In vitro methyltransferase assay, co-IP with disease mutants, Mettl5 KO mice, ribosome profiling","pmids":["35033535"],"confidence":"High","gaps":["Patient-derived cells not yet tested","Whether partial loss of TRMT112 interaction produces intermediate phenotypes unknown"]},{"year":2021,"claim":"Extension of METTL5's translational regulatory role to cancer showed it enhances c-Myc translation in pancreatic cancer and USP5 translation in hepatocellular carcinoma (the latter stabilizing c-Myc protein), revealing convergent oncogenic mechanisms operating through distinct translational targets in different tumor types.","evidence":"Polysome profiling, siRNA/overexpression, m6A quantification in pancreatic cancer; GST pulldown, ubiquitination assays, polysome profiling in HCC","pmids":["34970694","36602428"],"confidence":"Medium","gaps":["Whether METTL5 directly methylates mRNA m6A sites (as suggested for c-Myc mRNA) or acts solely through 18S rRNA modification is unresolved","Single-lab studies in each cancer type"]},{"year":2022,"claim":"Identifying SUZ12 as a METTL5-dependent translational target in cardiac hypertrophy, with cardiac-specific Mettl5 KO mice showing enhanced pathological remodeling, extended the gene's physiological role beyond stem cells and neurons to the heart.","evidence":"Cardiac-specific Mettl5 conditional KO mice, polysome profiling, pressure-overload model","pmids":["35295259"],"confidence":"Medium","gaps":["Direct ribosome profiling in cardiomyocytes not performed","Whether SUZ12 is the sole effector in cardiac hypertrophy not established"]},{"year":2023,"claim":"Discovery that METTL5 loss inhibits translation of G-quadruplex-containing mRNAs (enriched in TGF-β pathway genes) in cholangiocarcinoma revealed a structural feature of mRNAs that may explain METTL5's selective translational effects.","evidence":"Ribosome profiling, liver-specific Mettl5 KO and overexpression mouse models, G-quadruplex mRNA translation analysis","pmids":["37735874"],"confidence":"Medium","gaps":["G-quadruplex selectivity not validated by mutation of G4 structures in individual mRNAs","Whether this selectivity applies broadly or is context-specific unknown"]},{"year":2025,"claim":"Multiple studies established METTL5 as a regulator of anti-tumor immunity: loss of METTL5 reduces ATF4 translation (enhancing ferroptosis sensitivity and T cell killing in ovarian cancer) and reduces CXCL16 translation (increasing CD8+ T cell infiltration in cholangiocarcinoma), positioning METTL5 as a potential immunotherapy target.","evidence":"METTL5 KO tumor models, ATF4 rescue epistasis, scRNA-seq/scTCR-seq, liver-specific KO mice, LNP-siRNA combined with PD-1 blockade","pmids":["41042068","41431992"],"confidence":"Medium","gaps":["Whether neoantigen generation from reduced translation fidelity contributes to immune phenotype in these models not tested in peer-reviewed work","Therapeutic window for METTL5 inhibition not established"]},{"year":2025,"claim":"METTL5-null mutations cause male infertility (oligoasthenoteratozoospermia) in humans and mice by compromising translational efficiency of spermiogenesis-specific mRNAs without affecting global translation, demonstrating tissue-specific translational selectivity.","evidence":"Human genetics, Mettl5 KO mice, ribosome profiling of spermatogenic cells","pmids":["40783785"],"confidence":"Medium","gaps":["How transcript-specific selectivity is achieved in germ cells not mechanistically resolved","Whether female fertility is also affected not fully characterized"]},{"year":2025,"claim":"A co-crystal structure of a covalent stereoprobe bound at TRMT112 C100 within the METTL5–TRMT112 complex — a site templated exclusively by the heterodimer interface — revealed the first allosteric modulator of METTL5 catalytic activity and demonstrated that the complex is druggable at a composite pocket.","evidence":"Chemical proteomics, X-ray co-crystal structure, in vitro methyltransferase activity assay","pmids":["41507545"],"confidence":"High","gaps":["Allosteric agonism rather than inhibition was observed; therapeutic inhibitors not yet available","Cellular efficacy of stereoprobes on endogenous rRNA m6A not demonstrated","Selectivity over other TRMT112 complexes in cells not fully validated"]},{"year":null,"claim":"Key unresolved questions include: (1) the structural basis by which m6A1832 in the decoding center confers transcript-selective translation, (2) whether reported METTL5 effects on mRNA m6A/stability reflect direct mRNA methylation or are indirect consequences of rRNA modification, and (3) how METTL5 activity is regulated in different tissues and developmental contexts.","evidence":"","pmids":[],"confidence":"High","gaps":["No cryo-EM structure of m6A1832-modified human ribosome in translating state","No consensus on whether METTL5 has any direct mRNA methyltransferase activity","Upstream signals controlling METTL5 expression/stability beyond TRIM28 are poorly defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,1,2,3,4,5,22]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[6]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,5]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1,2,3,5]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[0,1,4]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[1,3,6,7,12]}],"complexes":["METTL5–TRMT112 heterodimer"],"partners":["TRMT112","TRIM28","USP21"],"other_free_text":[]},"mechanistic_narrative":"METTL5 is the dedicated N6-methyladenosine (m6A) methyltransferase for 18S ribosomal RNA, installing m6A at position A1832 within the ribosomal decoding center to modulate translation initiation and the selective translational efficiency of specific mRNAs. METTL5 requires heterodimerization with the adaptor protein TRMT112 for metabolic stability and catalytic competence; crystal structures reveal an RNA-binding mode distinct from mRNA m6A writers and an adenosine-extrusion catalytic mechanism [PMID:31328227, PMID:35033535]. Loss of METTL5 reduces polysome abundance, impairs translation of functionally diverse transcripts (including FBXW7, SUZ12, ATF4, CXCL16, SEPHS2, and spermiogenesis factors), and thereby disrupts stem cell pluripotency, neuronal development, cardiac homeostasis, spermatogenesis, and anti-tumor immune evasion [PMID:32217665, PMID:32783360, PMID:35295259, PMID:40783785, PMID:41042068]. Bi-allelic loss-of-function mutations in METTL5 cause autosomal recessive intellectual disability with microcephaly in humans [PMID:31564433, PMID:35033535]."},"prefetch_data":{"uniprot":{"accession":"Q9NRN9","full_name":"rRNA N(6)-adenosine-methyltransferase METTL5","aliases":["Methyltransferase-like protein 5"],"length_aa":209,"mass_kda":23.7,"function":"Catalytic subunit of a heterodimer with TRMT112, which specifically methylates the 6th position of adenine in position 1832 of 18S rRNA (PubMed:31328227, PubMed:32217665, PubMed:33357433, PubMed:33428944, PubMed:35033535). N6-methylation of adenine(1832) in 18S rRNA resides in the decoding center of 18S rRNA and is required for translation and embryonic stem cells (ESCs) pluripotency and differentiation (PubMed:33357433)","subcellular_location":"Nucleus; Presynapse; Postsynapse","url":"https://www.uniprot.org/uniprotkb/Q9NRN9/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/METTL5","classification":"Not Classified","n_dependent_lines":36,"n_total_lines":1208,"dependency_fraction":0.029801324503311258},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/METTL5","total_profiled":1310},"omim":[{"mim_id":"618665","title":"INTELLECTUAL DEVELOPMENTAL DISORDER, AUTOSOMAL RECESSIVE 72; MRT72","url":"https://www.omim.org/entry/618665"},{"mim_id":"618630","title":"tRNA METHYLTRANSFERASE SUBUNIT 11-2; TRMT112","url":"https://www.omim.org/entry/618630"},{"mim_id":"618628","title":"METHYLTRANSFERASE 5, N6-ADENOSINE; METTL5","url":"https://www.omim.org/entry/618628"},{"mim_id":"611792","title":"ZINC FINGER CCHC DOMAIN-CONTAINING PROTEIN 4; ZCCHC4","url":"https://www.omim.org/entry/611792"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoli","reliability":"Supported"},{"location":"Nucleoli fibrillar center","reliability":"Supported"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in 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N6-methyladenosine modification of human 18S rRNA, and must form a heterodimeric complex with TRMT112 to gain metabolic stability in cells. The first atomic resolution structure of METTL5-TRMT112 was solved, revealing an RNA-binding mode distinct from other m6A methyltransferases, and suggesting an adenosine extrusion mechanism analogous to DNA methyltransferases.\",\n      \"method\": \"In vitro methyltransferase assay, co-immunoprecipitation, X-ray crystallography, cellular stability assays\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution, crystal structure, and functional validation in single highly-cited study\",\n      \"pmids\": [\"31328227\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"METTL5 catalyzes m6A modification at position A1832 of 18S rRNA in vivo and in vitro. Loss of Mettl5 in mouse embryonic stem cells reduces global translation rate, causes spontaneous loss of pluripotency, and compromises differentiation potential.\",\n      \"method\": \"In vitro methyltransferase assay, Mettl5 knockout mESCs, polysome profiling, translation rate measurement\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro assay confirmed, KO phenotype with multiple orthogonal readouts, independently replicated\",\n      \"pmids\": [\"32217665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"METTL5 shows strong substrate preference for 18S A1832 and promotes p70-S6K activation and proper translation initiation; loss of METTL5 significantly reduces polysome abundance. Structural comparison with unmodified yeast ribosomes indicates the m6A modification may facilitate mRNA binding by inducing conformation changes in the decoding center.\",\n      \"method\": \"Methyltransferase substrate specificity assay, polysome profiling, p70-S6K activation assay, structural modeling\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including biochemical assays and polysome profiling, replicated across organisms\",\n      \"pmids\": [\"33357433\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Deletion of Mettl5 in mouse embryonic stem cells impairs efficient translation of FBXW7, a key regulator of cell differentiation, leading to c-MYC accumulation and delayed differentiation onset. METTL5 methylates 18S rRNA both in vivo and in vitro.\",\n      \"method\": \"Mettl5 knockout mESCs, polysome profiling, western blotting for FBXW7 and c-MYC, in vitro methyltransferase assay\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro assay plus KO with defined molecular mechanism linking rRNA modification to translational regulation of specific substrate\",\n      \"pmids\": [\"32783360\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Drosophila CG9666 (ortholog of human METTL5) directly interacts with CG12975 (ortholog of TRMT112) to deposit m6A specifically on 18S rRNA; depletion of CG9666 abolishes 18S rRNA m6A without compromising rRNA maturation, but impairs fly behavior.\",\n      \"method\": \"RNAi screen, mass spectrometry of RNA modifications, co-immunoprecipitation, behavioral assays\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal interaction confirmed, direct modification detected by MS, functional phenotype established\",\n      \"pmids\": [\"32350990\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The METTL5-TRMT112 complex installs m6A at position A1832 of human 18S rRNA; TRMT112 is required for METTL5 stability; human METTL5 mutations associated with microcephaly and intellectual disability disrupt the METTL5-TRMT112 interaction. Loss of METTL5 in human cancer cell lines and mice regulates gene expression at the translational level.\",\n      \"method\": \"In vitro methyltransferase assay, co-immunoprecipitation, Mettl5 knockout mice, ribosome profiling\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods, mechanistic link between disease mutations and protein interaction confirmed\",\n      \"pmids\": [\"35033535\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Bi-allelic frameshift variants in METTL5 cause intellectual disability and microcephaly; METTL5 protein is enriched in the nucleus and synapses of hippocampal neurons; truncating variants do not affect localization but alter protein expression levels. Mettl5 knockdown in zebrafish causes microcephaly.\",\n      \"method\": \"Exome sequencing, transfection of orthologous cells, immunofluorescence localization in hippocampal neurons, zebrafish knockdown\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — direct localization experiment with functional consequence, zebrafish phenotypic validation\",\n      \"pmids\": [\"31564433\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Mettl5 knockout in mESCs leads to abnormal craniofacial and nervous development; the METTL5 protein complex predominantly interacts with RNA binding proteins and ribosome proteins. Mettl5 knockout mice exhibit intellectual disability and impaired myelination in brain.\",\n      \"method\": \"Co-immunoprecipitation/mass spectrometry of METTL5 protein complex, Mettl5 knockout mice, behavioral testing, myelin staining\",\n      \"journal\": \"Genes & diseases\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — interactome by MS, KO mouse with defined cellular phenotype\",\n      \"pmids\": [\"35005123\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"METTL5 promotes pancreatic cancer cell proliferation, migration, and invasion through increased c-Myc translation. m6A modifications at the 5'UTR and CDS (near 5'UTR) of c-Myc mRNA are critical for this specific translational regulation. METTL5 and its cofactor TRMT112 synergistically promote cancer progression.\",\n      \"method\": \"Polysome profiling, siRNA knockdown/overexpression, m6A quantification, in vitro functional assays\",\n      \"journal\": \"International journal of oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — polysome profiling supports translational mechanism, single lab\",\n      \"pmids\": [\"34970694\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"METTL5-mediated 18S rRNA m6A modification modulates translation of SUZ12 (a core PRC2 component) to regulate transcriptomic shifts during cardiac hypertrophy. Cardiac-specific METTL5 knockout mice show enhanced pressure overload-induced hypertrophy.\",\n      \"method\": \"Cardiac-specific Mettl5 conditional knockout mice, polysome profiling, western blotting, cardiomyocyte gain- and loss-of-function assays\",\n      \"journal\": \"Frontiers in cardiovascular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with defined molecular mechanism linking rRNA methylation to translational control of specific target\",\n      \"pmids\": [\"35295259\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"METTL5 controls USP5 translation, which in turn stabilizes c-Myc by inhibiting K48-linked polyubiquitination via USP5 binding to c-Myc. CREB1/P300 acts as a transcriptional regulator promoting METTL5 transcription in HCC.\",\n      \"method\": \"GST pulldown, co-immunoprecipitation, polysome profiling, RNA sequencing, luciferase reporter assay, ubiquitination assay\",\n      \"journal\": \"Cancer communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple orthogonal methods from single lab, molecular mechanism established\",\n      \"pmids\": [\"36602428\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"METTL5 depletion impairs 18S rRNA m6A modification, hampers ribosome synthesis, and inhibits translation of G-quadruplex-containing mRNAs enriched in TGF-β pathway in intrahepatic cholangiocarcinoma. Liver-specific METTL5 knockout and overexpression ICC mouse models confirmed these effects.\",\n      \"method\": \"Loss- and gain-of-function in vitro and in vivo assays, ribosome profiling, m6A quantification, G-quadruplex mRNA translation analysis, liver-specific KO mouse models\",\n      \"journal\": \"Molecular therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple mouse models, ribosome profiling identifying specific mRNA class as targets\",\n      \"pmids\": [\"37735874\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"METTL5 regulates cranial suture fusion by controlling Wnt signaling; Mettl5 knockout mice show poor ossification, widened cranial sutures, increased proliferation and decreased osteogenic differentiation of suture mesenchymal stem cells.\",\n      \"method\": \"Mettl5 knockout mice, cell proliferation and differentiation assays, Wnt signaling pathway analysis\",\n      \"journal\": \"Fundamental research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — KO mice with defined cellular phenotype and pathway placement\",\n      \"pmids\": [\"38933773\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"METTL5 knockout in ovarian cancer disrupts ATF4 translation by altering 18S rRNA m6A levels, leading to downregulation of SLC7A11 and SLC3A2, thus enhancing ferroptosis sensitivity and tumor susceptibility to T cell-mediated antitumor immunity. ATF4 overexpression or ferroptosis inhibition reverses METTL5-KO immune-sensitive phenotypes.\",\n      \"method\": \"Genome-wide immune screens, METTL5 KO in cancer cells, rescue experiments with ATF4 overexpression, ferroptosis inhibitor, in vivo tumor models\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epistasis established via rescue, multiple orthogonal approaches linking rRNA methylation to specific translational target\",\n      \"pmids\": [\"41042068\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TRIM28 mediates Mettl5 ubiquitination and degradation in CD4+ T cells; reduced Mettl5 levels lead to hypomethylation at the Gata3 promoter and increased GATA3 transcription, promoting Th2 polarization. In airway allergy, Mettl5 also recruits USP21 to deubiquitinate GATA3, boosting IL-4 expression in M2 macrophages.\",\n      \"method\": \"Chromatin immunoprecipitation assay, co-immunoprecipitation, ubiquitination assay, Mettl5 conditional KO in macrophages/T cells, mouse allergy model\",\n      \"journal\": \"Frontiers in immunology / Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — identified ubiquitin writer (TRIM28) by ChIP and Co-IP, functional consequence in defined immune cell context\",\n      \"pmids\": [\"40391221\", \"40089091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"METTL5 depletion reduces selenophosphate synthetase 2 (SEPHS2) translation efficiency, leading to diminished selenoprotein synthesis and increased ROS, inducing apoptosis in multiple myeloma. Salvianolic acid C (SAC) was identified as a METTL5 inhibitor.\",\n      \"method\": \"Mettl5 knockdown, ribosome profiling/translation efficiency measurement, ROS assay, in vitro and in vivo myeloma models, drug inhibitor assay\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — translation efficiency of specific target measured, functional link to apoptosis established\",\n      \"pmids\": [\"40750759\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"METTL5-mediated 18S rRNA m6A modification promotes translation of CXCL16, enabling immune evasion in intrahepatic cholangiocarcinoma by excluding CD8+ T cells. Mettl5 liver-specific KO increases CD8+ T cell infiltration and reduces immunosuppressive tumor-associated macrophages.\",\n      \"method\": \"Liver-specific Mettl5 conditional KO mice, scRNA-seq, scTCR-seq, adoptive macrophage transfer, lipid nanoparticle siRNA delivery combined with PD-1 blockade\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple in vivo models with defined translational target and immune mechanism\",\n      \"pmids\": [\"41431992\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"METTL5 upregulation promotes NRF2 mRNA stability; IGF2BP1 mediates NRF2 mRNA stability via the METTL5/m6A/NRF2 axis, thereby inactivating ferroptosis and repressing anti-tumor immunity in gastric cancer.\",\n      \"method\": \"mRNA stability assay, RNA immunoprecipitation, loss-of-function experiments, co-culture with PBMCs\",\n      \"journal\": \"Cell death discovery\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, limited mechanistic detail on direct m6A site, functional link inferred\",\n      \"pmids\": [\"39261486\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"METTL5 positively regulates TPRKB expression by enhancing TPRKB mRNA stability via m6A modification in hepatocellular carcinoma.\",\n      \"method\": \"mRNA stability assay, METTL5 knockdown, rescue experiments with TPRKB overexpression\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, single method for m6A-stability link\",\n      \"pmids\": [\"39182664\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"METTL5-mediated m6A modification enhances UBE3C mRNA stability by enabling YTHDF1 to bind and protect the modified mRNA from degradation; UBE3C then promotes ubiquitination and degradation of AHNAK, suppressing ferroptosis in osteosarcoma.\",\n      \"method\": \"mRNA stability assay, RIP for YTHDF1 binding, UBE3C knockdown/overexpression, ferroptosis assay, Co-IP\",\n      \"journal\": \"Journal of molecular histology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, indirect mechanistic chain, limited direct m6A site validation\",\n      \"pmids\": [\"40696164\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"METTL5 promotes HCC recurrence after thermal ablation by enhancing PEX16 translation, which promotes peroxisomal biogenesis and β-oxidation of very long-chain fatty acids, thereby facilitating mitochondrial respiration under heat stress.\",\n      \"method\": \"Insufficient RFA in vitro and in vivo models, translation efficiency analysis, peroxisome biogenesis assay, fatty acid oxidation assay\",\n      \"journal\": \"Molecular therapy\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — mechanistic chain proposed with limited direct validation of m6A on PEX16 mRNA\",\n      \"pmids\": [\"41234012\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"METTL5 promotes corticospinal tract sprouting after traumatic brain injury by increasing translation efficiency of Cfl1 (cofilin) and Inpp5k, leading to cofilin activation, actin polymerization, and axon outgrowth.\",\n      \"method\": \"METTL5 overexpression in corticospinal neurons, ribosome profiling (translation efficiency), anterograde axonal tracing, cofilin activity assay\",\n      \"journal\": \"Experimental neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — ribosome profiling identifies specific translational targets, in vivo functional outcome established\",\n      \"pmids\": [\"39406306\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Bicyclopyrrolidine acrylamide stereoprobes react covalently with C100 of TRMT112 exclusively within the METTL5-TRMT112 complex (not other TRMT112 complexes). Co-crystal structure revealed a composite binding pocket templated by METTL5 at TRMT112's C100; stereoprobe binding causes allosteric agonism of METTL5 catalytic activity.\",\n      \"method\": \"Chemical proteomics, co-crystal structure (X-ray crystallography), in vitro methyltransferase activity assay, recombinant protein binding assays\",\n      \"journal\": \"Nature chemical biology / bioRxiv\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — co-crystal structure plus functional validation of allosteric mechanism, published in peer-reviewed journal\",\n      \"pmids\": [\"41507545\", \"40475643\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Drosophila Mettl5 regulates sleep by controlling translational output of proteasome components and clock genes; loss of Mettl5 or Trmt112 increases PERIOD protein levels, causing sleep phenotypes. Mettl5 functions predominantly within neurons and glia.\",\n      \"method\": \"Drosophila Mettl5 mutants, rescue experiments with tissue-specific expression, RNA-seq and Ribo-seq, PERIOD protein quantification\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Ribo-seq plus genetic rescue in Drosophila ortholog, preprint only\",\n      \"pmids\": [\"bio_10.1101_2024.10.24.620129\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"METTL5 deficiency decreases translation fidelity of ribosomes, increases non-canonical translation products, and generates tumor neoantigens that stimulate CD8+ T cell infiltration and TCR repertoire diversity in murine tumor models. This effect depends on intact antigen presentation pathways.\",\n      \"method\": \"Mettl5 knockout tumor models, antigen presentation pathway epistasis, TCR-seq, CD8+ T cell infiltration analysis\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic epistasis with antigen presentation, in vivo immune phenotype, preprint\",\n      \"pmids\": [\"bio_10.1101_2025.06.06.658288\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"METTL5 promotes METTL5-mediated m6A modification of 18S rRNA, which modulates MGST1 protein expression through its N6-methyladenosine catalytic function, suppressing ferroptosis in HCC.\",\n      \"method\": \"Tandem mass tagging proteomic quantification, METTL5 knockdown, ferroptosis assay, western blotting\",\n      \"journal\": \"Molecular and cellular biochemistry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, proteomics identifies MGST1 as downstream target but direct m6A mechanism not fully established\",\n      \"pmids\": [\"41557129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Cortical organoids from METTL5-KO human iPSCs show delayed neural stem cell proliferation and neuronal differentiation timing. CHCHD2, a nuclear-encoded mitochondrial gene, is significantly downregulated; overexpression of CHCHD2 rescues proliferation defects of METTL5-KO neural progenitors, linking METTL5-mediated rRNA modification to mitochondrial metabolism in human neurodevelopment.\",\n      \"method\": \"Human iPSC-derived cortical organoids, METTL5 KO, transcriptomic analysis, CHCHD2 rescue experiments\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — genetic rescue in human-specific organoid model establishes pathway placement, preprint\",\n      \"pmids\": [\"40672170\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"METTL5 promotes OSCC progression via m6A-mediated 18S rRNA methylation that enhances translation of CCND3 (cyclin D3), as identified by ribosome nascent-chain complex-bound mRNA sequencing (RNC-seq).\",\n      \"method\": \"METTL5 knockout, RNC-seq (ribosome nascent-chain complex-bound mRNA sequencing), in vitro and in vivo functional assays\",\n      \"journal\": \"Oncology letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — RNC-seq directly measures translation efficiency of specific downstream target\",\n      \"pmids\": [\"41743013\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"METTL5 deficiency in humans and mice (null mutation of Mettl5) leads to male infertility (oligoasthenoteratozoospermia) by compromising translational efficiency of mRNAs encoding proteins critical for spermiogenesis (Gk2, Akap4, Fsip2, Odf2, Pgk2) without affecting global translation.\",\n      \"method\": \"Human genetics (variant identification in infertility patients), Mettl5 knockout mice, ribosome profiling for translation efficiency, sperm functional analysis\",\n      \"journal\": \"Molecular therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ribosome profiling identifies specific translational targets, KO mouse phenotype confirms, human genetics corroborates\",\n      \"pmids\": [\"40783785\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"METTL5 interacts with IGF2BP3 in NSCLC cells, and IGF2BP3 expression is regulated downstream of METTL5; IGF2BP3 overexpression rescues METTL5 knockdown-impaired cell proliferation, placing IGF2BP3 in the METTL5 pathway.\",\n      \"method\": \"Co-immunoprecipitation, knockdown/overexpression rescue experiments, in vivo tumor model\",\n      \"journal\": \"Genetic testing and molecular biomarkers\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single Co-IP, pathway placement inferred from rescue, limited mechanistic detail\",\n      \"pmids\": [\"39023781\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"METTL5 forms an obligate heterodimeric complex with the adaptor protein TRMT112 (which stabilizes METTL5) and functions as the dedicated N6-methyladenosine (m6A) methyltransferase at position A1832 of 18S rRNA within the ribosomal decoding center; this modification modulates ribosome conformation to regulate translation initiation and the selective translational efficiency of specific mRNAs (including FBXW7, c-Myc/USP5, SUZ12, ATF4, CXCL16, and spermiogenesis factors), thereby controlling stem cell pluripotency, differentiation, neuronal development, cardiac remodeling, spermatogenesis, and immune evasion in cancer, while loss of METTL5 reduces translation fidelity and can generate neoantigens from non-canonical translation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"METTL5 is the dedicated N6-methyladenosine (m6A) methyltransferase for 18S ribosomal RNA, installing m6A at position A1832 within the ribosomal decoding center to modulate translation initiation and the selective translational efficiency of specific mRNAs. METTL5 requires heterodimerization with the adaptor protein TRMT112 for metabolic stability and catalytic competence; crystal structures reveal an RNA-binding mode distinct from mRNA m6A writers and an adenosine-extrusion catalytic mechanism [PMID:31328227, PMID:35033535]. Loss of METTL5 reduces polysome abundance, impairs translation of functionally diverse transcripts (including FBXW7, SUZ12, ATF4, CXCL16, SEPHS2, and spermiogenesis factors), and thereby disrupts stem cell pluripotency, neuronal development, cardiac homeostasis, spermatogenesis, and anti-tumor immune evasion [PMID:32217665, PMID:32783360, PMID:35295259, PMID:40783785, PMID:41042068]. Bi-allelic loss-of-function mutations in METTL5 cause autosomal recessive intellectual disability with microcephaly in humans [PMID:31564433, PMID:35033535].\",\n  \"teleology\": [\n    {\n      \"year\": 2019,\n      \"claim\": \"Establishing METTL5 as the 18S rRNA m6A methyltransferase and defining its obligate partnership with TRMT112 resolved the long-standing question of which enzyme installs m6A on eukaryotic ribosomal RNA.\",\n      \"evidence\": \"X-ray crystallography of METTL5–TRMT112, in vitro methyltransferase assays, and cellular stability assays\",\n      \"pmids\": [\"31328227\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No substrate RNA-bound co-crystal structure\", \"Mechanism of substrate recognition on intact ribosomal subunits not resolved\", \"Regulation of METTL5 expression or activity unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identification of bi-allelic METTL5 loss-of-function variants in families with intellectual disability and microcephaly established the first human disease link for this rRNA methyltransferase, and localization studies placed METTL5 in both nuclear and synaptic compartments of hippocampal neurons.\",\n      \"evidence\": \"Exome sequencing of affected families, immunofluorescence in hippocampal neurons, zebrafish morpholino knockdown recapitulating microcephaly\",\n      \"pmids\": [\"31564433\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Zebrafish knockdown does not prove causality in humans without rescue\", \"Precise neural cell-type requirement unresolved\", \"How rRNA m6A loss leads to microcephaly mechanistically unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstrating that Mettl5 knockout in mouse ESCs reduces global translation, causes spontaneous loss of pluripotency, and impairs differentiation — with FBXW7 identified as a translationally regulated target whose reduced expression leads to c-MYC accumulation — connected the rRNA modification to specific mRNA translational control and stem cell biology.\",\n      \"evidence\": \"Mettl5 KO mESCs, polysome profiling, FBXW7/c-MYC western blots, translation rate measurements across multiple labs\",\n      \"pmids\": [\"32217665\", \"32783360\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether translational selectivity is direct (codon usage, mRNA structure) or indirect not distinguished\", \"Genome-wide ribosome profiling in mESCs not performed at this stage\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Biochemical substrate specificity assays and polysome profiling showed METTL5 has strong preference for 18S A1832 and that this modification facilitates translation initiation, likely through conformational changes in the decoding center — providing the first mechanistic link between the specific modification site and ribosome function.\",\n      \"evidence\": \"Methyltransferase substrate specificity assays, p70-S6K phosphorylation, polysome profiling, structural modeling with yeast ribosome\",\n      \"pmids\": [\"33357433\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No direct cryo-EM structure of m6A1832-containing human ribosome\", \"Whether p70-S6K activation is a direct or indirect consequence remains uncertain\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Conservation of the METTL5–TRMT112 partnership and its specific role in 18S rRNA m6A deposition was confirmed in Drosophila, where loss causes behavioral deficits without affecting rRNA maturation, demonstrating an evolutionarily conserved post-transcriptional role in neuronal function.\",\n      \"evidence\": \"Drosophila RNAi, mass spectrometry of RNA modifications, co-IP, behavioral assays\",\n      \"pmids\": [\"32350990\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific neuronal mRNA targets in Drosophila not identified\", \"Whether behavioral phenotype maps to specific brain regions unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Disease-associated METTL5 mutations were shown to disrupt the METTL5–TRMT112 interaction, providing a direct molecular mechanism linking human microcephaly/intellectual disability variants to loss of rRNA methyltransferase function.\",\n      \"evidence\": \"In vitro methyltransferase assay, co-IP with disease mutants, Mettl5 KO mice, ribosome profiling\",\n      \"pmids\": [\"35033535\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Patient-derived cells not yet tested\", \"Whether partial loss of TRMT112 interaction produces intermediate phenotypes unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Extension of METTL5's translational regulatory role to cancer showed it enhances c-Myc translation in pancreatic cancer and USP5 translation in hepatocellular carcinoma (the latter stabilizing c-Myc protein), revealing convergent oncogenic mechanisms operating through distinct translational targets in different tumor types.\",\n      \"evidence\": \"Polysome profiling, siRNA/overexpression, m6A quantification in pancreatic cancer; GST pulldown, ubiquitination assays, polysome profiling in HCC\",\n      \"pmids\": [\"34970694\", \"36602428\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether METTL5 directly methylates mRNA m6A sites (as suggested for c-Myc mRNA) or acts solely through 18S rRNA modification is unresolved\", \"Single-lab studies in each cancer type\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identifying SUZ12 as a METTL5-dependent translational target in cardiac hypertrophy, with cardiac-specific Mettl5 KO mice showing enhanced pathological remodeling, extended the gene's physiological role beyond stem cells and neurons to the heart.\",\n      \"evidence\": \"Cardiac-specific Mettl5 conditional KO mice, polysome profiling, pressure-overload model\",\n      \"pmids\": [\"35295259\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct ribosome profiling in cardiomyocytes not performed\", \"Whether SUZ12 is the sole effector in cardiac hypertrophy not established\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Discovery that METTL5 loss inhibits translation of G-quadruplex-containing mRNAs (enriched in TGF-β pathway genes) in cholangiocarcinoma revealed a structural feature of mRNAs that may explain METTL5's selective translational effects.\",\n      \"evidence\": \"Ribosome profiling, liver-specific Mettl5 KO and overexpression mouse models, G-quadruplex mRNA translation analysis\",\n      \"pmids\": [\"37735874\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"G-quadruplex selectivity not validated by mutation of G4 structures in individual mRNAs\", \"Whether this selectivity applies broadly or is context-specific unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Multiple studies established METTL5 as a regulator of anti-tumor immunity: loss of METTL5 reduces ATF4 translation (enhancing ferroptosis sensitivity and T cell killing in ovarian cancer) and reduces CXCL16 translation (increasing CD8+ T cell infiltration in cholangiocarcinoma), positioning METTL5 as a potential immunotherapy target.\",\n      \"evidence\": \"METTL5 KO tumor models, ATF4 rescue epistasis, scRNA-seq/scTCR-seq, liver-specific KO mice, LNP-siRNA combined with PD-1 blockade\",\n      \"pmids\": [\"41042068\", \"41431992\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether neoantigen generation from reduced translation fidelity contributes to immune phenotype in these models not tested in peer-reviewed work\", \"Therapeutic window for METTL5 inhibition not established\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"METTL5-null mutations cause male infertility (oligoasthenoteratozoospermia) in humans and mice by compromising translational efficiency of spermiogenesis-specific mRNAs without affecting global translation, demonstrating tissue-specific translational selectivity.\",\n      \"evidence\": \"Human genetics, Mettl5 KO mice, ribosome profiling of spermatogenic cells\",\n      \"pmids\": [\"40783785\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How transcript-specific selectivity is achieved in germ cells not mechanistically resolved\", \"Whether female fertility is also affected not fully characterized\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A co-crystal structure of a covalent stereoprobe bound at TRMT112 C100 within the METTL5–TRMT112 complex — a site templated exclusively by the heterodimer interface — revealed the first allosteric modulator of METTL5 catalytic activity and demonstrated that the complex is druggable at a composite pocket.\",\n      \"evidence\": \"Chemical proteomics, X-ray co-crystal structure, in vitro methyltransferase activity assay\",\n      \"pmids\": [\"41507545\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Allosteric agonism rather than inhibition was observed; therapeutic inhibitors not yet available\", \"Cellular efficacy of stereoprobes on endogenous rRNA m6A not demonstrated\", \"Selectivity over other TRMT112 complexes in cells not fully validated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: (1) the structural basis by which m6A1832 in the decoding center confers transcript-selective translation, (2) whether reported METTL5 effects on mRNA m6A/stability reflect direct mRNA methylation or are indirect consequences of rRNA modification, and (3) how METTL5 activity is regulated in different tissues and developmental contexts.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No cryo-EM structure of m6A1832-modified human ribosome in translating state\", \"No consensus on whether METTL5 has any direct mRNA methyltransferase activity\", \"Upstream signals controlling METTL5 expression/stability beyond TRIM28 are poorly defined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4, 5, 22]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 2, 3, 5]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0, 1, 4]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [1, 3, 6, 7, 12]}\n    ],\n    \"complexes\": [\n      \"METTL5–TRMT112 heterodimer\"\n    ],\n    \"partners\": [\n      \"TRMT112\",\n      \"TRIM28\",\n      \"USP21\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}