Amplification of chromosomal material derived from 12q13-15 is common in human cancer and believed to result in overexpression of multiple collaborating oncogenes. To define the oncogenes involved, we overexpressed genes recurrently amplified in human liposarcoma using a zebrafish model of the disease. We found several genes whose overexpression collaborated with AKT in sarcomagenesis, including the tRNA methyltransferase METTL1. This was surprising, because AKT phosphorylates METTL1 to inactivate its enzymatic activity. Indeed, phosphomimetic S27D or catalytically dead alleles phenocopied the oncogenic activity of wild-type METTL1. We found that METTL1 binds the multi-tRNA synthetase complex, which contains many of the cellular aminoacyl-tRNA synthetases and promotes tRNA aminoacylation, polysome formation, and protein synthesis independent of its methyltransferase activity. METTL1-amplified liposarcomas were hypersensitive to actinomycin D, a clinical inhibitor of ribosome biogenesis. We propose that METTL1 overexpression promotes sarcomagenesis by stimulating tRNA aminoacylation, protein synthesis, and tumor cell growth independent of its methyltransferase activity.

tRNA quality control pathways have been identified in yeast, whereby aberrant and hypomodified mature tRNAs are targeted for 5’-3’ degradation by the rapid tRNA decay (RTD) pathway involving the Xrn1 and Rat1/Xrn2 exonucleases, whereas aberrant precursor tRNAs (pre-tRNAs) are targeted for 3’-5’ degradation by the nuclear surveillance pathway involving the RNA Exosome. However, the pathways controlling tRNA and pre-tRNA degradation in mammals have not yet been defined and the relevance of pre-tRNA surveillance pathways for normal cell physiology remains largely unknown. The RNA Exosome comprises a core of nine non-catalytic subunits (EXOSC1-9) to which the distinct, DIS3 and EXOSC10, 3’-5’ exonucleases associate. Here we find that EXOSC10 deficiency leads to accumulation of unspliced precursor tRNAs (pre-tRNAs) in mouse embryonic stem cells (ESCs) and is required for pre-tRNA decay in biochemical assays. Pre-tRNA overexpression causes diminished motor neuronal survival in a mouse ESC differentiation model. Our results identify a pre-tRNA decay pathway that links Exosome deficiency with neuron survival and provides insight into possible pathological mechanisms underlying human neurodevelopmental disorders caused by mutations in Exosome subunits and genes involved in tRNA biogenesis. ### Competing Interest Statement The authors have declared no competing interest.

Transfer RNAs (tRNAs) are subject to various chemical modifications that influence their stability or function. Adenosine to Inosine (A-to-I) editing in the tRNA anticodon at position A34 is an important modification that expands anticodon-codon recognition at the wobble position and is required for normal mRNA translation. The relevance of tRNA editing in cancer remains unexplored. Here we show that the genes encoding the ADAT2/3 deaminase complex, responsible for A-to-I tRNA editing in humans, are commonly amplified and/or overexpressed in several tumor types including liposarcoma (LPS). We find that LPS cell growth and tumorigenicity is dependent on ADAT2/3 tRNA editing activity. Mechanistically, we find decreased tRNA editing upon ADAT2 depletion, defective translation of a subset of mRNAs, and altered protein homeostasis. Thus, ADAT2 promotes oncogenesis and the translation of growth promoting mRNAs that are enriched in NNC codons that lack cognate tRNAs and therefore depend on A-I tRNA editing for decoding and mRNA translation. Our results identify ADAT2/3 as a potential new cancer therapeutic target.

The epitranscriptome includes a diversity of RNA modifications that influence gene expression. N3-methylcytidine (m(3)C) mainly occurs in the anticodon loop (position C32) of certain tRNAs yet its role is poorly understood. Here, using HAC-Seq, we report comprehensive METTL2A/2B-, METTL6-, and METTL2A/2B/6-dependent m(3)C profiles in human cells. METTL2A/2B modifies tRNA-arginine and tRNA-threonine members, whereas METTL6 modifies the tRNA-serine family. However, decreased m(3)C32 on tRNA-Ser-GCT isodecoders is only observed with combined METTL2A/2B/6 deletion. Ribo-Seq reveals altered translation of genes related to cell cycle and DNA repair pathways in METTL2A/2B/6-deficient cells, and these mRNAs are enriched in AGU codons that require tRNA-Ser-GCT for translation. These results, supported by reporter assays, help explain the observed altered cell cycle, slowed proliferation, and increased cisplatin sensitivity phenotypes of METTL2A/2B/6-deficient cells. Thus, we define METTL2A/2B/6-dependent methylomes and uncover a particular requirement of m(3)C32 tRNA modification for serine codon-biased mRNA translation of cell cycle, and DNA repair genes.

RNA is subject to a multitude of different chemical modifications that collectively represent the epitranscriptome. Individual RNA modifications including N6-methyladenosine (m6A) on mRNA play essential roles in the posttranscriptional control of gene expression. Recent technological advances have enabled the transcriptome-wide mapping of certain RNA modifications, to reveal their broad relevance and characteristic distribution patterns. However, convenient methods that enable the simultaneous mapping of multiple different RNA marks within the same sample are generally lacking. Here we present EpiPlex RNA modification profiling, a bead-based proximity barcoding assay with sequencing readout that expands the scope of molecular recognition-based RNA modification detection to multiple targets, while providing relative quantification and enabling low RNA input. Measuring signal intensity against spike-in controls provides relative quantification, indicative of the RNA mod abundance at each locus. We report on changes in the modification status of HEK293T cells upon treatment with pharmacological inhibitors separately targeting METTL3, the dominant m6A writer enzyme, and the EIF4A3 component of the exon junction complex (EJC). The treatments resulted in decreased or increased m6A levels, respectively, without effect on inosine levels. Inhibiting the helicase activity of EIF4A3 and EIF4A3 knockdown both cause a significant increase of m6A sites near exon junctions, consistent with the previously reported role of EIF4A3 in shaping the m6A landscape. Thus, EpiPlex offers a reliable and convenient method for simultaneous mapping of multiple RNA modifications to facilitate epitranscriptome studies.

Stress granules (SGs) are crucial in RNA regulation, affecting cell fate and function. SGs contain RNAs, some of which can be methylated. We studied m6A RNA modifications during the human CD34+ HSPCs (hCD34+) differentiating into erythroid cells and found that mRNAs encoding many erythroid-specific proteins had decreased methylation during differentiation. Increased levels of ALKBH5 demethylase during erythropoiesis control the levels of the 3'UTR methylation of these mRNAs. hCD34+ carrying ALKBH5 mutations demonstrated a block in erythropoiesis, and mass-spectrometry studies of the mutant cells showed decreased levels of SG proteins, including the core granule protein ATXN2. ALKBH5 directly regulates the methylation of the mRNA of ATXN2. ATXN2 overexpression accelerated the erythroid differentiation of HSPCs and rescued the erythroid differentiation of ALKBH5 mutant cells. Very few SGs are found in normal human erythroid progenitors. SGs accumulated substantially in ALKBH5 mutant cells, and surprisingly overexpression of ATNX2 reduced SG numbers to normal. Polysome analysis demonstrated m6A-modified RNAs to be enriched in the pre-polysome fractions that were less translated. This work establishes a mechanism by which during stress, ATXN2 facilitates the release of SG-stored m6A-modified RNAs including erythroid-specific and SG-enriched RNAs that are loaded onto functional ribosomes, allowing better translation and accelerated erythroid differentiation during stress. ### Competing Interest Statement The authors have declared no competing interest.

AbstractN6-methyladenosine (m6A) is the most abundant chemical modification in mRNA and plays important roles in human and mouse embryonic stem cell pluripotency, maintenance, and differentiation. We have recently reported that m6A is involved in the postnatal control of β-cell function in physiological states and in type 1 and 2 diabetes. However, the precise mechanisms by which m6A acts to regulate the development of human and mouse pancreas are unexplored. Here, we show that the m6A landscape is dynamic during human pancreas development, and that METTL14, one of the m6A writer complex proteins, is essential for the early differentiation of both human and mouse pancreatic cells.

Abstract It is becoming increasingly appreciated that RNA modifications are widespread in development and homeostasis, regulating RNA stability and translation, and that alterations to these modifications are associated with cancer development and progression. Although 170 different RNA modifications have been identified using mass spectrometry, there is a paucity of convenient, validated tools immediately available to cancer researchers to explore these modifications using relevant clinical samples in sufficient numbers, and accurately determine their suitability for use as diagnostic or drug targets. In addition, most existing methods concentrate only on m6A, the most prevalent modification in mRNA. Alida Bio has developed an end-to-end assay platform with an integrated bioinformatics solution that detects multiple modifications in the same reaction. This platform exploits targeted, multiplexed barcoding to reveal the quantitative abundance of modified transcripts, co-localization of multiple RNA modifications to the same gene, and gene expression profiles. Alida Bio's mission is to equip translational researchers with tools that will significantly improve their understanding of gene regulation through seamless measurement of RNA modifications. Citation Format: Andrew Price, Zachary Miles, John Chevillet, Byron Purse, Richard I. Gregory, Gudrun Stengel. AlidaBio EpiPlex: A platform for multiplexed detection of RNA modifications in clinical samples [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1741.

Abstract N6-methyladenosine (m6A) is the most prevalent modification in eukaryotic mRNA. Increasing evidence shows that m6A is involved in the biological functions of cancer cells, including proliferation, invasion, metastasis, and drug resistance. Dysregulation of m6A deposition and its associated machinery, including writers, erasers and readers, is observed in multiple cancer types, and the dysregulation profiles have potential as diagnostic, prognostic and/or predictive biomarkers. In healthy cells, m6A modifications are installed co-transcriptionally by the writer enzyme METTL3, resulting in an enrichment of m6A in the 3’UTR of genes. For many years, the mechanistic origin for the m6A enrichment in the 3’UTR was unclear. Recently, the Gregory lab and others have developed a model where the exon junction complex (EJC) plays a key role in directing m6A deposition by hindering access of METTL3 to short exons and exon/intron junctions. In this study, we build on this model using a novel, proximity-barcoding based assay (EpiPlex™) for the simultaneous detection of m6A and inosine. Working with HEK293T cells, we modulated the activity of a central component of the EJC, the RNA helicase EIF4A3. Both genetic knockdown and chemical inhibition of EIF4A3 resulted in increased m6A levels and more diffuse localization at the 3’UTR. New m6A sites appear on short exons and near exon/intron junctions. These data corroborate the necessity of EIF4A3 for EJC assembly and confirm the model that the EJC prevents METTL3 from accessing and methylating exon junctions. Additionally, we find that blocking of the exon junction is reliant on EIF4A3’s helicase activity. Although the role of EJC in the cell cycle and cancer are still investigational, it is likely that m6A dysregulation is induced by aberrant EJC function, which presents a potential molecular mechanism for the dysregulation of multiple genetic pathways in cancer progression. Citation Format: Andrew Price, Erdem Sendinc, Byron Purse, Richard I Gregory, Gudrun Stengel. Binding of the exon junction complex shapes the landscape of m6A in RNA - a possible source of m6A dysregulation in cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: RNAs as Drivers, Targets, and Therapeutics in Cancer; 2024 Nov 14-17; Bellevue, Washington. Philadelphia (PA): AACR; Mol Cancer Ther 2024;23(11_Suppl):Abstract nr A011.

Transfer RNAs (tRNAs) are subject to various chemical modifications that influence their stability or function. Adenosine to Inosine (A-to-I) editing in the tRNA anticodon at position A34 is an important modification that expands anticodon-codon recognition at the wobble position and is required for normal mRNA translation. The relevance of tRNA editing in cancer remains unexplored. Here we show that the genes encoding the ADAT2/3 deaminase complex, responsible for A-to-I tRNA editing in humans, are commonly amplified and/or overexpressed in several tumor types including liposarcoma (LPS). We find that knockdown of the ADAT complex suppresses LPS cell growth and tumorigenicity. Mechanistically, we find that decreased tRNA editing upon ADAT2 depletion leads to defective translation of a subset of mRNAs. Thus, ADAT-mediated tRNA modification promotes oncogenesis by enhancing the translation of growth promoting mRNAs that are enriched in NNC codons that lack cognate tRNAs and therefore depend on A-I tRNA editing for decoding and mRNA translation. Our results uncover an oncogenic role of tRNA editing and identify ADAT2/3 as a potential new cancer therapeutic target. ### Competing Interest Statement R.I.G. is a co-founder, scientific advisory board member, and equity holder of Redona Therapeutics (formerly 28/7 Therapeutics), and advisor to Alida Biosciences. The Gregory lab receives or has received research funding from Sanofi, Astellas, and Ono. All other authors declare no competing interests.

Abstract Upstream open reading frames (uORFs) are typically defined as translation sites located within the 5′ untranslated region upstream of the main protein coding sequence (CDS) of messenger RNAs (mRNAs). Although uORFs are prevalent in eukaryotic mRNAs and modulate the translation of downstream CDSs, a comprehensive resource for uORFs is currently lacking. We developed Ribo-uORF (http://rnainformatics.org.cn/RiboUORF) to serve as a comprehensive functional resource for uORF analysis based on ribosome profiling (Ribo-seq) data. Ribo-uORF currently supports six species: human, mouse, rat, zebrafish, fruit fly, and worm. Ribo-uORF includes 501 554 actively translated uORFs and 107 914 upstream translation initiation sites (uTIS), which were identified from 1495 Ribo-seq and 77 quantitative translation initiation sequencing (QTI-seq) datasets, respectively. We also developed mRNAbrowse to visualize items such as uORFs, cis-regulatory elements, genetic variations, eQTLs, GWAS-based associations, RNA modifications, and RNA editing. Ribo-uORF provides a very intuitive web interface for conveniently browsing, searching, and visualizing uORF data. Finally, uORFscan and UTR5var were developed in Ribo-uORF to precisely identify uORFs and analyze the influence of genetic mutations on uORFs using user-uploaded datasets. Ribo-uORF should greatly facilitate studies of uORFs and their roles in mRNA translation and posttranscriptional control of gene expression.

The cells in your body contain genes made of DNA. Genes store the genetic information passed on to you by your parents. This information serves as the recipe to make proteins, and proteins build, maintain, and heal every tissue in your body. The cellular machinery that makes proteins reads this recipe with the help of small molecules called transfer RNAs (tRNAs), which supply the necessary building blocks in the correct order to construct specific proteins. To function properly, tRNAs must fold into the correct three-dimensional shape—a process that requires tRNA to be decorated with chemical modifications. Scientists have discovered that cancer hijacks and boosts this decorating process for its own benefit, favoring the production of proteins involved in cell division. This is an exciting finding because it could allow for the development of better ways to diagnose and treat cancers in the future.

The world has moved into a new stage of managing the SARS-CoV-2 pandemic with minimal restrictions and reduced testing in the population, leading to reduced genomic surveillance of virus variants in individuals. Wastewater-based epidemiology (WBE) can provide an alternative means of tracking virus variants in the population but decision-makers require confidence that it can be applied to a national scale and is comparable to individual testing data. We analysed 19,911 samples from 524 wastewater sites across England at least twice a week between November 2021 and February 2022, capturing sewage from >70% of the English population. We used amplicon-based sequencing and the phylogeny based de-mixing tool Freyja to estimate SARS-CoV-2 variant frequencies and compared these to the variant dynamics observed in individual testing data from clinical and community settings. We show that wastewater data can reconstruct the spread of the Omicron variant across England since November 2021 in close detail and aligns closely with epidemiological estimates from individual testing data. We also show the temporal and spatial spread of Omicron within London. Our wastewater data further reliably track the transition between Omicron subvariants BA1 and BA2 in February 2022 at regional and national levels. Our demonstration that WBE can track the fast-paced dynamics of SARS-CoV-2 variant frequencies at a national scale and closely match individual testing data in time shows that WBE can reliably fill the monitoring gap left by reduced individual testing in a more affordable way.

Amplification of chromosomal material derived from 12q is pathognomonic in a subset of soft tissue sarcomas (STS), including well-differentiated and dedifferentiated liposarcoma. However, it remains unclear which of the amplified genes are oncogenic drivers, obstacles to rational therapeutic development. We defined a minimal 12q amplicon in human liposarcoma, and tested the oncogenic activity of each recurrently amplified gene to accelerate the onset of AKT-induced STS in a genetically engineered zebrafish model of the disease. This revealed several genes whose overexpression accelerated the onset of AKT-induced STS, including METTL1, best-known for its ability to catalyze methylation of tRNAs. Surprisingly, catalytically defective mutants of METTL1 exhibited oncogenic activity that was at least as potent as the wild-type gene in zebrafish and human STS, indicating enzyme-independent oncogenic functions. We found that METTL1 promotes ribosome assembly and oncogenic translation independent of its enzymatic activity. In human liposarcoma cells and mouse embryonic fibroblasts, METTL1 overexpression was sufficient to stimulate polysome formation, and this effect was phenocopied by catalytically dead mutants of METTL1. METTL1 overexpression also robustly stimulated the rate of protein synthesis in cells (P < 0.0001), and in a cell-free biochemical assay for translation of a reporter mRNA (P < 0.001). The ability of METTL1 to stimulate ribosomal function triggered a therapeutically targetable dependency, because small molecule inhibitors of ribosome biogenesis had potent therapeutic activity against METTL1-amplified (P < 0.0001), but not METTL1 wild-type, sarcoma cells. Thus, METTL1 is a soft tissue sarcoma oncogene that stimulates oncogenic translation independent of its enzymatic activity, an oncogenic function that can be targeted therapeutically. Citation Format: Raja Hussain Ali, Brianna Silverman, Esteban A. Orellana, Alyssa Kennedy, Caitlin Bowers, Ashley Gutierrez, David Papke, Christopher D. Fletcher, Antonio P. Atayde, Akiko Shimamura, Richard I. Gregory, Alejandro Gutierrez. A noncatalytic role for mettl1 in oncogenic translation in soft tissue sarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3500.

Background Many countries have moved into a new stage of managing the SARS-CoV-2 pandemic with minimal restrictions and reduced testing in the population, leading to reduced genomic surveillance of virus variants in individuals. Wastewater-based epidemiology (WBE) can provide an alternative means of tracking virus variants in the population but is lacking verifications of its comparability to individual testing data. Methods We analysed more than 19,000 samples from 524 wastewater sites across England at least twice a week between November 2021 and February 2022, capturing sewage from >70% of the English population. We used amplicon-based sequencing and the phylogeny based de-mixing tool Freyja to estimate SARS-CoV-2 variant frequencies and compared these to the variant dynamics observed in individual testing data from clinical and community settings. Findings We show that wastewater data can reconstruct the spread of the Omicron variant across England since November 2021 in close detail and aligns closely with epidemiological estimates from individual testing data. We also show the temporal and spatial spread of Omicron within London. Our wastewater data further reliably track the transition between Omicron subvariants BA1 and BA2 in February 2022 at regional and national levels. Interpretation Our demonstration that WBE can track the fast-paced dynamics of SARS-CoV-2 variant frequencies at a national scale and closely match individual testing data in time shows that WBE can reliably fill the monitoring gap left by reduced individual testing in a more affordable way. Funding Department of Health and Social Care, UK, Natural Environmental Research Council, UK, COG-UK Evidence before this study Genomic monitoring of wastewater for SARS-CoV-2 variants has been introduced in several countries and shown to effectively detect the spread of known variants in multiple studies. However, verification of its alignment with individual testing data at a national scale has so far been reported only for Austria, where sampling covered around 5.4million people. Further and larger scale verifications of the reliability of wastewater-based epidemiology (WBE) are needed to increase confidence in its use for public health monitoring. Added value of this study We provide evidence that WBE was able to closely track the spread of the emerging SARS-CoV-2 variant Omicron, as well as its sub lineage dynamics, at a regional and national scale across England. Our sampling covered >70% of the English population, equivalent to 39.4 million people. We thereby demonstrate the scalability of our approach to national levels. We also show how WBE is able to track dynamics in different regions of the UK and at a finer scale within London. Its close alignment, in estimated epidemiological timings, with results from intensive individual testing in the same timeframe provides evidence that wastewater-based monitoring can be a reliable alternative when large scale data from individual testing is not available. Implications of all the available evidence Altogether, evidence is accumulating that WBE is a reliable approach for monitoring SARS-CoV-2 variant dynamics and informing public health measures across spatial scales. ### Competing Interest Statement The authors have declared no competing interest. ### Clinical Protocols ### Funding Statement Funding was provided by DHSC UK (2020\_097) and NERC (NE/V003860/1). This report is independent research funded by the Department of Health and Social Care. COG-UK is supported by funding from the Medical Research Council (MRC) part of UK Research & Innovation (UKRI), the National Institute of Health Research (NIHR) [grant code: MC\_PC_19027], and Genome Research Limited, operating as the Wellcome Sanger Institute. The authors acknowledge use of data generated through the COVID-19 Genomics Programme funded by the Department of Health and Social Care. The views expressed are those of the authors and not necessarily those of the Department of Health and Social Care or UKHSA. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Use of surplus nucleic acid derived from routine diagnostics and associated patient data was approved through the COG-UK consortium by the Public Health England Research Ethics and Governance Group (R&D NR0195). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes Wastewater sequencing data are publicly available on the European Nucleotide Archive under Study ID PRJEB55313. The clinical case data used in this study are visualised at . A filtered, privacy conserving version of the lineage-LTLA-week dataset is publicly available online () and gives access to almost all used data, despite a small number of cells having been suppressed to conserve patient privacy.

Chemical modifications of RNA have key roles in many biological processes 1 – 3 . N 7 -methylguanosine (m 7 G) is required for integrity and stability of a large subset of tRNAs 4 – 7 . The methyltransferase 1–WD repeat-containing protein 4 (METTL1–WDR4) complex is the methyltransferase that modifies G46 in the variable loop of certain tRNAs, and its dysregulation drives tumorigenesis in numerous cancer types 8 – 14 . Mutations in WDR4 cause human developmental phenotypes including microcephaly 15 – 17 . How METTL1–WDR4 modifies tRNA substrates and is regulated remains elusive 18 . Here we show, through structural, biochemical and cellular studies of human METTL1–WDR4, that WDR4 serves as a scaffold for METTL1 and the tRNA T-arm. Upon tRNA binding, the αC region of METTL1 transforms into a helix, which together with the α6 helix secures both ends of the tRNA variable loop. Unexpectedly, we find that the predicted disordered N-terminal region of METTL1 is part of the catalytic pocket and essential for methyltransferase activity. Furthermore, we reveal that S27 phosphorylation in the METTL1 N-terminal region inhibits methyltransferase activity by locally disrupting the catalytic centre. Our results provide a molecular understanding of tRNA substrate recognition and phosphorylation-mediated regulation of METTL1–WDR4, and reveal the presumed disordered N-terminal region of METTL1 as a nexus of methyltransferase activity.

N6-methyladenosine (m6A), the most abundant modification of mRNA, is essential for normal development and dysregulation promotes cancer. m6A is highly enriched in the 3' untranslated region (UTR) of a large subset of mRNAs to influence mRNA stability and/or translation. However, the mechanism responsible for the observed m6A distribution remains enigmatic. Here we find the exon junction complex shapes the m6A landscape by blocking METTL3-mediated m6A modification close to exon junctions within coding sequence (CDS). Depletion of EIF4A3, a core component of the EJC, causes increased METTL3 binding and m6A modification of short internal exons, and sites close to exon-exon junctions within mRNA. Reporter gene experiments further support the role of splicing and EIF4A3 deposition in controlling m6A modification via the local steric blockade of METTL3. Our results explain how characteristic patterns of m6A mRNA modification are established and uncover a role of the EJC in shaping the m6A epitranscriptome.

Abstract Understanding compound metabolism in early drug discovery aids medicinal chemistry in designing molecules with improved safety and ADME properties. While advancements in metabolite prediction brings increased confidence, structural decisions require experimental data. In vitro metabolism studies using liquid chromatography and high-resolution mass spectrometry (LC–MS) are generally resource intensive and performed on very few compounds, limiting the chemical space that can be examined. Here, we describe a novel metabolism strategy increasing compound throughput using residual in vitro clearance samples conducted at drug concentrations of 0.5 µM. Analysis by robust ultra high-performance liquid chromatography separation and accurate-mass MS detection ensures major metabolites are identified from a single injection. In silico prediction (parent cLogD) tailors chromatographic conditions, with data-dependent tandem mass spectroscopy targeting predicted metabolites. Software-assisted data mining, structure elucidation and automatic reporting are used. Confidence in the globally aligned workflow is demonstrated with 16 marketed drugs. The approach is now implemented routinely across our laboratories. To date, the success rate for identification of at least one major metabolite is 85%. The utility of these data has been demonstrated across multiple projects, allowing earlier medicinal chemistry decisions to increase efficiency and impact of the design–make–test cycle thus improving the translatability of early in vitro metabolism data.

tRNAs are key adaptor molecules that decipher the genetic code during translation of mRNAs in protein synthesis. In contrast to the traditional view of tRNAs as ubiquitously expressed housekeeping molecules, awareness is now growing that tRNA-encoding genes display tissue-specific and cell type-specific patterns of expression, and that tRNA gene expression and function are both dynamically regulated by post-transcriptional RNA modifications. Moreover, dysregulation of tRNAs, mediated by alterations in either their abundance or function, can have deleterious consequences that contribute to several distinct human diseases, including neurological disorders and cancer. Accumulating evidence shows that reprogramming of mRNA translation through altered tRNA activity can drive pathological processes in a codon-dependent manner. This Review considers the emerging evidence in support of the precise control of functional tRNA levels as an important regulatory mechanism that coordinates mRNA translation and protein expression in physiological cell homeostasis, and highlights key examples of human diseases that are linked directly to tRNA dysregulation.