From form to function: m6A methylation links mRNA structure to metabolism

Reversible N6-methyladenosine (m6A) RNA modification is a posttranscriptional epigenetic modification of the RNA that regulates many key aspects of RNA metabolism and function. In this review, we highlight major recent advances in the field, with special emphasis on the potential link between m6A modifications and RNA structure. We will also discuss the role of RNA methylation of neuronal transcripts, and the emerging evidence of a potential role in RNA transport and local translation in dendrites and axons of transcripts involved in synaptic functions and axon growth

A molecular‐level perspective on the frequency, distribution, and consequences of messenger RNA modifications

Cells use chemical modifications to alter the sterics, charge, and conformations of large biomolecules, modulating their biogenesis, function, and stability. Until recently post‐transcriptional RNA modifications were thought to be largely limited to nonprotein coding RNA species. However, this dogma has rapidly transformed with the discovery of a host of modifications in protein coding messenger RNAs (mRNAs). Recent advancements in genome‐wide sequencing technologies have enabled the identification of mRNA modifications as a potential new frontier in gene regulation—leading to the development of the epitranscriptome field. As a result, there has been a flurry of multiple groundbreaking discoveries, including new modifications, nucleoside modifying enzymes (“writers” and “erasers”), and RNA binding proteins that recognize chemical modifications (“readers”). These discoveries opened the door to understanding how post‐transcriptional mRNA modifications can modulate the mRNA lifecycle, and established a link between the epitranscriptome and human health and disease. Despite a rapidly growing recognition of their importance, fundamental questions regarding the identity, prevalence, and functional consequences of mRNA modifications remain to be answered. Here, we highlight quantitative studies that characterize mRNA modification abundance, frequency, and interactions with cellular machinery. As the field progresses, we see a need for the further integration of quantitative and reductionist approaches to complement transcriptome wide studies in order to establish a molecular‐level framework for understanding the consequences of mRNA chemical modifications on biological processes.This article is categorized under:RNA Structure and Dynamics > RNA Structure, Dynamics and ChemistryRNA Processing > RNA Editing and ModificationThe integration of biochemical, structural, and transcriptome wide approaches is shaping a quantitative framework for understanding the biological consequences of mRNA modifications.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155973/1/wrna1586.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155973/2/wrna1586_am.pd

Elucidating the Functions of Non-Coding RNAs from the Perspective of RNA Modifications

It is now commonly accepted that most of the mammalian genome is transcribed as RNA, yet less than 2% of such RNA encode for proteins. A majority of transcribed RNA exists as non-protein-coding RNAs (ncRNAs) with various functions. Because of the lack of sequence homologies among most ncRNAs species, it is difficult to infer the potential functions of ncRNAs by examining sequence patterns, such as catalytic domains, as in the case of proteins. Added to the existing complexity of predicting the functions of the ever-growing number of ncRNAs, increasing evidence suggests that various enzymes modify ncRNAs (e.g., ADARs, METTL3, and METTL14), which has opened up a new field of study called epitranscriptomics. Here, we examine the current status of ncRNA research from the perspective of epitranscriptomics

RNA Methylation and Ythdf Readers in Posttranscriptional Regulation and Development

Development in animals requires precise and coordinated changes in gene expression. This genetic remodeling is achieved through extensive regulatory networks of proteins and RNAs that function together to specify new cell fates and patterns. One developmental event heavily reliant on these regulatory networks is the maternal-to-zygotic transition (MZT), a universal step in metazoan embryogenesis in which a fertilized oocyte is reprogrammed into a pluripotent embryo. The earliest stages of the MZT are governed by maternally inherited gene products, which are required for cellular functions in the initially transcriptionally silent embryo. To shift developmental control to the zygote, these maternal mRNAs are massively degraded through multiple posttranscriptional mechanisms. The RNA modification, N6-methyladenosine (m6A) has been proposed as a master regulator of mRNA decay during developmental transitions, but the direct effects of this pathway on maternal transcript clearance remain unclear. To determine whether m6A facilitates gene expression changes during the MZT, I employed zebrafish embryos as a model system to dissect the contributions of RNA methylation and its reader proteins to maternal transcript fate. Through transcriptome analysis and reporter assays, I found that m6A controls maternal mRNA degradation by promoting deadenylation. To understand how RNA methylation fits into the framework of known decay pathways, I compared transcripts co-targeted by m6A and miR-430, a microRNA that controls mRNA clearance in zebrafish. This revealed that these mechanisms function independently but additively to promote mRNA degradation, reflecting that methylation modulates transcript abundance in concert with known regulators. To disentangle the roles of the Ythdf proteins that mediate the effects of m6A on mRNA, I generated zebrafish genetic mutants of Ythdf1, Ythdf2, and Ythdf3. Through transcriptomic and phenotypic analysis of these mutants, I determined that global maternal mRNA clearance, zygotic genome activation, and development proceed normally in the absence of any one reader. This revealed that individual Ythdf protein have limited effects on the removal of methylated maternal mRNAs during the MZT. To test if this restricted impact of single Ythdf loss stems from functional redundancy between the readers, I produced double mutants of Ythdf2 and Ythdf3. Double Ythdf deletion prevents female gonad development, indicating that these factors exert overlapping activities during oogenesis. Finally, to fully establish functionally redundancy, I created triple Ythdf mutants, which were larval lethal. I observed this same phenotype in zebrafish lacking the methylases that add m6A to mRNA, indicating that RNA methylation is essential for developmental viability. Together, this work provides insight into the contributions of the m6A modification and its Ythdf effectors to maternal mRNA clearance, and establishes how these key regulators coordinate the gene expression changes that underlie embryonic reprogramming

Insights into the Molecular Mechanisms of the N6-Methyladenosine (m6A) Methylation Machinery in the Regulation of the Infection Cycle of RNA Plant Viruses

[ES] La N6-metiladenosina (m6A) es una modificación generalizada en los ARN celulares de diferentes organismos que puede afectar muchos procesos y vías celulares. En las plantas, ocurre mediante un complejo de metilación que contiene varias proteínas: MTA, MTB, FIP37, VIR y HAKAI. Esta modificación es eliminada por desmetilasas de la familia AlkB, mientras que los miembros de la familia ETC son las proteínas mejor descritas que reconocen y procesan los ARN m6A-modificados. Estudios de epitransciptómica viral han revelado un papel igualmente importante de m6A durante la infección por virus; sin embargo, no existe una función pro- o antiviral de m6A generalizada. El laboratorio donde se ha llevado a cabo este trabajo ha sido pionero en el estudio del efecto de m6A en la interacción planta-virus, utilizando como virus modelo el AMV. El AMV pertenece a la familia Bromoviridae, y su genoma está formado por tres (+)ssARN. Los ARN1/2 codifican las subunidades de replicasa (P1 y P2), mientras que el ARN3 codifica la proteína de movimiento (MP) y sirve como molde para la síntesis del sgARN4, que codifica la proteína de cubierta (CP). Al comienzo de esta tesis, nuestro laboratorio ya había informado sobre: la presencia de supuestos motivos m6A en el 3'UTR/RNA3, una región crítica para la replicación de AMV, la primera m6A-desmetilasa de Arabidopsis (ALKBH9B), la relevancia funcional de ALKBH9B para mantener niveles adecuados de m6A/A para la correcta replicación de AMV, la capacidad de la CP de AMV para interactuar con ALKBH9B, posiblemente para usurpar la actividad de ALKBH9B, y la capacidad de las proteínas de Arabidopsis ECT2/3/5 para interactuar con el ARNv de AMV que contienen m6A. Dada la relevancia funcional de m6A en la biología de AMV, en esta tesis se decidió profundizar en el conocimiento de las implicaciones del mecanismo de regulación de m6A en el ciclo infeccioso viral de AMV. Para ello, se decidió: profundizar en la comprensión funcional de la m6A-desmetilasa ALKBH9B, evaluar la función in vivo de los supuestos dos sitios m6A presentes en el 3'UTR/ARN3, y explorar una posible implicación de algunas m6A metiltransferasas en la infección causada por AMV. El mapeo de los subdominios funcionales de atALKBH9B determinó la presencia de IDRs en la región N-terminal, dentro del dominio interno similar a AlkB y en la región C-terminal. Alrededor del 78% del RBD identificado en ALKBH9B está contenido en el IDR C-terminal. Debido a que las IDRs se localizan con frecuencia en proteínas que se someten a LLPS, un proceso que probablemente contribuye a la formación y estabilidad de los gránulos de ARN, es posible que las IDR y la RBD de ALKBH9B puedan actuar de manera cooperativa para promover la formación de gránulos de ARN. El análisis de los putativos motivos DRACH localizados en el bucle de hpB y en el tallo inferior de hpE del 3'UTR/ARN3 de AMV demostró que son sitios críticos involucrados en la replicación in vivo de AMV. La identidad de los residuos 2012A, 2013A y 2014A en el bucle hpB parece ser un requisito estructural clave para la replicación y/o acumulación de AMV. Con respecto a hpE, nuestros resultados determinaron que el supuesto residuo de m6A (1902A), así como el apareamiento de bases del tallo inferior de hpE, también son requisitos esenciales para la síntesis in vivo de ARNs de cadena positiva en AMV. Hasta donde sabemos, esta es la primera evidencia en AMV que muestra que el bucle de hpB y el tallo inferior de hpE están involucrados en la replicación/acumulación viral y la síntesis de ARNs de cadena positiva, respectivamente. Finalmente, en cuanto al estudio de la influencia de las m6A-metiltransferasas en el ciclo de infección viral de AMV, no se determinó un efecto proviral y/o antiviral en el complejo m6A-ARNm metiltransferasa conformado por atMTA:atMTB, ni en el putativo complejo m6A- ARNr metiltransferasa conformado por atMETTL5-like:atTRMT112-like sobre la biología de AMV.[CA] La N6-metiladenosina (m6A) és una modificació generalitzada en els ARN cellulars de diferents organismes que pot afectar molts processos i vies cellulars. En les plantes, ocorre mitjançant un complex de metilació que conté diverses proteïnes: MTA, MTB, FIP37, VIR i HAKAI. Aquesta modificació és eliminada per desmetilasas de la família AlkB, mentre que els membres de la família ETC són les proteïnes més ben descrites que reconeixen i processen els ARN m6A-modificats. Estudis de epitransciptómica viral han revelat un paper igualment important de m6A durant la infecció per virus; no obstant això, no existeix una funció pro- o antiviral de m6A generalitzada. El laboratori on s'ha dut a terme aquest treball ha sigut pioner en l'estudi de l'efecte de m6A en la interacció planta-virus, utilitzant com a virus model el AMV. El AMV pertany a la família Bromoviridae, i el seu genoma està format per tres (+) ssARN. Els ARN1/2 codifiquen les subunitats de replicasa (P1 i P2), mentre que l'ARN3 codifica la MP i serveix com a motle per a la síntesi del sgARN4, que codifica la CP. Al començament d'aquesta tesi, el nostre laboratori ja havia informat sobre: la presència de suposats motius m6A en el 3'UTR/RNA3, una regió crítica per a la replicació de AMV, la primera m6A-desmetilasa de Arabidopsis (ALKBH9B), la rellevància funcional d'ALKBH9B per a mantindre nivells adequats de m6A/A per a la correcta replicació de AMV, la capacitat de la CP de AMV per a interactuar amb ALKBH9B, possiblement per a usurpar l'activitat d'ALKBH9B, i la capacitat de les proteïnes de Arabidopsis ECT2/3/5 per a interactuar amb el ARNv de AMV que contenen m6A. Donada la rellevància funcional de m6A en la biologia de AMV, en aquesta tesi es va decidir aprofundir en el coneixement de les implicacions del mecanisme de regulació de m6A en el cicle infecciós viral de AMV. Per a això, es va decidir: aprofundir en la comprensió funcional de la m6A-desmetilasa ALKBH9B, avaluar la funció in vivo dels supòsits dos llocs m6A presents en el 3'UTR/ARN3, i explorar una possible implicació d'algunes m6A metiltransferasas en la infecció causada per AMV. El mapatge dels subdominis funcionals de atALKBH9B va determinar la presència de IDRs a la regió N-terminal, dins del domini intern similar a AlkB i a la regió C-terminal. Al voltant del 78% del RBD identificat en ALKBH9B està contingut en el IDR C-terminal. Pel fet que les IDRs es localitzen amb freqüència en proteïnes que se sotmeten a LLPS, un procés que probablement contribueix a la formació i estabilitat dels grànuls d'ARN, és possible que les IDR i la RBD d'ALKBH9B puguen actuar de manera cooperativa per a promoure la formació de grànuls d'ARN. L'anàlisi dels putatius motius DRACH localitzats en el bucle de hpB i en la tija inferior de hpE del 3'UTR/ARN3 de AMV va demostrar que són llocs crítics involucrats en la replicació in vivo de AMV. La identitat dels residus 2012A, 2013A i 2014A en el bucle hpB sembla ser un requisit estructural clau per a la replicació i/o acumulació de AMV. Respecte a hpE, els nostres resultats van determinar que el suposat residu de m6A (1902A), així com l'aparellament de bases de la tija inferior de hpE, també són requisits essencials per a la síntesi in vivo de ARNs de cadena positiva en AMV. Fins on sabem, aquesta és la primera evidència en AMV que mostra que el bucle de hpB i la tija inferior de hpE estan involucrats en la replicació/acumulació viral i la síntesi de ARNs de cadena positiva, respectivament. Finalment, quant a l'estudi de la influència de les m6A-metiltransferasas en el cicle d'infecció viral de AMV, no es va determinar un efecte proviral i/o antiviral en el complex m6A-ARNm metiltransferasa conformat per atMTA:atMTB, ni en el putatiu complex m6A-ARNr metiltransferasa conformat per atMETTL5-like:atTRMT112-like sobre la biologia de AMV.[EN] N6-methyladenosine (m6A) is a widespread modification on cellular RNAs of different organisms that can impact many cellular processes and pathways. In plants, m6A-methylation is mainly installed by a methylation complex containing several proteins: MTA, MTB, FIP37, VIR, and HAKAI. This modification is removed by demethylases of the AlkB family, and members of the ECT family are the best described proteins that recognize and process m6A-modified RNAs. Studies of viral epitransciptomics have revealed an equally important role of m6A during virus infection; however, there is no global pro- or antiviral role of m6A that can be generalized. The laboratory where this work was carried out has been a pioneer in the study of the effect of m6A on plant-viruses, using AMV as a model-virus. AMV belongs to the Bromoviridae family and, as the rest of the members of this family, its genome consists of three (+)ssRNAs. RNA1 and RNA2 encode the replicase subunits (P1 and P2), whereas RNA 3 encodes the MP and serves as a template for the synthesis of sgRNA 4, which encodes CP. At the beginning of this thesis, our laboratory had already reported on: the presence of putative m6A-motifs in the 3'UTR RNA3, a critical region for AMV replication, the first Arabidopsis m6A-demethylase (ALKBH9B), the functional relevance of ALKBH9B to maintain adequate m6A/A levels for correct AMV replication, the ability of AMV-CP to interact with ALKBH9B, possibly to usurp ALKBH9B activity, and the capability of Arabidopsis ECT2/3/5 to interact with m6A-containing AMV vRNAs. Given the functional relevance of m6A on the biology of AMV, in this thesis it was decided to deepen the knowledge of the implications of the m6A regulation mechanism on the viral infectious cycle of AMV. For this, it was decided: deepen the functional understanding of the m6A-demethylase ALKBH9B, evaluate the in vivo function of the putative two m6A-sites present in the 3'UTR-RNA 3, and explore a possible involvement of some m6A-methyltransferases in infection caused by AMV. We mapped functional subdomains in the atALKBH9B m6A-demethylase required for its binding to the vRNA and to the CP of AMV. Remarkably, it was observed the presence of IDRs in the N-terminal region, within the internal domain like AlkB and in the C-terminal region. About 78% of the RBD identified in ALKBH9B is contained in the C-terminal IDR. In this context, it has been proposed that the capability to specifically target different RNAs in RBPs containing IDRs is due to conformational flexibility as well as the establishment of extended conserved electrostatic interfaces with RNAs. Additionally, due that IDRs are frequently localized in proteins that undergo LLPS, a process that likely contributes to the formation and stability of RNA granules, it's possible that the IDRs and the RBD of ALKBH9B could act cooperatively to promote RNA granule formation. The analysis of the putative DRACH-motifs located in the hpB loop and the lower-stem of hpE in the 3'UTR RNA 3 present hot sites involved in AMV replication in vivo. The identity of residues 2012A, 2013A and 2014A in the hpB loop appears to be a key structural requirement for AMV replication and/or accumulation. Regarding hpE, our results determined that the putative m6A-residue 1902A, as well as the base pairing of the lower-stem of hpE, are also essential requirements for the in vivo plus-strand synthesis in AMV. To our knowledge, this is the first evidence in AMV to show that the hpB loop and the lower-stem of hpE are involved in viral replication/accumulation and plus-strand synthesis, respectively. Finally, regarding the study of the influence of m6A-methyltransferases on the viral infection cycle of AMV, a non-proviral and/or antiviral effect was determined in the m6A-mRNA methyltransferase complex made up of atMTA:atMTB, nor of the putative m6A-rRNA methyltransferase complex made up of atMETTL5-like:atTRMT112-like on the biology of AMV.Alvarado Marchena, LF. (2022). Insights into the Molecular Mechanisms of the N6-Methyladenosine (m6A) Methylation Machinery in the Regulation of the Infection Cycle of RNA Plant Viruses [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/185122TESI

Post-Transcriptional Regulation Of The Eulkaryotic Transcriptome By The Covalent Rna Modicication N6-Methyladenosine

Post-Transcriptional regulation of the eukaryotic transcriptome by the covalent RNA modification N6-methyladenosine Stephen James Anderson Brian Gregory Once a messenger RNA molecule is transcribed, a myriad of RNA fate decisions must be made. How these fate decisions are made is often unclear, and elucidating factors determining these fate outcomes is an essential task in order to fully understand gene regulation. One poorly- understood but undoubtedly important factor in post-transcriptional gene regulation is the covalent modification of ribonucleotides. Much like DNA can have chemical groups added to a nucleotide within its primary sequence, RNA can be modified in a similar manner. These covalent modifications of RNA are a ubiquitous feature found within the RNA of all organisms. Dozens of these modifications have been described to date, yet the function or importance of most of these modifications remains unclear. One crucial RNA modification is N6-methyladenosine (m6A), as it is the most abundant known non-cap modification within the eukaryotic transcriptome. In this work, we characterize the role of m6A in the Arabidopsis transcriptome using various sequencing methods that demonstrate that m6A is an abundant mark that is largely maintained across differing Arabidopsis tissues and developmental stages. This prevalent mark promotes transcript stability in mNRAs involved in many important and diverse biological processes, such as salt stress. The absence of this mark results in endonucleolytic cleavage and degradation of the transcript in a highly specific and local manner. We further demonstrate that this modification modulates secondary structure throughout the transcriptome, and that m6A is associated with changes in RNA-binding protein association. Lastly, we turn our view to how an association between m6A and the m6A-specific binding protein YTHDC1 influences the development and transcriptome-wide splicing and polyadenylation pattern in the mouse germline. We demonstrate that in the absence of YTHDC1, widespread developmental, splicing, and polyadenylation defects occur, resulting in non-functional gametes. In total, this work greatly expands our knowledge and understanding of the biological importance and mechanisms of m6A-mediated post-transcriptional regulation

Comprehensive Analysis of mRNA Methylation Reveals Enrichment in 3′ UTRs and near Stop Codons

SummaryMethylation of the N6 position of adenosine (m6A) is a posttranscriptional modification of RNA with poorly understood prevalence and physiological relevance. The recent discovery that FTO, an obesity risk gene, encodes an m6A demethylase implicates m6A as an important regulator of physiological processes. Here, we present a method for transcriptome-wide m6A localization, which combines m6A-specific methylated RNA immunoprecipitation with next-generation sequencing (MeRIP-Seq). We use this method to identify mRNAs of 7,676 mammalian genes that contain m6A, indicating that m6A is a common base modification of mRNA. The m6A modification exhibits tissue-specific regulation and is markedly increased throughout brain development. We find that m6A sites are enriched near stop codons and in 3′ UTRs, and we uncover an association between m6A residues and microRNA-binding sites within 3′ UTRs. These findings provide a resource for identifying transcripts that are substrates for adenosine methylation and reveal insights into the epigenetic regulation of the mammalian transcriptome

M6A RNA methylation in diabetes induced endothelial damage and ischaemic disease

Diabetes mellitus exposes endothelial cells (ECs) to a chronic hyperglycaemic milieu, leading to dysfunction of the vascular endothelium. The resulting microvasculature rarefaction leads to tissue hypoperfusion and propagates the occurrence of ischaemic events, such as critical limb ischaemia and ischaemic heart disease. Moreover, hyperglycaemia impairs the angiogenic potential of ECs thereby compromising post-ischaemic reparative neovascularisation. N6-methyladenosine (m6A) is emerging as a new layer for fine-tuning gene expression. The functional importance of m6A has been revealed in a plethora of fundamental bioprocesses, while its dysregulation has been linked to several diseases including diabetes. However, our understanding of the precise roles of m6A in the cardiovascular system is still in its infancy and its significance in diabetes associated complications of the vasculature remains completely unexplored. This study elucidates a novel role for METTL3, the primary m6A methylase, in the regulation of angiogenesis. Loss and gain of function studies reveal METTL3 to be crucial in the modulation of EC processes that are conducive to angiogenesis in vitro and in vivo. Mechanistically, METTL3 modulates angiogenesis by mediating the endothelial bioprocessing of the angiogenic miRNAs let-7e and the miR-17-92 cluster. Expressional analysis revealed a dysregulation of m6A and METTL3 in human ECs exposed to diabetic and ischaemic mimicking conditions, ECs derived from a murine model of diabetic LI and in left ventricular tissue and ECs isolated from diabetic mouse hearts. The therapeutic potential of endothelial METTL3 was demonstrated using murine models of diabetic limb ischaemia and myocardial infarction. Here, the adenovirus mediated overexpression of METTL3 in ischaemic limb muscles improved post-ischaemic muscular neovascularisation. Additionally, infarcted hearts treated with Ad.METTL3 showed an increase in arteriole and capillary densities while exhibiting improved contractile function. Thus, the findings in this thesis suggest that the modulation of METTL3 could represent novel therapeutic target for ischaemic complications in diabetic patients.Open Acces