Cracking the epitranscriptome

The RMaP challenge of predicting RNA modifications by nanopore sequencing

The field of epitranscriptomics is undergoing a technology-driven revolution. During past decades, RNA modifications like N6-methyladenosine (m6A), pseudouridine (ψ), and 5-methylcytosine (m5C) became acknowledged for playing critical roles in cellular processes. Direct RNA sequencing by Oxford Nanopore Technologies (ONT) enabled the detection of modifications in native RNA, by detecting noncanonical RNA nucleosides properties in raw data. Consequently, the field's cutting edge has a heavy component in computer science, opening new avenues of cooperation across the community, as exchanging data is as impactful as exchanging samples. Therefore, we seize the occasion to bring scientists together within the RNA Modification and Processing (RMaP) challenge to advance solutions for RNA modification detection and discuss ideas, problems and approaches. We show several computational methods to detect the most researched mRNA modifications (m6A, ψ, and m5C). Results demonstrate that a low prediction error and a high prediction accuracy can be achieved on these modifications across different approaches and algorithms. The RMaP challenge marks a substantial step towards improving algorithms' comparability, reliability, and consistency in RNA modification prediction. It points out the deficits in this young field that need to be addressed in further challenges.

Exploring the methyl-verse: Dynamic interplay of epigenome and m6A epitranscriptome

The orchestration of dynamic epigenetic and epitranscriptomic modifications is pivotal for the fine-tuning of gene expression. However, these modifications are traditionally examined independently. Recent compelling studies have disclosed an interesting communication and interplay between m6A RNA methylation (m6A epitranscriptome) and epigenetic modifications, enabling the formation of feedback circuits and cooperative networks. Intriguingly, the interaction between m6A and DNA methylation machinery, coupled with the crosstalk between m6A RNA and histone modifications shape the transcriptional profile and translational efficiency. Moreover, m6A modifications interact also with non-coding RNAs, modulating their stability, abundance, and regulatory functions. In the light of these findings, m6A imprinting acts as a versatile checkpoint, linking epigenetic and epitranscriptomic layers toward a multilayer and time-dependent control of gene expression and cellular homeostasis. The scope of the present review is to decipher the m6A-coordinated circuits with DNA imprinting, chromatin architecture, and non-coding RNAs networks in normal physiology and carcinogenesis. Ultimately, we summarize the development of innovative CRISPR-dCas engineering platforms fused with m6A catalytic components (m6A writers or erasers) to achieve transcript-specific editing of m6A epitranscriptomes that can create new insights in modern RNA therapeutics.

Defining epitranscriptomic hallmarks at the host-parasite interface and their roles in virulence and disease progression in Theileria annulata-infected leukocytes

Theileria parasites are known to induce the transformation of host bovine leukocytes, involved in rapid proliferation, evasion from apoptotic mechanisms, and increased dissemination. In this study, we reveal the involvement of m6A RNA modification in T. annulata infection-induced transformation of bovine leukocytes. We conducted m6A sequencing and bioinformatics analysis to map the mRNA methylation patterns of T. annulata-infected host leukocytes. We observe specific mRNA modifications for T. annulata-infected leukocytes and a strong correlation between the proliferation rate of the infected Leukocytes with m6A modifications We observe that the increased amounts of m6A seem to impact some cell cycle dynamics, potentially via modifications of E2F4 mRNA. Moreover, we further identify HIF-1α as a possible driver of these m6A RNA modifications that have clear relevance to cellular proliferation dynamics. Overall, our results provide insights into the role of m6A mRNA methylation in the molecular crosstalk between Theileria and their host leukocytes, emphasizing the critical role of mRNA methylation in host-parasite interaction.

Current progress in strategies to profile transcriptomic m6A modifications

Various methods have been developed so far for detecting N 6-methyladenosine (m6A). The total m6A level or the m6A status at individual positions on mRNA can be detected and quantified through some sequencing-independent biochemical methods, such as LC/MS, SCARLET, SELECT, and m6A-ELISA. However, the m6A-detection techniques relying on high-throughput sequencing have more effectively advanced the understanding about biological significance of m6A-containing mRNA and m6A pathway at a transcriptomic level over the past decade. Various SGS-based (Second Generation Sequencing-based) methods with different detection principles have been widely employed for this purpose. These principles include m6A-enrichment using antibodies, discrimination of m6A from unmodified A-base by nucleases, a fusion protein strategy relying on RNA-editing enzymes, and marking m6A with chemical/biochemical reactions. Recently, TGS-based (Third Generation Sequencing-based) methods have brought a new trend by direct m6A-detection. This review first gives a brief introduction of current knowledge about m6A biogenesis and function, and then comprehensively describes m6A-profiling strategies including their principles, procedures, and features. This will guide users to pick appropriate methods according to research goals, give insights for developing novel techniques in varying areas, and continue to expand our boundary of knowledge on m6A.

RNA Pol II-dependent transcription efficiency fine-tunes A-to-I editing levels

A-to-I RNA editing is a widespread epitranscriptomic phenomenon leading to the conversion of adenosines to inosines, which are primarily interpreted as guanosines by cellular machines. Consequently, A-to-I editing can alter splicing or lead to recoding of transcripts. As misregulation of editing can cause a variety of human diseases, A-to-I editing requires tight regulation of the extent of deamination, particularly in protein-coding regions. The bulk of A-to-I editing occurs cotranscriptionally. Thus, we studied A-to-I editing regulation in the context of transcription and pre-mRNA processing. We show that stimulation of transcription impacts editing levels. Activation of the transcription factor MYC leads to an up-regulation of A-to-I editing, particularly in transcripts that are suppressed upon MYC activation. Moreover, low pre-mRNA synthesis rates and low pre-mRNA expression levels support high levels of editing. We also show that editing levels greatly differ between nascent pre-mRNA and mRNA in a cellular system, as well as in mouse tissues. Editing levels can increase or decrease from pre-mRNA to mRNA and can vary across editing targets and across tissues, showing that pre-mRNA processing is an important layer of editing regulation. Several lines of evidence suggest that the differences emerge during pre-mRNA splicing. Moreover, actinomycin D treatment of primary neuronal cells and editing level analysis suggests that regulation of editing levels also depends on transcription.

The potential role of RNA modification in skin diseases, as well as the recent advances in its detection methods and therapeutic agents

RNA modification is considered as an epigenetic modification that plays an indispensable role in biological processes such as gene expression and genome editing without altering nucleotide sequence, but the molecular mechanism of RNA modification has not been discussed systematically in the development of skin diseases. This article mainly presents the whole picture of theoretical achievements on the potential role of RNA modification in dermatology. Furthermore, this article summarizes the latest advances in clinical practice related with RNA modification, including its detection methods and drug development. Based on this comprehensive review, we aim to illustrate the current blind spots and future directions of RNA modification, which may provide new insights for researchers in this field.

Simultaneous RNA and DNA Adductomics Using Single Data-Independent Acquisition Mass Spectrometry Analysis

Adductomics studies are used for the detection and characterization of various chemical modifications (adducts) of nucleic acids and proteins. The advancements in liquid chromatography coupled with high-resolution tandem mass spectrometry (HRMS/MS) have resulted in efficient methods for qualitative and quantitative adductomics. We developed an HRMS-based method for the simultaneous analysis of RNA and DNA adducts in a single run and demonstrated its application using Baltic amphipods, useful sentinels of environmental disturbances, as test organisms. The novelty of this method is screening for RNA and DNA adducts by a single injection on an Orbitrap HRMS instrument using full scan and data-independent acquisition. The MS raw files were processed with an open-source program, nLossFinder, to identify and distinguish RNA and DNA adducts based on the characteristic neutral loss of ribonucleosides and 2'-deoxyribonucleosides, respectively. In the amphipods, in addition to the nearly 150 putative DNA adducts characterized earlier, we detected 60 putative RNA adducts. For the structural identification of the detected RNA adducts, the MODOMICS database was used. The identified RNA adducts included simple mono- and dimethylation and other larger functional groups on different ribonucleosides and deaminated product inosine. However, 54 of these RNA adducts are not yet structurally identified, and further work on their characterization may uncover new layers of information related to the transcriptome and help understand their biological significance. Considering the susceptibility of nucleic acids to environmental factors, including pollutants, the developed multi-adductomics methodology with further advancement has the potential to provide biomarkers for diagnostics of pollution effects in biota.

The importance of pseudouridylation: human disorders related to the fifth nucleoside

Pseudouridylation is one of the most abundant RNA modifications in eukaryotes, making pseudouridine known as the "fifth nucleoside." This highly conserved alteration affects all non-coding and coding RNA types. Its role and importance have been increasingly widely researched, especially considering that its absence or damage leads to serious hereditary diseases. Here, we summarize the human genetic disorders described to date that are related to the participants of the pseudouridylation process.

Loss of the m6A methyltransferase METTL3 in monocyte-derived macrophages ameliorates Alzheimer's disease pathology in mice

Alzheimer's disease (AD) is a heterogeneous disease with complex clinicopathological characteristics. To date, the role of m6A RNA methylation in monocyte-derived macrophages involved in the progression of AD is unknown. In our study, we found that methyltransferase-like 3 (METTL3) deficiency in monocyte-derived macrophages improved cognitive function in an amyloid beta (Aβ)-induced AD mouse model. The mechanistic study showed that that METTL3 ablation attenuated the m6A modification in DNA methyltransferase 3A (Dnmt3a) mRNAs and consequently impaired YTH N6-methyladenosine RNA binding protein 1 (YTHDF1)-mediated translation of DNMT3A. We identified that DNMT3A bound to the promoter region of alpha-tubulin acetyltransferase 1 (Atat1) and maintained its expression. METTL3 depletion resulted in the down-regulation of ATAT1, reduced acetylation of α-tubulin and subsequently enhanced migration of monocyte-derived macrophages and Aβ clearance, which led to the alleviated symptoms of AD. Collectively, our findings demonstrate that m6A methylation could be a promising target for the treatment of AD in the future.

lncRNA ZNRD1-AS1 promotes malignant lung cell proliferation, migration, and angiogenesis via the miR-942/TNS1 axis and is positively regulated by the m6A reader YTHDC2

RATIONALE

Lung cancer is the most prevalent form of cancer and has a high mortality rate, making it a global public health concern. The N⁶-methyladenosine (m⁶A) modification is a highly dynamic and reversible process that is involved in a variety of essential biological processes. Using in vitro, in vivo, and multi-omics bioinformatics, the present study aims to determine the function and regulatory mechanisms of the long non-coding (lnc)RNA zinc ribbon domain-containing 1-antisense 1 (ZNRD1-AS1).

METHODS

The RNAs that were bound to the m⁶A 'reader' were identified using YTH domain-containing 2 (YTHDC2) RNA immunoprecipitation (RIP)-sequencing. Utilizing methylated RIP PCR/quantitative PCR, pull-down, and RNA stability assays, m⁶A modification and ZNRD1-AS1 regulation were analyzed. Using bioinformatics, the expression levels and clinical significance of ZNRD1-AS1 in lung cancer were evaluated. Using fluorescent in situ hybridization and quantitative PCR assays, the subcellular location of ZNRD1-AS1 was determined. Using cell migration, proliferation, and angiogenesis assays, the biological function of ZNRD1-AS1 in lung cancer was determined. In addition, the tumor suppressor effect of ZNRD1-AS1 in vivo was validated using a xenograft animal model. Through bioinformatics analysis and in vitro assays, the downstream microRNAs (miRs) and competing endogenous RNAs were also predicted and validated.

RESULTS

This study provided evidence that m⁶A modification mediates YTHDC2-mediated downregulation of ZNRD1-AS1 in lung cancer and cigarette smoke-exposed cells. Low levels of ZNRD1-AS1 expression were linked to adverse clinicopathological characteristics, immune infiltration, and prognosis. ZNRD1-AS1 overexpression was shown to suppress lung cancer cell proliferation, migration, and angiogenesis in vitro and in vivo, and to reduce tumor growth in nude mice. ZNRD1-AS1 expression was shown to be controlled by treatment of cells with either the methylation inhibitor 3-Deazaadenosine or the demethylation inhibitor Meclofenamic. Furthermore, the miR-942/tensin 1 (TNS1) axis was demonstrated to be the downstream regulatory signaling pathway of ZNRD1-AS1.

CONCLUSIONS

ZNRD1-AS1 serves an important function and has clinical relevance in lung cancer. In addition, the findings suggested that m⁶A modification could mediate the regulation of the ZNRD1-AS1/miR-942/TNS1 axis via the m⁶A reader YTHDC2.

Reduction of Methyltransferase-like 3-Mediated RNA N6-Methyladenosine Exacerbates the Development of Psoriasis Vulgaris in Imiquimod-Induced Psoriasis-like Mouse Model

N6-methyladenosine (m⁶A) methylation is the most pervasive and intensively studied mRNA modification, which regulates gene expression in different physiological processes, such as cell proliferation, differentiation, and inflammation. Studies of aberrant m⁶A in human diseases such as cancer, obesity, infertility, neuronal disorders, immune diseases, and inflammation are rapidly evolving. However, the regulatory mechanism and physiological significance of m⁶A methylation in psoriasis vulgaris are still poorly understood. In this study, we found that m⁶A methylation and Methyltransferase-like 3 (METTL3) were both downregulated in psoriatic skin lesions and were negatively correlated with Psoriasis Area and Severity Index (PASI) scores. Inhibiting m⁶A methylation by knocking down Mettl3 promoted the development of psoriasis and increased its severity in imiquimod-induced psoriasis-like model mice. Our results indicate a critical role of METTL3- mediated m⁶A methylation in the pathogenesis of psoriasis vulgaris.

The role of RNA modification in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a highly mortal type of primary liver cancer. Abnormal epigenetic modifications are present in HCC, and RNA modification is dynamic and reversible and is a key post-transcriptional regulator. With the in-depth study of post-transcriptional modifications, RNA modifications are aberrantly expressed in human cancers. Moreover, the regulators of RNA modifications can be used as potential targets for cancer therapy. In RNA modifications, N6-methyladenosine (m6A), N7-methylguanosine (m7G), and 5-methylcytosine (m5C) and their regulators have important regulatory roles in HCC progression and represent potential novel biomarkers for the confirmation of diagnosis and treatment of HCC. This review focuses on RNA modifications in HCC and the roles and mechanisms of m6A, m7G, m5C, N1-methyladenosine (m1A), N3-methylcytosine (m3C), and pseudouridine (ψ) on its development and maintenance. The potential therapeutic strategies of RNA modifications are elaborated for HCC.

At the crossroads of RNA biology, genome integrity and cancer

This article is the synthesis of the scientific presentations that took place during two international courses at Institute Curie, one on post-transcriptional gene regulation and the other on genome instability and human disease, that were joined together in their 2021 edition. This joined course brought together the knowledge on RNA metabolism and the maintenance of genome stability.

Chemical modifications to mRNA nucleobases impact translation elongation and termination

Messenger RNAs (mRNAs) serve as blueprints for protein synthesis by the molecular machine the ribosome. The ribosome relies on hydrogen bonding interactions between adaptor aminoacyl-transfer RNA molecules and mRNAs to ensure the rapid and faithful translation of the genetic code into protein. There is a growing body of evidence suggesting that chemical modifications to mRNA nucleosides impact the speed and accuracy of protein synthesis by the ribosome. Modulations in translation rates have downstream effects beyond protein production, influencing protein folding and mRNA stability. Given the prevalence of such modifications in mRNA coding regions, it is imperative to understand the consequences of individual modifications on translation. In this review we present the current state of our knowledge regarding how individual mRNA modifications influence ribosome function. Our comprehensive comparison of the impacts of 16 different mRNA modifications on translation reveals that most modifications can alter the elongation step in the protein synthesis pathway. Additionally, we discuss the context dependence of these effects, highlighting the necessity of further study to uncover the rules that govern how any given chemical modification in an mRNA codon is read by the ribosome.

A systematic dissection of determinants and consequences of snoRNA-guided pseudouridylation of human mRNA

RNA can be extensively modified post-transcriptionally with >170 covalent modifications, expanding its functional and structural repertoire. Pseudouridine (Ψ), the most abundant modified nucleoside in rRNA and tRNA, has recently been found within mRNA molecules. It remains unclear whether pseudouridylation of mRNA can be snoRNA-guided, bearing important implications for understanding the physiological target spectrum of snoRNAs and for their potential therapeutic exploitation in genetic diseases. Here, using a massively parallel reporter based strategy we simultaneously interrogate Ψ levels across hundreds of synthetic constructs with predesigned complementarity against endogenous snoRNAs. Our results demonstrate that snoRNA-mediated pseudouridylation can occur on mRNA targets. However, this is typically achieved at relatively low efficiencies, and is constrained by mRNA localization, snoRNA expression levels and the length of the snoRNA:mRNA complementarity stretches. We exploited these insights for the design of snoRNAs targeting pseudouridylation at premature termination codons, which was previously shown to suppress translational termination. However, in this and follow-up experiments in human cells we observe no evidence for significant levels of readthrough of pseudouridylated stop codons. Our study enhances our understanding of the scope, 'design rules', constraints and consequences of snoRNA-mediated pseudouridylation.

m6A RNA modification in transcription regulation

RNA modifications are prevalent among all the classes of RNA, regulate diverse biological processes, and have emerged as a key regulatory mechanism in post-transcriptional control of gene expression. They are subjected to precise spatial and temporal control and shown to be critical for the maintenance of normal development and physiology. For example, m⁶A modification of mRNA affects stability, recruitment of RNA binding protein (RBP), translation, and splicing. The deposition of m6A on the RNA happens co-transcriptionally, allowing the tight coupling between the transcription and RNA modification machinery. The m⁶A modification is affected by transcriptional dynamics, but recent insights also suggest that m⁶A machinery impacts transcription and chromatin signature.

The XRN1-regulated RNA helicase activity of YTHDC2 ensures mouse fertility independently of m6A recognition

The functional consequence of N⁶-methyladenosine (m⁶A) RNA modification is mediated by "reader" proteins of the YTH family. YTH domain-containing 2 (YTHDC2) is essential for mammalian fertility, but its molecular function is poorly understood. Here, we identify U-rich motifs as binding sites of YTHDC2 on 3' UTRs of mouse testicular RNA targets. Although its YTH domain is an m⁶A-binder in vitro, the YTH point mutant mice are fertile. Significantly, the loss of its 3'→5' RNA helicase activity causes mouse infertility, with the catalytic-dead mutation being dominant negative. Biochemical studies reveal that the weak helicase activity of YTHDC2 is enhanced by its interaction with the 5'→3' exoribonuclease XRN1. Single-cell transcriptomics indicate that Ythdc2 mutant mitotic germ cells transition into meiosis but accumulate a transcriptome with mixed mitotic/meiotic identity that fail to progress further into meiosis. Finally, our demonstration that ythdc2 mutant zebrafish are infertile highlights its conserved role in animal germ cell development.

The RNA methyltransferase METTL8 installs m3C32 in mitochondrial tRNAsThr/Ser(UCN) to optimise tRNA structure and mitochondrial translation

Modified nucleotides in tRNAs are important determinants of folding, structure and function. Here we identify METTL8 as a mitochondrial matrix protein and active RNA methyltransferase responsible for installing m3C32 in the human mitochondrial (mt-)tRNAThr and mt-tRNASer(UCN). METTL8 crosslinks to the anticodon stem loop (ASL) of many mt-tRNAs in cells, raising the question of how methylation target specificity is achieved. Dissection of mt-tRNA recognition elements revealed U34G35 and t6A37/(ms2)i6A37, present concomitantly only in the ASLs of the two substrate mt-tRNAs, as key determinants for METTL8-mediated methylation of C32. Several lines of evidence demonstrate the influence of U34, G35, and the m3C32 and t6A37/(ms2)i6A37 modifications in mt-tRNAThr/Ser(UCN) on the structure of these mt-tRNAs. Although mt-tRNAThr/Ser(UCN) lacking METTL8-mediated m3C32 are efficiently aminoacylated and associate with mitochondrial ribosomes, mitochondrial translation is mildly impaired by lack of METTL8. Together these results define the cellular targets of METTL8 and shed new light on the role of m3C32 within mt-tRNAs.

Epitranscriptomics of cardiovascular diseases (Review)

RNA modifications have recently become the focus of attention due to their extensive regulatory effects in a vast array of cellular networks and signaling pathways. Just as epigenetics is responsible for the imprinting of environmental conditions on a genetic level, epitranscriptomics follows the same principle at the RNA level, but in a more dynamic and sensitive manner. Nevertheless, its impact in the field of cardiovascular disease (CVD) remains largely unexplored. CVD and its associated pathologies remain the leading cause of death in Western populations due to the limited regenerative capacity of the heart. As such, maintenance of cardiac homeostasis is paramount for its physiological function and its capacity to respond to environmental stimuli. In this context, epitranscriptomic modifications offer a novel and promising therapeutic avenue, based on the fine‑tuning of regulatory cascades, necessary for cardiac function. This review aimed to provide an overview of the most recent findings of key epitranscriptomic modifications in both coding and non‑coding RNAs. Additionally, the methods used for their detection and important associations with genetic variations in the context of CVD were summarized. Current knowledge on cardiac epitranscriptomics, albeit limited still, indicates that the impact of epitranscriptomic editing in the heart, in both physiological and pathological conditions, holds untapped potential for the development of novel targeted therapeutic approaches in a dynamic manner.

METTL3 induces PLX4032 resistance in melanoma by promoting m6A-dependent EGFR translation

Acquired resistance often limits therapeutic efficacy of the BFAF (V600E) kinase inhibitor PLX4032 in patients with advanced melanoma. Epitranscriptomic modification of mRNAs by N⁶-methyladenosine (m⁶A) modification contributes to melanoma pathogenesis; however, its role in acquired PLX4032 resistance remains unexplored. Here, we showed that m⁶A methyltransferase METTL3 expression is upregulated in A375R cells, a PLX4032-resistant subline of A375 melanoma cells, compared with the parental cells. Moreover, METTL3 increased the m⁶A modification of epidermal growth factor receptor (EGFR) mRNA in A375R cells, which promoted its translation efficiency. In turn, increased EGFR expression facilitated rebound activation of the RAF/MEK/ERK pathway in A375R cells, inducing PLX4032 resistance. In contrast, knockout of METTL3 in A375R cells reduced EGFR expression and restored PLX4032 sensitivity. PLX4032 treatment following METTL3 knockout induced apoptosis and reduced colony formation in A375R cells and reduced A375R cell-derived tumor growth in BALB/c nude mice. These findings indicate that METTL3 promotes rebound activation of the RAF/MEK/ERK pathway through EGFR upregulation and highlight a critical role for METTL3-induced m⁶A modification in acquired PLX4032 resistance in melanoma, implicating METTL3 as a potential candidate for targeted chemotherapy.

The human pseudouridine synthase PUS7 recognizes RNA with an extended multi-domain binding surface

The human pseudouridine synthase PUS7 is a versatile RNA modification enzyme targeting many RNAs thereby playing a critical role in development and brain function. Whereas all target RNAs of PUS7 share a consensus sequence, additional recognition elements are likely required, and the structural basis for RNA binding by PUS7 is unknown. Here, we characterize the structure–function relationship of human PUS7 reporting its X-ray crystal structure at 2.26 Å resolution. Compared to its bacterial homolog, human PUS7 possesses two additional subdomains, and structural modeling studies suggest that these subdomains contribute to tRNA recognition through increased interactions along the tRNA substrate. Consistent with our modeling, we find that all structural elements of tRNA are required for productive interaction with PUS7 as the consensus sequence of target RNA alone is not sufficient for pseudouridylation by human PUS7. Moreover, PUS7 binds several, non-modifiable RNAs with medium affinity which likely enables PUS7 to screen for productive RNA substrates. Following tRNA modification, the product tRNA has a significantly lower affinity for PUS7 facilitating its dissociation. Taken together our studies suggest a combination of structure-specific and sequence-specific RNA recognition by PUS7 and provide mechanistic insight into its function.

Identification of the function and mechanism of m6A reader IGF2BP2 in Alzheimer's disease

Alzheimer’s disease, the most common form of dementia in the elderly, is a kind of neurodegenerative disease. However, its pathogenesis and diagnosis remain unclear. M6A is related to nervous system development and neurodegenerative diseases. Here in this study, using multiple RNA-seq datasets of Alzheimer’s brain tissues, along with bioinformatic analysis, we innovatively found that m6A reader protein IGF2BP2 was abnormally highly expressed in Alzheimer’s patients. After compared between Alzheimer’s and normal brain samples, and between IGF2BP2- high and IGF2BP2- low subgroups of Alzheimer’s patients, we took the shared differentially expressed genes as the relevant gene sets of IGF2PB2 affecting Alzheimer’s disease occurrence for subsequent analysis. Then, weight gene correlation analysis was conducted and 17 functional modules were identified. The module that most positively correlated with Alzheimer’s disease and IGF2PB2-high subgroups were mainly participated in ECM receptor interaction, focal adhesion, cytokine-cytokine receptor interaction, and TGF-beta signaling pathway. Afterwards, a hub gene-based model including 20 genes was constructed by LASSO regression and validated by ROC curve for Alzheimer diagnosis. Finally, we preliminarily elucidated that IGF2BP2 could bind with mRNAs in a m6A-dependent manner. This study first elucidates the pathogenic role of IGF2BP2 in Alzheimer’s disease. IGF2BP2 and its relevant m6A modifications are potential to be new diagnostic and therapeutic targets for Alzheimer’s patients.

Mechanism of noncoding RNA-associated N6-methyladenosine recognition by an RNA processing complex during IgH DNA recombination

Immunoglobulin heavy chain (IgH) locus-associated G-rich long noncoding RNA (SμGLT) is important for physiological and pathological B cell DNA recombination. We demonstrate that the METTL3 enzyme-catalyzed N6-methyladenosine (m6A) RNA modification drives recognition and 3' end processing of SμGLT by the RNA exosome, promoting class switch recombination (CSR) and suppressing chromosomal translocations. The recognition is driven by interaction of the MPP6 adaptor protein with nuclear m6A reader YTHDC1. MPP6 and YTHDC1 promote CSR by recruiting AID and the RNA exosome to actively transcribe SμGLT. Direct suppression of m6A modification of SμGLT or of m6A reader YTHDC1 reduces CSR. Moreover, METTL3, an essential gene for B cell development in the bone marrow and germinal center, suppresses IgH-associated aberrant DNA breaks and prevents genomic instability. Taken together, we propose coordinated and central roles for MPP6, m6A modification, and m6A reader proteins in controlling long noncoding RNA processing, DNA recombination, and development in B cells.

Targeting Epigenetic Mechanisms to Treat Alcohol Use Disorders (AUD)

BACKGROUND

The impact of abusive alcohol consumption on human health is remarkable. According to the World Health Organization (WHO), approximately 3.3 million people die annually because of harmful alcohol consumption (the figure represents around 5.9% of global deaths). Alcohol Use Disorder (AUD) is a chronic disease where individuals exhibit compulsive alcohol drinking and present negative emotional states when they do not drink. In the most severe manifestations of AUD, the individuals lose control over intake despite a decided will to stop drinking. Given the multiple faces and the specific forms of this disease, the term AUD often appears in the plural (AUDs). Since only a few approved pharmacological treatments are available to treat AUD and they do not apply to all individuals or AUD forms, the search for compounds that may help to eliminate the burden of the disease and complement other therapeutical approaches is necessary.

METHODS

This work reviews recent research focused on the involvement of epigenetic mechanisms in the pathophysiology of AUD. Excessive drinking leads to chronic and compulsive consumption that eventually damages the organism. The central nervous system is a key target and is the focus of this study. The search for the genetic and epigenetic mechanisms behind the intricated dysregulation induced by ethanol will aid researchers in establishing new therapy approaches.

CONCLUSION

Recent findings in the field of epigenetics are essential and offer new windows for observation and research. The study of small molecules that inhibit key epienzymes involved in nucleosome architecture dynamics is necessary in order to prove their action and specificity in the laboratory and to test their effectivity and safety in clinical trials with selected patients bearing defined alterations caused by ethanol.

General Principles for the Detection of Modified Nucleotides in RNA by Specific Reagents

Epitranscriptomics heavily rely on chemical reagents for the detection, quantification, and localization of modified nucleotides in transcriptomes. Recent years have seen a surge in mapping methods that use innovative and rediscovered organic chemistry in high throughput approaches. While this has brought about a leap of progress in this young field, it has also become clear that the different chemistries feature variegated specificity and selectivity. The associated error rates, e.g., in terms of false positives and false negatives, are in large part inherent to the chemistry employed. This means that even assuming technically perfect execution, the interpretation of mapping results issuing from the application of such chemistries are limited by intrinsic features of chemical reactivity. An important but often ignored fact is that the huge stochiometric excess of unmodified over-modified nucleotides is not inert to any of the reagents employed. Consequently, any reaction aimed at chemical discrimination of modified versus unmodified nucleotides has optimal conditions for selectivity that are ultimately anchored in relative reaction rates, whose ratio imposes intrinsic limits to selectivity. Here chemical reactivities of canonical and modified ribonucleosides are revisited as a basis for an understanding of the limits of selectivity achievable with chemical methods.

Synthesis of N4 -Methylcytidine (m4 C) and N4 ,N4 -Dimethylcytidine (m4 2 C) Modified RNA

This article summarizes the protocols for phosphoramidite chemistry and solid phase synthesis of RNA oligonucleotides containing N⁴ -methylcytidine (m⁴ C) and N⁴ ,N⁴ -dimethylcytidine (m⁴ ₂ C) residues for base-pairing, structural, and enzymatic activity studies. The two key m⁴ C and m⁴ ₂ C phosphoramidite building blocks can be synthesized starting from the partially protected cytidine nucleosides, followed by solid-phase synthesis and HPLC purification of the modified target RNA oligonucleotides. These modified RNA strands are then prepared for base pairing stability, specificity, and structural studies using UV-melting temperature (T_m ) measurements and X-ray crystallography. Functional studies are performed by reverse transcription assays in primer extension reactions employing different enzymes. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Chemical synthesis of m⁴ C phosphoramidite Basic Protocol 2: Synthesis of m⁴ ₂ C phosphoramidite Basic Protocol 3: Synthesis and purification of m⁴ C and m⁴ ₂ C containing RNA oligonucleotides.

Multiplexed profiling facilitates robust m6A quantification at site, gene and sample resolution

N⁶-methyladenosine (m6A) is the most prevalent modification of messenger RNA in mammals. To interrogate its functions and dynamics, there is a critical need to quantify m6A at three levels: site, gene and sample. Current approaches address these needs in a limited manner. Here we develop m6A-seq2, relying on multiplexed m6A-immunoprecipitation of barcoded and pooled samples. m6A-seq2 allows a big increase in throughput while reducing technical variability, requirements of input material and cost. m6A-seq2 is furthermore uniquely capable of providing sample-level relative quantitations of m6A, serving as an orthogonal alternative to mass spectrometry-based approaches. Finally, we develop a computational approach for gene-level quantitation of m6A. We demonstrate that using this metric, roughly 30% of the variability in RNA half life in mouse embryonic stem cells can be explained, establishing m6A as a main driver of RNA stability. m6A-seq2 thus provides an experimental and analytic framework for dissecting m6A-mediated regulation at three different levels.

Micro-flow hydrophilic interaction liquid chromatography coupled with triple quadrupole mass spectrometry detects modified nucleosides in the transfer RNA pool of cyanobacteria

Post-transcriptional modification of nucleosides is observed in almost all elements of RNA. Modified nucleosides finely tune the structure of RNA molecules and affect vital functions, such as the modified wobble position 34 of transfer RNAs expanding the reading preference of anticodons to codons. Recent investigations have revealed that the modification species and their frequencies in an RNA element are not stable but vary with specific cellular factors including metabolites and particular proteins (writers, readers, and erasers). To understand the link between dynamic RNA modifications and biological processes, sensitive and reliable methods for determining modified nucleosides are required. In this study, micro-flow (8 μL/min) hydrophilic interaction liquid chromatography was coupled with triple quadrupole mass spectrometry for the simultaneous determination of adenosine, uridine, cytidine, guanosine, and 20 modified nucleosides. The method was calibrated using 0.1-1000 nM standards (∼0.03-300 ng/mL) and successfully applied to the determination of transfer RNA modifications in the model cyanobacterium Synechococcus elongatus PCC 7942. A protocol for the isolation of a clean transfer RNA pool was optimized, requiring only 25 ng for the identification and quantification of transfer RNA modifications. This micro-flow liquid chromatography-tandem mass spectrometry method constitutes the first step toward monitoring dynamic ribonucleoside modifications in a limited RNA sample.

From Antisense RNA to RNA Modification: Therapeutic Potential of RNA-Based Technologies

Therapeutic oligonucleotides interact with a target RNA via Watson-Crick complementarity, affecting RNA-processing reactions such as mRNA degradation, pre-mRNA splicing, or mRNA translation. Since they were proposed decades ago, several have been approved for clinical use to correct genetic mutations. Three types of mechanisms of action (MoA) have emerged: RNase H-dependent degradation of mRNA directed by short chimeric antisense oligonucleotides (gapmers), correction of splicing defects via splice-modulation oligonucleotides, and interference of gene expression via short interfering RNAs (siRNAs). These antisense-based mechanisms can tackle several genetic disorders in a gene-specific manner, primarily by gene downregulation (gapmers and siRNAs) or splicing defects correction (exon-skipping oligos). Still, the challenge remains for the repair at the single-nucleotide level. The emerging field of epitranscriptomics and RNA modifications shows the enormous possibilities for recoding the transcriptome and repairing genetic mutations with high specificity while harnessing endogenously expressed RNA processing machinery. Some of these techniques have been proposed as alternatives to CRISPR-based technologies, where the exogenous gene-editing machinery needs to be delivered and expressed in the human cells to generate permanent (DNA) changes with unknown consequences. Here, we review the current FDA-approved antisense MoA (emphasizing some enabling technologies that contributed to their success) and three novel modalities based on post-transcriptional RNA modifications with therapeutic potential, including ADAR (Adenosine deaminases acting on RNA)-mediated RNA editing, targeted pseudouridylation, and 2′-O-methylation.

RNA-based therapies: A cog in the wheel of lung cancer defense

Lung cancer (LC) is a heterogeneous disease consisting mainly of two subtypes, non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC), and remains the leading cause of death worldwide. Despite recent advances in therapies, the overall 5-year survival rate of LC remains less than 20%. The efficacy of current therapeutic approaches is compromised by inherent or acquired drug-resistance and severe off-target effects. Therefore, the identification and development of innovative and effective therapeutic approaches are critically desired for LC. The development of RNA-mediated gene inhibition technologies was a turning point in the field of RNA biology. The critical regulatory role of different RNAs in multiple cancer pathways makes them a rich source of targets and innovative tools for developing anticancer therapies. The identification of antisense sequences, short interfering RNAs (siRNAs), microRNAs (miRNAs or miRs), anti-miRs, and mRNA-based platforms holds great promise in preclinical and early clinical evaluation against LC. In the last decade, RNA-based therapies have substantially expanded and tested in clinical trials for multiple malignancies, including LC. This article describes the current understanding of various aspects of RNA-based therapeutics, including modern platforms, modifications, and combinations with chemo-/immunotherapies that have translational potential for LC therapies.

The Regulation of RNA Modification Systems: The Next Frontier in Epitranscriptomics?

RNA modifications, long considered to be molecular curiosities embellishing just abundant and non-coding RNAs, have now moved into the focus of both academic and applied research. Dedicated research efforts (epitranscriptomics) aim at deciphering the underlying principles by determining RNA modification landscapes and investigating the molecular mechanisms that establish, interpret and modulate the information potential of RNA beyond the combination of four canonical nucleotides. This has resulted in mapping various epitranscriptomes at high resolution and in cataloguing the effects caused by aberrant RNA modification circuitry. While the scope of the obtained insights has been complex and exciting, most of current epitranscriptomics appears to be stuck in the process of producing data, with very few efforts to disentangle cause from consequence when studying a specific RNA modification system. This article discusses various knowledge gaps in this field with the aim to raise one specific question: how are the enzymes regulated that dynamically install and modify RNA modifications? Furthermore, various technologies will be highlighted whose development and use might allow identifying specific and context-dependent regulators of epitranscriptomic mechanisms. Given the complexity of individual epitranscriptomes, determining their regulatory principles will become crucially important, especially when aiming at modifying specific aspects of an epitranscriptome both for experimental and, potentially, therapeutic purposes.

AlkAniline-Seq: A Highly Sensitive and Specific Method for Simultaneous Mapping of 7-Methyl-guanosine (m7G) and 3-Methyl-cytosine (m3C) in RNAs by High-Throughput Sequencing

Epitranscriptomics is an emerging field where the development of high-throughput analytical technologies is essential to profile the dynamics of RNA modifications under different conditions. Despite important advances during the last 10 years, the number of RNA modifications detectable by next-generation sequencing is restricted to a very limited subset. Here, we describe a highly efficient and fast method called AlkAniline-Seq to map simultaneously two different RNA modifications: 7-methyl-guanosine (m⁷G) and 3-methyl-cytosine (m³C) in RNA. Our protocol is based on three subsequent chemical/enzymatic steps allowing the enrichment of RNA fragments ending at position n + 1 to the modified nucleotide, without any prior RNA selection. Therefore, AlkAniline-Seq demonstrates an outstanding sensitivity and specificity for these two RNA modifications. We have validated AlkAniline-Seq using bacterial, yeast, and human total RNA, and here we present, as an example, a synthetic view of the complete profiling of these RNA modifications in S. cerevisiae tRNAs.

Comparison of RNA m6A and DNA methylation profiles between mouse female germline stem cells and STO cells

N⁶-methyladenosine (m⁶A) methylation modification is the most prevalent and abundant internal modification of eukaryotic mRNAs. Increasing evidence has shown that mRNA m⁶A plays important roles in the development of stem cells. However, to the best of our knowledge, no reports about the roles of mRNA m⁶A in mouse female germline stem cells (mFGSCs) have been published. In this study, we compared the genome-wide profiles of mRNA m⁶A methylation and DNA methylation between FGSCs and sandosinbred mice (SIM) embryo-derived thioguanine and ouabain-resistant (STO) cells. qRT-PCR revealed that the expression levels of mRNA m⁶A-related genes (Mettl3, Alkbh5, Ythdf1, Ythdf2, Ythdc1, and Ythdc2) in FGSCs were significantly higher than those in STO cells. m⁶A RNA immunoprecipitation sequencing (MeRIP-seq) data further showed that the unique m⁶A-methylated mRNAs in FGSCs and STO cells were related to cell population proliferation and somatic development, respectively. Additionally, knockdown of Ythdf1 inhibited FGSC self-renewal. Comparison of methylated DNA immunoprecipitation sequencing (MeDIP-seq) results between FGSCs and STO cells identified that DNA methylation contributed to FGSC proliferation by suppressing the somatic program. These results suggested that m⁶A regulated FGSC self-renewal possibly through m⁶A binding protein YTHDF1, and DNA methylation repressed somatic programs in FGSCs to maintain FGSC characteristics.

The epitranscriptome beyond m6A

Following its transcription, RNA can be modified by >170 chemically distinct types of modifications - the epitranscriptome. In recent years, there have been substantial efforts to uncover and characterize the modifications present on mRNA, motivated by the potential of such modifications to regulate mRNA fate and by discoveries and advances in our understanding of N ⁶-methyladenosine (m⁶A). Here, we review our knowledge regarding the detection, distribution, abundance, biogenesis, functions and possible mechanisms of action of six of these modifications - pseudouridine (Ψ), 5-methylcytidine (m⁵C), N ¹-methyladenosine (m¹A), N ⁴-acetylcytidine (ac⁴C), ribose methylations (N_m) and N ⁷-methylguanosine (m⁷G). We discuss the technical and analytical aspects that have led to inconsistent conclusions and controversies regarding the abundance and distribution of some of these modifications. We further highlight shared commonalities and important ways in which these modifications differ with respect to m⁶A, based on which we speculate on their origin and their ability to acquire functions over evolutionary timescales.

Altered Expression of the m6A Methyltransferase METTL3 in Alzheimer's Disease

Cognitive impairment in Alzheimer’s disease (AD) is associated with dysregulation of the RNA and protein expression profiles in the brain. Recent studies have highlighted the importance of RNA post-transcriptional regulation (epitranscriptomics) in higher order brain functions. Specifically, N6-methyladenosine (m6A), which controls RNA stability, splicing, translation and trafficking, plays an important role in learning and memory. This raises the question of whether m6A signaling is perturbed in AD. To address this, we investigated the expression profile of known m6A-regulatory genes using a public RNA-seq dataset and identified a subset of genes which were significantly dysregulated in the human AD brain. Among these, genes encoding the m6A methyltransferase, METTL3, and a member of the m6A methyltransferase complex (MACOM), RBM15B, were downregulated and upregulated in the hippocampus, respectively. These findings were validated at the protein level using an independent cohort of postmortem human brain samples. Unexpectedly, we observed an accumulation of methyltransferase-like 3 (METTL3), but not RBM15B, in the insoluble fractions, which positively correlated with the levels of insoluble Tau protein in the postmortem human AD samples. Aberrant expression and distribution of METTL3 in the hippocampus of the AD brain may therefore represent an epitranscriptomic mechanism underlying the altered gene expression patterns associated with disease pathogenesis.

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 Chemistry RNA Processing > RNA Editing and Modification.

Quantifying RNA Editing in Deep Transcriptome Datasets

Massive transcriptome sequencing through the RNAseq technology has enabled quantitative transcriptome-wide investigation of co-/post-transcriptional mechanisms such as alternative splicing and RNA editing. The latter is abundant in human transcriptomes in which million adenosines are deaminated into inosines by the ADAR enzymes. RNA editing modulates the innate immune response and its deregulation has been associated with different human diseases including autoimmune and inflammatory pathologies, neurodegenerative and psychiatric disorders, and tumors. Accurate profiling of RNA editing using deep transcriptome data is still a challenge, and the results depend strongly on processing and alignment steps taken. Accurate calling of the inosinome repertoire, however, is required to reliably quantify RNA editing and, in turn, investigate its biological and functional role across multiple samples. Using real RNAseq data, we demonstrate the impact of different bioinformatics steps on RNA editing detection and describe the main metrics to quantify its level of activity.

HIV protease cleaves the antiviral m6A reader protein YTHDF3 in the viral particle

N⁶-methyladenosine (m⁶A) is the most abundant HIV RNA modification but the interplay between the m⁶A reader protein YTHDF3 and HIV replication is not well understood. We found that knockout of YTHDF3 in human CD4+ T-cells increases infection supporting the role of YTHDF3 as a restriction factor. Overexpression of the YTHDF3 protein in the producer cells reduces the infectivity of the newly produced viruses. YTHDF3 proteins are incorporated into HIV particles in a nucleocapsid-dependent manner permitting the m⁶A reader protein to limit infection in the new target cell at the step of reverse transcription. Importantly, HIV protease cleaves the virion-incorporated full-length YTHDF3 protein, a process which is blocked by HIV protease inhibitors used to treat HIV infected patients. Mass-spectrometry confirmed the proteolytic processing of YTHDF3 in the virion. Thus, HIV protease cleaves the virion-encapsidated host m⁶A effector protein in addition to the viral polyproteins to ensure optimal infectivity of the mature virion.

The human transcriptome contains a large number of post-transcriptional modifications such as N6-methyladenosine (m⁶A). Several recent studies indicate that the HIV RNA contains numerous m⁶A modifications but their impact on viral replication (e.g., antiviral or proviral) remains controversial. Here we report that the m⁶A reader protein YTHDF3 is incorporated into HIV particles in a nucleocapsid-dependent manner and reduces viral infectivity in the next cycle of infection. Importantly, we show that HIV protease cleaves the virion-incorporated full-length YTHDF3 protein, a process which can be blocked by FDA-approved HIV protease inhibitors. Mass-spectrometry analyses confirmed the proteolytic processing of YTHDF3 in the virion and identified at least two distinct cleavage sites. These results point to virus incorporated YTHDF3 acting as a regulator of HIV biology if left unchecked by the HIV protease.

Dysregulations of Functional RNA Modifications in Cancer, Cancer Stemness and Cancer Therapeutics

More than a hundred chemical modifications in coding and non-coding RNAs have been identified so far. Many of the RNA modifications are dynamic and reversible, playing critical roles in gene regulation at the posttranscriptional level. The abundance and functions of RNA modifications are controlled mainly by the modification regulatory proteins: writers, erasers and readers. Modified RNA bases and their regulators form intricate networks which are associated with a vast array of diverse biological functions. RNA modifications are not only essential for maintaining the stability and structural integrity of the RNA molecules themselves, they are also associated with the functional outcomes and phenotypic attributes of cells. In addition to their normal biological roles, many of the RNA modifications also play important roles in various diseases particularly in cancer as evidenced that the modified RNA transcripts and their regulatory proteins are aberrantly expressed in many cancer types. This review will first summarize the most commonly reported RNA modifications and their regulations, followed by discussing recent studies on the roles of RNA modifications in cancer, cancer stemness as wells as functional RNA modification machinery as potential cancer therapeutic targets. It is concluded that, while advanced technologies have uncovered the contributions of many of RNA modifications in cancer, the underlying mechanisms are still poorly understood. Moreover, whether and how environmental pollutants, important cancer etiological factors, trigger abnormal RNA modifications and their roles in environmental carcinogenesis remain largely unknown. Further studies are needed to elucidate the mechanism of how RNA modifications promote cell malignant transformation and generation of cancer stem cells, which will lead to the development of new strategies for cancer prevention and treatment.

RNA N6-Methyladenosine Modifications and the Immune Response

N⁶-methyladenosine (m⁶A) is the most important modification of messenger RNAs (mRNAs) and long noncoding RNAs (lncRNAs) in higher eukaryotes. Modulation of m⁶A modifications relies on methyltransferases and demethylases. The discovery of binding proteins confirms that the m⁶A modification has a wide range of biological effects and significance at the molecular, cellular, and physiological levels. In recent years, techniques for investigating m⁶A modifications of RNA have developed rapidly. This article reviews the biological significance of RNA m⁶A modifications in the innate immune response, adaptive immune response, and viral infection.

RNA-modifying enzymes and their function in a chromatin context

Exciting research has connected specific RNA modifications to chromatin, providing evidence for co-transcriptional deposition and function in gene regulation. Here we review insights gained from studying the co-transcriptional roles of RNA modifications, and their influence in normal and disease contexts. We also discuss how the availability of novel technical approaches could raise the translational potential of targeting RNA-modifying enzymes for the treatment of disease.

RNAs and RNA-Binding Proteins in Immuno-Metabolic Homeostasis and Diseases

The increasing prevalence of worldwide obesity has emerged as a major risk factor for type 2 diabetes (T2D), hepatosteatosis, and cardiovascular disease. Accumulating evidence indicates that obesity has strong inflammatory underpinnings tightly linked to the development of metabolic diseases. However, the molecular mechanisms by which obesity induces aberrant inflammation associated with metabolic diseases are not yet clearly defined. Recently, RNAs have emerged as important regulators of stress responses and metabolism. RNAs are subject to changes in modification status, higher-order structure, and cellular localization; all of which could affect the affinity for RNA-binding proteins (RBPs) and thereby modify the RNA-RBP networks. Proper regulation and management of RNA characteristics are fundamental to cellular and organismal homeostasis, as well as paramount to health. Identification of multiple single nucleotide polymorphisms (SNPs) within loci of fat mass- and obesity-associated protein (FTO) gene, an RNA demethylase, through genome-wide association studies (GWAS) of T2D, and functional assessments of FTO in mice, support the concept that disruption in RNA modifications leads to the development of human diseases including obesity and metabolic disorder. In obesity, dynamic alterations in modification and localization of RNAs appear to modulate the RNA-RBP networks and activate proinflammatory RBPs, such as double-stranded RNA (dsRNA)-dependent protein kinase (PKR), Toll-like receptor (TLR) 3 and TLR7, and RNA silencing machinery. These changes induce aberrant inflammation and the development of metabolic diseases. This review will describe the current understanding of the underlying causes of these common and altered characteristics of RNA-RBP networks which will pave the way for developing novel approaches to tackle the pandemic issue of obesity.

AtTrm5a catalyses 1-methylguanosine and 1-methylinosine formation on tRNAs and is important for vegetative and reproductive growth in Arabidopsis thaliana

Modified nucleosides on tRNA are critical for decoding processes and protein translation. tRNAs can be modified through 1-methylguanosine (m¹G) on position 37; a function mediated by Trm5 homologs. We show that AtTRM5a (At3g56120) is a Trm5 ortholog in Arabidopsis thaliana. AtTrm5a is localized to the nucleus and its function for m¹G and m¹I methylation was confirmed by mutant analysis, yeast complementation, m¹G nucleoside level on single tRNA, and tRNA in vitro methylation. Arabidopsis attrm5a mutants were dwarfed and had short filaments, which led to reduced seed setting. Proteomics data indicated differences in the abundance of proteins involved in photosynthesis, ribosome biogenesis, oxidative phosphorylation and calcium signalling. Levels of phytohormone auxin and jasmonate were reduced in attrm5a mutant, as well as expression levels of genes involved in flowering, shoot apex cell fate determination, and hormone synthesis and signalling. Taken together, loss-of-function of AtTrm5a impaired m¹G and m¹I methylation and led to aberrant protein translation, disturbed hormone homeostasis and developmental defects in Arabidopsis plants.

CRISPR Tools for Systematic Studies of RNA Regulation

RNA molecules perform diverse functions in mammalian cells, including transferring genetic information from DNA to protein and playing diverse regulatory roles through interactions with other cellular components. Here, we discuss how clustered regularly interspaced short palindromic repeat (CRISPR)-based technologies for directed perturbations of DNA and RNA are revealing new insights into RNA regulation. First, we review the fundamentals of CRISPR-Cas enzymes and functional genomics tools that leverage these systems. Second, we explore how these new perturbation technologies are transforming the study of regulation of and by RNA, focusing on the functions of DNA regulatory elements and long noncoding RNAs (lncRNAs). Third, we highlight an emerging class of RNA-targeting CRISPR-Cas enzymes that have the potential to catalyze studies of RNA biology by providing tools to directly perturb or measure RNA modifications and functions. Together, these tools enable systematic studies of RNA function and regulation in mammalian cells.

Nucleotide resolution sequencing of N4-acetylcytidine in RNA

Posttranscriptional modifications of RNA represent an emerging class of regulatory elements in human biology. Improved methods for studying how these elements are controlled and where they occur has the potential to transform our understanding of gene expression in development and disease. Here we describe a chemical method for nucleotide resolution sequencing of N4-acetylcytidine (ac4C), a highly conserved modified nucleobase whose formation is catalyzed by the essential cytidine acetyltransferase enzyme NAT10. This approach enables the sensitive, PCR-amplifiable detection of individual ac4C sites from nanograms of unfractionated cellular RNA. The sensitive and quantitative nature of this assay provides a powerful tool to understand how cytidine acetylation is targeted, profile RNA acetyltransferase dynamics, and validate the sites and stoichiometry of ac4C in novel RNA species.

Social Environment and Epigenetics

Our social environment, from the microscopic to the macro-social, affects us for the entirety of our lives. One integral line of research to examine how interpersonal and societal environments can get "under the skin" is through the lens of epigenetics. Epigenetic mechanisms are adaptations made to our genome in response to our environment which include tags placed on and removed from the DNA itself to how our DNA is packaged, affecting how our genes are read, transcribed, and interact. These tags are affected by social environments and can persist over time; this may aid us in responding to experiences and exposures, both the enriched and the disadvantageous. From memory formation to immune function, the experience-dependent plasticity of epigenetic modifications to micro- and macro-social environments may contribute to the process of learning from comfort, pain, and stress to better survive in whatever circumstances life has in store.