Ribosome structure and activity are altered in cells lacking snoRNPs that form pseudouridines in the peptidyl transferase center

Ribosomal RNA modification enzymes stimulate large ribosome subunit assembly in E. coli

Ribosomal RNA modifications are introduced by specific enzymes during ribosome assembly in bacteria. Deletion of individual modification enzymes has a minor effect on bacterial growth, ribosome biogenesis, and translation, which has complicated the definition of the function of the enzymes and their products. We have constructed an Escherichia coli strain lacking 10 genes encoding enzymes that modify 23S rRNA around the peptidyl-transferase center. This strain exhibits severely compromised growth and ribosome assembly, especially at lower temperatures. Re-introduction of the individual modification enzymes allows for the definition of their functions. The results demonstrate that in addition to previously known RlmE, also RlmB, RlmKL, RlmN and RluC facilitate large ribosome subunit assembly. RlmB and RlmKL have functions in ribosome assembly independent of their modification activities. While the assembly stage specificity of rRNA modification enzymes is well established, this study demonstrates that there is a mutual interdependence between the rRNA modification process and large ribosome subunit assembly.

Structural and mechanistic insights into the function of Leishmania ribosome lacking a single pseudouridine modification

Leishmania is the causative agent of cutaneous and visceral diseases affecting millions of individuals worldwide. Pseudouridine (Ψ), the most abundant modification on rRNA, changes during the parasite life cycle. Alterations in the level of a specific Ψ in helix 69 (H69) affected ribosome function. To decipher the molecular mechanism of this phenotype, we determine the structure of ribosomes lacking the single Ψ and its parental strain at ∼2.4-3 Å resolution using cryo-EM. Our findings demonstrate the significance of a single Ψ on H69 to its structure and the importance for its interactions with helix 44 and specific tRNAs. Our study suggests that rRNA modification affects translation of mRNAs carrying codon bias due to selective accommodation of tRNAs by the ribosome. Based on the high-resolution structures, we propose a mechanism explaining how the ribosome selects specific tRNAs.

Loss of Conserved rRNA Modifications in the Peptidyl Transferase Center Leads to Diminished Protein Synthesis and Cell Growth in Budding Yeast

Ribosomal RNAs (rRNAs) are extensively modified during the transcription and subsequent maturation. Three types of modifications, 2'-O-methylation of ribose moiety, pseudouridylation, and base modifications, are introduced either by a snoRNA-driven mechanism or by stand-alone enzymes. Modified nucleotides are clustered at the functionally important sites, including peptidyl transferase center (PTC). Therefore, it has been hypothesised that the modified nucleotides play an important role in ensuring the functionality of the ribosome. In this study, we demonstrate that seven 25S rRNA modifications, including four evolutionarily conserved modifications, in the proximity of PTC can be simultaneously depleted without loss of cell viability. Yeast mutants lacking three snoRNA genes (snR34, snR52, and snR65) and/or expressing enzymatically inactive variants of spb1(D52A/E679K) and nop2(C424A/C478A) were constructed. The results show that rRNA modifications in PTC contribute collectively to efficient translation in eukaryotic cells. The deficiency of seven modified nucleotides in 25S rRNA resulted in reduced cell growth, cold sensitivity, decreased translation levels, and hyperaccurate translation, as indicated by the reduced missense and nonsense suppression. The modification m5C2870 is crucial in the absence of the other six modified nucleotides. Thus, the pattern of rRNA-modified nucleotides around the PTC is essential for optimal ribosomal translational activity and translational fidelity.

RNA modifications in cellular metabolism: implications for metabolism-targeted therapy and immunotherapy

Cellular metabolism is an intricate network satisfying bioenergetic and biosynthesis requirements of cells. Relevant studies have been constantly making inroads in our understanding of pathophysiology, and inspiring development of therapeutics. As a crucial component of epigenetics at post-transcription level, RNA modification significantly determines RNA fates, further affecting various biological processes and cellular phenotypes. To be noted, immunometabolism defines the metabolic alterations occur on immune cells in different stages and immunological contexts. In this review, we characterize the distribution features, modifying mechanisms and biological functions of 8 RNA modifications, including N6-methyladenosine (m6A), N6,2'-O-dimethyladenosine (m6Am), N1-methyladenosine (m1A), 5-methylcytosine (m5C), N4-acetylcytosine (ac4C), N7-methylguanosine (m7G), Pseudouridine (Ψ), adenosine-to-inosine (A-to-I) editing, which are relatively the most studied types. Then regulatory roles of these RNA modification on metabolism in diverse health and disease contexts are comprehensively described, categorized as glucose, lipid, amino acid, and mitochondrial metabolism. And we highlight the regulation of RNA modifications on immunometabolism, further influencing immune responses. Above all, we provide a thorough discussion about clinical implications of RNA modification in metabolism-targeted therapy and immunotherapy, progression of RNA modification-targeted agents, and its potential in RNA-targeted therapeutics. Eventually, we give legitimate perspectives for future researches in this field from methodological requirements, mechanistic insights, to therapeutic applications.

scaRNA20 promotes pseudouridylatory modification of small nuclear snRNA U12 and improves cardiomyogenesis

Non-coding RNAs, particularly small Cajal-body associated RNAs (scaRNAs), play a significant role in spliceosomal RNA modifications. While their involvement in ischemic myocardium regeneration is known, their role in cardiac development is unexplored. We investigated scaRNA20's role in iPSC differentiation into cardiomyocytes (iCMCs) via overexpression and knockdown assays. We measured scaRNA20-OE-iCMCs and scaRNA20-KD-iCMCs contractility using Particle Image Velocimetry (PIV), comparing them to control iCMCs. We explored scaRNA20's impact on alternative splicing via pseudouridylation (Ψ) of snRNA U12, analyzing its functional consequences in cardiac differentiation. scaRNA20-OE-iPSC differentiation increased beating colonies, upregulated cardiac-specific genes, activated TP53 and STAT3, and preserved contractility under hypoxia. Conversely, scaRNA20-KD-iCMCs exhibited poor differentiation and contractility. STAT3 inhibition in scaRNA20-OE-iPSCs hindered cardiac differentiation. RNA immunoprecipitation revealed increased Ψ at the 28th uridine of U12 RNA in scaRNA20-OE iCMCs. U12-KD iCMCs had reduced cardiac differentiation, which improved upon U12 RNA introduction. In summary, scaRNA20-OE in iPSCs enhances cardiomyogenesis, preserves iCMC function under hypoxia, and may have implications for ischemic myocardium regeneration.

How snoRNAs can contribute to cancer at multiple levels

snoRNAs are a class of non-coding RNAs known to guide site specifically RNA modifications such as 2'-O-methylation and pseudouridylation. Recent results regarding snoRNA alterations in cancer has been made available and suggest their potential evaluation as diagnostic and prognostic biomarkers. A large part of these data, however, was not consistently confirmed and failed to provide mechanistic insights on the contribution of altered snoRNA expression to the neoplastic process. Here, we aim to critically review the available literature on snoRNA in cancer focusing on the studies elucidating the functional consequences of their deregulation. Beyond the canonical guide function in RNA processing and modification we also considered additional roles in which snoRNA, in various forms and through different modalities, are involved and that have been recently reported.

Small but strong: the emerging role of small nucleolar RNA in cardiovascular diseases

Cardiovascular diseases (CVDs) are the leading cause of mortality and disability worldwide. Numerous studies have demonstrated that non-coding RNAs (ncRNAs) play a primary role in CVD development. Therefore, studies on the mechanisms of ncRNAs are essential for further efforts to prevent and treat CVDs. Small nucleolar RNAs (snoRNAs) are a novel species of non-conventional ncRNAs that guide post-transcriptional modifications and the subsequent maturation of small nuclear RNA and ribosomal RNA. Evidently, snoRNAs are extensively expressed in human tissues and may regulate different illnesses. Particularly, as the next-generation sequencing techniques have progressed, snoRNAs have been shown to be differentially expressed in CVDs, suggesting that they may play a role in the occurrence and progression of cardiac illnesses. However, the molecular processes and signaling pathways underlying the function of snoRNAs remain unidentified. Therefore, it is of great value to comprehensively investigate the association between snoRNAs and CVDs. The aim of this review was to collate existing literature on the biogenesis, characteristics, and potential regulatory mechanisms of snoRNAs. In particular, we present a scientific update on these snoRNAs and their relevance to CVDs in an effort to cast new light on the functions of snoRNAs in the clinical diagnosis of CVDs.

Effects of Mitochondrial Transplantation on Transcriptomics in a Polymicrobial Sepsis Model

Previously, we demonstrated that mitochondrial transplantation has beneficial effects in a polymicrobial sepsis model. However, the mechanism has not been fully investigated. Mitochondria have their own genes, and genomic changes in sepsis are an important issue in terms of pathophysiology, biomarkers, and therapeutic targets. To investigate the changes in transcriptomic features after mitochondrial transplantation in a polymicrobial sepsis model, we used a rat model of fecal slurry polymicrobial sepsis. Total RNA from splenocytes of sham-operated (SHAM, n = 10), sepsis-induced (SEPSIS, n = 7), and sepsis receiving mitochondrial transplantation (SEPSIS + MT, n = 8) samples was extracted and we conducted a comparative transcriptome-wide analysis between three groups. We also confirmed these results with qPCR. In terms of percentage of mitochondrial mapped reads, the SEPSIS + MT group had a significantly higher mapping ratio than the others. RT1-M2 and Cbln2 were identified as highly expressed in SEPSIS + MT compared with SEPSIS. Using SHAM expression levels as another control variable, we further identified six genes (Fxyd4, Apex2l1, Kctd4, 7SK, SNORD94, and SNORA53) that were highly expressed after sepsis induction and observed that their expression levels were attenuated by mitochondrial transplantation. Changes in transcriptomic features were identified after mitochondrial transplantation in sepsis. This might provide a hint for exploring the mechanism of mitochondrial transplantation in sepsis.

Human SHQ1 variants R335C and A426V lead to severe ribosome biogenesis defects when expressed in yeast

SHQ1 is an essential chaperone that binds the pseudouridine synthase dyskerin in the cytoplasm and escorts the enzyme to the nucleus, where dyskerin is assembled into small nucleolar RNPs (snoRNPs) of the H/ACA class. These particles carry out pseudouridine formation in ribosomal RNAs (rRNAs) and participate in maturation of rRNA precursors (pre-rRNAs). Variants of human SHQ1 have been linked to neurodevelopmental deficiencies; here we focused on two compound heterozygous mutations identified in a child showing a severe neurological disorder comprising cerebellar degeneration. To investigate the molecular defects caused by mutations R335C and A426V we used a conditional yeast strain that can be depleted of the endogenous Shq1 protein while constitutively expressing human SHQ1 (wild-type or variants). Although wild-type SHQ1 complemented the Shq1-depleted strain, cells expressing variant R335C could not support growth, and cells expressing variant A426V were temperature-sensitive. When shifted to restrictive conditions, yeast cells progressively lost H/ACA snoRNAs and accumulated unprocessed pre-rRNAs, which led to reduced production of ribosomes. Levels of Cbf5 (yeast homologue of dyskerin) were decreased in yeast cells expressing SHQ1 variants under restrictive conditions. Immunoprecipitation experiments revealed that interaction of Cbf5 with SHQ1 variants was weakened but not abolished, and yeast two-hybrid assays showed that mutation R335C is more deleterious than mutation A426V. Our data provide additional evidence for the critical role of SHQ1 in chaperoning the pseudouridine synthase dyskerin, and how its inadequate function has detrimental consequences on the production of H/ACA snoRNPs and ribosomes.

Regulation of translation by ribosomal RNA pseudouridylation

Pseudouridine is enriched in ribosomal, spliceosomal, transfer, and messenger RNA and thus integral to the central dogma. The chemical basis for how pseudouridine affects the molecular apparatus such as ribosome, however, remains elusive owing to the lack of structures without this natural modification. Here, we studied the translation of a hypopseudouridylated ribosome initiated by the internal ribosome entry site (IRES) elements. We analyzed eight cryo-electron microscopy structures of the ribosome bound with the Taura syndrome virus IRES in multiple functional states. We found widespread loss of pseudouridine-mediated interactions through water and long-range base pairings. In the presence of the translocase, eukaryotic elongation factor 2, and guanosine 5'-triphosphate hydrolysis, the hypopseudouridylated ribosome favors a rare unconducive conformation for decoding that is partially recouped in the ribosome population that remains modified at the P-site uridine. The structural principles learned establish the link between functional defects and modification loss and are likely applicable to other pseudouridine-associated processes.

Alterations of ribosomal RNA pseudouridylation in human breast cancer

RNA modifications are key regulatory factors for several biological and pathological processes. They are abundantly represented on ribosomal RNA (rRNA), where they contribute to regulate ribosomal function in mRNA translation. Altered RNA modification pathways have been linked to tumorigenesis as well as to other human diseases. In this study we quantitatively evaluated the site-specific pseudouridylation pattern in rRNA in breast cancer samples exploiting the RBS-Seq technique involving RNA bisulfite treatment coupled with a new NGS approach. We found a wide variability among patients at different sites. The most dysregulated positions in tumors turned out to be hypermodified with respect to a reference RNA. As for 2'O-methylation level of rRNA modification, we detected variable and stable pseudouridine sites, with the most stable sites being the most evolutionary conserved. We also observed that pseudouridylation levels at specific sites are related to some clinical and bio-pathological tumor features and they are able to distinguish different patient clusters. This study is the first example of the contribution that newly available high-throughput approaches for site specific pseudouridine detection can provide to the understanding of the intrinsic ribosomal changes occurring in human tumors.

RNA methylation and cellular response to oxidative stress-promoting anticancer agents

Disruption of the complex network that regulates redox homeostasis often underlies resistant phenotypes, which hinder effective and long-lasting cancer eradication. In addition, the RNA methylome-dependent control of gene expression also critically affects traits of cellular resistance to anti-cancer agents. However, few investigations aimed at establishing whether the epitranscriptome-directed adaptations underlying acquired and/or innate resistance traits in cancer could be implemented through the involvement of redox-dependent or -responsive signaling pathways. This is unexpected mainly because: i) the effectiveness of many anti-cancer approaches relies on their capacity to promote oxidative stress (OS); ii) altered redox milieu and reprogramming of mitochondrial function have been acknowledged as critical mediators of the RNA methylome-mediated response to OS. Here we summarize the current state of understanding on this topic, as well as we offer new perspectives that might lead to original approaches and strategies to delay or prevent the problem of refractory cancer and tumor recurrence.

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.

The epitranscriptome in ageing and stress resistance: A systematic review

Modifications of RNA, collectively called the "epitranscriptome", might provide novel biomarkers and innovative targets for interventions in geroscience but are just beginning to be studied in the context of ageing and stress resistance. RNA modifications modulate gene expression by affecting translation initiation and speed, miRNA binding, RNA stability, and RNA degradation. Nonetheless, the precise underlying molecular mechanisms and physiological consequences of most alterations of the epitranscriptome are still only poorly understood. We here systematically review different types of modifications of rRNA, tRNA and mRNA, the methodology to analyze them, current challenges in the field, and human disease associations. Furthermore, we compiled evidence for a connection between individual enzymes, which install RNA modifications, and lifespan in yeast, worm and fly. We also included resistance to different stressors and competitive fitness as search criteria for genes potentially relevant to ageing. Promising candidates identified by this approach include RCM1/NSUN5, RRP8, and F33A8.4/ZCCHC4 that introduce base methylations in rRNA, the methyltransferases DNMT2 and TRM9/ALKBH8, as well as factors involved in the thiolation or A to I editing in tRNA, and finally the m⁶A machinery for mRNA.

Detection technologies for RNA modifications

To date, more than 170 chemical modifications have been characterized in RNA, providing a new layer of gene expression regulation termed the 'epitranscriptome'. RNA modification detection methods and tools advance the functional studies of the epitranscriptome. According to the detection throughput and principles, existing RNA modification detection technologies can be categorized into four classes, including quantification methods, locus-specific detection methods, next-generation sequencing-based detection technologies and nanopore direct RNA sequencing-based technologies. In this review, we summarize the current knowledge about these RNA modification detection technologies and discuss the challenges for the existing detection tools, providing information for a comprehensive understanding of the epitranscriptome.

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.

Small but strong: Pivotal roles and potential applications of snoRNAs in hematopoietic malignancies

Small nucleolar RNAs (snoRNAs) belong to a family of noncoding RNAs that are 60-300 nucleotides in length, and they are classified into two classes according to their structure and function: C/D box snoRNAs, playing an essential role in 2’-O-methylation modification on ribosomal RNA; H/ACA box snoRNAs, involved in the pseudouridylation of rRNA. SnoRNAs with unclear functions, no predictable targets, and unusual subcellular locations are called orphan snoRNAs. Recent studies have revealed abnormal expression and demonstrated the pivotal roles of snoRNAs and their host genes in various types of hematological malignancies. This review discusses recent discoveries concerning snoRNAs in a variety of hematological malignancies, including multiple myeloma, lymphoma and leukemia, and sheds light on the application of snoRNAs as diagnostic and prognostic markers as well as therapeutic targets of hematological malignancies in the future.

Lytic Reactivation of the Kaposi’s Sarcoma-Associated Herpesvirus (KSHV) Is Accompanied by Major Nucleolar Alterations

The nucleolus is a subnuclear compartment whose primary function is the biogenesis of ribosomal subunits. Certain viral infections affect the morphology and composition of the nucleolar compartment and influence ribosomal RNA (rRNA) transcription and maturation. However, no description of nucleolar morphology and function during infection with Kaposi’s sarcoma-associated herpesvirus (KSHV) is available to date. Using immunofluorescence microscopy, we documented extensive destruction of the nuclear and nucleolar architecture during the lytic reactivation of KSHV. This was manifested by the redistribution of key nucleolar proteins, including the rRNA transcription factor UBF. Distinct delocalization patterns were evident; certain nucleolar proteins remained together whereas others dissociated, implying that nucleolar proteins undergo nonrandom programmed dispersion. Significantly, the redistribution of UBF was dependent on viral DNA replication or late viral gene expression. No significant changes in pre-rRNA levels and no accumulation of pre-rRNA intermediates were found by RT-qPCR and Northern blot analysis. Furthermore, fluorescent in situ hybridization (FISH), combined with immunofluorescence, revealed an overlap between Fibrillarin and internal transcribed spacer 1 (ITS1), which represents the primary product of the pre-rRNA, suggesting that the processing of rRNA proceeds during lytic reactivation. Finally, small changes in the levels of pseudouridylation (Ψ) and 2′-O-methylation (Nm) were documented across the rRNA; however, none were localized to the functional domain. Taken together, our results suggest that despite dramatic changes in the nucleolar organization, rRNA transcription and processing persist during lytic reactivation of KSHV. Whether the observed nucleolar alterations favor productive infection or signify cellular anti-viral responses remains to be determined.

The Arabidopsis Mitochondrial Pseudouridine Synthase Homolog FCS1 Plays Critical Roles in Plant Development

As the most abundant RNA modification, pseudouridylation has been shown to play critical roles in Escherichia coli, yeast and humans. However, its function in plants is still unclear. Here, we characterized leaf curly and small 1 (FCS1), which encodes a pseudouridine synthase in Arabidopsis. fcs1 mutants exhibited severe defects in plant growth, such as delayed development and reduced fertility, and were significantly smaller than the wild type at different developmental stages. FCS1 protein is localized in the mitochondrion. The absence of FCS1 significantly reduces pseudouridylation of mitochondrial 26S ribosomal RNA (rRNA) at the U1692 site, which sits in the peptidyl transferase center. This affection of mitochondrial 26S rRNA may lead to the disruption of mitochondrial translation in the fcs1-1 mutant, causing high accumulation of transcripts but low production of proteins. Dysfunctional mitochondria with abnormal structures were also observed in the fcs1-1 mutant. Overall, our results suggest that FCS1-mediated pseudouridylation of mitochondrial 26S rRNA is required for mitochondrial translation, which is critical for maintaining mitochondrial function and plant development.

The plant epitranscriptome: revisiting pseudouridine and 2'-O-methyl RNA modifications

There is growing evidence that post-transcriptional RNA modifications are highly dynamic and can be used to improve crop production. Although more than 172 unique types of RNA modifications have been identified throughout the kingdom of life, we are yet to leverage upon the understanding to optimize RNA modifications in crops to improve productivity. The contributions of internal mRNA modifications such as N6-methyladenosine (m⁶ A) and 5-methylcytosine (m⁵ C) methylations to embryonic development, root development, leaf morphogenesis, flowering, fruit ripening and stress response are sufficiently known, but the roles of the two most abundant RNA modifications, pseudouridine (Ψ) and 2'-O-methylation (Nm), in the cell remain unclear due to insufficient advances in high-throughput technologies in plant development. Therefore, in this review, we discuss the latest methods and insights gained in mapping internal Ψ and Nm and their unique properties in plants and other organisms. In addition, we discuss the limitations that remain in high-throughput technologies for qualitative and quantitative mapping of these RNA modifications and highlight future challenges in regulating the plant epitranscriptome.

Ribosomal RNA Pseudouridylation: Will Newly Available Methods Finally Define the Contribution of This Modification to Human Ribosome Plasticity?

In human rRNA, at least 104 specific uridine residues are modified to pseudouridine. Many of these pseudouridylation sites are located within functionally important ribosomal domains and can influence ribosomal functional features. Until recently, available methods failed to reliably quantify the level of modification at each specific rRNA site. Therefore, information obtained so far only partially explained the degree of regulation of pseudouridylation in different physiological and pathological conditions. In this focused review, we provide a summary of the methods that are now available for the study of rRNA pseudouridylation, discussing the perspectives that newly developed approaches are offering.

CryoEM structures of pseudouridine-free ribosome suggest impacts of chemical modifications on ribosome conformations

Pseudouridine, the most abundant form of RNA modification, is known to play important roles in ribosome function. Mutations in human DKC1, the pseudouridine synthase responsible for catalyzing the ribosome RNA modification, cause translation deficiencies and are associated with a complex cancer predisposition. The structural basis for how pseudouridine impacts ribosome function remains uncharacterized. Here, we characterized structures and conformations of a fully modified and a pseudouridine-free ribosome from Saccharomyces cerevisiae in the absence of ligands or when bound with translocation inhibitor cycloheximide by electron cryomicroscopy. In the modified ribosome, the rearranged N1 atom of pseudouridine is observed to stabilize key functional motifs by establishing predominately water-mediated close contacts with the phosphate backbone. The pseudouridine-free ribosome, however, is devoid of such interactions and displays conformations reflective of abnormal inter-subunit movements. The erroneous motions of the pseudouridine-free ribosome may explain its observed deficiencies in translation.

Experimental evolution links post-transcriptional regulation to Leishmania fitness gain

The protozoan parasite Leishmania donovani causes fatal human visceral leishmaniasis in absence of treatment. Genome instability has been recognized as a driver in Leishmania fitness gain in response to environmental change or chemotherapy. How genome instability generates beneficial phenotypes despite potential deleterious gene dosage effects is unknown. Here we address this important open question applying experimental evolution and integrative systems approaches on parasites adapting to in vitro culture. Phenotypic analyses of parasites from early and late stages of culture adaptation revealed an important fitness tradeoff, with selection for accelerated growth in promastigote culture (fitness gain) impairing infectivity (fitness costs). Comparative genomics, transcriptomics and proteomics analyses revealed a complex regulatory network associated with parasite fitness gain, with genome instability causing highly reproducible, gene dosage-independent and -dependent changes. Reduction of flagellar transcripts and increase in coding and non-coding RNAs implicated in ribosomal biogenesis and protein translation were not correlated to dosage changes of the corresponding genes, revealing a gene dosage-independent, post-transcriptional mechanism of regulation. In contrast, abundance of gene products implicated in post-transcriptional regulation itself correlated to corresponding gene dosage changes. Thus, RNA abundance during parasite adaptation is controled by direct and indirect gene dosage changes. We correlated differential expression of small nucleolar RNAs (snoRNAs) with changes in rRNA modification, providing first evidence that Leishmania fitness gain in culture may be controlled by post-transcriptional and epitranscriptomic regulation. Our findings propose a novel model for Leishmania fitness gain in culture, where differential regulation of mRNA stability and the generation of modified ribosomes may potentially filter deleterious from beneficial gene dosage effects and provide proteomic robustness to genetically heterogenous, adapting parasite populations. This model challenges the current, genome-centric approach to Leishmania epidemiology and identifies the Leishmania transcriptome and non-coding small RNome as potential novel sources for the discovery of biomarkers that may be associated with parasite phenotypic adaptation in clinical settings.

Genome instability plays a central yet poorly understood role in human disease. Gene amplifications and deletions drive cancer development, microbial infection and therapeutic failure. The molecular mechanisms that harness the deleterious effects of genome instability to generate beneficial phenotypes in pathogenic systems are unknown. Here we study this important open question in the protozoan parasite Leishmania that causes devastating human diseases termed leishmaniases. Leishmania parasites lack transcriptional control and instead exploit genome instability to adapt to their host environment. Analyzing in vitro adaptation of hamster-derived parasites via gene copy number (genomic level) and gene expression changes (transcriptomic and proteomic levels), we show that these parasites likely exploit small nucleolar RNAs (snoRNAs) to mitigate toxic effects of genome instability by post-transcriptional regulation and the establishment of modified ribosomes. Our findings propose non-coding RNAs as potential novel biomarkers with diagnostic and prognostic value that may be linked to changes in parasite tissue tropism or drug susceptibility. This novel insight into Leishmania adaptation will be likely applicable to other fast evolving eukaryotic systems with unstable genomes, such as fungi or cancer cells.

Computational identification of Plasmodium falciparum RNA pseudouridylate synthase as a viable drug target, its physicochemical properties, 3D structure prediction and prediction of potential inhibitors

The increased resistance to the currently effective antimalarial drugs against Plasmodium falciparum has necessitated the development of new drugs for malaria treatment. Many proteins have been predicted using various means as potential drug targets for the treatment of the P. falciparum malaria infection. Meanwhile, only a few studies went on to predict the 3-dimensional (3D) structure of potential target. Therefore, this study aimed to predict potential antimalarial drug targets against the deadliest malaria parasite P. falciparum as well as to determine the 3D structure and possible inhibitors of one of the targets. We employed machine learning approach to predict suitable drug targets in P. falciparum. Five of the predicted protein targets were considered as potential drug targets as they were non-homologous to their human counterparts. Out of these, we determined the physicochemical properties, predicted the 3D structure and carried out docking-based virtual screening of P. falciparum RNA pseudouridylate synthase, putative (PfRPuSP). The PfRPuSP was one of the potential five target proteins. Homology modelling and the ab initio methods were used to predict the 3D structure of PfRPuSP. Then, a compound library of 5621 molecules was constructed from PubChem and ChEMBL databases using 5-fluorouridine as the control inhibitor. Docking-based virtual screening was performed using Autodock 4.2 and Autodock Vina to select compounds with high binding affinity. A total of 11 compounds were selected based on their binding energies from 881 compounds which were manually examined after docking. Seven of the 11 compounds that exhibited remarkable interactions with the residues in the active sites of PfRPuSP were analysed. These compounds performed favourably when compared to the control inhibitor and predicted to bind better than 5-fluorouridine. These seven compounds are suggested as new potential lead structures for antimalarial treatment.

Genome instability drives epistatic adaptation in the human pathogen Leishmania

Chromosome and gene copy number variations often correlate with the evolution of microbial and cancer drug resistance, thus causing important human mortality. How genome instability is harnessed to generate beneficial phenotypes and how deleterious gene dosage effects are compensated remain open questions. The protist pathogen Leishmania exploits genome instability to regulate expression via gene dosage changes. Using these parasites as a unique model system, we uncover complex epistatic interactions between gene copy number variations and compensatory transcriptomic responses as key processes that harness genome instability for adaptive evolution in Leishmania. Our results propose a model of eukaryotic fitness gain that may be broadly applicable to pathogenic fungi or tumor cells known to exploit genome instability for adaptation.

How genome instability is harnessed for fitness gain despite its potential deleterious effects is largely elusive. An ideal system to address this important open question is provided by the protozoan pathogen Leishmania, which exploits frequent variations in chromosome and gene copy number to regulate expression levels. Using ecological genomics and experimental evolution approaches, we provide evidence that Leishmania adaptation relies on epistatic interactions between functionally associated gene copy number variations in pathways driving fitness gain in a given environment. We further uncover posttranscriptional regulation as a key mechanism that compensates for deleterious gene dosage effects and provides phenotypic robustness to genetically heterogenous parasite populations. Finally, we correlate dynamic variations in small nucleolar RNA (snoRNA) gene dosage with changes in ribosomal RNA 2′-O-methylation and pseudouridylation, suggesting translational control as an additional layer of parasite adaptation. Leishmania genome instability is thus harnessed for fitness gain by genome-dependent variations in gene expression and genome-independent compensatory mechanisms. This allows for polyclonal adaptation and maintenance of genetic heterogeneity despite strong selective pressure. The epistatic adaptation described here needs to be considered in Leishmania epidemiology and biomarker discovery and may be relevant to other fast-evolving eukaryotic cells that exploit genome instability for adaptation, such as fungal pathogens or cancer.

The ribosome epitranscriptome: inert-or a platform for functional plasticity?

A universal property of all rRNAs explored to date is the prevalence of post-transcriptional ("epitranscriptional") modifications, which expand the chemical and topological properties of the four standard nucleosides. Are these modifications an inert, constitutive part of the ribosome? Or could they, in part, also regulate the structure or function of the ribosome? In this review, we summarize emerging evidence that rRNA modifications are more heterogeneous than previously thought, and that they can also vary from one condition to another, such as in the context of a cellular response or a developmental trajectory. We discuss the implications of these results and key open questions on the path toward connecting such heterogeneity with function.

Small but Mighty-The Emerging Role of snoRNAs in Hematological Malignancies

Over recent years, the long known class of small nucleolar RNAs (snoRNAs) have gained interest among the scientific community, especially in the clinical context. The main molecular role of this interesting family of non-coding RNAs is to serve as scaffolding RNAs to mediate site-specific RNA modification of ribosomal RNAs (rRNAs) and small nuclear RNAs (snRNAs). With the development of new sequencing techniques and sophisticated analysis pipelines, new members of the snoRNA family were identified and global expression patterns in disease backgrounds could be determined. We will herein shed light on the current research progress in snoRNA biology and their clinical role by influencing disease outcome in hematological diseases. Astonishingly, in recent studies snoRNAs emerged as potent biomarkers in a variety of these clinical setups, which is also highlighted by the frequent deregulation of snoRNA levels in the hema-oncological context. However, research is only starting to reveal how snoRNAs might influence cellular functions and the connected disease hallmarks in hematological malignancies.

Recent technical advances in the study of nucleic acid modifications

Enzyme-mediated chemical modifications of nucleic acids are indispensable regulators of gene expression. Our understanding of the biochemistry and biological significance of these modifications has largely been driven by an ever-evolving landscape of technologies that enable accurate detection, mapping, and manipulation of these marks. Here we provide a summary of recent technical advances in the study of nucleic acid modifications with a focus on techniques that allow accurate detection and mapping of these modifications. For each modification discussed (N6-methyladenosine, 5-methylcytidine, inosine, pseudouridine, and N4-acetylcytidine), we begin by introducing the "gold standard" technique for its mapping and detection, followed by a discussion of techniques developed to address any shortcomings of the gold standard. By highlighting the commonalities and differences of these techniques, we hope to provide a perspective on the current state of the field and to lay out a guideline for development of future technologies.

Small nucleolar RNA is potential as a novel player in leukemogenesis and clinical application

Lack of clarity of the mechanisms that underlie leukemogenesis obstructs the diagnosis, prognosis, and treatment of leukemia. Research has found that small nuclear RNA (snoRNA) plays an essential role in leukemia. These small non-coding RNAs are involved in ribosome biogenesis, including the 2′-O-methylation and pseudouridylation of precursor ribosomal RNA (pre-rRNA), and pre-rRNA splicing. Recently, many snoRNAs were found to be orphans that have no predictable RNA modification targets, but these RNAs have always been found to be located in different subcellular organelles, and they play diverse roles. Using high-throughput technology, snoRNA expression profiles have been revealed in leukemia, and some of the deregulated snoRNAs may regulate the cell cycle, differentiation, proliferation, and apoptosis in leukemic cells and confer drug resistance during leukemia treatment. In this review, we discuss the expression profiles and functions of snoRNAs, particularly orphan snoRNAs, in leukemia. It is possible that the dysregulated snoRNAs are promising diagnosis and prognosis markers for leukemia, which may serve as potential therapeutic targets in leukemia treatment.

The importance of RNA modifications: From cells to muscle physiology

Naturally occurring post-transcriptional chemical modifications serve critical roles in impacting RNA structure and function. More directly, modifications may affect RNA stability, intracellular transport, translational efficiency, and fidelity. The combination of effects caused by modifications are ultimately linked to gene expression regulation at a genome-wide scale. The latter is especially true in systems that undergo rapid metabolic and or translational remodeling in response to external stimuli, such as the presence of stressors, but beyond that, modifications may also affect cell homeostasis. Although examples of the importance of RNA modifications in translation are accumulating rapidly, still what these contribute to the function of complex physiological systems such as muscle is only recently emerging. In the present review, we will introduce key information on various modifications and highlight connections between those and cellular malfunctions. In passing, we will describe well-documented roles for modifications in the nervous system and use this information as a stepping stone to emphasize a glaring paucity of knowledge on the role of RNA modifications in heart and skeletal muscle, with particular emphasis on mitochondrial function in those systems. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Processing > RNA Editing and Modification.

Characterizing RNA Pseudouridylation by Convolutional Neural Networks

Pseudouridine (Ψ) is the most prevalent post-transcriptional RNA modification and is widespread in small cellular RNAs and mRNAs. However, the functions, mechanisms, and precise distribution of Ψs (especially in mRNAs) still remain largely unclear. The landscape of Ψs across the transcriptome has not yet been fully delineated. Here, we present a highly effective model based on a convolutional neural network (CNN), called PseudoUridyLation Site Estimator (PULSE), to analyze large-scale profiling data of Ψ sites and characterize the contextual sequence features of pseudouridylation. PULSE, consisting of two alternatively-stacked convolution and pooling layers followed by a fully-connected neural network, can automatically learn the hidden patterns of pseudouridylation from the local sequence information. Extensive validation tests demonstrated that PULSE can outperform other state-of-the-art prediction methods and achieve high prediction accuracy, thus enabling us to further characterize the transcriptome-wide landscape of Ψ sites. We further showed that the prediction results derived from PULSE can provide novel insights into understanding the functional roles of pseudouridylation, such as the regulations of RNA secondary structure, codon usage, translation, and RNA stability, and the connection to single nucleotide variants. The source code and final model for PULSE are available at https://github.com/mlcb-thu/PULSE.

Saccharomyces cerevisiae, a Powerful Model for Studying rRNA Modifications and Their Effects on Translation Fidelity

Ribosomal RNA is a major component of the ribosome. This RNA plays a crucial role in ribosome functioning by ensuring the formation of the peptide bond between amino acids and the accurate decoding of the genetic code. The rRNA carries many chemical modifications that participate in its maturation, the formation of the ribosome and its functioning. In this review, we present the different modifications and how they are deposited on the rRNA. We also describe the most recent results showing that the modified positions are not 100% modified, which creates a heterogeneous population of ribosomes. This gave rise to the concept of specialized ribosomes that we discuss. The knowledge accumulated in the yeast Saccharomyces cerevisiae is very helpful to better understand the role of rRNA modifications in humans, especially in ribosomopathies.

Pseudouridines on Trypanosoma brucei mRNAs are developmentally regulated: Implications to mRNA stability and protein binding

The parasite Trypanosoma brucei cycles between an insect and a mammalian host and is the causative agent of sleeping sickness. Here, we performed high-throughput mapping of pseudouridines (Ψs) on mRNA from two life stages of the parasite. The analysis revealed ~273 Ψs, including developmentally regulated Ψs that are guided by homologs of pseudouridine synthases (PUS1, 3, 5, and 7). Mutating the U that undergoes pseudouridylation in the 3' UTR of valyl-tRNA synthetase destabilized the mRNA level. To investigate the mechanism by which Ψ affects the stability of this mRNA, proteins that bind to the 3' UTR were identified, including the RNA binding protein RBSR1. The binding of RBSR1 protein to the 3' UTR was stronger when lacking Ψ compared to transcripts carrying the modification, suggesting that Ψ can inhibit the binding of proteins to their target and thus affect the stability of mRNAs. Consequently, Ψ modification on mRNA adds an additional level of regulation to the dominant post-transcriptional control in these parasites.

Shaping the Bacterial Epitranscriptome-5'-Terminal and Internal RNA Modifications

All domains of life utilize a diverse set of modified ribonucleotides that can impact the sequence, structure, function, stability, and the fate of RNAs, as well as their interactions with other molecules. Today, more than 160 different RNA modifications are known that decorate the RNA at the 5'-terminus or internal RNA positions. The boost of next-generation sequencing technologies sets the foundation to identify and study the functional role of RNA modifications. The recent advances in the field of RNA modifications reveal a novel regulatory layer between RNA modifications and proteins, which is central to developing a novel concept called "epitranscriptomics." The majority of RNA modifications studies focus on the eukaryotic epitranscriptome. In contrast, RNA modifications in prokaryotes are poorly characterized. This review outlines the current knowledge of the prokaryotic epitranscriptome focusing on mRNA modifications. Here, it is described that several internal and 5'-terminal RNA modifications either present or likely present in prokaryotic mRNA. Thereby, the individual techniques to identify these epitranscriptomic modifications, their writers, readers and erasers, and their proposed functions are explored. Besides that, still unanswered questions in the field of prokaryotic epitranscriptomics are pointed out, and its future perspectives in the dawn of next-generation sequencing technologies are outlined.

The Diabetes Gene JAZF1 Is Essential for the Homeostatic Control of Ribosome Biogenesis and Function in Metabolic Stress

The ability of pancreatic β-cells to respond to increased demands for insulin during metabolic stress critically depends on proper ribosome homeostasis and function. Excessive and long-lasting stimulation of insulin secretion can elicit endoplasmic reticulum (ER) stress, unfolded protein response, and β-cell apoptosis. Here we show that the diabetes susceptibility gene JAZF1 is a key transcriptional regulator of ribosome biogenesis, global protein, and insulin translation. JAZF1 is excluded from the nucleus, and its expression levels are reduced upon metabolic stress and in diabetes. Genetic deletion of Jazf1 results in global impairment of protein synthesis that is mediated by defects in ribosomal protein synthesis, ribosomal RNA processing, and aminoacyl-synthetase expression, thereby inducing ER stress and increasing β-cell susceptibility to apoptosis. Importantly, JAZF1 function and its pleiotropic actions are impaired in islets of murine T2D and in human islets exposed to metabolic stress. Our study identifies JAZF1 as a central mediator of metabolic stress in β-cells.

H/ACA Small Ribonucleoproteins: Structural and Functional Comparison Between Archaea and Eukaryotes

During ribosome synthesis, ribosomal RNA is modified through the formation of many pseudouridines and methylations which contribute to ribosome function across all domains of life. In archaea and eukaryotes, pseudouridylation of rRNA is catalyzed by H/ACA small ribonucleoproteins (sRNPs) utilizing different H/ACA guide RNAs to identify target uridines for modification. H/ACA sRNPs are conserved in archaea and eukaryotes, as they share a common general architecture and function, but there are also several notable differences between archaeal and eukaryotic H/ACA sRNPs. Due to the higher protein stability in archaea, we have more information on the structure of archaeal H/ACA sRNPs compared to eukaryotic counterparts. However, based on the long history of yeast genetic and other cellular studies, the biological role of H/ACA sRNPs during ribosome biogenesis is better understood in eukaryotes than archaea. Therefore, this review provides an overview of the current knowledge on H/ACA sRNPs from archaea, in particular their structure and function, and relates it to our understanding of the roles of eukaryotic H/ACA sRNP during eukaryotic ribosome synthesis and beyond. Based on this comparison of our current insights into archaeal and eukaryotic H/ACA sRNPs, we discuss what role archaeal H/ACA sRNPs may play in the formation of ribosomes.

Regulation of translation by methylation multiplicity of 18S rRNA

N6-methyladenosine (m6A) is a conserved ribonucleoside modification that regulates many facets of RNA metabolism. Using quantitative mass spectrometry, we find that the universally conserved tandem adenosines at the 3' end of 18S rRNA, thought to be constitutively di-methylated (m62A), are also mono-methylated (m6A). Although present at substoichiometric amounts, m6A at these positions increases significantly in response to sulfur starvation in yeast cells and mammalian cell lines. Combining yeast genetics and ribosome profiling, we provide evidence to suggest that m6A-bearing ribosomes carry out translation distinctly from m62A-bearing ribosomes, featuring a striking specificity for sulfur metabolism genes. Our work thus reveals methylation multiplicity as a mechanism to regulate translation.

Translation machinery reprogramming in programmed cell death in Saccharomyces cerevisiae

Programmed cell death involves complex molecular pathways in both eukaryotes and prokaryotes. In Escherichia coli, the toxin-antitoxin system (TA-system) has been described as a programmed cell death pathway in which mRNA and ribosome organizations are modified, favoring the production of specific death-related proteins, but also of a minor portion of survival proteins, determining the destiny of the cell population. In the eukaryote Saccharomyces cerevisiae, the ribosome was shown to change its stoichiometry in terms of ribosomal protein content during stress response, affecting the relative proportion between ohnologs, i.e., the couple of paralogs derived by a whole genome duplication event. Here, we confirm the differential expression of ribosomal proteins in yeast also during programmed cell death induced by acetic acid, and we highlight that also in this case pairs of ohnologs are involved. We also show that there are different trends in cytosolic and mitochondrial ribosomal proteins gene expression during the process. Moreover, we show that the exposure to acetic acid induces the differential expression of further genes coding for products related to translation processes and to rRNA post-transcriptional maturation, involving mRNA decapping, affecting translation accuracy, and snoRNA synthesis. Our results suggest that the reprogramming of the overall translation apparatus, including the cytosolic ribosome reorganization, are relevant events in yeast programmed cell death induced by acetic acid.

The role of m6A, m5C and Ψ RNA modifications in cancer: Novel therapeutic opportunities

RNA modifications have recently emerged as critical posttranscriptional regulators of gene expression programmes. Significant advances have been made in understanding the functional role of RNA modifications in regulating coding and non-coding RNA processing and function, which in turn thoroughly shape distinct gene expression programmes. They affect diverse biological processes, and the correct deposition of many of these modifications is required for normal development. Alterations of their deposition are implicated in several diseases, including cancer. In this Review, we focus on the occurrence of N⁶-methyladenosine (m⁶A), 5-methylcytosine (m⁵C) and pseudouridine (Ψ) in coding and non-coding RNAs and describe their physiopathological role in cancer. We will highlight the latest insights into the mechanisms of how these posttranscriptional modifications influence tumour development, maintenance, and progression. Finally, we will summarize the latest advances on the development of small molecule inhibitors that target specific writers or erasers to rewind the epitranscriptome of a cancer cell and their therapeutic potential.

Adaptation of Human Ribosomal RNA for Nanopore Sequencing of Canonical and Modified Nucleotides

Historically, RNA has been sequenced as cDNA copies derived from reverse transcription of cellular RNA followed by PCR amplification. Recently, RNA sequencing using nanopores has emerged as an alternative. Using this technology, individual cellular RNA strands are read directly as they are driven through nanoscale pores by an applied voltage. The speed of translocation is regulated by a helicase that is loaded onto each RNA strand by an adapter that also facilitates capture by the nanopore electric field. Here we describe a technique for adapting human ribosomal RNA subunits for nanopore sequencing. Using this strategy, a single Oxford Nanopore MinION run delivered 470,907 sequence reads of which 396,048 aligned to ribosomal RNA, with 28S, 18S, 5.8S, and 5S coverage of 6053, 369,472, 16,058, and 4465 reads, respectively. Example alignments that reveal putative nucleotide modifications are provided.

H/ACA snoRNA levels are regulated during stem cell differentiation

H/ACA small nucleolar RNAs (snoRNAs) guide pseudouridylation as part of a small nucleolar ribonucleoprotein complex (snoRNP). Disruption of H/ACA snoRNA levels in stem cells impairs pluripotency, yet it remains unclear how H/ACA snoRNAs contribute to differentiation. To determine if H/ACA snoRNA levels are dynamic during differentiation, we comprehensively profiled H/ACA snoRNA abundance in multiple murine cell types and during differentiation in three cellular models, including mouse embryonic stem cells and mouse myoblasts. We determined that the profiles of H/ACA snoRNA abundance are cell-type specific, and we identified a subset of snoRNAs that are specifically regulated during differentiation. Additionally, we demonstrated that a decrease in Snora27 abundance upon differentiation corresponds to a decrease in pseudouridylation of its target site within the E-site transfer RNA (tRNA) binding region of the 28S ribosomal RNA (rRNA) in the large ribosomal subunit. Together, these data point toward a potential model in which H/ACA snoRNAs are specifically regulated during differentiation to alter pseudouridylation and fine tune ribosome function.

snR30/U17 Small Nucleolar Ribonucleoprotein: A Critical Player during Ribosome Biogenesis

The small nucleolar RNA snR30 (U17 in humans) plays a unique role during ribosome synthesis. Unlike most members of the H/ACA class of guide RNAs, the small nucleolar ribonucleoprotein (snoRNP) complex assembled on snR30 does not direct pseudouridylation of ribosomal RNA (rRNA), but instead snR30 is critical for 18S rRNA processing during formation of the small subunit (SSU) of the ribosome. Specifically, snR30 is essential for three pre-rRNA cleavages at the A₀/01, A₁/1, and A₂/2a sites in yeast and humans, respectively. Accordingly, snR30 is the only essential H/ACA guide RNA in yeast. Here, we summarize our current knowledge about the interactions and functions of snR30, discuss what remains to be elucidated, and present two non-exclusive hypotheses on the possible molecular function of snR30 during ribosome biogenesis. First, snR30 might be responsible for recruiting other proteins including endonucleases to the SSU processome. Second, snR30 may contribute to the refolding of pre-rRNA into a required conformation that serves as a checkpoint during ribosome biogenesis facilitating pre-rRNA cleavage. In both scenarios, the snR30 snoRNP may have scaffolding and RNA chaperoning activity. In conclusion, the snR30 snoRNP is a crucial player with an unknown molecular mechanism during ribosome synthesis, posing many interesting future research questions.

Emerging roles and potential clinical applications of noncoding RNAs in hepatocellular carcinoma

Hepatocellular carcinoma(HCC) is one of the most common forms of cancer, and accounts for a high proportion of cancer-associated deaths. Growing evidences have demonstrated that non- protein-coding regions of the genome could give rise to transcripts, termed noncoding RNA (ncRNA), that form novel functional layers of the cellular activity. ncRNAs are implicated in different molecular mechanisms and functions at transcriptional, translational and post-translational levels. An increasing number of studies have demonstrated a complex array of molecular and cellular functions of ncRNAs in different stages of the HCC tumorigenesis, either in an oncogenic or tumor-suppressive manner. As a result, several pre-clinical studies have highlighted the great potentials of ncRNAs as novel biomarkers for cancer diagnosis or therapeutics in targeting HCC progression. In this review, we briefly described the characteristics of several representative ncRNAs and summarized the latest findings of their roles and mechanisms in the development of HCC, in order to better understand the cancer biology and their potential clinical applications in this malignancy.

Discrimination of common isomerides of methyl nucleosides by collision-induced dissociation tandem mass spectrometry

The methyl-modified nucleosides (methyladenosine, methylguanosine, methylcytidine, and methyluridine) occur widely in nucleic acids and serve as biomarkers for a variety of types of diseases. Their isomers have the same parent ions in MS spectra and need further discrimination. Here, electrospray ionization mass spectrometry (ESI-MS) coupled with collision induced dissociation (CID) was used to distinguish the common isomerides of methyl-nucleosides. The various fragmentation patterns had been discussed in comparison of the different methyl modified nucleosides and were studied as a function of normalized collision energy. Then, structurally relevant fragments were obtained to efficiently identify characterization of methyl-nucleoside isomerides by collision induced dissociation. Therefore, this study provides a promising method using CID-MS for the discrimination of the isomeric methyl nucleosides, which could be useful to quantitative study of methyl nucleosides and detect of unknown methyl nucleosides.

snoRNPs: Functions in Ribosome Biogenesis

Ribosomes are perhaps the most critical macromolecular machine as they are tasked with carrying out protein synthesis in cells. They are incredibly complex structures composed of protein components and heavily chemically modified RNAs. The task of assembling mature ribosomes from their component parts consumes a massive amount of energy and requires greater than 200 assembly factors. Among the most critical of these are small nucleolar ribonucleoproteins (snoRNPs). These are small RNAs complexed with diverse sets of proteins. As suggested by their name, they localize to the nucleolus, the site of ribosome biogenesis. There, they facilitate multiple roles in ribosomes biogenesis, such as pseudouridylation and 2′-O-methylation of ribosomal (r)RNA, guiding pre-rRNA processing, and acting as molecular chaperones. Here, we reviewed their activity in promoting the assembly of ribosomes in eukaryotes with regards to chemical modification and pre-rRNA processing.

Death by lipids: The role of small nucleolar RNAs in metabolic stress

Excess fatty acid accumulation in nonadipose tissues leads to cell dysfunction and cell death that is linked to the pathogenesis of inherited and acquired human diseases. Study of this process, known as lipotoxicity, has provided new insights into the regulation of lipid homeostasis and has revealed new molecular pathways involved in lipid-induced cellular stress. The discovery that disruption of specific small nucleolar RNAs protects against fatty acid-induced cell death and remodels metabolism in vivo opens new opportunities for understanding how nutrient signals influence cellular and systemic metabolic homeostasis through RNA biology.

Positive-sense RNA viruses reveal the complexity and dynamics of the cellular and viral epitranscriptomes during infection

More than 140 post-transcriptional modifications (PTMs) are known to decorate cellular RNAs, but their incidence, identity and significance in viral RNA are still largely unknown. We have developed an agnostic analytical approach to comprehensively survey PTMs on viral and cellular RNAs. Specifically, we used mass spectrometry to analyze PTMs on total RNA isolated from cells infected with Zika virus, Dengue virus, hepatitis C virus (HCV), poliovirus and human immunodeficiency virus type 1. All five RNA viruses significantly altered global PTM landscapes. Examination of PTM profiles of individual viral genomes isolated by affinity capture revealed a plethora of PTMs on viral RNAs, which far exceeds the handful of well-characterized modifications. Direct comparison of viral epitranscriptomes identified common and virus-specific PTMs. In particular, specific dimethylcytosine modifications were only present in total RNA from virus-infected cells, and in intracellular HCV RNA, and viral RNA from Zika and HCV virions. Moreover, dimethylcytosine abundance during viral infection was modulated by the cellular DEAD-box RNA helicase DDX6. By opening the Pandora's box on viral PTMs, this report presents numerous questions and hypotheses on PTM function and strongly supports PTMs as a new tier of regulation by which RNA viruses subvert the host and evade cellular surveillance systems.

Expression profiling of snoRNAs in normal hematopoiesis and AML

Small nucleolar RNAs (snoRNAs) are noncoding RNAs that contribute to ribosome biogenesis and RNA splicing by modifying ribosomal RNA and spliceosome RNAs, respectively. We optimized a next-generation sequencing approach and a custom analysis pipeline to identify and quantify expression of snoRNAs in acute myeloid leukemia (AML) and normal hematopoietic cell populations. We show that snoRNAs are expressed in a lineage- and development-specific fashion during hematopoiesis. The most striking examples involve snoRNAs located in 2 imprinted loci, which are highly expressed in hematopoietic progenitors and downregulated during myeloid differentiation. Although most snoRNAs are expressed at similar levels in AML cells compared with CD34⁺, a subset of snoRNAs showed consistent differential expression, with the great majority of these being decreased in the AML samples. Analysis of host gene expression, splicing patterns, and whole-genome sequence data for mutational events did not identify transcriptional patterns or genetic alterations that account for these expression differences. These data provide a comprehensive analysis of the snoRNA transcriptome in normal and leukemic cells and should be helpful in the design of studies to define the contribution of snoRNAs to normal and malignant hematopoiesis.