REDItools: high-throughput RNA editing detection made easy

The complete mitochondrial genome of Aglaia odorata, insights into its genomic structure and RNA editing sites

Aglaia odorata, native to Guangdong, Guangxi, and Hainan provinces in China, has long been utilized as an herbal remedy in ancient China. In this study, we assembled and annotated the complete mitochondrial genome (mitogenome) of A. odorata, which spans a total length of 537,321 bp. Conformation of the A. odorata recombination was verified through PCR experiments and Sanger sequencing. We identified and annotated 35 protein-coding genes (PCGs), 22 tRNA genes, and 3 rRNA genes within the mitogenome. Analysis of repeated elements revealed the presence of 192 SSRs, 29 pairs of tandem repeats, and 333 pairs of dispersed repeats in the A. odorata mitogenome. Additionally, we analyzed codon usage and mitochondrial plastid DNAs (MTPTs). Twelve MTPTs between the plastome and mitogenome of A. odorata were identified, with a combined length of 2,501 bp, accounting for 0.47% of the mitogenome. Furthermore, 359 high-confidence C to U RNA editing sites were predicted on PCGs, and four selected RNA editing sites were specially examined to verify the creation of start and/or stop codons. Extensive genomic rearrangement was observed between A. odorata and related mitogenomes. Phylogenetic analysis based on mitochondrial PCGs were conducted to elucidate the evolutionary relationships between A. odorata and other angiosperms.

Tumor neoantigens derived from RNA editing events show significant clinical relevance in melanoma patients treated with immunotherapy

This study aimed to investigate the clinical significance of RNA editing (RE) and RNA editing derived (RED-) neoantigens in melanoma patients treated with immunotherapy. Vardict and VEP were used to identify the somatic mutations. RE events were identified by Reditools2 and filtered by the custom pipeline. miRTar2GO was implemented to predict the RE whether located in miRNA targets within the 3' UTR region. NetMHCpan and NetCTLpan were used to identify and characterize RED-neoantigens. In total, 7116 RE events were identified, most of which were A-to-I events. Using our custom pipeline, 631 RED-neoantigens were identified that show a significantly greater peptide-MHC affinity, and facilitate epitope processing and presentation than wild-type peptides. The OS of the patients with high RED-neoantigens burden was significantly longer ( P  = 0.035), and a significantly higher RED-neoantigens burden was observed in responders ( P  = 0.048). The area under the curve of the RED-neoantigen was 0.831 of OS. Then, we validated the reliability of RED-neoantigens in predicting the prognosis in an independent cohort and found that patients with high RED-neoantigens exhibited a longer OS ( P  = 0.008). To our knowledge, this is the first study to systematically assess the clinical relevance of RED-neoantigens in melanoma patients treated with immunotherapy.

Strand-selective base editing of human mitochondrial DNA using mitoBEs

A number of mitochondrial diseases in humans are caused by point mutations that could be corrected by base editors, but delivery of CRISPR guide RNAs into the mitochondria is difficult. In this study, we present mitochondrial DNA base editors (mitoBEs), which combine a transcription activator-like effector (TALE)-fused nickase and a deaminase for precise base editing in mitochondrial DNA. Combining mitochondria-localized, programmable TALE binding proteins with the nickase MutH or Nt.BspD6I(C) and either the single-stranded DNA-specific adenine deaminase TadA8e or the cytosine deaminase ABOBEC1 and UGI, we achieve A-to-G or C-to-T base editing with up to 77% efficiency and high specificity. We find that mitoBEs are DNA strand-selective mitochondrial base editors, with editing results more likely to be retained on the nonnicked DNA strand. Furthermore, we correct pathogenic mitochondrial DNA mutations in patient-derived cells by delivering mitoBEs encoded in circular RNAs. mitoBEs offer a precise, efficient DNA editing tool with broad applicability for therapy in mitochondrial genetic diseases.

Malignant A-to-I RNA editing by ADAR1 drives T cell acute lymphoblastic leukemia relapse via attenuating dsRNA sensing

Leukemia-initiating cells (LICs) are regarded as the origin of leukemia relapse and therapeutic resistance. Identifying direct stemness determinants that fuel LIC self-renewal is critical for developing targeted approaches. Here, we show that the RNA-editing enzyme ADAR1 is a crucial stemness factor that promotes LIC self-renewal by attenuating aberrant double-stranded RNA (dsRNA) sensing. Elevated adenosine-to-inosine editing is a common attribute of relapsed T cell acute lymphoblastic leukemia (T-ALL) regardless of molecular subtype. Consequently, knockdown of ADAR1 severely inhibits LIC self-renewal capacity and prolongs survival in T-ALL patient-derived xenograft models. Mechanistically, ADAR1 directs hyper-editing of immunogenic dsRNA to avoid detection by the innate immune sensor melanoma differentiation-associated protein 5 (MDA5). Moreover, we uncover that the cell-intrinsic level of MDA5 dictates the dependency on the ADAR1-MDA5 axis in T-ALL. Collectively, our results show that ADAR1 functions as a self-renewal factor that limits the sensing of endogenous dsRNA. Thus, targeting ADAR1 presents an effective therapeutic strategy for eliminating T-ALL LICs.

Liver cancer-specific mutations in functional domains of ADAR2 lead to the elevation of coding and non-coding RNA editing in multiple tumor-related genes

Mutation is the major cause of phenotypic innovations. Apart from DNA mutations, the alteration on RNA such as the ADAR-mediated A-to-I RNA editing could also shape the phenotype. These two layers of variations have not been systematically combined to study their collective roles in cancers. We collected the high-quality transcriptomes of ten hepatocellular carcinoma (HCC) and the matched control samples. We systematically identified HCC-specific mutations in the exonic regions and profiled the A-to-I RNA editome in each sample. All ten HCC samples had mutations in the CDS of ADAR2 gene (dsRNA-binding domain or catalytic domain). The consequence of these mutations converged to the elevation of ADAR2 efficiency as reflected by the global increase of RNA editing levels in HCC. The up-regulated editing sites (UES) were enriched in the CDS and UTR of oncogenes and tumor suppressor genes (TSG), indicating the possible roles of these target genes in HCC oncogenesis. We present the mutation-ADAR2-UES-oncogene/TSG-HCC axis that explains how mutations at different layers would finally lead to abnormal phenotype. In the light of central dogma, our work provides novel insights into how to fully take advantage of the transcriptome data to decipher the consequence of mutations.

The first mitogenome of Lauraceae (Cinnamomum chekiangense)

•The first reported mitochondrial genome (Cinnamomum chekiangense) of the Lauraceae family.•The mitogenome of C. chekiangense retains almost all of the ancestral protein-coding genes and has the highest RNA editing number in angiosperms.•Both of the plastid and mitochondrial phylogenetic trees support the magnoliids as a sister group of monocots and eudicots.

Unraveling C-to-U RNA editing events from direct RNA sequencing

In mammals, RNA editing events involve the conversion of adenosine (A) in inosine (I) by ADAR enzymes or the hydrolytic deamination of cytosine (C) in uracil (U) by the APOBEC family of enzymes, mostly APOBEC1. RNA editing has a plethora of biological functions, and its deregulation has been associated with various human disorders. While the large-scale detection of A-to-I is quite straightforward using the Illumina RNAseq technology, the identification of C-to-U events is a non-trivial task. This difficulty arises from the rarity of such events in eukaryotic genomes and the challenge of distinguishing them from background noise. Direct RNA sequencing by Oxford Nanopore Technology (ONT) permits the direct detection of Us on sequenced RNA reads. Surprisingly, using ONT reads from wild-type (WT) and APOBEC1-knock-out (KO) murine cell lines as well as in vitro synthesized RNA without any modification, we identified a systematic error affecting the accuracy of the Cs call, thereby leading to incorrect identifications of C-to-U events. To overcome this issue in direct RNA reads, here we introduce a novel machine learning strategy based on the isolation Forest (iForest) algorithm in which C-to-U editing events are considered as sequencing anomalies. Using in vitro synthesized and human ONT reads, our model optimizes the signal-to-noise ratio improving the detection of C-to-U editing sites with high accuracy, over 90% in all samples tested. Our results suggest that iForest, known for its rapid implementation and minimal memory requirements, is a promising tool to denoise ONT reads and reliably identify RNA modifications.

An orthology-based methodology as a complementary approach to retrieve evolutionarily conserved A-to-I RNA editing sites

Adar-mediated adenosine-to-inosine (A-to-I) mRNA editing is a conserved mechanism that exerts diverse regulatory functions during the development, evolution, and adaptation of metazoans. The accurate detection of RNA editing sites helps us understand their biological significance. In this work, with an improved genome assembly of honeybee (Apis mellifera), we used a new orthology-based methodology to complement the traditional pipeline of (de novo) RNA editing detection. Compared to the outcome of traditional pipeline, we retrieved many novel editing sites in CDS that are deeply conserved between honeybee and other distantly related insects. The newly retrieved sites were missed by the traditional de novo identification due to the stringent criteria for controlling false-positive rate. Caste-specific editing sites are identified, including an Ile>Met auto-recoding site in Adar. This recoding was even conserved between honeybee and bumblebee, suggesting its putative regulatory role in shaping the phenotypic plasticity of eusocial Hymenoptera. In summary, we proposed a complementary approach to the traditional pipeline and retrieved several previously unnoticed CDS editing sites. From both technical and biological aspects, our works facilitate future researches on finding the functional editing sites and advance our understanding on the connection between RNA editing and the great phenotypic diversity of organisms.

The impacts of thermal heterogeneity across microhabitats on post-settlement selection of intertidal mussels

Rapid genetic selection is critical for allowing natural populations to adapt to different thermal environments such as those that occur across intertidal microhabitats with high degrees of thermal heterogeneity. To address the question of how thermal regimes influence selection and adaptation in the intertidal black mussel Mytilisepta virgata, we continuously recorded environmental temperatures in both tidal pools and emergent rock microhabitats and then assessed genetic differentiation, gene expression patterns, RNA editing level, and cardiac performance. Our results showed that the subpopulations in the tidal pool and on emergent rocks had different genetic structures and exhibited different physiological and molecular responses to high-temperature stress. These results indicate that environmental heterogeneity across microhabitats is important for driving genetic differentiation and shed light on the importance of post-settlement selection for adaptively modifying the genetic composition and thermal responses of these intertidal mussels.

Identification and Interpretation of A-to-I RNA Editing Events in Insect Transcriptomes

Adenosine-to-inosine (A-to-I) RNA editing is the most prevalent RNA modification in the nervous systems of metazoans. To study the biological significance of RNA editing, we first have to accurately identify these editing events from the transcriptome. The genome-wide identification of RNA editing sites remains a challenging task. In this review, we will first introduce the occurrence, regulation, and importance of A-to-I RNA editing and then describe the established bioinformatic procedures and difficulties in the accurate identification of these sit esespecially in small sized non-model insects. In brief, (1) to obtain an accurate profile of RNA editing sites, a transcriptome coupled with the DNA resequencing of a matched sample is favorable; (2) the single-cell sequencing technique is ready to be applied to RNA editing studies, but there are a few limitations to overcome; (3) during mapping and variant calling steps, various issues, like mapping and base quality, soft-clipping, and the positions of mismatches on reads, should be carefully considered; (4) Sanger sequencing of both RNA and the matched DNA is the best verification of RNA editing sites, but other auxiliary evidence, like the nonsynonymous-to-synonymous ratio or the linkage information, is also helpful for judging the reliability of editing sites. We have systematically reviewed the understanding of the biological significance of RNA editing and summarized the methodology for identifying such editing events. We also raised several promising aspects and challenges in this field. With insightful perspectives on both scientific and technical issues, our review will benefit the researchers in the broader RNA editing community.

Elevated A-to-I RNA editing in COVID-19 infected individuals

Given the current status of coronavirus disease 2019 (COVID-19) as a global pandemic, it is of high priority to gain a deeper understanding of the disease's development and how the virus impacts its host. Adenosine (A)-to-Inosine (I) RNA editing is a post-transcriptional modification, catalyzed by the ADAR family of enzymes, that can be considered part of the inherent cellular defense mechanism as it affects the innate immune response in a complex manner. It was previously reported that various viruses could interact with the host's ADAR enzymes, resulting in epigenetic changes both to the virus and the host. Here, we analyze RNA-seq of nasopharyngeal swab specimens as well as whole-blood samples of COVID-19 infected individuals and show a significant elevation in the global RNA editing activity in COVID-19 compared to healthy controls. We also detect specific coding sites that exhibit higher editing activity. We further show that the increment in editing activity during the disease is temporary and returns to baseline shortly after the symptomatic period. These significant epigenetic changes may contribute to the immune system response and affect adverse outcomes seen in post-viral cases.

Deep transcriptome profiling reveals limited conservation of A-to-I RNA editing in Xenopus

BACKGROUND

Xenopus has served as a valuable model system for biomedical research over the past decades. Notably, ADAR was first detected in frog oocytes and embryos as an activity that unwinds RNA duplexes. However, the scope of A-to-I RNA editing by the ADAR enzymes in Xenopus remains underexplored.

RESULTS

Here, we identify millions of editing events in Xenopus with high accuracy and systematically map the editome across developmental stages, adult organs, and species. We report diverse spatiotemporal patterns of editing with deamination activity highest in early embryogenesis before zygotic genome activation and in the ovary. Strikingly, editing events are poorly conserved across different Xenopus species. Even sites that are detected in both X. laevis and X. tropicalis show largely divergent editing levels or developmental profiles. In protein-coding regions, only a small subset of sites that are found mostly in the brain are well conserved between frogs and mammals.

CONCLUSIONS

Collectively, our work provides fresh insights into ADAR activity in vertebrates and suggest that species-specific editing may play a role in each animal's unique physiology or environmental adaptation.

Complete mitochondrial genome of Mentha spicata L. reveals multiple chromosomal configurations and RNA editing events

Mentha spicata L. is a valuable plant that yields spearmint oil, widely utilized in the pharmaceutical, chemical, and cosmetic industries. The mitochondrial genome (mitogenome) is an essential material for molecular breeding and evolution studies. Here, the mitogenome of M. spicata was assembled by combining Nanopore and Illumina reads. It consisted of a linear chromosome (Ch1) and two circular chromosomes (Ch2 and Ch3). Furthermore, we showed two pairs of repeats (R1 and R2) mediated recombinations resulting in multiple chromosomal configurations. The R1-mediated-recombination generated a large molecule formed by joining Ch2 and Ch1. Similarly, the R2-mediated-recombination generated a large molecule formed by joining Ch3 and Ch1. Then, we identified 17 mitochondrial plastid DNAs (MTPTs) by comparing the mitogenome and cpgenome. The MTPT14 was conserved in multiple species, which has undergone the same evolutionary process as the two organellar genomes among M. spicata, Hesperelaea palmeri and Castilleja paramensis. Based on the RNA-seq reads, 246 RNA editing sites were predicted, resulting in the conversion of cytosine to uracil bases. Furthermore, we successfully validated 40 out of 43 predicted sites. This project reported a complex structure of the M. spicata mitogenome resulting from repeat-mediated recombinations, which will provide valuable information for gene function study and the breeding of different varieties.

DYW cytidine deaminase domains have a long-range impact on RNA recognition by the PPR array of chimeric plant C-to-U RNA editing factors and strongly affect target selection

The protein factors for the specific C-to-U RNA editing events in plant mitochondria and chloroplasts possess unique arrays of RNA-binding pentatricopeptide repeats (PPRs) linked to carboxy-terminal cytidine deaminase DYW domains via the extension motifs E1 and E2. The E1 and E2 motifs have distant similarities to tetratricopeptide repeats known to mediate protein-protein interactions but their precise function is unclear. Here, we investigate the tolerance of PPR56 and PPR65, two functionally characterized RNA editing factors of the moss Physcomitrium patens, for the creation of chimeras by variably replacing their C-terminal protein regions. Making use of a heterologous RNA editing assay system in Escherichia coli we find that heterologous DYW domains can strongly restrict or widen the spectrum of off-targets in the bacterial transcriptome for PPR56. Surprisingly, our data suggest that these changes are not only caused by the preference of a given heterologous DYW domain for the immediate sequence environment of the cytidine to be edited but also by a long-range impact on the nucleotide selectivity of the upstream PPRs.

Genome-wide perturbations of A-to-I RNA editing dysregulated circular RNAs promoting the development of cervical cancer

Cervical cancer, the second most common female malignant tumor, seriously threatens women's health and lives. Despite the availability of the HPV vaccine, effective treatment options for cervical cancer are still lacking. New research perspectives now clarify that RNA editing dysregulation and changes in circRNA expression are jointly involved in disease pathogenesis, so molecular changes associated with circRNA and RNA editing may provide clues for the development of new therapeutic strategies for cervical cancer. In this study, we designed a series of pipelines to identify and analyze dysregulated RNA editing events in circRNAs. Our findings indicate a decrease in A-to-I RNA editing levels in cervical cancer compared to normal tissues, and editing may influence the back-splicing process of circRNAs through structural modifications of Alu elements. Moreover, our research reveals that RNA editing could modulate circRNA biogenesis by influencing RNA binding protein (RBP) binding on a transcriptome-wide scale, as well as influence the expression and coding potential of circRNAs. Importantly, we identified three RNA editing sites that could serve as potential biomarkers. In summary, our study presents a comprehensive landscape of RNA editing perturbations in circRNAs, providing new insights into the complex relationship between RNA editing and circRNA dysregulation in cervical cancer.

Genome-Wide Analysis on Driver and Passenger RNA Editing Sites Suggests an Underestimation of Adaptive Signals in Insects

Adenosine-to-inosine (A-to-I) RNA editing leads to a similar effect to A-to-G mutations. RNA editing provides a temporo-spatial flexibility for organisms. Nonsynonymous (Nonsyn) RNA editing in insects is over-represented compared with synonymous (Syn) editing, suggesting adaptive signals of positive selection on Nonsyn editing during evolution. We utilized the brain RNA editome of Drosophila melanogaster to systematically study the LD (r2) between editing sites and infer its impact on the adaptive signals of RNA editing. Pairs of editing sites (PESs) were identified from the transcriptome. For CDS PESs of two consecutive editing sites, their occurrence was significantly biased to type-3 PES (Syn-Nonsyn). The haplotype frequency of type-3 PES exhibited a significantly higher abundance of AG than GA, indicating that the rear Nonsyn site is the driver that promotes the editing of the front Syn site (passenger). The exclusion of passenger Syn sites dramatically amplifies the adaptive signal of Nonsyn RNA editing. Our study for the first time quantitatively demonstrates that the linkage between RNA editing events comes from hitchhiking effects and leads to the underestimation of adaptive signals for Nonsyn editing. Our work provides novel insights for studying the evolutionary significance of RNA editing events.

The Genome-Wide Characterization of Alternative Splicing and RNA Editing in the Development of Coprinopsis cinerea

Coprinopsis cinerea is one of the model species used in fungal developmental studies. This mushroom-forming Basidiomycetes fungus has several developmental destinies in response to changing environments, with dynamic developmental regulations of the organism. Although the gene expression in C. cinerea development has already been profiled broadly, previous studies have only focused on a specific stage or process of fungal development. A comprehensive perspective across different developmental paths is lacking, and a global view on the dynamic transcriptional regulations in the life cycle and the developmental paths is far from complete. In addition, knowledge on co- and post-transcriptional modifications in this fungus remains rare. In this study, we investigated the transcriptional changes and modifications in C. cinerea during the processes of spore germination, vegetative growth, oidiation, sclerotia formation, and fruiting body formation by inducing different developmental paths of the organism and profiling the transcriptomes using the high-throughput sequencing method. Transition in the identity and abundance of expressed genes drive the physiological and morphological alterations of the organism, including metabolism and multicellularity construction. Moreover, stage- and tissue-specific alternative splicing and RNA editing took place and functioned in C. cinerea. These modifications were negatively correlated to the conservation features of genes and could provide extra plasticity to the transcriptome during fungal development. We suggest that C. cinerea applies different molecular strategies in its developmental regulation, including shifts in expressed gene sets, diversifications of genetic information, and reversible diversifications of RNA molecules. Such features would increase the fungal adaptability in the rapidly changing environment, especially in the transition of developmental programs and the maintenance and balance of genetic and transcriptomic divergence. The multi-layer regulatory network of gene expression serves as the molecular basis of the functioning of developmental regulation.

Transcriptome-wide profiling of A-to-I RNA editing by Slic-seq

Adenosine-to-inosine (A-to-I) RNA editing is a post-transcriptional processing event involved in diversifying the transcriptome and is responsible for various biological processes. In this context, we developed a new method based on the highly selective cleavage activity of Endonuclease V against Inosine and the universal activity of sodium periodate against all RNAs to enrich the inosine-containing RNA and accurately identify the editing sites. We validated the reliability of our method in human brain in both Alu and non-Alu elements. The conserved sites of A-to-I editing in human cells (HEK293T, HeLa, HepG2, K562 and MCF-7) primarily occurs in the 3'UTR of the RNA, which are highly correlated with RNA binding and protein binding. Analysis of the editing sites between the human brain and mouse brain revealed that the editing of exons is more conserved than that in other regions. This method was applied to three neurological diseases (Alzheimer's, epilepsy and ageing) of mouse brain, reflecting that A-to-I editing sites significantly decreased in neuronal activity genes.

A-to-I RNA editing shows dramatic up-regulation in osteosarcoma and broadly regulates tumor-related genes by altering microRNA target regions

A-to-I RNA editing is a prevalent type of RNA modification in animals. The dysregulation of RNA editing has led to multiple human cancers. However, the role of RNA editing has never been studied in osteosarcoma, a complex bone cancer with unknown molecular basis. We retrieved the RNA-sequencing data from 24 primary osteosarcoma patients and 3 healthy controls. We systematically profiled the RNA editomes in these samples and quantitatively identified reliable differential editing sites (DES) between osteosarcoma and normal samples. RNA editing efficiency is dramatically increased in osteosarcoma, presumably due to the significant up-regulation of editing enzymes ADAR1 and ADAR2. Up-regulated DES in osteosarcoma are enriched in 3'UTRs. Strikingly, such 3'UTR sites are further enriched in microRNA binding regions of gene EMP2 and other oncogenes, abolishing the microRNA suppression on target genes. Accordingly, the expression of these tumor-promoting genes is elevated in osteosarcoma. There might be an RNA editing-dependent pathway leading to osteosarcoma. We expanded our knowledge on the potential roles of RNA editing in oncogenesis. Based on these molecular features, our work is valuable for future prognosis and diagnosis of osteosarcoma.

Benchmarking RNA Editing Detection Tools

RNA, like DNA and proteins, can undergo modifications. To date, over 170 RNA modifications have been identified, leading to the emergence of a new research area known as epitranscriptomics. RNA editing is the most frequent RNA modification in mammalian transcriptomes, and two types have been identified: (1) the most frequent, adenosine to inosine (A-to-I); and (2) the less frequent, cysteine to uracil (C-to-U) RNA editing. Unlike other epitranscriptomic marks, RNA editing can be readily detected from RNA sequencing (RNA-seq) data without any chemical conversions of RNA before sequencing library preparation. Furthermore, analyzing RNA editing patterns from transcriptomic data provides an additional layer of information about the epitranscriptome. As the significance of epitranscriptomics, particularly RNA editing, gains recognition in various fields of biology and medicine, there is a growing interest in detecting RNA editing sites (RES) by analyzing RNA-seq data. To cope with this increased interest, several bioinformatic tools are available. However, each tool has its advantages and disadvantages, which makes the choice of the most appropriate tool for bench scientists and clinicians difficult. Here, we have benchmarked bioinformatic tools to detect RES from RNA-seq data. We provide a comprehensive view of each tool and its performance using previously published RNA-seq data to suggest recommendations on the most appropriate for utilization in future studies.

Beyond a PPR-RNA recognition code: Many aspects matter for the multi-targeting properties of RNA editing factor PPR56

The mitochondrial C-to-U RNA editing factor PPR56 of the moss Physcomitrium patens is an RNA-binding pentatricopeptide repeat protein equipped with a terminal DYW-type cytidine deaminase domain. Transferred into Escherichia coli, PPR56 works faithfully on its two native RNA editing targets, nad3eU230SL and nad4eU272SL, and also converts cytidines into uridines at over 100 off-targets in the bacterial transcriptome. Accordingly, PPR56 is attractive for detailed mechanistic studies in the heterologous bacterial setup, allowing for scoring differential RNA editing activities of many target and protein variants in reasonable time. Here, we report (i) on the effects of numerous individual and combined PPR56 protein and target modifications, (ii) on the spectrum of off-target C-to-U editing in the bacterial background transcriptome for PPR56 and two variants engineered for target re-direction and (iii) on combinations of targets in tandem or separately at the 5'- and 3'-ends of large mRNAs. The latter experimentation finds enhancement of RNA editing at weak targets in many cases, including cox3eU290SF as a new candidate mitogenome target. We conclude that C-to-U RNA editing can be much enhanced by transcript features also outside the region ultimately targeted by PPRs of a plant editing factor, possibly facilitated by its enrichment or scanning along transcripts.

Lessons from discovery of true ADAR RNA editing sites in a human cell line

BACKGROUND

Conversion or editing of adenosine (A) into inosine (I) catalyzed by specialized cellular enzymes represents one of the most common post-transcriptional RNA modifications with emerging connection to disease. A-to-I conversions can happen at specific sites and lead to increase in proteome diversity and changes in RNA stability, splicing, and regulation. Such sites can be detected as adenine-to-guanine sequence changes by next-generation RNA sequencing which resulted in millions reported sites from multiple genome-wide surveys. Nonetheless, the lack of extensive independent validation in such endeavors, which is critical considering the relatively high error rate of next-generation sequencing, leads to lingering questions about the validity of the current compendiums of the editing sites and conclusions based on them.

RESULTS

Strikingly, we found that the current analytical methods suffer from very high false positive rates and that a significant fraction of sites in the public databases cannot be validated. In this work, we present potential solutions to these problems and provide a comprehensive and extensively validated list of A-to-I editing sites in a human cancer cell line. Our findings demonstrate that most of true A-to-I editing sites in a human cancer cell line are located in the non-coding transcripts, the so-called RNA 'dark matter'. On the other hand, many ADAR editing events occurring in exons of human protein-coding mRNAs, including those that can recode the transcriptome, represent false positives and need to be interpreted with caution. Nonetheless, yet undiscovered authentic ADAR sites that increase the diversity of human proteome exist and warrant further identification.

CONCLUSIONS

Accurate identification of human ADAR sites remains a challenging problem, particularly for the sites in exons of protein-coding mRNAs. As a result, genome-wide surveys of ADAR editome must still be accompanied by extensive Sanger validation efforts. However, given the vast number of unknown human ADAR sites, there is a need for further developments of the analytical techniques, potentially those that are based on deep learning solutions, in order to provide a quick and reliable identification of the editome in any sample.

Low RNA stability signifies increased post-transcriptional regulation of cell identity genes

Cell identity genes are distinct from other genes with respect to the epigenetic mechanisms to activate their transcription, e.g. by super-enhancers and broad H3K4me3 domains. However, it remains unclear whether their post-transcriptional regulation is also unique. We performed a systematic analysis of transcriptome-wide RNA stability in nine cell types and found that unstable transcripts were enriched in cell identity-related pathways while stable transcripts were enriched in housekeeping pathways. Joint analyses of RNA stability and chromatin state revealed significant enrichment of super-enhancers and broad H3K4me3 domains at the gene loci of unstable transcripts. Intriguingly, the RNA m6A methyltransferase, METTL3, preferentially binds to chromatin at super-enhancers, broad H3K4me3 domains and their associated genes. METTL3 binding intensity is positively correlated with RNA m6A methylation and negatively correlated with RNA stability of cell identity genes, probably due to co-transcriptional m6A modifications promoting RNA decay. Nanopore direct RNA-sequencing showed that METTL3 knockdown has a stronger effect on RNA m6A and mRNA stability for cell identity genes. Our data suggest a run-and-brake model, where cell identity genes undergo both frequent transcription and fast RNA decay to achieve precise regulation of RNA expression.

Profiling A-to-I RNA editing during mouse somatic reprogramming at the single-cell level

Mouse somatic cells can be reprogrammed into induced pluripotent stem cells through a highly heterogeneous process regulated by numerous biological factors, including adenosine-to-inosine (A-to-I) RNA editing. In this study, we analyzed A-to-I RNA editing sites using a single-cell RNA sequencing (scRNA-seq) dataset with high-depth and full-length coverage. Our method revealed that A-to-I RNA editing frequency varied widely at the single-cell level and underwent dynamic changes. We also found that A-to-I RNA editing level was correlated with the expression of the RNA editing enzyme ADAR1. The analysis combined with gene ontology (GO) enrichment revealed that ADAR1-dependent A-to-I editing may downregulate the expression levels of Igtp, Irgm2, Mndal, Ifi202b, and Tapbp in the early stage, to inhibit the pathways of cellular response to interferon-beta and regulation of protein complex stability to promote mesenchymal-epithelial transition (MET). Notably, we identified a negative correlation between A-to-I RNA editing frequency and the expression of certain genes, such as Nras, Ube2l6, Zfp987, and Adsl.

Striated muscle-specific base editing enables correction of mutations causing dilated cardiomyopathy

Dilated cardiomyopathy is the second most common cause for heart failure with no cure except a high-risk heart transplantation. Approximately 30% of patients harbor heritable mutations which are amenable to CRISPR-based gene therapy. However, challenges related to delivery of the editing complex and off-target concerns hamper the broad applicability of CRISPR agents in the heart. We employ a combination of the viral vector AAVMYO with superior targeting specificity of heart muscle tissue and CRISPR base editors to repair patient mutations in the cardiac splice factor Rbm20, which cause aggressive dilated cardiomyopathy. Using optimized conditions, we repair >70% of cardiomyocytes in two Rbm20 knock-in mouse models that we have generated to serve as an in vivo platform of our editing strategy. Treatment of juvenile mice restores the localization defect of RBM20 in 75% of cells and splicing of RBM20 targets including TTN. Three months after injection, cardiac dilation and ejection fraction reach wild-type levels. Single-nuclei RNA sequencing uncovers restoration of the transcriptional profile across all major cardiac cell types and whole-genome sequencing reveals no evidence for aberrant off-target editing. Our study highlights the potential of base editors combined with AAVMYO to achieve gene repair for treatment of hereditary cardiac diseases.

ADAR1-mediated RNA editing promotes B cell lymphomagenesis

Diffuse large B cell lymphoma (DLBCL) is one of the most common types of aggressive lymphoid malignancies. Here, we explore the contribution of RNA editing to DLBCL pathogenesis. We observed that DNA mutations and RNA editing events are often mutually exclusive, suggesting that tumors can modulate pathway outcomes by altering sequences at either the genomic or the transcriptomic level. RNA editing targets transcripts within known disease-driving pathways such as apoptosis, p53 and NF-κB signaling, as well as the RIG-I-like pathway. In this context, we show that ADAR1-mediated editing within MAVS transcript positively correlates with MAVS protein expression levels, associating with increased interferon/NF-κB signaling and T cell exhaustion. Finally, using targeted RNA base editing tools to restore editing within MAVS 3'UTR in ADAR1-deficient cells, we demonstrate that editing is likely to be causal to an increase in downstream signaling in the absence of activation by canonical nucleic acid receptor sensing.

Malignant A-to-I RNA editing by ADAR1 drives T-cell acute lymphoblastic leukemia relapse via attenuating dsRNA sensing

Leukemia initiating cells (LICs) are regarded as the origin of leukemia relapse and therapeutic resistance. Identifying direct stemness determinants that fuel LIC self-renewal is critical for developing targeted approaches to eliminate LICs and prevent relapse. Here, we show that the RNA editing enzyme ADAR1 is a crucial stemness factor that promotes LIC self-renewal by attenuating aberrant double-stranded RNA (dsRNA) sensing. Elevated adenosine-to-inosine (A-to-I) editing is a common attribute of relapsed T-ALL regardless of molecular subtypes. Consequently, knockdown of ADAR1 severely inhibits LIC self-renewal capacity and prolongs survival in T-ALL PDX models. Mechanistically, ADAR1 directs hyper-editing of immunogenic dsRNA and retains unedited nuclear dsRNA to avoid detection by the innate immune sensor MDA5. Moreover, we uncovered that the cell intrinsic level of MDA5 dictates the dependency on ADAR1-MDA5 axis in T-ALL. Collectively, our results show that ADAR1 functions as a self-renewal factor that limits the sensing of endogenous dsRNA. Thus, targeting ADAR1 presents a safe and effective therapeutic strategy for eliminating T-ALL LICs.

Temperature-dependent RNA editing in octopus extensively recodes the neural proteome

In poikilotherms, temperature changes challenge the integration of physiological function. Within the complex nervous systems of the behaviorally sophisticated coleoid cephalopods, these problems are substantial. RNA editing by adenosine deamination is a well-positioned mechanism for environmental acclimation. We report that the neural proteome of Octopus bimaculoides undergoes massive reconfigurations via RNA editing following a temperature challenge. Over 13,000 codons are affected, and many alter proteins that are vital for neural processes. For two highly temperature-sensitive examples, recoding tunes protein function. For synaptotagmin, a key component of Ca2+-dependent neurotransmitter release, crystal structures and supporting experiments show that editing alters Ca2+ binding. For kinesin-1, a motor protein driving axonal transport, editing regulates transport velocity down microtubules. Seasonal sampling of wild-caught specimens indicates that temperature-dependent editing occurs in the field as well. These data show that A-to-I editing tunes neurophysiological function in response to temperature in octopus and most likely other coleoids.

Meta-Analysis of Keratoconus Transcriptomic Data Revealed Altered RNA Editing Levels Impacting Keratin Genomic Clusters

Introduction

Keratoconus (KC) is an ocular disorder with a multifactorial origin. Transcriptomic analyses (RNA-seq) revealed deregulations of coding (mRNA) and non-coding RNAs (ncRNAs) in KC, suggesting that mRNA-ncRNA co-regulations can promote the onset of KC. The present study investigates the modulation of RNA editing mediated by the adenosine deaminase acting on dsRNA (ADAR) enzyme in KC.

Materials

The level of ADAR-mediated RNA editing in KC and healthy corneas were determined by two indexes in two different sequencing datasets. REDIportal was used to localize known editing sites, whereas new putative sites were de novo identified in the most extended dataset only and their possible impact was evaluated. Western Blot analysis was used to measure the level of ADAR1 in the cornea from independent samples.

Results

KC was characterized by a statistically significant lower RNA-editing level compared to controls, resulting in a lower editing frequency, and less edited bases. The distribution of the editing sites along the human genome showed considerable differences between groups, particularly relevant in the chromosome 12 regions encoding for Keratin type II cluster. A total of 32 recoding sites were characterized, 17 representing novel sites. JUP, KRT17, KRT76, and KRT79 were edited with higher frequencies in KC than in controls, whereas BLCAP, COG3, KRT1, KRT75, and RRNAD1 were less edited. Both gene expression and protein levels of ADAR1 appeared not regulated between diseased and controls.

Conclusions

Our findings demonstrated an altered RNA-editing in KC possibly linked to the peculiar cellular conditions. The functional implications should be further investigated.

The ADAR1 editome reveals drivers of editing-specificity for ADAR1-isoforms

Adenosine deaminase acting on RNA ADAR1 promotes A-to-I conversion in double-stranded and structured RNAs. ADAR1 has two isoforms transcribed from different promoters: cytoplasmic ADAR1p150 is interferon-inducible while ADAR1p110 is constitutively expressed and primarily localized in the nucleus. Mutations in ADAR1 cause Aicardi - Goutières syndrome (AGS), a severe autoinflammatory disease associated with aberrant IFN production. In mice, deletion of ADAR1 or the p150 isoform leads to embryonic lethality driven by overexpression of interferon-stimulated genes. This phenotype is rescued by deletion of the cytoplasmic dsRNA-sensor MDA5 indicating that the p150 isoform is indispensable and cannot be rescued by ADAR1p110. Nevertheless, editing sites uniquely targeted by ADAR1p150 remain elusive. Here, by transfection of ADAR1 isoforms into ADAR-less mouse cells we detect isoform-specific editing patterns. Using mutated ADAR variants, we test how intracellular localization and the presence of a Z-DNA binding domain-α affect editing preferences. These data show that ZBDα only minimally contributes to p150 editing-specificity while isoform-specific editing is primarily directed by the intracellular localization of ADAR1 isoforms. Our study is complemented by RIP-seq on human cells ectopically expressing tagged-ADAR1 isoforms. Both datasets reveal enrichment of intronic editing and binding by ADAR1p110 while ADAR1p150 preferentially binds and edits 3'UTRs.

A DddA ortholog-based and transactivator-assisted nuclear and mitochondrial cytosine base editors with expanded target compatibility

Bacterial double-stranded DNA (dsDNA) cytosine deaminase DddA_tox-derived cytosine base editor (DdCBE) and its evolved variant, DddA11, guided by transcription-activator-like effector (TALE) proteins, enable mitochondrial DNA (mtDNA) editing at TC or HC (H = A, C, or T) sequence contexts, while it remains relatively unattainable for GC targets. Here, we identified a dsDNA deaminase originated from a Roseburia intestinalis interbacterial toxin (riDddA_tox) and generated CRISPR-mediated nuclear DdCBEs (crDdCBEs) and mitochondrial CBEs (mitoCBEs) using split riDddA_tox, which catalyzed C-to-T editing at both HC and GC targets in nuclear and mitochondrial genes. Moreover, transactivator (VP64, P65, or Rta) fusion to the tail of DddA_tox- or riDddA_tox-mediated crDdCBEs and mitoCBEs substantially improved nuclear and mtDNA editing efficiencies by up to 3.5- and 1.7-fold, respectively. We also used riDddA_tox-based and Rta-assisted mitoCBE to efficiently stimulate disease-associated mtDNA mutations in cultured cells and in mouse embryos with conversion frequencies of up to 58% at non-TC targets.

Characterization of A-to-I Editing in Pigs under a Long-Term High-Energy Diet

Long-term high-energy intake has detrimental effects on pig health and elevates the risk of metabolic disease. RNA editing modifying RNA bases in a post-transcriptional process has been extensively studied for model animals. However, less evidence is available that RNA editing plays a role in the development of metabolic disorders. Here, we profiled the A-to-I editing in three tissues and six gut segments and characterized the functional aspect of editing sites in model pigs for metabolic disorders. We detected 64,367 non-redundant A-to-I editing sites across the pig genome, and 20.1% correlated with their located genes' expression. The largest number of A-to-I sites was found in the abdominal aorta with the highest editing levels. The significant difference in editing levels between high-energy induced and control pigs was detected in the abdominal aorta, testis, duodenum, ileum, colon, and cecum. We next focused on 6041 functional A-to-I sites that detected differences or specificity between treatments. We found functional A-to-I sites specifically involved in a tissue-specific manner. Two of them, located in gene SLA-DQB1 and near gene B4GALT5 were found to be shared by three tissues and six gut segments. Although we did not find them enriched in each of the gene features, in correlation analysis, we noticed that functional A-to-I sites were significantly enriched in gene 3'-UTRs. This result indicates, in general, A-to-I editing has the largest potential in the regulation of gene expression through changing the 3'-UTRs' sequence, which is functionally involved in pigs under a long-term high-energy diet. Our work provides valuable knowledge of A-to-I editing sites functionally involved in the development of the metabolic disorder.

The RNA editor ADAR2 promotes immune cell trafficking by enhancing endothelial responses to interleukin-6 during sterile inflammation

Immune cell trafficking constitutes a fundamental component of immunological response to tissue injury, but the contribution of intrinsic RNA nucleotide modifications to this response remains elusive. We report that RNA editor ADAR2 exerts a tissue- and stress-specific regulation of endothelial responses to interleukin-6 (IL-6), which tightly controls leukocyte trafficking in IL-6-inflamed and ischemic tissues. Genetic ablation of ADAR2 from vascular endothelial cells diminished myeloid cell rolling and adhesion on vascular walls and reduced immune cell infiltration within ischemic tissues. ADAR2 was required in the endothelium for the expression of the IL-6 receptor subunit, IL-6 signal transducer (IL6ST; gp130), and subsequently, for IL-6 trans-signaling responses. ADAR2-induced adenosine-to-inosine RNA editing suppressed the Drosha-dependent primary microRNA processing, thereby overwriting the default endothelial transcriptional program to safeguard gp130 expression. This work demonstrates a role for ADAR2 epitranscriptional activity as a checkpoint in IL-6 trans-signaling and immune cell trafficking to sites of tissue injury.

The Potential Regulation of A-to-I RNA Editing on Genes in Parkinson's Disease

Parkinson's disease (PD) is characterized by dopaminergic neurodegeneration and an abnormal accumulation of α-synuclein aggregates. A number of genetic factors have been shown to increase the risk of PD. Exploring the underlying molecular mechanisms that mediate PD's transcriptomic diversity can help us understand neurodegenerative pathogenesis. In this study, we identified 9897 A-to-I RNA editing events associated with 6286 genes across 372 PD patients. Of them, 72 RNA editing events altered miRNA binding sites and this may directly affect miRNA regulations of their host genes. However, RNA editing effects on the miRNA regulation of genes are more complex. They can (1) abolish existing miRNA binding sites, which allows miRNAs to regulate other genes; (2) create new miRNA binding sites that may sequester miRNAs from regulating other genes; or (3) occur in the miRNA seed regions and change their targets. The first two processes are also referred to as miRNA competitive binding. In our study, we found 8 RNA editing events that may alter the expression of 1146 other genes via miRNA competition. We also found one RNA editing event that modified a miRNA seed region, which was predicted to disturb the regulation of four genes. Considering the PD-related functions of the affected genes, 25 A-to-I RNA editing biomarkers for PD are proposed, including the 3 editing events in the EIF2AK2, APOL6, and miR-4477b seed regions. These biomarkers may alter the miRNA regulation of 133 PD-related genes. All these analyses reveal the potential mechanisms and regulations of RNA editing in PD pathogenesis.

Highly Efficient A-to-G Editing in PFFs via Multiple ABEs

Cytosine base editors (CBEs) and adenine base editors (ABEs) are recently developed CRISPR-mediated genome-editing tools that do not introduce double-strand breaks. In this study, five ABEs, ABE7.10, ABEmax, NG-ABEmax, ABE8e and NG-ABE8e, were used to generate A-to-G (T-to-C) conversions in five genome loci in porcine fetal fibroblasts (PFFs). Variable yet appreciable editing efficiencies and variable activity windows were observed in these targeting regions via these five editors. The strategy of two sgRNAs in one vector exhibited superior editing efficiency to that of using two separate sgRNA expression vectors. ABE-mediated start-codon mutation in APOE silenced its expression of protein and, unexpectedly, eliminated the vast majority of its mRNA. No off-target DNA site was detected for these editors. Substantial off-target RNA events were present in the ABE-edited cells, but no KEGG pathway was found to be significantly enriched. Our study supports that ABEs are powerful tools for A-to-G (T-to-C) point-mutation modification in porcine cells.

Mitochondrial genome of Artemisia argyi L. suggested conserved mitochondrial protein-coding genes among genera Artemisia, Tanacetum and Chrysanthemum

BACKGROUND

Artemisia argyi L., also known as mugwort, is a perennial herb whose leaves are commonly used as source of traditional medicines. However, the evolution and structure of the mitochondrial genome (mitogenome) in A. argyi remain unclear. In this study, the mitogenome of A. argyi was assembled and characterized for the first time.

RESULTS

The mitogenome of A. argyi was a circular molecule of 229,354 bp. It encodes 56 genes, including 33 protein-coding genes (PCGs), 20 tRNA genes, and three rRNA genes, and three pseudogenes. Five trans-spliced introns were observed in three PCGs namely, nad1, nad2 and nad5. Repeat analysis identified 65 SSRs, 14 tandem repeats, and 167 dispersed repeats. The A. argyi mitogenome contains 12 plastid transfer sequences from 79 bp to 2552 bp. Five conserved MTPTs were identified in all 18 Asteraceae species. Comparison of mitogenome between A. argyi and one Artemisia specie and two Chrysanthemum species showed 14 conserved gene clusters. Phylogenetic analysis with organelle genomes of A. argyi and 18 others Anthemideae plants showed inconsistent phylogenetic trees, which implied that the evolutionary rates of PCGs and rrna genes derived from mitochondrion and plastid were incongruent. The Ka/Ks ratio of the 27 shared protein-coding genes in the 18 Anthemideae species are all less than 1 indicating that these genes were under the effect of purifying selection. Lastly, a total 568 RNA editing sites in PCGs were further identified. The average editing frequency of non-synonymous changes was significantly higher than that of synonymous changes (one-sample Student's t-test, p-values≤0.05) in three tissues (root, leaf and stem).

CONCLUSIONS

In this study, the gene content, genome size, genome comparison, mitochondrial plastid sequences, dN/dS analysis of mitochondrial protein-coding genes, and RNA-editing events in A. argyi mitogenome were determined, providing insights into the phylogenetic relationships of Asteraceae plant.

Characterisation of the complete mitochondrial genome of Taraxacum mongolicum revealed five repeat-mediated recombinations

We reported the mitochondrial genome of Taraxacum mongolicum for the first time. Five pairs of repeats that can mediate recombination were validated, leading to multiple conformations of genome. Taraxacum mongolicum belongs to the Asteraceae family and has important pharmaceutical value. To explore the possible interaction between the organelle genomes, we assembled the complete mitochondrial genome (mitogenome) of T. mongolicum using Illumina and Oxford Nanopore sequencing data. This genome corresponded to a circular molecule 304,467 bp long. It encodes 52 unique genes including 31 protein-coding, 3 ribosomal RNA (rRNA) and 18 transfer RNA (tRNA) genes. In addition to the single circular conformation, the existence of alternative conformations mediated by five repetitive sequences in the mitogenome was identified and validated. Recombination mediated by the inverted repeats resulted in two conformations. Conversely, recombination mediated by the two direct repeats broke one large circular molecule into two subgenomic circular molecules. Furthermore, we identified 12 homologous fragments by comparing the sequences of mitogenome and plastome, including eight complete tRNA genes. Lastly, we identified a total of 278 RNA-editing sites in protein-coding sequences based on RNA-seq data. Among them, cox1 and nad5 gene has the most sites (21), followed by the nad2 gene with 19 sites. We successfully validated 213 predicted RNA-editing sites using PCR amplification and Sanger sequencing. This project reported the first mitogenome of T. mongolicum and demonstrated its multiple conformations generated by repeat-mediated recombination. This genome could provide critical information for the molecular breeding of T. mongolicum, and also be used as a reference genome for other species of the genus Taraxacum.

Retrospect of the Two-Year Debate: What Fuels the Evolution of SARS-CoV-2: RNA Editing or Replication Error?

Mutation is one of the mechanisms of the evolutionary divergence of an organism. Under this global COVID-19 pandemic, the fast evolution of SARS-CoV-2 became one of the most worrying issues. Some researchers believed that the hosts' RNA deamination systems (APOBECs and ADARs) are the major source of mutations and have driven the evolution of SARS-CoV-2. However, apart from RNA editing, the RDRP (RNA-dependent RNA polymerase)-mediated replication errors may also contribute to the mutation of SARS-CoV-2 (just like the single-nucleotide polymorphisms/variations in eukaryotes caused by DNA replication errors). Unfortunately, it is technically unable to distinguish RNA editing and replication errors (SNPs) in this RNA virus. Here comes a fundamental question: we indeed observed the fast evolution of SARS-CoV-2, but what exactly fuels its evolution: RNA editing or replication errors? This debate lasts for 2 years. In this piece, we will retrospect the 2-year debate on RNA editing versus SNPs.

Mitochondrial Genome Sequence of Salvia officinalis (Lamiales: Lamiaceae) Suggests Diverse Genome Structures in Cogeneric Species and Finds the Stop Gain of Genes through RNA Editing Events

Our previous study was the first to confirm that the predominant conformation of mitochondrial genome (mitogenome) sequence of Salvia species contains two circular chromosomes. To further understand the organization, variation, and evolution of Salvia mitogenomes, we characterized the mitogenome of Salvia officinalis. The mitogenome of S. officinalis was sequenced using Illumina short reads and Nanopore long reads and assembled using a hybrid assembly strategy. We found that the predominant conformation of the S. officinalis mitogenome also had two circular chromosomes that were 268,341 bp (MC1) and 39,827 bp (MC2) in length. The S. officinalis mitogenome encoded an angiosperm-typical set of 24 core genes, 9 variable genes, 3 rRNA genes, and 16 tRNA genes. We found many rearrangements of the Salvia mitogenome through inter- and intra-specific comparisons. A phylogenetic analysis of the coding sequences (CDs) of 26 common protein-coding genes (PCGs) of 11 Lamiales species and 2 outgroup taxa strongly indicated that the S. officinalis was a sister taxon to S. miltiorrhiza, consistent with the results obtained using concatenated CDs of common plastid genes. The mapping of RNA-seq data to the CDs of PCGs led to the identification of 451 C-to-U RNA editing sites from 31 PCGs of the S. officinalis mitogenome. Using PCR amplification and Sanger sequencing methods, we successfully validated 113 of the 126 RNA editing sites from 11 PCGs. The results of this study suggest that the predominant conformation of the S. officinalis mitogenome are two circular chromosomes, and the stop gain of rpl5 was found through RNA editing events of the Salvia mitogenome.

Pan-cancer investigation of C-to-U editing reveals its important role in cancer development and new targets for cancer treatment

RNA editing is prevalent in the transcriptome and is important for multiple cellular processes. C-to-U RNA editing sites (RES) are relatively rare and understudied in humans, compared to A-to-I editing. However, the functional impact of C-to-U editing in human cancers also remains elusive. Here, we conducted the first comprehensive survey of pan-cancer C-to-U RESs. Surprisingly, we found that the same subset of RESs were associated with multiple features, including patient survival, cancer stemness, tumor mutation burden (TMB), and tumor-infiltrated immune cell compositions (ICC), suggesting an RES-mediated close relationship between these features. For example, editing sites for GALM or IFI6 that led to higher expression were linked to lower survival and more cancer stemness. Also, TMB was found to be lower in prostate cancer cases with ICC-associated RESs in CAVIN1 or VWA8 or higher in prostate cancer cases with thymoma. With experimental support, we also found RESs in CST3, TPI1, or TNC that are linked to immune checkpoint blockade by anti-PD1. We also confirmed through experiments that two C-to-U RESs in CSNK2B or RPS14 had different effects on colon cancer cells. Patients with CSNK2B editing, which increased the expression of the oncogene CLDN18, had a lower response to drugs. On the other hand, drugs worked better on people who had RPS14 editing, which greatly increased ribosome production. In summary, our study demonstrated the important roles of C-to-U RESs across cancers and shed light on personalized cancer therapy.

Spatial transcriptomics reveals niche-specific enrichment and vulnerabilities of radial glial stem-like cells in malignant gliomas

Diffuse midline glioma-H3K27M mutant (DMG) and glioblastoma (GBM) are the most lethal brain tumors that primarily occur in pediatric and adult patients, respectively. Both tumors exhibit significant heterogeneity, shaped by distinct genetic/epigenetic drivers, transcriptional programs including RNA splicing, and microenvironmental cues in glioma niches. However, the spatial organization of cellular states and niche-specific regulatory programs remain to be investigated. Here, we perform a spatial profiling of DMG and GBM combining short- and long-read spatial transcriptomics, and single-cell transcriptomic datasets. We identify clinically relevant transcriptional programs, RNA isoform diversity, and multi-cellular ecosystems across different glioma niches. We find that while the tumor core enriches for oligodendrocyte precursor-like cells, radial glial stem-like (RG-like) cells are enriched in the neuron-rich invasive niche in both DMG and GBM. Further, we identify niche-specific regulatory programs for RG-like cells, and functionally confirm that FAM20C mediates invasive growth of RG-like cells in a neuron-rich microenvironment in a human neural stem cell derived orthotopic DMG model. Together, our results provide a blueprint for understanding the spatial architecture and niche-specific vulnerabilities of DMG and GBM.

Polymeric structure of the Cannabis sativa L. mitochondrial genome identified with an assembly graph model

Cannabis sativa L. belongs to the family Cannabaceae in Rosales. It has been widely used as medicines, building materials, and textiles. Elucidating its genome is critical for molecular breeding and synthetic biology study. Many studies have shown that the mitochondrial genomes (mitogenomes) and even chloroplast genomes (plastomes) had complex polymeric structures. Using the Nanopore sequencing platform, we sequenced, assembled, and analyzed its mitogenome and plastome. The resulting unitig graph suggested that the mitogenome had a complex polymeric structure. However, a gap-free, circular sequence was further assembled from the unitig graph. In contrast, a circular sequence representing the plastome was obtained. The mitogenome major conformation was 415,837 bp long, and the plastome was 153,927 bp long. To test if the repeat sequences promote recombination, which corresponds to the branch points in the structure, we tested the sequences around repeats by long-read mapping. Among 208 pairs of predicted repeats, the mapping results supported the presence of cross-over around 25 pairs of repeats. Subsequent PCR amplification confirmed the presence of cross-over around 15 of the 25 repeats. By comparing the mitogenome and plastome sequences, we identified 19 mitochondria plastid DNAs, including seven complete genes (trnW-CCA, trnP-UGG, psbJ, trnN-GUU, trnD-GUC, trnH-GUG, trnM-CAU) and nine gene fragments. Furthermore, the selective pressure analysis results showed that five genes (atp1, ccmB, ccmC, cox1, nad7) had 19 positively selected sites. Lastly, we predicted 28 RNA editing sites. A total of 8 RNA editing sites located in the coding regions were successfully validated by PCR amplification and Sanger sequencing, of which four were synonymous, and four were nonsynonymous. In particular, the RNA editing events appeared to be tissue-specific in C. sativa mitogenome. In summary, we have confirmed the major confirmation of C. sativa mitogenome and characterized its structural features in detail. These results provide critical information for future variety breeding and resource development for C. sativa.

The Profiles and Functions of RNA Editing Sites Associated with High-Altitude Adaptation in Goats

High-altitude environments dramatically influenced the genetic evolution of vertebrates. However, little is known about the role of RNA editing on high-altitude adaptation in non-model species. Here, we profiled the RNA editing sites (RESs) of heart, lung, kidney, and longissimus dorsi muscle from Tibetan cashmere goats (TBG, 4500 m) and Inner Mongolia cashmere goats (IMG, 1200 m) to reveal RNA editing-related functions of high-altitude adaptation in goats. We identified 84,132 high-quality RESs that were unevenly distributed across the autosomes in TBG and IMG, and more than half of the 10,842 non-redundant editing sites were clustered. The majority (62.61%) were adenosine-to-inosine (A-to-I) sites, followed by cytidine-to-uridine (C-to-U) sites (19.26%), and 32.5% of them had a significant correlation with the expression of catalytic genes. Moreover, A-to-I and C-to-U RNA editing sites had different flanking sequences, amino acid mutations, and alternative splicing activity. TBG had higher editing levels of A-to-I and C-to-U than IMG in the kidney, whereas a lower level was found in the longissimus dorsi muscle. Furthermore, we identified 29 IMG and 41 TBG population-specific editing sites (pSESs) and 53 population-differential editing sites (pDESs) that were functionally involved in altering RNA splicing or recoding protein products. It is worth noting that 73.3% population-differential, 73.2% TBG-specific, and 80% IMG-specific A-to-I sites were nonsynonymous sites. Moreover, the pSESs and pDESs editing-related genes play critical functions in energy metabolisms such as ATP binding molecular function, translation, and adaptive immune response, which may be linked to goat high-altitude adaptation. Our results provide valuable information for understanding the adaptive evolution of goats and studying plateau-related diseases.

ADAR RNA editing on antisense RNAs results in apparent U-to-C base changes on overlapping sense transcripts

Despite hundreds of RNA modifications described to date, only RNA editing results in a change in the nucleotide sequence of RNA molecules compared to the genome. In mammals, two kinds of RNA editing have been described so far, adenosine to inosine (A-to-I) and cytidine to uridine (C-to-U) editing. Recent improvements in RNA sequencing technologies have led to the discovery of a continuously growing number of editing sites. These methods are powerful but not error-free, making routine validation of newly-described editing sites necessary. During one of these validations on DDX58 mRNA, along with A-to-I RNA editing sites, we encountered putative U-to-C editing. These U-to-C edits were present in several cell lines and appeared regulated in response to specific environmental stimuli. The same findings were also observed for the human long intergenic non-coding RNA p21 (hLincRNA-p21). A more in-depth analysis revealed that putative U-to-C edits result from A-to-I editing on overlapping antisense RNAs that are transcribed from the same loci. Such editing events, occurring on overlapping genes transcribed in opposite directions, have recently been demonstrated to be immunogenic and have been linked with autoimmune and immune-related diseases. Our findings, also confirmed by deep transcriptome data, demonstrate that such loci can be recognized simply through the presence of A-to-I and U-to-C mismatches within the same locus, reflective A-to-I editing both in the sense-oriented transcript and in the cis-natural antisense transcript (cis-NAT), implying that such clusters could be a mark of functionally relevant ADAR1 editing events.

A Bibliometric Study for Plant RNA Editing Research: Trends and Future Challenges

RNA editing is a post-transcriptional process that introduces changes in RNA sequences encoded by nuclear, mitochondrial, or plastid genomes. To understand the research progress of plant RNA editing, we comprehensively analyze the articles on plant RNA editing from 2001 to 2022 through bibliometric methods. Nucleic Acids Research, Plant Journal and Plant cell are the journals that deserve attention with their high production, total local citation scores (TLCS), and h-indexes. The USA, China, and Germany are the top three countries with highly productive publications. Ulm University, Cornell University, and Chinese Acad Sci are excellent cooperative institutions with a high level of influence in the field, and KNOOP V and TAKENAKA M are good partnership. Plant RNA editing researches concentrate on the subject categories of Biochemistry & Molecular Biology, Plant Sciences, Genetics & Heredity, etc. Plant mitochondria, genome editing and messenger-RNA may be the research hotspots in the future. The main plant RNA editing research tools are JACUSA, SPRINT, and REDO, and the main databases are REDIdb, PED, and dbRES. At present, the research streams are (1) RNA editing sites; (2) Pentapeptide repeat protein (PPR) involved in RNA editing; (3) RNA editing factors. Overall, this article summarizes the research overview of plant RNA editing until 2022 and provides theoretical implications for its possible future directions.

Profiling RNA Editing in Single Cells

RNA editing is a widespread molecular phenomenon occurring in a variety of organisms. In humans, it mainly involves the deamination of adenosine to inosine (A-to-I) in double-stranded RNAs by ADAR enzymes. A-to-I RNA editing has been investigated in different tissues as well as in diverse experimental and pathological conditions. By contrast, its biological role in single cells has not been explored in depth. Recent methodologies for cell sorting in combination with deep sequencing technologies have enabled the study of eukaryotic transcriptomes at single cell resolution, paving the way to the profiling of their epitranscriptomic dynamics.Here we describe a step-by-step protocol to detect and characterize A-to-I events occurring in publicly available single-cell RNAseq experiments from human alpha and beta pancreatic cells.

Altered RNA Editing in Atopic Dermatitis Highlights the Role of Double-Stranded RNA for Immune Surveillance

Atopic dermatitis (AD) is associated with dysregulated type 1 IFN‒mediated responses, in parallel with the dominant type 2 inflammation. However, the pathophysiology of this dysregulation is largely unknown. Adenosine-to-inosine RNA editing plays a critical role in immune regulation by preventing double-stranded RNA recognition by MDA5 and IFN activation. We studied global adenosine-to-inosine editing in AD to elucidate the role played by altered editing in the pathophysiology of this disease. Analysis of three RNA-sequencing datasets of AD skin samples revealed reduced levels of adenosine-to-inosine RNA editing in AD. This reduction was seen globally throughout Alu repeats as well as in coding genes and in specific pre-mRNA loci expected to create long double-stranded RNA, the main substrate of MDA5 leading to type I IFN activation. Consistently, IFN signature genes were upregulated. In contrast, global editing was not altered in systemic lupus erythematosus and systemic sclerosis, despite IFN activation. Our results indicate that altered editing leading to impairment of the innate immune response may be involved in the pathogenesis of AD. Possibly, it may be relevant for additional autoimmune and inflammatory diseases.

ABE8e adenine base editor precisely and efficiently corrects a recurrent COL7A1 nonsense mutation

Base editing introduces precise single-nucleotide edits in genomic DNA and has the potential to treat genetic diseases such as the blistering skin disease recessive dystrophic epidermolysis bullosa (RDEB), which is characterized by mutations in the COL7A1 gene and type VII collagen (C7) deficiency. Adenine base editors (ABEs) convert A-T base pairs to G-C base pairs without requiring double-stranded DNA breaks or donor DNA templates. Here, we use ABE8e, a recently evolved ABE, to correct primary RDEB patient fibroblasts harboring the recurrent RDEB nonsense mutation c.5047 C > T (p.Arg1683Ter) in exon 54 of COL7A1 and use a next generation sequencing workflow to interrogate post-treatment outcomes. Electroporation of ABE8e mRNA into a bulk population of RDEB patient fibroblasts resulted in remarkably efficient (94.6%) correction of the pathogenic allele, restoring COL7A1 mRNA and expression of C7 protein in western blots and in 3D skin constructs. Off-target DNA analysis did not detect off-target editing in treated patient-derived fibroblasts and there was no detectable increase in A-to-I changes in the RNA. Taken together, we have established a highly efficient pipeline for gene correction in primary fibroblasts with a favorable safety profile. This work lays a foundation for developing therapies for RDEB patients using ex vivo or in vivo base editing strategies.

U-to-C RNA editing by synthetic PPR-DYW proteins in bacteria and human culture cells

Programmable RNA editing offers significant therapeutic potential for a wide range of genetic diseases. Currently, several deaminase enzymes, including ADAR and APOBEC, can perform programmable adenosine-to-inosine or cytidine-to-uridine RNA correction. However, enzymes to perform guanosine-to-adenosine and uridine-to-cytidine (U-to-C) editing are still lacking to complete the set of transition reactions. It is believed that the DYW:KP proteins, specific to seedless plants, catalyze the U-to-C reactions in mitochondria and chloroplasts. In this study, we designed seven DYW:KP domains based on consensus sequences and fused them to a designer RNA-binding pentatricopeptide repeat (PPR) domain. We show that three of these PPR-DYW:KP proteins edit targeted uridine to cytidine in bacteria and human cells. In addition, we show that these proteins have a 5′ but not apparent 3′ preference for neighboring nucleotides. Our results establish the DYW:KP aminase domain as a potential candidate for the development of a U-to-C editing tool in human cells.

DYW:KP domains, designed on proteins found in the mitochondria and chloroplasts of seedless plants, are fused to a designer RNA-binding pentatricopeptide repeat (PPR) domain to edit targeted uridine to cytidine in bacteria and human cells.

Exploring RNA modifications, editing, and splicing changes in hyperuricemia and gout

Hyperuricemia and gout are two of the most common metabolic disorders worldwide; their incidence is increasing with changes in lifestyle, and they are correlated with many diseases, including renal and cardiovascular diseases. The majority of studies on hyperuricemia and gout have focused on the discovery of the associated genes and their functions and on the roles of monocytes and neutrophils in the development of gout. Virtually no studies investigating the epigenomics of gout disease or exploring the clinical significance of such research have been conducted. In this study, we observed that the expression of enzymes involved in RNA modifications or RNA editing was affected in uric acid (UA)- or monosodium urate (MSU)-treated cell lines. RNA alternative splicing and splicing factors were also affected by UA or MSU treatment. We used transcriptome sequencing to analyze genome-wide RNA splicing and RNA editing and found significant changes in RNA splicing and RNA editing in MSU- or UA-treated THP-1 and HEK293 cells. We further found significant changes of RNA modifications, editing, and splicing in patients with gout. The data indicate that RNA modifications, editing, and splicing play roles in gout. The findings of this study may help to understand the mechanism of RNA splicing and modifications in gout, facilitating the development of new diagnostic and therapeutic strategies.