Showing papers on "RNA published in 2019"

RNA sequencing: the teenage years

Abstract: Over the past decade, RNA sequencing (RNA-seq) has become an indispensable tool for transcriptome-wide analysis of differential gene expression and differential splicing of mRNAs. However, as next-generation sequencing technologies have developed, so too has RNA-seq. Now, RNA-seq methods are available for studying many different aspects of RNA biology, including single-cell gene expression, translation (the translatome) and RNA structure (the structurome). Exciting new applications are being explored, such as spatial transcriptomics (spatialomics). Together with new long-read and direct RNA-seq technologies and better computational tools for data analysis, innovations in RNA-seq are contributing to a fuller understanding of RNA biology, from questions such as when and where transcription occurs to the folding and intermolecular interactions that govern RNA function.

SHERLOCK: nucleic acid detection with CRISPR nucleases.

Abstract: Rapid detection of nucleic acids is integral to applications in clinical diagnostics and biotechnology. We have recently established a CRISPR-based diagnostic platform that combines nucleic acid pre-amplification with CRISPR-Cas enzymology for specific recognition of desired DNA or RNA sequences. This platform, termed specific high-sensitivity enzymatic reporter unlocking (SHERLOCK), allows multiplexed, portable, and ultra-sensitive detection of RNA or DNA from clinically relevant samples. Here, we provide step-by-step instructions for setting up SHERLOCK assays with recombinase-mediated polymerase pre-amplification of DNA or RNA and subsequent Cas13- or Cas12-mediated detection via fluorescence and colorimetric readouts that provide results in <1 h with a setup time of less than 15 min. We also include guidelines for designing efficient CRISPR RNA (crRNA) and isothermal amplification primers, as well as discuss important considerations for multiplex and quantitative SHERLOCK detection assays.

The role of m 6 A RNA methylation in human cancer

Abstract: N6-methyladenosine (m6A) is identified as the most common, abundant and conserved internal transcriptional modification, especially within eukaryotic messenger RNAs (mRNAs). M6A modification is installed by the m6A methyltransferases (METTL3/14, WTAP, RBM15/15B and KIAA1429, termed as “writers”), reverted by the demethylases (FTO and ALKBH5, termed as “erasers”) and recognized by m6A binding proteins (YTHDF1/2/3, IGF2BP1 and HNRNPA2B1, termed as “readers”). Acumulating evidence shows that, m6A RNA methylation has an outsize effect on RNA production/metabolism and participates in the pathogenesis of multiple diseases including cancers. Until now, the molecular mechanisms underlying m6A RNA methylation in various tumors have not been comprehensively clarified. In this review, we mainly summarize the recent advances in biological function of m6A modifications in human cancer and discuss the potential therapeutic strategies.

Bulk tissue cell type deconvolution with multi-subject single-cell expression reference

Abstract: Knowledge of cell type composition in disease relevant tissues is an important step towards the identification of cellular targets of disease. We present MuSiC, a method that utilizes cell-type specific gene expression from single-cell RNA sequencing (RNA-seq) data to characterize cell type compositions from bulk RNA-seq data in complex tissues. By appropriate weighting of genes showing cross-subject and cross-cell consistency, MuSiC enables the transfer of cell type-specific gene expression information from one dataset to another. When applied to pancreatic islet and whole kidney expression data in human, mouse, and rats, MuSiC outperformed existing methods, especially for tissues with closely related cell types. MuSiC enables the characterization of cellular heterogeneity of complex tissues for understanding of disease mechanisms. As bulk tissue data are more easily accessible than single-cell RNA-seq, MuSiC allows the utilization of the vast amounts of disease relevant bulk tissue RNA-seq data for elucidating cell type contributions in disease. Bulk tissue RNA-seq data reveals transcriptomic profiles but masks the contributions of different cell types. Here, the authors develop a new method for estimating cell type proportions from bulk tissue RNA-seq data guided by multi-subject single-cell expression reference.

Mechanism of Inhibition of Ebola Virus RNA-Dependent RNA Polymerase by Remdesivir.

Abstract: Remdesivir (GS-5734) is a 1′-cyano-substituted adenosine nucleotide analogue prodrug that shows broad-spectrum antiviral activity against several RNA viruses. This compound is currently under clinical development for the treatment of Ebola virus disease (EVD). While antiviral effects have been demonstrated in cell culture and in non-human primates, the mechanism of action of Ebola virus (EBOV) inhibition for remdesivir remains to be fully elucidated. The EBOV RNA-dependent RNA polymerase (RdRp) complex was recently expressed and purified, enabling biochemical studies with the relevant triphosphate (TP) form of remdesivir and its presumptive target. In this study, we confirmed that remdesivir-TP is able to compete for incorporation with adenosine triphosphate (ATP). Enzyme kinetics revealed that EBOV RdRp and respiratory syncytial virus (RSV) RdRp incorporate ATP and remdesivir-TP with similar efficiencies. The selectivity of ATP against remdesivir-TP is ~4 for EBOV RdRp and ~3 for RSV RdRp. In contrast, purified human mitochondrial RNA polymerase (h-mtRNAP) effectively discriminates against remdesivir-TP with a selectivity value of ~500-fold. For EBOV RdRp, the incorporated inhibitor at position i does not affect the ensuing nucleotide incorporation event at position i+1. For RSV RdRp, we measured a ~6-fold inhibition at position i+1 although RNA synthesis was not terminated. Chain termination was in both cases delayed and was seen predominantly at position i+5. This pattern is specific to remdesivir-TP and its 1′-cyano modification. Compounds with modifications at the 2′-position show different patterns of inhibition. While 2′-C-methyl-ATP is not incorporated, ara-ATP acts as a non-obligate chain terminator and prevents nucleotide incorporation at position i+1. Taken together, our biochemical data indicate that the major contribution to EBOV RNA synthesis inhibition by remdesivir can be ascribed to delayed chain termination. The long distance of five residues between the incorporated nucleotide analogue and its inhibitory effect warrant further investigation.

The Critical Role of RNA m6A Methylation in Cancer

Abstract: Since the identification of the first RNA demethylase and the establishment of methylated RNA immunoprecipitation-sequencing methodology 6 to 7 years ago, RNA methylation has emerged as a widespread phenomenon and a critical regulator of transcript expression. This new layer of regulation is termed “epitranscriptomics.” The most prevalent RNA methylation, N6-methyladenosine (m6A), occurs in approximately 25% of transcripts at the genome-wide level and is enriched around stop codons, in 5′- and 3′-untranslated regions, and within long internal exons. RNA m6A modification regulates RNA splicing, translocation, stability, and translation into protein. m6A is catalyzed by the RNA methyltransferases METTL3, METTL14, and METTL16 (writers), is removed by the demethylases FTO and ALKBH5 (erasers), and interacts with m6A-binding proteins, such as YTHDF1 and IGF2BP1 (readers). RNA methyltransferases, demethylases, and m6A-binding proteins are frequently upregulated in human cancer tissues from a variety of organ origins, increasing onco-transcript and oncoprotein expression, cancer cell proliferation, survival, tumor initiation, progression, and metastasis. Although RNA methyltransferase inhibitors are not available yet, FTO inhibitors have shown promising anticancer effects in vitro and in animal models of cancer. Further screening for selective and potent RNA methyltransferase, demethylase, or m6A-binding protein inhibitors may lead to compounds suitable for future clinical trials in cancer patients.

METTL3 facilitates tumor progression via an m6A-IGF2BP2-dependent mechanism in colorectal carcinoma

Abstract: Colorectal carcinoma (CRC) is one of the most common malignant tumors, and its main cause of death is tumor metastasis. RNA N6-methyladenosine (m6A) is an emerging regulatory mechanism for gene expression and methyltransferase-like 3 (METTL3) participates in tumor progression in several cancer types. However, its role in CRC remains unexplored. Western blot, quantitative real-time PCR (RT-qPCR) and immunohistochemical (IHC) were used to detect METTL3 expression in cell lines and patient tissues. Methylated RNA immunoprecipitation sequencing (MeRIP-seq) and transcriptomic RNA sequencing (RNA-seq) were used to screen the target genes of METTL3. The biological functions of METTL3 were investigated in vitro and in vivo. RNA pull-down and RNA immunoprecipitation assays were conducted to explore the specific binding of target genes. RNA stability assay was used to detect the half-lives of the downstream genes of METTL3. Using TCGA database, higher METTL3 expression was found in CRC metastatic tissues and was associated with a poor prognosis. MeRIP-seq revealed that SRY (sex determining region Y)-box 2 (SOX2) was the downstream gene of METTL3. METTL3 knockdown in CRC cells drastically inhibited cell self-renewal, stem cell frequency and migration in vitro and suppressed CRC tumorigenesis and metastasis in both cell-based models and PDX models. Mechanistically, methylated SOX2 transcripts, specifically the coding sequence (CDS) regions, were subsequently recognized by the specific m6A “reader”, insulin-like growth factor 2 mRNA binding protein 2 (IGF2BP2), to prevent SOX2 mRNA degradation. Further, SOX2 expression positively correlated with METTL3 and IGF2BP2 in CRC tissues. The combined IHC panel, including “writer”, “reader”, and “target”, exhibited a better prognostic value for CRC patients than any of these components individually. Overall, our study revealed that METTL3, acting as an oncogene, maintained SOX2 expression through an m6A-IGF2BP2-dependent mechanism in CRC cells, and indicated a potential biomarker panel for prognostic prediction in CRC.

Advantages of Single-Nucleus over Single-Cell RNA Sequencing of Adult Kidney: Rare Cell Types and Novel Cell States Revealed in Fibrosis

Abstract: Background A challenge for single-cell genomic studies in kidney and other solid tissues is generating a high-quality single-cell suspension that contains rare or difficult-to-dissociate cell types and is free of both RNA degradation and artifactual transcriptional stress responses. Methods We compared single-cell RNA sequencing (scRNA-seq) using the DropSeq platform with single-nucleus RNA sequencing (snRNA-seq) using sNuc-DropSeq, DroNc-seq, and 10X Chromium platforms on adult mouse kidney. We validated snRNA-seq on fibrotic kidney from mice 14 days after unilateral ureteral obstruction (UUO) surgery. Results A total of 11,391 transcriptomes were generated in the comparison phase. We identified ten clusters in the scRNA-seq dataset, but glomerular cell types were absent, and one cluster consisted primarily of artifactual dissociation – induced stress response genes. By contrast, snRNA-seq from all three platforms captured a diversity of kidney cell types that were not represented in the scRNA-seq dataset, including glomerular podocytes, mesangial cells, and endothelial cells. No stress response genes were detected. Our snRNA-seq protocol yielded 20-fold more podocytes compared with published scRNA-seq datasets (2.4% versus 0.12%, respectively). Unexpectedly, single-cell and single-nucleus platforms had equivalent gene detection sensitivity. For validation, analysis of frozen day 14 UUO kidney revealed rare juxtaglomerular cells, novel activated proximal tubule and fibroblast cell states, and previously unidentified tubulointerstitial signaling pathways. Conclusions snRNA-seq achieves comparable gene detection to scRNA-seq in adult kidney, and it also has substantial advantages, including reduced dissociation bias, compatibility with frozen samples, elimination of dissociation-induced transcriptional stress responses, and successful performance on inflamed fibrotic kidney.

Spatial transcriptome profiling by MERFISH reveals subcellular RNA compartmentalization and cell cycle-dependent gene expression.

Abstract: The expression profiles and spatial distributions of RNAs regulate many cellular functions. Image-based transcriptomic approaches provide powerful means to measure both expression and spatial information of RNAs in individual cells within their native environment. Among these approaches, multiplexed error-robust fluorescence in situ hybridization (MERFISH) has achieved spatially resolved RNA quantification at transcriptome scale by massively multiplexing single-molecule FISH measurements. Here, we increased the gene throughput of MERFISH and demonstrated simultaneous measurements of RNA transcripts from ∼10,000 genes in individual cells with ∼80% detection efficiency and ∼4% misidentification rate. We combined MERFISH with cellular structure imaging to determine subcellular compartmentalization of RNAs. We validated this approach by showing enrichment of secretome transcripts at the endoplasmic reticulum, and further revealed enrichment of long noncoding RNAs, RNAs with retained introns, and a subgroup of protein-coding mRNAs in the cell nucleus. Leveraging spatially resolved RNA profiling, we developed an approach to determine RNA velocity in situ using the balance of nuclear versus cytoplasmic RNA counts. We applied this approach to infer pseudotime ordering of cells and identified cells at different cell-cycle states, revealing ∼1,600 genes with putative cell cycle-dependent expression and a gradual transcription profile change as cells progress through cell-cycle stages. Our analysis further revealed cell cycle-dependent and cell cycle-independent spatial heterogeneity of transcriptionally distinct cells. We envision that the ability to perform spatially resolved, genome-wide RNA profiling with high detection efficiency and accuracy by MERFISH could help address a wide array of questions ranging from the regulation of gene expression in cells to the development of cell fate and organization in tissues.

Transcriptome-wide off-target RNA editing induced by CRISPR-guided DNA base editors

Abstract: CRISPR-Cas base-editor technology enables targeted nucleotide alterations, and is being increasingly used for research and potential therapeutic applications1,2. The most widely used cytosine base editors (CBEs) induce deamination of DNA cytosines using the rat APOBEC1 enzyme, which is targeted by a linked Cas protein-guide RNA complex3,4. Previous studies of the specificity of CBEs have identified off-target DNA edits in mammalian cells5,6. Here we show that a CBE with rat APOBEC1 can cause extensive transcriptome-wide deamination of RNA cytosines in human cells, inducing tens of thousands of C-to-U edits with frequencies ranging from 0.07% to 100% in 38-58% of expressed genes. CBE-induced RNA edits occur in both protein-coding and non-protein-coding sequences and generate missense, nonsense, splice site, and 5' and 3' untranslated region mutations. We engineered two CBE variants bearing mutations in rat APOBEC1 that substantially decreased the number of RNA edits (by more than 390-fold and more than 3,800-fold) in human cells. These variants also showed more precise on-target DNA editing than the wild-type CBE and, for most guide RNAs tested, no substantial reduction in editing efficiency. Finally, we show that an adenine base editor7 can also induce transcriptome-wide RNA edits. These results have implications for the use of base editors in both research and clinical settings, illustrate the feasibility of engineering improved variants with reduced RNA editing activities, and suggest the need to more fully define and characterize the RNA off-target effects of deaminase enzymes in base editor platforms.

m 6 A enhances the phase separation potential of mRNA

Abstract: N6-methyladenosine (m6A) is the most prevalent modified nucleotide in mRNA1,2, with around 25% of mRNAs containing at least one m6A. Methylation of mRNA to form m6A is required for diverse cellular and physiological processes3. Although the presence of m6A in an mRNA can affect its fate in different ways, it is unclear how m6A directs this process and why the effects of m6A can vary in different cellular contexts. Here we show that the cytosolic m6A-binding proteins-YTHDF1, YTHDF2 and YTHDF3-undergo liquid-liquid phase separation in vitro and in cells. This phase separation is markedly enhanced by mRNAs that contain multiple, but not single, m6A residues. Polymethylated mRNAs act as a multivalent scaffold for the binding of YTHDF proteins, juxtaposing their low-complexity domains and thereby leading to phase separation. The resulting mRNA-YTHDF complexes then partition into different endogenous phase-separated compartments, such as P-bodies, stress granules or neuronal RNA granules. m6A-mRNA is subject to compartment-specific regulation, including a reduction in the stability and translation of mRNA. These studies reveal that the number and distribution of m6A sites in cellular mRNAs can regulate and influence the composition of the phase-separated transcriptome, and suggest that the cellular properties of m6A-modified mRNAs are governed by liquid-liquid phase separation principles.

Genomic encoding of transcriptional burst kinetics

Abstract: Mammalian gene expression is inherently stochastic1,2, and results in discrete bursts of RNA molecules that are synthesized from each allele3–7. Although transcription is known to be regulated by promoters and enhancers, it is unclear how cis-regulatory sequences encode transcriptional burst kinetics. Characterization of transcriptional bursting, including the burst size and frequency, has mainly relied on live-cell4,6,8 or single-molecule RNA fluorescence in situ hybridization3,5,8,9 recordings of selected loci. Here we determine transcriptome-wide burst frequencies and sizes for endogenous mouse and human genes using allele-sensitive single-cell RNA sequencing. We show that core promoter elements affect burst size and uncover synergistic effects between TATA and initiator elements, which were masked at mean expression levels. Notably, we provide transcriptome-wide evidence that enhancers control burst frequencies, and demonstrate that cell-type-specific gene expression is primarily shaped by changes in burst frequencies. Together, our data show that burst frequency is primarily encoded in enhancers and burst size in core promoters, and that allelic single-cell RNA sequencing is a powerful model for investigating transcriptional kinetics. Allele-specific single-cell RNA sequencing provides insights into transcription kinetics, with data indicating that core promoter sequences affect burst size, whereas enhancers mainly affect burst frequency.

Nanopore native RNA sequencing of a human poly(A) transcriptome.

Abstract: High-throughput complementary DNA sequencing technologies have advanced our understanding of transcriptome complexity and regulation. However, these methods lose information contained in biological RNA because the copied reads are often short and modifications are not retained. We address these limitations using a native poly(A) RNA sequencing strategy developed by Oxford Nanopore Technologies. Our study generated 9.9 million aligned sequence reads for the human cell line GM12878, using thirty MinION flow cells at six institutions. These native RNA reads had a median length of 771 bases, and a maximum aligned length of over 21,000 bases. Mitochondrial poly(A) reads provided an internal measure of read-length quality. We combined these long nanopore reads with higher accuracy short-reads and annotated GM12878 promoter regions to identify 33,984 plausible RNA isoforms. We describe strategies for assessing 3' poly(A) tail length, base modifications and transcript haplotypes.

Organization and regulation of gene transcription.

Abstract: The regulated transcription of genes determines cell identity and function. Recent structural studies have elucidated mechanisms that govern the regulation of transcription by RNA polymerases during the initiation and elongation phases. Microscopy studies have revealed that transcription involves the condensation of factors in the cell nucleus. A model is emerging for the transcription of protein-coding genes in which distinct transient condensates form at gene promoters and in gene bodies to concentrate the factors required for transcription initiation and elongation, respectively. The transcribing enzyme RNA polymerase II may shuttle between these condensates in a phosphorylation-dependent manner. Molecular principles are being defined that rationalize transcriptional organization and regulation, and that will guide future investigations. Structural and microscopy studies of gene transcription underpin a model in which phosphorylation controls the shuttling of RNA polymerase II between promoter and gene-body condensates to regulate transcription initiation and elongation.

Long noncoding RNA LINC00336 inhibits ferroptosis in lung cancer by functioning as a competing endogenous RNA

Abstract: The regulatory loop between long noncoding RNAs (lncRNAs) and microRNAs has a dynamic role in transcriptional and translational regulation, and is involved in cancer. However, the regulatory circuitry between lncRNAs and microRNAs in tumorigenesis remains elusive. Here we demonstrate that a nuclear lncRNA LINC00336 is upregulated in lung cancer and functions as an oncogene by acting as a competing endogenous RNA (ceRNAs). LINC00336 bound RNA-binding protein ELAVL1 (ELAV-like RNA-binding protein 1) using nucleotides 1901–2107 of LINC00336 and the RRM interaction domain and key amino acids (aa) of ELAVL1 (aa 101–213), inhibiting ferroptosis. Moreover, ELAVL1 increased LINC00336 expression by stabilizing its posttranscriptional level, whereas LSH (lymphoid-specific helicase) increased ELAVL1 expression through the p53 signaling pathway, further supporting the hypothesis that LSH promotes LINC00336 expression. Interestingly, LINC00336 served as an endogenous sponge of microRNA 6852 (MIR6852) to regulate the expression of cystathionine-β-synthase (CBS), a surrogate marker of ferroptosis. Finally, we found that MIR6852 inhibited cell growth by promoting ferroptosis. These data show that the network of lncRNA and ceRNA has an important role in tumorigenesis and ferroptosis.

METTL3-mediated N6-methyladenosine modification is critical for epithelial-mesenchymal transition and metastasis of gastric cancer

Abstract: As one of the most frequent chemical modifications in eukaryotic mRNAs, N6-methyladenosine (m6A) modification exerts important effects on mRNA stability, splicing, and translation. Recently, the regulatory role of m6A in tumorigenesis has been increasingly recognized. However, dysregulation of m6A and its functions in tumor epithelial-mesenchymal transition (EMT) and metastasis remain obscure. qRT-PCR and immunohistochemistry were used to evaluate the expression of methyltransferase-like 3 (METTL3) in gastric cancer (GC). The effects of METTL3 on GC metastasis were investigated through in vitro and in vivo assays. The mechanism of METTL3 action was explored through transcriptome-sequencing, m6A-sequencing, m6A methylated RNA immunoprecipitation quantitative reverse transcription polymerase chain reaction (MeRIP qRT-PCR), confocal immunofluorescent assay, luciferase reporter assay, co-immunoprecipitation, RNA immunoprecipitation and chromatin immunoprecipitation assay. Here, we show that METTL3, a major RNA N6-adenosine methyltransferase, was upregulated in GC. Clinically, elevated METTL3 level was predictive of poor prognosis. Functionally, we found that METTL3 was required for the EMT process in vitro and for metastasis in vivo. Mechanistically, we unveiled the METTL3-mediated m6A modification profile in GC cells for the first time and identified zinc finger MYM-type containing 1 (ZMYM1) as a bona fide m6A target of METTL3. The m6A modification of ZMYM1 mRNA by METTL3 enhanced its stability relying on the “reader” protein HuR (also known as ELAVL1) dependent pathway. In addition, ZMYM1 bound to and mediated the repression of E-cadherin promoter by recruiting the CtBP/LSD1/CoREST complex, thus facilitating the EMT program and metastasis. Collectively, our findings indicate the critical role of m6A modification in GC and uncover METTL3/ZMYM1/E-cadherin signaling as a potential therapeutic target in anti-metastatic strategy against GC.

Multiplexed detection of proteins, transcriptomes, clonotypes and CRISPR perturbations in single cells

Abstract: Multimodal single-cell assays provide high-resolution snapshots of complex cell populations, but are mostly limited to transcriptome plus an additional modality. Here, we describe expanded CRISPR-compatible cellular indexing of transcriptomes and epitopes by sequencing (ECCITE-seq) for the high-throughput characterization of at least five modalities of information from each single cell. We demonstrate application of ECCITE-seq to multimodal CRISPR screens with robust direct single-guide RNA capture and to clonotype-aware multimodal phenotyping of cancer samples.

CasX enzymes comprise a distinct family of RNA-guided genome editors

Abstract: The RNA-guided CRISPR-associated (Cas) proteins Cas9 and Cas12a provide adaptive immunity against invading nucleic acids, and function as powerful tools for genome editing in a wide range of organisms. Here we reveal the underlying mechanisms of a third, fundamentally distinct RNA-guided genome-editing platform named CRISPR-CasX, which uses unique structures for programmable double-stranded DNA binding and cleavage. Biochemical and in vivo data demonstrate that CasX is active for Escherichia coli and human genome modification. Eight cryo-electron microscopy structures of CasX in different states of assembly with its guide RNA and double-stranded DNA substrates reveal an extensive RNA scaffold and a domain required for DNA unwinding. These data demonstrate how CasX activity arose through convergent evolution to establish an enzyme family that is functionally separate from both Cas9 and Cas12a.

The interplay between m6A RNA methylation and noncoding RNA in cancer

Abstract: N6-methyladenosine (m6A) methylation, one of the most common RNA modifications, has been reported to execute important functions that affect normal life activities and diseases. Most studies have suggested that m6A modification can affect the complexity of cancer progression by regulating biological functions related to cancer. M6A modification of noncoding RNAs regulates the cleavage, transport, stability, and degradation of noncoding RNAs themselves. It also regulates cell proliferation and metastasis, stem cell differentiation, and homeostasis in cancer by affecting the biological function of cells. Interestingly, noncoding RNAs also play significant roles in regulating these m6A modifications. Additionally, it is becoming increasingly clear that m6A and noncoding RNAs potentially contribute to the clinical application of cancer treatment. In this review, we summarize the effect of the interactions between m6A modifications and noncoding RNAs on the biological functions involved in cancer progression. In particular, we discuss the role of m6A and noncoding RNAs as possible potential biomarkers and therapeutic targets in the treatment of cancers.

5-methylcytosine promotes pathogenesis of bladder cancer through stabilizing mRNAs.

Abstract: Although 5-methylcytosine (m5C) is a widespread modification in RNAs, its regulation and biological role in pathological conditions (such as cancer) remain unknown. Here, we provide the single-nucleotide resolution landscape of messenger RNA m5C modifications in human urothelial carcinoma of the bladder (UCB). We identify numerous oncogene RNAs with hypermethylated m5C sites causally linked to their upregulation in UCBs and further demonstrate YBX1 as an m5C 'reader' recognizing m5C-modified mRNAs through the indole ring of W65 in its cold-shock domain. YBX1 maintains the stability of its target mRNA by recruiting ELAVL1. Moreover, NSUN2 and YBX1 are demonstrated to drive UCB pathogenesis by targeting the m5C methylation site in the HDGF 3' untranslated region. Clinically, a high coexpression of NUSN2, YBX1 and HDGF predicts the poorest survival. Our findings reveal an unprecedented mechanism of RNA m5C-regulated oncogene activation, providing a potential therapeutic strategy for UCB.

Functionally diverse type V CRISPR-Cas systems

Abstract: Type V CRISPR-Cas systems are distinguished by a single RNA-guided RuvC domain-containing effector, Cas12. Although effectors of subtypes V-A (Cas12a) and V-B (Cas12b) have been studied in detail, the distinct domain architectures and diverged RuvC sequences of uncharacterized Cas12 proteins suggest unexplored functional diversity. Here, we identify and characterize Cas12c, -g, -h, and -i. Cas12c, -h, and -i demonstrate RNA-guided double-stranded DNA (dsDNA) interference activity. Cas12i exhibits markedly different efficiencies of CRISPR RNA spacer complementary and noncomplementary strand cleavage resulting in predominant dsDNA nicking. Cas12g is an RNA-guided ribonuclease (RNase) with collateral RNase and single-strand DNase activities. Our study reveals the functional diversity emerging along different routes of type V CRISPR-Cas evolution and expands the CRISPR toolbox.

Off-target RNA mutation induced by DNA base editing and its elimination by mutagenesis

Abstract: Recently developed DNA base editing methods enable the direct generation of desired point mutations in genomic DNA without generating any double-strand breaks1-3, but the issue of off-target edits has limited the application of these methods. Although several previous studies have evaluated off-target mutations in genomic DNA4-8, it is now clear that the deaminases that are integral to commonly used DNA base editors often bind to RNA9-13. For example, the cytosine deaminase APOBEC1-which is used in cytosine base editors (CBEs)-targets both DNA and RNA12, and the adenine deaminase TadA-which is used in adenine base editors (ABEs)-induces site-specific inosine formation on RNA9,11. However, any potential RNA mutations caused by DNA base editors have not been evaluated. Adeno-associated viruses are the most common delivery system for gene therapies that involve DNA editing; these viruses can sustain long-term gene expression in vivo, so the extent of potential RNA mutations induced by DNA base editors is of great concern14-16. Here we quantitatively evaluated RNA single nucleotide variations (SNVs) that were induced by CBEs or ABEs. Both the cytosine base editor BE3 and the adenine base editor ABE7.10 generated tens of thousands of off-target RNA SNVs. Subsequently, by engineering deaminases, we found that three CBE variants and one ABE variant showed a reduction in off-target RNA SNVs to the baseline while maintaining efficient DNA on-target activity. This study reveals a previously overlooked aspect of off-target effects in DNA editing and also demonstrates that such effects can be eliminated by engineering deaminases.

LncRNA LINRIS stabilizes IGF2BP2 and promotes the aerobic glycolysis in colorectal cancer

Abstract: Long noncoding RNAs (lncRNAs) play nonnegligible roles in the epigenetic regulation of cancer cells. This study aimed to identify a specific lncRNA that promotes the colorectal cancer (CRC) progression and could be a potential therapeutic target. We screened highly expressed lncRNAs in human CRC samples compared with their matched adjacent normal tissues. The proteins that interact with LINRIS (Long Intergenic Noncoding RNA for IGF2BP2 Stability) were confirmed by RNA pull-down and RNA immunoprecipitation (RIP) assays. The proliferation and metabolic alteration of CRC cells with LINRIS inhibited were tested in vitro and in vivo. LINRIS was upregulated in CRC tissues from patients with poor overall survival (OS), and LINRIS inhibition led to the impaired CRC cell line growth. Moreover, knockdown of LINRIS resulted in a decreased level of insulin-like growth factor 2 mRNA-binding protein 2 (IGF2BP2), a newly found N6-methyladenosine (m6A) ‘reader’. LINRIS blocked K139 ubiquitination of IGF2BP2, maintaining its stability. This process prevented the degradation of IGF2BP2 through the autophagy-lysosome pathway (ALP). Therefore, knockdown of LINRIS attenuated the downstream effects of IGF2BP2, especially MYC-mediated glycolysis in CRC cells. In addition, the transcription of LINRIS could be inhibited by GATA3 in CRC cells. In vivo experiments showed that the inhibition of LINRIS suppressed the proliferation of tumors in orthotopic models and in patient-derived xenograft (PDX) models. LINRIS is an independent prognostic biomarker for CRC. The LINRIS-IGF2BP2-MYC axis promotes the progression of CRC and is a promising therapeutic target.