M6A level and isoform characterization sequencing (m6A-LAIC-seq) reveal the census and complexity of the m6A epitranscriptome
ABSTRACT: N6-methyladenosine (m6A) is a widespread reversible chemical modification of RNAs, implicated in many aspects of RNA metabolism. Little quantitative information exists as to either how many transcript copies of particular genes are m6A modified (“m6A levels”), or the relationship of m6A modification(s) to alternative RNA isoforms. To deconvolute the m6A epitranscriptome, we developed m6A level and isoform-characterization sequencing (m6A-LAIC-seq). We found that cells exhibit a broad range of non-stoichiometric m6A levels with cell type specificity. At the level of isoform characterization, we discovered widespread differences in use of tandem alternative polyadenylation (APA) sites by methylated and nonmethylated transcript isoforms of individual genes. Strikingly, there is a strong bias for methylated transcripts to be coupled with proximal APA sites, resulting in shortened 3’ untranslated regions (3’-UTRs), while nonmethylated transcript isoforms tend to use distal APA sites. m6A-LAIC-seq yields a new perspective on transcriptome complexity and links APA usage to m6A modifications. m6A-LAIC-seq of H1-ESC and GM12878 cell lines, each cell line has two replicates
Project description:Alternative cleavage and polyadenylation (APA) is emerging as an important mechanism of gene regulation in eukaryotes and plays important regulatory roles in human development and diseases. Despite the widespread application of Second Generation Sequencing (SGS) technology for polyadenylation site identification, matching each identified polyadenylation site within a gene to its derived isoform remains a major challenge. To achieve the isoform-resolved APA analysis, we developed a tool termed “IDP-APA” that constructs truly expressed isoforms and identifies polyadenylation sites by integrating the respective strengths of Third Generation Sequencing (TGS) long reads and SGS short reads. Compared to existing tools, IDP-APA demonstrated superior performance in both isoform reconstruction and polyadenylation site identification. Applications to human embryonic stem cells, breast cancer cells and brain tissue from a patient with Alzheimer’s disease revealed prevalent APA events and cell-/tissue-specific APA patterns, especially in an isoform-resolved way. Overall design: Construct expressed isoform and analyze APA events in two human samples with TGS (PacBio) long read and SGS (Illumina) short read data: human embryonic stem cells (H1 cell line, H1-hESC) and brain tissue from a patient with Alzheimer’s disease (Brain-AD).
Project description:Polyomaviruses are a family of small DNA tumor viruses that includes several pathogenic human members, including Merkel cell polyomavirus, BK virus and JC virus. As is characteristic of DNA tumor viruses, gene expression in polyomaviruses is temporally regulated into an early phase, consisting of the viral regulatory proteins, and a late phase, consisting of the viral structural proteins. Previously, the late transcripts expressed by the prototypic polyomavirus simian virus 40 (SV40) were reported to contain several adenosines bearing methyl groups at the N6 position (m6A), although the precise location of these m6A residues, and their phenotypic effects, have not been investigated. Here, we first demonstrate that overexpression of the key m6A reader protein YTHDF2 induces more rapid viral replication, and larger viral plaques, in SV40 infected BSC40 cells, while mutational inactivation of the endogenous YTHDF2 gene, or the m6A methyltransferase METTL3, has the opposite effect, thus suggesting a positive role for m6A in the regulation of SV40 gene expression. To directly test this hypothesis, we mapped sites of m6A addition on SV40 transcripts and identified two m6A sites on the viral early transcripts and eleven m6A sites on the late mRNAs. Using synonymous mutations, we inactivated the majority of the m6A sites on the SV40 late mRNAs and observed that the resultant viral mutant replicated more slowly than wild type SV40. Alternative splicing of SV40 late mRNAs was unaffected by the reduction in m6A residues and our data instead suggest that m6A enhances the translation of viral late transcripts. Together, these data argue that the addition of m6A residues to the late transcripts encoded by SV40 plays an important role in enhancing viral gene expression and, hence, replication. Overall design: PA-m6A-seq on SV40 RNA in BSC40 cells; GFP/YTHDF2/YTHDF3 PAR-CLIP of SV40 RNA in BSC40 cell; PA-m6A-seq validation of m6A removal by VPm mutations and corresponding WT SV40 control, in BSC40 cells; PA-m6A-seq validation of early transcript m6A mutants and WT control. The Early transcript m6A mutant validation WT control also acts as PA-m6A-seq repeat 2.
Project description:N6-methyl-adenosine (m6A) is the most abundant modification on messenger RNAs and is linked to human diseases, but its functions in mammalian development are poorly understood. Here we reveal the evolutionary conservation and function of m6A by mapping the m6A methylome in mouse and human embryonic stem cells. Thousands of messenger and long noncoding RNAs show conserved m6A modification, including transcripts encoding core pluripotency transcription factors. m6A is enriched over 3’ untranslated regions at defined sequence motifs, and marks unstable transcripts, including transcripts turned over upon differentiation. Genetic inactivation or depletion of mouse and human Mettl3, one of the m6A methylases, led to m6A erasure on select target genes, prolonged Nanog expression upon differentiation, and impaired ESC’s exit from self-renewal towards differentiation into several lineages in vitro and in vivo. Thus, m6A is a mark of transcriptome flexibility required for stem cells to differentiate to specific lineages. Examing m6A modification differences in two different cell types
Project description:RNA modifications are integral to regulation of RNA metabolism. One such abundant mRNA modification is m6A, which impacts various aspects of RNA metabolism including splicing, transport and degradation. Current knowledge about proteins recruited to m6A to carry out these molecular processes is still limited. Here we describe a comprehensive and systematic mass spectrometry-based screening of m6A interactors in various cell types and species. Amongst the main findings, we identified G3BP1 as a protein, which is repelled by m6A and which positively regulates mRNA stability in an m6A regulated manner. Furthermore, we identified FMR1 as a novel, RNA sequence context dependent m6A reader, thus revealing a connection between an mRNA modification and an autism spectrum disorder. Collectively, our data represents a rich resource for the community and sheds further light on the complex interplay between m6A, m6A interactors and mRNA homeostasis.
Project description:By adapting UV cross-linking immune precipitation for m6A (m6A-CLIP), we developed several novel genomic approaches with single-nucleotide resolution to accurately locate tens of thousands of m6A residues in human cells and mouse brain mRNAs. We found over 70% of these residues in the last exon with a very sharp rise (six-fold) within 150-400 nucleotides of the last exon, which overlaps the beginning of many 3′ untranslated region (UTRs). The 3′ UTRs contain ~two-thirds of the last exon m6A and 40 to 45% of the total of this base modification in mRNA. Contrary to earlier studies, we found no preference for location of m6A sites in the coding sequences around STOP codons. Many mRNA 3′ UTRs contain multiple polyA sites at least some of which are subject to regulated choices when cells change growth rate or differentiation state. The m6A density is at a peak early in the 3′ UTR and gradually diminishes in the more distal region of the last exon suggesting a possible inhibitory role of the proximal m6A residues to allow polyA choice of more distal polyA sites. This possibility was supported by finding that a main switch from distal to proximal polyA site choice is associated with m6A loss after triple knockdown of the m6A methylase complex. There is a significant overlap of m6A with identified binding sites for Ago complexes that carry microRNAs known to regulate mRNA stability which might possibly represent cooperation in function. With higher accuracy of m6A identification it is now more realistic to engage in highly localized mutagenesis to more definitively identify m6A function. Overall design: Precise mapping m6A sites in mouse brain and liver tissues, human CD8 T cells and A549 cells by m6A-CLIP/IP; PolyA sites mapping by PolyA-Seq (Derti et al., 2012) in the same tissues and cells
Project description:Most eukaryotic genes express alternative polyadenylation (APA) isoforms with different lengths of 3’ untranslated region (3’UTR). Here we show arsenic stress elicits global shortening of 3’UTRs through two mechanisms. First, stress leads to immediate shortening of 3’UTR due to preferential usage of proximal cleavage and polyadenylation sites (PASs), as revealed by 3’ end sequencing of newly made RNAs that are metabolically labeled with 4-thiouridine. Second, long 3’UTR isoforms are more rapidly degraded during recovery from stress as compared to short 3’UTR isoforms, further shortening 3’UTR lengths in the cell. Using ribonucleoprotein immunoprecipitation coupled with 3’ end sequencing (3’READS+RIP), we show that the RNA-binding protein T cell-restricted intracellular antigen-1 (Tia1) preferentially interacts with long 3’UTR isoforms via U-rich elements in alternative 3’UTR sequences, and the interaction correlates with stress granule (SG) association during stress and with mRNA decay during recovery from stress, indicating SG-mediated RNA clearance mechanism post stress. Importantly, genes whose 3’UTRs are shortened by APA during stress can evade stress-induced 3’UTR size-based mRNA degradation, leading to higher transcript abundance post stress. Moreover, proliferating and differentiated cells display different extents of 3’UTR shortening after stress, indicating cell type-specific of impact of stress on the 3’UTR landscape. Together, our data indicate that 3’UTR length plays important roles in gene expression in stressed cells, and APA functions as an adaptive stress response mechanism to preserve mRNAs. Overall design: 4 RNA-seq libraries from NIH3T3 cells for gene expression analysis; 4 3'READS libraries for analysis of APA using total RNA from NIH3T3 cells treated with sodium arsenite for 1h; 6 3'READS libraries for analysis of APA time course using total RNA from NIH3T3 cells treated with sodium arsenite for 1h and recovered for different amount of time; 8 3'READS libraries for analysis of APA isoform stability using 4sU metabolic labeling in NIH3T3 cells; 8 3'READS libraries for analysis of stress response of proliferating and differented C2C12 cells using cytoplasmic RNA; 4 3'READS libraries for the analysis of APA during C2C12 cell differentiation.
Project description:We present here a photo-crosslinking-assisted m6A sequencing strategy to more accurately define sites with m6A modifications. Using this strategy, we obtained a high-resolution map of m6A in a human transcriptome. The map resembles the general distribution pattern observed previously, and reveals new m6A sites at base resolution. Our results provide insights into the relationship between the methylation regions and the binding sites of RNA-binding proteins. Overall design: Anti-m6A antibody capture and enrichment based photo-crosslinking-assisted m6A sequencing strategy
Project description:Eukaryotic genes generate multiple mRNA transcript isoforms though alternative transcription, splicing, and polyadenylation. However, the relationship between human transcript diversity and protein production is complex as each isoform can be translated differently. We fractionated a polysome profile and reconstructed transcript isoforms from each fraction, which we term Transcript Isoforms in Polysomes sequencing (TrIP-seq). Analysis of these data revealed regulatory features that control ribosome occupancy and translational output of each transcript isoform. We extracted a panel of 5′ and 3′ untranslated regions that control protein production from an unrelated gene in cells over a 100-fold range. Select 5′ untranslated regions exert robust translational control between cell lines, while 3′ untranslated regions can confer cell-type-specific expression. These results expose the large dynamic range of transcript-isoform-specific translational control, identify isoform-specific sequences that control protein output in human cells, and demonstrate that transcript isoform diversity must be considered when relating RNA and protein levels. Total cytoplasmic and eight polysomal fractions of RNA were purified from HEK 293T cells in biological duplicate. Ribosomal RNA was depleted using Ribo-Zero (Human/Mouse/Rat; Epicenter) and libraries were prepared using the TruSeq RNA v2 kit (RS-122-2001; Illumina) skipping the polyA selection step. Reads are paired-end 75bp and sequencing adapters are GATCGGAAGAGCACACGTCTGAACTCCAGTCAC (read1) and AGATCGGAAGAGCGTCGTGTAGGGAAAGAGTGT (read2).
Project description:m6A is a ubiquitous RNA modification in eukaryotes. Transcriptome-wide m6A patterns in Arabidopsis have been assayed recently. However, m6A differential patterns among organs have not been well characterized. The goal of the study is to comprehensively analyze m6A patterns of numerous types of RNAs, the relationship between transcript level and m6A methylation extent, and m6A differential patterns among organs in Arabidopsis. In total, 18 libraries were sequneced. For the 3 organs: leaf, flower and root, each organ has mRNA-Seq, m6A-Seq and Input sequenced. And each sequence has 2 replicats.
Project description:N6-methyladenosine (m6A) represents the most prevalent internal modification on messenger RNA, and requires a multicomponent m6A methyltransferase complex in mammals. How their plant counterparts determine the global m6A modification landscape and its molecular link to plant development remain elusive. Here we show that FKBP12 INTERACTING PROTEIN 37 KD (FIP37) is a core component of the m6A methyltransferase complex, which underlies control of shoot stem cell fate in Arabidopsis. The mutants lacking FIP37 exhibit massive overproliferation of shoot meristems and a transcriptome-wide loss of m6A RNA modifications. We further demonstrate that FIP37 mediates m6A RNA modification on key shoot meristem genes inversely correlated with their mRNA stability, thus confining their transcript levels to prevent shoot meristem overproliferation. Our results suggest an indispensable role of FIP37 in mediating m6A mRNA modification, which is required for maintaining the shoot meristem as a renewable source for continuously producing all aerial organs in plants. m6A-seq in Arabidopsis thaliana (Col-0) wild-type and fip37-4 LEC1:FIP37, two replicates for each sample