Project description:N6-methyladenosine (m6A) is the most abundant modified base in eukaryotic mRNA and has been linked to diverse effects on mRNA fate and function. Current m6A mapping approaches rely on immunoprecipitation of m6A-containing RNA fragments to identify regions of transcripts that contain m6A. This approach localizes m6A residues to 100-200 nt-long regions of transcripts. The precise position of m6A in mRNAs cannot be identified on a transcriptome-wide level because there are no chemical methods to distinguish between m6A and adenosine. Here we show that anti-m6A antibodies can induce specific mutational signatures at m6A residues after ultraviolet light-induced antibody-RNA crosslinking and reverse transcription. Similarly, we find these antibodies induce mutational signatures at N6, 2’-O-dimethyladenosine (m6Am), a nucleotide found at the first encoded position of certain mRNAs. Using these mutational signatures, we map m6A and m6Am at single-nucleotide resolution in human and mouse mRNA and identify snoRNAs as a novel class of m6A-containing ncRNAs. UV-crosslinking and immunoprecipitation with m6A-specific antibodies was used to map m6A and m6Am in cellular RNA with single nucleotide resolution.
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.
Project description:we performed infrared crosslinking immunoprecipitation followed by sequencing (irCLIP-seq) (Zarnegar et al., 2016) for Rbm15 to directly map its binding sites on RNA. As a principle of concept, the cells were engineered to simultaneously express emGFP-Rbm15 and Xist RNA together, as Rbm15 strongly interacts with Xist A-repeat to deposit the m6A methylation downstream. Cross-linking induced truncation site (CITS or RT stops) is the main signature occurring at our irCLIP-seq datasets. RNA meta-profile plot against normalized transcripts shows that these CITSs reside across the transcript, with 2 main peaks in transcript starts and near the stop-codon regions, in agreement with the RBM15/15B binding profile in human cells (Patil et al., 2016).Motif analysis against CITSs revealed that Rbm15 binding sites prefer U-rich stretches, namely 3 or 4 consecutive Us. This is also true for crosslinking induced mutations (CIMS).
Project description:N6-methyladenosine (m6A) is a widespread internal RNA modification whose function is poorly understood. Here we report that m6A residues within the 5'UTR promote a novel form of cap-independent translation which is mediated through an interaction between m6A residues and the translation initiation factor, eIF3. We present eIF3a PAR-iCLIP data which demonstrate that eIF3 predominantly binds mRNAs within the 5'UTR. eIF3 binding sites are also in proximity to m6A residues within the 5'UTR of cellular mRNAs. Two replicates of eIF3a PAR-iCLIP in HEK293T cells.
Project description:We have developed a modified eCLIP-based method (meCLIP) to identify m6A residues at single-nucleotide resolution. By coupling the improvements of eCLIP with an easy-to-use computational pipeline, we have successfully identified over 50,000 unique m6A residues in the two breast cancer cell lines that were analyzed (MCF-7 and MDA-MB-231) and over 8,000 unique residues in HEK-293 cells. We compared these residues to the sites called using the currently most utilized m6A identification method (miCLIP).
Project description:We developed a novel approach, m6A-seq, for high-resolution mapping of the transcriptome-wide m6A landscape, based on antibody-mediated capture followed by massively parallel sequencing. Identification of m6A modified sequences in HepG2 cells.