Project description:Nm-seq maps 2'-O-methylation sites in human mRNA with base precision The ribose of rna nucleotides can be 2′-O-methylated (nm). despite advances in high-throughput detection, the inert chemical nature of nm still limits sensitivity and precludes mapping in mrna. We leveraged the differential reactivity of 2′-O-methylated and 2′-hydroxylated nucleosides to periodate oxidation to develop nm-seq, a sensitive method for transcriptome-wide mapping of nm with base precision. nm-seq uncovered thousands of nm sites in human mrna with features suggesting functional roles.
Project description:2’-O-methylation (Nm) is a prevalent post-transcriptional RNA modification present in many cellular RNAs and plays a critical role in modulating both the physical properties and regulation of eukaryotic RNAs. Studies of Nm modifications in RNA have long been hampered by a lack of effective mapping methods. Previously reported approaches can work well for detecting Nm modifications on abundant RNAs, but face challenges when applied to low-abundant RNAs, such as mRNA, lack stoichiometric information, and are challenged by issues of RNA sample degradation due to chemical treatment. Here, we present Nm-Mut-seq, a mutation signature-based Nm mapping method, which uses a custom reverse transcriptase (RT) that installs mutations at Am, Cm, and Gm-modified sites (Um is undetectable by this method). Our work provides a much-needed approach to detect Nm at base resolution in low abundant RNAs and to estimate the stoichiometry of each modified site transcriptome-wide.
Project description:Non-coding RNAs contain dozens of chemically distinct modifications, of which only a few have been identified in mRNAs. The recent discovery that certain tRNA modifying enzymes also target mRNAs suggests the potential for many additional mRNA modifications. Here, we show that conserved tRNA 2′-O-methyltransferases Trm3, 7,13 and 44, and rRNA 2′-O-methyltransferase Spb1, interact with specific mRNA sites in yeast by crosslinking immunoprecipitation and sequencing (CLIP-seq). We developed sequencing of methylation at two prime hydroxyls (MeTH-seq) for transcriptome-wide mapping of 2′-O-methyl ribose (Nm) with single-nucleotide resolution, and discover thousands of potential Nm sites in mRNAs. Genetic analysis identified hundreds of mRNA targets for the Spb1 methyltransferase, which can target both mRNA and non-coding RNA for environmentally regulated modification. Our work identifies Nm as a prevalent mRNA modification that is likely to be conserved and provides methods to investigate its distribution and regulation.
Project description:Non-coding RNAs contain dozens of chemically distinct modifications, of which only a few have been identified in mRNAs. The recent discovery that certain tRNA modifying enzymes also target mRNAs suggests the potential for many additional mRNA modifications. Here, we show that conserved tRNA 2′-O-methyltransferases Trm3, 7,13 and 44, and rRNA 2′-O-methyltransferase Spb1, interact with specific mRNA sites in yeast by crosslinking immunoprecipitation and sequencing (CLIP-seq). We developed sequencing of methylation at two prime hydroxyls (MeTH-seq) for transcriptome-wide mapping of 2′-O-methyl ribose (Nm) with single-nucleotide resolution, and discover thousands of potential Nm sites in mRNAs. Genetic analysis identified hundreds of mRNA targets for the Spb1 methyltransferase, which can target both mRNA and non-coding RNA for environmentally regulated modification. Our work identifies Nm as a prevalent mRNA modification that is likely to be conserved and provides methods to investigate its distribution and regulation.
Project description:Topo-Seq is a ChIP-Seq-based methodology that allows high-throughput identification of topoisomerases binding (cleavage) sites with a single-base precision. On a first stage of the project DNA-gyrase binding sites on a Escherichia coli DY330 genome are investigated.
Project description:DNA methylation stabilizes developmentally programmed gene expression states. Aberrant methylation is associated with disease progression and is a common feature of cancer genomes. Presently, few methods enable quantitative, large-scale, single-base resolution mapping of DNA methylation states in desired regions of a complex mammalian genome. Here, we present an approach that combines array-based hybrid selection and massively parallel bisulfite sequencing to profile DNA methylation in genomic regions spanning hundreds of thousands of bases. This single molecule strategy enables methylation variable positions to be quantitatively examined with high sampling precision. Using bisulfite capture, we assessed methylation patterns across 324 randomly selected CpG islands (CGI) representing more than 25,000 CpG sites. A single lane of Illumina sequencing permitted methylation states to be definitively called for >90% of target sties. The accuracy of the hybrid-selection approach was verified using conventional bisulfite capillary sequencing of cloned PCR products amplified from a subset of the selected regions. This confirmed that even partially methylated states could be successfully called. A comparison of human primary and cancer cells revealed multiple differentially methylated regions. More than 25% of islands showed complex methylation patterns either with partial methylation states defining the entire CGI or with contrasting methylation states appearing in specific regional blocks within the island. We observed that transitions in methylation state often correlate with genomic landmarks, including transcriptional start sites and intron-exon junctions. Methylation, along with specific histone marks, was enriched in exonic regions, suggesting that chromatin states can foreshadow the content of mature mRNAs. Keywords: DNA methylation profiling by massively parallel sequencing Keywords: Epigenetics Targeted examination of DNA methylation in two human cell types by combining array capture and bisulfite sequencing. In addition, this study examined two histone marks in the breast tumor cell line MDA-MB-231.
Project description:N6-methyladenosine (m6A) is a common modification of mRNA, with potential roles in fine-tuning the RNA life cycle, but little is known about the pathways regulating this process and its physiological role. Here, we used mass-spectrometry to identify a dense network of proteins physically interacting with METTL3, a core component of the methyltransferase complex, and show that two of them, WTAP and KIAA1429, are required for methylation. Combining high resolution m6A-Seq with knockdown of WTAP allowed us to define accurate maps, at near single-nucleotide resolution, of sites of mRNA methylation across four dynamic programs in human and mouse, including development, differentiation, reprogramming and immune response. Internal WTAP-dependent methylation sites were largely static across the different surveyed conditions and present in the majority of mRNAs. However, methylations were found at much lower levels within highly expressed mRNAs, and methylation is inversely correlated with mRNA stability, consistent with a role in establishing an overall basal, cell-type invariant, distribution of degradation rates. In addition, we identify thousands of WTAP-independent methylation sites at transcription initiation sites, forming part of the mRNA cap structure. We show that the methylations occur at the first transcribed nucleotide, and find that thousands of transcripts are present in different isoforms differing in the methylation state of the first transcribed nucleotide, a previously unappreciated complexity of the transcriptome. Together, our data sheds new light on the proteomic and transcriptional underpinnings of this epitranscriptomic modification in mammals. Examination of m6A methylation across different knockdowns using shRNAs in mouse embryonic fibroblasts, in embyronic and adult brains, and in dendritic cell stimulated with LPS.
Project description:Various methylases and demethylases catalyze methylation and demethylation of N6-methyladenosine (m6A) and N6,2?-O-dimethyladenosine (m6Am) but precise methylomes uniquely mediated by each methylase/demethylase are still lacking. Here, we developed m6A-Crosslinking-Exonuclease-sequencing (m6ACE-seq) to map m6A and m6Am at transcriptome-wide single-base-resolution. m6ACE-seq's ability to quantify relative differences in methylation levels across samples enabled the generation of a comprehensive atlas of distinct methylomes uniquely mediated by every individual known methylase/demethylase. We determined METTL16 to indirectly impact manifold methylation targets beyond its consensus target motif, and highlighted the importance of precision in mapping PCIF1-dependent m6Am. Rather than reverse RNA methylation, we found that both ALKBH5 and FTO demethylases instead maintain their regulated sites in an unmethylated steady-state. In FTO's absence, anomalous m6Am disrupts snRNA interaction with nuclear export machinery, potentially causing aberrant pre-mRNA splicing events. We propose a model whereby RNA demethylases ensure normal RNA metabolism by suppressing disruptive RNA methylation in the nucleus.