Project description:This is an oligonucleotide-based proof-of-concept study for a method to detect 5-hydroxymethyluracil (5hmU) in a single base-resolution on NGS platform. The method will be useful to identify the effect of 5hmU to genome functions.
Project description:Transfected siRNAs regulate numerous transcripts sharing limited complementarity to the RNA duplex. This unintended (“off-target”) silencing can hinder the use of RNAi to define gene function. Here we describe position-specific, sequence-independent chemical modifications that reduced silencing of partially-complementary transcripts by all siRNAs tested. Silencing of perfectly-matched targets was unaffected by these modifications. The chemical modification also reduced off-target phenotypes in growth inhibition studies. Key to the modification was 2’-O-methyl ribosyl substitution at position 2 in the guide strand, which reduced silencing of most off-target transcripts with complementarity to the seed region of the siRNA guide strand. The sharp position-dependence of 2’-O-methyl ribosyl modification contrasts with the broader position dependence of base pair substitutions within the seed region, suggesting a role for position 2 of the guide strand distinct from its effects on pairing to target transcripts. Keywords: Microarray analysis, chemical modification walk, dose response Overall design: Please see RNA. 2006 Jul;12(7):1197-205 for details. We used consensus genelists for clustering; please see attached tables for genelists.
Project description:Chemical probing has the power to provide insight into RNA conformation in vivo and in vitro, but interpreting the results depends on methods to detect the chemically modified nucleotides. Traditionally, the presence of modified bases was inferred from their ability to halt reverse transcriptase during primer extension and the locations of termination sites observed by electrophoresis or sequencing. More recently, modification-induced mutations have been used as a readout for chemical probing data. Given variable propensity for mismatch incorporation and read-through with different reverse transcriptases, we examined how termination and mutation events compare to each other in the same chemical probing experiments. We found that mutations and terminations induced by dimethyl sulfate probing are both specific for methylated bases, but these two measures have surprisingly little correlation and represent largely non-overlapping indicators of chemical modification data. We also show that specific biases for modified bases depend partly on local sequence context, and that different reverse transcriptases show different biases toward reading a modification as a stop or a mutation. These results support approaches that incorporate analysis of both termination and mutation events into RNA probing experiments. Overall design: Chemical probing using dimethylsulfate reactivity with structured RNAs Xist and 18S in mouse, with analysis of modification induced reverse transcriptase mutations or stops. This series contains only 18S samples.
Project description:We report the identification and quantification of Watson-Crick modifications in tRNA and rRNA through the use of high throughput sequencing. We apply the recently published DM-tRNA-Seq method to generate demethylase treated and untreated 293T samples, and using computational methods we are able to flag sites using a modification index. This index allows us to generate site-resolved information about modification that we can use to identify and quantify Watson-Crick face modifications in tRNA and rRNA. With the demethylase treated samples, we are able to validate numerous nucleotide modifications from demethylase substrates, and the absence of demethylase action also serves to aid in identification. We find numerous novel modification sites in tRNA as well as striking comparisons between tissues cultures lines. Our study reports a comprehensive analysis of the tRNA modification landscape by identifying sites of modification as well as quantifying modification levels. Overall design: Comprehensive comparative analysis of high throughput sequencing data to determine a quantitative metric of modification
Project description:Pluripotent stem cells can be generated from somatic cells by using pure chemicals.However, the cell fate dynamics and molecular events that occur during the chemical reprogramming process remain unclear. In this study, we found that the chemical reprogramming process requires the early formation of extra-embryonic endoderm (XEN)-like cells and a late transition from XEN-like cells to CiPSCs, a new route that differs from the pathway of transcription factor-induced reprogramming. Moreover, by more precisely manipulating the cell fate transition in a step-wise manner through the XEN-like state, we identified small-molecule boosters and established a robust chemical reprogramming system, with a yield up to 1,000-fold greater than that of the previously reported protocol. These findings demonstrate that chemical reprogramming is a unique and promising approach in the future manipulation of cell fates. We analyzed the gene expression profiles of intermediate cells obtained from diferent timepoints during chemical reprogramming process,using RNA-Sequencing. Embryo-derived XEN cells (eXENs), chemically-derived eXEN cell lines (CeXENs), embryonic stem cells (ESCs) and chemically-induced pluripotent stem cells (CiPSCs) are used as controls.
Project description:N6-methyladenosine (m6A) RNA methylation is the most abundant modification on mRNAs and plays important roles in various biological processes. The formation of m6A is catalyzed by a methyltransferase complex including methyltransferase like 3 (METTL3) as a key factor. However, the in vivo functions of METTL3 and m6A modification in mammalian development remain unclear. Here we show that specific inactivation of Mettl3 in mouse nervous system causes severe developmental defects in the brain. Mettl3 conditional knockout mice manifest cerebellar hypoplasia caused by drastically enhanced apoptosis of new born cerebellar granule cells (CGCs) in the external granular layer (EGL). METTL3 depletion induced loss of m6A modification causes extended RNA half-lives and aberrant splicing events, consequently leading to dysregulation of transcriptome-wide gene expression and premature CGC death. Our findings reveal a critical role of METTL3-mediated m6A in regulating the development of mammalian cerebellum. Overall design: The mRNA expression and m6A modification were analyzed in wildtype and Mettl3 conditional knockout (Nestin-Cre) mice using postnatal day 7 and day 14 mouse cerebellums.
Project description:5-Methylcytosine (5-mC) is an important DNA modification found in eukaryotes that impacts gene regulation and disease pathogenesis. Recently, 5-hydroxymethylcytosine (5-hmC), another form of DNA modification, has been identified in substantial amounts in certain mammalian cell types; however, its roles as well as its distribution in mammalian genomes are unknown. Here we present a selective chemical labeling method for 5-hmC by utilizing T4 bacteriophage BGT-glucosyltransferase to transfer an engineered glucose moiety containing an azide group onto the hydroxyl group of 5-hmC, which in turn can chemically incorporate a biotin group for detection, affinity enrichment, and sequencing of 5-hmC in mammalian genomes. Using this highly effective method, we demonstrate that 5-hmC is present in human cell lines beyond those previously recognized. We also find a gene expression level-dependent enrichment of intragenic 5-hmC in mouse cerebellum and an age-dependent acquisition of this modification in specific gene bodies linked to neurodegenerative disorders Identification of 5hmC enriched genmoic regions in mouse cerebellum
Project description:During the bloodstream stage of the Trypanosoma brucei lifecycle, the parasite exists as the proliferative slender-form or the non-proliferative, transmissible, stumpy-form. The transition from the slender to stumpy-form is stimulated by a density-dependent mechanism and is important in infection dynamics, ordered antigenic variation and disease transmissibility. Here, we use a monomorphic reporter cell line in a whole-cell fluorescence-based assay to screen over 6000 small molecules from a kinase-focussed compound library for their ability to induce stumpy-like formation in a high-throughput screening programme. This identified one compound able to induce modest, yet specific, changes in gene expression indicative of a partial differentiation to stumpy forms. This not only provides a potential tool for the further understanding of stumpy formation, but also demonstrates the use of high throughput screening in the identification of compounds able to induce specific phenotypes, such as differentiation, in African trypanosomes. Examination of gene expression in response to treatment with DDD00015314.