Mark Helm

Analysis of RNA modifications by liquid chromatography-tandem mass spectrometry.

The analysis of RNA modifications is of high importance in order to address a wide range of biological questions. Therefore, a highly sensitive and accurate method such as liquid chromatography-tandem mass spectrometry (LC-MS/MS) has to be available. By using different LC-MS/MS procedures, it is not only possible to quantify very low amounts of RNA modifications, but also to detect probably unknown modified nucleosides. For these cases the dynamic multiple reaction monitoring and the neutral loss scan are the most common techniques. Here, we provide the whole workflow for analyzing RNA samples regarding their modification content. This includes an equipment list, the preparation of required solutions/enzymes and the creation of an internal standard or nucleoside stocks for internal or external calibration. Furthermore, we describe the preparation of RNA samples for the subsequent LC-MS/MS analysis and the corresponding analysis process.

High-throughput sequencing for 1-methyladenosine (m1A) mapping in RNA

Detection and mapping of modified nucleotides in RNAs is a difficult and laborious task. Several physico-chemical approaches based on differential properties of modified nucleotides can be used, however, most of these methods do not allow high-throughput analysis. Here we describe in details a method for mapping of rather common 1-methyladenosine (m(1)A) residues using high-throughput next generation sequencing (NGS). Since m(1)A residues block primer extension during reverse transcription (RT), the accumulation of abortive products as well as the nucleotide misincorporation can be detected in the sequencing data. The described library preparation protocol allows to capture both types of cDNA products essential for further bioinformatic analysis. We demonstrate that m(1)A residues produce characteristic arrest and mismatch rates and combination of both can be used for their detection as well as for discrimination of m(1)A from other modified A residues present in RNAs.

In vitro tRNA methylation assay with the Entamoeba histolytica DNA and tRNA methyltransferase Dnmt2 (Ehmeth) enzyme.

Protozoan parasites are among the most devastating infectious agents of humans responsible for a variety of diseases including amebiasis, which is one of the three most common causes of death from parasitic disease. The agent of amebiasis is the amoeba parasite Entamoeba histolytica that exists under two stages: the infective cyst found in food or water and the invasive trophozoite living in the intestine. The clinical manifestations of amebiasis range from being asymptomatic to colitis, dysentery or liver abscesses. E. histolytica is one of the rare unicellular parasite with 5-methylcytosine (5mC) in its genome. It contains a single DNA methyltransferase, Ehmeth, that belongs to the Dnmt2 family. A role for Dnmt2 in the control of repetitive elements has been established in E. histolytica, Dictyostelium discoideum and Drosophila. Our recent work has shown that Ehmeth methylates tRNA(Asp), and this finding indicates that this enzyme has a dual DNA/tRNA(Asp) methyltransferase activity. This observation is in agreement with the dual activity that has been reported for D. discoideum and D. melanogaster. The functional significance of the DNA/tRNA specificity of Dnmt2 enzymes is still unknown. To address this question, a method to determine the tRNA methyltransferase activity of Dnmt2 proteins was established. In this video, we describe a straightforward approach to prepare an adequate tRNA substrate for Dnmt2 and a method to measure its tRNA methyltransferase activity.

RNA Intramolecular Dynamics by Single‐Molecule FRET

Investigation of single RNA molecules using fluorescence resonance energy transfer (FRET) is a powerful approach to investigate dynamic and thermodynamic aspects of the folding process of a given RNA. Its application requires interdisciplinary work from the fields of chemistry, biochemistry, and physics. The present work gives detailed instructions on the synthesis of RNA molecules labeled with two fluorescent dyes interacting by FRET, as well as on their investigation by single‐molecule fluorescence spectroscopy. Curr. Protoc. Nucleic Acid Chem. 34:11.12.1‐11.12.22.

FRET Imaging of Cells Transfected with siRNA/Liposome Complexes

By monitoring the efficiency of fluorescence resonance energy transfer of dyes attached to the different strands of siRNA, the structural integrity of the latter can be traced inside cells. Here, the experimental details of dye-labeled siRNA construction, tissue culture, and transfection with liposomally formulated siRNAs are given, as well as the conditions for confocal microscopy and an algorithm allowing the visualization of intact siRNA after image data treatment. The method allows rapid screening of different liposomal siRNA formulations, obtained by small scale dual asymmetric centrifugation with high entrapping efficiency.

A Post-Labeling Approach for the Characterization and Quantification of RNA Modifications Based on Site-Directed Cleavage by DNAzymes

Deoxyribozymes or DNAzymes are small DNA molecules with catalytic activity originating from in vitro selection experiments. Variants of the two most popular DNAzymes with RNase activity, the 10-23 DNAzyme and the 8-17 DNAzyme, promote efficient in vitro cleavage of the phosphodiester bond in at least 11 out of 16 possible dinucleotide permutations. Judicious choice of the sequences flanking the active core of the DNAzymes permits to direct cleavage activity with high sequence specificity. Here, the harnessing of these features for the analysis of RNA nucleotide modifications by a post-labeling approach is described in detail. DNAzymes are designed such that RNase cleavage is directed precisely to the 5 end of the nucleotide to be analyzed. Iterative complex formation of DNAzyme and RNA substrate and subsequent cleavage are performed by temperature cycling. The DNAzyme activity liberates the analyte nucleotide on the very 5-end of an RNA fragment, whose hydroxyl group can be conveniently phosphorylated with (32)P. The labeled RNA is digested to mononucleotides, and analyzed by thin layer chromatography.

Recognition of Specified RNA Modifications by the Innate Immune System.

Microbial nucleic acids have been described as important activators of human innate immune responses by triggering so-called pattern recognition receptors (PRRs) that are expressed on innate immune cells, including plasmacytoid dendritic cells and monocytes. Although host and microbial nucleic acids share pronounced chemical and structural similarities, they significantly differ in their posttranscriptional modification profile, allowing the host to discriminate between self and nonself. In this regard, ribose 2-O-methylation has been discovered as suppressor of RNA-induced PRR activation. Although 2-O-methylation occurs with higher frequencies in eukaryotic than in prokaryotic RNA, the immunosuppressive properties of 2-O-methylated nucleotides may be misused by certain bacteria as immune evasion mechanism. In the course of identifying inhibitory RNA modifications, our groups have synthesized and comparatively analyzed a series of differentially modified RNAs, so-called modivariants, for their immune stimulatory capacities. In this chapter, we will detail the protocols for the design and synthesis of RNA modivariants by molecular cut-and-paste techniques (referred to as molecular surgery) and describe testing of their immune stimulatory properties upon transfection into peripheral blood mononuclear cells.

Positioning Europe for the EPITRANSCRIPTOMICS challenge

ABSTRACT The genetic alphabet consists of the four letters: C, A, G, and T in DNA and C,A,G, and U in RNA. Triplets of these four letters jointly encode 20 different amino acids out of which proteins of all organisms are built. This system is universal and is found in all kingdoms of life. However, bases in DNA and RNA can be chemically modified. In DNA, around 10 different modifications are known, and those have been studied intensively over the past 20 years. Scientific studies on DNA modifications and proteins that recognize them gave rise to the large field of epigenetic and epigenomic research. The outcome of this intense research field is the discovery that development, ageing, and stem-cell dependent regeneration but also several diseases including cancer are largely controlled by the epigenetic state of cells. Consequently, this research has already led to the first FDA approved drugs that exploit the gained knowledge to combat disease. In recent years, the ~150 modifications found in RNA have come to the focus of intense research. Here we provide a perspective on necessary and expected developments in the fast expanding area of RNA modifications, termed epitranscriptomics.

Regulatory RNAs and beyond

The dynamic regulation of biological processes by RNA has emerged as a key field in recent years, and was the topic of the 62nd Mosbacher Colloquium of the German Society for Biochemistry and Molecular Biology (GBM). The 2011 Colloquium, held in April in the romantic Neckar-river region, was also a celebration of the tenth anniversary of the RNA Biochemistry study group within the GBM, which acts as platform for RNA biologists and chemists within Germany and in other European countries.

LC-MS Analysis of Methylated RNA

The detection and quantification of methylated RNA can be beneficial to understand certain cellular regulation processes such as transcriptional modulation of gene expression, immune response, or epigenetic alterations. Therefore, it is necessary to have methods available, which are extremely sensitive and accurate, for instance liquid chromatography-tandem mass spectrometry (LC-MS/MS). Here, we describe the preparation of RNA samples by enzymatic hydrolysis and the subsequent analysis of ribonucleosides by LC-MS/MS via NLS (Neutral loss scan) and DMRM (Dynamic multiple reaction monitoring). Also, we provide variations of these methods including chromatographic techniques and different kinds of quantification.