Project description:Background: Adenosine deaminases that act on RNA (ADARs) bind to double-stranded and structured RNAs and deaminate adenosines to inosines. This A to I editing is widespread and required for normal life and development. Besides mRNAs and repetitive elements, ADARs can target miRNA precursors. Editing of miRNA precursors can affect processing efficiency and alter target specificity. Interestingly, ADARs can also influence miRNA abundance independent of RNA-editing. In mouse embryos where editing levels are low, ADAR2 was found to be the major ADAR protein that affects miRNA abundance. Here we extend our analysis to adult mouse brains where high editing levels are observed. Results: Using Illumina deep sequencing we compare the abundances of mature miRNAs and editing events within them, between wild-type and ADAR2 knockout mice in the adult mouse brain. Reproducible changes in abundance of specific miRNAs are observed in ADAR2 deficient mice. Most of these quantitative changes seem unrelated to A to I editing events. However, many A to G transitions in cDNAs prepared from mature miRNA sequences, reflecting A to I editing events in the RNA, are observed with frequencies reaching up to 80%. About half of these editing events are primarily caused by ADAR2 while a few miRNAs show increased editing in the absence of ADAR2, suggesting preferential editing by ADAR1. Moreover, novel, previously unknown editing events were identified in several miRNAs. In general 64% of all editing events are located within the seed region of mature miRNAs. In one of these cases retargeting of the edited miRNA could be verified in reporter assays. Also, altered processing efficiency upon editing near a processing site could be experimentally verified. Conclusions: ADAR2 can significantly influence the abundance of certain miRNAs in the brain. Only in a few cases changes in miRNA abundance can be explained by miRNA editing. Thus, ADAR2 binding to miRNA precursors, without editing them, may influence their processing and thereby abundance. ADAR1 and ADAR2 have both overlapping and distinct specificities for editing of miRNA editing sites. Over 60% of editing occurs in the seed region possibly changing target specificities for many edited miRNAs. Examination of the effect of ADAR2 on gene expression in mature mouse wildtype and ADAR2 knockout brain using AffymetrixM-BM-. GeneChipM-BM-. Whole Transcript (WT) Expression Arrays (Analysis by KFB Regensburg, Germany)

Project description:Background: Adenosine deaminases that act on RNA (ADARs) bind to double-stranded and structured RNAs and deaminate adenosines to inosines. This A to I editing is widespread and required for normal life and development. Besides mRNAs and repetitive elements, ADARs can target miRNA precursors. Editing of miRNA precursors can affect processing efficiency and alter target specificity. Interestingly, ADARs can also influence miRNA abundance independent of RNA-editing. In mouse embryos where editing levels are low, ADAR2 was found to be the major ADAR protein that affects miRNA abundance. Here we extend our analysis to adult mouse brains where high editing levels are observed. Results: Using Illumina deep sequencing we compare the abundances of mature miRNAs and editing events within them, between wild-type and ADAR2 knockout mice in the adult mouse brain. Reproducible changes in abundance of specific miRNAs are observed in ADAR2 deficient mice. Most of these quantitative changes seem unrelated to A to I editing events. However, many A to G transitions in cDNAs prepared from mature miRNA sequences, reflecting A to I editing events in the RNA, are observed with frequencies reaching up to 80%. About half of these editing events are primarily caused by ADAR2 while a few miRNAs show increased editing in the absence of ADAR2, suggesting preferential editing by ADAR1. Moreover, novel, previously unknown editing events were identified in several miRNAs. In general 64% of all editing events are located within the seed region of mature miRNAs. In one of these cases retargeting of the edited miRNA could be verified in reporter assays. Also, altered processing efficiency upon editing near a processing site could be experimentally verified. Conclusions: ADAR2 can significantly influence the abundance of certain miRNAs in the brain. Only in a few cases changes in miRNA abundance can be explained by miRNA editing. Thus, ADAR2 binding to miRNA precursors, without editing them, may influence their processing and thereby abundance. ADAR1 and ADAR2 have both overlapping and distinct specificities for editing of miRNA editing sites. Over 60% of editing occurs in the seed region possibly changing target specificities for many edited miRNAs.

Project description:ADARs, short for adenosine deaminases acting on RNA, were first found by their characteristic activity of deaminating up to 50% of all adenosines in double-stranded RNA in vitro. C. elegans has two ADARs, only one is found in the fly, and mammals express three ADARs. Importantly, the spectrum of physiological roles of these enzymes in the different organisms remains largely unknown. ADARs are ~750-1150 amino acids in size, feature 2-3 N-terminal double-stranded RNA binding motifs, an enzymatic domain related to that of prokaryotic cytidine deaminases, and a ~190 residue extended C-terminal domain of unknown function. The mammalian ADARs are detectable in many if not all tissues, with relatively prominent expression in the central nervous system, predicting tissue- or cell type-specific tasks for the mammalian ADARs. Studies over the last decade collectively indicated that one function of ADARs is the editing of nuclear transcripts to introduce select amino acid substitutions in proteins. Arguably the best-studied example for this type of RNA editing (‘A-to-I editing’) in the mammal is performed by ADAR2 and occurs in primary transcripts for the GluA2 subunit (also known as GluR-B or GluR2 subunit) of AMPA receptors mediating fast excitatory neurotransmission. A particular glutamine codon (CAG) in the exonic sequence for the inner lining of the glutamate-activated AMPA receptor is converted by deamination of the central adenosine into an unusual arginine codon (CIG; the resultant inosine is seen as guanosine by the protein translation machinery). This substitution of the gene-encoded glutamine codon by the edited arginine codon is found in nearly 100% of all GluA2 cDNA derived from brain mRNA. RNA editing in this instance ensures that GluA2-containing AMPA receptors become impermeable to Ca2+. In addition to switching a key functional determinant in GluA2 to nearly 100%, ADAR2 has been implicated in generating numerous amino acid substitutions at lower levels in various mammalian neurotransmitter receptors and voltage-gated ion channels, primarily but not exclusively of nervous tissue. Most of these substitutions elicit distinct functional consequences, which led to the notion that site-selective RNA editing by ADAR2 may ensure the functional fine-tuning of the affected transmembrane proteins. Such fine-tuning should reflect the expansion of the protein sequence directed by the respective gene into sequence subpopulations, each differing in particular functional aspects, such as transmitter efficacy, desensitization, or voltage threshold. If this notion is correct, ADAR2 knockout should elicit phenotypes, which might range from subtle to severe, depending on the physiological role(s) of the ADAR2 targets in different tissues. ADAR2 knockout mice, however, die soon after birth from severe epileptic seizures, a consequence of the changed ion conductance properties of AMPA receptors containing unedited GluA2. Fortunately, mice lacking ADAR2 are robust and have normal life span if they carry GluA2 alleles genetically altered to contain the particular arginine codon for a Ca2+ impermeable ion channel pore of AMPA receptors, thus rescinding the need for ADAR2-mediated GluA2 transcript editing. These mice are thus eminently suitable to study the phenotypic consequences of failure to edit all ADAR2 targets excepting GluA2. We therefore tested cohorts of ADAR2-/-/GluA2(R)/(R) mice in 16 well-established paradigms for central and peripheral phenotypic abnormalities. We report that we found few differences to control mice (GluA2(R)/(R)) and hence, the lack of ADAR2 appears not to affect most of the physiological functions tested. Brain of four mutant animals of ADAR-/-/GluR-BR/R versus a pool of four reference (wildtype) mice; two technical replicates for each mutant mouse including a dye swap experiment - in total 8 chip hybridisations

Dataset Information

ADAR2 reproducibly changes abundance and sequence of mature microRNAs in the mouse brain [RNA-Seq]

Publications

ADAR2 induces reproducible changes in sequence and abundance of mature microRNAs in the mouse brain.

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