The Other Face of an Editor : ADAR1 Functions in EditingIndependent Ways

The RNA editing enzyme ADAR1 seemingly has more functions besides RNA editing. Mouse models lacking ADAR1 and sensors of foreign RNA show that RNA editing by ADAR1 plays a crucial role in the innate immune response. Still, RNA editing alone cannot explain all observed phenotypes. Thus, additional roles for ADAR1 must exist. Binding of ADAR1 to RNA is independent of its RNA editing function. Thus, ADAR1 may compete with other RNAbinding proteins. A very recent manuscript elaborates on this and reports competition of ADAR1 with STAUFEN1, thereby modulating RNAdegradation. ADAR1 is also known to recruit proteins such as DROSHA to nascent transcripts. Still, many open questions remain. For instance, the biological role of the ZDNA binding domains in ADAR1 is not defined. Moreover, the impact of ADAR1 on the RNAfolding landscape is unclear. In sum, moonlighting functions of ADAR1 may be manifold and have a great impact on the transcriptome.(VLID)483913

Testicular adenosine to inosine RNA editing in the mouse is mediated by ADARB1†,‡.

Adenosine to inosine (A-to-I) RNA editing occurs in a wide range of tissues and cell types and can be catalyzed by one of the two adenosine deaminase acting on double-stranded RNA enzymes, ADAR and ADARB1. Editing can impact both coding and noncoding regions of RNA, and in higher organisms has been proposed to function in adaptive evolution. Neither the prevalence of A-to-I editing nor the role of either ADAR or ADARB1 has been examined in the context of germ cell development in mammals. Computational analysis of whole testis and cell-type specific RNA-sequencing data followed by molecular confirmation demonstrated that A-to-I RNA editing occurs in both the germ line and in somatic Sertoli cells in two targets, Cog3 and Rpa1. Expression analysis demonstrated both Adar and Adarb1 were expressed in both Sertoli cells and in a cell-type dependent manner during germ cell development. Conditional ablation of Adar did not impact testicular RNA editing in either germ cells or Sertoli cells. Additionally, Adar ablation in either cell type did not have gross impacts on germ cell development or male fertility. In contrast, global Adarb1 knockout animals demonstrated a complete loss of A-to-I RNA editing in spite of normal germ cell development. Taken together, these observations demonstrate ADARB1 mediates A-to-I RNA editing in the testis and these editing events are dispensable for male fertility in an inbred mouse strain in the lab. Biol Reprod 2017 Jan 1; 96(1):244-253

3′-cyclic phosphorylation of U6 snRNA leads to recruitment of recycling factor p110 through LSm proteins

Pre-mRNA splicing proceeds through assembly of the spliceosome complex, catalysis, and recycling. During each cycle the U4/U6.U5 tri-snRNP is disrupted and U4/U6 snRNA base-pairing unwound, releasing separate post-spliceosomal U4, U5, and U6 snRNPs, which have to be recycled to the splicing-competent tri-snRNP. Previous work implicated p110—the human ortholog of the yeast Prp24 protein—and the LSm2-8 proteins of the U6 snRNP in U4/U6 recycling. Here we show in vitro that these proteins bind synergistically to U6 snRNA: Both purified and recombinant LSm2-8 proteins are able to recruit p110 protein to U6 snRNA via interaction with the highly conserved C-terminal region of p110. Furthermore, the presence of a 2′,3′-cyclic phosphate enhances the affinity of U6 snRNA for the LSm2-8 proteins and inversely reduces La protein binding, suggesting a direct role of the 3′-terminal phosphorylation in RNP remodeling during U6 biogenesis

Adenosine to Inosine editing frequency controlled by splicing efficiency

Alternative splicing and adenosine to inosine (A to I) RNA-editing are major factors leading to co- and post-transcriptional modification of genetic information. Both, A to I editing and splicing occur in the nucleus. As editing sites are frequently defined by exon-intron basepairing, mRNA splicing efficiency should affect editing levels. Moreover, splicing rates affect nuclear retention and will therefore also influence the exposure of pre-mRNAs to the editing-competent nuclear environment. Here, we systematically test the influence of splice rates on RNA-editing using reporter genes but also endogenous substrates. We demonstrate for the first time that the extent of editing is controlled by splicing kinetics when editing is guided by intronic elements. In contrast, editing sites that are exclusively defined by exonic structures are almost unaffected by the splicing efficiency of nearby introns. In addition, we show that editing levels in pre- and mature mRNAs do not match. This phenomenon can in part be explained by the editing state of an RNA influencing its splicing rate but also by the binding of the editing enzyme ADAR that interferes with splicing.P 26845-B20(VLID)310356

Additional file 2: Table S1. of Transcriptome-wide effects of inverted SINEs on gene expression and their impact on RNA polymerase II activity

describing all DNA primers used in this study for regular and quantitative PCR analysis. (PDF 57 kb

Additional file 1: of Transcriptome-wide effects of inverted SINEs on gene expression and their impact on RNA polymerase II activity

Figure S1. Alu elements in iSINE containing constructs are edited, indicating that iSINEs can form double-stranded structures. Figure S2. Minimum free energy structures of the Znf708 UTR and the designed UTRs. Figure S3. ZNF-analogs mimicking the folding of the wildtype ZNF are edited, indicating that they form double-stranded structures. Figure S4. iSINEs do not lead to nuclear retention of RNAs. Figure S5. iSINE mediated gene repression is independent of dsRNA-activated kinase PKR and DICER or DROSHA activity. Figure S6. iSINEs do not interfere with mRNA polyadenylation. (PDF 2738 kb