The RNA editing enzyme ADAR1 is a key regulatory of innate immune responses to RNA

The ADAR RNA editing enzymes deaminate adenosine bases to inosines in cellular RNAs, recoding open reading frames. Human ADAR1 mutations cause Aicardi-Goutieres Syndrome (AGS) and Adar1 mutant mice showing an aberrant interferon response and death by embryonic day E12.5 model the human disease. Searches have not identified key ADAR1 RNA editing sites recoding immune/haematopoietic proteins but editing is widespread in Alu sequences. We show that Adar1 embryonic lethality is rescued in Adar1; Mavs double mutant mice in which general antiviral responses to cytoplasmic dsRNA are prevented. We propose that inosine bases are epigenetic marks identifying cellular RNA as innate immune ÒselfÓ. Consistent with this idea we show that an editing-active cytoplasmic ADAR is required to prevent aberrant immune responses in Adar1 mutant mouse embryo fibroblasts. No dramatic increase in repetitive transcripts is observed. AGS mutations in ADAR1 affect editing by the interferon-inducible cytoplasmic ADAR1 isoform. Overall design: RNA-seq expression profiling in Adar1 and Adar1/Mavs knockout mice embryos.

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Mannion NM, Greenwood SM, Young R, Cox S, Brindle J, Read D, Nellåker C, Vesely C, Ponting CP, McLaughlin PJ, Jantsch MF, Dorin J, Adams IR, Scadden AD, Ohman M, Keegan LP, O'Connell MA