RNA editing is the essential function of ADAR1 and, in the absence of MDA5, is dispensable for normal adult homeostasis [RNAseq (Adult Brain)]

Adenosine-to-Inosine (A-to-I) editing of dsRNA by ADAR proteins is a pervasive feature of the epitranscriptome. There are estimated to be over 100 million potential A-to-I editing sites in humans and A-to-I editing can have varying consequences for gene expression. Whilst editing resulting in protein recoding defines the role of ADAR2, ADAR1 has been proposed to have both editing-dependent and -independent functions. The relative contribution of these putative functions to ADAR1 biology is unclear. We demonstrate that the absence of ADAR1-mediated editing is well tolerated when the cytosolic dsRNA sensor MDA5 is deleted. These mice have normal hematopoiesis, tissue patterning and life span. A direct comparison of the complete deletion of ADAR1 and the specific loss of A-to-I editing activity demonstrates that RNA editing is the only essential function of ADAR1 in adult mice. Therefore, preventing MDA5 substrate formation by endogenous RNA is the essential in vivo function of ADAR1-mediated editing. RNAseq of Feotal Brain in a E861A point mutant of ADAR on a MDA5 knockout background generated by deep sequencing, in triplicate using Illumina NextSeq500ADAR蛋白介导的双链RNA（dsRNA）腺苷-肌苷（A-to-I）编辑，是表观转录组（epitranscriptome）的普遍特征。据估计，人类体内存在超过1亿个潜在A-to-I编辑位点，且A-to-I编辑对基因表达的调控效应存在多样性。虽然介导蛋白质重编码的编辑功能定义了ADAR2的核心生物学角色，但ADAR1被认为同时具备依赖编辑与不依赖编辑的双重功能。上述两类推定功能对ADAR1生物学的相对贡献目前仍不明确。本研究证实，当胞质dsRNA感受器MDA5缺失时，ADAR1介导的RNA编辑缺失可被良好耐受。此类小鼠的造血功能、组织形态及寿命均表现正常。通过直接对比ADAR1完全敲除与A-to-I编辑活性特异性缺失的表型，可证明RNA编辑是成年小鼠体内ADAR1唯一的必需功能。因此，通过内源性RNA阻断MDA5底物的形成，正是ADAR1介导的RNA编辑在体内的核心必需功能。本研究采用Illumina NextSeq500平台，对MDA5敲除背景下ADAR的E861A点突变小鼠的胎儿脑组织进行了三次重复深度测序，获取了其转录组测序（RNAseq）数据。