Adar RNA editing-dependent and -independent effects are required for brain and innate immune functions in Drosophila

Patricia Deng,Nagraj Sambrani,Anzer Khan,Dionna Jacobson,Xianghua Li,Liam P Keegan,Aswathy Jayasree,Jan Hejatko,Leeanne Mcgurk,Jin Billy Li,Galit Shohat-Ophir,Mary A O’Connell

doi:10.1038/s41467-020-15435-1

Abstract

ADAR RNA editing enzymes are high-affinity dsRNA-binding proteins that deaminate adenosines to inosines in pre-mRNA hairpins and also exert editing-independent effects. We generated a Drosophila AdarE374A mutant strain encoding a catalytically inactive Adar with CRISPR/Cas9. We demonstrate that Adar adenosine deamination activity is necessary for normal locomotion and prevents age-dependent neurodegeneration. The catalytically inactive protein, when expressed at a higher than physiological level, can rescue neurodegeneration in Adar mutants, suggesting also editing-independent effects. Furthermore, loss of Adar RNA editing activity leads to innate immune induction, indicating that Drosophila Adar, despite being the homolog of mammalian ADAR2, also has functions similar to mammalian ADAR1. The innate immune induction in fly Adar mutants is suppressed by silencing of Dicer-2, which has a RNA helicase domain similar to MDA5 that senses unedited dsRNAs in mammalian Adar1 mutants. Our work demonstrates that the single Adar enzyme in Drosophila unexpectedly has dual functions.

Highlights

ADAR RNA editing enzymes are high-affinity double-stranded RNA (dsRNA)-binding proteins that deaminate adenosines to inosines in pre-mRNA hairpins and exert editing-independent effects
RNA editing occurs in long dsRNAs formed by inverted repetitive elements in both mammals and Drosophila; in humans this additional ADAR RNA editing occurs at millions of sites, mostly non- and at low efficiency in Alu dsRNA hairpins embedded in protein-coding transcripts[3,4,5]
We find that loss of Adar RNA editing activity in Drosophila leads to severe locomotion defects and age-dependent neurodegeneration similar to Adar5G1 null mutant flies[24]

Summary

Introduction

ADAR RNA editing enzymes are high-affinity dsRNA-binding proteins that deaminate adenosines to inosines in pre-mRNA hairpins and exert editing-independent effects. The catalytically inactive protein, when expressed at a higher than physiological level, can rescue neurodegeneration in Adar mutants, suggesting editing-independent effects. A-to-I RNA editing, the ADAR (adenosine deaminase acting on RNA) enzyme binds to double-stranded RNA (dsRNA) and deaminates specific adenosines to inosines. RNA editing occurs in long dsRNAs formed by inverted repetitive elements in both mammals and Drosophila; in humans this additional ADAR RNA editing occurs at millions of sites, mostly non- and at low efficiency in Alu dsRNA hairpins embedded in protein-coding transcripts[3,4,5]. ADARs strongly affect processing of many pri-miRNAs even though very few mature miRNAs are themselves edited[12,13]

Methods

Results

Conclusion