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Transcriptome analysis of C. elegans embryos lacking ADARs and the 26G pathway

ABSTRACT: Adenosine deaminases that act on RNA (ADARs) catalyze the conversion of adenosine to inosine in dsRNA. C. elegans ADARs, ADR-1 and ADR-2, promote the expression of genes containing dsRNA structures by preventing their processing into siRNAs and silencing by RNAi. The 26G endogenous siRNA (endo-siRNA) pathway generates a subset of siRNAs distinct from those made in adr-1;adr-2 mutants, but using many of the same factors. We found that adr-1;adr-2;rrf-3 mutants, lacking both ADARs and the RNA-dependent RNA polymerase RRF-3 required for the 26G pathway, display a bursting phenotype rescued by the RNAi factors RDE-1 and RDE-4. To determine what gene expression changes underlie the synthetic phenotype of adr-1;adr-2;rrf-3 mutants, we sequenced poly(A)+ RNA from adr-1;adr-2;rrf-3 embryos, their parent strains, and strains rescued with mutations in rde-1 and rde-4. We found that genes associated with edited structures were robustly downregulated in adr-1;adr-2;rrf-3 mutants in a manner partially dependent on rde-1 and rde-4. Additionally, genes induced during Orsay virus infections were induced in rrf-3 mutants and further upregulated in adr-1;adr-2;rrf-3 mutants, again dependent in part on rde-1 and rde-4.

ORGANISM(S): Caenorhabditis elegans

PROVIDER: GSE106647 | GEO | 2018/02/23

REPOSITORIES: GEO

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Project description:A-to-I RNA editing is widespread in eukaryotic transcriptomes and plays an essential role in the creation of proteomic and phenotypic diversity. Loss of ADARs, the proteins responsible for A-to-I editing, results in lethality in mammals. In C. elegans, knocking out both ADARs, ADR-1 and ADR-2, results in aberrant behavior and abnormal development. Studies have shown that ADR-2 can actively deaminate dsRNA while ADR-1 cannot. However, as most studies of C. elegans ADARs were performed on worms mutated in both ADAR genes, the effects observed cannot be attributed to a single ADAR or to the interactions between ADAR genes. Therefore, we set to study the effects of each C. elegans ADAR on RNA editing, gene expression, protein levels and the contribution of each of ADAR to the phenotypes observed in worms mutated in both genes, in order to elucidate their distinct functions. We found significant differences in the phenotypes observed in worms mutated in a single ADAR gene. Worms harboring adr-1 mutations have a significant reduction in their lifespan, while worms harboring adr-2 mutations have extended lifespan. We also observed severe abnormalities in vulva formation mainly in adr-1 mutants, and we suggest that these phenotypes are a result of an RNA editing independent function of ADR-1. Mutations in each ADAR resulted in expressional changes in hundreds of genes, and a significant downregulation of edited genes. However, very few changes in the protein levels were observed. In addition, we found that ADR-1 binds many edited genes. Our results suggest that ADR-1 has a significant function in the RNA editing process and by altering editing levels it causes the severe phenotypes that we observed. In contrast, a complete lack of RNA editing is less harmful to the worms. Furthermore, our results indicate that the effect of RNA editing on the protein content in the cell is minor and probably the main purpose of these modifications is to antagonize or enhance other gene regulatory mechanisms that act on RNA.

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Transcriptome analysis of C. elegans embryos lacking ADARs and the 26G pathway

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