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Viral suppressors of RNA silencing hinder exogenous and endogenous small RNA pathways in Drosophila.

Berry B, Deddouche S, Kirschner D, Imler JL, Antoniewski C - PLoS ONE (2009)

Bottom Line: While VSRs in Drosophila melanogaster were shown to inhibit RNAi through different modes of action, whether they act on other silencing pathways remained unexplored.Here we show that expression of various plant and insect VSRs in transgenic flies does not perturb the Drosophila microRNA (miRNA) pathway; but in contrast, inhibits antiviral RNAi and the RNA silencing response triggered by inverted repeat transcripts, and injection of dsRNA or siRNA.Strikingly, these VSRs also suppressed transposon silencing by endogenous siRNAs (endo-siRNAs).

View Article: PubMed Central - PubMed

Affiliation: Institut Pasteur, Drosophila Genetics and Epigenetics, CNRS-URA2578, Paris, France.

ABSTRACT

Background: In plants and insects, RNA interference (RNAi) is the main responder against viruses and shapes the basis of antiviral immunity. Viruses counter this defense by expressing viral suppressors of RNAi (VSRs). While VSRs in Drosophila melanogaster were shown to inhibit RNAi through different modes of action, whether they act on other silencing pathways remained unexplored.

Methodology/principal findings: Here we show that expression of various plant and insect VSRs in transgenic flies does not perturb the Drosophila microRNA (miRNA) pathway; but in contrast, inhibits antiviral RNAi and the RNA silencing response triggered by inverted repeat transcripts, and injection of dsRNA or siRNA. Strikingly, these VSRs also suppressed transposon silencing by endogenous siRNAs (endo-siRNAs).

Conclusions/significance: Our findings identify VSRs as tools to unravel small RNA pathways in insects and suggest a cosuppression of antiviral RNAi and endo-siRNA silencing by viruses during fly infections.

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Related in: MedlinePlus

VSRs inhibit retrotransposon silencing by endo-siRNAs.297 and ZAM retrotransposon silencing is impaired by B2, 1A and P19 VSRs. RNA levels of 297 and ZAM were measured in heads and ovaries of 1 day-old female flies heterozygous for the da>GAL4 driver and the indicated UAS>VSR transgene. Fold changes in RNA levels were calculated relative to the 297 and ZAM RNA levels measured in heterozygous da>GAL4 control flies. Fold changes in homozygous ago2414 mutants were calculated relative to the 297 and ZAM RNA levels measured in heterozygous ago2414 flies. Therefore, the weaker effect of the ago2 mutation on 297 expression observed in adult heads may result from variations in copy number of 297 between the ago2 mutant stock and the VSR transgenic stocks. Error bars indicate the standard deviation from triplicate qPCR experiments.
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pone-0005866-g005: VSRs inhibit retrotransposon silencing by endo-siRNAs.297 and ZAM retrotransposon silencing is impaired by B2, 1A and P19 VSRs. RNA levels of 297 and ZAM were measured in heads and ovaries of 1 day-old female flies heterozygous for the da>GAL4 driver and the indicated UAS>VSR transgene. Fold changes in RNA levels were calculated relative to the 297 and ZAM RNA levels measured in heterozygous da>GAL4 control flies. Fold changes in homozygous ago2414 mutants were calculated relative to the 297 and ZAM RNA levels measured in heterozygous ago2414 flies. Therefore, the weaker effect of the ago2 mutation on 297 expression observed in adult heads may result from variations in copy number of 297 between the ago2 mutant stock and the VSR transgenic stocks. Error bars indicate the standard deviation from triplicate qPCR experiments.

Mentions: A class of endogenous siRNAs is produced from sense and antisense transcription of transposable elements. In somatic tissues, these endo-siRNAs were shown to silence TEs from where they originate in a negative feedback loop [4], [6]. To further characterize the activity of B2, 1A and P19 on the fly endo-siRNA pathway, we analyzed the effects of their overexpression on two retrotransposons in female adult heads and ovaries (Fig. 5).


Viral suppressors of RNA silencing hinder exogenous and endogenous small RNA pathways in Drosophila.

Berry B, Deddouche S, Kirschner D, Imler JL, Antoniewski C - PLoS ONE (2009)

VSRs inhibit retrotransposon silencing by endo-siRNAs.297 and ZAM retrotransposon silencing is impaired by B2, 1A and P19 VSRs. RNA levels of 297 and ZAM were measured in heads and ovaries of 1 day-old female flies heterozygous for the da>GAL4 driver and the indicated UAS>VSR transgene. Fold changes in RNA levels were calculated relative to the 297 and ZAM RNA levels measured in heterozygous da>GAL4 control flies. Fold changes in homozygous ago2414 mutants were calculated relative to the 297 and ZAM RNA levels measured in heterozygous ago2414 flies. Therefore, the weaker effect of the ago2 mutation on 297 expression observed in adult heads may result from variations in copy number of 297 between the ago2 mutant stock and the VSR transgenic stocks. Error bars indicate the standard deviation from triplicate qPCR experiments.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2689938&req=5

pone-0005866-g005: VSRs inhibit retrotransposon silencing by endo-siRNAs.297 and ZAM retrotransposon silencing is impaired by B2, 1A and P19 VSRs. RNA levels of 297 and ZAM were measured in heads and ovaries of 1 day-old female flies heterozygous for the da>GAL4 driver and the indicated UAS>VSR transgene. Fold changes in RNA levels were calculated relative to the 297 and ZAM RNA levels measured in heterozygous da>GAL4 control flies. Fold changes in homozygous ago2414 mutants were calculated relative to the 297 and ZAM RNA levels measured in heterozygous ago2414 flies. Therefore, the weaker effect of the ago2 mutation on 297 expression observed in adult heads may result from variations in copy number of 297 between the ago2 mutant stock and the VSR transgenic stocks. Error bars indicate the standard deviation from triplicate qPCR experiments.
Mentions: A class of endogenous siRNAs is produced from sense and antisense transcription of transposable elements. In somatic tissues, these endo-siRNAs were shown to silence TEs from where they originate in a negative feedback loop [4], [6]. To further characterize the activity of B2, 1A and P19 on the fly endo-siRNA pathway, we analyzed the effects of their overexpression on two retrotransposons in female adult heads and ovaries (Fig. 5).

Bottom Line: While VSRs in Drosophila melanogaster were shown to inhibit RNAi through different modes of action, whether they act on other silencing pathways remained unexplored.Here we show that expression of various plant and insect VSRs in transgenic flies does not perturb the Drosophila microRNA (miRNA) pathway; but in contrast, inhibits antiviral RNAi and the RNA silencing response triggered by inverted repeat transcripts, and injection of dsRNA or siRNA.Strikingly, these VSRs also suppressed transposon silencing by endogenous siRNAs (endo-siRNAs).

View Article: PubMed Central - PubMed

Affiliation: Institut Pasteur, Drosophila Genetics and Epigenetics, CNRS-URA2578, Paris, France.

ABSTRACT

Background: In plants and insects, RNA interference (RNAi) is the main responder against viruses and shapes the basis of antiviral immunity. Viruses counter this defense by expressing viral suppressors of RNAi (VSRs). While VSRs in Drosophila melanogaster were shown to inhibit RNAi through different modes of action, whether they act on other silencing pathways remained unexplored.

Methodology/principal findings: Here we show that expression of various plant and insect VSRs in transgenic flies does not perturb the Drosophila microRNA (miRNA) pathway; but in contrast, inhibits antiviral RNAi and the RNA silencing response triggered by inverted repeat transcripts, and injection of dsRNA or siRNA. Strikingly, these VSRs also suppressed transposon silencing by endogenous siRNAs (endo-siRNAs).

Conclusions/significance: Our findings identify VSRs as tools to unravel small RNA pathways in insects and suggest a cosuppression of antiviral RNAi and endo-siRNA silencing by viruses during fly infections.

Show MeSH
Related in: MedlinePlus