Zografidis Aris, Van Nieuwerburgh Filip, Kolliopoulou Anna, Apostolou-Karampelis Konstantinos, Head Steven R, Deforce Dieter, Smagghe Guy, Swevers Luc
Insect Molecular Genetics and Biotechnology, Institute of Biosciences and Applications, National Centre for Scientific Research Demokritos, Aghia Paraskevi, Athens, Greece
Laboratory of Pharmaceutical Biotechnology, Faculty of Pharmaceutical Science, Ghent University, Ghent, Belgium.
J Virol. 2015 Nov;89(22):11473-86. doi: 10.1128/JVI.01695-15. Epub 2015 Sep 2.
The lepidopteran innate immune response against RNA viruses remains poorly understood, while in other insects several studies have highlighted an essential role for the exo-RNAi pathway in combating viral infection. Here, by using deep-sequencing technology for viral small-RNA (vsRNA) assessment, we provide evidence that exo-RNAi is operative in the silkworm Bombyx mori against both persistent and pathogenic infection of B. mori cytoplasmic polyhedrosis virus (BmCPV) which is characterized by a segmented double-stranded RNA (dsRNA) genome. Further, we show that Dicer-2 predominantly targets viral dsRNA and produces 20-nucleotide (nt) vsRNAs, whereas an additional pathway is responsive to viral mRNA derived from segment 10. Importantly, vsRNA distributions, which define specific hot and cold spot profiles for each viral segment, to a considerable degree overlap between Dicer-2-related (19 to 21 nt) and Dicer-2-unrelated vsRNAs, suggesting a common origin for these profiles. We found a degenerate motif significantly enriched at the cut sites of vsRNAs of various lengths which link an unknown RNase to the origins of vsRNAs biogenesis and distribution. Accordingly, the indicated RNase activity may be an important early factor for the host's antiviral defense in Lepidoptera.
This work contributes to the elucidation of the lepidopteran antiviral response against infection of segmented double-stranded RNA (dsRNA) virus (CPV; Reoviridae) and highlights the importance of viral small-RNA (vsRNA) analysis for getting insights into host-pathogen interactions. Three vsRNA pathways are implicated in antiviral defense. For dsRNA, two pathways are proposed, either based on Dicer-2 cleavage to generate 20-nucleotide vsRNAs or based on the activity of an uncharacterized endo-RNase that cleaves the viral RNA substrate at a degenerate motif. The analysis also indicates the existence of a degradation pathway that targets the positive strand of segment 10.
鳞翅目昆虫对RNA病毒的先天性免疫反应仍知之甚少，而在其他昆虫中，多项研究强调了外切核糖核酸酶RNA干扰（exo-RNAi）途径在对抗病毒感染中的重要作用。在此，我们通过使用深度测序技术评估病毒小RNA（vsRNA），提供证据表明exo-RNAi在家蚕中对家蚕细胞质多角体病毒（BmCPV）的持续感染和致病性感染均起作用，BmCPV的特征是具有分段双链RNA（dsRNA）基因组。此外，我们表明Dicer-2主要靶向病毒dsRNA并产生20个核苷酸（nt）的vsRNA，而另一条途径则对源自第10节段的病毒mRNA有反应。重要的是，vsRNA分布为每个病毒节段定义了特定的热点和冷点图谱，在很大程度上，Dicer-2相关的（19至21 nt）和Dicer-2不相关的vsRNA之间存在重叠，表明这些图谱有共同的起源。我们发现一个简并基序在各种长度的vsRNA切割位点显著富集，这将一种未知的核糖核酸酶与vsRNA生物合成和分布的起源联系起来。因此，所示的核糖核酸酶活性可能是鳞翅目宿主抗病毒防御的一个重要早期因素。
这项工作有助于阐明鳞翅目昆虫对分段双链RNA（dsRNA）病毒（CPV；呼肠孤病毒科）感染的抗病毒反应，并强调了病毒小RNA（vsRNA）分析对于深入了解宿主-病原体相互作用的重要性。三种vsRNA途径参与抗病毒防御。对于dsRNA，提出了两种途径，一种是基于Dicer-2切割产生20个核苷酸的vsRNA，另一种是基于一种未表征的内切核糖核酸酶的活性，该酶在一个简并基序处切割病毒RNA底物。分析还表明存在一条靶向第10节段正链的降解途径。
