Abstract
There are several RNA interference (RNAi) pathways in insects. The small interfering RNA pathway is considered to be the main antiviral mechanism of the innate immune system; however, virus-specific P-element-induced Wimpy testis gene (PIWI)-interacting RNAs (vpiRNAs) have also been described, especially in mosquitoes. Understanding the antiviral potential of the RNAi pathways is important, given that many human and animal pathogens are transmitted by mosquitoes, such as Zika virus, dengue virus and chikungunya virus. In recent years, significant progress has been made to characterize the piRNA pathway in mosquitoes (including the possible antiviral activity) and to determine the differences between mosquitoes and the model organism Drosophila melanogaster. The new findings, especially regarding vpiRNA in mosquitoes, as well as important questions that need to be tackled in the future, are discussed in this review.
Highlights
There are several RNA interference (RNAi) pathways in insects
RNA interference (RNAi) plays a major role in controlling gene expression in most eukaryotes, including humans; the basis of RNAi is the generation of small RNAs (20–31 nt) that are bound to an Argonaute (Ago) protein and thereby help it to find its target RNA via sequence complementarity
P-element-induced Wimpy testis gene (PIWI) proteins and PIWI-interacting small RNA (piRNA) are mainly expressed in the gonads of eukaryotes, whereas the prototype PIWI protein is encoded by the Drosophila piwi gene, which was originally shown to be important for germline development [1, 7]
Summary
Many organisms have developed a pathway that involves proteins transcribed from the PIWI family gene collection and their associated piRNAs, primarily to safeguard their germline from the genomic disruption caused by transposable elements [29]. Elucidating the potential antiviral properties of small RNAs, including virus-specific piRNAs, will help in understanding differences in the vector competence of mosquito species. This is especially relevant for risk assessments concerning viruses that are of public health concern, such as Zika virus (ZIKV), dengue virus (DENV) and chikungunya virus (CHIKV). In contrast to Aedes spp., one-to-one orthologues of the Drosophila Ago, Aub and Piwi proteins have been found in Anopheles gambiae and Anopheles stephensi mosquitoes. These vpiRNAs all had strong bias for uridine at position 1, no preference for adenine at position 10 could be
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