| Summary: | <p>Abstract</p> <p>Background</p> <p>MicroRNAs (miRNAs) are small non-coding RNAs that post-transcriptionally regulate gene expression in a variety of organisms, including insects, vertebrates, and plants. miRNAs play important roles in cell development and differentiation as well as in the cellular response to stress and infection. To date, there are limited reports of miRNA identification in mosquitoes, insects that act as essential vectors for the transmission of many human pathogens, including flaviviruses. West Nile virus (WNV) and dengue virus, members of the <it>Flaviviridae </it>family, are primarily transmitted by <it>Aedes </it>and <it>Culex </it>mosquitoes. Using high-throughput deep sequencing, we examined the miRNA repertoire in <it>Ae. albopictus </it>cells and <it>Cx. quinquefasciatus </it>mosquitoes.</p> <p>Results</p> <p>We identified a total of 65 miRNAs in the <it>Ae. albopictus </it>C7/10 cell line and 77 miRNAs in <it>Cx. quinquefasciatus </it>mosquitoes, the majority of which are conserved in other insects such as <it>Drosophila melanogaster </it>and <it>Anopheles gambiae</it>. The most highly expressed miRNA in both mosquito species was miR-184, a miRNA conserved from insects to vertebrates. Several previously reported <it>Anopheles </it>miRNAs, including miR-1890 and miR-1891, were also found in <it>Culex </it>and <it>Aedes</it>, and appear to be restricted to mosquitoes. We identified seven novel miRNAs, arising from nine different precursors, in C7/10 cells and <it>Cx. quinquefasciatus </it>mosquitoes, two of which have predicted orthologs in <it>An. gambiae</it>. Several of these novel miRNAs reside within a ~350 nt long cluster present in both <it>Aedes </it>and <it>Culex</it>. miRNA expression was confirmed by primer extension analysis. To determine whether flavivirus infection affects miRNA expression, we infected female <it>Culex </it>mosquitoes with WNV. Two miRNAs, miR-92 and miR-989, showed significant changes in expression levels following WNV infection.</p> <p>Conclusions</p> <p><it>Aedes </it>and <it>Culex </it>mosquitoes are important flavivirus vectors. Recent advances in both mosquito genomics and high-throughput sequencing technologies enabled us to interrogate the miRNA profile in these two species. Here, we provide evidence for over 60 conserved and seven novel mosquito miRNAs, expanding upon our current understanding of insect miRNAs. Undoubtedly, some of the miRNAs identified will have roles not only in mosquito development, but also in mediating viral infection in the mosquito host.</p>
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