[show abstract][hide abstract] ABSTRACT: MicroRNAs have emerged as key players in the regulation of various biological processes in eukaryotes, including host-pathogen interactions. Recent studies suggest that viruses encode miRNAs to manipulate their host gene expression to ensure their effective proliferation, whereas the host limits virus infection by differentially expressing miRNAs that target essential viral genes. Here, we demonstrate that an insect virus, Bombyx mori nucleopolyhedrosis virus (BmNPV), modulates the small-RNA-mediated defense of its host, B. mori, by encoding an miRNA (bmnpv-miR-1) that downregulates the expression of the host GTP-binding nuclear protein Ran, an essential component of the exportin-5-mediated nucleocytoplasmic transport machinery mainly involved in small-RNA transport from the nucleus to the cytoplasm. We demonstrate the sequence-dependent interaction of bmnpv-miR-1 with Ran mRNA using cell culture and in vivo assays, including RNA interference (RNAi) of Ran. Our results clearly show that bmnpv-miR-1 represses Ran, leading to reduction in the host small-RNA population, and consequently, the BmNPV load increases in the infected larvae. Blocking of bmnpv-miR-1 resulted in higher expression levels of Ran and a decrease in BmNPV proliferation. In contrast, blockage of host miRNA, bmo-miR-8, which targets the immediate-early gene of the virus and whose production was repressed upon bmnpv-miR-1 and Ran dsRNA administration, resulted in a significant increase in the virus load in the infected B. mori larvae. The present study provides an insight into one of the evasion strategies used by the virus to counter the host defense for its effective proliferation and has relevance to the development of insect virus control strategies.
Journal of Virology 05/2012; 86(15):7867-79. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: MicroRNAs (miRNAs) have emerged as key players in host-pathogen interaction. Recently, many virus-encoded miRNAs have been identified from different mammalian species. However, the large family of invertebrate viruses of Baculoviridae, which infects diverse species of beneficial insects and agriculture pests, has hardly been investigated for elucidating the role of miRNAs in host-pathogen interaction. In the study reported here, we have identified four Bombyx mori nucleopolyhedrosis virus (BmNPV)-encoded miRNAs using a combination of in silico and experimental methods. Unlike other reported viral miRNAs, the BmNPV-encoded miRNAs identified in the present study were found to be evolutionarily conserved among many closely related baculoviruses. Besides, we have computationally predicted 8 viral and 64 cellular targets of these virus-encoded miRNAs and the putative functions of these targets suggest a key role of viral miRNAs in insect-pathogen interactions by modulating several viral replication genes as well as those involved in host immune defense machinery.
[show abstract][hide abstract] ABSTRACT: MicroRNAs (miRNAs), are endogenous, ~22-nucleotide-long RNA molecules. They bind to the complementary sites on target mRNAs and regulate protein production of the target transcript by unknown mechanisms. Since the discovery of first miRNA in Caenorhabditis elegans, different approaches have been pursued for the prediction of miRNAs and their target(s). Because of many difficulties and limitations involved in the experimental identification of spatially and temporally expressed miRNAs, many computational approaches have been successfully employed for prediction of miRNAs and their target(s). In the present study, we demonstrate a genome-wide computational approach to predict miRNAs and their target(s) in the red flour beetle, Tribolium castaneum. We have predicted and characterized 45 miRNAs by genome-wide homology search against all the reported miRNAs. These miRNAs were further validated by statistical and phylogenetic analyses. In addition, we have also attempted to predict the putative targets of these miRNAs, by making use of 3' untranslated regions of mRNAs from T. castaneum. These miRNAs and their targets in T. castaneum will serve as useful resources for initiating studies on their experimental validation and functional analyses of miRNA-regulated phenotypes in T. castaneum through gene knockdown and transgenesis.