In vitro treatment of seroin proteins to BmNPV budded virions suppresses viral proliferation in Bombyx mori larvae and ectopic overexpression of host-miRNAs downregulates the expression of Seroin2 mRNA in BmN cells

Abstract

The domesticated silkworm, Bombyx mori is not only an economically important insect but also a suitable model for the study of insect immunity and molecular genetics. The silk of B. mori is composed of mainly sericin and fibroin proteins, but few other proteins are found associated with silk. Seroin proteins are the silk-associated proteins, which play a crucial role in the protection of silk from microbes. Seroin proteins have been shown to inhibit the growth of Bombyx mori nuclear polyhedrosis virus (BmNPV) in B. mori, but the mechanism of action and their regulation is not known. Here to get insight into the mechanism, in vitro incubation of seroin proteins with BmNPV budded virions prior to infection was carried out. Subsequently, infection was done using these budded virions that resulted in suppression of virus proliferation in B. mori larvae. On the other hand, the microRNA-mediated regulation of Seroin2 in BmN cells of B. mori was studied. MicroRNAs (miRNAs) are the class of small non-coding RNAs that regulate several vital biological processes through post-transcriptional gene regulation. Target sites for host-encoded miRNAs on mRNA of Seroin2 were predicted using RNAhybrid software. Bmo-miR-71 and bmo-miR-252 were found to have target sites on the mRNA of Seroin2. Ectopic overexpression of bmo-miR-71 and bmo-miR-252 in the BmN cells resulted in the significant downregulation of Seroin2 expression at the transcript level, as determined by RT-qPCR. These results indicate that seroin proteins’ direct interaction with BmNPV may decrease its infectivity and Seroin2 is plausibly under the regulation of host miRNAs.