Identification of Regulatory Host Genes Involved in Sigma Virus Replication Using RNAi Knockdown in Drosophila

Abstract

The Drosophila melanogaster sigma virus, a member of the Rhabdoviridae family, specifically propagates itself in D. melanogaster. It contains six genes in the order of 3′-N–P–X–M–G–L-5′. The sigma virus is the only arthropod-specific virus of the Rhabdoviridae family. Sigma-virus-infected Drosophila may suffer from irreversible paralysis when exposed to a high CO2 concentration, but generally, no other symptoms are reported. A recent study reported that host gene expression in immune pathways was not changed in sigma-virus-infected Drosophila, which does not necessarily suggest that they are not involved in virus–host interactions. The present study aimed to identify host genes associated with sigma virus replication. Immune pathways JAK-STAT and IMD were selected for detailed study. The results showed that the genome copy number of the sigma virus increased after knocking down the immune pathway genes domeless and PGRP-LC in Drosophila S2 cells. The knocking down of domeless and PGRP-LC significantly up-regulated the expression of the L gene compared to the other viral genes. We propose that the immune pathways respond to sigma virus infection by altering L expression, hence suppressing viral replication. This effect was further tested in vivo, when D. melanogaster individuals injected with dsdome and dsPGRP-LC showed not only an increase in sigma virus copy number, but also a reduced survival rate when treated with CO2. Our study proved that host immunity influences viral replication, even in persistent infection. Knocking down the key components of the immune process deactivates immune controls, thus facilitating viral expression and replication. We propose that the immunity system of D. melanogaster regulates the replication of the sigma virus by affecting the L gene expression. Studies have shown minimal host–virus interaction in persistent infection. However, our study demonstrated that the immunity continued to affect viral replication even in persistent infection because knocking down the key components of the immune process disabled the relevant immune controls and facilitated viral expression and replication.

Antimicrobial Peptides as Potential Antiviral Factors in Insect Antiviral Immune Response

“…A considerable number of AMP genes have been identified in Drosophila , the honey bee Apis cerana and the silkworm Bombyx mori ( 18 – 20 ). However, two antiviral screening experiments failed to show that AMPs are a class of antiviral factors in Drosophila ( 21 , 22 ). Intriguingly, other data in the literature have indicated that AMPs have antiviral function in Drosophila and B. mori ( 23 , 24 ).…”

Viruses in Laboratory Drosophila and Their Impact on Host Gene Expression

“…The authors also reported no differentially expressed immune genes in response to DMelSV [ 134 ]. However, another study found an increase in DMelSV replication in PGRP-LC and domeless knockout flies, suggesting the recruitment of IMD and JAK/STAT pathways respectively in DMelSV infection [ 135 ].…”

Role of Elevated Intracellular S-Adenosylhomocysteine in the Pathogenesis of Alcohol-Related Liver Disease

“…Importantly, ablation of these PLINs causes significant increases in VLDL secretion [ 33 ] to improve hepatic steatosis [ 33 , 34 , 35 ]. PLIN5 is another LD family of protein that is highly expressed in oxidative tissues including liver [ 36 ]. Trevino et al reported that a rise of PLIN5 in the liver drives lipid accumulation [ 37 ] by impairing lipolysis through its interaction with lipolysis regulatory proteins [ 38 ].…”