IDENTIFICATION OF GENES INVOLVED IN THE ANTIVIRAL RESPONSE THROUGH GENETIC SCREENS IN DROSOPHILA

Abstract

Innate immunity is essential for the host to defend against invading pathogens, such as viruses and bacteria. To identify novel genes or molecules that are involved in innate immunity, we carried out two genetic screens in Drosophila. From a forward screen of flies mutagenized with Ethyl methane sulfonate (EMS), four mutants with increased susceptibility to Drosophila X virus (DXV) were found. In this study, we focused on the rogue mutant and identified a novel antiviral gene rogue. The rogue mutant is highly susceptible to DXV infection and is unable to control viral replication during infection. The expression of rogue in either the hemocytes or the fat body is required for flies to control viral accumulation and to survive a viral infection. At an early stage of infection, rogue is induced and the amount of Rogue protein that locates to the nucleus increases. In addition, we confirm that the Rogue protein interacts with the polyA binding protein (PABP), and we propose that rogue restricts viral replication via translation regulation in Drosophila. The rogue mutant also has a phagosome maturation defect, which may contribute to its susceptibility to Staphylococcus aureus infection. RNAi knockdown of rogue in the fat body or the hemocytes in wild type flies results in high bacterial susceptibility. Introducing the rogue transgene in the hemocytes of the rogue mutant can rescue the mutant survival to both DXV and S. aureus. Together, our results demonstrate that rogue plays a critical role in defending against DXV and S. aureus infections. We performed another genetic screen on wild derived inbred flies from the Drosophila Genetic Reference Panel (DGRP). From a genome wide association study (GWAS) in these flies, we found four single nucleotide polymorphisms (SNPs) associated with susceptibility of flies to DXV. One allele contributed most to the susceptibility is located in the intron of Socs36E, a negative regulator of the JAK-STAT pathway, implicating that the JAK-STAT pathway plays a role in the immune responses against DXV. Our study also shows that natural genetic variation can be used as a tool for identifying novel genes or pathways involved in antiviral immunity.