Skandalis et al. 



JESO Volume 139, 2008 



severe problems, both for insects (de Miranda et al. 2008) and for humans, as for example 

 in the case of tick-borne encephalitis virus or the mosquito-born West Nile virus (Brauchli 

 et al. 2008; Orshan et al. 2008). Moreover, elucidation of the interactions between insect 

 viruses and their hosts would help in increasing the efficacy of the many schemes currently 

 underway to use viruses as agents of biological control against insects and for high- 

 throughput production of proteins in insect hosts (Nicholson 2007; Possee et al. 2008). 



In order to elucidate host-virus interactions in insects, an appropriate model system 

 is Drosophila because it has been the subject of extensive genetic investigations and its gene 

 makeup is largely known (Warren et al. 2006; Lai et al. 2007). Drosophila relies on a large 

 repertoire of innate immune defense mechanisms against microbial infections (Lemaitre 

 and Hoffman, 2007). However, with respect to viral infections, RNAi is the only known 

 effector mechanism that has been identified in Drosophila (Wang et al. 2006). Microarray 

 analysis of genes expressed in Drosophila infected with Drosophila C virus (DCV) indicated 

 a transcriptional response to viral infection that differed from bacterial or fungal infection 

 (Dostert et al. 2005). In particular, viral infection was accompanied by an upregulation of 

 the JAK-STAT pathway, which also plays an important role in mammalian viral infections. 

 Several prominent immune reactions and pathways are shared between Drosophila and 

 mammals, such as phagocytosis and the Toll-mediated pathways (Lemaitre and Hoffman, 

 2007). These similarities point to a common evolutionary ancestry in immune reactions to 

 microbial infection and suggest other common reactions. In mammals, viral infection may 

 also be accompanied by changes in host post-transcriptional RN A processing and translation 

 (Adair et al. 2006). Some mammalian DNA and RNA viruses, lacking introns, such as 

 Herpes simplex virus, can completely shut down host mRNA splicing machinery without 

 affecting viral gene expression (Muhlemann et al. 2000; Lindberg et al. 2002). On the other 

 hand, vaccinia virus and adenovirus rely on the host splicing machinery to process their 

 genes (Yue et al. 1999; Huang et al. 2002). Conversely, mammalian hosts have been shown 

 to use alternative transcripts to combat viral infection (Dinesh-Kumar et al. 2000; Fridborg 

 et al. 2004). It is not currently known whether these mammalian infection responses also 

 occur in insects. 



In this study we have investigated the changes in Drosophila post-transcriptional 

 RNA processing following infection by Flock House Virus (FHV). FHV is a positive 

 strand RNA virus belonging to the Nodaviridae family and its RNA replication and virion 

 assembly take place on the outer mitochondrial membrane of the infected cells (Ball et al. 

 1992; Miller et al. 2001). It can infect in several orders of insects, including Coleoptera, 

 Lepidoptera, Diptera, and Hemiptera, as well as a nematode, plants, and yeast (Dasgupta et 

 al. 2007). 



We have analyzed splice variant transcripts of the Drosophila melanogaster 

 8-oxoguanine DNA glycosylase {Oggl) gene following infection of macrophage-like 

 Drosophila line 2 cells (DL2) with FHV. Oggl is a DNA repair gene that is neither directly 

 involved in host antiviral defense nor evidently useful to an RNA virus. It was selected 

 to enable us to determine whether splicing instability is targeted to loci associated with 

 viral infection and defense or whether its effects are broader. In this communication we 

 report changes in the frequency and types of partially spliced Oggl transcripts during FHV 

 infection. We suggest that some of the splice variants observed during infection may be the 

 result of infection-associated reduction in splicing efficiency. 



50 



