Antiviral RNAi response in the Ixodes scapularis derived IDE8 cells

Several arboviruses that cause severe disease in human and life stock are transmitted by ticks. RNA interference (RNAi) and the production of virus specific small RNAs is the major antiviral response in insects (e.g. mosquitoes); however little is known about this in ticks. This study analysed the production of small RNAs in the Ixodes scapularis derived IDE8 cells for different viruses, their derived replicons (TBEV, LGTV and SCRV) or a transfected dsRNA molecule. Most small RNAs are 22 nucleotide long and map with similar frequency to the genome/ coding strand or antigenome/ non-coding strand; however their mapping along the viral genomes differs. Small RNAs of eGFP and SCRV map along the whole coding/ non coding strand suggesting dsRNA as inducer molecule; compared to LGTV and TBEV specific small RNAs that map mostly to the 5` and 3` termini. Interestingly, time course experiments of the replication deficient NS5 GAA mutant in IDE8 cells behaved similar to the wildtype replicon and showed similar production of small RNAs; suggesting replication of the NS5 GAA mutant in IDE8 cells (either by the viral replicase or other enzymes present in the IDE8 cells) in contrast to mammalian cells. This is the first time that endogenous and exogenous derived small RNAs produced in tick cells are characterized. The results increase our understanding how/ when virus specific small RNAs are induced during viral infection in tick cells and highlight the differences of small RNAs produced in tick cells versus other arboviral vectors, like mosquitoes and midges.