Small RNA response to infection of the insect-specific Lammi virus and Hanko virus in an Aedes albopictus cell line. Aedes albopictus

The RNA interference (RNAi) mediated antiviral immunity is thought to be the primary defense against viral infection in mosquitoes. Production of virus-specific small RNA have been demonstrated in mosquitoes and mosquito-derived cell lines for viruses in all of the major arbovirus families. However, many if not all mosquitoes are infected with a group of viruses known as insect-specific viruses (ISVs) and the immune response to this group of viruses is unknown. Therefore, we have sequenced small RNA libraries from an Aedes albopictus-derived cell line infected with either Lammi virus (LamV) or Hanko virus (HakV). These viruses belongs to two distinct phylogenetic groups of insect-specific flaviviruses (ISFVs). Results revealed that Both viruses elicited a strong vsiRNA response in the cells that increase over time and targeted the whole viral genome with a few predominant hotspots. Further, only the LamV infected cells produced virus-derived Piwi-like RNA, that were mainly derived from the antisense genome and did not show the typical ping-pong signatures. HakV is more distantly related to the dual-host flaviviruses than LamV, which indicate that the virus-derived Piwi-like RNA production could be specific for certain unknown sequence elements that the classical ISFVs lack. Our findings increase the understanding of the mosquito innate immunity and the ISFVs effect on its host.