title: Wolbachia Blocks Viral Genome Replication Early in Infection without a Transcriptional Response by the Endosymbiont or Host Small RNA Pathways.
abstract: The intracellular endosymbiotic bacterium Wolbachia can protect insects against viral infection, and is being introduced into mosquito populations in the wild to block the transmission of arboviruses that infect humans and are a major public health concern. To investigate the mechanisms underlying this antiviral protection, we have developed a new model system combining Wolbachia-infected Drosophila melanogaster cell culture with the model mosquito-borne Semliki Forest virus (SFV; Togaviridae, Alphavirus). Wolbachia provides strong antiviral protection rapidly after infection, suggesting that an early stage post-infection is being blocked. Wolbachia does appear to have major effects on events distinct from entry, assembly or exit as it inhibits the replication of an SFV replicon transfected into the cells. Furthermore, it causes a far greater reduction in the expression of proteins from the 3' open reading frame than the 5' non-structural protein open reading frame, indicating that it is blocking the replication of viral RNA. Further to this separation of the replicase proteins and viral RNA in transreplication assays shows that uncoupling of viral RNA and replicase proteins does not overcome Wolbachia's antiviral activity. This further suggests that replicative processes are disrupted, such as translation or replication, by Wolbachia infection. This may occur by Wolbachia mounting an active antiviral response, but the virus did not cause any transcriptional response by the bacterium, suggesting that this is not the case. Host microRNAs (miRNAs) have been implicated in protection, but again we found that host cell miRNA expression was unaffected by the bacterium and neither do our findings suggest any involvement of the antiviral siRNA pathway. We conclude that Wolbachia may directly interfere with early events in virus replication such as translation of incoming viral RNA or RNA transcription, and this likely involves an intrinsic (as opposed to an induced) mechanism.
authors.affiliation: MRC-University of Glasgow Centre for Virus Research, Glasgow, Scotland, United Kingdom.
authors.forename: Stephanie M
authors.initials: SM
authors.lastname: Rainey
authors.affiliation: Department of Genetics, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Julien
authors.initials: J
authors.lastname: Martinez
authors.affiliation: MRC-University of Glasgow Centre for Virus Research, Glasgow, Scotland, United Kingdom.
authors.forename: Melanie
authors.initials: M
authors.lastname: McFarlane
authors.affiliation: Department of Genetics, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Punita
authors.initials: P
authors.lastname: Juneja
authors.affiliation: MRC Clinical Sciences Centre, Imperial College London, London, United Kingdom.
authors.forename: Peter
authors.initials: P
authors.lastname: Sarkies
authors.affiliation: Institute of Technology, University of Tartu, Tartu, Estonia.
authors.forename: Aleksei
authors.initials: A
authors.lastname: Lulla
authors.affiliation: MRC-University of Glasgow Centre for Virus Research, Glasgow, Scotland, United Kingdom.
authors.forename: Esther
authors.initials: E
authors.lastname: Schnettler
authors.affiliation: MRC-University of Glasgow Centre for Virus Research, Glasgow, Scotland, United Kingdom.
authors.forename: Margus
authors.initials: M
authors.lastname: Varjak
authors.affiliation: Institute of Technology, University of Tartu, Tartu, Estonia.
authors.forename: Andres
authors.initials: A
authors.lastname: Merits
authors.affiliation: Gurdon Institute and Department of Genetics, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Eric A
authors.initials: EA
authors.lastname: Miska
authors.affiliation: Department of Genetics, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Francis M
authors.initials: FM
authors.lastname: Jiggins
authors.affiliation: MRC-University of Glasgow Centre for Virus Research, Glasgow, Scotland, United Kingdom.
authors.forename: Alain
authors.initials: A
authors.lastname: Kohl
mesh_terms: D000818:Animals; D002460:Cell Line; D004331:Drosophila melanogaster / Q000235:genetics*; D016679:Genome, Viral / Q000235:genetics; D006801:Humans; D035683:MicroRNAs / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D012367:RNA, Viral / Q000235:genetics*; D012672:Semliki forest virus; D013559:Symbiosis; D014158:Transcription, Genetic; D014779:Virus Replication / Q000502:physiology*; D020577:Wolbachia / Q000378:metabolism*
chemical_list: D035683:MicroRNAs; D034741:RNA, Small Interfering; D012367:RNA, Viral