Transgene‐mediated suppression of the RNA interference pathway in A edes aegypti interferes with gene silencing and enhances S indbis virus and dengue virus type 2 replication

RNA interference ( RNA i) is the major innate antiviral pathway in A edes aegypti that responds to replicating arboviruses such as dengue virus ( DENV) and S indbis virus ( SINV) . On the one hand, the mosquito's RNAi machinery is capable of completely eliminating DENV2 from A e. aegypti . On the other, transient silencing of key genes of the RNAi pathway increases replication of SINV and DENV2 , allowing the viruses to temporally overcome dose‐dependent midgut infection and midgut escape barriers ( MEB ) more efficiently. Here we expressed Flock house virus B2 ( FHV ‐B2) from the poly‐ubiquitin ( PUb ) promoter in A e. aegypti using the Φ C 31 site‐directed recombination system to investigate the impact of transgene‐mediated RNAi pathway suppression on infections with SINV‐TR339eGFP and DENV2‐QR94 , the latter of which has been shown to be confronted with a strong MEB in A e. aegypti . FHV‐B2 was constitutively expressed in midguts of sugar‐ and blood‐fed mosquitoes of transgenic line PUbB2 P 61. B 2 over‐expression suppressed RNA silencing of carboxypeptidase A‐1 ( AeCPA ‐1 ) in midgut tissue of PUbB2 P 61 mosquitoes. Following oral challenge with SINV‐TR339eGFP or DENV2‐QR94 , mean titres in midguts of PUbB2 P61 females were significantly higher at 7 days post‐bloodmeal (pbm) than in those of nontransgenic control mosquitoes. At 14 days pbm, infection rates of carcasses were significantly increased in PubB2 P61 mosquitoes infected with SINV ‐ TR339eGFP . Following infection with DENV2‐QR94 , midgut infection rates were significantly increased in the B 2‐expressing mosquitoes at 14 days pbm. However, B 2 expression in PUbB2 P 61 did not increase the DENV2‐QR94 dissemination rate, indicating that the infection phenotype was not primarily controlled by RNAi .