A whole transcriptome approach to investigate the genes involved in permethrin resistance in the Southern house mosquito Culex quinquefasciatus

A large number of studies have shown that multiple genes may be responsible for insecticide resistance and differential gene expression has been observed in resistant mosquitoes. In the current study, for the first time, we investigated the gene expression profiles between a field strain of Culex quinquefasciatus, HAmCq^G0, having a low level (10-fold) of permethrin resistance, and its 8th generation permethrin-selected progeny, HAmCq^G8, exhibiting a ~2700-fold high level of resistance using a whole-transcriptome sequencing approach. Overall, ~30 - 35% of all Cx. quinquefasciatus putative transcripts were expressed with at least 3x coverage, whereas, another ~30% of them were detected at lower coverage rates. Among the transcripts identified, about 2000 of them were differentially expressed between the field parental strain HAmCq^G0 and its permethrin-selected offspring HAmCq^G8 , including genes that are involved in cellular and molecular metabolism and detoxification, cellular signaling transduction, protective immunity, muscle composition, and protein biosynthesis and degradation. Furthermore, when the sequences of these transcripts were compared to those in the completely sequenced Cx. quinquefasciatus strain Johannesburg, ~56,000 SNPs were identified in HAmCq^G0 while <38,000 were present in HAmCq^G8, suggesting that the selection pressure of the permethrin may be a factor for the reduction of the SNPs in HAmCq^G8. This study provided a global profile of all differentially expressed genes between low and highly-resistant mosquitoes and the findings of this study will directly impact the understanding of the complex processes responsible for insecticide resistance in mosquitoes.