MiR-279-3p regulates deltamethrin resistance through CYP325BB1 in Culex pipiens pallens

Background The overuse of insecticides to control insect vectors has promoted extensive insecticide resistance in mosquitoes. In this study, the functions of microRNA (miR)-279-3p and its target CYP325BB1 in the regulation of deltamethrin resistance in Culex pipiens pallens was investigated. Methods Quantitative real-time reverse transcription PCR was used to detect the expression levels of miR-279-3p and CYP325BB1 . Then, the dual-luciferase reporter assay system, RNA interference, CDC bottle bioassay and Cell Counting Kit-8 (CCK-8) assay were used to explore the roles of these molecules in deltamethrin resistance both in vivo and in vitro. Results The expression patterns of miR-279-3p and CYP325BB1 were compared between deltamethrin-sensitive (DS-strain) and deltamethrin-resistant (DR-strain) mosquitoes. Luciferase activity was downregulated by miR-279-3p, the effect of which was ablated by a mutation of the putative binding site for CYP325BB1 . In DR-strain mosquitoes, the expression of miR-279-3p was increased by microinjection and oral feeding of miR-279-3p agomir (mimic). CYP325BB1 mRNA levels were downregulated, which resulted in a higher mortality of the mosquitoes in miR-279-3p mimic-treated groups. In the DS-strain mosquitoes, microinjection of a miR-279-3p inhibitor decreased miR-279-3p expression, whereas the expression of CYP325BB1 was increased; the mortality of these mosquitoes decreased significantly. In addition, overexpression of pIB/V5-His- CYP325BB1 changed the sensitivity of C6/36 cells to deltamethrin in vitro. Also in DR-strain mosquitoes, downregulation of CYP325BB1 expression by microinjection of si- CYP325BB1 increased mosquito mortality in vivo. Conclusions These findings provide empirical evidence of the involvement of miRNAs in the regulation of insecticide resistance and indicate that miR-279-3p suppresses the expression of CYP325BB1 , which in turn decreases deltamethrin resistance, resulting in increased mosquito mortality. Taken together, the results provide important information for use in the development of future mosquito control strategies. Graphical abstract