Sigificantly elevated expression of the CYP9 genes in a permethrin resistant strain of Aedes aegypti

Aedes aegypti is major carrier to transmit a wide variety of human and veterinary diseases including yellow fever, dengue fever, and dengue hemorrhagic fever. Up to date, effective control this vector still highly dependent on chemical insecticides. However, resistance to pyrethroid insecticides in mosquitoes has occurred and becomes a major threat to disease control programs after routine application. Mutations of para gene associated with knockdown resistance in Per-R resistant strain of Ae. aegypti have been identified. In contrast, little is known about other metabolic resistance mechanisms. Cytochome P450s are enzymes mediated detoxification of both endogenous compounds and xenobiotics. The LC50 values of permethrin in Per-R dropped from 334.5 to 21.3 ng/ml when assayed with piperonyl butoxide (PBO). The synergistic effect gave the first clue that cytochome P450 contribute to permethrin resistance development. Moreover, the total monooxygenase activity also increase 1.9-fold in Per-R was found compared to it in susceptible Bora Bora strain. Recently, Strode et al. reported an unusual expansion of CYP9 gene family in Ae. aegypti. To test whether or not the CYP9 expression involves in permethrin resistance, we designed primer sets from conserved region of CYP9 to identify expressed potential targets in Ae. aegypti. Expression profiles of eight candidates, 9J24, 9J26, 9J27, 9J30, 9J32, 9J9v1, 9J9v2, and 9M6, in both larva and adult stages were analyzed using RT-real time PCR. After internal calibration with ribosomal protein gene S17 (RpS17), 9J27, and 9M6 revealed 4.3- and 20.2-fold elevation in resistant larva. In Per-R adults, 9J26, 9J27, 9J9v1, and 9M6 gave 4.3-, 20.5-, 5.0- and 11.4-fold over expression, respectively. The elevation of CYP9 expression in Per-R provides another line of evidence that the cytochome P450 might involved in permethrin resistance development. The capability of these CYP9 enzymes to metabolize pyrethroid insecticides will be examined soon.