Abstract
BackgroundInsects may use various biochemical pathways to enable them to tolerate the lethal action of insecticides. For example, increased cytochrome P450 detoxification is known to play an important role in many insect species. Both constitutively increased expression (overexpression) and induction of P450s are thought to be responsible for increased levels of detoxification of insecticides. However, unlike constitutively overexpressed P450 genes, whose expression association with insecticide resistance has been extensively studied, the induction of P450s is less well characterized in insecticide resistance. The current study focuses on the characterization of individual P450 genes that are induced in response to permethrin treatment in permethrin resistant house flies.ResultsThe expression of 3 P450 genes, CYP4D4v2, CYP4G2, and CYP6A38, was co-up-regulated by permethrin treatment in permethrin resistant ALHF house flies in a time and dose-dependent manner. Comparison of the deduced protein sequences of these three P450s from resistant ALHF and susceptible aabys and CS house flies revealed identical protein sequences. Genetic linkage analysis located CYP4D4v2 and CYP6A38 on autosome 5, corresponding to the linkage of P450-mediated resistance in ALHF, whereas CYP4G2 was located on autosome 3, where the major insecticide resistance factor(s) for ALHF had been mapped but no P450 genes reported prior to this study.ConclusionOur study provides the first direct evidence that multiple P450 genes are co-up-regulated in permethrin resistant house flies through the induction mechanism, which increases overall expression levels of P450 genes in resistant house flies. Taken together with the significant induction of CYP4D4v2, CYP4G2, and CYP6A38 expression by permethrin only in permethrin resistant house flies and the correlation of the linkage of the genes with resistance and/or P450-mediated resistance in resistant ALHF house flies, this study sheds new light on the functional importance of P450 genes in response to insecticide treatment, detoxification of insecticides, the adaptation of insects to their environment, and the evolution of insecticide resistance.
Highlights
Insects may use various biochemical pathways to enable them to tolerate the lethal action of insecticides
Response of P450 genes to permethrin challenge in resistant and susceptible house flies Based on this pilot experiment, we focused our study on CYP4D4v2, CYP4G2, and CYP6A38 in order to further characterize their overexpression in response to permethrin challenge in resistant and susceptible house flies using the quantitative real-time PCR method, as described below under Materials and Methods
To determine whether there is a causal link between the P450 genes and insecticide resistance, we examined the genetic linkage of CYP4D4v2, CYP4G2, and CYP6A38 with 5 back-cross (BC1) house fly lines derived from crosses of ALHF and a susceptible morphological marker strain, aabys, by allele specific single nucleotide polymorphism (SNP) determination
Summary
Insects may use various biochemical pathways to enable them to tolerate the lethal action of insecticides. Increased cytochrome P450 detoxification is known to play an important role in many insect species Both constitutively increased expression (overexpression) and induction of P450s are thought to be responsible for increased levels of detoxification of insecticides. A significant characteristic of insect P450s that is associated with enhanced metabolic detoxification of insecticides in insects is the constitutively increased levels of P450 proteins and P450 activity that result from constitutively transcriptional overexpression of P450 genes in insecticide resistant insects [3,6,7,8,9,13,14] Another feature of insect P450 genes is that the expression of some P450 genes can be induced by exogenous and endogenous compounds [3], a phenomenon known as induction. It has been suggested that the induction of P450s and their activities in insects is involved in the adaptation of insects to their environment and the development of insecticide resistance [15,16]
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