Abstract
Ten constitutively differentially expressed miRNAs were previously described between DDT-resistant 91-R and -susceptible control Drosophila melanogaster strains, and among their predicted target genes were those associated with metabolic DDT resistance mechanisms. The present study evaluated the inducibility of miRNA expression and putative downstream regulation of cytochrome P450s in response to DDT exposure in a time-dependent manner in 91-R and the susceptible Canton-S strain. Specifically, RT-qPCR analysis showed that DDT exposures led to the significant down-regulation (repression) of miR-310-3p, miR-311-3p, miR-312-3p, miR-313-3p, and miR-92a-3p levels in Canton-S. This is contrasted with the lack of significant changes in 91-R at most time-points following DDT exposure. The levels of expression among miRNAs exhibited opposite expression patterns compared to their corresponding putative target cytochrome P450s at the same time points after DDT exposure. Collectively, results from this study suggest that miR-310-3p, miR-311-3p, miR-312-3p, miR-313-3p, and miR-92a-3p might have a potential role in the control of DDT detoxification through the post-transcriptional regulation of target cytochrome P450s in Canton-S. Conversely, the lack of significant changes of these same miRNAs in 91-R following DDT-exposure suggests a possible adaptive mutation that removes repressive control mechanisms. These data are important for the understanding impact of adaptive changes in miRNA expression on post-transcriptional regulatory mechanism involved in the evolution of DDT resistance in 91-R.
Highlights
For well over half a century, second generation insecticides have been used across the globe as one of the most cost-effective ways to control pest insects, directly impacting human health through methods of crop production and the management of vector-borne diseases
No significant changes were detected in miRNA expression for any of the eight miRNAs within acetonetreated control flies from either strain across any sampling time points (P-values ≥ 0.05; Supplementary Table S2)
At 72 h after DDT exposure, the expression of miR-310-3p, miR-311-3p, and miR-313-3p showed no significant difference compared with acetone-treated flies (Figures 1A,B,D), whereas the miR-312-3p and miR-92a-3p remained down-regulated after 72 h post-DDT treatment in Canton-S with approximate 0.6- and 0.42-fold reductions (Figures 1C,E)
Summary
For well over half a century, second generation insecticides have been used across the globe as one of the most cost-effective ways to control pest insects, directly impacting human health through methods of crop production and the management of vector-borne diseases. The organochlorine insecticide dichlorodiphenyltrichloroethane (DDT) was widely used in the decades post-WWII for the control of agricultural and disease vectoring pest insects (Edman, 2004; Hemingway, 2009), it was banned in most countries due to deleterious environmental side effects as well as its impacts on non-target mammalian and avian species (Krupke et al, 2007). In some Drosophila strains, historically, moderate and high levels of DDT resistance have been considered to be polygenic and associated with contribution of multiple resistance genes to the phenotype (Kim et al, 2018), including metabolic-based resistance influenced by the alteration of enzyme activities that degrade or sequester insecticides (Li et al, 2007). DDT resistance in the Drosophila strain 91-R has been associated with genetic and signal transduction pathways that converge to modify stress response, cell survival, and neurological functions (Seong et al, 2017)
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