Transcriptomic analysis reveals pronounced changes in gene expression due to sub-lethal pyrethroid exposure and ageing in insecticide resistance Anopheles coluzzii

Abstract

Background: Malaria control is heavily reliant on the use of insecticides that target and kill the adult female Anopheline vector. The intensive use of insecticides of the pyrethroid class has led to widespread resistance in mosquito populations. The intensity of pyrethroid resistance in some settings in Africa means mosquitoes can contact bednets treated with this insecticide class multiple times with minimal mortality effects. Furthermore, both ageing and diel cycle have been shown to have large impacts on the resistance phenotype. Together, these traits may affect other aspects of vector biology controlling the vectorial capacity or fitness of the mosquito.

Results: Here we show that sublethal exposure of a highly resistant Anopheles coluzzii population originally from Burkina Faso to the pyrethroid deltamethrin results in large and sustained changes to transcript expression. We identify five clear patterns in the data showing changes to transcripts relating to: DNA repair, respiration, translation, behaviour and oxioreductase processes. Further, we highlight differential regulation of transcripts from detoxification families previously linked with insecticide resistance, in addition to clear down-regulation of the oxidative phosphorylation pathway both indicative of changes in metabolism post-exposure. Finally, we show that both ageing and diel cycle have major effects on known insecticide resistance related transcripts.

Conclusion: Sub-lethal pyrethroid exposure, ageing and the diel cycle results in large-scale changes in the transcriptome of the major malaria vector Anopheles coluzzii. Our data strongly supports further phenotypic studies on how transcriptional changes such as reduced expression of the oxidative phosphorylation pathway or pyrethroid induced changes to redox state might impact key mosquito traits, such as vectorial capacity and life history traits.

Keywords: Anopheles coluzzii; Insecticide resistance; Pyrethroids; Sub-lethal exposure; Transcriptome.

Fig. 1

Time series trends. Five rows demonstrating the temporal transcript pattern change and the associated enrichments for each trend. Experimental design is shown on the bottom two rows, with the time points (i) post 0.05% deltamethrin WHO tube exposure and (ii) matched unexposed controls. Dark rings represent darkness in the 12:12 photoperiod

Fig. 2

Transcripts significant across all time points. Expression levels as fold changes (y) across all time points (x) for each transcript significantly differentially expressed across all time points (adjusted p < 0.05). Titles of the graphs include both transcript IDs and gene names

Fig. 3

Cytochrome p450 pyrethroid metabolisers. Transcript expression level for 8 cytochrome p450s that have previously been shown to bind insecticide directly [16, 37, 38]. Dark grey boxes represent non-significant transcripts

Fig. 4

Transcripts in the oxidative phosphorylation pathway down regulated by pyrethroid exposure. Modified KEGG pathway showing all transcripts in the oxidative phosphorylation in An. gambiae (KEGG organism: aga). Darkened boxes represent transcripts that are significantly down regulated in at least one time point in the time course data. ND1–6 are not represented on the microarray as they are mitochondrial genes