Integration of whole genome sequencing and transcriptomics reveals a complex picture of the reestablishment of insecticide resistance in the major malaria vector Anopheles coluzzii

Abstract

Insecticide resistance is a major threat to gains in malaria control, which have been stalling and potentially reversing since 2015. Studies into the causal mechanisms of insecticide resistance are painting an increasingly complicated picture, underlining the need to design and implement targeted studies on this phenotype. In this study, we compare three populations of the major malaria vector An. coluzzii: a susceptible and two resistant colonies with the same genetic background. The original colonised resistant population rapidly lost resistance over a 6-month period, a subset of this population was reselected with pyrethroids, and a third population of this colony that did not lose resistance was also available. The original resistant, susceptible and re-selected colonies were subject to RNAseq and whole genome sequencing, which identified a number of changes across the transcriptome and genome linked with resistance. Firstly, an increase in the expression of genes within the oxidative phosphorylation pathway were seen in both resistant populations compared to the susceptible control; this translated phenotypically through an increased respiratory rate, indicating that elevated metabolism is linked directly with resistance. Genome sequencing highlighted several blocks clearly associated with resistance, including the 2Rb inversion. Finally, changes in the microbiome profile were seen, indicating that the microbial composition may play a role in the resistance phenotype. Taken together, this study reveals a highly complicated phenotype in which multiple transcriptomic, genomic and microbiome changes combine to result in insecticide resistance.

Sympatric Populations of the Anopheles gambiae Complex in Southwest Burkina Faso Evolve Multiple Diverse Resistance Mechanisms in Response to Intense Selection Pressure with Pyrethroids

“…RNA was extracted from pools of 5, 3–5 day old presumed-mated adult females, snap frozen in the −80 °C at 10 am, using a PicoPure kit (Applied Biosystems Thermo Fisher, Waltham, MA, USA, after homogenisation with a motorised pestle. Quality and quantity of the RNA was analysed using an Agilent TapeStation (Santa Clara, CA, USA) and Nanodrop (Thermo Fisher) respectively, and three (Moz, Gaoua-ara, N’Gousso, Tiefora) or four (Banfora, VK72014, Kisumu, Bakaridjan) replicates from each strain sent for sequencing at Centre for Genomics, Liverpool, UK (RNA extractions for Banfora were performed as part of a separate study [ 31 ] but using the same methodology).…”

New insights into cypermethrin insecticide resistance mechanisms of Culex pipiens pallens by proteome analysis

“…In fact, an increased respiratory rate appears to directly contribute to pyrethroid resistance through upregulation of the oxidative phosphorylation pathway in resistant populations of Anopheles coluzzii. 57 In the present study, the changes in the oxidative phosphorylation pathway in cypermethrin-resistant Cx. pipiens pallens compared to the susceptible strain may be linked with cypermethrin resistance.…”

Vector control: agents of selection on malaria parasites?

“…Due to insecticide decay and insecticide resistance (IR) mechanisms, exposure to sublethal insecticide doses occur. In the short term, this stimulates changes to detoxification and redox metabolism gene expression [30,33], and reduces host-seeking and blood feeding [20,77]. Longer term effects include reduced survival of both IR and insecticide-susceptible (IS) mosquitoes [77,78], but lifespan is not affected in some highly resistant populations [79].…”

“…Altered resource allocation Like all organisms, mosquitoes have a finite amount of resources, and face life history trade-offs where they must differentially allocate resources between life history traits (e.g., immune defences vs. reproduction, antioxidants vs. immune defences). Life history trade-offs may explain in part the reduced fecundity of IR mosquitoes compared to their susceptible counterparts [27], as well as their differences in microbiota [28], immune gene expression [29], respiration rate [30], and lifespan [31]. Additionally, most IR mechanisms involve overproduction of proteins, which requires the investment of resources.…”

“…Yet, if maintaining physiological health and fecundity comes at the expense of lifespan, parasites may suffer from premature vector mortality. Thus, the net effects of mosquito life history strategies on parasite transmission may pivot on mechanisms that affect ROS levels in potentially contrasting ways [30,33]. This complexity is highlighted by the contrasting effects of the detoxification enzymes, the P450s and GSTs (Box 1), which elevate and reduce oxidative stress respectively [10].…”