Identification of the key genes, its variants and structural variations associated with insecticide resistance in the Sahelo-Sudanian and Savannah populations of a major malaria vector

Abstract applies to Sahel data only (not Gounougou samples). Information on common metabolic resistance mechanisms and their molecular basis in populations of the major malaria vectors from different regions/countries, sharing similar eco-climatic characteristics will facilitate proper coordination of malaria control. Here, we characterized populations of the major malaria vector Anopheles coluzzii from the Sahel and Sudan savannah regions (hereby after, the Sahel) of sub-Saharan Africa (Nigeria, Niger, Chad and Cameroon). RNAseq-based transcriptional analysis, coupled with qRT-PCR identified the major genes linked with pyrethroid resistance across the Sahelo-Sudanian region, including key cytochrome P450s, glutathione S- transferases, carboxylesterases, and a range of proteins previously linked with cuticular resistance. Signatures of selective sweeps were observed in some of the most commonly overexpressed genes, as well as high frequencies of the 2La, 2Rb and 2Rc chromosomal inversion polymorphisms, which encode some of the most overexpressed metabolic resistance genes. Functional characterisation of the two most commonly overexpressed genes across the Sahel (GSTe2 and CYP6Z2) validated their role in multiple resistance. Transgenic Drosophila melanogaster flies expressing GSTe2 exhibited significant and extremely high resistance toward DDT and permethrin. Investigation of the role of 5' regulatory elements in overexpression of GSTe2 identified nucleotide variants putatively linked to its overexpression. Transgenic flies expressing CYP6Z2 exhibited marginal resistance to phenoxybenzyl alcohol (a primary product of pyrethroid hydrolysis) and a-cypermethrin. However, significantly higher mortalities were obtained in transgenic files expressing CYP6Z2 compared with controls on exposure to the neonicotinoid clothianidin, which suggests possible bioactivation of a toxic intermediate of this insecticide. This result indicates that clothianidin may form a useful tool against An. coluzzii over-expression CYP6Z2. The translated data from this study will facilitate cross border collaborations within the Sahel region and refine implementation strategies by refocussing interventions and rationalization of scant resources, improving evidence-based cross-border policy towards local and ultimately regional malaria pre-elimination.