Introgression of a synthetic sex ratio distortion transgene into different genetic backgrounds of Anopheles coluzzii

The development of genetically modified mosquitoes (GMM) and their subsequent fieldrelease offers innovative approaches for vector control of malaria. A non-gene drive selflimitingmale-bias Ag(PMB)1 strain has been developed in a 47-year-old laboratory G3 strainof Anopheles gambiae s.l. When Ag(PMB)1 males are crossed to wild-type females, expressionof the endonuclease I-PpoI during spermatogenesis causes the meiotic cleavage of theX chromosome in sperm cells, leading to fertile offspring with a 95% male bias. However,World Health Organization states that the functionality of the transgene could differ wheninserted in different genetic backgrounds of Anopheles coluzzii which is currently a predominantspecies in several West-African countries and thus a likely recipient for a potentialrelease of self-limiting GMMs. In this study, we introgressed the transgene from the donorAg(PMB)1 by six serial backcrosses into two recipient colonies of An. coluzzii that had beenisolated in Mali and Burkina Faso. Scans of informative Single Nucleotide Polymorphism(SNP) markers and whole-genome sequencing analysis revealed a nearly complete introgressionof chromosomes 3 and X, but a remarkable genomic divergence in a large region ofchromosome 2 between the later backcrossed (BC6) transgenic offspring and the recipientpaternal strains. These findings suggested to extend the backcrossing breeding strategybeyond BC6 generation and increasing the introgression efficiency of critical regions thathave ecological and epidemiological implications through the targeted selection of specificmarkers. Disregarding differential introgression efficiency, we concluded that the phenotypeof the sex ratio distorter is stable in the BC6 introgressed An. coluzzii strains.