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

The development of genetically modified mosquitoes (GM) and their subsequent field release offers innovative approaches for vector control of malaria. The Ag(PMB)1 strain of Anopheles gambiae mosquitoes shows sex ratio distortion caused by the Mendelian-inherited transgene [3xP3-DsRed]β2-eGFP::I-PpoI-124L that was generated into the genetic background of the G3 laboratory strain. When Ag(PMB)1 males are crossed to wild-type females, expression of the endonuclease I-PpoI during spermatogenesis causes the meiotic cleavage of the X chromosome in sperm cells, leading to fertile offspring with a 95% male bias. In line with World Health Organization guidelines for testing genetic vector control tools, the dynamics of Ag(PMB)1 have been assessed in indoor large cages, testing the potential of GM mosquitoes to control vector populations and providing a demonstration of the self-limiting nature of the transgene. In this study, the introgression of the transgene from the donor Ag(PMB)1 by six serial backcrosses into two recipient colonies of An. coluzzii that had been isolated in Mali and Burkina Faso demonstrated phenotypic stability of the sex ratio distorter in distinct genetic backgrounds. Scans of informative SNP markers and whole-genome sequencing analysis revealed a nearly complete introgression of chromosome 3 and X, but a remarkable genomic divergence in a large region of the chromosome 2 between the later backcrossed (BC6) transgenic offspring and the recipient paternal strains. These findings suggested to extend the backcrossing breeding strategy beyond BC6 generation and increase the introgression efficiency of critical regions that have ecological and epidemiological implications through the targeted selection of specific markers.