The haplolethal gene wupA of Drosophila exhibits potential as a target for an X-poisoning gene drive

Abstract

A synthetic gene drive that targets haplolethal genes on the X-chromosome can skew the sex ratio towards males. Like an ‘X-shredder’ it does not involve ‘homing’ and that has advantages including the reduction of gene drive resistance allele formation. We examine this ‘X-poisoning’ strategy by targeting four of the 11 known X-linked haplolethal/haplosterile genes of Drosophila melanogaster with CRISPR/Cas9. We find that targeting the wupA gene during spermatogenesis skews the sex ratio so fewer than 14% of progeny are daughters. That is unless we cross the mutagenic males to X^XY female flies that bear attached-X chromosomes, which reverses the inheritance of the poisoned X chromosome so that sons inherit it from their father; in which case only 2% of the progeny are sons. These sex ratio biases suggests that most of the CRISPR/Cas9 mutants we induced in the wupA gene are haplolethal but some are recessive lethal. The males generating wupA mutants do not suffer from reduced fertility rather the haplolethal mutants arrest development in the late stages of embryogenesis well after fertilized eggs have been laid. This provides a distinct advantage over genetic manipulation strategies involving sterility which can be countered by the remating of females. We also find that wupA mutants that destroy the nuclear localization signal of shorter isoforms are not haplolethal as long as the open reading frame remains intact. Like D. melanogaster wupA orthologs of D. suzukii and Anopheles mosquitos are found on X chromosomes making wupA a viable X-poisoning target in multiple species.

Targeting mosquito X-chromosomes reveals complex transmission dynamics of sex ratio distorting gene drives

“…Postzygotic lethality of a significant fraction of the offspring from X-poisoning males was observed and corresponded with a highly male-biased sex ratio among survivors reaching adulthood (92% males), indicative of developmental lethality of females receiving mutant X-linked alleles. In a second Drosophila study, targeting a different X-linked HI gene involved in wing development also resulted in significant postzygotic lethality of female offspring 9 . Here, we develop and test the X-poisoning system in the malaria vector An.…”