Abstract
Homing-based gene drives, engineered using CRISPR/Cas9, have been proposed to spread desirable genes throughout populations. However, invasion of such drives can be hindered by the accumulation of resistant alleles. To limit this obstacle, we engineer a confinable population modification home-and-rescue (HomeR) drive in Drosophila targeting an essential gene. In our experiments, resistant alleles that disrupt the target gene function were recessive lethal and therefore disadvantaged. We demonstrate that HomeR can achieve an increase in frequency in population cage experiments, but that fitness costs due to the Cas9 insertion limit drive efficacy. Finally, we conduct mathematical modeling comparing HomeR to contemporary gene drive architectures for population modification over wide ranges of fitness costs, transmission rates, and release regimens. HomeR could potentially be adapted to other species, as a means for safe, confinable, modification of wild populations.
Highlights
Effective insect control strategies are necessary for preventing human diseases, such as malaria and dengue virus, and protecting crops from pests
We chose DNA Polymerase gamma subunit 2 (PolG2, DNA polymerase Ɣ 35-kDa, CG33650), required for the replication and repair of mitochondrial DNA (Carrodeguas, 2000; Carrodeguas et al, 2001) whose LOF results in lethality (Iyengar et al, 2002)
We found that only exuperantia (CG8994) large fragment (exuL)-Cas9 induced the male-specific super-Mendelian inheritance of PolG2HomeR; transheterozygous males, but not females, transmitted PolG2HomeR to more than 50% of F1 progeny
Summary
Effective insect control strategies are necessary for preventing human diseases, such as malaria and dengue virus, and protecting crops from pests. When these alleles are positively selected they can hinder HGD spread in laboratory cage populations (Champer et al, 2017; Hammond et al, 2017; Kandul et al, 2020; KaramiNejadRanjbar et al., 2018; Oberhofer et al, 2018), with one exception that targeted a conserved sex determination gene for population suppression (Kyrou et al, 2018; Simoni et al, 2020) This resistance arises from, in addition to HDR, Cas9/gRNA-directed DNA cuts are repaired by alternative DNA end joining (EJ) repair pathways, including non-homologous (NHEJ) and microhomologymediated end-joining (MMEJ), that can introduce insertions or deletions (indels) at the target site(s). Given the simplistic design this system could be adapted to other species
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