Conditional and female lethal approaches for mosquito control - PROJECT SUMMARY Gene drives (GDs) are a cutting-edge technology with the potential to improve human health, but gene drives have many limitations that impede their useful application in the wild, particularly population suppression drives. GD spread needs to outpace the fitness cost imposed on the population; otherwise, the GD will be rapidly eliminated, and the population will persist. Many species have homing efficiencies that need to be higher to overcome the high fitness load imparted on a population by population suppression drives. We aim to develop new tools in Aedes aegypti, an important disease vector with intrinsically lower homing CRISPR gene drive (HCGD) homing efficiencies, to improve the population suppression technologies to control this vector. First, we will evaluate conditional and sex-specific lethal systems that can restrict lethal transgene expression so they have a reduced fitness load on the population. These will include temperature-inducible (TI) systems with gene drive elements (GDe) that have minimal fitness costs in the population until they are exposed to high temperatures. We will also evaluate transactivating systems that are repressed in the presence of small molecules or if binary until they are crossed. These approaches will generate female lethal effectors that are confined in space and time, and, therefore, easier to drive into a population to achieve strong suppression. Since it has already proven challenging to increase homing efficiencies in Ae. aegypti, we will focus on reducing the formation and persistence of resistant alleles, another impediment to the drive. Over time, imperfect repair mechanisms cause drive target sites to become resistant to drive cleavage. As these cleavage-resistant sites accumulate over time due to increased repair errors and/or positive selection of the resistance allele, the gene drive frequency reduces in the population and may ultimately go to extinction. We will, therefore, develop a toxin-antidote (TA) drive, termed Home-and-Rescue (HomeR), to reduce the accumulation of drive alleles and improve drive performance. We will study the impact of this design on resistance allele formation, link the drive to a TI-female killing effector, and determine whether the drive can spread to fixation and cause population suppression in population cage experiments. Furthermore, we will leverage our work on the MGDrivE framework and its applications to explore the population dynamics of these sex-specific and conditional-lethal drives in Ae. aegypti. This work will allow us to better predict how a lethal HomeR drive will perform in wild populations and may elucidate essential considerations for safety, efficacy, and future HCGD designs in Ae. aegypti. Therefore, combining conditional lethal and sex-specific killing systems and a HomeR drive may overcome the low gene conversion rates in Aedes aegypti to build novel and robust population suppression drives in this important disease vector.
