Mosquitoes are carriers of many diseases, such as yellow fever virus, West Nile virus and malaria. One potential strategy for managing the transmission of diseases from mosquitoes to humans is genetic modification, in which the introduction of transgenes could allow mosquito populations to be controlled, suppressed or altered to reduce the possibility of transmission. However, any genetic modification strategy will require that great precautions be taken to prevent the unintentional, permanent alteration of wild populations. Researchers at Texas A&M AgriLife Research have now developed a method that would allow temporary genetic modifications in mosquitoes to eliminate themselves over generations, ensuring that gene modification strategies can be tested safely and responsibly.
The transgene removal system designed by the researchers is based on single-strand annealing (SSA), a DNA repair mechanism in eukaryotic organisms. The system was tested by inserting transgenes for DsRED and EGFP into the gene that controls eye color in Aedes aegypti mosquitoes. The DsRED and EGFP transgenes were flanked by direct repeat sequences, and induction of DNA double-strand breaks triggered removal of the transgenes and repair of the wild-type gene via the SSA pathway. With this removal and repair system preprogrammed into the transgenic sequence, the researchers could ensure elimination of the transgene and restoration of the wild-type over multiple generations.
The modified mosquitoes had white eyes, red fluorescence in the eyes and green fluorescence in the body. As the mosquitos were bred over several generations, the amount of modified mosquitoes substantially decreased, with populations regaining normal eye pigment and losing red and green fluorescence. This proof-of-principle study demonstrates the possibility of a self-deleting, temporary transgene that would protect wild populations from permanent alteration as genetic modification strategies are tested. This research was published in PNAS Nexus.
“Many groups are developing genetic methods for mosquito population control,” said corresponding author Zach Adelman. “Our method provides a braking system that can restore sequences in the wild.”
Because the SSA repair pathway is shared across many different organisms, the researchers believe the same concept could potentially be applied in genetic modification of other species.