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Researchers convert Zika and Dengue carrying female mosquitoes to nonbiting males.

Often described as a global health emergency, the Zika virus can cause catastrophic birth defects whilst presenting with no symptoms, and when atypical disease traits do manifest they usually resemble dengue fever, a form of hemorrhagic fever. This symptomatic-based similarity can cause even further confusion as Dengue is far more prevalent than Zika with cases now doubling annually. Both viruses present with fever, skin rashes, conjunctivitis, muscle and joint pain, malaise, and headache. Furthermore, the Aedes aegypti mosquito (A. aegypti) is the main mode of transmission for both dengue and Zika, with sexual intercourse also an established mode of infection for the latter disease. Historically, prevention has comprised of vector control in affected regions, however, eradicating mosquito populations has been marred by economic status, arthropod resistance to pesticide, and construction work depleting natural habitats. Therefore, the desired solution would involve an efficient way to alter the insect’s genetic makeup resulting in a permanent knock-on effect for multiple generations throughout whole regions. Now, a study from researchers led by Virginia Tech identifies a single gene, known as Nix, capable of converting female A. aegypti mosquitoes into fertile male mosquitoes, as well as pinpointing the gene needed for male mosquitoes to fly. The team states the Nix gene has great potential for developing vector control techniques to reduce A. aegypti numbers through female-to-male gender conversion. The opensource study is published in the Proceedings of the National Academy of Sciences.

Previous studies have indicated the male A. aegypti mosquito does not bite meaning they are unable to transmit pathogens to humans. In contrast, female A. aegypti mosquitoes need blood to breed and are, therefore, capable of biting. As female A. aegypti require blood to produce eggs acquired through biting animals, they are the primary carriers of the Zika and dengue viruses, meaning their male counterparts are innocuous in comparison. Research into this mosquito species has confirmed the existence of a male-determining locus (M locus) only inherited by male offspring, which is responsible for divining the male gender in A. aegypti mosquitoes. The A. aegypti mosquito M-locus contains 30 genes, including the Nix gene, the aforementioned male-determining factor. The current study investigates whether the Nix gene alone is sufficient to convert females into fertile males permanently affecting all progeny to cause sex-conversion.

The current study inserts the Nix gene into the sex-determining chromosomal region only inherited by female A. aegypti mosquitoes. Results show the Nix gene alone, even without the M locus, was sufficient to convert females into males possessing male-like dimorphic features and gene expression. Data findings show the Nix-induced gender conversion was found to be highly permeating and non-degradable over many generations in the laboratory, meaning these eugenics will be inherited for generations to come.

The lab also identified a second gene in the M locus, named myo-sex, they then went on to show was needed for male-only flight, an ability crucial for them to mate. They explain even though the Nix gene was able to convert the females into males, the converted males could not fly as they did not inherit the myo-sex gene, which is also located in the M locus. This was confirmed by knocking out myo-sex in wild-type males resulting in the mosquitos being unable to fly, which in turn verifies that the lack of the myo-sex gene in gender-converted males is the reason they cannot fly or mate.

The team surmises they successfully converted Zika and Dengue vector female mosquitoes to nonbiting males with serious implications for mosquito control. For the future, the researchers state they now plan to investigate a method for converting females into fertile, flying male mosquitoes by inserting both the Nix and myo-sex genes into their gender-determining chromosomal region.

Source: Virginia Tech

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