Genetic Tweak Could Make All Mosquitoes Harmless Males

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Janet Fang 21 May 2015, 19:32

You don’t have to hate all mosquitoes, just the females. They’re the ones that feed on blood and transmit pathogens in the process. Female Aedes aegypti mosquitoes, in particular, are responsible for spreading viruses that cause painful and sometimes deadly diseases. Now, researchers may have identified a gene that helps determine sex in that species. They call it Nix. If this works, that means future mosquito control strategies may center around converting bloodsucking females into harmless males -- or at least selectively eliminating deadlier females. The findings were published in Science this week. 

According to the World Health Organization, several hundreds of millions of people across the planet are at risk for the mosquito-borne viral infections dengue, yellow fever, and chikungunya. Unfortunately, it’s really difficult to identify single genes in the part of the insect genome where their version of our Y chromosome sits. That’s why researchers haven’t been able to pinpoint a single male-determining gene -- called an M factor -- until now. 

After analyzing male Aedes aegypti genomic DNA, a team led by Virginia Tech’s Zach Adelman and Zhijian Tu identified a candidate gene that was expressed in both adult males and early on as the embryos were still developing. They used a gene-editing tool to control the expression of this gene, the M factor Nix, and found that it’s necessary to kick off male development. Not only is it required, it’s sufficient. “The exact sequence of events that leads to mosquitoes developing as males is not clear," Adelman tells Science. “But we know that Nix is at the top of that cascade and that is what counts.”

Changes to Nix actually resulted in deformed sex organs: When they silenced the gene completely, the mutant males lost certain features on their genitals, and when the gene was expressed on other parts of the genome, mutant females ended up with masculinized genitalia. 

"Nix provides us with exciting opportunities to harness mosquito sex in the fight against infectious diseases because maleness is the ultimate disease-refractory trait," Tu says in a news release. While the researchers weren’t able to completely convert the sex with a flip of the Nix switch, these resulting mosquitos were infertile and couldn’t pass on their genes. It’s a start, and maybe one day they’ll be able to uncover more M factors that could help control the spread of disease.

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