A global team of scientists have found a way to turn female mosquito embryos into males at a genetic level, according to a paper published in Science Express. The finding could really come in handy, since females are the ones that bite, constantly hunting for blood to develop their eggs.
For some of us, mosquitoes are merely an annoyance we can solve with a simple swat or two. But in many parts of the world they carry deadly diseases and are major threat to the health of a population. There are about 200,000 cases of yellow fever each year. And of these, 30,000 result in death. There has been a number of efforts over the years to solve this problem, but the process usually involves breeding a large number of mosquitoes — which can be time-consuming and costly — and releasing the sterile males into high-risk areas.
30,000 people die of yellow fever each year
To streamline this process, researchers tried to find a genetic switch that could turn females into males. They didn’t quite do that, but they did find a way to alter their genitals. The team discovered a male-determining factor gene called "Nix" in the Aedes aegypti species of mosquito. Aedes aegypti isn't known for carrying malaria, but it is responsible for spreading other deadly diseases like yellow fever, dengue fever, and the chikungunya virus.
"When we injected Nix into mosquito embryos, we found that more than two-thirds of the female mosquitoes developed male genitals and testes," says Brantley Hall, a computational biology researcher and co-author on the paper. And when the team removed the Nix gene from male mosquitoes, they developed female genitals.
Scientists have known for about 70 years that there was a gene which controls a mosquito's sex, but no one was able to find it, according to lead author Zhijian Jake Tu, a professor of biochemistry in the College of Agriculture and Life Sciences. There's so much information to sift through that it was simply too daunting of a numbers game. Zach Adelman, an associate professor of entomology and a co-author of the paper, likens the problem to a puzzle. Even if you have 700 pieces assembled, it can still be hard to make sense of the ones that remain.
The mosquito genome is like an unfinished puzzle
"Jake and his students found a way to look in those pieces and find a really, really important gene just sitting there," Adelman says. "That [gene] wasn’t part of the assembly because no one could find it. It looked like all the other pieces."
The researchers did this by developing a much more effective computational method that examines information buried in what's referred to as the "black hole" of the genome — regions full of duplicate information that are extremely hard to sequence. It was there where they discovered Nix. Although scientists have performed many sterile male mosquito releases over the years, the practice is fraught with inefficiencies and extra costs. For example, companies that perform these releases have no way of breeding only males. "They're throwing away half of the mosquitoes that they rear because they’re females," Adelman says. "If we have a strain that doesn’t even make females then you don’t have to spend all the labor costs associating with separating those out, and you don’t have to spend the money rearing them and then throwing them away."
We're still years away from this process being used
Adelman says they are still a "number of years" away from perfecting the method. Right now they are only able to activate this male-determining gene by changing it in mosquito embryos, which means that the gene doesn’t always reach all the cells. As a result of this, the rest of the adult bodies weren't completely converted to male form. The team wants to get past modifying embryos and eventually exploit this male-determining factor by using transgenics, essentially changing this specific gene in mosquitoes on a deep enough cellular level that they pass it on to any offspring. "You would have a much stronger effect," Tu says. "It could be a converted, full, sterile male."
If the team can get to this point, the efficiency of mass releasing sterile males would drastically increase. When that day comes, we'll have our best weapon yet in the fight against mosquito-borne diseases.