Selfish, Jumping Genes Might Stop Mosquitoes From Spreading Malaria

Selfish genes could help destroy mosquitoes’ ability to carry malaria.

What’s the News: Many scientists have played with the idea of creating a genetically modified mosquito that won’t transmit malaria, which kills about 850,000 people a year, and releasing it into the wild. But in the face of the millions of mosquitoes out there that do ferry malaria around, how would the trait spread fast enough to make a difference?

Now, scientists have developed a way to cause a “selfish” gene to spread to more than half of a mosquito population over just a few generations, suggesting a method to quickly and broadly disrupt genes required for carrying malaria.

What’s the Context:

• One of the main ways scientists are hoping to spread malaria resistance is by harnessing the endless self-promotion of selfish genes, which make copies of themselves throughout a genome.
• The team used a selfish gene that insinuates itself into the genome of all of a mosquito’s offspring, rather than the usual half; in essence, it makes sure it’s present on both chromosomes, not just one. This means it can spread especially quickly.
• If it could take a gene bearing malaria resistance along with it, or, in its constant quest to insert itself all over the genome, jump into the middle of a gene that lets mosquitoes carry malaria and thus destroy it, it could mean a sea change in how we fight the disease.

How the Heck:

• The team inserted the selfish gene into a small number of mosquitoes and released them into the cages of mosquitoes that glowed in the dark, thanks to a gene for a green fluorescent protein.
• The selfish gene was designed specifically to jump into the gene for the green protein in mosquitoes’ sperm, thus destroying it. The selfish gene would be passed down to the mosquito’s offspring instead, and the cages would grow darker over time, allowing the researchers to watch the change as it happened.
• At first, the selfish gene-carrying mosquitoes made up only 1% of the population. But over time, more and more of the green proteins winked out, and by 12 generations, the gene had taken over 60% of the population, an incredibly quick victory. When the invading mosquitoes made up more of the population, the conversion happened even faster.

The Future Holds: Now that they have a way to spread a gene rapidly through a mosquito population, scientists will be looking for ways to hitch the selfish gene to malaria resistance. The team’s lead researcher told ScienceNOW that the search has already begun:

The next step, he says, is to make [the selfish gene] break up not the fluorescent protein gene but one that is crucial for malaria transmission. It could be an odor-recognition gene that helps the mosquito finds its host, for instance, or one that the malaria parasite needs to enter the mosquito’s salivary glands; the team already has 10 to 15 candidates.

Reference: Nikolai Windbichler, Miriam Menichelli, Philippos Aris Papathanos, Summer B. Thyme, Hui Li, Umut Y. Ulge, Blake T. Hovde, David Baker, Raymond J. Monnat, Austin Burt, Andrea Crisanti. A synthetic homing endonuclease-based gene drive system in the human malaria mosquito. Nature, 2011; doi:10.1038/nature09937