Like flying syringes, mosquitoes excel at pricking your skin and drawing blood. But some species also inadvertently spread diseases, like malaria. Now researchers have taken an important step toward genetically altering mosquitoes so that they are incapable of transmitting disease. A report in the current issue of the Proceedings of the National Academy of Sciences describes a new method to insert genes into a mosquito that get passed on to its offspring.
One obstacle to genetically engineering mosquitoes has been the lack of a clear "marker"--a distinctive genetic trait that can reveal whether a gene was successfully inserted. Biologist Frank Collins of the University of Notre Dame in Indiana realized that the answer was as close as the lab next door, which for 30 years had been maintaining a colony of mutant mosquitoes with white eyes instead of the usual reddish brown. Collins and Anthony James of the University of California, Irvine, thought they might use the mutant bug to test a fancy trick: Take a bit of DNA, called a transposon, that likes to wiggle into genomes, and use it to insert a fruit fly gene for darker eye color into a mosquito's DNA.
The researchers hitched the genes for dark eyes to the transposons as cargo. Then one of the team members painstakingly injected the transposon into 900 white-eyed mosquito embryos--each about the size of a typewritten 'i.' They aimed for the part of the embryo that produces sperm or eggs in the adult. One generation later, they had their proof that the approach works: Of 120 surviving adults, three had offspring with eye colors that were reddish brown instead of white, Collins says.
The work is just the first step on the long road to engineering disease-resistant mosquitoes, says Becky Wattan, a biologist at the University of Arizona. The next step is to home in on the mutation that knocks out disease transmission and rig it to spread through a population.