Kill-save gene combo might fight malaria.

A technique that might someday enlist mosquitoes in the fight against malaria has passed an early test in lab fruit flies. Researchers have been working for years to genetically engineer mosquitoes so that they don't spread the disease. The effort revealed some malaria-resistance genes, but a thornier problem has been how to disperse those genes throughout a wild population.

California researchers modeled their work on a genetic element, called Medea, in flour beetles. It spreads rapidly because offspring of a cartier mother survive only if they also carry it.

The molecular workings of Medea in flour beetles remain a mystery, so Bruce Hay of the California Institute of Technology in Pasadena, Calif., and his colleagues invented a genetic construct that has the same effect in fruit flies.

Hay's team used a short bit of RNA, a microRNA, that switches off the activity of mpd88, a gene critical for development of a fruit fly embryo. They combined the gene for that microRNA with a version of myd88 that's insensitive to the microRNA.

If a fruit fly mother carries the combo, she makes egg cells that are packed with the destructive microRNA. After the eggs are fertilized, the resulting embryos thrive if they contain the construct with the insensitive version of myd88. But in the embryos that didn't receive the Medea-like element with its rescue capability, the microRNA from the egg sabotages the embryo.

When the scientists put their engineered fruit flies in cages with three times as many unaltered fruit flies, all the offspring carried the new gene combo after 9 to 11 generations. The research now appears online at Science.