Fruit flies with a mutation in one copy of a gene that plays a role in energy metabolism live almost twice as long as their wild type cousins, according to a new study. Stephen L. Helfand and colleagues from the University of Connecticut appropriately named the gene Indy for "Im not dead yet"--a quote from Monty Python and the Holy Grail.

Living a longer life does not mean the mutated flies endure a lengthier old age. In fact, they lay just as many eggs and are just as active as ordinary Drosophila flies. The females actually remain fertile for longer. Their altered gene, Indy, encodes a protein that is very similar to a human membrane transport protein, which takes up certain molecules of the Kreb's cycle, a series of chemical reactions in the body that create energy. The Indy protein is made, among other fly tissues, in the midgut and in the fat body--the flys equivalent to a liver. Indy is not the first known gene that determines life span--Methuselah is another in flies--but it is the first that appears to have a direct role in metabolism. Therefore it "may represent a new class of longevity genes," the scientists write in an article in todays issue of Science.

Mutating the fly transporter may slow down energy metabolism, as does caloric restriction (eating less), a tactic known to increase the life span of mice. Some people already practice caloric restriction in the hopes of living longer (see The Famine of Youth), but there is no proof as yet that this strategy works in humans. Further examination of Indy, on the other hand, might provide a "point of access for genetic and pharmacological interventions for extending life span," the researchers write.