|An inserted Or83b gene, marked by flourescene and expressed in the antennae, restored this fly's ability to smell and shortened its life.|
Put a fruit fly on a near-starvation diet, and it is likely to live much longer than its well-fed relatives. But if it smells food, some of the life-stretching effects of the diet disappear. In a recent report in the journal Science, Dr. Gregg Roman from the Department of Biology and Biochemistry at the University of Houston and colleagues from Baylor College of Medicine and New Mexico State University report on a link between smell and life span in Drosophila. The scientists placed fruit flies on an ascetic diet known as calorie restriction, which slashes food intake and can extend an animal's life by up to 50%. The researchers then planted enticing (at least to a Drosophila) yeast paste in a screened-off end of the insects' home tubes; the flies could smell and see the goodies but not eat them. Although the calorie-restricted flies lived longer than normal, they died sooner than similarly hungry insects not exposed to the yeast scent. The smell had no impact on survival in well-fed Drosophila.
Further support that the sense of smell affects life span came when the researchers measured survival in flies harboring a mutant form of the protein Or83b. This molecule helps direct odor receptors into position in the fly's olfactory organs on the antennae. A faulty Or83b dulls the sense of smell. Interestingly, the inability to smell food stretches longevity by more than to 50%. Like many long-lived organisms, flies with mutant Or83b showed increased resistance to starvation. Restoring functional Or83b by genetic engineering restored fly longevity to normal. This study, thus, establishes that some component of the response to caloric restriction is olfactory.
"Not only can they not have their cake -- they can't smell their cake" without shortening their lifespans, said Wayne Van Voorhees, a faculty member in the Molecular Biology Program at New Mexico State University and a member of the research collaboration.
"It's incredibly exciting that the group has been able to show a link between the olfactory system and life span," says molecular geneticist Stephen Helfand of Brown University. The work reveals that the brain has control over the life span.