In addition, Or83b is found in widely divergent species of insects, including locusts, mosquitoes, moths, honeybees and medflies. "In all of these insects the gene is found in nearly all the olfactory neurons. The vast majority of cells responsible for smell have it," says Vosshall.
This is surprising because insects have evolved smell receptors tailored to their individual ecological niches: fruit flies detect fruit, for example, and mosquitoes sense humans and other warm-blooded animals. As a result, although different insect species have different genes coding for smell receptors, all of them have a gene that looks like the fruit fly Or83b gene.
Solving an old mystery
The ubiquitous Or83b gene has perplexed scientists since 1994, when Vosshall and her colleague Hubert Amrein, now at Duke University Medical Center, first identified it in fruit flies while they were postdoctoral fellows in Richard Axel's laboratory at Columbia University. But newly available genetic techniques allowed Vosshall to investigate its function by creating a strain of fruit flies lacking the gene.
"Only in fruit flies can you take the gene away and test the effect," she says, because -- unlike other insects -- fruit flies are common laboratory organisms with well-understood genetics.
The researchers wanted to know whether Or83b worked independently, like other odorant receptors, to sense a specific chemical, or played another more general role in the sense of smell. If Or83b receptors detected only one or a few odors, then flies without these receptors would still be able to smell other things. But if Or83b's function was a general one, underlying the fly's ability to smell, knocking it out would blind the insects to all odors.
Mutant flies lack a sense of smell