Chris Potter of Neuroscience on the fruit fly, Drosophila melanogaster, being an excellent tool for genetic research of neuronal function
What made you decide to study the olfactory system in fruit flies?
POTTER: For one thing, it’s a really beautiful system. There are a lot of genetic tools you can use to study its anatomy and function.
When I first entered the olfactory field, scientists had just worked out which odorants activated which olfactory receptors in the neurons of the fly antenna. (In people, the receptors reside in the nose.) Those findings made me want to figure out the next step, to characterize the populations of neurons in the brain that received this sensory input from the antenna and turned it into the perception we know as smell.
Which has a better sense of smell, people or fruit flies?
POTTER: We do. The fly has about 60 odorant receptors. Humans have about 400 functional receptors. But there isn’t a one-to-one relationship between odorant recognition and odorant receptor numbers. An odorant might activate five different receptors. To be safe, we can say that the number of odorants that can be detected is an order of magnitude (or about 10 times) more than the number of receptors a species has. So flies can likely detect more than 600 odors, and humans can detect more than 4,000 different odors.
Dogs are better smellers than humans because they have more functional odorant receptors, around 800. Mice, however, might be able to outperform all of those animals. With around 1,000 functional odorant receptors, they might be able to sense 10,000 different smells.
What’s been surprising to you about olfaction in the fly?
POTTER: When I started, I was fairly naïve about the fly olfactory system. I thought its neurons would be something like a straight stick. But now I know that those neurons are extremely complicated. They make intricate projection patterns with numerous branches, just like a human neuron. A neuron might reach from the right side of the brain to the left, making many branches and taking side routes along the way.
And for a fly to take olfactory information and turn it into behavioral output, an olfactory neuron must have a lot of cross talk with other systems. For example, a male fly might smell a pheromone that signals that a female fly has already been mated, and at the same time see a female fly. The neurons that process that odor might also receive input from the visual system, which conveys the fact that a female fly is present, and also communicate to the motor neurons a message that tells the fly: Walk away from the already mated female fly. It’s unbelievably complicated.
So the brain of our little fruit fly is more powerful at understanding this world than any supercomputer we have. It’s just incredible.
-Interviewed by Melissa Hendricks