Geneticists Create 3,500 Fly Strains To Find One That Moonwalks

Sometimes you have to take a step backward to make an advance.

Fruit fly

Wikimedia Commons

How does the brain tell the body to walk backward? Scientists don't know. To find out, researchers developed 3,500 different strains of fruit flies. Each genetically-modified fly carried genetic switches in different parts of the brain that are activated by heat, a technique called thermogenetics. When these genetic switches were activated, they caused different neurons to fire. The scientists finally found a fly that began walking backward when its genetic switches were activated by heat, and from there they found which neurons were firing.

As it turns out, walking backward (at least in fruit flies) is controlled by two neurons. As Science Magazine explains:

One [neuron] lived in the brain and extended its connections to the end of the ventral nerve cord—the fly’s version of a spine, which runs along its belly. The other neuron had the opposite orientation—it started at the bottom of the nerve cord and sent its messaging cables—or axons—into the brain. The neuron in the brain acted like a reverse gear in a car; when turned on, it triggered reverse walking.

The first neuron appears to be the "initiator," compelling the fly to "moonwalk" when it encounters certain cues, like an obstacle. And the second gene acts like a brake, perhaps preventing it from backing into something. The researchers, whose study was published in Science, will use these neurons as a starting point to find other networks involved in walking backward, such as those responsible for touch, sight, and smell.