Will Fruit Fly Intestines Tell a Human Tale?

Microscopy often yields striking snapshots, but these colorful compositions have a less-than-glamorous subject: fruit fly intestines.

The insides of these humble critters may help researchers understand the human digestive system. Each of us has something like 500 million intestinal nerve cells, yet little is known about what they're up to. According to a recent Wellcome Trust press release, fruit fly feces have helped researchers at the University of Cambridge understand how the gut's nerve cells affect metabolism.

"We reasoned that what comes out of the gut may be able to tell us about what is going on inside," says Irene Miguel-Aliaga, who headed the study. "So, we devised a method to extract information about several metabolic features from the flies' fecal deposits-which are actually rather pretty and don't smell bad. Then we turned specific neurons on and off and examined what came out."

Gallery: Picking Out Human Clues From a Fruit Fly's Gut

Examining fruit fly poo allowed the scientists to assign different functions to different intestinal neurons. Some regulate appetite, for example, while others adjust intestinal water balance during reproduction.

Fly poo also revealed some fruit fly sex secrets. The scientists discovered that when fruit flies copulate, the male injects a sex hormone into the female that activates a group of intestinal neurons, triggering constipation and bloating. Different sex hormones cause the same symptoms in pregnant women, suggesting the mechanism may have originated long ago in some common ancestor.

But is there a benefit to being constipated when pregnant? During constipation, water is retained, intestinal contents become more concentrated, and the gut is emptied less often. The researchers argue that the resulting increase in nutrient absorption could help women meet the greater nutritional demands of pregnancy.

Boosting nutrient absorption seems like a great thing to do all the time, but there are other reasons to avoid constant constipation; it could lead to built-up metabolic waste products and changes in gut flora that shorten the lifespan. In fact, death comes sooner for female fruit flies injected with the sex hormone.

"Our research suggests that in addition to paying attention to what we eat, which has been the focus of longevity research, we may also have to consider what our body does with the food and what goes on in our guts," Miguel-Aliaga says.

By Sarah Stanley
Reprinted with permission from Discover