Flies in Space

Fruit flies are bug-eyed and spindly and they love rotten bananas. Following orders from their pin-sized brains, they can lay hundreds of eggs every day. But in a genetic research lab, at least, they can be good substitutes for humans.

Genetically speaking, people and fruit flies—Drosophila melanogaster—are surprisingly alike, explains biologist Sharmila Bhattacharya of NASA’s Ames Research Center. “About 61 percent of known human disease genes have a recognizable match in the genetic code of fruit flies,” she says, “and 50 percent of fly protein sequences have mammalian analogues.”

Because fruit flies reproduce quickly, many generations can be studied in a short time, and their genome has been completely mapped. “Drosophila is being used as a genetic model for several human diseases,” Bhattacharya says, “including Parkinson’s and Huntington’s.”

They’re about to become genetic models for astronauts too.

Rice University’s Kate Beckingham, professor of biochemistry and cell biology, working with Bhattacharya and Douglas Armstrong at the University of Edinburgh, is planning to send fruit flies to the International Space Station (ISS). The flies will begin their journey as eggs, hatch en route, and arrive at the space station in larval form. Beckingham expects the baby flies to grow and breed, producing the foundation of a swarm that will orbit Earth for 90 days. That’s not long for humans, but it is many generations of fruit flies.

The purpose of their experiment is to discover how space travel affects Drosophila—and by extension, human—genes. This is a matter of much interest to NASA. During a typical space voyage, astronauts are exposed to a range of gravitational forces. On a trip to Mars, for instance, an explorer would weigh several gravities at launch, zero gravities during the long interplanetary cruise, several more gravities descending to Mars, and 0.38 gravities while staying on the Red Planet. Beckingham and her colleagues are hoping to find out how genes will react to these gravitational changes and whether they will express themselves in new or unexpected ways.

“Genes ‘express themselves’ by commanding cells to make proteins,” Beckingham says. There are about 50,000 different proteins in the human body, and they do just about everything from digesting food to clotting blood to healing wounds. Proteins are the building blocks of cells and tissues. “If genes command a different set of proteins in space because low-gravity tells them to,” Beckingham says, “many of these things could change. There’s already evidence that weightlessness alters genetic expression.”

In 1999, scientists grew human kidney cells onboard the space shuttle. More than 1,000 of the cells’ genes behaved differently. Among other things, they produced extra vitamin D receptors. Surplus vitamin D receptors can reduce the risk of prostate cancer in men. Perhaps that’s a benefit of space flight.

Other changes are less positive. Studies have shown that disease-fighting cells in astronauts’ immune systems don’t attack germs as ferociously as they do on Earth. If an astronaut gets sick in space, it might be harder to get well again. Astronauts’ bones weaken during long voyages, and without lots of exercise, their muscles experience atrophy. “All of these things are rooted in genetic expression,” Beckingham says.

The fact that space travel affects genetic activity is not controversial. However, researchers can’t yet predict which genes will be affected or precisely how gravity signals a gene to change its ways, and this is where the fruit fly can help. Beckingham’s team will breed as many as nine generations of Drosophila onboard the ISS, with some 120 flies per generation. Back on Earth, researchers can analyze the flies to see which genes were more active or less active.

The flies will be contained inside a special habitat onboard the ISS, so the researchers can monitor their behavior. “We’ll be watching their courtship rituals, their running speed, how they fly,” Beckingham says. “These are clues to genetic activity.”

The flies also will spend some time spinning inside small centrifuges that can be adjusted to simulate different levels of gravity. This will allow the scientists to explore Moon gravity (.17g) and Mars gravity to see how genetic expressions could change on those planets.

One day many generations of humans, too, may live in space. If genetic changes accumulate from generation to generation—an unknown of space travel—settlers on the moon or Mars might diverge genetically from their Earth relatives. Living on Mars really could turn an Earthling into a Martian. Fruit flies could give us a preview of that process, if it exists.

Meanwhile, it’s time to start packing ISS supply rockets with bananas. Rotten, if you please.

—Tony Phillips