Fly me to the Moon

Fly me to the Moon

Professor uses fruit flies in space to study gravity’s effect on genes

BY TONY PHILLIPS
Special to the Rice News

Because fruit flies are genetically similar to humans, they are a common subject of genetic research, such as that being conducted by Kate Beckingham, professor of biochemistry and cell biology.

Fruit flies are bug-eyed and spindly, they love rotten bananas and, following orders from their pin-sized brains, they can lay hundreds of eggs every day.

Humans have a lot in common with fruit flies.

Genetically speaking, people and fruit flies are surprisingly alike, explained 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, and 50 percent of fly protein sequences have mammalian analogues,” she said.

That’s why fruit flies, known to scientists as Drosophila melanogaster, are commonplace in genetic research labs. They can be good substitutes for people.

Because they 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, including Parkinson’s and Huntington’s,” Bhattacharya said.

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 some fruit flies to the International Space Station (ISS). The purpose of their experiment, ”Drosophila Behavior and Gene Expression in Microgravity,” is to discover how space travel affects genes — both Drosophila and human.

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 feel several gs during launch, 0 g during the long interplanetary cruise, several more gs descending to Mars and 0.38 g during their stay on the Red Planet.

Beckingham and her colleagues are hoping to find out how genes will react to these changes and whether they will express themselves in new or unexpected ways.

”Genes ‘express themselves’ by commanding cells to make proteins,” Beckingham said.

There are about 50,000 different proteins in the human body, and they do just about everything. They help digest food, clot blood and heal 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, many of these things could change,” she said.

”There’s already evidence that weightlessness alters genetic expression.”

In 1999, for instance, scientists grew human kidney cells onboard the space shuttle. More than one thousand 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 said.

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.

Scientists hope the fruit fly can help. Beckingham’s team will breed as many as nine generations of Drosophila onboard the International Space Station (ISS), with some 120 flies per generation. About 30 from each batch will be collected by astronauts and frozen. Eventually the frozen flies will be returned to Earth, where researchers can analyze their messenger RNA (mRNA), and thus their proteins, to see which genes were more active or less active in orbit.

Beckingham said the flies will be contained inside a special habitat onboard the ISS. Clear walls and a video camera allow the researchers to monitor fly behavior. ”We’ll be watching their courtship rituals, their running speed, how they fly; these are clues to genetic activity,” she said.

The flies will also spend some time spinning inside small centrifuges. ”We can adjust the spin to simulate different levels of gravity, ranging from near weightlessness to twice the full gravity of Earth,” Beckingham said.

Scientists may also explore moon gravity (1/6 g) and Mars gravity to see how genetic expressions could change on those planets.

Fruit flies will travel to the ISS onboard the space shuttle after it returns to flight. They’ll 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 a human, but it is many generations of fruit flies.

One day many generations of people, 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 a human into a Martian. Fruit flies could give us a preview of that process (if it exists).

”Nine generations of Drosophila are not enough to draw strong conclusions about inherited changes,” Bhattacharya said.

But it’s a start. The 90-day experiment will pinpoint some of the genes most affected by space travel and test the design of the habitat where more generations of flies can live.

Beckingham said she believes hundreds of generations would be needed to properly study genetic evolution in space. ”That’s for the future,” she said.

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

—Tony Phillips is production editor of Science@NASA ( http://science.nasa.gov ), a Web site designed to educate the public on the latest NASA research.