The Fruit Fly in You
NASA-supported researchers are going to send fruit flies to the International Space Station to learn what space travel does to the genes of astronauts.
February 3, 2004: 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.
We have a lot in common.
Genetically speaking, people and fruit flies are surprisingly alike, explains biologist Sharmila Bhattacharya of NASA's Ames Research Center. "About 61% of known human disease genes have a recognizable match in the genetic code of fruit flies, and 50% of fly protein sequences have mammalian analogues."
Right: Side by side, a female and a male fruit fly.
That's why fruit flies, known to scientists as Drosophila melanogaster, are commonplace in genetic research labs. They can be good substitutes for people. They reproduce quickly, so that 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," notes Bhattacharya.
They're about to become genetic models for astronauts.
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 g's during launch, 0-g during the long interplanetary cruise, several more g's descending to Mars, and 0.38 g during their stay on the red planet. How are genes going to react to these changes? Will they express themselves in new or unexpected ways?
"Genes 'express themselves' by commanding cells to make proteins," explains Beckingham. There are about 50,000 different proteins in the human body, and they do just about everything. They help us digest our food, clot blood and heal wounds. They're 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."
Above: When genes are expressed, the genetic information on DNA is first copied to a molecule of messenger RNA (mRNA) . The mRNA carries that information from the cell nucleus to the cytoplasm, where proteins are assembled from amino acids. [more]
"There's already evidence that weightlessness alters genetic expression," she adds. 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 astronaut immune systems don't attack germs as ferociously as they do on Earth. If you get sick in space, it might be harder to get well again. Astronauts bones weaken during long voyages, and without lots of exercise, their muscles atrophy. "All of these things are rooted in genetic expression," Beckingham says.
That space travel affects genetic activity is uncontroversial. But researchers can't yet predict which genes will be affected, or precisely how gravity signals a gene to change its ways.
Hence the fruit fly. Beckingham's team will breed as many as nine generations of Drosophila onboard the 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.
Right: With fruit flies onboard, the ISS will become a genetics research lab. [larger image]
Onboard the ISS, "the flies will be contained inside a special insect habitat," notes Beckingham. 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."
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," says Beckingham. "We might also explore Moon gravity (1/6 g) and Mars gravity" to see how genetic expression might change on those worlds.
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, will 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 would turn you into a Martian. Fruit flies could give us a preview of that process (if it exists).
Left: Prof. Kate Beckingham of Rice University. [more]
"Nine generations of Drosophila are not enough to draw strong conclusions about inherited changes," cautions Bhattacharya. But it's a beginning. 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. Hundreds of generations would be needed to properly study genetic evolution in space, believes Beckingham. "That's for the future," she says.
Meanwhile, maybe, it's time to start packing ISS supply rockets with bananas. Rotten, if you please.
Stay tuned to Science@NASA for more information about this research,
including an upcoming story describing the astronaut selection process
... for fruit flies.