February 3, 2004
Worms have 'the right stuff' for space genomics experiments
By Dawn Levy
One small wiggle for wormkind -- one giant leap for flies, yeast, bacteria and weeds.
Because its genetic blueprint is known and gene changes can be detected, the nematode roundworm Caenorhabditis elegans has "the right stuff" to be launched into space in the name of science. Complete genetic sequences, or genomes, are also known for the fruit fly Drosophila melanogaster, the yeast cell Saccharomyces cerevisiae, the bacterium Escherichia coli and the mustard weed Arabidopsis thaliana. They're lab rats of a new field -- space genomics -- in which scientists study the way weightlessness and space radiation affect an organism's genes. Since diverse organisms share many of the same genes, such studies may give scientists a better understanding of how space travel may affect human genes.
"The real question about long-term space habitation for organisms including humans is: What actually does space do to you?" asked Gregory T. A. Kovacs, an associate professor of electrical engineering and principal investigator of a Stanford experiment that used balloons to launch worms into the stratosphere on Jan. 18 and 19. "Does lack of gravity really cause anything at the cellular level? It's amazing to me that, on a superficial level anyway, we don't know the answer, because we've been putting living things in space for a long time." (Laika the dog was the first living thing put into orbit in 1957.)
Kovacs, who worked on the Columbia Accident Investigation Board and is principal investigator for the newly initiated Stanford-NASA National Center for Space Biological Technologies, noted that worms survived the space shuttle crash. They were on board for a study by Stuart Kim of Stanford and Catharine Conley of NASA to see if worms could live in space unattended.
In 2002, before Columbia's crash, Stanford and NASA scientists teamed up to launch worms into the upper atmosphere using balloons. Conley, who heads a C. elegans lab at NASA, came up with interesting scientific questions, and Kovacs' group created the hardware to answer them. The balloon experiment is an important steppingstone to others, including NemaSat, a Stanford-based project to launch worms into orbit aboard small satellites in the near future. Since the life span of a worm is about three weeks, catapulting worms into low-Earth orbit will allow multigenerational studies. The balloon launches are also necessary precursors for ISGEN (for In Situ Genetics Experiments on Nanosatellites), a NASA-led project in which sequenced organisms including worms, bacteria and flies are targeted for launch as soon as late 2005.
"To eventually make it to Mars, many experiments launching surrogate humans -- such as worms -- will be required to better understand the long-term effects of space radiation and microgravity," said John Hines, manager of NASA's Astrobionics Integrated Program/Project Team and a Stanford alumnus (MSEE '75). After the Columbia disaster, getting such experiments into space became more difficult. When Hines showed Kovacs a website describing 4-inch-cube satellites built by Consulting Professor Bob Twiggs and his students in the Aeronautics and Astronautics Department at Stanford, they knew they were staring at the solution. "Why don't we put some biology on these?" Hines asked.
The idea, Kovacs explained, was to build a toaster-sized payload harboring a living organism that could go into a low-Earth orbit for a few generations. The goal was a fully automated experiment to find out what genes get turned on and off in space. The experiment would circle the Earth until its orbit decays and its payload burns up in the atmosphere.
Kovacs and Hines orchestrated a collaboration with Stanford students and industrial consultants primarily managing the electronics and NASA workers, the biology. Professional consultants included Chris Storment, who with Kovacs leads NemaSat's development of the biological payload, as well as retired Lockheed aerospace engineer Dan Saldana and NASA Astrobionics Chief Engineer Bob Ricks. The technologies and concepts developed by students and professionals for NemaSat will be incorporated in ISGEN, which has a FY '04 budget of $2 million and nearly a dozen full-time staff working to meet NASA quality control standards.
"NASA gets the exuberance of faculty and students to try new things and advanced concepts in a low-risk, low-cost approach," Hines said, explaining how NASA benefits from student involvement. "It can leverage the technology and knowledge base and train the next generation of scientists and engineers doing this in 2025 when we finally go to Mars."
Ride, wormy, ride
You'll never catch a trout using C. elegans for bait. This worm is so small -- 1 millimeter in length -- that 100 can fit in a drop of water. Its small size is just one reason it is ideal for space experiments.
"Worms are one of the hardiest specimens that we can work with in this environment," Hines said.
The first multicellular organism whose genome was sequenced, C. elegans is about as primitive a life form as one can find that allows exploration of processes relevant to human biology. It was the experimental model used in the studies of genetic regulation of organ development and programmed cell death that won the Nobel Prize in 2002. Because scientists have identified genes responsible for aging that are the same in both worms and humans, C. elegans has long been a workhorse in studies on aging. The worm does everything it has to do -- including develop, reproduce, react to its environment, even "learn" -- with only 959 cells.
The January experiment used balloons to launch the worms from a NASA-funded facility at the University of Iowa. Since rocket launches are costly and subject to delays that endanger the lives of experimental organisms onboard, balloon launches may be an important precursor to future rocket-launched experiments such as ISGEN. They allow researchers including Stanford postdoctoral fellow Dirk Lange to hone their skills in producing systems in which biological packages can survive the vacuum at an altitude of 100,000 feet and frigid temperatures around minus 50 degrees Celsius (-58 F). The balloon-launch experiments focused on the effects of lessened gravity on worms during 40 seconds of free fall, but the technology developed for the launches could aid longer experiments addressing other aspects of space travel in different types of organisms.
"The idea is to basically get a foot in the door of this kind of autonomous biological payload," Kovacs said. "Nobody can really say they have a lot of experience in launching a fully self-contained genomics experiment and then afterward analyzing it via only telemetry. So we're really going through what we hope is an accelerated learning curve for this stuff."
For the January launches, which were refinements of two carried out in August 2003, scientists placed the worms in a small container monitored by a camera. They attached the container to a helium-filled latex weather balloon, which ascended high into the atmosphere and burst an hour later, sending the worms into about 40 seconds of free fall ? a basically weightless state during which telemetry communicated their behavior to the researchers. Then a parachute deployed to soften the worms' landing in a snow-crusted fallow cornfield.
The mission control center of the Iowa balloon launch facility tracked payload location and spied on the worms using real-time telemetry. Staffers coordinated with the Federal Aviation Administration so the balloons would not run into commercial aircraft. They used weather software to predict, within half a mile, where the balloons would land.
"The objective here is to do a quick and inexpensive experiment where we get a look at worms in 1 g transitioning to almost 0 g then back to 1 g again to see if their physical behavior changes," explained Kovacs. While a camera records the worms' movements, micromachined accelerometers record the force and direction of gravity.
On the second day, the payload made it to a record height of 107,000 feet (20 miles). While that altitude wasn't quite high enough to earn the worms astronaut status -- NASA reserves that honor for those who have traveled above 50 miles -- the experiment demonstrated the viability of quickly and cheaply launching biological payloads.
"The balloon flights were spectacular," says Kovacs. "As if in a tribute to the STS-107 [Space Transportation System Flight 107, the Columbia flight that crashed] families, the second balloon burst at almost exactly 107,000 feet for a perfect recovery of the payload -- the same type of worms that survived the STS-107 breakup."
How will space affect a Mars-bound body?
"If we send people to the moon and Mars, they will be exposed to high radiation and microgravity for long periods of time -- missions of up to three years," Hines said, noting that biological research subjects always are sent up prior to exposing humans.
There's still a lot we don't know about what space does to the body. What happens to living systems exposed to near-zero gravity over the long term? Exactly how bad is space radiation?
NASA astronaut Yvonne Cagle, a consulting professor of medicine at Stanford who collaborates with Kovacs on physiological monitors, was a key participant in the first two balloon launches. She said space genomics experiments will allow scientists to capitalize on what they've already learned in space -- that the human body has a remarkable and robust way of adapting to weightlessness.
"Now that we have the ability to do gene mapping and look at things on a genetic level, we can actually start to identify what genetic changes take place on not just a gene level but [also] on a molecular level, on a proteomic [analysis of an organism's complete protein content] level," she said. "We can start building those blocks that result in whole body systems called humans and start to have a better understanding about why we're able to so successfully adapt to environments that challenge our ability to live and work in space for long periods of time."
Muscle loss and cardiac deconditioning happen in space, Cagle said. So does bone loss at a rate of 1 to 2 percent per month, leveling off around 17 percent total loss. Crews tend to sleep less. A suppressed immune system can lead to viral reactivations, and reduced production of red blood cells further weakens the immune system.
"With diet and exercise and with implementing a strict sleep regime, the majority of these effects are reversible within about three weeks of returning to Earth in our current rehabilitation program," Cagle said. "The only effect that tends to persist is bone loss. However, there are some exciting diet and pharmacologic regimens that appear to prove promising." Essential amino acids and bisphosphonates (such as the drug Fosamax) may thwart bone loss, she said.
Space radiation remains a serious concern -- it can compromise the immune system and cause unnoticeable cellular changes as well as skin rashes, sickness and even cancer. Once we leave our protective atmosphere and ozone layer, we become exposed and vulnerable to space radiation in the form of galactic cosmic rays and solar flares, Cagle said.
"You have a different radiation energy spectrum in space," Kovacs said. "Going to Mars would be a long transit with lots of exposure. What are the cancer rates going to be? What other things might we see in humans and animals and plants carried along? That's one class of experiments where you can't really simulate that radiation here. ... You pretty much have to go up into space."
Hines pointed out that an experiment to study space radiation would have to be far enough from Earth to escape the protection of the Van Allen belt. In a space genomics experiment, he suggested, scientists could fluorescently label genes and monitor how that fluorescent signature changes as the genes are exposed to space radiation and microgravity. In the case of space radiation, which causes dangerous breaks in DNA, scientists could look for the expression of DNA repair enzymes.
"If we can better understand the amount of radiation that causes damage and on what level we see the damage, we may be able to biologically protect the body through pharmaceutical and nutritional interventions in addition to shielding of the body in the vehicle," Cagle said.
Still, it's hard to disassociate what space does to the body from what stress does to the body. If the immune response weakens, was that caused by the stress response to a noisy, shaky space launch or by lessened gravity? Kovacs asks. If genes in cells express different proteins in lessened gravity, was it due to mechanical damage to the cells or altered fluid mechanics?
Someday Kovacs hopes to study the effects of space on sea monkeys. Dormant when dry, these brine shrimp can be launched in a dehydrated state to avoid the stress of launch, then rehydrated once in orbit.
But for now, it looks like fruit flies may be the next organisms deemed, in NASA lingo, "good to go." Kovacs is working with Mario Goins, a NASA astrobionics researcher, and Omer Inan, a coterminal degree student in electrical engineering, to design innovative electronics to spy on the flies.
Photos are available at http://newsphotos.stanford.edu. C. elegans photo courtesy Stuart Kim; all other photos courtesy Gregory Kovacs.