Life at the extreme of temperatures, saltiness, acids, pressures, and radiation levels--whether high or low--presents surprising chances for viewing adaptation and survival. But surviving changes in gravity is one of those uniquely terrestrial environments that not only may need an extreme organism to study, but also an extreme laboratory. The chance to explore such radical modifications led Principal Investigator, Catharine Conley, a biologist at NASA Ames, to flatten some already flat-worms (or nematodes). The researchers hope to pinpoint any genetic changes in the only animal with a fully-sequenced genome.
|Image of flattened worms or nematodes of the species name, C. elegans. C. elegans is currently the only animal with a fully-sequenced genome.
Image Credit: NASA Ames
Enduring spinning forces that would kill a human being, the tiny worms are being observed by a student-designed video system in NASA studies seeking to explore how life adapts to gravity beyond Earth.
Miniature worms, only 1 millimeter long and so small they are hard to see with the naked eye, are being spun in a centrifuge for as long as four days -- at forces of 20- to 100-times that of Earth's gravity (1 G). In contrast, human pilots not wearing anti-G suits can black out at as low as 3 Gs, and prolonged exposure at higher Gs can be life threatening. According to Conley, humans die after one minute at 10 G because the blood gets centrifuged from the head. But the worms, with no circulatory system and a sturdy constitution, don't have that problem. In fact, these worms can naturally withstand 1,000,000 G or a force-equivalent of over a million-times their terrestrial weight.
To examine the worms as they spin, scientists are using a video system designed and constructed by students at Harvey Mudd College, Claremont, Calif.
"By looking at what changes occur in the worms when they transition from high-G forces to normal gravity, we think we can predict what will happen to them when they experience near weightlessness during space flight," said Conley. "In the future, we want to fly the worms in space, subjecting them to microgravity to see if our predictions are correct." Microgravity (one-million times less than terrestrial levels) is close to 'zero gravity.'
"Radiation levels in space are much higher than they are on the Earth's surface," Conley said. "We know that elevated radiation increases the mutation rate of living things. Because these worms reproduce every four days, we can look quickly at many worm generations in space to see how radiation and microgravity may cause changes later," she explained.
|Dr. Elena Kozak works with nematode cultures in a laboratory at NASA Ames in the Gravitational Research Branch.
Image Credit: NASA Ames
"Worms have already flown aboard the space shuttle, and it was found that they went through several generations without gross structural changes to their bodies," Conley said. "We want to test the gene expression in worms that have flown in space versus those that have not, to see if changes in worms are similar to changes seen in vertebrates that have experienced space flight." Expression is how a gene affects a characteristic such as eye color, or susceptibility to a disease or condition.
During preliminary tests, scientists spun the 1 mm worms (technically known as Caenorhabditis elegans [C. elegans], a soil-dwelling nematode worm) in a large 20-G centrifuge at NASA Ames for four days, but they could see what happened to the worms only after the centrifuge, designed to carry human passengers, stopped. At 20 Gs, the worms are subjected to forces that are 20 times their normal weight.
"Should our hypothesis prove correct, it will validate Caenorhabditis elegans [nemotode] as an extremely useful and cost-effective model organism for studying responses to space flight at the molecular, genetic and whole-organism levels," Conley said.
When Conley was planning her current experiments that utilize a smaller, desktop centrifuge, she realized she would need a camera no bigger than an ice cube that could broadcast signals from the spinning apparatus to a TV monitor and recorder in real time. So she turned to the Student Engineering Clinic at Harvey Mudd College to produce the camera system. Five Harvey Mudd students spent an academic year on the project. They bought off-the-shelf components, but they had to overcome several engineering challenges to enable the system to work well.
"The camera had to be supported to withstand the 100-Gs force," said Professor Joseph King, director of the clinic. "All this stuff is designed so it is compatible with the geometry of the centrifuge." The equipment also has two broadcast systems, an infrared system to control the camera, and a wireless, video transmission system to broadcast movies of the worms.
A Picture in a Thousand Cells
"During spinning there are changes in the worms' gene expression that seem to help them compensate for the increased apparent gravity, allowing them to survive," Conley said. The worm has about 19,000 genes, and it has nerves, muscles and some of the same types of organs in people that are affected by weightlessness.
|C. elegans cDNA microarray. DNA microarrays are available that contain nearly every one of the 19,000 genes in the C. elegans genome. cDNA microarray expression analysis permits identification and evaluation of many physiological changes at once.
Image Credit: NASA Ames
After the worms endure high G forces riding in a centrifuge, the animals' behavior alters. That is part of what the scientists look for to find out how the creatures handle changes in gravity's force. Normally, under 1-G conditions, the miniscule creatures look like small, clear wiggly rods that swim snake-style through a thin layer of water and nutrients in which they live in a laboratory environment. The worms commonly are found in soil and rotting vegetation, and have about a thousand cells.
Astronauts can suffer from motion sickness, bone loss, muscle degeneration (atrophy) and blood vessel problems during weightlessness. "By studying how the worms produce different levels of proteins that help the tiny organisms cope with high-G situations, we think we eventually can develop treatments, perhaps even oral drugs, for astronauts to serve as countermeasures to problems due to weightlessness." Conley hopes that by 2004-2005, there will be a semi-permanent culture of worms on the International Space Station.
The investigators hope first to validate the worm as a high-gravity model organism. In vertebrates, muscular decay, slowed DNA repair, and accelerated aging are just a few of the changes that gravity may influence. C. elegans is a popular model for studying the process of aging, and a number of single gene mutants have been identified that influence its' lifespan.
The NASA Fundamental Biology program and the NASA Astrobiology Institute fund the worms-in-space project. Life sciences research at Ames is supported by NASA's Office of Biological and Physical Research, which promotes basic and applied research to support human exploration of space and to take advantage of the space environment as a laboratory. More information is available at: http://spaceresearch.nasa.gov/. The cDNA microarray analysis will progress in collaboration with Dr. Stuart Kim of Stanford.
Related Web Sites:
NASA Ames Press Release
Dr. Conley's Research
Harvey Mudd Engineering Clinic