C. elegans worms, pictured above, are a model organism for studying cell behavior in space. Photo by Flickr via snickclunk.
In December 2006, the Discovery space shuttle launched into orbit carrying a seven-member crew, its first Scandinavian astronaut and 400 soil-dwelling, bacteria-munching microscopic worms.
Though not the first worms in space, they were still pioneers, becoming the first to produce 12 new generations of offspring, and do so inside a remotely automated system with no need for a biologist on board to oversee it. Meanwhile, back on Earth, a team of scientists observed the worms and gathered data via video beamed back from space.
"At a very simple level, we wanted to see if an animal could go through more generations than any animal ever looked at in space," said Nathaniel Szewczyk of the University of Nottingham, senior author of the study, published on Wednesday in the Journal of the Royal Society, Interface.
Szewczyk's team found that throughout the 12 generations, the Caenorhabditis elegans, or C. elegans worm developed normally from egg to adulthood, moved as it should when fully fed and recovered after a period of induced starvation. "These observations establish C. elegans as a biological model that can be used to detect changes in animal growth, development, reproduction and behavior in response to environmental conditions during long-duration spaceflight," according to the paper.
"Twelve generations in space is good," said Paul Sternberg, a nematode geneticist at the California Institute of Technology, who has worked extensively with the C. elegans species, but was not involved in this study. "It means radiation isn't beating the crap out of them. So this is definitely an advance."
The C. elegans is a hardy worm, easy to transfer because it's so tiny and quick to produce offspring -- its reproductive cycle lasts three to four days. Females are hermaphrodites, meaning they produce their own sperm without mating, which makes reproduction easy and uncomplicated. And a variety of genetic pathways in C. elegans match those in humans. Roughly a third of the worm's 20,000 genes code like human genes, which means that many of the genes and proteins and DNA processes are conserved.
"As a model, if we want to send organisms into deep space, it makes sense to not send humans first," Sternberg said. "Humans are great and would be more poetic about what they see or feel or experience, but bacteria would probably be a good start. After that, the worm's your ticket."
Scientists are looking to these worms to provide insight into some big unanswered questions about the physiology of space travel. One big one: "how important is it for gravity to control the development and life span of organisms," said Gregory Nelson, a professor of radiation medicine at Loma Linda University and the first scientist to send a crop of c.elegans worms to space in 1991.
Gravity is capable of profoundly altering the development of some animals, which raises questions on whether humans can safely reproduce in zero gravity. If the weight of a frog or chicken egg isn't redistributed properly during development, for example, gravity will establish an improper body axis that can lead to deformities, Nelson said. "This is the first time that any organism has been allowed to propogate [without gravity] over so many generations."
A known problem for astronauts is losing bone and muscle mass in orbit; this includes cardiac muscle. Even strenuous exercise can't always compensate for these losses, and some astronauts who stay in space long term are never able to regain all of their muscle mass. Studying muscle genes in worms could help scientists understand why this is happening.
The worms can also be used to detect spaceflight-induced changes at the molecular level and to study in-flight radiation exposure, study authors say.
One way to better study radiation exposure and test radiation-shielding technologies would be to send worms beyond the Van Allen radiation belt, a belt around the Earth containing trapped energetic protons, a high radiation source. Worms on Apollo missions to the moon that crossed the Van Allen belt came back sterile, a likely side effect of radiation, Szewczyk said.
To research all of this, you want a biological system that is easier to study than mammals, Nelson said. "It turns out this little animal, the C. elegans, is very good at predicting the kind of control circuits in all animals," he said.
So could a wormed-mission to Mars be in our future?
Szewczyk hopes so. This type of model has become even more important with the end of the U.S. shuttle program and the high cost of manned space missions, he said.
"From a U.S. perspective, we're facing a point in which we don't have our own manned access to space, and the world continues to look at us as a leader. One of the things we could do as a leader is to find new ways to conduct biology experiments in space."
