Figure 2-07. The worms C. elegans are mostly transparent at all stages. So, investigators using a simple microscope can view their internal organs/cells without any sort of invasive techniques. Experiments are in planning to examine worms on the Space Station with a video camera so that investigators on Earth can view their development and examine them for differences between Earth-grown worms. Photo courtesy of NASA.

When the genome C. elegans was deciphered in 1998, it was found that approximately one third of the worm's proteins—more than 6,000—are similar to those of mammals. Since then, more than 1,400 gene functions have been identified. More than 65% of human disease genes have homologues in the C. elegans genome, and essential aspects of mammalian cell biology, neurobiology and development are faithfully recapitulated in this organism. Specifically, a gene that governs the rate of aging in worms has been found to be active in both yeast and mice, and may have a counterpart in humans. This finding is relevant to space biology since during spaceflight astronauts rapidly experience some of the physiological changes associated with the aging process on Earth.

Since the life span of a worm is about three weeks, catapulting worms into low-Earth orbit will allow multigenerational studies. Nematodes have a generation time, a period from birth to reproduction, of about three days. Each individual worm produces 280 offspring through self-fertilization. They are ideal for genetic studies because the ancestry of every cell in their bodies is known from the time of fertilization. The majority of the nematodes flown on the Space Shuttle were maintained at a dormant larval stage known as dauer larva. Dauer larvae do not feed and require minimal levels of oxygen and care. Other nematodes were launched as young larvae and were allowed to develop for up to two generations during the flight.

C. elegans development has been extensively studied in terrestrial environments and this species offers the advantage of having a genome that has been completely sequenced. A complete map of its development is available with tracking of each cell division from egg to adult. Like Drosophila, it shares extensive homology with vertebrates at the molecular level, has a short life cycle, is small, develops externally, can be placed into cold storage and a large database of mutants is available. Also, the developmental patterns of several genes are known and GFP-marker lines1 are available.

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