Sci. Aging Knowl. Environ., 13 March 2002
Staying Cool When Dry: Worms surmount desertlike assault (Stress resistance)
R. John Davenporthttp://sageke.sciencemag.org/cgi/content/abstract/sageke;2002/10/nw32
Key Words: nematode Caenorhabditis elegans Aphelenchus avenae anhydrobiosis desiccation
Abstract: Even a camel can't match this trick for surviving extreme drought. The minute nematode Aphelenchus avenae can lose nearly all its body water, then rebound years later to its slippery self when conditions moisten. New work uncovers several genes that might contribute to this creature's antidesiccation powers. Understanding its resilience could give researchers insight into how living things handle the more modest but related stresses of aging.
A. avenae and other anhydrobiotic plants and animals--creatures that can live without water--produce large amounts (up to 20% of a cell's mass) of certain sugar molecules that harden into a semisolid state. Molecules enmeshed in this gel are locked into place, which freezes the random chemical movements that normally cause them to deteriorate. The sugars contain many polar chemical groups, which substitute for water and stabilize cellular proteins and membranes until the parched period is over. Recent studies have suggested that numerous genes, in addition to those involved in sugar synthesis, are required for plants to survive extreme dehydration.
Now researchers have found that at least one of these genes also functions in the nematode. Browne and colleagues dried out A. avenae individuals and sought genes that ramp up in response. One of the several they identified resembles a plant gene called LEA that's also turned on by desiccation. The results raise the possibility that nematodes and plants use some of the same equipment to fight drought. Researchers don't know how these pieces of molecular machinery prevent living things from withering, but previous work in plants suggests that the genes produce ultrastable proteins that help form the protective sugar mesh.
Many mutations and treatments that extend life-span in model organisms also enhance the ability to withstand harsh conditions (see "Survivor!"). For instance, the nematode Caenorhabditis elegans can enter a semidormant state known as a dauer to wait out hard times. Animals that carry certain mutations in genes required for dauer formation live much longer than normal worms do and are more resistant to heat and damaging chemicals. C. elegans does not possess the same ability to survive without water as A. avenae does, and the two species are only distantly related. But C. elegans also harbors a gene similar to LEA, according to co-author Ann Burnell, a geneticist at the National University of Ireland in Maynooth, although its function has not been pinpointed.
No one knows how the capacity to endure dryness might influence nematode aging, says Burnell. But such feats of endurance could lead researchers to fundamental mechanisms by which organisms stave off the environmental assaults that likely contribute to their demise.
--R. John Davenport
Citation: R. J. Davenport, Staying Cool When Dry: Worms surmount desertlike assault (Stress resistance). Science's SAGE KE (13 March 2002), http://sageke.sciencemag.org/cgi/content/abstract/sageke;2002/10/nw32
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