Sci. Aging Knowl. Environ., 5 January 2005
Novel method clocks yeast longevity
R. John Davenporthttp://sageke.sciencemag.org/cgi/content/full/2005/1/nf3
A stopwatch is the best tool for assessing yeast aging, according to a new study. Timing how long a yeast cell squeezes out offspring is a better gauge of its life span than standard measures, the authors suggest. But other researchers caution that further work is necessary to validate the technique and doubt that it will supplant current approaches.
To understand how and why complex organisms age, some scientists have turned to a simpler creature: yeast. Its short life span and genetic pliability have sped the search for mechanisms that retard or accelerate aging, and researchers hope that lessons from yeast will illuminate our own deterioration (see Kaeberlein Perspective). However, methods for quantifying longevity in yeast differ from those used for mammals and other creatures, in which researchers clock the time between birth and death. Researchers commonly assess aging in the fungus by counting the number of times a yeast cell produces an offspring cell or measuring how long a cell can withstand starvation--so-called replicative and chronological life spans, respectively. Because reproductive output might not reflect survival time, Minois and colleagues aimed to measure yeast life span in a manner similar to that used for other organisms.
To do so, they recorded reproductive life span--the length of time during which a yeast cell buds offspring--and postreproductive life span--how long after a cell stops reproducing until it dies. The researchers gauged death by adding to yeast food a dye that only enters expired cells. After gleaning data for nearly 400 individuals from four different genetic lines, the team found that reproductive life span and number of progeny did not match up. Although the cells that spawned the fewest buds had the shortest reproductive life span, the strain with the most progeny did not show the longest reproductive life span. Three strains in which cells produced different numbers of daughter cells had almost identical reproductive life spans. In addition, budding prowess didn't correlate with postreproductive life span. The authors conclude that number of offspring is a poor predictor of longevity in yeast and that future experiments should take into account reproductive and postreproductive life span.
"It's an interesting way of looking at things and should be followed up further," says molecular biologist Brian Kennedy of the University of Washington, Seattle. For instance, he says, researchers should analyze other strains with mutations that perturb life span according to the existing assays. However, the techniques need improvement, he says. For instance, the scientists moved yeast cells into a refrigerator at night to slow their budding. "That's definitely going to affect their metabolic rate" and therefore their rate of aging. And the new approach won't replace the replicative or chronological measures, he says. The existing methods might not provide direct clues about how entire organisms wither, but they can reveal insights into how dividing and nondividing cells in those creatures become decrepit. Further work should clarify how the novel method will fit into yeast researchers' bag of tools.
January 5, 2005
Science of Aging Knowledge Environment. ISSN 1539-6150