The Fission Yeast S Pombe As An Emerging Model System In Aging

As mentioned previously in the Yeast Telomere Protein Components section, fission yeast utilizes the same telomere maintenance machinery as budding yeast and humans, and in some cases contain orthologs that show more sequence similarity to the human sequences than do those of budding yeast (e.g., pot1+ of S. pombe and Pot1 of humans are more similar than either protein is to S. cerevisiae CDC13). Fission yeast also exhibits gene silencing at telomeres, silent mating type cassettes, the rDNA, and centromeres. Thus, many of the characteristics that make budding yeast a useful model system for both short telomere-induced senescence and release of factors from telomeres are also present in fission yeast. Because these two yeasts are evolutionarily quite distant and show many physiological and genomic differences (e.g., fission yeast has fewer genes than budding yeast, and only 3/4 of the fission yeast genes have clear budding yeast orthologs (Sanger_Institute, 2005)), analysis of fission yeast aging could reveal evolutionarily conserved mechanisms that control lifespan and guide the work in more difficult mammalian systems.

One provocative report has been published that claims that fission yeast shows replicative aging. While fission yeasts divide to produce two equally sized sister progeny, after several cell divisions an asymmetry develops such that the "older" cell becomes more round and visually distinguishable from the "younger" sister (Barker and Walmsley, 1999). Chronological aging, the length of time cells in culture can survive in stationary phase and form colonies when transferred to fresh medium, has also been tested in S. pombe and provides similar results to work in budding yeast (Fabrizio and Longo, 2003) (B.-R. Chen and K.W. Runge, in preparation). Following up these results and development of high-throughput replicative and chronological aging assays will greatly enhance the utility of fission yeast as a model system for aging.

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