Identification of a Lifespan Extending Mutation in the Schizosaccharomyces pombe Cyclin Gene clg1 + by Direct Selection of Long-Lived Mutants

Model organisms such as budding yeast, worms and flies have proven instrumentalin the discovery of genetic determinants of aging, and the fission yeastSchizosaccharomycespombe is a promising new system for thesestudies. We devised an approach to directly select for long-livedS.pombe mutants from a random DNA insertionlibrary. Each insertion mutation bears a unique sequence tag called a bar codethat allows one to determine the proportion of an individual mutant in a culturecontaining thousands of different mutants. Aging these mutants in cultureallowed identification of a long-lived mutant bearing an insertion mutation inthe cyclin gene clg1⁺. Clg1p, likePas1p, physically associates with the cyclin-dependent kinase Pef1p. Weidentified a third Pef1p cyclin, Psl1p, and found that only loss of Clg1p orPef1p extended lifespan. Genetic and co-immunoprecipitation results indicatethat Pef1p controls lifespan through the downstream protein kinase Cek1p. WhilePef1p is conserved as Pho85p in Saccharomycescerevisiae, and as cdk5 in humans, genome-widesearches for lifespan regulators in S. cerevisiae havenever identified Pho85p. Thus, the S. pombe systemcan be used to identify novel, evolutionarily conserved lifespan extendingmutations, and our results suggest a potential role for mammalian cdk5 as alifespan regulator.