Accumulation of a senescence factor in yeast cells

A mathematical model is used to describe the increase in generation time with age of mother cells in the asymmetrically dividing yeast Saccharomyces cerevisiae. It is postulated that the generation time increases linearly with the amount of a senescence factor present in each cell. The senescence factor, which inhibits cell division is produced continuously. Although it is not degraded or destroyed, it may be diluted by cell division. The model is formally identical to one which was successful in describing waste dilution in populations of aging human diploid fibroblasts (Hirsch, 1978). The relation between aging in yeast and in fibroblasts is explored. Agreement between calculated results and yeast cell generation-time data is adequate. The results indicate that the senescence factor accumulates with little or no dilution in aging yeast mother cells.