DAUGHTER CELLS OF SACCHAROMYCES-CEREVISIAE FROM OLD MOTHERS DISPLAY AREDUCED LIFE-SPAN

The yeast Saccharomyces cerevisiae typically divides asymmetrically to give a large mother cell and a smaller daughter cell. As mother cells become old, they enlarge and produce daughter cells that are larger t han daughters derived from young mother cells. We found that occasiona l daughter cells were indistinguishable in size from their mothers, gi ving rise to a symmetric division. The frequency of symmetric division s became greater as mother cells aged and reached a maximum occurrence of 30% in mothers undergoing their last cell division. Symmetric divi sions occurred similarly in rad9 and ste12 mutants. Strikingly, daught ers from old mothers, whether they arose from symmetric divisions or n ot, displayed reduced life spans relative to daughters from young moth ers. Because daughters from old mothers were larger than daughters fro m young mothers, we investigated whether an increased size per se shor tened life span and found that it did not. These findings are consiste nt with a model for aging that invokes a senescence substance which ac cumulates in old mother cells and is inherited by their daughters.