Egilmez N K, Jazwinski S M
Department of Biochemistry, Louisiana State University Medical Center, New Orleans 70112.
J Bacteriol. 1989 Jan;171(1):37-42. doi: 10.1128/jb.171.1.37-42.1989.
The life spans of individual Saccharomyces cerevisiae cells were determined microscopically by counting the number of buds produced by each cell to provide a measure of the number of cell generations (age) before death. As the cells aged, their generation times increased five- to sixfold. The generation times of daughter cells were virtually identical to those of their mothers throughout the life spans of the mothers. However, within two to three cell divisions after the daughters were detached from their mothers by micromanipulation, their generation times reverted to that characteristic of their own age. Recovery from the mother cell effect was also observed when the daughters were left attached to their mothers. The results suggest that senescence, as manifested by the increase in generation time, is a phenotypically dominant feature in yeast cells and that it is determined by a diffusible cytoplasmic factor(s) that undergoes turnover. This factor(s) appeared to be transmitted by a cell not only to its daughter, but also indirectly to its granddaughter. In separate studies, it was determined that the induced deposition of chitin, the major component of the bud scar, in the yeast cell wall had no appreciable effect on life span. We raise the possibility that the cytoplasmic factor(s) that appears to mediate the "senescent phenotype" is a major determinant of yeast life span. This factor(s) may be the product of age-specific gene expression.
通过显微镜计数每个酿酒酵母细胞产生的芽的数量来确定其个体寿命，以此衡量细胞死亡前的细胞世代数（年龄）。随着细胞老化，它们的世代时间增加了五到六倍。在母细胞的整个寿命期间，子细胞的世代时间与母细胞的几乎相同。然而，在通过显微操作将子细胞从母细胞分离后的两到三次细胞分裂内，它们的世代时间恢复到其自身年龄所特有的水平。当子细胞仍与母细胞相连时，也观察到了从母细胞效应中的恢复。结果表明，以世代时间增加为表现的衰老在酵母细胞中是一种表型上占主导的特征，并且它由经历周转的一种或多种可扩散的细胞质因子决定。这种因子似乎不仅由一个细胞传递给它的子代，还间接传递给它的孙代。在单独的研究中，已确定酵母细胞壁中芽痕的主要成分几丁质的诱导沉积对寿命没有明显影响。我们提出这样一种可能性，即似乎介导“衰老表型”的细胞质因子是酵母寿命的主要决定因素。这种因子可能是年龄特异性基因表达的产物。
