Apoptosis at Inflection Point in Liquid Culture of Budding Yeasts

概要

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Budding yeasts are highly suitable for aging studies, because the number of bud scars (stage) proportionally correlates withage. Its maximum stages are known to reach at 20–30 stages on an isolated agar medium. However, their stage dynamics ina liquid culture is virtually unknown. We investigate the population dynamics by counting scars in each cell. Here one celldivision produces one new cell and one bud scar. This simple rule leads to a conservation law: ‘‘The total number of budscars is equal to the total number of cells.’’ We find a large discrepancy: extremely fewer cells with over 5 scars thanexpected. Almost all cells with 6 or more scars disappear within a short period of time in the late log phase (corresponds tothe inflection point). This discrepancy is confirmed directly by the microscopic observations of broken cells. This findingimplies apoptosis in older cells (6 scars or more).
2011-04-27