Suicidal yeast

Programmed cell death (PCD) in multicellular eukaryotes is a form of altruism, in which one cell activates its own death for the greater benefit of the organism. But it is more difficult to envision a benefit for a single-celled microbe. Now, Fedor Severin and Anthony Hyman (Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany) demonstrate that PCD is indeed a normal physiological process for yeast cells during mating.

Mating in yeast is initiated by a and α mating pheromones. High levels of, or prolonged exposure to, the mating factor is toxic to the cells. The group's results now show that the toxicity is due to the onset of PCD. Exogenous addition of α factor to a cells induced several markers of PCD, including production of reactive oxygen species and initiation of DNA degradation, in ∼30% of a cells. The cell death was also sensitive to an inhibitor of apoptosis.

PCD also occurred in native conditions with mixed a and α cells. Successful mating prevented mating factor-induced cell death, indicating that yeast may use the process to weed out old or otherwise damaged cells. “When yeast cells mate, this is the only moment in time when [they] show communal behavior,” says Severin. “If a particular cell is surrounded by mating partners and still cannot mate, it determines that it is weak, and for the sake of the community, the cell commits suicide.” ▪

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