Multiple signaling pathways regulate yeast cell death during the response to mating pheromones

Department of Biology and Whitaker Institute for Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21218, USA.
Molecular Biology of the Cell (Impact Factor: 4.47). 09/2006; 17(8):3409-22. DOI: 10.1091/mbc.E06-03-0177
Source: PubMed


Mating pheromones promote cellular differentiation and fusion of yeast cells with those of the opposite mating type. In the absence of a suitable partner, high concentrations of mating pheromones induced rapid cell death in approximately 25% of the population of clonal cultures independent of cell age. Rapid cell death required Fig1, a transmembrane protein homologous to PMP-22/EMP/MP20/Claudin proteins, but did not require its Ca2+ influx activity. Rapid cell death also required cell wall degradation, which was inhibited in some surviving cells by the activation of a negative feedback loop involving the MAP kinase Slt2/Mpk1. Mutants lacking Slt2/Mpk1 or its upstream regulators also underwent a second slower wave of cell death that was independent of Fig1 and dependent on much lower concentrations of pheromones. A third wave of cell death that was independent of Fig1 and Slt2/Mpk1 was observed in mutants and conditions that eliminate calcineurin signaling. All three waves of cell death appeared independent of the caspase-like protein Mca1 and lacked certain "hallmarks" of apoptosis. Though all three waves of cell death were preceded by accumulation of reactive oxygen species, mitochondrial respiration was only required for the slowest wave in calcineurin-deficient cells. These findings suggest that yeast cells can die by necrosis-like mechanisms during the response to mating pheromones if essential response pathways are lacking or if mating is attempted in the absence of a partner.

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    • "Upon failure of either one of these processes, triggering PCD cleans the population from infertile or damaged cells, thus ensuring fitness and survival. In this line, haploid cells undergo PCD upon long-term exposure to pheromones without subsequent mating (Severin and Hyman, 2002; Zhang et al., 2006). Moreover, during meiosis of diploids to generate long-lived spores, a fraction of cells undergoes apoptosis (Knorre et al., 2005). "
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    • "Cytoplasmic TUNEL staining has been described, but RNA fragmentation is rarely suggested as a possible cause. Nevertheless, TUNEL protocols often advise the use of RNAse treatment to clear the so-called cytoplasmic background (Zhang et al., 2006). However, as RNA integrity has been analyzed in an indirect way, further experiments like mass spectrometry would be necessary to confirm the alteration of RNA in KO-Tau mice. "
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