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

Programmed cell death (PCD) has been extensively studied in the animal kingdom. Recently, it was also reported to occur in Saccharomyces cerevisiae responding to mating pheromones. This first report of apoptosis induced by a natural stimulus outside of the animal kingdom opened the door to investigate the possible existence of apoptosis in fungi. In this study, we have reevaluated the presence of apoptotic death in S. cerevisiae, improved apoptotic assays on yeast cells, and found the activation of a voltage gated calcium channel Cch1 and its downstream target calcineurin can promote cell survival, but the factors required for a low affinity calcium influx system seem to promote cell death during the response to mating pheromones. Interestingly the similar phenomena can be observed in neurons. Ca2+ through L-type calcium channel prevents death, but Ca2+ through NMDA receptors causes excitotoxicity. No apoptosis hallmark was observed and no apoptotic factor seemed to be involved in any kind of death. Our findings argue against the notion of apoptotic death during responding to mating pheromones, and instead suggest the normal events of yeast conjugation can be lethal when attempted without appropriate feedback mechanisms or when attempted without a partner. We also identified Fig1 as the first fungal homolog of Stargazin/VGCC-gamma/claudin/EMP/PERP superfamily in mammals, and showed it was involved in the regulation of ion channels after induced by mating pheromones. From a genetic screen, we identified two channel candidates, Prm6 and it paralogue, Prm60. They are strongly required for the activation of Cch1, and localized or delivered to the plasma membrane, indicating they could be new calcium channel subunits or channel regulators.