Developmental Coordination of Gamete Differentiation with Programmed Cell Death in Sporulating Yeast

The gametogenesis program of the budding yeast Saccharomyces cerevisiae, also known as sporulation, employs unusual internal meiotic divisions, after which all four meiotic products differentiate within the parental cell. We showed previously that sporulation is typically accompanied by the destruction of discarded immature meiotic products through their exposure to proteases released from the mother cell vacuole, which undergoes an apparent programmed rupture. Here we demonstrate that vacuolar rupture contributes to de facto programmed cell death (PCD) of the meiotic mother cell itself. Meiotic mother cell PCD is accompanied by an accumulation of depolarized mitochondria, organelle swelling, altered plasma membrane characteristics, and cytoplasmic clearance. To ensure that the gametes survive the destructive consequences of developing within a cell that is executing PCD, we hypothesized that PCD is restrained from occurring until spores have attained a threshold degree of differentiation. Consistent with this hypothesis, gene deletions that perturb all but the most terminal postmeiotic spore developmental stages are associated with altered PCD. In these mutants, meiotic mother cells exhibit a delay in vacuolar rupture and then appear to undergo an alternative form of PCD associated with catastrophic consequences for the underdeveloped spores. Our findings reveal yeast sporulation as a context of bona fide PCD that is developmentally coordinated with gamete differentiation.