Probing the evolutionary origins of apoptosis.

因为它们的作用与细胞存活直接相反，程序性细胞死亡机制最初是如何进化的问题长期以来一直是一个谜。单细胞微生物中明显细胞死亡途径的发现加深了这一悖论。事实上，尽管这些途径的真正生物学功能尚不清楚，但在出芽酵母酿酒酵母中，死亡途径利用已知在后生动物中起作用的保守细胞杀伤机制。我们假设酵母可能利用这些“杀死途径”中的一些来实现与细胞死亡无关的功能。我们最近描述了酵母在配子体发生阶段（通常称为孢子形成）生命周期功能的一个新方面，我们将其命名为“孢子发育”。酵母孢子脱落涉及到互补的细胞死亡相关途径，这些途径会聚在一起完成未包装的减数分裂细胞核的破坏。虽然我们的第一篇论文广泛描述了孢子脱落的空泡/自噬途径的功能，但我们也提供了强有力的证据，支持存在与哺乳动物凋亡相关的线粒体途径，至少部分平行起作用。具体来说，我们发现在孢子分裂过程中，未包装细胞核的核基因组分裂成核小体阶梯，这是长期以来公认的哺乳动物细胞凋亡的标志。此外，孢子落基因组片段化需要同源内切酶G的功能，这是一种古老的线粒体蛋白，在哺乳动物凋亡过程中也起着完成同源事件的作用。在本提案中，我描述了进一步阐明酵母配子体发生过程中endoG/线粒体途径功能的初步结果，以及旨在促进我们对该途径理解的实验。我们的研究对细胞死亡机制的进化具有重要意义。

Because they act in direct opposition to cell survival, the question of how programmed cell death mechanisms might have first evolved has for long been a mystery. The discovery of apparent cell death pathways acting in single celled microbes has served to deepen this paradox. Indeed, although the bona fide biological functions for these pathways has remained unclear, in the budding yeast Saccharomyces cerevisiae, death pathways utilize conserved cell-killing machinery known to act in metazoans. We hypothesized that yeast might utilize some of these "killing pathways" for non cell-death related functions. We have recently described a novel aspect of the yeast lifecycle functioning during its gametogenesis phase (more commonly known as sporulation) which we have named "sporoptosis". Yeast sporoptosis involves complimentary cell death-related pathways that converge to accomplish the destruction of unpackaged meiotic nuclei. While our first paper describing sporoptosis extensively characterized the function of a vacuolar/autophagic pathway, we also provided strong evidence supporting the existence of a mitochondrial pathway related to mammalian apoptosis that acts at least partly in parallel. Specifically, we found that during sporoptosis, the nuclear genome of unpackaged nuclei is fragmented into nucleosomal ladders, a long-acknowledged hallmark of mammalian apoptosis. Moreover, sporoptotic genome fragmentation requires the function of an ortholog of endonuclease G, an ancient mitochondrial protein which also functions to accomplish the homologous event during mammalian apoptosis. In this proposal, I describe preliminary results that further illuminate the functions of the endoG/mitochondrial pathway during yeast gametogenesis, and experiments designed to advance our understanding of this pathway. Our studies have important implications for the evolution of cell death mechanisms.