Probing the evolutionary origins of apoptosis.

由于它们与细胞存活直接对立，程序性细胞死亡机制可能最初是如何进化的问题长期以来一直是一个谜。作用于单细胞微生物的表面细胞死亡路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，但在萌芽酵母中，死亡途径利用了已知的作用于后生动物的保守的细胞杀伤机制。我们假设酵母菌可能利用其中的一些“杀死途径”来发挥非细胞死亡相关的功能。我们最近描述了酵母生命周期的一个新的方面，在其配子发生阶段(更常见的是孢子形成)，我们将其命名为“孢子下垂”。酵母菌孢子衰退涉及与细胞死亡相关的互补途径，这些途径汇聚在一起完成对未包装的减数分裂核的破坏。虽然我们的第一篇论文广泛描述了空泡/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细胞凋亡相关的线粒体途径，该途径至少部分平行地起作用。具体地说，我们发现在孢子脱落期间，未包装核的核基因组被分裂成核小体梯形，这是长期以来公认的哺乳动物细胞凋亡的标志。此外，孢子光基因组片段化需要内切酶G的同源基因的功能，这是一种古老的线粒体蛋白，也在哺乳动物凋亡过程中完成同源事件。在这个提案中，我描述了进一步阐明Endog/线粒体途径在酵母配子发生中的功能的初步结果，以及旨在促进我们对这一途径的理解的实验。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.