Origins and Molecular Evolution of Meiosis

在了解减数分裂如何运作方面已经取得了很大进展，但仅限于少数生物体。因此，尚不清楚减数分裂中的哪些方面和功能是最基本的。尽管如此，来自这些生物体的数据为在更多样化的真核生物样本中启动减数分裂（更具体地说，减数分裂基因及其编码的蛋白质）的进化研究提供了坚实的基础。该项目的中心目标是更好地了解减数分裂过程及其分子机制的进化和功能。为了实现这一目标，研究人员将通过（a）从代表主要真核谱系的其他原生生物物种中分离这些基因，以及（b）调查recA家族中可能的基因丢失案例，其中一些与推定的无性物种有关，从而扩展他正在进行的对原生生物真核recA基因家族（RAD51和DMC1）的进化研究。为了补充和支持拟议的实验研究，他将采用和开发适当的计算工具，对其他减数分裂基因和蛋白质进行系统和全面的生物信息学分析。这种生物信息学“数据挖掘”应该能够从所有可用的真核生物（尤其是原生生物）物种中识别和初步表征编码减数分裂蛋白的关键基因。除了提供有关减数分裂蛋白的功能和进化的信息之外，这项工作的一个主要优先事项是确定减数分裂何时进化，无论是在现存的真核生物进化过程中（留下一些幸存的无性真核生物，因为它们从未进化出减数分裂），还是在真核生物多样化之前（使当代无性真核生物只是失去这种能力的有性物种的后代）。对从原生生物中鉴定出的减数分裂基因的系统发育分析将用于直接解决这个问题，特别是那些已经复制并偏离先前非减数分裂功能的基因。该项目的结果将指导未来从其他相关真核细胞谱系中分离和研究特定减数分裂基因的实验工作。减数分裂是一种特殊的细胞分裂周期，其中二倍体细胞“还原”为单倍体细胞（例如卵子和精子），然后融合产生新的（二倍体）个体。因此，减数分裂是有性生殖的核心，并且对于真核生物的进化和成功至关重要。然而，性的起源和进化仍然是生物学的主要谜团之一。对关键减数分裂机制有更清晰的进化理解不仅可以广泛地阐明我们对有性过程的理解，而且有助于深入了解蛋白质及其运作的大分子组合的进化。最后，这些研究应该清楚地证明在比较进化框架中将来自模型真核遗传系统的信息与来自研究较少的生物体的数据相结合的重要性。

Much progress has been made toward understanding how meiosis works, but in only a few organisms. It is, thus, unclear which aspects and functions in meiosis are most fundamental. Nonetheless, the data from these organisms provide a solid basis for initiating an evolutionary investigation of meiosis--more specifically, meiotic genes and their encoded proteins--in a more diverse sampling of eukaryotes. The central goal of this project is to better understand the evolution and function of the meiotic process and its molecular machinery. To accomplish this, the investigator will expand his ongoing evolutionary studies of the eukaryotic recA gene family (RAD51 and DMC1) in protists by (a) isolating these genes from additional protist speciesrepresenting major eukaryotic lineages, and (b) investigating possible cases of gene loss in the recA family, some of which are associated with putatively asexual species. To complement and support the proposedexperimental studies, he will employ and develop appropriate computational tools to carry out a systematic and comprehensive bioinformatic analysis of additional meiotic genes and proteins. This bioinformatic "data-mining" should result in the identification and initial characterization of key genes encoding meiotic proteins from all available eukaryotic (especially protist) species. In addition to providing information on the function and evolution of meiotic proteins, a major priority of this work is to establish when meiosis evolved, be it during extant eukaryotic evolution (leaving some surviving asexual eukaryotes that lack meiosis because they never evolved it), or alternatively, prior to the diversification of eukaryotes (making contemporary asexual eukaryotes simply the descendants of sexual species which have lost this ability). Phylogenetic analyses of the meiotic genes identified from protists will be used to directly address this issue, especially those genes that have duplicated and diverged from prior non-meiotic functions. The results from this project will guide future experimental efforts to isolate and study particular meiotic genes from other relevant eukaryotic lineages.Meiosis is the specialized cellular division cycle in which diploid cells are "reduced" to haploid cells (such as eggs and sperm), which then fuse to generate new (diploid) individuals. Meiosis is, thus, central to sexualreproduction and has been crucial in the evolution and success of eukaryotes. However, the origin and evolution of sex remains one of the major enigmas in biology. Developing a clearer evolutionary understanding of key meiotic mechanisms will not only broadly illuminate our understanding of the sexual process, but also lend insight into the evolution of proteins and the macromolecular assemblages in which they operate. Finally, these studies should clearly demonstrate the importance of combining information from model eukaryotic genetic systems with data from less well-studied organisms in a comparative evolutionary framework.