Origins and Molecular Evolution of Meiosis

在了解减数分裂如何工作方面已经取得了很大进展，但只在少数几个生物体中取得了进展。因此，减数分裂的哪些方面和功能是最基本的还不清楚。尽管如此，来自这些生物的数据为在更多样化的真核细胞样本中启动减数分裂--更具体地说，减数分裂基因及其编码蛋白--的进化研究提供了坚实的基础。这个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，研究人员将扩展他正在进行的原生动物真核recA基因家族(RAD51和DMC1)的进化研究，方法是：(A)从代表主要真核生物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情况，其中一些与假定的无性物种有关。为了补充和支持拟议的实验研究，他将使用和开发适当的计算工具，对更多的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。这种生物信息学的“数据挖掘”应该导致识别和初步表征编码所有可用真核生物(特别是原生生物)减数分裂蛋白的关键基因。除了提供关于减数分裂蛋白功能和进化的信息外，这项工作的一个主要优先事项是确定减数分裂的进化时间，无论是在现有的真核生物进化期间(留下一些幸存的无性真核生物，因为它们从未进化过减数分裂)，还是在真核生物多样化之前(使当代无性真核生物仅仅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直接解决这一问题，特别是那些与先前的非减数分裂功能重复和偏离的基因。该项目的结果将指导未来从其他相关真核系中分离和研究特定减数分裂基因的实验努力。减数分裂是一种特殊的细胞分裂周期，在这个周期中，二倍体细胞被“减少”为单倍体细胞(如卵子和精子)，然后单倍体细胞融合产生新的(二倍体)个体。因此，减数分裂是有性生殖的中心，在真核生物的进化和成功中起着至关重要的作用。然而，性的起源和进化仍然是生物学中的主要谜团之一。发展对减数分裂关键机制的更清晰的进化理解不仅将广泛地阐明我们对有性过程的理解，而且还将有助于洞察蛋白质的进化及其作用于其中的大分子组合。最后，这些研究应该清楚地证明，在一个比较的进化框架内，将来自真核生物模型遗传系统的信息与来自研究较少的生物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.