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题名	从藻类到动物的古老水平基因转移及其进化意义
作者	倪婷
学位类别	硕士
答辩日期	2012-05
授予单位	中国科学院研究生院
授予地点	北京
导师	文建凡
关键词	基因转移 内共生 质体 动物进化
其他题名	Ancient Horizontal Gene Transfer from Algae to Animals and Its Evolutionary Significance
学位专业	细胞生物学
中文摘要	水平基因转移又称侧向基因转移，是指具有生殖隔离的物种之间发生的遗传信息的交换事件，是相对于遗传信息从亲代垂直传递到子代的另一种交流模式，在物种的进化和基因组的革新方面具有重要的影响。水平基因转移事件大量发生，并且发生在原核生物中的比在真核生物中的要多，多细胞生物通过水平基因转移获得外源基因的案例相对较少。然而，近年来在与后生动物亲缘关系最近的现存的单细胞生物领鞭毛虫中发现了许多来源于多种藻类的基因，因此我们推测古老的水平基因转移事件可能也会发生在后生动物的单细胞祖先（领鞭毛虫最近的姐妹枝）中，甚至可能会对动物的长期进化具有一定影响。 目前对水平基因转移的研究主要通过系统发生分析法、内含子分析法和碱基组成分析法等多种方法，其中系统发生分析法应用最广，被誉为研究水平基因转移的“黄金法则”，因此本工作主要采用系统发生分析法来进行研究。通过基因转移候选者的筛选、系统发生分析和结构域分析，我们在海鞘 Ciona intestinalis 中鉴定出了 92 个基因可能来源于多种光合真核生物（藻类）。它们又可以进一步被归为 14 个基因家族，几乎所有的这些基因家族都广泛分布于多种后生动物中，这表明它们最有可能是被后生动物的共同祖先通过水平转移获得的。由于水平转移的推定供体多种多样，这些基因不可能是一个特定的藻类内共生体遗留下来的，即不是通过某种藻的内共生基因转移获得的。进一步的功能分析表明，绝大多数鉴定出的藻类基因与分子转运、细胞调节及甲基化信号等功能相关，这提示着这些基因的获得可能有助于动物祖先中细胞间的交流。 因为真核生物光合作用的细胞器——叶绿体产生于蓝细菌的初次内共生或多种藻类的二次、三次甚至更高次的内共生，真核生物中这些藻类/蓝细菌的基因常常被认为是早期藻类或蓝细菌内共生体的遗迹。而我们的发现为无质体真核生物中的藻类基因并不都来源于曾经存在过的质体提供了额外的证据，这对于阐释真核生物光合作用的进化具有重要意义。更重要的是，我们的结果首次发现了动物中存在许多早期通过水平基因转移获得的基因，而且这种古老的水平基因转移事件可能对整个后生动物门的进化形成具有重要影响。
英文摘要	Horizontal gene transfer (HGT), which is also called lateral gene transfer, refers to movement of genetic information between more or less distantly related organisms and plays an important role in organismal evolution and genome novelty. Up to now, massive horizontal gene transfer events have been reported, and much more HGT are found in prokaryotes than in eukaryotes. HGT is still traditionally considered to be rare in multicellular eukaryotes such as animals. However, recently, many genes of miscellaneous algal origins were discovered in choanoflagellates. Considering that choanoflagellates are the existing closest relatives of animals, we speculated that ancient HGT might have occurred on the unicellular ancestor of animals and have had impact on the long-term evolution of animals. Currently, the methods of detecting and evaluating cases of HGT include phylogenetic analysis, intron analysis, base composition analysis, etc. Of all the methods, phylogenetic incongruence is the most commonly used and considered to be the gold standard for indentifying HGT. So, here, we chose phylogenetic analysis as the main approach to perform research. Through candidate screening, phylogenetic and domain analyses, we identified 14 gene families, which include 92 genes, in the tunicate Ciona intestinalis that are likely derived from miscellaneous photosynthetic eukaryotes. Almost all of these gene families are distributed in diverse animals, suggesting that they were mostly acquired by the common ancestor of animals. Their miscellaneous origins also suggest that these genes are not derived from a particular algal endosymbiont. In addition, most genes identified in our analyses are functionally related to molecule transport, cellular regulation and methylation signaling, suggesting that the acquisition of these genes might have facilitated the intercellular communication in the animal ancestor. Because eukaryotic photosynthesis is derived from a primary endosymbiosis with a cyanobacterium as well as secondary and tertiary endosymbioses with miscellaneous algae, these algal/cyanobacterial genes in eukaryotes are frequently interpreted as relicts of earlier algal/cyanobacterial endosymbionts. However, our findingsprovide additional evidence that algal genes in aplastidic eukaryotes are not exclusively derived from historical plastids and thus important for interpreting the evolution of eukaryotic photosynthesis. Most importantly, our data represent the first evidence that more anciently acquired genes might exist in animals and that ancient HGT events have played an important role in animal evolution.
语种	中文
公开日期	2012-06-07
内容类型	学位论文
源URL	[http://159.226.149.42:8088/handle/152453/6967]
专题	昆明动物研究所_真核细胞进化基因组
推荐引用方式 GB/T 7714	倪婷. 从藻类到动物的古老水平基因转移及其进化意义[D]. 北京. 中国科学院研究生院. 2012.

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