贾第虫的核仁基因组与真核细胞核仁的起源进化
文献类型：学位论文
| 作者 | 辛德东 |
| 学位类别 | 博士 |
| 答辩日期 | 2005-06 |
| 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 | 贾第虫 核糖体合成系统 核仁起源进化 |
| 其他题名 | Nucleolar Genome of Giardia lamblia and the Origin and Evolution of the Nucleolus |
| 中文摘要 | 核仁是真核细胞核中最明显的结构，是rRNA转录、加工和核糖体亚基组装的场所。核仁的起源进化无疑是真核细胞起源进化问题的一个极为重要的方面。但迄今为止，这方面的研究很少。本文首先对"不具核仁"的低等单细胞真核生物贾第虫的"核仁"基因及核糖体合成系统的基因群进行了研究，进而对已知的核仁蛋白质组的生物进行了比较基因组研究，从而从基因和基因组的角度对核仁的起源进化问题进行了较为深入的研究。获得了如下结，和结论：1）在"不具核仁"的贾第虫中分离鉴定出了典型真核细胞参与pre-rRNA加工的krr］基因；表明贾第虫中的pre-rRNA加工机制与典型真核细胞的是一致的。在具有核仁结构的典型真核细胞中，krr1基因所编码的KRRIP蛋白是参与Pre一rRNA加工的核仁定位蛋白之一。我们在一度被认为是极为原始的"不具核仁结构"的真核生物－贾弟虫的基因组中分离鉴定出了该基因，并证明该基因在贾第虫中是活跃转录的。同时，还调查发现与KRRIP形成蛋白复合体从而发挥功能的众场，其基因在贾第虫中也是存在的，这提示贾第虫的pre寸RNA加工机制与具有核仁结构的典型真核细胞是一致的。2）对贾第虫核糖体合成系统的基因群／亚基因组进行了全面调查，发现在典型真核生物中所共有的参与核搪体合成的129条保守蛋白基因中有89条在贾第虫基因组具有相应的直系同源基因，包括编码参与rRNA申基化和假尿嗜陡化的蛋白复合体成员以及存在于905、405和605复合体中的蛋白等诸多重要基因。这表明贾第虫的核糖体合成系统与典型的真核生物相似，只是参与的成分相对简单些。以上1）、2）的结果表明贾第虫虽然没有核仁结构，但其核糖体合成机制却与具核仁结构的典型真核细胞一致。这可能意味着真核细胞核仁的核糖体合成功能的起源形成是在核仁结构形成之前，那么核仁结构的形成可能是在此功能之外另有"新意"；另外也可能是由于贾第虫因适应寄生生活而导致核仁"退化"之故，虽然这种可能性偏少，但若果真如此也是生物适应性进化中的一个重要现象，值得深入研究。3）对已知核仁蛋白质组的人、酵母和拟南芥进行了比较基因组学研究。通过搜索KOG直系同源蛋白簇数据库，发现约74％的人的核仁蛋白，约75％的酵母的核仁蛋白以及约84％的拟南芥的核仁蛋白在动物、真菌和植物中都保守。这表明这些高等真核生物的核仁蛋白大都在它们分化之前就已起源形成。进一步的调查发现：共同定位于人和酵母核仁中的同源蛋白中，人有154条蛋白对应于酵母的134条蛋白，其中人的核仁蛋白相对于酵母的有10条蛋白发生了基因重复；同样的分析发现，人的核仁蛋自相对于拟南芥的有21条蛋白发生了基因重复。这些事实表明：随着真核生物的进化，至少在高等真核生物中基因重复是核仁成分复杂化和核仁进化的重要途径。4）用人的442条核仁蛋白（它们在植物和真菌中也都存在同源蛋白，但不一定是核仁蛋白）对原核生物基因组进行了搜索。结果表明，在真细菌和原（古）细菌中都能找到好多同源物，但发现下列重要现象：只在原（古）细菌有同源物的核仁蛋白要比只在真细菌中有同源物的核仁蛋白多得多，包括了RNA修饰蛋白、核糖体蛋自以及参与翻译的相关蛋白等；而只在真细菌中有同源物的核仁蛋白只是RNA螺旋酶和WD重复蛋白。因此，我们认为核仁可能是由真细菌和原细菌复合起源的，但其主体起源于原细菌。 |
| 英文摘要 | Nucleolus is the most prominent nuclear subcompartment in eukaryotes, where ribosomal RNA transcription and processing and their assembly into ribosomal subunits before exporting to the cytoplasm occur. The nucleolar evolution is one of the most important issues in consideration of the eukaryotic evolution. But until now, there are only few studies regarding to its evolution. We have first studied the genes involved in ribosome biogenesis in the anucleoate Giardia. Then, by comparative genomic analysis, we tried to provide some insights into the origin and the evolution of the nucleolus. Our results are as follows: 1) From anucleoate Giardia, we have cloned the gene of KRRlp homolog, which is presented in eukaryotes and involved in pre-rRNA processing. It is suggested that although Giardia doesn't possess nucleolus, its mechanism and pathway of ribosome biogenesis is similar to that of typical eukaryotes. In the typical eukaryotic cells with nucleoli, as one of the nucleolus proteins, KRRlp encoded by krrl gene is one of the proteins involved in pre-rRNA processing. Giardia'was once considered to be one of the most primitive eukaryotes. Lack of nucleolus is one of the supporting features. We have cloned the gene of KRR1P homolog in Giardia and demonstrated that it was actively transcribed. KRRlp physically and functionally interacts with a protein Krilp to form a complex, which is required for 40S ribosome biogenesis in the nucleolus in yeast. Our database searches indicated that Krilp homolog was also presented in G. lamhlia. It is suggested that the mechanism and pathway of ribosome biogenesis in Giardia is similar to that of typical eukaryotes. 2) Investigating genes involved in ribosome biogenesis in the anucleoate Giardia comprehensively, we found that there are 89 orthologs of the 129 ribosomal biogenesis proteins in Giardia, including those involved in rRNA methylation or pseudoiiridine and present in 90S, pre-40S and pre-60S particles. These data suggest the ribosome biogenesis system of Giardia is similar to that of typical eukaryotes, but probably simpler, and is different from that of prokaryotes. According to the result 1 and 2, we argued that although Giardia does not possess nucleolus, its mechanism and pathway of ribosome biogenesis is similar to that of typical eukaryotes. This may imply that the origin of ribosome biogenesis function is earlier than the formation of nucleolus in eukaryotes evolution. So it is possible that the real reason for the forming of nucleolar structure is for the newly uncovered, nontodMonal roles. But there is still another possibility that the anucleolate state is due to the reductive evolution during the parasite lifestyle of Giardia. If this is true, such reductive evolution is also an important phenomenon of adaptive evolution and deserves further study. 3) The proteins of the nucleolar proteome of the human, arabidopsis and yeast were characterized successively. Using these sequences to search KOG database, we found that about 74% human nucleolar proteins, 75% yeast nucleolus proteins and 84% arabidopsis nucleolus proteins are conserved in animal, fungi and plant. It indicated that most nucleolar proteins may originate earlier than higher eukaryotes divergence. There are 154 human proteins and 134 yeast proteins localized in both human, and yeast nucleolus. What makes -the difference of the protein number between the human and yeast is 10 eases of gene duplication in human. Similarly, we found there are 21 cases of gene duplication in humaa among the proteins, which are localized in both human and arabidopsis nucleolus. So we concluded that along with the evolution of eukaryotes., gene duplication is an important way of the nucleolus evolution, 442 human nucleolus proteins, which are also conserved in fungi and plant, were used to search the bacteria and archaea genomes. The results showed that there exist homologs in both genomes, but proteins only having homologs in archaea are more than those only having homologs in bacteria. When classifying these proteins according to their fimction annotations, we found that proteins, which only have homoles in archaea, were those involved in RNA modification transcription, and ribosomal proteins. Proteins only having homologs in bacteria were those such as RNA helicase and WD repeat proteins. So we argued that though the nucleolus has a complex origin, the main part of it might originate from archaea. |
| 语种 | 中文 |
| 公开日期 | 2010-10-15 |
| 源URL | [http://159.226.149.42:8088/handle/152453/6173]  |
| 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 | 辛德东. 贾第虫的核仁基因组与真核细胞核仁的起源进化[D]. 北京. 中国科学院研究生院. 2005. |
入库方式： OAI收割
来源：昆明动物研究所
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