單細胞原生動物——賈第蟲（Giarida）被認為是目前已知的最原始的真核生物,，然而它卻能寄生在動物界中進化程度最高的脊椎動物（特別是哺乳動物）上,。在生物界中這么早就分化出來的原始真核生物后來是如何成功地寄生于比它出現(xiàn)晚得多的高等生物上的呢,？它勢必經(jīng)歷了一個從早期的非寄生生活向寄生生活的進化,，且該進化過程是一個十分成功的適應性進化過程,，以使它能廣泛適應地寄生于許多脊椎動物上,。那么這種適應性進化的發(fā)生在基因組存在怎樣的機制呢,？
中國科學院昆明動物研究所真核細胞進化基因組文建凡研究員指導的博士研究生孫雋,，通過對藍氏賈第蟲（Giardia lamblia）全基因組中基因重復(duplication)的系統(tǒng)性研究，發(fā)現(xiàn)該寄生原蟲的基因組在進化歷史上發(fā)生過兩次大規(guī)模的基因重復,。其中,，最近的一次包括了與寄生蟲逃避宿主的免疫系統(tǒng)的攻擊有關的VSP（Variant-specific Surface Proteins，即變化的特異表面蛋白）基因的大量重復,。且發(fā)現(xiàn)該次基因迅速擴增事件發(fā)生的時間與有胎類哺乳類動物的輻射分化時間相吻合,。
該研究結(jié)果提示：賈第蟲實現(xiàn)由自由生活到寄生到多種哺乳類生物上的成功進化與VSP基因的大量重復密切相關,，從而從基因組進化的角度揭示了這一生物進化現(xiàn)象的內(nèi)在機制。
該研究成果近期已在進化生物學領域的重要刊物BMC Evol. Biol.上發(fā)表,。論文發(fā)表后引起國際上的廣泛關注,。(生物谷Bioon.com)
生物谷推薦原文出處：
BMC Evolutionary Biology doi:10.1186/1471-2148-10-49
Gene duplication in the genome of parasitic Giardia lamblia.
Jun Sun1,2* , Huifeng Jiang1,3* , Roberto Flores3 and Jianfan Wen1
1 State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences (CAS), Kunming, Yunnan 650223, PR China
2 Graduate School of Chinese Academy Sciences, Beijing 100039, PR China
3 Division of Nutritional Sciences, Cornell University, Ithaca, NY 14853, USA
Background
Giardia are a group of widespread intestinal protozoan parasites in a number of vertebrates. Much evidence from G. lamblia indicated they might be the most primitive extant eukaryotes. When and how such a group of the earliest branching unicellular eukaryotes developed the ability to successfully parasitize the latest branching higher eukaryotes (vertebrates) is an intriguing question. Gene duplication has long been thought to be the most common mechanism in the production of primary resources for the origin of evolutionary novelties. In order to parse the evolutionary trajectory of Giardia parasitic lifestyle, here we carried out a genome-wide analysis about gene duplication patterns in G. lamblia.
Results
Although genomic comparison showed that in G. lamblia the contents of many fundamental biologic pathways are simplified and the whole genome is very compact, in our study 40% of its genes were identified as duplicated genes. Evolutionary distance analyses of these duplicated genes indicated two rounds of large scale duplication events had occurred in G. lamblia genome. Functional annotation of them further showed that the majority of recent duplicated genes are VSPs (Variant-specific Surface Proteins), which are essential for the successful parasitic life of Giardia in hosts. Based on evolutionary comparison with their hosts, it was found that the rapid expansion of VSPs in G. lamblia is consistent with the evolutionary radiation of placental mammals.
Conclusions
Based on the genome-wide analysis of duplicated genes in G. lamblia, we found that gene duplication was essential for the origin and evolution of Giardia parasitic lifestyle. The recent expansion of VSPs uniquely occurring in G. lamblia is consistent with the increment of its hosts. Therefore we proposed a hypothesis that the increment of Giradia hosts might be the driving force for the rapid expansion of VSPs.
