| 其他摘要 | 地球上的生物对生存环境都有一定的要求，越过一定的界限就不能存活。但是，一些生物能够在一般生物承受的环境阈值之外极端环境中生存，它们被称为极端环境生物。极端环境生物适应性进化机制一直是进化生物学领域需要解决的问题。对极端环境生物适应性复杂性状的解析有助于人类发掘有价值的生物信息、生物技术或者生物能源，有利于生物学、生物医学和人类疾病事业的发展。本文以高原鼢鼠和海陆蛙为例（分别隶属于哺乳类和两栖类），从低氧适应和高盐适应两个角度探讨动物适应极端环境的遗传基础。啮齿类哺乳动物是研究整个哺乳类低氧适应性进化不可或缺的一部分，在啮齿类中，地下鼠类是研究极端缺氧环境适应的绝佳模型。在第三章，我们以高原鼢鼠为例利用比较基因组学手段对其适应高原低氧的遗传机制进行解析，发现大量能量代谢基因在高原鼢鼠基因组中发生了快速进化。在高原鼢鼠支系中正选择基因显著富集在ATP酶活性、血管发育和呼吸气体交换等基因功能类群，这些类群明显与低氧适应相关。其中，呼吸气体交换这一功能类群被显著富集可能是高原鼢鼠特有的适应性改变，因为该类群并没有在其它高原哺乳类的正选择基因富集中筛选到，这些正选择基因可能参与改善高原鼢鼠的呼系统的功能。此外，787个基因在高原鼢鼠和裸鼹鼠支系间发生了趋同进化，这些基因被显著富集到缺氧反应、氧气平衡和红血球平衡等功能类群，其中EPAS1和AJUBA基因被广泛报道牵涉缺氧反应。该研究为理解整个哺乳类的低氧适应性进化遗传机制提供了补充材料。两栖类由于皮肤裸露很少能够在高渗透浓度的海水（渗透浓度高达1,100 mosmol/kgH2O）中生存。海陆蛙━属于广盐性两栖类，它们是目前为止唯一能够在海水中生存的两栖类物种，拥有比外界水环境略高的渗透浓度，因此它们成为探讨两栖类高盐适应性进化的理想模型。在第四章，我们以海陆蛙为例利用比较基因组学和比较转录组学等手段对海陆蛙的高盐适应性复杂性状进行解析。在基因序列水平上，发现在海陆蛙基因组中大量离子转运相关基因发生快速进化。在基因表达水平上发现相比于其它近缘物种，海陆蛙的肾脏中存在大量差异表达的基因，这些差异表达基因有快的进化速率，这就暗示了海陆蛙肾脏已经发生了功能进化。此外，我们发现肾素-血管紧张肽-醛固酮系统在海陆蛙的高盐渗透调控中扮演重要角色。该研究为深入探讨两栖类的高盐适应性遗传机制奠定了基础。 综上所述，我们从基因组进化速率、快速进化的基因功能类群、正达尔文选择、平行进化、差异表达基因等方面入手，揭示了高原鼢鼠和海陆蛙对极端环境的适应性进化遗传机制，为后续的研究指明了方向和功能靶点。; Lives in the world have certain adaptive bounds for living environments and if crossing over extreme bounds, lives can not survive. Actually, sevral species, named as extremely environmental biological species (EEBS), can endure severe environmental thresholds that other species did not touch at all. The mechanisms of adaptive evolution of EEBS always is a primary mission of evolutionary biology. The analyses of adaptive complex traits for EEBS are very conducive for human to discover valuable bioinformation, biotechnologies or biological energy sources, and these will aid to rapid developments of biology, biomedicine and human disease. Herein, the Myospalax baileyi and Fejervarya cancrivora, respectively attached to mammalian and amphibian, were chose as research models to explore their genetic mechanisms to adaptations of extremely low oxygen concentration and high osmotic environment. Rodent mammals play essential roles in studying hypoxic adaptation of whole mammals, and the subterranean rodents are perfect models to explore the adaptative mechanism of extremely hypoxic environment in rodents. In the third chapter the M. baileyi was regarded as a research object and we utilized a series of comparative genomics approaches to reveal the genetic bases of M. baileyi adapting to plateau hypoxic environment. This study uncovered many candidate genes related to energy metabolism underwent accelerated evolution in the M. baileyi. Furthermore, in the M. baileyi branch we found that positively selected genes were significantly enriched in the gene categories involved in ATPase activity, blood vessel development and respiratory gaseous exchange, and these functional categories are obviously relevant to adaptations of extremely low oxygen concentration. The GO category━respiratory gaseous exchange may be specific to the M. baileyi and involved in the adaptive evolution of the respiratory system, because it was not found in positively selected genes of other plateau mammals. In addition, 787 genes underwent parallel evolution between M. baileyi and naked mole rat branches, and they ere significantly overrepresented in the GO categories such as response to hypoxia, oxygen homeostasis and erythrocyte homeostasis and gene EPAS1 and AJUBA ever were broadly reported as hypoxic adaptive genes. This study supplied supplementary materials for elucidating hypoxic adaptation of whole mammals. Amphibians with bare skin can rarely be in high osmotic seawater (Osmotic concentration is as high as 1100 mosmol/kg H2O) to survive. The F. cancrivora, attached to euryhaline amphibian, is reported to be so far the only amphibian species that can survive in seawater, has a slightly higher osmotic concentration than the outside environment, so that it become an ideal model to explore the adaptive mechanism to extremely high salt water-environment in amphibians. In the fourth chapter the F. cancrivora was chose as a research model, and we used comparative genomics and transcriptomic approaches to perform analyses for the complex traits of the crab-eating frog to high salinity adaptation. On gene sequence level, our study discovered that many genes associated with ion transport appear to have evolved rapidly in the F. cancrivora. On the gene expression level, compared to other closely related species, the F. cancrivora hosted abundant differentially expressed genes in kidney and these genes showed significantly elevated mean dN/dS and suggest the kidney of F. cancrivora had underwent functional evolution. Additionally, we documented that renin-angiotensin-aldosterone-system may also play an important role in regulating the osmotic equilibrium of F. cancrivora. To sum up, we utilized a series of analytical methods including whole genomic evolutionary rate, rapidly evolving GO functional categories, Darwin positive selection, parallel evolution, differentially expressed genes, revealed adaptively evolutionary mechanisms of two groups, M. baileyi and F. cancrivora, for extreme environments, and pointed out the direction for the subsequent research and functional experimental targets. |
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