基于基因序列变异和表达水平探讨鱼类适应青藏高原极端环境的趋同进化研究

As the three fish groups, Tibetan Loaches, Schizothoracine fishes and Glyptosternoid fishes are specially distributed in the Tibetan Plateau. The cold climate on the Tibetan Plateau, with hypoxic conditions and strong ultraviolet radiation, creates environments that are extremely hostile to them. Nevertheless, the three fish groups living in the Tibetan Plateau are well adapted to these harsh environmental conditions. Thus, they should have evolved adaptively at the molecular level to cope with the extreme environment. However, up to now, we know little about the molecular basis of adaptation to the extreme environment and convergent evolution at the molecular level in these three fish groups. In the present study, we plan to integrate the transcriptome data of the three groups of Tibetan fishes, in combination with transcriptome data of fishes from low latitude, and with systematic analyses of comparative transcriptome and bioinformatics analysis at the level of sequence variation and gene expression level, to identify positive selection genes which is related to adaptation to the Tibetan Plateau. Through investigations of the evolutionary pattern and convergent evolution of these candidate genes, validation in more species using gene clone and the function experiments of genes of strong interest, we aim to reveal the genetic basis of adaptation and convergent evolution of the three groups of Tibetan fishes.

高原鳅属鱼类，裂腹鱼类和鰋鮡鱼类是青藏高原特有的三大鱼类类群。青藏高原寒冷、低氧和强紫外线的极端环境条件，对其生存带来了严峻的挑战，但这三大鱼类类群对青藏高原极端环境都表现出了极强的适应性。因此，它们在分子水平上可能已经发生了适应性的变化，从而来应对青藏高原的极端环境。然而，迄今为止对于这三大鱼类类群适应青藏高原极端环境的分子机制及在分子水平上的趋同进化所知甚少。本项目拟整合三大高原鱼类的转录组数据，并与近源低海拔鱼类的转录组数据比较，从序列变异及基因表达水平进行系统的比较转录组学和生物信息学分析，以筛选高原鱼类基因组水平上受到正选择作用的且和高原适应相关的重要功能基因，揭示这些基因在三大高原鱼类中的进化格局及趋同适应，并对重要功能基因进行更多物种的克隆验证和功能实验验证，较为系统地揭示不同谱系高原鱼类之间趋同进化的遗传学基础。

高海拔的极端环境给当地土著物种的适应性进化提供了较强的推动力。但是对于不同谱系物种尤其是鱼类趋同适应的遗传学机制却还不清楚。作为研究趋同进化最好的模型软刺裸鲤、硬刺高原鳅、黑斑原鮡三大高原鱼类能很好的适应青藏高原的极端环境，但是其中的遗传机制并不清楚。通过高原鱼类和低海拔鱼类的比较基因组测序，我们检测到三大高原鱼类适应青藏高原趋同进化的基因组水平的信号：（1）高原鱼类与低海拔的参照物种相比基因组水平上呈现进化速率显著加快；（2）在三大高原鱼类中共检测到368个正选择基因，富集到能量代谢和低氧适应的通路中；（3）在三大高原鱼类中鉴定到其分子水平上平行替代的氨基酸位点是普遍存在的，经历了正选择的趋同替代和高原适应密切相关。VHL基因的功能验证，暗示了相比于低海拔鱼类高原鱼类有更强的抗低氧的能力。研究结果为青藏高原鱼类的高海拔适应的趋同进化遗传基础提供了基因组学和功能水平上证据。