裂腹鱼类心血管系统低氧适应表型的分子基础

How animals adapt to the environment at the molecular level is one of the fundamental questions in evolutionary biology. Schizothoracine fish inhabits in rivers and lakes of the Qinghai-Tibetan Plateau where the dissolved oxygen level is low. The phenotypic adjustments, caused by the accumulation of the beneficial gene mutations, play an essential role in the functional adaption of Schizothoracine fish to the low oxygen concentration. Because cardiovascular system is responsible for the oxygen uptake and transport, adaptive change in cardiovascular structure is a prerequisite for the long-term hypoxia adaption in human and animals. Our preliminary findings reveal that the heart/body ratio increases dramatically with the increase of altitude and decrease of the dissolved oxygen levels, suggesting a correlation between oxygen level and heart development. Furthermore, the heart anatomies of Gymncypris eckloni and Gymnocypris przewalskii are different from hypoxia sensitive Hypophthalmichthys molitrix. Additionally, hemoglobin gene of G. przewalskii shows the signal of positive selection. Therefore, we hypothesizes that phenotypic variations shaped by the hypoxic environment require gene evolution. To test the hypothesis, we plan to conduct: 1) physiological and biochemical analyses of the cardiovascular system in 3 closely related Schizothoracine fishes (Gymnocypris chilianensis, Gymnocypris przewalskii, Gymncypris eckloni) from 3 altitude gradients and their hypoxia intolerant relative Hypophthalmichthys molitrix; 2) transcriptomic comparison of 4 species to identify positively selected genes and related pathways; 3) the functional assay of positively selected genes by the in vitro and in vivo experiments. Eventually, we expect to elucidate the interactions among gene mutations, phenotypic alteration and hypoxic environment.

动物对极端环境的适应是进化生物学领域的重要科学问题。青藏高原低氧环境使裂腹鱼类进化出独特的生理结构和生化特征，这些特征的基础是基因变异。心血管系统是氧气摄取转运的中枢，其适应性改变是低氧习服的必然结果。前期研究显示，随着海拔升高和水体溶解氧含量降低，裂腹鱼类心脏比重增加，心脏壁增厚，暗示裂腹鱼类心血管系统发生了适应性进化，而基因突变为这些表型演化提供了原始素材。为探讨裂腹鱼类心脏表型变异的遗传机制，本研究拟进行：1）选取分别分布在海拔<2000米、3200米和4300米的3个裂腹鱼类近缘物种，以低氧敏感鲢鱼为参照，寻找裂腹鱼类心血管系统低氧适应的表型特征；2）通过对心脏比较转录组分析，挖掘与心血管系统表型适应相关的低氧耐受基因，并结合体内外实验对基因功能进行验证，阐述基因、表型和环境之间的关系。研究结果将为裂腹鱼类低氧适应机制提供新的证据，并为发掘和利用鱼类抗逆基因奠定基础。

裂腹鱼类是青藏高原特有的鱼类区系，经长期进化，形成了独特的形态结构和生理特征适应青藏高原的极端水环境。研究发现随着海拔升高和水体溶解氧含量降低，裂腹鱼类近缘物种祁连裸鲤（~1200米）、青海湖裸鲤（~3200米）和花斑裸鲤（~4300米），心脏壁逐渐增厚，暗示裂腹鱼类心血管系统发生了适应性进化。通过对心脏比较转录组分析，发现正选择基因富集于心脏形态结构相关通路，与表型观察结果一致。同时，获得了花斑裸鲤的线粒体基因组，为进一步分析裂腹鱼类的线粒体基因组进化提供了基础数据。与斑马鱼等外类群比较显示，裂腹鱼类基因受高原环境选择，进化速率加快，其功能与应激、免疫反应相关。其中，应激反应基因MAPK2在低氧条件下高表达，表明其参与了低氧应答。功能分析发现，青海湖裸鲤IL8基因趋化成熟中性粒细胞，可能与低氧下的应激与炎症反应相关。研究结果为裂腹鱼类低氧适应机制提供新的证据，并为发掘和利用鱼类抗逆基因奠定基础。