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| 哺乳动物若干类群甜味、鲜味和苦味基因分子进化与食性相关性研究 | |
| 其他题名 | Molecular evolution and diets correlation ananlysis of sweet, umami and bitter taste genes of some species in mammal |
| 刘广建 | |
| 出版年 | 2015 |
| 学位类型 | 博士 |
| 导师 | 李明 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 味觉（Taste）是动物的基本功能之一，在一定程度上决定了动物对食物的选择。味觉包括甜、鲜、苦、咸和酸5种基本感觉，其中，甜味和鲜味与碳水化合物、蛋白质等营养物质的摄入相关，而苦味味觉则能够防止动物摄入对机体不利的物质。因而，面对复杂的自然环境和食物来源，味觉在动物的进化历程中必然扮演着重要角色。到目前为止，有关甜味、鲜味和苦味基因的研究已经在多个物种中开展。然而，大多数甜味和鲜味基因（Tas1rs）的研究主要着眼于食性特化物种中假基因的发现；苦味基因（TAS2Rs）的研究则主要关注食性对物种间苦味基因数量差异的影响。本论文，我们首次在以植物为主要食物的狭鼻灵长类（Catarrhine primates）中全面开展了甜味和鲜味基因适应性进化分析，探讨了食性差异对基因进化的影响。另外，我们还通过比较基因组研究，系统探讨了劳亚兽总目（Laurasiatheria）苦味基因进化历程以及适应不同生态动物类群间的苦味基因进化差异。 狭鼻灵长类是灵长动物（Primates）中的一个重要分类单元，包括猴科（Cercopithecidae）、人科（Hominidae）及长臂猿科（Hylobatidae）。长期的进化过程中，不同类群的狭鼻灵长动物分化出明显差异的食性特点。狭鼻灵长类甜味和鲜味分子进化分析结果显示，疣猴（Colobinae）祖先Tas1r2序列经历了显著选择压力放松，这可能与其食叶特性及特殊的消化方式相关。另外，我们的分析还发现猴科Tas1r1，猴亚科、疣猴亚科和长臂猿科Tas1r2以及猕猴属Tas1r3均在进化过程中经历了显著的正选择，并且存在显著正选择位点。我们还在猴亚科、疣猴亚科以及白臀叶猴中发现了一些已经被验证能够改变受体敏感性的位点突变。本研究中检测到的大多数正选择位点均位于负责与味觉物质结合的TAS1Rs受体蛋白膜外区，并且通过蛋白模建和分子对接结果验证了部分甜味和鲜味分子的结合位点。 劳亚兽总目，包括猬形目（Erinaceomorpha）、鼩形目（Soricomorpha）、翼手目（Chiroptera）、鳞甲目（Pholidota）、食肉目（Carnivora）、奇蹄目（Perissodactyla）、和鲸偶蹄目（Cetartiodactyla），为哺乳动物的四个总目之一，与灵长总目（Euarchontoglires）共同组成北方兽类（Boreoeutheria），不同劳亚兽类群呈现出多样的生态适应。在本研究中，我们基于全基因组同源序列搜索，在40种劳亚兽总目物种中开展了苦味基因分子进化研究。基因系统发育关系重建以及基因进化历程构建结果显示劳亚兽物种间完整苦味基因（Intact bitter taste gene）数目存在极大差异（从0到52不等），并且它们的共同祖先至少存在25条完整苦味基因。随着物种的分化，不同物种中苦味基因的数量经历了普遍的丢失和至少8次枝系特异性（Lineage-specific）基因增加过程，这些基因数量的增加主要是物种特异性基因复制的结果。一般认为，苦味基因的丢失和增加与动物食性的改变相关，我们在海洋哺乳动物中检测到普遍的TAS2Rs失活及基因丢失；荒漠或高原分布的骈足动物中苦味基因的数量显著少于其它食草动物；鼩鼱作为体型最小的哺乳动物却拥有最多的苦味基因数量，这可能是其不断进食以维持极高的代谢水平的需要；穿山甲则是劳亚兽中完整苦味基因数量最少的陆生哺乳动物，这可能是长期专一食蚁的进化结果。这些发现展示了不同生态位（Ecological niches）中的苦味基因适应性进化，并为劳亚兽味觉多样性的分子机制研究提供了新的视野。 |
| 英文摘要 | Taste is one of the most important functions, and would determin food selection of animals in a certain degree. Among these five basic tastes (sweet, umami, bitter, salty and sour), sweet and umami allow animals to recognize diets with nutritious carbohydrates and proteins respectively, and bitter taste is responsible for preventing the ingestion of poisonous substances. Until recently, analyses of umami and sweet taste were performed on various domestic and wild animals. Most of these studies focused on the pseudogenization of taste genes (Tas1rs), which occur mostly in carnivores and species with absolute feeding specialization, but omnivores and herbivores were more or less neglected. Studies of bitter taste were maily concentrated on number variation of pupative bitter taste genes among different species with diverse diets preferences. Here, we conducted the most comprehensive investigation to date of selection pressure on sweet and umami taste genes in catarrhine primates to test whether specific adaptive evolution occurred during their diversification, in association with particular plant diets. Additionally, evolution analyses of bitter taste genes were also implemented in Laurasiatheria species with various ecological niches based on comparative genomic analysis. Catarrhine primates are a group of herbivorous animals (feeding mostly on plants) with significant divergence in dietary preference.We documented significant relaxation of selective constraints on sweet taste gene Tas1r2 in the ancestral branch of Colobinae, which might correlate with their unique ingestion and digestion of leaves. Additionally, we identified positive selection acting on the umami taste gene Tas1r1 of Cercopithecidae lineages, on Tas1r2 of the Cercopithecinae and extant Colobinae and Hylobatidae lineages, and on Macaca lineages for Tas1r3. Our research further identified several site mutations in Cercopithecidae, Colobinae and Pygathrix, which were detected by previous studies altering the sensitivity of receptors (TAS1Rs). The positively selected sites were located mostly on the extra-cellular region of taste TAS1Rs. Among these positively selected sites, two vital sites for TAS1R1 and four vital sites for TAS1R2 in extra-cellular region were identified as being responsible for the binding of certain sweet and umami taste molecules through molecular modelling and docking. Laurasiatheria (including six orders, i.e. Eulipotyphla, Perissodactyla, Carnivora, Pholidota, Chiroptera, and Cetartiodactyla) is one of the four major groups of extant eutherian mammals and forms Boreoeutheria together with Euarchontoglires. Many species in this clade are characterized by their successful adaptive radiation to various ecological niches. In this study, we investigated the evolutionary trajectory of bitter taste receptor genes (TAS2Rs) in 40 Euarchontoglires species based on homology searches of corresponding whole-genome assemblies. The Laurasiatheria species possessed variable numbers of intact TAS2Rs, which ranged from 0 to 52, and their last common ancestor had at least 25 intact TAS2Rs. The gene tree showed that there have been at least eight lineage-specific events involving massive gene duplications. Most of these gene duplications were found to be species-specific and suggested to be correlated with diets specialization. We confirmed widely TAS2Rs gene disruption or even loss in marine mammals (cetaceans and two pinenipedia), and the number of TAS2Rs in camel and alpaca was examined to be significant less than other herbivores animals. All these gene number variations were suggested to be adaptive evolution of bitter taste to special oceanic and desert environment. These findings provide insights into the roles of adaptive sensory evolution in various ecological niches and important clues related to the molecular mechanisms that underlie taste diversity in Laurasiatheria mammalian species. |
| 中文关键词 | 甜味基因 ; 鲜味基因 ; 苦味基因 ; 狭鼻灵长类 ; 劳亚兽总目 ; 食性分化 ; 适应性进化 |
| 英文关键词 | Sweet umami and bitter taste genes Catarrhine primates Laurasiatheria Feeding characteristics Adaptive evolution |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 生态学 |
| 来源机构 | 中国科学院动物研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287507 |
| 推荐引用方式 GB/T 7714 | 刘广建. 哺乳动物若干类群甜味、鲜味和苦味基因分子进化与食性相关性研究[D]. 中国科学院大学,2015. |
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