Modularity in the Development and Evolution of the Dentition of Teleost Fishes

[92487 . stock]有一种假说认为，促进生物进化能力的一个关键特征是，它们的整体形态组织成独立变化的单元或模块，这些单元或模块在独立遗传途径的控制下发育。提出的研究使用脊椎动物牙列来检查这种模块化组织是否适用于分生系统，即由多个相似构造部分组成的系统。需要验证的具体假设是，已知的鱼类牙列中独立进化的区域是在不同组基因的控制下发育的。将对斑马鱼（Danio rerio）和墨西哥四环鱼（Astyanax mexicanus）这两个物种的牙齿进行发育遗传学分析。前者是一种流行的发育遗传研究模型系统，仅在咽区具有牙齿，而后者既具有咽齿又具有沿口腔边缘排列的牙齿。该项目的目标是确定口腔和咽区域牙齿发育遗传控制的模块化程度，并描述斑马鱼谱系在保留咽牙的同时失去口腔牙齿的机制。待检测的基因是Fgf（成纤维细胞生长因子）、Hh（刺猬）和Bmp（骨形态发生蛋白）信号通路的成员，已知它们参与哺乳动物牙齿的发育。模块化遗传控制的牙列将调查通过比较口腔和咽区域在两个物种。这些比较将包括基因表达模式、Fgf和Hh信号的药理抑制效果，以及（在斑马鱼中）每种信号通路组分中突变对形态学和基因表达的影响。潜在的结果包括在两种类型的牙齿中使用由单独的起始信号触发的相同遗传途径，而不是在整个途径中存在广泛的差异。通过了解特定区域牙齿脱落的机制，可以进一步了解齿列中的模块性。在斑马鱼谱系中，口腔牙齿的进化损失将通过比较两个物种的口腔区域之间的基因表达模式来研究。在口腔表达中表现出差异的基因可能参与了口腔和咽齿的独立进化。在拟议的研究中收集的数据将为其他分生系统（如鳞片和四肢）成员的发育和进化机制提供建议。

0092487StockIt has been hypothesized that a key feature contributing to the capacity of organisms to evolve is the organization of their overall morphology into independently varying units, or modules, that develop under the control of independent genetic pathways. The proposed research uses the vertebrate dentition to examine whether such modular organization applies to meristic systems, i.e. those composed of multiple similarly-constructed parts. The specific hypothesis to be tested is that regions of the dentition of fishes known to evolve independently develop under the control of different sets of genes. Developmental genetic analyses of the dentition will be carried out in two species, the zebrafish (Danio rerio), and the Mexican tetra (Astyanax mexicanus). The former species, a popular model system for developmental genetic studies, possesses teeth only in the pharyngeal region, while the latter possesses both pharyngeal teeth and teeth lining the margins of the oral cavity. The objectives of the project are to determine the extent of modularity in the genetic control of tooth development in oral and pharyngeal regions, and to characterize the mechanism(s) by which the zebrafish lineage has lost oral teeth while retaining pharyngeal teeth. The genes to be examined are members of the Fgf (fibroblast growth factor), Hh (hedgehog), and Bmp (bone morphogenetic protein) signaling pathways known to be involved in the development of the mammalian dentition. Modular genetic control of the the dentition will be investigated by comparisons of oral and pharyngeal regions within both species. These comparisons will include gene expression patterns, the effects of pharmacological inhibition of Fgf and Hh signaling, and (in the zebrafish) the consequences for morphology and gene expression of mutations in components of each signaling pathway. Potential outcomes include the use of identical genetic pathways triggered by separate initiation signals in the two types of teeth versus the existence of extensive differences throughout the pathways.Further insight on modularity in the dentition can be gained by an understanding of the mechanisms of region-specific tooth loss. Evolutionary loss of oral teeth in the zebrafish lineage will be investigated by comparison of gene expression patterns between the oral regions of both species. Genes exhibiting differences in oral expression are likely to have been involved in the independent evolution of oral and pharyngeal teeth. The data to be collected in the proposed research will suggest mechanisms for the development and evolution of members of other meristic systems such as scales and limbs.