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

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

0092487 Stock It 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.