Teeth are examples of tissues that vary both within an organism and between species. The genetic factors that govern developmental and evolutionary variations in teeth morphology are unknown. The timing of the gene expression of members of the gene family of bone morphogenetic proteins (Bmps) have been found to differ in developing teeth of different teleost fish species, specifically zebrafish and Mexican tetras. To test whether these expression differences actually cause differences in tooth development in these species, two strategies will be used to alter Bmp gene expression in fish tooth development. First, beads soaked in Bmp proteins or Bmp antagonists (such as noggin) will be applied to the developing oral regions of fish embryos. Second, normal Bmp gene expression will be inactivated in embryos of both fish species by injecting morpholino antisense oligonucleotides (modified RNA sequences which prevent normal mRNA processing or translation). The effects of these two types of treatments will be measured using in situ hybridization for genes likely to be regulated by Bmp expression. The morphology of teeth in older experimentally perturbed embryos will also be examined with the use of histological stains. Perturbation of Bmp gene function is expected to alter or prevent the development of teeth, and to alter the expression of genes important to the development of teeth. The results of this work will determine the function of Bmp genes in tooth development in fishes, and test whether changes in Bmp expression could be involved in the evolution of different patterns of tooth development in fishes. Overall, this work will shed light on mechanisms of morphological evolution in vertebrates.
