STOCK, D.W.; Univ. of Colorado, Boulder: Comparative studies of tooth development in teleost fishes

My laboratory uses the zebrafish (Ostariophysi: Cypriniformes) as part of a three taxon statement for investigating the developmental genetic basis of macroevolution in the vertebrate dentition. Comparisons of gene expression, regulation and function are carried out with an additional ostariophysan, the characiform Astyanax mexicanus (Mexican tetra), and an acanthopterygian outgroup, the beloniform Oryzias latipes (Japanese medaka). These comparisons allow an analysis of several morphological transformations of the teleost fish dentition, with our current focus being the loss of cypriniform oral teeth. The most distinctive gene expression difference we identified between these species is the absence of expression from the zebrafish oral epithelium of three members of the Dlx family of transcription factors that are expressed in dental epithelium of the other two species. Reporter transgenic analysis of one of these genes, dlx2b, suggests that loss of its expression is the result of changes in trans-acting regulators. Two candidates for such regulators are the Fibroblast growth factor (Fgf) and Bone morphogenetic protein (Bmp) signal transduction pathways, as we and others have shown them to be upstream of epithelial Dlx expression. We have identified expression differences in Bmp ligands between the zebrafish and the other two species and are investigating individual Fgf ligands for similar differences. Experiments to rescue zebrafish oral tooth development by transgenic mis-expression are also underway and may shed light on whether the genetic changes involved in cypriniform tooth loss have constrained the evolution of feeding mechanisms in this group.