WISE, S. B.*; STOCK, D. W.; University of Colorado at Boulder: Bone morphogenetic protein expression, regulation, and function in teleost tooth development and evolution

Bone morphogenetic proteins (Bmps) have been shown to be important in tooth development in the mouse and the evolution of dentition in rodents and birds, but little comparable data is available from teleost fishes. Teleost teeth vary greatly in location, number, and shape, both within individuals and between species. To determine whether Bmps affect this variation, we examined the expression of bmp2a, bmp2b, and bmp4 during tooth development in the zebrafish and the Mexican tetra (Astyanax mexicanus). Both species possess pharyngeal teeth, while oral teeth are found only in the latter. All three genes are expressed in developing teeth of both species, with overlapping but distinct patterns. While few differences were found between oral and pharyngeal teeth, none of the genes is expressed in the toothless oral region of the zebrafish. Examination of an outgroup species, the Japanese medaka (Oryzias latipes), indicated that the zebrafish condition is derived, suggesting that Bmps may have been involved in the evolutionary loss of teeth in the zebrafish lineage. We also found evidence for a difference in Bmp function between the zebrafish and the tetra using morpholino-based gene knockdown. Specifically, bmp4 is necessary for pharyngeal tooth development in the zebrafish, but not in the tetra. Finally, we are investigating the regulation of Bmp expression to understand the mechanism of oral expression loss in the zebrafish. To date we have investigated one candidate pathway, Fibroblast growth factor signaling, and have found dental expression of bmp2a and bmp4 to be downstream of this process in the zebrafish. We conclude that Bmps have diverged in expression and function during evolution of teleost teeth, with some changes correlated with morphological divergence and others not.