Meeting Abstract
65.4 Wednesday, Jan. 6 Reversal of dorsal pharyngeal tooth loss in the zebrafish through over-expression of ectodysplasin AIGLER, S.R.; STOCK, D.W.**; University of Colorado, Boulder; University of Colorado, Boulder David.Stock@Colorado.edu
The irreversibility of the loss of complex structures has been considered a “law” of evolution, and explained as the result of the degeneration of genes required for their development. Little empirical evidence is available for such degeneration, however, and the extensive pleiotropy of developmental regulatory genes calls its likelihood into question. The reduction of dentition in the lineage leading to the zebrafish, Danio rerio, provides an opportunity to investigate the developmental and genetic changes associated with the loss of complex structures. Teeth in the zebrafish, as in other members of the order Cypriniformes, are restricted to a single pair of bones, the fifth ceratobranchials of the ventral, posterior pharynx. Reduction of dentition to this state occurred through the loss of teeth from the oral cavity and dorsal pharynx over fifty million years ago. Among the candidate causes of cypriniform dentition reduction is modification of the signaling ligand ectodysplasin. This gene has been shown by others to be necessary for pharyngeal tooth development in the zebrafish, and we found through comparative analyses that loss of its expression is associated with cypriniform dentition reduction. To test whether reversal of this expression loss represents a potential mechanism for the re-evolution of lost teeth, we used transgenic methods to express ectodysplasin ubiquitously and continuously throughout zebrafish development. Although such over-expression failed to restore oral dentition, it resulted in the appearance of dorsal pharyngeal teeth, which have been missing from cypriniforms for a similar period of time. This result suggests that, at least in the case of meristic systems, long absent structures have the potential to reappear through surprisingly simple genetic changes.
