Objective: To examine the influence of Edar deficiency in oral and pharyngeal teeth in rs-3 medaka, and gain insights into putative evolutional pathways from scales to teeth.
Methods: Adult rs-3 and normal medaka of both sexes were used for the analysis. After counting scale numbers, the entire numbers of oral and pharyngeal teeth were counted in each medaka. Scales, jaws and tooth-bearing pharyngeal bones were embedded in plastic and processed for histological and histochemical analyses.
Results: The number of functional teeth was much smaller in rs-3 medaka compared with that of normal medaka in both oral and pharyngeal regions. Magnitude of tooth loss, structural changes and erratic arrangement of teeth were more prominent in the pharyngeal regions relative to those in the jaws. The number of remaining scales varied considerably among the individual rs-3 medaka but no apparent correlation was noted among the scale number, oral tooth number and pharyngeal tooth number.
Conclusion: These data indicate that lack of Eda receptor impairs tooth formation in medaka, most prominently in the pharyngeal regions where teeth are thought to develop through endodermal epithelial-mesenchymal interactions.