The Mechanism of Trace-element Accumulation into Tooth Enameloid/Enamel and Its Evolutionary Changes.

点击翻译按钮获取中文摘要

In the past studies, it was postulated that accumulation of iron or other trace elements in fish enameloid should be related to feeding habits of the fishes. However, the results of the present investigation yielded no supportive evidence for those previous concept. The present studies indicate that the mineral phase of enameloid in both cartilagineous and bony fishes is most adequately characterized as fluoridated carbonatoapatites. However, the degree of fluoridation, Fe accumulation, and carbonation of the apatite lattice vary among the species and, within a species, at different developmental stages. It is of interest to consider that the observed accumulation of fluoride and iron may reflect the composition of ancient body fluid or in the mineralizing milieu. The overall results suggest that the accumulation of iron and fluoride into fish enameloid realized in the Actinopterygian lineage. In light of the evidence obtained, the origin of the F accumulation into tooth enameloid can be traced back to the cladistian stage of Actinoperygian evolution, while that of high fluoride concentration to the Neopterygian stage. Most likely, the iron accumulation mechanism has been evolved prior to the F accumulation, probably emerging with the brachiopterygian or relevant species. Indeed, there are no teleostean fishes which exhibits a combination of high F and low Fe, except for sharks. Thus it seems likely that the mechanisms of F and Fe accumulation have been developed independently with different evolutionary backgrounds and that its accumulation mechanisms have been buried in the evolutionary process from fishes through amphibian to mammals. At present, it is most likely that iron accumulation into developing enameloid has been lost during the evolution from the Acanthuridae to the Tetraodontoidei, based on the finding that a shatp contrast with respect to the iron content was obtained between the enameloid of the Tetraodontoidei and Acanthuridae.