Evolution of the amelogenin gene in toothed and toothless vertebrates.

Amelogenin proteins constitute the major organic contents in forming enamel, but some previously published data indicate that the amelogenin gene could be present in several species lacking teeth or functional enamel. Therefore, amelogenin could have another, still unknown, function other than contributing to enamel formation. In order to test this hypothesis, the presence of this gene has been searched for in various vertebrates. We first compared the mammalian amelogenin sequences available in the literature to obtain the best chance of a successful detection of this gene in phylogenetically distant species. Using this analysis, we have shown that the occurrence of the amelogenin gene in the Y chromosome of primates and of an artiodactyl species is probably due to two independent duplications from genes on the X chromosome. Primers for PCR have therefore been synthesized and tested in eight species, five possessing teeth (human, two phylogenetically distant lizards, and two phylogenetically distant actinopterygians) and three lacking teeth (chicken and two phylogenetically distant turtles). The amelogenin gene has been detected in all species except those lacking teeth. This result indicates that the unique role of amelogenin in amniotes is to contribute to enamel formation.