Molecular strategies of tooth enamel formation are highly conserved during vertebrate evolution

The vertebrate body plan is determined by a variety of morphoregulatory genes that are highly conserved throughout evolution. This review presents a phylogenetic analysis of selected molecular and morphological features in vertebrates with particular emphasis upon the phylogeny of tooth morphogenesis and enamel formation. Three lines of evidence support our hypothesis that the agnathans (e.g. hagfishes) are the most primitive extant vertebrates and that enamel gene products are highly conserved during vertebrate evolution. First, an antibody raised against the polypeptide produced by exon 4 of the mouse amelogenin gene recognizes proteins in hagfish, sharks, reptiles and mammals. Second, electron photomicrographic evidence suggests heterochronic shifts in the relative time and rate of enamel formation during vertebrate tooth evolution. Third, mRNA phenotyping suggests significant homology between amelogenin transcripts expressed in species of various vertebrate phyla including agnathans and mammals. These three lines of evidence indicate that amelogenin gene products are expressed in agnathan, reptilian and mammalian teeth.