Correlation between molecular evolution of amelogenin gene and the phenotype of tooth enamel

2003 Fiscal Year Final Research Report Summary

• Project/Area Number: 14571755
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Morphological basic dentistry
• Research Institution: The Nippon Dental University
• Principal Investigator: ISHIYAMA Mikio The Nippon Dental University, School of Dentistry at Niigata, Department of Histology, Associate Professor, 新潟歯学部, 助教授 (70120607)
• Project Period (FY): 2002 – 2003
• Keywords: Gene / Amelogenin / Mammals / Molecular evolution Tooth enamel / Phenotype / PCR / PCR

Research Abstract

In order to identify and characterize the amelogenin gene in mammals, PCR and RT-PCR were performed by using the genomic DNA (16 species) and cDNA (3 species) in several mammals and some reptiles, with special reference to the correlation with the expression of teeth and the variations of the tooth enamel structure. The specimens used present study were selected to focus on the species which express the unique dental characteristics i.e. edenturous, lacking a tooth enamel and the unique expression of an enamel prisms in non-mammalian species. It is consequently revealed that the exon 6 of amelogenin gene in mammals and reptiles encode 140 amino acids, but only 121 amino acids in porpoise. In the specimens used, however, the PCR products were not obtained in the anteater (Bradypus), jugong (Dugong) and kangaroo (Macropus). As the latter two species possess the teeth with a tooth enamel, the loss of the PCR products were considered to be the less fitting of the primers with the sequences of the amelogenin genes. On the other hand, the loss of the products in the edenturous anteater was speculated to be the result of the degeneration of the teeth. Our previous study demonstrated the conservation of the amelogenin gene in edenturous baleen whales, therefore, the degeneration of the teeth in the anteater are estimated to be rather earlier phylogenetically than the degeneration in baleen whales. The present study further demonstrates the presence of the stop codon in the central portion of the exon 6 in the sloth (Bradypus). It is reported that the teeth of the sloth do not have the tooth enamel. The mutation of the exon 6 in the sloth, therefore, might cause the lacking of the tooth enamel. In the agamid lizard Uromaslyx, which uniquely expressess a enamel prism among non-mammalian species, marked insertion of the 24 amino acids (mainly proline) was detected at the central portion of the exon 6. It is, thus, demonstrated that the correlaton between the expression of the unique dental characteristics and the mutations of the amelogenin genes in mammals and reptiles.