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

为了鉴定哺乳动物的釉原蛋白基因，本研究利用16种哺乳动物和3种爬行动物的基因组DNA和cDNA进行了PCR和RT-PCR，并着重研究了釉原蛋白基因与牙齿表达和牙釉质结构变化的关系。选择本研究所用的标本，重点是在非哺乳动物物种中表达独特的牙齿特征，即缺牙，缺乏牙釉质和独特的釉质棱柱表达的物种。结果表明，哺乳动物和爬行动物釉原蛋白基因第6外显子编码140个氨基酸，而海豚釉原蛋白基因第6外显子编码121个氨基酸。然而，在所使用的标本中，在食蚁兽（Bradypus）、儒艮（Dugong）和袋鼠（Macropus）中未获得PCR产物。由于后两个物种具有带牙釉质的牙齿，PCR产物的丢失被认为是引物与序列的不匹配 ...更多信息 牙釉原蛋白基因。另一方面，无齿食蚁兽的产物损失被推测是牙齿退化的结果。我们以前的研究证明了无牙须鲸的釉原蛋白基因的保守性，因此，食蚁兽的牙齿退化估计比须鲸的牙齿退化要早得多。本研究进一步证明了在树懒（Bradypus）的外显子6的中心部分的终止密码子的存在。据报道，树懒的牙齿没有牙釉质。因此，树懒第6外显子的突变可能导致牙釉质缺失。在唯一表达非哺乳动物物种中的釉质棱柱的虫媒蜥蜴Uromaslyx中，在外显子6的中心部分检测到24个氨基酸（主要是脯氨酸）的显著插入。这表明哺乳动物和爬行动物牙齿特征的表达与釉原蛋白基因突变之间存在着密切联系。少

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 … More 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. Less