Amelogenin protein in tooth germs of the snake Elaphe quadrivirgata, immunohistochemistry, cloning and cDNA sequence

In the snake, Elaphe quadrivirgata, the occurrence of amelogenin was immuno histochemically demonstrated in the enamel of developing tooth germs. Teeth of the snake are covered with a thin true enamel layer about 1-2 mu m in t hickness. Light and electron microscopic immunohistochemistry indicated an intense amelogenin immunoreactivity occurring in the enamel layer during th e secretory stage of tooth development. Cloning and cDNA sequence of snake amelogenin was performed by RT-PCR. The amino acid sequence of the snake am elogenin cDNA-in its portion corresponding to the area from exon 5 to exon 7 of human X189 amelogenin gene-showed 45% homology with humans. Regions of both the N-terminus and C-terminus were well conserved. Furthermore, the p ositions of prolin in the amino acid alignment of the snake amelogenin corr esponded well with those of human amelogenin. It is suggested that prolin i s an essential constituent of amelogenin and therefore its positions in the molecule have been conserved after the evolutionary divergence of reptiles and mammals. This study using reptiles is the first detection of specific amelogenin imm unoreactivity by high resolutional immunoelectron microscopy and the first cloning of amelogenin cDNA in a non-mammalian animal.