Immunocytochemical and immunochemical study of amelogenesis

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Amelogenesis of the porcine tooth germ was investigated by means of biochemical, immunochemical, immunocytochemical and cell biological methods. The results are summarized as follows.1.The cDNAs encoding porcine sheath proteins, which are low molecular weight proteins concentrated in the prism sheath in immature enamel, were cloned and characterized. The translation products of these clones might be secreted proteins having 395 and 380 residues. We proposed the term "sheathlin" for the translation products and their proteolytic cleavage products. Full length sheathlin and rat ameloblastin shear 67% identity in their amino acid sequences.2.The N terminal cleaved peptides of sheathlin had about 100 to 150 amino acid residues and were specifically localized in the prism sheath. The C-terminal cleaved peptides were identified as calcium binding proteins having molecular weights of 29kDa and 27 kDa, both of which might be phosphorylated and glycosylated and were localized outer most layr of immature enamel.3.The cDNA encoding enamelin was cloned. The porcine enamelin composed 1104 amino acid residues. Secreted enamelin having molecular weight of about 150 kDa were localized in immature enamel just adjacent to the plasma membrane of the ameloblast, and showed no affinity for apatite crystals. The N-terminal cleaved protein of the 150 kDa enamelin was 89 kDa enamelin which showed affinity for apatite crystals. The amino acid sequence of the 32kDa enamelin was located in the middle portion of the 89 kDa enamelin.4.In conclusion, three categories of enamel proteins play different roles in the amelogenesis. Amelogenin primarily form the shape of enamel, enamelin control the initial calcification and the growth of the apatite crystals, and the sheathlin produce prism sheaths which might act as a way through which enamel protein escape during enamel calcification.