Immunochemical and immunohistochemical studies, using antisera against porcine 25 kDa amelogenin, 89 kDa enamelin and the 13?17 kDa nonamelogenins, on immature enamel of the pig and rat

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Abstract
Summary Enamel proteins were extracted from the newly formed layer of immature porcine enamel, and the 25 kDa amelogenin, 89 kDa enamelin and 13–17 kDa nonamelogenins were purified. Specific antisera were raised against these proteins. Antibodies specific to the C-terminal region (residues 149–173) of the 25 kDa amelogenin were generated by absorption of the anti-25 kDa amelogenin serum with 20 kDa amelogenin, which contains residues 1–148 of the antigen. Immunoelectrotransfer blotting of the extracted porcine enamel proteins showed that the anti-25 kDa amelogenin serum recognized the 25 kDa and other low and high molecular weight amelogenins. The C-terminal specific anti-25 kDa amelogenin serum reacted only with amelogenins having molecular weights over 23 kDa. The anti-89 kDa enamelin serum recognized the 89 kDa enamelin and lower molecular weight proteins, but neither the amelogenins nor the 13–17 kDa nonamelogenins. The antiserum against the 13–17 kDa nonamelogenins showed no cross reactivity to the 89 kDa enamelin, but recognized higher molecular weight nonamelogenins. In immunohistochemical preparations of the porcine tooth germs, the 25 kDa amelogenin-like immunoreactivity over immature enamel decreased in a gradient from the enamel surface to the middle layer. In the inner layer immunoreactivity was concentrated over the prism sheaths. The C-terminal specific 25 kDa amelogenin-like immunoreactivity was intense at the outer layer of immature enamel and decreased sharply toward the middle layer. Prism sheaths were intensely stained by the antiserum to the 13–17 kDa nonamelogenins. The 89 kDa enamelin-like immunoreactivity over enamel prisms was intense at the outer layer and decreased toward the middle layer. Staining by the anti-89 kDa enamelin serum of prism sheaths was faint. In immature rat incisor enamel, the C-terminal specific 25 kDa amelogenin antiserum demonstrated a staining pattern similar to that in the immature enamel of the pig. Distinct 13–17 kDa nonamelogenin-like and 89 kDa enamelin-like immunoreactivities were found especially in the layer adjacent to the Tomes' process. We conclude that some enamel proteins are degraded soon after their secretion from the secretory ameloblast in the rat and the pig. The specific enamel proteins which reacted with the antiserum to the 13–17 kDa nonamelogenins seem to be involved with the formation of prism sheaths in immature porcine enamel, but not in rat incisor enamel.