Immunohistochemical and molecular biological study of enamel proteins with special reference to molecular isoforms.

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Enamel proteins, such as amelogenins and sheath proteins, have several isoforms produced by alternative splicing of mRNAs. In order to clarify the role of molecular isoforms of sheath proteins, we have developed region specific antibodies that can recognize special molecular forms. Enamel organ and immature enamel matrix from the rat incisor and the porcine tooth germ were analyzed by means of immunochemistry and immunohistochemistry. The results are summarized as follows.1. Immunochemical analysis of the enamel organ from the matrix formation stage and the early maturation stage in the rat incisor showed that ameloblastin and amelin, two isoforms of rat sheath proteins, were synthesized as 56 kDa and 54 kDa core proteins, respectively. The amount of amelin and ameloblastin contained in the enamel organ was not so different at the matrix formation stage, while the former was significantly lower than the latter at the early maturation stage.2. Immunohistochemistry of rat incisor has showed that immunolocalization of ameloblastin and amelin was essentially identical. However, the degradation of amelin seemed to be faster than that of ameloblastin because of weak immunoreaction of amelin at the middle to deep layer of enamel matrix.3. Immunohistochemical analysis of porcine immature enamel has revealed that antibody that recognize short-form of sheathlin (porcine sheath protein) clearly stained prism sheath at the entire layer. However, after the immunostaining with antibody that recognize short-form of sheathlin, prism sheath at the surface layer was not so clear.4. At the late transition to early maturation stages, immunoreactivity of the short-form of sheathlin at the surface layer was significantly weaker than that of the long-form of sheathlin, suggesting the degradation of short-form of sheathlin occurs faster than the long-form of sheathlin.