Volume 54 (1991) Issue 5 Pages 527-538
Porcine tooth germ was investigated immunochemically and immunocytochemically using antibodies against a synthetic N-terminal peptide fragment from a 32kDa nonamelogenin found in the inner (old) secretory enamel. In immunochemical preparations, these antibodies reacted to many proteins of differing molecular weights, especially to 140kDa, 89kDa, 56kDa, 45kDa, and 32kDa proteins. Analysis of the layers of enamel suggested that the 140kDa and/or 89kDa proteins, both of which were found in newly formed enamel, were the parental proteins secreted by the ameloblasts, and that they were degraded to produce 32kDa and other low molecular-weight proteins associated with progressive mineralization. In immunohistochemical preparation, immunoreactivity at the differentiation stage was detected initially over the amorphous dense material or fine fibrils around calcified globules in predentin, while the stippled material was devoid of immunoreactivity. The amorphous dense material seemed to give rise to a continuous layer of initial enamel. At the matrix formation stage, the immunoreactivity of immature enamel just beneath the putative secretory face of the Tomes' processes was intense. From the surface of the enamel matrix to a depth of about 100μm, immunoreactivity of prism sheaths was weaker than that of enamel prisms, producing a reverse honeycomb pattern. In the enamel matrix deeper than 100μm, immunoreactivity was weak and homogeneously distributed. The Golgi apparatus and secretory granules of the secretory ameloblasts showed immunoreactivity. These results suggest that the likely parent proteins of the 32kDa nonamelogenin protein, i. e., the 140kDa and/or 89kDa proteins, play a significant role in the calcification of the enamel matrix.