Role of sulfated glycoconjugates ectodermally derived hard tissue formation

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U1trastructural distribution and histochemical properties of sulfated glycoconjugates in ameloblasts and enamel matrices of rat and newt were investigated by use of the high iron diamine thiocarbohydrazide silver proteinate (HID-TCH-SP), enzymatic digestion methods, and 35S-autoradiography. The HID-TCH-SP staining was detected on the interdigitating cell membrane of Tomes' process, inside most secretory granules, and on the surface layer of rat prism enamel matrix. The staining resisted enzymatic digestion not only by testicular hyaluronidase but also by heparitinase. In the developing newt prismless enamel, after deposition of the mantle dentin matrix to a certain thickness, the first enamel matrix, globular in shape, appeared in juxtaposition to the dental basement membrane and tended to be intermixed with the previously deposited dentin matrix. Subsequently, enamel matrix was deposited outside (ameloblasticside) of the dental basement membrane and formed a true enamel matrix. The staining was found in the mixed matrix and was identified as chondroitin sulfate; in contrast, the true enamel matrix contained no sulfated glycoconjugates. Although newt dentin and bone matrices incorporated a very high concentration of 35S, no radioactive reaction was observed in enamel matrix. On the surface layer of developing mammalian enamel where large amounts of sulfated glycoconjugates were detected, immunolabelling of enamel protein was significantly weak. The data available suggest that certain sulfated substances, probably sulfated glycoproteins but not glycosaminoglycans, are required in the process of prismatic enamel formation; hence they represent phylogenetically advanced elements.