The distribution of hydrolytic enzymes and lipids in the enamel epithelium of man and the macaque monkey

Abstract

The intracellular localization of acid phosphatase, non-specific esterase and lipids has been investigated in fresh cold microtome sections of human and monkey enamel epithelium. Acid phosphatase and non-specific esterase activity showed a similar pattern of localization in the enamel epithelium prior to amelogenesis and occurred as small droplets distributed mainly around the nucleus and at the cell periphery. The apparently coincident sites of enzyme activity stained positively with techniques for lipid. These findings were interpreted as demonstrating the existence of lysosomes or lysosome-like particles in enamel epithelium. Changes in this pattern of lysosome distribution occurred in the enamel epithelium at the completion of amelogenesis and were associated with the onset of cell degeneration. At the completion of amelogenesis, over the occlusal surface of the tooth, the ameloblast layer contained larger and irregularly distributed lysosomes, whilst the cells of the outer layer retained a fine regular droplet pattern of lysosome distribution. Over the nonocclusal surface of the tooth the change in lysosome pattern which occurred in the ameloblast layer also occurred in the cells of the outer layer and, following these changes, oral epithelium cells were found on the connective tissue surface of the enamel epithelium. Distinction between the oral epithelium and enamel epithelium was possible by virtue of the fact that only the cells of the outer layer of enamel epithelium contained alkaline phosphatase activity. The significance of these changes in lysosome pattern and their relationship to enamel epithelium function is discussed.