Ultrastructural and Cytochemical Studies on the Matrix Vesicle Calcification in the Teeth of the Killifish, Oryzias latipes

Abstract

Tooth germs of killifish were examined by both ultrastructural and cytochemical methods. The ultrastructure of dentin in the early calcification stage of development resembled that of mammals. Numerous extracellular membrane-bounded vesicles, matrix vesicles, were seen in the predentinal space, especially abundantly in the basal portion of the tooth germ. They were more numerous and more uniform in appearance than in any other higher vertebrates. Where calcification was beginning, slightly identifiable needles of apatite crystals were found in the vesicular structures. Crystals increased, filling up the vesicles and then their surroundings, finally to form many calcified spherules. Where calcification was more extensive, the matrix vesicles were no longer visible having been buried calcified among spherules. There was no relationship between collagen fibrils and the initial deposits of minerals, i.e., collagen fibrils did not seem to work as the initial site of calcification. Matrix vesicles and plasma membranes of odontoblasts were likely involved in calcification as they both showed alkaline phosphatase activity. Calcification of killifish tooth germs apparently was not initiated in the enamel, but in the dentin by matrix vesicles liberated into the dentin matrix from odontoblasts by way of cell process fragmentation.