Type X collagen in human enamel development: a possible role in mineralization

Although type X collagen is one of the key molecules in endochondral ossifi cation, no data are available on whether it is present in dental structures when mineralization is proceeding. We therefore monitored the appearance o f type X collagen in tooth germs of human samples ranging in gestational ag e from 17-week-old fetuses to 9-week-old newborn. Using immunohistochemistr y, ELISA techniques, and Western blotting, we show that type X collagen is present in human tooth germ during enamel maturation. Intense immunohistoch emical staining for collagen type X was observed in the enamel and in the a pical parts of secretory ameloblast at the bell stage when the dentine and enamel matrix were already under formation. The odontoblasts, the dentine, and the pulp were not stained. In the early (9-week) postnatal stage, the s taining for collagen type X in the enamel matrix was diminished, and only a very weak signal could be detected in the secretory ameloblasts. A positiv e reaction for collagen type X was also observed in ELISA assay of extracts obtained from human embryonic enamel and hypertrophic cartilage samples. T he Western blot analysis of the enamel demonstrated that size of the molecu le detected by MoAb X53 is characteristic of the type X collagen. This corr elates well with our immunohistochemical findings. Based on these data, we propose that type X collagen is one of the candidate molecules present in t he enamel matrix that might be involved in mineralization of the enamel.