Expression of amelogenins in developing embryonic and neonatal rat teeth.

OBJECTIVE: Tooth enamel is formed by ameloblasts, which are derived from epitheliums and secrete an extracellular matrix containing a complex arrangement of protein components. The epithelial component, referred to as the enamel organ, contains a layer of cells that secrete an organic matrix that biomineralizes to become tooth enamel. Adjacent ectomesenchyme cells differentiate to become dentinproducing odontoblasts. These two mineralized matrices form the crown of the vertebrate tooth. Therefore, amelogenins play a critical role in tooth enamel formation. We have examined the expression patterns and tissue distribution of amelogenins in their developmental stages in order to build a foundation for further study. METHODS: Amelogenin expression patterns and tissue distribution in developing teeth of embryonic (E17E19) and neonatal (1 to 9 days old) Wistar rats were examined by immunohistochemistry. RESULTS: Positive immunostaining for amelogenin was first observed in the late embryonic stage, E18. The highest level of amelogenin was noted in neonatal secretary ameloblasts, fully engaged in enamel matrix deposition (3 to 5 days old). After that, amelogenin expression continued at a lower level (6, 7, 8 days old). There was no amelogenin staining observed in the maturation stage of development (9 days old). CONCLUSIONS: Amelogenin expression occurs as early as the polarization stage of pre-ameloblasts. Amelogenin was also expressed, but at a low level, in post-secretary stages of amelogenesis. Odontoblasts did not contain detectable amelogenin.