Histochemical and immunohistochemical examination of odontoblasts (petroblasts) in petrodentine formation of lungfish.

Petrodentine, the core of the lungfish tooth plate, is a well-mineralized tissue similar to mammalian enamel and analogous to enameloid in fish teeth. Petrodentine is formed solely by petroblasts, which are specialized odontoblasts, whereas enameloid is a composite tissue produced by both odontoblasts and dental epithelial cells. To clarify the details of petrodentine formation, petroblasts were investigated using histochemical and immunohistochemical techniques. Extant lungfish (Lepidosiren paradoxa) were used in this study. Tooth plates during the stage of petrodentine formation were observed by means of histochemistry and immunohistochemistry. Commercial kits were used to detect enzyme activity. Correlative sections were immunostained using antibodies against selected peptides. Routine staining such as periodic acid-Schiff (PAS) reaction to identify glycogen and Elastica van Gieson staining for the detection of elastic fibers in histological sections were performed. In addition, conventional transmission electron microscopy was used for observing the fine structure. Petroblasts showed marked acid and alkaline phosphatase activities, and positive immunoreactivities against anti-nestin, anti-V-ATPase, and anti-Ca The results in this study suggested that petroblasts have two functional stages, matrix formation and maturation, and glycogen plays an important role in the modulation of petroblasts.