Temporal and spatial localization of the dentin matrix proteins during dentin biomineralization

Formation of bone and dentin are classical examples of matrix-mediated mineralization. The mineral phase is essentially the same in these two tissues and primarily consists of a carbonated hydroxyapatite, but the difference lies in the crystal size and shape. There are three components that are necessary for proper mineralization, namely the proper synthesis and secretion of the non-collagenous proteins (NCPs), self-assembly of the collagenous matrix, and delivery of calcium and phosphate ions to the extracellular matrix. Three major NCPs present in the dentin matrix are dentin matrix protein 1 (DMP1), dentin phosphophorin (DPP), and dentin sialoprotein (DSP). In this study, we show the temporal and spatial localization of these NCPs and correlate their expression with the presence of collagenous matrix and calcified deposits in developing mouse incisors and molars. DMP1, an acidic protein, is present predominantly at the mineralization front and in the nucleus of undifferentiated preodontoblast cells. DPP, the major NCP, is present in large amounts at the mineralization front and might function to regulate the size of the growing hydroxyapatite crystals. For the first time, we report the localization of DPP in the nucleus of preodontoblast cells, suggesting a signaling function during the odontoblast differentiation process. DSP is localized predominantly in the dentinal tubules at the site of peritubular dentin, which is highly mineralized in nature. Thus, the precise localization of DMP1, DPP, and DSP in the dentin tissue suggests that a concerted effort between several NCPs is necessary for dentin formation.