Search

The sodium pump Na+/K+- ATPase, expressed in virtually all cells of higher organisms, is involved in establishing a resting membrane potential and in creating a sodium gradient to facilitate a number of membrane-associated transport activities. Na+/K+- ATPase is an oligomer of α, β, and γ subunits. Four unique genes encode each of the α and β subunits. In dental enamel cells, the spatiotemporal expression of Na+/K+- ATPase is poorly characterized. Using the rat incisor as a model, this study provides a comprehensive expression profile of all four α and all four β Na+/K+- ATPase subunits throughout all stages of amelogenesis. Real-time PCR, western blot analysis, and immunolocalization revealed that α1, β1, and β3 are expressed in the enamel organ and that all three are most highly expressed during late-maturation-stage amelogenesis. Expression of β3 was significantly higher than expression of β1, suggesting that the dominant Na+/K+- ATPase consists of an α1 β3 dimer. Localization of α1, β1, and β3 subunits in ameloblasts was primarily to the cytoplasm and occasionally along the basolateral membranes. Weaker expression was also noted in papillary layer cells during early maturation. Our data support that Na+/K+- ATPase is functional in maturation-stage ameloblasts. [ABSTRACT FROM AUTHOR]

Dentin sialophosphoprotein (DSPP) is a large precursor protein that is proteolyti-cally processed into a NH2-terminal fragment [composed of dentin sialoprolein (DSP) and a proteoglycan form (DSP-PG)] and a COOH-terminal fragment [dentin phosphoprotein (DPP)]. In vitro studies indicate that DPP is a strong initiator and regulator of hydroxyapatite crystal formation and growth, but the role(s) of the NH2-terminal fragment of DSPP (i.e. DSP and DSP-PG) in dentinogenesis remain unclear. This study focuses on the function of the NH2-terminal fragment of DSPP in dentinogenesis. Here, transgenic (Tg) mouse lines expressing the NHi-lerminal fragment of DSPP driven by a 3.6-kb type I collagen promoter (Col lal) were generated and cross-bred with Dspp null mice to obtain mice that express the transgene but.lack the endogenous Dspp (Dspp KO/DSP Tg). We found that dentin from the Dspp KO/DSP Tg mice was much thinner, more poorly mineralized, and remarkably disorganized compared with dentin from the Dspp KO mice. The fact that Dspp KO/DSP Tg mice exhibited more severe dentin defects than did the Dspp null mice indicates that the NHi-lerminal fragment of DSPP may inhibit dentin mineralization or may serve as an antagonist against the accelerating action of DPP and serve to prevent predentin from being mineralized too rapidly during dentinogenesis [ABSTRACT FROM AUTHOR]

The established structural proteins of the enamel matrix are amelogenin, ameloblastin, and enamelin. Historically, tuftelin and tuftelin-interacting protein 11 (TFIP11) have also been discussed as possible enamel proteins. Protein complexes are achieved by protein–protein interactions, and it is protein complexes that control biomineralization. The purpose of our recent studies was to catalog protein partners for these proteins that are, or have been, implicated in tooth formation. We used the sensitive yeast two-hybrid assay to identify proteins that interact directly with amelogenin, ameloblastin, enamelin, the leucine-rich amelogenin peptide (LRAP) and TFIP11. In this manuscript we refer to, or document, potential protein partners for the proteins listed above. The yeast two-hybrid assay may ultimately prove to be a valuable proteomics methodology for using to decipher molecular events that ultimately result in enamel biomineralization. [ABSTRACT FROM AUTHOR]