In bone and dentin biomineralization, the nature of the hydroxyapatite crystals deposited are under the precise control of the collagen template as well as the noncollagenous acidic proteins. These acidic proteins have been postulated to play a critical role in de novo mineral nucleation, regulating hydroxyapatite crystal size as well as its morphology. Acidic matrix proteins are incorporated into the crystal lattice of hydroxyapatite in a well ordered manner, thus making dentin a composite with high tensile strength. The collagen matrix provides the space and milieu in which the mineral crystals are initiated. Therefore, dentinogenesis is a dynamic process that involves a cascade of cellular and extracellular events. Specific interactive events like cell-cell, cell-matrix and matrix-matrix are responsible for odontoblast differentiation and the assembly of the mineralized dentin matrix. Problems in the mineralization process are evident in a number of dental pathologies. Successful dentin regeneration and repair in dentistry relies on the ability to recruit odontoblast precursors to the site followed by maturation process of these cells, matrix deposition and ultimately mineralization of the organic matrix. Dentin matrix protein 1 (DMP1) is an extracellular matrix protein that was first cloned by us from the mineralized dentin matrix. DMP1 is typically polyanionic having a high content of aspartic, glutamic and phosphoserine residues making it a protein highly suitable for calcium binding. Very little is known about the mechanism responsible for initiation and regulation of this mineralized matrix. The objective of this proposed investigation is to move forward from the identification and localization of the DMP1 to the study of the regulation of the expression of the protein, and to its potential involvement in the mineralization process. We now propose the following specific aims: (1) To characterize the DMP1 promoter and to identify specific sites within the 3 kb upstream sequence that are involved in cell and tissue specific expression; (2) To identify the mechanisms involved during the differentiation of embryonic mesenchymal cells to odontoblast-like cells by constitutive overexpression of DMP1; (3) To demonstrate the role of DMP1 as a potential nucleator for hydroxyapatite formation; (4) To study the distribution of DMP1 protein in the dentin matrix and thus determine the functional role of DMP1 during the process of mineralization. Understanding the mineralization process is important to the biomedical and dentistry fields because the disruption of normal biomineralization can lead to pathological mineralization or demineralization process. The long-term goal is to understand the regulatory mechanism of DMP1 in dentin mineralization.
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