Bone sialoprotein (BSP) is a phosphorylated glycoprotein, expressed specifically at sites of new bone formation. BSP, which contains an arginine-glycine-aspartic acid cell adhesion sequence, promotes attachment of a variety of cell types. Presently, the cell surface integrin, alpha/v/beta3, is the only cell surface receptor known to bind to BSP. Specificity of BSP to bone, and its expression at sites of new mineralization have stimulated interest in it, as a likely nucleator of mineralization. However, this has not been confirmed and the specific role for BSP in mineralized tissues remains to be determined. The hypotheses upon which this proposal is based are that; 1) follicle cells are responsible for secreting BSP onto the tooth root matrix; 2) BSP is critical for the formation of cementum on this matrix; and 3) that cell surface receptors, notably Alpha v Beta 3, is increasingly expressed by cells in the local environment, concomitant with increased secretion of BSP onto the root surface. Our studies to date demonstrate that BSP mRNA is expressed in follicle cells during cementogenesis, and BSP is localized to the root surface, consistent with the spatial and temporal initiation of cementum formation. We predict that BSP secretion onto the root surface by follicle cells is necessary for cementum formation. Moreover, the expression of specific surface receptors on cell during development is required for controlling the migration and attachment of cells onto the root surface matrix. Specifically, the studies detailed in this proposal are directed at establishing that BSP and follicle cells are responsible for inducing cementum formation and that adhesion receptors are essential in this process. The major objectives of these studies are to 1) establish the time during tooth development at which follicle cells express characteristics of cementoblast-osteoblast-like properties, in situ, including BSP mRNA, 2) prove that BSP, synthesized by follicle cells, is essential for mineralization of cementum; and 3) determine the spatial and temporal expression of alpha/v/Beta3 during cementum formation and correlate its expression with that of BSP. These studies will fill major gaps in our understanding of factors/mechanisms and cell controlling cementogenesis. Furthermore, they will clarify the role of BSP in the mineralization process. This information is critical for the development of therapies that can predictably regenerate periodontal tissues, as well as other mineralized tissues.
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