Cementum, a mineralized tissue localized on tooth root surfaces, is considered critical for development and regeneration of a functional periodontal apparatus. Studies to date have been limited to examining the properties of cementum in situ. Advanced technologies now enable us to ask critical questions as to the cellular and molecular mechanisms regulating cementoblast activity which will ultimately result in improved strategies for regeneration of periodontal tissues. Based on studies to date using a murine tooth root model system we hypothesize that 1) cells lining the root surface, cementoblasts, secrete a matrix for cementum formation; 2) bone sialoprotein (BSP) secreted by these root surface cells, is a critical protein, required for cementum formation 3) expression of BSP by cementoblasts is regulated by specific promoter sequences which bind cementum-specific transcription activators; and 4) cementoblasts exhibit a protein profile different from that of cells associated with bone, dentin, and/or enamel. These hypotheses are supported by results to date which include the finding that timed and spatial expression of BSP, a protein implicated in mineral formation, by root surface cells coincides with the initiation of cementogenesis. These hypotheses will be tested under three specific aims. 1) To prove that cementoblasts induce mineral matrix formation, in vitro and regeneration of cementum, in vivo and furthermore, that expression of BSP is required for biomineralization to occur; 2) To delineate BSP promoter sequences and related transcription factors controlling cementum-specific expression of BSP; and 3) To determine the molecular profile of cementoblasts. The information obtained from these studies will fill major gaps in our knowledge as to cellular and molecular mechanisms regulating development of the periodontium. This foundation is required for understanding various pathologies, e.g., hypophosphatasia, cementomas, and Paget's associated hypercementosis, and for designing effective clinical procedures for regeneration of periodontal tissues, as well as other mineralized tissues.
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