The long-term goal of this proposed work is to characterize protein-protein interactions involving the enamel extracellular matrix proteins, as well as proteins integral to the plasma membrane of ameloblast cells, and characterize how these interactions regulate enamel formation. To achieve this the molecular biochemistry of biglycan, Cd63, Anxa2 and Lampl, and their relationship to the major enamel matrix proteins, will be studied. The hypothesis of this grant application is "protein-protein interactions involving secreted enamel matrix proteins and the secretory surface of ameloblast cells (Tomes'processes) play a key role in the formation of the enamelprismatic structure." To test this hypothesis we propose three specific aims. These are to: 1) define, using in situ hybridization and mouse-specific antibodies, the spatiotemporal expression patterns for Cd63, Anxa2 and Lampl within the murine developing incisor tooth, and relate these expression profiles to those of their respective ligand (enamel matrix protein partner), and the stages of enamel biomineralization;2) demonstrate that the protein-protein interactions previously identified for the enamel matrix proteins and biglycan, Cd63, Anxa2 and Lampl occur in vivo and have physiological significance, and to define the minimal binding domains of Cd63 and Lampl that enable their interaction with amelogenin;3) define and disrupt the receptor-mediated molecular mechanism that permits the enamel matrix expression levels of biglycan to influence or control amelogenin expression levels, and the subsequent events of enamel biomineralization. Knowledge gained from this and related studies may lead to better dental and non-dental materials, or biomimetics. This data will be critical to others in their pursuits to regenerate an entire tooth. For tooth regeneration to become a reality, the protein- protein interactions involving the key dental proteins must be known and understood.