PROJECT SUMMARY 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. Noncollagenous acidic proteins have been postulated to play a regulatory role in de novo mineral nucleation, regulating hydroxyapatite crystal size as well as its morphology. Dentin matrix protein 1 (DMP1) is an extracellular matrix protein that was first cloned by us from an odontoblast cDNA library. DMP1 is typically anionic and has multiple calcium binding sites and is thought to promote mineralization by nucleating hydroxyapatite. An intriguing finding that we have reported is that DMP1 can perform multiple functions. Non-phosphorylated DMP1 was found to translocate to the nucleus during early differentiation of odontoblasts and function in regulating the expression of biomineralization-specific genes. The central hypothesis of the proposed studies is that DMP1 plays an important and unique role during maturation of odontoblasts, leading to the formation of mineralized dentin. Therefore 3 specific aims are proposed to pursue the mechanisms responsible for DMP1 mediated odontoblast differentiation and mineralized matrix formation: (1) To study the cellular targets of DMP1 during odontoblast differentiation; (2) To elucidate the molecular mechanisms of DMP1 gene regulation during odontoblast differentiation; (3) To determine if DMP1 can induce odontoblast lineage in stem cells. Understanding the mineralization process is important to the biomedical and dentistry fields as disruption of normal biomineralization can lead to pathological calcification or demineralization process. The long-term goal is to understand the regulatory mechanism by which DMP1 plays a unique role in dentin mineralization.