In the developing tooth, epithelial-mesenchymal interactions initiate signals responsible for the expression of a hierarchical genetic program leading to morphogenesis, cell determination and the expression of gene products associated with control of biomineralization. Understanding the molecular nature of these reciprocal-, instructive-interactions between odontogenic epithelia and mesenchyme which control morphogenesis and terminal phenotype differentiation requires an enhanced molecular analysis of gene expression. Detailed molecular studies of gene expression during mammalian odontogenesis have been hampered by: 1) the absence of isolated cell model systems; 2) a lack of knowledge defining the odontogenic gene repertoire, and 3) ignorance for the temporal- and spatial-restricted pattern of gene expression. Advances to our knowledge now permit the formulation of an experimental strategy designed to analyze mechanisms for oral epithelia determination to the ameloblast phenotype as measured by amelogenin expression. Recent advances in cell and molecular biology now permit enhanced capacity to derive isolated odontogenic cell lineages for analysis of regulated amelogenin transcription, to identify DNAase hypersensitivity sites suggestive of putative regulatory protein-DNA interactions, to derive DNA sequence information for amelogenin and to compare such data to known transcription regulatory motifs and to identify molecular clones for AMEL-specific transcription factors. We will identify the minimal control element regulating amelogenin expression employing progressive deletions of putative regulatory elements by determining their effect on transcription using isolated odontogenic epithelia in transient expression assays. Finally, the DNA binding proteins will be isolated and characterized in order to identify corresponding cDNA clones. These studies will facilitate an understanding of epithelial-mesenchymal instructive signals required for de novo amelogenin expression in a tissue- , temporal- and spatial-restricted fashion during mouse odontogenesis.
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