The dentition is a segmented organ whose evolutionary history and morphology strongly resemble other segmental systems like the vertebral column or limb. However, teeth use different genes, and perhaps different mechanisms, to attain that end. This is an effort, with four related components, of gene identification, expression, function and characterization for the homeobox developmental genes. In Specific Aim 1, classes of developmental genes from mouse tooth germ cDNA will be isolated and screened to identify regulatory genes, especially members of the homeobox gene family and related genes, that are expressed specifically in teeth or only in incisors or molars. This family is known to be involved in dental development. Mid-gestation incisor and molar cDNA libraries will also be made. In Specific Aim 2 expression maps of Dlx-5, a distal-less class homeobox gene identified in developing mouse teeth, and closely related developmental genes expressed in teeth, will be characterized by in situ hybridization of antisense probes to developing tooth germs across gestation, looking for timed expression patterns of these genes within and between teeth. Specific Aim 3 proposes to explore the function of Dlx-5 relative to its expression map. Dlx-5 expression will be inactivated by exposing embryonic teeth cultured in vitro to antisense RNA to the gene. Specific Aim 4 proposes to clone and sequence Dlx-5 to identify its structure and chromosomal map location. If expression and function studies confirm its importance in tooth development, the intergenic and regulatory regions of Dlx- 5 will be sequenced, and closely linked genes identified. The systematic approach to dental morphogenetics outlined in this application is important because combinatorial gene expression is probably the key to this process.