Normal development of the mammalian palate is contingent upon a series of events that include cellular migration, morphogenetic movements, differential cellular proliferation and cellular differentiation. Disturbance of any of these events can result in cleft palate. The long-term objective of this study is to delineate the mechanisms responsible for normal and abnormal craniofacial morphogenesis. The specific aim is to test the hypothesis that retinoids disrupt normal craniofacial morphogenesis by altering polyamine-dependent regulation of normal cellular responses. This study will: 1) determine whether localized changes in mesenchymal cell density vary with murine palatal epithelial morphogenesis, and whether these changes are accompanied by changes in ODCase activity, ODCase mRNA, endogenous retinoids and polyamine levels and 2) determine whether retinoids influence mesenchymal cell density and growth in developing murine palates through a mechanism which modulates ODCase activity and polyamine levels by altering the abundance and distribution of ODCase mRNA. Ornithine decarboxylase mRNA will be characterized in developing palates and retinoid-treated palates using in situ hybridization and Northern Blot analysis. Endogenous retinoids, ODCase activity and polyamines will be assayed using high performance liquid chromatography. The effects of exogenous retinoids on mesenchymal cell density and cell growth will be determined by quantitating mesenchymal cell distribution across the developing palates and by measuring DNA synthesis in these tissues. These experiments will determine the relationship of ornithine decarboxylase, polyamines, retinoids and mesenchymal cell density during palatogenesis.