The purpose of this research project is to understand at the morphological, cellular, and biochemical levels various aspects of normal and abnormal embryonic development, especially relating to craniofacial development. Retinoids are craniofacial teratogens in the human and our results using mouse whole embryo culture demonstrate that they exert a direct effect on the embryo. Cell culture studies with neural crest cells indicate that this may be the target cell type for retinoid-induced craniofacial anomalies. Growth and differentiation of secondary palatal epithelial cells in culture are dependent upon epidermal growth factor (EGF) and a fibronectin-rich extracellular matrix (ECM) substrate. Cyclic AMP greatly enhances the EGF effect and transforming growth factor-Alpha (TGF) Alpha, but not TGF Beta, substitutes for EGF with the palatal epithelial cells in culture. These observations reinforce our hypothesis that TGF Alpha is an important embryo-derived growth factor during development. EGF and TGF Alpha enhance the synthesis of important ECM components in the palate including hyaluronic acid, Type V collagen, fibronectin, and laminin. The dioxin TCDD is a potent cleft palate inducer and our results indicate that this is due to a receptor-dependent inhibition of palatal epithelial cell differentiation. Glucocorticoids exert receptor-dependent alterations in phosphatidylinositol (PI) metabolism in cultured palatal mesenchymal cells by increasing the degradation of pre-existing PI. Chemically-induced growth inhibition of an established line of human embryonic palatal mesenchymal cells, along with a liver-derived metabolic activating system, has been developed as a short-term screening assay for potential human teratogens.
