Chapter 8 Role of Epidermal Growth Factor in Embryonic Development

This chapter focuses on the question whether keratinization process is adult or embryonic. The embryonic development of the secondary palate (roof of the mouth) provides an excellent model system to understand the cellular and molecular biology of the keratinization process. There are three cell types that initially constitute the palatal epithelium, and it is the oral cell type that is of greatest interest in the chapter. The oral epithelial cells are somehow programmed differently during embryogenesis from the nasal and medial palatal epithelial cells and they become the squamous keratinizing cells that line the roof of the mouth. Without this essential programming during development, the palate will not form normally and a cleft palate is formed as a result. The developing secondary palate constitutes an ideal morphogenetic system because its development occurs towards the end of embryogenesis in the rodent, and the palate is easily accessible and large enough for a number of experimental manipulations including cell and organ culture. The growth and differentiation of the oral epithelium are especially dependent upon epidermal growth factor (EGF); hence, most of the chapter focuses on the details of the studies that have convinced that EGF or a related growth factor found in the embryo (transforming growth factor-α) is a very important regulatory molecule in the palate.