The effects of epidermal growth factor, transforming growth factors alpha and beta and platelet-derived growth factor on murine palatal shelves in organ culture.

Palatal shelves isolated from day-13 embryonic mice were explanted on to the surfaces of collagen gels either singly or in pairs with their medial edges in contact, and cultured submerged in a 1:1 mixture of Dulbecco's modified Eagle's medium/Ham's F12 medium. The medium was supplemented with either 10 ng/ml epidermal growth factor (EGF), 10 ng/ml transforming growth factor alpha (TGF alpha), 1 ng/ml transforming growth factor beta (TGF beta 1) or 2 ng/ml platelet-derived growth factor (PDGF) all in the presence or absence of 2.5% donor calf serum (DCS). Cultures were terminated after 0, 24, 48 or 72 h and processed for histological and immunocytochemical examination. In serum-free medium and medium supplemented with 2.5% DCS the palatal epithelia differentiated in a manner similar to that seen in vivo (oral, keratinization; nasal, pseudostratified, ciliated columnar cells and medial edge, epithelial degeneration). A similar pattern was obtained in serum-free medium supplemented with either EGF or TGF alpha. However in cultures with either EGF or TGF alpha plus 2.5% DCS present in the medium, medial-edge epithelial degeneration was inhibited and the oral epithelia were more heavily keratinized. The mesenchyme of such cultures stained more intensely for various extracellular matrix molecules. In TGF beta 1-supplemented cultures (with, but especially without, serum supplementation) the epithelia were thin, medial-edge epithelial degeneration was marked, and the fibronectin content of the mesenchyme was increased. PDGF prevented medial-edge epithelial degeneration in the presence, but not in the absence, of serum; mesenchymal extracellular molecules were not as prevalent as with the EGF treatment. These results indicate that exogenous growth factors (including those present in serum) exert effects on organ-cultured mouse palatal shelves in a fashion similar to their effects in cell culture and that controlled physiological levels of such factors may be important in mouse palatal development.