FGF alters epithelial competence for EGF at the initiation of branching morphogenesis of mouse submandibular gland

Abstract

Embryonic day 13 mouse submandibular gland (E13-SMG) rudiments with two to four clefts have been commonly used in culture experiments to show that growth factors, such as epidermal growth factor (EGF) -family and fibroblast growth factor (FGF) -family ligands, are involved in branching morphogenesis. In the present study, we focused on E12 rudiments and attempted to elucidate the roles of EGF- and FGF-family ligands in SMG development from E12 to E13. In mesenchyme-free, Matrigel-embedded cultures, EGF + lysophosphatidic acid (LPA) induced branching in E13 epithelium, whereas E12 epithelium remained spherical and no branching occurred under the same culture conditions; however, both E12 and E13 epithelia elongated in response to FGF10. Reverse transcriptase- polymerase chain reaction studies showed that the expression of ErbB1 among four EGF receptors and Lpa3 among three LPA receptors was lower in E12 than in E13 epithelia. Fgf10, Fgf7, and their major receptor Fgfr2b were highly and equally expressed in E12 and E13 rudiments. After 24 hr of mesenchyme-free culture with FGF10 or FGF7, E12 epithelium was primed to initiate branching morphogenesis in response to EGF + LPA coincident with ErbB1 and Lpa3 up-regulation. These results suggest that the EGF-family ligand-receptor system is undeveloped at E12 and that it becomes primed on E13 by the FGF ligand-receptor system to play an important role in the induction of branching morphogenesis. © 2008 Wiley-Liss, Inc.