Formation of In Vitro Murine Cleft Palate by Abrogation of Fibroblast Growth Factor Signaling

Abstract

A strong association between fibroblast growth factors (FGFs) and palatal anatomy suggest their role in proper palatal development. The purpose of this study was to establish whether fibroblast growth factor signaling is essential for normal palate development, improve the understanding of the biology of palatal fusion, and create a new in vitro cleft palate model. Palatal pairs excised from embryonic day 13.5 mouse palatal shelves were divided into three equal groups (n = 18 pairs) and cultured with the nasal side down and their medial edge epithelia in close apposition. Controls received vehicle only (n = 6 pairs) or LacZ recombinant virus (n = 6 pairs). The experimental group (n = 6 pairs) received truncated FGF-R1 recombinant virus with hemagglutinin epitope tag (1 x 10(9) plaque-forming units), which abrogated signal transduction by FGF-R1, FGF-R2, and FGF-R3. Tissue sectioning and staining was used to assess palatal continuity at 96 hours and immunohistochemistry was used to localize expression of the truncated receptors. Both groups 1 (control, vehicle only) and 2 (LacZ) showed complete fusion of palatal shelves after 96 hours in five of six specimens and near fusion in the remaining specimen. Beta-galactosidase staining indicated effective delivery of the LacZ virus to targeted epithelial cells. None of the group 3 specimens (FGF-R1) showed histologic resolution of the medial edge epithelia seam. Immunohistochemistry for the hemagglutinin epitope tag indicated infection by the truncated FGF-R1 virus throughout the epithelium and mesenchyme of the epithelium. By abrogating signal transduction by FGF-R1, FGF-R2, and FGF-R3, the authors have demonstrated that such signaling is essential for normal mammalian palate development.