The distribution of epidermal growth factor binding sites in the developing mouse palate

The distribution of epidermal growth factor (EGF) receptors in the developing mouse palate was mapped using 125I-EGF labeling of paired palate organ cultures. 125I-EGF binding sites were localized throughout the palate mesenchyme except in a region immediately adjacent to the midline seam. The EGF receptor was detected in all palatal epithelia at the beginning of culture, but as seam formation and subsequent degeneration took place it was down-regulated in the medial edge epithelia. Using submerged culture the mechanism of this down-regulation was investigated by treating with various growth factors such as EGF, basic fibroblast growth factor (bFGF), insulin-like growth factor-II (IGF-II) and transforming growth factors alpha and beta (TGF-alpha, TGF-beta). Conventional Trowell organ culture was not used because it was observed that the Millipore filter blocked growth factor uptake. All three TGF-beta isoforms accelerated palate fusion and TGF-beta 1 reduced 125I-EGF binding throughout the palate, suggesting a potential level of regulation during palatogenesis. Contrary to previous reports, EGF treatment in the absence of serum prevented palatal shelf fusion, and also down-regulated subsequent 125I-EGF binding.