Immunohistochemical study on the expression and localization of the epidermal growth factor receptor during morphogenesis

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1. Immunohistochemical studies using the anti-human EGF receptor(EGF-R)rabbit antibody revealed that fetal mouse palates show regional heterogeneity and temporal sequence in EGF-R expression during development. On days 12 and 13, the immunoreactive products were predominantly positive on the oral and medial edge epithelia but minimally on the epithelium of the vertical shelf. The EGF-R immunoreactivity was less intense in the posterior palate as compared with the midpalatal region. The palatal mesenchyme also showed regional heterogeneity and temporal sequence in EGF-R expression.2. Explanted palates of day-12 mouse fetuses were cultured in a chemically-defined medium and the effects of all-trans-retinoic acid(RA)were examined. RA was added to the culture medium at the concentrations 3-300 ng/ml. RA inhibited palatal fusion dependently on its concentration, although palatal shelves of -normal size tonned and made contact at 3-30 ng/ml. Scanning electron microscopic studies showed that … More the medial cells of RA-treated palates failed to undergo programmed cell death which occurs in control palates. The oral epithelium of control palates lost microvilli and became squamous after palatal fusion, but RA-exposed cells remained ciliated and simulated nasal-hke epithelial cells.During in vitro palatogenesis, both palatal epithelium and mesenchyme showed regional heterogeneity and temporal sequence in EGF-R expression. During normal palatal development, the EGF-R immunoreactivity became less intense in the medial epithelia. However, in retinoic acid-treated palates, the medial epithelia were continuously positive for EGF-R immunoreactivity. In retinoic acid-treated palates, medial cells were continuously covered with microvilli which disappeared in untreated palates. The alteration in EGF-R expression and epithelial cell differentiation may be responsible for the altered differentiation of palatal shelves and retinoic acid-induced cleft palate.3. The localization of EGF-R in normal human embryos(Carnegie stages 15, 16, and 20)was examined immunohistochemically. Embryonic tissues were fixed in 4% paraformaldehyde, embedded in paraffin, and serialy sectioned. The sections were stained by avidin-biodn-peroxidase complex method(Vectastain elite ABC kit)with polyclonal anti-human EGF-R antibody. The immunoreactive products against EGF-R were positive in the periderm, the epithelium of the digestive and respiratory tracts, the notochord, the epithelium of the Ratlike's pouch, the fetal cortex of the adrenal gland, germ cells in the gonad, the myocardium and cartilaginous tissue. In the myocardium, the immunoreactivity was intense at Carnegie stages 15 and 16, but became weaker by stage 20. The regional heterogeneity of EGF-R expression was observed in the Ratlike's pouch. Less