Effects of retinoic acid on receptors for epidermal growth factor in mouse palatal mesenchymal cells in vitro

Retinoic acid (RA), one of the inducers of cleft palate in vivo, specifically increased the ¹²⁵I-epidermal growth factor (EGF) binding capacity of embryonic palatal mesenchymal cells; the increase was completely inhibited by actinomycin D, suggesting that transcription is required for this change. When the increase in EGF receptors was related to the stimulation of DNA synthesis by EGF in the presence of various concentrations of RA, the maximum stimulation of [³H]-thymidine by EGF was at 10^-9 M RA, but the maximum increase in the number of EGF receptors was at 10^-6 M RA. Thus the increase in the number of EGF receptors cannot be related to EGF-stimulated DNA synthesis.