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The epidermal growth factor receptor (EGFR), a c-erbB protooncogene product, is known to control cell growth and cell differentiation. EGFR gene expression is also known to be regulated by retinoic acid (RA). In the present study, the temporal and spatial patterns of EGFR gene expression in normal and RA-treated chick wing buds have been examined by in situ hybridization. In normal wing bud, a strong signal of EGFR gene expression was noted at the anterior and distal areas of epidermal and subepidermal tissues during Hamburger- Hamilton stages 18-26, while the signal was weak in the posterior area. In the RA-treated wing bud, at 1 and 2 days after treatment (stages 24 and 26, respectively), the area of EGFR gene expression expanded to the more posterior region, while the expression of EGFR was suppressed in the RA-applied area implying that EGFR gene expression was suppressed by RA treatment in the developing chick wing bud. In the subepidermal area, EGFR gene was continuously expressed until stage 30. These results suggest that EGFR might be involved in the tissue interactions for the patterning of developing chick wing bud.
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