THE EFFECTS OF RETINOIC ACID ON THE EPIDERMAL GROWTH-FACTOR RECEPTOR GENE-EXPRESSION IN THE DEVELOPING CHICK WING BUD

The epidermal growth factor receptor (EGFR), a c-erbB protooncogene pr oduct, is known to control cell growth and cell differentiation. EGFR gene expression is also known to be regulated by retinoic acid (RA). I n the present study, the temporal and spatial patterns of EGFR gene ex pression in normal and RA-treated chick wing buds have been examined b y in situ hybridization. In normal wing bud, a strong signal of EGFR g ene expression was noted at the anterior and distal areas of epidermal . and subepidermal tissues during Hamburger-Hamilton stages 18-26, whi le the signal was weak in the posterior area. In the RA-treated wing b ud, 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 i mplying that EGFR gene expression was suppressed by RA treatment in th e developing Chick wing bud. In the subepidermal area, EGFR gene was c ontinuously expressed until stage 30. These results suggest that EGFR might be involved in the tissue interactions for the patterning of dev eloping chick wing bud.