Expression of Epidermal Growth Factor Receptor in Fetal Mouse Submandibular Gland Detected by a Biotinyltyramide-based Catalyzed Signal Amplification Method

Branching morphogenesis of the fetal mouse submandibular gland (SMG) can be modulated in vitro by stimulation or inhibition of the epidermal growth factor receptor (EGFR). Because the mRNAs for EGF and EGFR are detectable in RNA of SMG rudiments isolated directly from fetuses, the EGF system probably operates physiologically as a regulator of SMG morphogenesis. However, neither EGFR protein nor its precise cellular localization has been characterized in the fetal SMG. Here we show EGFR protein in fetal mouse SMG by immunoprecipitation, affinity labeling, ligandinduced autophosphorylation, and immunohistochemistry. SMGs from E16 fetuses (day of vaginal plug = EO) were labeled with [35S]-cysteine/methionine and homogenized. After addition of specific antibody to EGFR, the immunoprecipitate was isolated, resolved by polyacrylamide gel electrophoresis, and detected by autoradiography. A single band of 170 kD was detected, corresponding to the EGFR protein. Affinity labeling with [125I]-EGF of the membrane fra...