Detection of epidermal growth factor-urogastrone and its receptor during fetal mouse development

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Abstract
Using a radioimmunoassay and a radioreceptor assay, content of mouse epidermal growth factor-urogastrone (EGF-URO) was estimated in fetal mice at 11.5-17.5 days of gestation. Concurrently, the amount of specific EGF-URO receptor binding was determined in crude membrane fractions from the embryos. EGF-URO receptor binding is readily detected in membranes from the youngest embryos (day 11.5) and rises steadily up to parturition (18 days); the rise is more marked in embryo membranes derived from a potential target tissue, such as the maxilla and secondary palate. In the embryonic extracts, EGF-URO proved to be labile, requiring the presence of soybean trypsin inhibitor and sodium azide to stabilize the recovery of added EGF-URO in test samples. Even with added stabilizing agents, immunoreactive EGF-URO was barely detectable before day 14.5 (< 20 fmol[femtomol]/embryo); a substantial increase was observed from day 15.5 to 17.5 (from 70 to 200 fmol/embryo). Radioreceptor assay detected appreciable amounts of an EGF-URO-like substance at 11.5 days (50 fmol/embryo); values estimated by radioreceptor assay (about 10-fold higher than by radioimmunoassay) also increase markedly between days 15.5 and 17.5 (on average from 500 to 3000 fmol/embryo). During fetal mouse development there is an increase in the receptors for EGF-URO and in a substance (presumably a fetal growth factor) that can occupy the receptor. The differences between the radioreceptor and radioimmunoassay estimates for the EGF-URO content suggest that the fetal form of mouse EGF-URO differs from the adult molecule.