Ontogeny of the epidermal growth factor receptor during development of the fetal bovine mesonephros and associated organs of the urogenital tract.

A primary cell culture system was developed to study the epidermal growth factor (EGF) receptor in the fetal bovine mesonephros and its urogenital derivatives. Radioreceptor assays demonstrated EGF binding as early as Day 37 in mesonephric cells and in cells derived from the fetal reproductive ducts, gonads, and metanephros--all mesonephric derivatives. Immunocytochemical studies revealed that EGF receptors were localized in the ductal and tubular epithelium of these urogenital organs. EGF induced DNA synthesis and tyrosine phosphorylation in the bovine mesonephric cells, suggesting that EGF receptors detected in these cells were functional. In addition, transforming growth factor alpha, the putative fetal ligand for the EGF receptor, was found to specifically compete for EGF binding to the receptor, as well as to induce DNA synthesis in a manner similar to that of EGF. Estrogen did not regulate EGF receptors or specifically bind to bovine mesonephric cells. The development of estrogen receptors in the bovine species occurs markedly later than that of the EGF receptor, in contrast to the mouse, where both receptors are observed at very early stages of reproductive tract development.