A role for epidermal growth factor in the growth and development of embryonic chicken lung systems

Epidermal growth factor (EGF) is known to be mitogenic for a variety of growing tissues, and is thought to play a role in embryonic development. The first aim of this study was to establish whether embryonic chicken lung explants respond to mouse EGF and if so, to determine whether this responsiveness varies with the age of the embryo. Autoradiographic analysis of thymidine incorporation into 3-, 4-, 5- and 6-day old explants revealed them to be highly responsive mitogenically to EGF, with this responsiveness increasing with the age of the explant. Binding studies using 125I-EGF were then carried out to determine whether embryonic chicken lung explants contained specific receptors for EGF. It was found that the lung explants rapidly bound EGF, with a gradual plateau in binding occurring after six hours, suggesting that EGF receptors might be present. Finally an attempt was made to demonstrate the presence of an EGF-like molecule in extracts of embryonic chickens. Furthermore it was found that while both fractions were equally able to compete with 125I-EGF in receptor-binding assays, the LMW fraction was far more potent a stimulator of DNA synthetic acticity than the HMW fraction. The incorporation, by labelling, of 3H-TdR was used in this experimental studies. The results presented in this study show that embryonic chicken lungs contain specific EGF receptors, respond mitogenically to mouse EGF and furthermore it would appear that they produce and endogenous EGF-like molecule. These results strongly suggest that EGF plays and important role in embryonic chicken lung growth