Short-term effects of thyroid hormones during development: Focus on signal transduction.
In this work, the proliferative activity of chick embryo hepatocytes and its regulation by factors affecting cell growth, such as epidermal growth factor (EGF) and retinoic acid, were studied. The transport of nutritional molecules, like amino acids, was also investigated; in particular, the uptake mediated by the Na+ -dependent system A, known to be under hormonal and growth factor control. Moreover, some steps in the transduction pathway of mitogenic signal were analyzed, both for EGF and retinoic acid treatment. Results obtained suggest that chick embryo hepatocytes growth in an exclusive serum dependent way shows an early sensibility to EGF stimulation as regards to the proliferative activity and amino acid transport, responds to retinoic acid treatment and lack of contact inhibition. Moreover, as far as the signal transduction is concerned, at early stages, they do not seem to be able to utilize the same signal molecules as observed in adult life.