INSULIN-LIKE GROWTH-FACTORS IN CHICK-EMBRYO RETINA DURING DEVELOPMENT

Evidence exists supporting an important role for insulin-like growth f actors (IGFs) during fetal growth. In the present report we performed studies to define whether developing chick retina contains IGFs and wh ether IGFs play a role in the growth of this tissue. We have shown tha t both IGF-I and IGE-II are present in chick embryo retina throughout development (7th-18th day). The highest values, when expressed as ng/g of tissue, were found in the youngest retinas studied (7th-9th day) a nd at 16th-18th day of development. During whole development the conte nt of IGF-II was about two to three times higher than that ascertained for IGF-I. The tissue also contains cell-surface binding for IGFs. Ho wever, the developmental pattern of ICE-I binding was quite different from that found for IGFs, showing the highest values during the second week of development. Competitive studies showed that this receptor ha s a high affinity for IGF-I, a lower affinity for IGE-II, and a very m uch lower affinity for insulin. Also anti-IGE-I receptor antibody (alp ha IR3) inhibited I-125-labeled IGF-I binding to the receptor. Such re sults indicate the presence of type I IGF receptor in chick embryo ret ina. Affinity labeling experiments have confirmed this hypothesis. We have also shown that cultured retinal explants contain, synthesize and release into the medium appreciable amounts of IGFs. Both exogenous I CE-I and IGF-II added to the culture medium stimulated DNA synthesis o f retinal explants. Evidence that the retinas produce IGFs and possess IGF-IR together with the growth-promoting effect of IGFs suggests tha t these factors play an important role as regulators of retinal growth .