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Insulin and IGF-I binding in developing chick neural retina and pigment epithelium: a characterization of binding and
R J Waldbillig1, D R Arnold, R T Fletcher
1Laboratory of Retinal Cell and Molecular Biology, National Eye Institute, National Institutes of Health, Bethesda, MD 20892.
Insights
Developing chick retinas and pigment epithelia have distinct insulin and insulin-like growth factor I (IGF-I) binding sites. These growth factor bindings are developmentally regulated, with the retina being a primary target.
Area of Science:
- Developmental Biology
- Neuroscience
- Endocrinology
Background:
- Insulin and Insulin-like Growth Factor I (IGF-I) are crucial for development.
- Their roles in the developing avian eye, specifically the retina and pigment epithelium (PE), are not fully understood.
- Understanding these roles is key to comprehending ocular development and function.
Purpose of the Study:
- To characterize insulin and IGF-I binding sites in the developing chick retina and PE.
- To compare these binding sites with those in the brain and liver.
- To investigate the developmental regulation of these binding sites.
Main Methods:
- Radioligand binding assays were used to quantify insulin and IGF-I binding.
- Characterization of binding site properties, including affinity and molecular weight of receptor subunits.
- Analysis of binding site levels at different developmental stages (embryonic day 10, 14, and 2-week post-hatching).
Main Results:
- Both retina and PE possess specific, high-affinity binding sites for insulin and IGF-I.
- IGF-I binding was 2-3 times higher than insulin binding in both tissues.
- Retinal binding was 4-6 times greater than PE binding, and significantly higher than brain binding.
- Insulin receptor subunits differed between retina/brain (neuraminidase-insensitive, 116 kD) and PE/liver (neuraminidase-sensitive, 126 kD).
- Developmental regulation showed a decrease in retinal binding and a complex pattern in PE binding.
Conclusions:
- The retina is a major target tissue for insulin and IGF-I during development.
- Insulin and IGF-I binding in the retina and PE are independently and developmentally regulated.
- Distinct molecular properties of insulin receptor subunits suggest tissue-specific functions.
Abstract:
We have characterized insulin and insulin-like growth factor I (IGF-I) binding sites in developing chick retina and pigment epithelium (10- and 14-day embryonic, and 2-week post-hatched). For comparison, binding sites in brain and liver were also examined. Both the retina and pigment epithelium (PE) contain separate, specific, high affinity binding sites for insulin and IGF-I. In both tissues, IGF-I binding exceeds insulin binding by two to threefold. Insulin and IGF-I binding in the retina is four to six times greater than in PE. Insulin and IGF-I binding in the retina and PE exhibit independent developmental regulation. In the retina, the number of binding sites decreases by approximately 50% between embryonic day 10 and 2 weeks post-hatching. In the PE, binding decreases slightly between embryonic day 10 and 14 and then, in the 2-week post-hatched chick, increases threefold. Insulin receptor binding subunits in the retina and brain are similar in that both are neuraminidase insensitive and have apparent molecular weights of 116 kD. In contrast, binding subunits in the PE and liver have higher molecular weights (about 126 kD), and are sensitive to neuraminidase. At the embryonic stages examined, the levels of retinal insulin and IGF-I binding exceed those of the brain by five to 13-fold. Taken together, these data suggest that the retina is a major target of insulin and IGF-I and that the binding of these growth factors is developmentally regulated.