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Insulin and IGF-1 binding in chick sclera
R J Waldbillig1, D R Arnold, R T Fletcher
1Laboratory of Retinal Cell and Molecular Biology, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892.
Insights
Insulin and insulin-like growth factor-1 (IGF-1) binding sites in chick sclera decrease with development. This reduction is due to fewer binding sites, not altered affinity, indicating developmental regulation of these growth factor receptors.
Area of Science:
- Ophthalmology
- Developmental Biology
- Endocrinology
Background:
- The sclera, the eye's protective outer layer, plays a role in ocular development.
- Insulin and insulin-like growth factor-1 (IGF-1) are crucial for growth and development.
- Understanding growth factor signaling in the sclera is key to comprehending ocular development.
Purpose of the Study:
- To investigate the presence and characteristics of insulin and IGF-1 binding sites in embryonic and young adult chick sclera.
- To determine how these binding sites change during development and their specificity.
Main Methods:
- Radioligand binding assays were used to quantify insulin and IGF-1 binding in scleral tissue.
- Competition assays were performed to assess the specificity of the binding sites for insulin and IGF-1.
- Analysis of binding site characteristics across different developmental stages (embryonic vs. posthatching).
Main Results:
- Distinct binding sites for insulin and IGF-1 were identified in chick sclera.
- A significant decrease (nearly 50%) in both insulin and IGF-1 binding was observed between embryonic and young adult stages.
- Binding site affinity remained stable, suggesting a decrease in the number of sites during development.
- Specific IGF-1 binding sites showed improved specificity in young adults compared to embryonic stages.
Conclusions:
- Insulin and IGF-1 binding sites in the chick sclera are developmentally regulated, with numbers decreasing post-hatching.
- The observed decrease in binding is attributed to a reduction in the quantity of binding sites, not a change in their affinity.
- These findings highlight the dynamic role of insulin and IGF-1 signaling in scleral development and ocular growth.
Abstract:
The sclera of embryonic (days 10 and 14) and young adult (2-week posthatching chicks) contains distinct binding sites for insulin and for insulin-like growth factor-1 (IGF-1). Since there is a nearly 50% decrease in insulin and IGF-1 binding between embryonic day 10 and the 2nd week posthatching, it is clear that these sites are developmentally regulated. The affinity of each binding site for its ligand is stable across development. This suggests that the developmental decrease in binding is the result of a decrease in the number of binding sites. The insulin binding site in the sclera is specific for insulin since it has a high affinity for insulin and a lower affinity for IGF-1 (IC50 for unlabeled insulin = 0.4 nM; unlabeled IGF-1 = 5.0 nM). The embryonic chick sclera also contains two high-affinity IGF-1 binding sites. One of these sites exhibits poor binding specificity since it has an equal affinity for insulin and IGF-1. However, the specificity of this site increases in the young adult. The second IGF-1 binding site exhibits a more conventional specificity in that it has a higher affinity for IGF-1 than for insulin. The specificity of this binding site also improves in the young adult. The presence of insulin and IGF-1 receptor binding site subtypes is not correlated with structurally different receptor binding subunits since only a single population of binding subunits is observed (apparent molecular weight of 125 +/- 2.7 kD) in embryonic and adult sclera.(ABSTRACT TRUNCATED AT 250 WORDS)