Localization of insulin-like growth factor-1 binding sites in the embryonic chicken eye.

Insulin-like growth factor-1 (IGF-1) binding sites were localized in the embryonic chicken lens, retina, and retinal pigmented epithelium (RPE) with the use of autoradiography. Each of the ocular tissues exhibited specific binding of radiolabeled ligand. Labeling occurred over the entire surface of the lens from 6-day-old embryos, including the epithelium, basal ends of the fiber cells, and the annular pad. There was relatively little labeling over the lens nucleus. A similar pattern was seen in lenses from 19-day-old embryos. In isolated retinas from embryos of this age, the inner and outer plexiform layers were most heavily labeled. In the 19-day-old RPE, only the apical surface of the cells was heavily labeled. Electron microscopic studies revealed an apical layer of membranous material that may represent outer photoreceptor segments that remained attached to the RPE during dissection. It was uncertain, therefore, whether the IGF-1 was binding to sites on the RPE or to these membrane fragments.