Insulin-like growth factor-I binds in the inner plexiform layer and circumferential germinal zone in the retina of the goldfish.

Results of the previous study suggest that insulin-related peptides regulate proliferation of retinal progenitors in the adult goldfish. Because of their known roles in retinal neurogenesis, we have chosen to focus future studies on insulin-like growth factor I (IGF-I) and the IGF-I receptor. In the study described here, we characterized the spatial distribution and specificity of IGF-I binding sites in the retina of the adult goldfish by performing receptor-binding autoradiography with [125I]-IGF-I alone and with unlabeled IGF-I-related molecules (IGF-I, IGF-II, insulin, and des-[1-3]-IGF-I) as competitive inhibitors of [125I]-IGF-I binding. The results of these experiments show that IGF-I binds in two locations in the retina of the adult goldfish, within the inner plexiform layer of the differentiated retina and the circumferential germinal zone. The competition experiments suggest that [125I]-IGF-I binds at sites specific for IGF-I, and that both IGF-I receptors and IGF-I binding proteins are present in the retina.