DIFFERENTIAL TEMPORAL AND SPATIAL EXPRESSION OF INSULIN-LIKE GROWTH-FACTOR BINDING PROTEIN-2 IN DEVELOPING CHICK OCULAR-TISSUES

Purpose, To determine the developmental expression and localization of mRNA for insulinlike growth factor binding protein-2 (IGFBP-2), a maj or binding protein of IGF-I and IGF-II, in ocular tissues of the embry onic and early posthatched chick. Methods, In situ hybridization and n orthern blot analysis were used to analyze the cellular origin and rel ative expression of IGFBP-2 mRNA in ocular tissues. Results, Wholemoun t in situ hybridization reveals that, as early as 3.5 days of embryoni c development (E3.5), IGFBP-2 mRNA is already expressed in many areas of the embryo, including surface ectoderm, certain regions of the brai n, pharyngeal clefts, somites, and limb buds. In the eye, IGFBP-2 mRNA is expressed only in the presumptive corneal epithelium at this time. By E6, IGFBP-2 mRNA expression is present in both the corneal epithel ium and endothelium. By E12, IGFBP-2 mRNA is detected clearly in the c orneal stroma as well as in several other ocular structures, such as t he sclera, eyelid, and ciliary body. In the neural retina, a low, diff use expression of IGFBP-2 mRNA is found at E6, which becomes more loca lized to the nuclear layers by E12. Northern blot analysis confirms th at a high level of IGFBP-2 expression is present in the cornea and scl era by E8 to E12. A high level of IGFBP-2 mRNA expression, however, is not observed in the retina until E18. At posthatch day 2 (P2), northe rn blot analyses of ocular tissues reveal that the cornea contains the highest ocular level of IGFBP-2 mRNA expression, a value equal to tha t of brain and liver. Conclusions. The early appearance, along with di fferential temporal and spatial expression of IGFBP-2 mRNA in developi ng ocular tissues, suggests a role for IGFBP-2 in the regulation of gr owth and differentiation of several ocular tissues, including the corn ea, sclera, and retina.