Differential temporal and spatial expression of insulin-like growth factor binding protein-2 in developing chick ocular tissues.
OBJECTIVE
To determine the developmental expression and localization of mRNA for insulin-like growth factor binding protein-2 (IGFBP-2), a major binding protein of IGF-I and IGF-II, in ocular tissues of the embryonic and early posthatched chick.


METHODS
In situ hybridization and northern blot analysis were used to analyze the cellular origin and relative expression of IGFBP-2 mRNA in ocular tissues.


RESULTS
Wholemount in situ hybridization reveals that, as early as 3.5 days of embryonic development (E3.5), IGFBP-2 mRNA is already expressed in many areas of the embryo, including surface ectoderm, certain regions of the brain, 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 epithelium and endothelium. By E12, IGFBP-2 mRNA is detected clearly in the corneal stroma as well as in several other ocular structures, such as the sclera, eyelid, and ciliary body. In the neural retina, a low, diffuse expression of IGFBP-2 mRNA is found at E6, which becomes more localized to the nuclear layers by E12. Northern blot analysis confirms that a high level of IGFBP-2 expression is present in the cornea and sclera 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), northern blot analyses of ocular tissues reveal that the cornea contains the highest ocular level of IGFBP-2 mRNA expression, a value equal to that of brain and liver.


CONCLUSIONS
The early appearance, along with differential temporal and spatial expression of IGFBP-2 mRNA in developing ocular tissues, suggests a role for IGFBP-2 in the regulation of growth and differentiation of several ocular tissues, including the cornea, sclera, and retina.
D000375:Aging / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D015152:Blotting, Northern; D002642:Chick Embryo; D002645:Chickens; D005314:Embryonic and Fetal Development; D005123:Eye / Q000196:embryology / Q000254:growth & development / Q000378:metabolism*; D017403:In Situ Hybridization; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D013997:Time Factors
D018971:Insulin-Like Growth Factor Binding Protein 2; D012333:RNA, Messenger