Ontogeny of Expression of Insulin-like Growth Factor (IGF) and IGF Binding Protein mRNAs in the Guinea-pig Placenta and Uterus

Abstract

To determine the temporal and spatial distribution of insulin-like growth factor (IGF) and its family of binding proteins (IGFBPs), guinea-pig yolk sac and chorioallantoic placentae were collected at 15, 20, 25, 29, 44–45, 55 and 65–66 days of gestation. Messenger RNAs for IGF I, IGF II and IGFBP 1–6 were identified in tissue sections by in situ hybridization, using35S-cRNA probes. Epithelial and mesenchymal cell types were identified by immunohistochemistry for cytokeratin and vimentin, respectively. At 15 days of gestation, IGF-II mRNA was expressed in ectoplacental mesoderm, cytotrophoblasts and syncytiotrophoblast, and IGFBP-5 mRNA was detected in the syncytiotrophoblast. In the mid-gestation placenta, IGFBP-5 mRNA was expressed in the marginal and interlobular syncytium and IGF-II mRNA in the labyrinth. Near term, when expansion of the labyrinth was complete, IGFBP-5 mRNA was coexpressed with IGF-II mRNA in the marginal and interlobular syncytium. These observations suggest that interaction between IGF-II and IGFBP-5 plays a role in the vascularization of the placenta by fetal vessels. IGF-II mRNA was not expressed in the maternal tissues at any gestational age. IGFBP-2, -3 and -5 mRNAs were expressed in the endometrial stroma at 7–12 days of gestation but, following establishment of the placenta, IGFBP mRNAs were more abundant in the myometrium than in the decidua. IGF-II mRNA was detected in trophoblasts invading the walls of maternal vessels, and the endothelium of the preplacental vessels expressed IGFBP-4 mRNA, while IGFBP-2 and IGFBP-5 mRNAs were present in the tunica media of mesometrial arteries that had not been invaded by trophoblast. These findings suggest that IGF-II produced by the trophoblast acts in an autocrine and/or paracrine fashion to promote trophoblast invasion and that this process is modulated by interaction with IGFBPs present in maternal tissues.