Ontogeny of expression of insulin-like growth factor (IGF) and IGF bindingprotein mRNAs in the guinea-pig placenta and uterus

To determine the temporal and spatial distribution of insulin-like growth f actor (IGF) and its family of binding proteins (IGFBPs), guinea-pig yolk sa c 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 I- ti were identified in tissue sections by in situ hybridization, using S-35- cRNA probes. Epithelial and mesenchymal cell types were identified by immun ohistochemistry for cytokeratin and vimentin, respectively. At 15 days of g estation, IGF-II mRNA was expressed in ectoplacental mesoderm, cytotrophobl asts and syncytiotrophoblast, and IGFBP-5 mRNA was detected in the syncytio trophoblast. In the mid-gestation placenta, IGFBP-5 mRNA was expressed in t he marginal and interlobular syncytium and IGF-II mRNA in the labyrinth. Ne ar term, when expansion of the labyrinth was complete, IGFBP-5 mRNA was coe xpressed with IC;F-XI mRNA in the marginal and interlobular syncytium. Thes e 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 w as 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 ges tation 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 o f 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 n ot been invaded by trophoblast. These findings suggest that IGF-II produced by the trophoblast acts in an autocrine and/or paracrine fashion to promot e trophoblast invasion and that this process is modulated by interaction wi th IGFBPs present in maternal tissues. (C) 1999 W. B. Saunders Company Ltd.