Revealing the Sptio-temporal Expression of the FGF Family Receptors Throughout Pregnancy in Sheep

Several uterine-derived growth factors are involved in establishing a functional placenta. One class of interest is the fibroblast growth factors (FGFs). This large family of endocrine, paracrine and autocrine factors contains 23 members and 4 receptors (FGFR1-4) in most mammals. All four FGF receptors are expressed in ovine pre-implantation conceptuses. In the mouse, FGFR2-null embryos developed normally to the blastocyst stage and underwent the initial stages of implantation, but the TE cell layer failed to develop normally. This phenotype suggests that FGFR2 is essential for early placental development. The aim of this study was identifying FGFRs spatio-temporal expression in ovine from pre-implantation embryo to mature placenta in sheep. For this purpose, blastocysts and placentas from different stages of pregnancy were collected and analyzed for FGFRs mRNA and protein expression and localization. We found that FGFR2 but not FGFR1 is expressed in the trophoblast cells of the blastocyst as well as in the embryo, just prior to implantation. In addition, FGFR2 mRNA is 4-fold greater in abundance than FGFR1 mRNA in the ovine placenta on days 50 and 70 of gestation, whereas FGFR3 and 4 mRNA cannot be detected. In agreement with this, in day 70, FGFR2 protein levels are higher than FGFR1 expression levels in sheep placenta. Finally, at days 50 and 70 FGFR2 is localized in the fetal villi of the placenta. Our results suggest that similar to mice, FGFR2-dependent activities likely exist in the ruminant`s trophoblast cells at pre-implantation embryo as well as in the mature placenta.