Norrin immunolocalization and its possible functions in rat endometrium during the estrus cycle and early pregnancy

Mutations in Norrie Disease Pseudoglioma (NDP) gene cause serious sight loss, deafness and mental retardation in Norrie disease patients via the impairment of angiogenesis. Since norrin is a Wnt pathway ligand, it could function in several tissues other than eye and nervous systems. Therefore, the aim of the present study was to determine the possible function of norrin in angiogenesis, cellular differentiation in stroma and in decidua and the survival of those cells using immunofluorescent labeling. While norrin had a uniform distribution in stroma and in blood vessels, it had a strong expression in luminal and glandular epithelia during the estrus cycle. Norrin had strong immunolocalization in the antimesometrial decidual reaction zone on day 7 of gestation, whereas it had a decreased expression in the mesometrial uterine luminal epithelium along with an increased localization in blood vessels and decidual cells of the same region on day 8 of gestation. As from day 9 of gestation, norrin demonstrated rather strong expression in the decidual cells and blood vessels of the mesometrial region in which the chorioallantoic placenta was going to develop. In all periods studied, norrin had rather weak expression in the primary decidual zone surrounding the embryo. Findings of the present study suggested that norrin might regulate the decidual reaction and the placental angiogenesis along with the survival and the differentiation of luminal and glandular epithelial and decidual cells in rats. In addition, it could play indirect important roles in the control of trophoblastic invasion and the programmed cell death.