Wnt genes in the mouse uterus: potential regulation of implantation

Wnt genes are involved in critical developmental and growth processes. The present study comprehensively analyzed temporal and spatial alterations in Wnt and Fzd gene expression in the mouse uterus during peri-implantation of pregnancy. Expression of Wnt4, Wnt5a, Wnt7a, Wnt7b, Wnt11, Wnt16, Fzd2, Fzd4, and Fzd6 was detected in the uterus during implantation. Wnt4 mRNA was most abundant in the decidua, whereas Wnt5a mRNA was restricted to the mesometrial decidua during decidualization. Wnt7a, Wnt7b, and Wnt11 mRNAs were abundantly detected in the endometrial epithelia. The expression of Wnt7b was robust in the luminal epithelium (LE) at the implantation site on Gestational Day 5, whereas Wnt11 mRNA disappeared in the LE adjacent to the embryo in the antimesometrial implantation chamber but remained abundant in the LE. Wnt16 mRNA was localized to the stroma surrounding the LE on Day 4 and remained in the stroma adjacent to the LE but not in areas undergoing the decidual reaction. Fzd2 mRNA was detected in the decidua, Fzd4 mRNA was in the vessels and stroma surrounding the embryo, and Fzd6 mRNA was observed in the endometrial epithelia, stroma, and some blood vessels during implantation. Ovarian steroid hormone treatment was found to regulate Wnt genes and Fzd receptors in ovariectomized mice. Especially, single injections of progesterone stimulated Wnt11 mRNA, and estrogen stimulated Wnt4 and Wnt7b. The temporal and spatial alterations in Wnt genes likely play a critical role during implantation and decidualization in mice.