Wingless ligands and beta‐catenin expression in the rat endometrium: The role of Wnt3 and Wnt7a/beta‐catenin pathway at the embryo–uterine interface

Wnt/beta‐catenin signaling may play an essential role in endometrial decidualization, placentation, and the establishment of pregnancy. We investigate here the possible roles, immunolocalizations, and synthesis of the Wnt3, Wnt7a, and beta‐catenin proteins in the rat endometrium during the estrous cycle and early postimplantation period. Wnt3 and Wnt7a had a similar localization and dynamic expression relative to the endometrial stages. Wnt7a immunostaining was not limited only to the luminal epithelial cells, but also to strong stainings in the stromal and endothelial cells. Wnt3, Wnt7a, and beta‐catenin were highly synthesized and colocalized at the trophoblast‐decidual interface; and were more obvious in the primary decidual zone, the GTCs, and the ectoplacental cone. Beta‐catenin was strongly localized at the borders of the mature decidual cells; however, Wnt3 and Wnt7a immunolocalizations were decreased in those cells. As such, the immunolocalization of Wnt3, Wnt7a, and beta‐catenin shifted with decidualization and placentation. The expression level of Wnt3, Wnt7a, and beta‐catenin messenger RNAs increased in early pregnancy, and especially between Days 8.5 and 9.5. The dramatic changes in the expression of Wnt3, Wnt7a, and beta‐catenin observed during the early days of pregnancy and the estrous cycle may indicate their roles in decidualization, stromal cell proliferation, and trophoblast invasion. Wnt3 and Wnt7a/beta‐catenin signaling pathway may be a key modulator in the embryo–uterine dialog by controlling the trophoblast invasion/differentiation, the placentation, and the stromal cell transformation. Moreover, the overexpression and particular localization of Wnt3 may provide a new insight in the reproductive field.