Purpose: Events in the uterus during the peri-implantation period include embryo development, acquisition of uterine receptivity, implantation and decidualization. Hippo signaling pathway regulates cell proliferation, apoptosis and differentiation. We aimed to determine localization and expressions of pYAP (Phospho Yes-associated protein), YAP (Yes-associated protein), TEAD1 (TEA domain family member 1) and CTGF (Connective tissue growth factor), members of the Hippo signaling pathway, in the mouse uterus during the peri-implantation period.

Methods: Pregnant mice were randomly separated into 5 groups: 1st, 4th, 5th, 6th, and 8th days of pregnancy groups. Non-pregnant female mice in estrous phase were included in the estrous group. Uteri and implantation sites were collected. Also, inter-implantation sites were collected from the 5th day of pregnancy group. pYAP, YAP, TEAD-1 and CTGF were detected by immunohistochemistry and Western blotting.

Results: We observed that the expressions of YAP, TEAD-1 and CTGF were increased in the luminal and glandular epithelium on the 1st and 4th days of pregnancy when epithelial proliferation occurred. pYAP expression was high, and YAP and CTGF expressions were low in the luminal epithelium of the implantation sites on the 5th day of pregnancy, when epithelial differentiation occurred. pYAP expression was low, YAP and CTGF expressions were high at implantation sites on the 6th and 8th days of pregnancy, where decidua was formed.

Conclusion: Our findings suggest that the Hippo signaling pathway might be involved in implantation and decidualization. Our findings will guide further studies and may help to elucidate underlying causes of implantation failure and pregnancy loss.