Abstract: To explore the expression of p38 mitogenactivated protein kinase（p38MAPK）in early embryos and the endometrium during periimplantation in mice. MethodsEarly embryos at different stages and uterus of the non-pregnant, and pregnant uterus of 1 to 8 days pseudopregnancy in mice were obtained. The expression and changes of p38MAPK in early embryos and the peri-implantation mouse endometrium were examined by immunohistochemistry. An image analysis was also performed. Results① p38MAPKpositive staining was found in the preimplanted embryos and gradually increased with development. ② In the pregnant group, p38MAPKpositive expression was weak at 3 days and peaked at 4 to 5 days in the endometrium of pregnant mice, then declined in the lumina epithelium, but increased in decidual cells. In the pseudopregnant group ,weak staining of p38MAPK was only observed on the 4th day of gestation, and negative staining was observed on the other days. p38MAPK was expressed weakly in the endometrium of non-pregnant mice. Conclusion① p38MAPK activity may be required to support embryo development through the murine pre-implantation interval. ② p38MAPK, in addition to relating to blastocyst implantation,may indirectly participate in the process of endometrial decidualization. ③ The expression of p38MAPK in mouse endometrium is regulated not only by maternal factors (steroid hormones), but also by the implanted embryos.

Key words: p38MAPK, Blastocyst, Implantation, Endometrium, Mouse