BACKGROUND:Previous studies have confirmed that as an exogenous origin of endometrial epithelial cel s, bone marrow stem cel s are involved in the functional reconstruction of the injured endometrium. OBJECTIVE:To discuss whether bone marrow mesenchymal stem cel s can differentiate into endometrial epithelial cel s in vitro. METHODS:Passage 2 bone marrow mesenchymal stem cel s and endometrial stromal cel s were col ected and subjected to different treatments:bone marrow mesenchymal stem cel s were cultured alone in the DMEM/F12 medium containing 2%fetal bovine serum or in the DMEM/F12 medium containing 2%fetal bovine serum, 10-7 mol/Lβ-estradiol and 10μg/L epidermal growth factor as groups 1 and 2, respectively;bone marrow mesenchymal stem cel s co-cultured with endometrial stromal cel s by Transwel chamber were cultured in the DMEM/F12 medium containing 2%fetal bovine serum or in the DMEM/F12 medium containing 2%fetal bovine serum, 10-7 mol/Lβ-estradiol and 10μg/L epidermal growth factor as groups 3 and 4, respectively. After 5 days culture, bone marrow mesenchymal stem cel s at the bottom of the culture plate were col ected to detect expressions of epithelial cel markers, such as CK7, CK18, CK1 and EMA by RT-PCR technology, and to determine keratin expression using immunofluorescence assay. Besides, expressions of these epithelial cel markers in the group 3 were detected using RT-PCR at 1, 3, 5 and 7 days of culture, respectively. RESULTS AND CONCLUSION:mRNA expression of CK7 showed a significant successive rise in the groups 1, 2, 3, 4 and it was highest in the group 4. mRNA expressions of CK18 and CKl9 in the later three groups had no significant differences, but al significantly higher than those in the group 1. Compared with the groups 1 and 3, mRNA expression of EMA in the groups 2, 4 were significantly higher, but no significant differences existed between groups. Expression of keratin was strongly positive in the group 4, weakly positive in the group 3 and negative in the groups 1, 2, respectively. Furthermore, with the increase of culture time, mRNA expression of CK7 exhibited a constant increase, which was significantly higher at 5 and 7 days than at 1 and 3 days;but there were no significant differences in expressions of CKl9, CKl8 and EMA at different time points. These results show that bone marrow mesenchymal stem cel s can differentiate into endometrial epithelial cel s in vitro under certain conditions. Moreover, it can remarkably promote the endometrial differentiation under the combined effects of some exogenous and endogenous factors.