Expression of angiopoietin-1/-2 in the process of mouse embryo implantation

This study examined the expression and distribution of angiopoietin-1/-2 (Ang-1/-2) in the endometrium of early pregnant mice. The expression of Ang-1/-2 was detected by immunohisto-chemical staining and in situ hybridization respectively. Computerized image analysis system was used to measure the average optical intensity of Ang-1/-2 in endometria at different time points after gestation. Mice were randomly divided into 5 groups: control group, D2 group (2 days after pregnancy), D4 group (4 days after pregnancy), D6 group (6 days after pregnancy) and D8 group (8 days after pregnancy), each containing 15 mice. The results showed that the expression of Ang-1 and Ang-2 was very different among 4 groups (P<0.01). Immunohistochemical staining revealed that Ang-1 was localized in the cytoplasma of stromal cells 2 days after pregnancy (day 2), and in luminal epithelial cells on day 4. The protein of Ang-2 was mainly expressed in the cytoplasma of glandular epithelia and stromal cells. With gestation time, the positive reactions of Ang-1/-2 were stronger in the endometria of the pregnant mice (P<0.01). In situ hybridization showed Ang-1 mRNA in stromal cells on day 2. Hybridization signal was localized in both stromal cells and vessel epithelial cells on day 4; Ang-2 mRNA was expressed in stromal cells and glandular epithelia on day 2; high mRNA levels appeared in stromal cells, glandular epithelia and vascular endothelia on day 4; an increasing in mRNA expression of Ang-1/-2 was observed on day 6 and day 8 (P<0.01). It is suggested that Ang-1/-2 may play an important role in the cross-talk between blastocyst and maternal endometrium during the process of embryo implantation.