It is necessary for estrogen to rapidly activate mouse blastocysts, so that they may attach to endometrial epithelium in implantation. Our previous and recent work has shown that estrogen induces the fast effect on mouse blastocysts in implantation which is mediated by G protein-coupled receptor 30 (GPR30). There also were evidences that integrins and their ligands are involved in embryo-endometrium interaction. Thus, we infer integrins may be involved in GPR30 mediating the fast effect of estrogen on mouse blastocysts in implantation. Firstly, blastocysts were collected from day 4 pregnant Kunming mice and divided into 5 groups, 3 embryos for each, which were treated respectively with the same amount of vehicle, 1μmol/L estradiol (E2), 1μmol/L E2 conjugated with bovine serum album (E2-BSA), 1μmol/L G1, a GPR30-specific agonist, and 1μmol/L E2-BSA with pretreatment of 1μmol/L G15, a GPR30-specific antagonist. Immunocytochemistry staining and confocal microscopy were used to examine the expression of integrins. The experiment was repeated three times. The result showed that E2, E2-BSA and G1 could induce their clustering, while G15 may block the clustering induced by E2-BSA (Fig 1). To explore GPR30 mediating the fast effect of estrogen on the affinity of integrins in mouse blastocysts. The collected some other blastocysts were pretreated as the above experiment, followed by the treatment of 50μg/L fibronectin labled with FITC (FN-120-FITC), one kind of integrin ligands, The flurescence intensity was examined which represented the affinity of integrins with their ligand. The result indicated that E2, E2-BSA and G1 could increase the FN binding activity of integrins in blastocyst cells, while G15 may block this effect of E2-BSA on it (Fig 2). In order to study integrins are involved in the effect of estrogen on mouse blastocysts in implantation, blastocysts (n=38) were pretreated with 1μmol/L E2, and then divided into two groups. One group was cultured in M2 medium containing RGD, (Arg-Ala-Asp) peptide (1mmol/L) for 30 minutes, which can specifically block the binding of integrins with their ligands, the other group was cultured in non-specific RGE peptide (1mmol/L) as control. Two groups of blastocysts were separately transplanted into the bilateral uterine horns of recipient mice on the pseudopregnant day 4 and the implantation rate between two groups were compared in 10 days. We found that the implantation rate in RGD group (3/19, 16%) was significantly lower than that in RGE group (13/19, 68%), P<0.05. In conclusion, GPR30 mediating the fast effect of estrogen may induce the clustering of integrins and increase the affinity of integrins with their ligand in mouse blastocysts, which play important roles in the process of implantation. Funding: This work was supported by the National Natural Science Foundation of China (Grant No.31100844)