The Implantation Of Asynchronously Transferred Embryos And The Expression Of Snail And COX-2 At The Site Of Implantation

Blastocyst implantation is a key step for successful establishment of pregnancy during mammalian reproduction. Successful implantation is dependent upon the interaction between the blastocyst and the uterus. The most fundamental feature of this process is the synchronized development of the embryo to the blastocyst stage and differentiation of the uterus to the receptive state. The expression of implantation-related molecules has not been examined after asynchronous embryo transfer. In this study, four groups had been designed, including (A) Zygotes and 8-cell stage embryos were transferred separately into the oviducts of the same recipient on day 1 of pseudopregnancy; (B) Embryos of zygotes and blastocysts were transferred separately into the oviducts of the same recipient on day 1 of pseudopregnancy; (C) Morula were transferred into the oviducts of the recipient on day 1 of pseudopregnancy; (D) Blastocysts were transferred into the oviducts of the recipient on day 1 of pseudopregnancy. Embryo implantation was examined at 16:00 and 20:00 of day 4, and at 8:00 of day 5 by intravenous injection of Chicago blue dye. The expression of both SNAIL and COX-2 at implantation sites was examined by immunohistochemistry. In this study, the embryos asynchronously transferred could implant in all of four groups. On day 5 posttransfer, the size of implanted embryos between each experimental groups was different, the difference in group A and between zygote and morula transferred in same day was very significant(P<0.01), the group B that the size of implanted zygotes was significantly smaller than that of blastocysts(P<0.05).The morphologies of implanted embryos were different between each group, having the embryos from attached blastocysts to egg cylinder. The immunostaining of both SNAIL and COX-2 was also different in each group. When the embryos were transferred at 8-cell, morula or blastocyst stage, the immunostaining for SNAIL and COX-2 was stronger than that transferred at zygote stage. These results suggest that the embryos transferred at advanced stage could implant prior to younger embryos, and implantation-related molecules were also expressed at implantation sites of mouse uterus when the advanced embryos were implanted.