Fate of Two Different Stages of Embryos Transferred to an Identical Recipient in Mice

To define the developmental fate of two different stages of embryos existing together in the mouse reproductive tract, different stages of fresh and frozen-thawed embryos were transferred separately into the oviducts of identical recipients. ICR and FvB embryos were flushed from the oviducts and/or uterus of superovulated females on Day 1 (2-4-cell stage) and Day 2 (8-cell-morula stage) of pregnancy. Day 1 embryos were transferred separately to the right or left oviduct of recipients, while the other oviduct received Day 2 embryos. There were no significant differences between Day 1 and Day 2 embryos with respect to the number of implantation sites and live fetuses in either the fresh or frozen-thawed embryos. These results concerning to the embryonic stage were similar to those of control experiments, in which Day 1 or Day 2 embryos were transferred to both right and left oviducts of recipients. Furthermore, no strain differences were observed in this study. No developmental retardation or anomalies were observed in fetuses derived from either Day 1 or Day 2 embryos. The embryo transfer in this study revealed that differences in developmental stage at preimplantation were synchronized by the maternal uterine environment.