Estrogen receptor is expressed in pig embryos during preimplantation development

Although estrogen is recognized as essential for embryonic development and maintenance of pregnancy, it remains unclear whether it has a direct role i n the embryos themselves. The aim of this study was to investigate whether estrogen can have any effect in pig embryos during preimplantation developm ent. Since the function of estrogen is mediated through its specific recept or, estrogen receptor (ER), the presence of ER mRNA and protein in pig embr yos collected in vivo at different stages of preimplantation development wa s determined and compared. Using reverse transcription polymerase chain rea ction, ER RNA was detected at the one-cell, two-cell, and four-cell stages. The level became undetectable at the five- to eight-cell stages and the mo rula stages and then reappeared again at the blastocyst stage. To determine whether the ER message observed in the embryos was translated into ER prot ein, immunocytochemical analysis was performed and the presence of ER prote in was detected in oocytes at one-cell and four-cell stages. However, the a mount of ER protein in porcine embryos at the blastocyst stage was still be low the detection limit. The presence of ER mRNA at the blastocyst stages s uggests that estrogen may start to act directly on pig embryos afterwards, and our results provide a basis for determining the direct role of estrogen in preimplantation pig embryos. (C) 2000 Wiley-Liss, Inc.