Stage-specific expression of estrogen receptor subtypes and estrogen responsive finger protein in preimplantational mouse embryos

In hope of understanding possible roles of estrogen during early embryogenesis, we examined the expression of both estrogen receptor alpha (ER alpha) and ER beta, a recently cloned novel subtype, in mouse oocytes and preimplantation embryos by means of reverse transcription polymerase chain reaction (RT-PCR). To investigate whether estrogen actually exerts its action, we further determined the expression of efp (estrogen-responsive finger protein), a newly characterized estrogen responsive gene belonging to the RING finger family. ER alpha mRNA was detected in whole ovaries, cumulus-oocyte complexes, denuded oocytes, 2-cell and 4-cell embryos, whereas it was undetected in 8-cell embryos. Interestingly it reappeared in morulae and blastocysts. ER beta mRNA was detected similarly to ER alpha except for the absence of ER beta mRNA in morulae. The efp mRNA was detected in whole ovaries, cumulus-oocyte complexes, 4-cell embryos, morulae and blastocysts. The stage specific expression of ER alpha and ER beta along with detection of the product of the estrogen responsive gene in early preimplantation embryos may indicate the possible physiological roles of estrogen in early embryogenesis.