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 embryogene sis, we examined the expression of both estrogen receptor alpha (ER alpha) and ER beta, a recently cloned novel subtype, in mouse oocytes and preimpla ntation embryos by means of reverse transcription polymerase chain reaction (RT-PCR). To investigate whether estrogen actually exerts its action, we f urther determined the expression of efp (estrogen-responsive finger protein ), a newly characterized estrogen responsive gene belonging to the RING fin ger family. ER alpha mRNA was detected in whole ovaries, cumulus-oocyte com plexes, denuded oocytes, 2-cell and 4-cell embryos, whereas it was undetect ed in 8-cell embryos. Interestingly it reappeared in morulae and blastocyst s. ER beta mRNA was detected similarly to ER alpha except for the absence o f ER beta mRNA in morulae. The efp mRNA was detected in whole ovaries, cumu lus-oocyte complexes, 4-cell embryos, morulae and blastocysts. The stage sp ecific expression of ER alpha and ER beta along with detection of the produ ct of the estrogen responsive gene in early preimplantation embryos may ind icate the possible physiological roles of estrogen in early embryogenesis.