Maternal estrogen receptor-β expression during mouse gestation

Problem: Although estrogen receptor (ER)-α has been well characterized, the recently identified novel ER-β has not. In some tissues, there is overlap of the ERs, which allows for rescue in cases of deficiency; in other tissues, the ERs appear to have opposite effects. The objective of this study was to evaluate the expression of ER-β during pregnancy. Method of study: Pregnant mouse uteri (embryonic days 6-14, 16, 18) were studied. ER-α and ER-β oligonucleotide probes were end-labeled and in situ hybridization histochemistry was performed. Results: ER-β was strongly expressed in maternal ovaries; there was no other evidence of strong expression during gestation. ER-α was expressed in the uterus throughout gestation, with decreasing intensity as gestation progressed, and in maternal ovarian tissue. Conclusions: Differential expression of the two ERs was apparent during pregnancy, with ER-α playing a dominant role. This may have implications for selective drug treatment targeting estrogen receptors.