Effects of ERα overexpression on female reproduction in mice

Recently, we generated transgenic mice in which ERα can be inducibly overexpressed in reproductive tissues (ERα overexpressors). These mice were used to test the hypothesis that prenatal and postnatal ERα overexpression reduces female fertility. To do so, litter sizes, ovulation, follicle numbers, uterine histology, implantation sites, and hormone levels were compared in ERα overexpressors and controls. The data indicate that ERα overexpressors have reduced fertility compared to controls and that the reduced fertility is not due to reduced ovulatory capacity, altered levels of estradiol, FSH, and LH, or impaired follicular growth. ERα overexpressors, however, had a higher number of apoptotic cells in the endometrial epithelium and a reduced number of implantation sites compared to controls. Thus, the increased number of apoptotic cells and reduced number of implantation sites observed in ERα overexpressing uteri compared to controls may, in part, account for the reduced litter size produced by ERα overexpressing females.