ESR1 and Infertility: In mice, the deletion of either ER induces various ovarian phenotypes, from subfertility (Esr2−/− mice) due to the disrupted growth and maturation of antral follicles leading to reduced ovulation rate to infertility due to the development of cystic follicles and anovulation (Esr1−/− mice); in the case of ERα, this effect on the ovary would be mainly indirect, via its regulation of pituitary gonadotropins, whereas ERβ deletion would impair directly GC proliferation and maturation [59,60,61,62].