The CYP19A1 gene encodes an aromatase that is a member of the cytochrome P450 superfamily, also known as estrogen synthase, an enzyme responsible for a key step in estrogen biosynthesis. Cytochrome P450 proteins are monooxygenases that catalyze many reactions involved in drug metabolism and the synthesis of cholesterol, steroids, and other lipids. This protein is located in the endoplasmic reticulum and catalyzes the final step in estrogen biosynthesis. The CYP19A1 aromatase is responsible for aromatizing androgens into estrogens and can be found in many tissues, including the gonads (granulosa cells), brain, adipose tissue, placenta, blood vessels, skin, and bone, as well as tissues from endometriosis, uterine fibroids, breast cancer, and endometrial carcinoma. It is an important factor in sexual development ^[1-2].

The Cyp19a1-IRES-Cre mice were constructed using gene editing technology to insert an IRES-Cre element downstream of the stop codon of the endogenous Cyp19a1 gene in mice. The expression pattern of Cre recombinase is similar to that of the endogenous gene. When this strain is crossed with mice containing loxP sites, sequence recombination between loxP sites mediated by Cre recombinase can occur in the granulosa cells of the ovaries of offspring mice.