Expression of estrogen receptor α mRNA in theca and granulosa layers of the ovary in relation to follicular growth in quail

Changes in expression of estrogen receptor alpha (ERα) mRNA were studied in special reference to follicular growth of the ovarian follicles in laying quail. Levels of mRNA were determined by RT-PCR in the ovarian stroma, each class of the ovarian follicles, oviductal parts and in the liver. Low levels of ERα mRNA were detected in stroma, the small white follicles, large white follicles and small yellow follicles and in the theca layer of the three largest preovulatoy follicles. Although the level in the granulosa layer of the F3 was also low, the level significantly increased in F2 and F1. Relatively higher levels were found in the liver and oviduct, and that in the magnum was the highest among all tissues examined. The level in the F1 granulosa layer was comparable to that in the liver which actively synthesises egg yolk proteins for the sake of estrogen and ER. The results of the present study demonstrate that (1) ERα mRNA is present in each compartment of the reproductive tissue in quail, (2) the marked expression of ERα mRNA in the granulosa layer of the largest follicle may indicate the involvement of estrogens in the biosynthesis of inhibin/activin, progesterone and yolk perivitelline layer protein, (3) very high expression of ERα in the oviductal tissues may be related to the role of estrogens in cell proliferation and protein synthesis in the oviduct.