Expression And Distribution Of Estrogen Receptors α And β In The Ovaries And Follicles Of Different Periods Of Laying Hens

To study the regulation mechanisms of follicle development in avian ovary is important for the understanding of reproductive p hysiology, improvement of egg production and efficient management of animal welfare and productivity. A whole reproductive cycle of an avian follicle includes primodial follicle development, selection of dominant follicle into the ovulation hierarchy, pre-ovulatory maturation, ovulation and post-ovulatory regression. The whole process requires finely controlled endocrine, paracrine and autocrine regulations in the streamlined hierarchical follicles of all different stages within the same ovary.Estrogen is a kind of steroid hormones synthesized and secreted by the granulosa and thecal cells. In the process of follicle growth, estrogen is a key regulatory molecule inside the follicle,which accelerates the proliferation of follicular granulosa cells and enhances the functions of FSH and LH on the proliferation and differentiation of ovarian cells. In addition, the estrogen can also regulate the hierarchical system of poultry. All in all, estrogens play a pivotal role in the development and maintenance of reproductive function. Most estrogen actions are mediated by two different types of nuclear receptors(ERα and ERβ). ERα and ERβ are major receptors of estrogen belonging to a superfamily of a ligand-activating dependent transcriptional factor. They can regulate proliferation and differentiation of target cells by participating in transcription.Previous studies had researched the expression of ERα and ERβ mRNA in different follicles of chicken. However, the expression and distribution of ERα and ERβ genes of in the ovaries during different stages has not yet been reported in the literature. Here, in order to understand the potential roles of ERα and ERβ in follicular development, qRT-PCR and Western Blotting were adopted in ovaries and follicles of different stages in 45-day-old(45d), 60-day-old(60d),90-day-old(90d),110-day-old(110d),120-day-old(120d)and160-day-old(160d) to elucidate the expression of ERα and ERβ. The expression of ERα mRNA in the chicken ovary of different stages exhibits a V- like pattern: From 45 d to 90 d, ERα mRNA level was gradually decreased, and from 90 d to 160 d, gradually increased. Its expression was significantly lower at 90 d compared to that of 45 d, and was significantly higher at 160 d compared to that of 90 d. The expression dynamics of ERα protein in the chicken ovary of different stages was similar to its mRNA. In the 45 day developing ovaries, ERα protein was predominately detected in the granulosa cells and oocytes of the ovaries. However, in prepubertal ovaries, a weak positive signal was also detected in the theca and cytoplasm. We also detected ERα protein expression in blood vessels, thereby confirming the important role of ERα in angiogenesis. On the mRNA level, the highest expression of ERα was detected in SY follicles, significantly higher than other sized follicles. But the level of ERα gene expression shows a trend of decreasing among SW, F5, F3 and F1 follicles. ERα protein was predominately detected in the granulosa cells in the follicles of different stages. ERα protein expression was significantly higher in SY and SW follicles than in other sized follicles including F5, F3 and F1 follicles. The results suggested an possibly autocrine/paracrine role of estrogens acting via ERα in the regulation of the ovarian and follicles function during development and for the process of successful reproduction. The expression of ERβ mRNA in the chicken ovary of different stages exhibits a L-like pattern: The highest expression of ERβ mRNA was detected at 45 d, followed by a rapid decrease till 90d; from 90 d to 160 d, its expression was not greatly changed, significantly lower that that of 45 d. For the dynamics of ERβ protein among different developmental stages, an obvious decline from 45 d to 160 d was observed, the highest and lowest levels appeared at 45 d and 160 d, respectively. For ERβ mRNA and protein, the highest expression was detected in SW follicles, along with the increase in follicle size(from SW to F1 follicles), its expression was significantly decreased. The expression of ERα and ERβ genes showed a significant difference in the ovaries of different periods and the follicles of different stages. The result indicated that the two types of receptors for laying hens have different effects on the developing ovaries and follicles, but the specific mechanism need to further study.