Mylène D'haeseleer

Localization of Oestrogen Receptors Within Various Bovine Ovarian Cell Types at Different Stages of the Oestrous Cycle

In the present study oestrogen receptor α(ERα) and oestrogen receptor β (ERβ) mRNA were localized in various ovarian cell types of 23 cows at different stages of the oestrous cycle. ERα was detected by immunohistochemistry and the localization of ERβ mRNA was examined using in situ hybridization. The immunostaining of ERα was low in the ovarian follicles, tunica albuginea and surface epithelium, but high in cells of the deep stroma and superficial stroma, which indicates a functional role of ERα in the cells surrounding the follicles. In contrast, ERβ mRNA scores were low to moderate in primordial and primary follicles, and increased with the development of the follicle. ERβ mRNA scores were higher in cystic follicles than in obliterative follicles. In the corpora lutea and corpora albicantia the scores for ERβ mRNA were moderate. Furthermore, in the corpora lutea, ERβ mRNA levels showed cyclic variations and were low during early dioestrus. The correlation between plasma progesterone levels and the score for ER was low and negative in all ovarian cell types. This study demonstrates the predominant role of ERβ over ERα in bovine ovarian structures. Furthermore, the colocalization of both ERβ mRNA and ERα in most cell types suggests possible interactions between both ER subtypes.

Cell-specific localization of oestrogen receptor beta (ESR2) mRNA within various bovine ovarian cell types using in situ hybridization.

The localization of oestrogen receptor beta (ESR2) mRNA, in this article denominated as (ERβ) mRNA, was examined using in situ hybridization in the ovaries of randomly selected cows, irrespective of the cycle stage of the animals. A 602‐bp fragment of ERβ mRNA was cloned, sequenced and digoxigenin (DIG)‐labelled. Semi‐quantitative evaluation showed that the scores for ERβ mRNA were moderate to high in the follicle cells of both primordial and primary follicles, but lower in granulosa cells of secondary follicles. In vital tertiary follicles, the total ERβ mRNA expression was low but varied between the different animals. In both obliterative and cystic atretic follicles, high to moderate ERβ mRNA scores were noticed in the granulosa cells. The stroma cells surrounding primordial and primary follicles and the theca cells of secondary follicles showed moderate ERβ mRNA levels, whereas the ERβ mRNA score in theca interna and theca externa cells of vital tertiary follicles was distinctly higher. In the theca cells of atretic follicles the score was even higher. Cells of corpora hemorrhagica and corpora lutea had moderate ERβ mRNA scores, while higher scores were seen in cells of corpora albicantia. Cells of the surface epithelium had a moderate score for ERβ mRNA, whereas cells of the tunica albuginea and deep stroma showed high ERβ mRNA scores. The present findings have clearly established a cell‐specific localization of ERβ mRNA in several cell types in the bovine ovary.