Expression of mRNAs encoding oestrogen receptor (ER) alpha and ERbeta, androgen receptor and progesterone receptor during gonadal and follicular development in the marsupial brushtail possum (Trichosurus vulpecula).
The objective of the present study was to determine which ovarian cells express mRNAs for oestrogen (ERalpha and ERbeta), androgen (AR) and progesterone (PR) receptors during ovarian and follicular development in the brushtail possum. Expression of ERalpha and/or ERbeta mRNA was observed from birth, initially in cells of the blastema, then in the medullary cords from Day 20. ERalpha was expressed in the oocytes and granulosa cells of secondary and antral follicles. Preovulatory follicles did not express ERalpha mRNA, although their oocytes were not examined for any gene. ERbeta mRNA was observed in oocytes at all follicular stages examined, but was not consistently observed in granulosa or theca cells. Expression of AR mRNA before Day 40 was very faint; thereafter, expression was observed in the medullary cords, peaking between Days 60 and 120. Oocytes, granulosa cells and theca of secondary and antral, but not preovulatory, follicles expressed AR mRNA. PR mRNA was expressed throughout the gonad by Day 20. Granulosa cells of some secondary and antral follicles and theca of antral follicles expressed PR mRNA. Thus, the expression of mRNAs encoding steroidogenic receptors in a time- and cell-specific manner supports a role for steroids in the process of ovarian follicular formation and growth.