Expression of inhibin/activin subunits and follistatin messenger ribonucleic acids and proteins in ovarian follicles and the corpus luteum during the human menstrual cycle.

Abstract

The physiological role of intraovarian activin (beta/beta) and inhibin (alpha/beta) dimers in humans in unclear. The identification of follistatin as a beta-subunit-specific high affinity binding protein has added complexities for the interpretation of in vitro studies concerning the functionalities of these ovarian peptides. We, therefore, have attempted to define in vivo compartmental distributions of gene expression and protein localization for inhibin and activin subunits (alpha, beta A, and beta B) concurrent with follistatin in ovarian follicles and corpus lutea obtained from a large number of human ovaries. In situ hybridization and immunohistochemistry were used for detecting the expression of genes encoding inhibin/activin subunits and follistatin and their gene products, the proteins. Granulosa cells of small antral follicles (1-8 mm) were found to express mRNA for alpha-, beta A-, and beta B-subunits as well as follistatin, and the strongest signals were localized in the cumulus granulosa cells. In the thecal cell layer, only alpha-subunit mRNA was detected. Proteins were localized in cellular compartments corresponding to their mRNA, but in addition, proteins for beta A-subunit and follistatin were detected in the thecal cell layers in the absence of gene expression, an observation compatible with a paracrine action. Thus, granulosa cells of the small antral follicle have the potential to form all dimers of inhibin and activin, and their autocrine and paracrine actions may be modulated by follistatin in both granulosa cell and thecal cell layers. With the development of a dominant follicle, remarkable switches in subunit gene expressions occurred; beta B-subunit mRNA was no longer detectable in any cell type, and beta A-subunit expression emerged in the thecal cells along with continued abundant expression of beta A-subunit and follistatin in the granulosa cells. Proteins were found only in granulosa cells corresponding to their mRNAs. In the corpus luteum, the inhibin/activin alpha- and beta A-subunits and follistatin mRNA and proteins were expressed exclusively in the luteinized granulosa cells. Luteinized thecal cells were devoid of detectable mRNA message or proteins. Thus, the inhibin-activin-follistatin system in the corpus luteum appears to function in an autocrine fashion.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of ovarian function by the TGF-beta superfamily and follistatin

“…Within the ovary, the granulosa cells in antral follicles and luteinized granulosa cells are the main sites that express follistatin mRNA and protein, whereas other structures, such as the theca cells, stroma and oocytes, appear to be devoid of follistatin mRNA (Shimasaki et al, 1989;Roberts et al, 1993;Braw-Tal, 1994;Tisdall et al, 1994), although follistatin mRNA has been observed in human oocytes (Sidis et al, 1998). However, follistatin protein was detected in the theca cell layers of human small antral follicles in the absence of follistatin mRNA expression, but then became undetectable with the development of a dominant follicle (Roberts et al, 1993).…”

“…However, follistatin protein was detected in the theca cell layers of human small antral follicles in the absence of follistatin mRNA expression, but then became undetectable with the development of a dominant follicle (Roberts et al, 1993). Thus, the granulosa cells are the type of cell in the ovary responsible for producing and secreting follistatin in most species.…”

“…It is important to note that the level of follistatin mRNA expression within the ovary depends on the developmental stages of follicles. Follistatin mRNA expression within the antral follicles increases as follicular maturation progresses and declines during the atretic process (Roberts et al, 1993;Lindsell et al, 1994). Moreover, the follistatin protein appears to be present in only the selected dominant follicles (Nakatani et al, 1991).…”

Testing the antagonistic effect of follistatin on BMP family members in ovine granulosa cells

“…Follistatin-288 is the predominant form present in human follicular fluid [4]. In mammalian ovaries, follistatin is highly expressed by the granulosa cells (GC) of developing follicles [5][6][7]. The level of follistatin mRNA expression within the antral follicles increases as follicular maturation progresses and declines during the atretic process [5,8].…”

“…In mammalian ovaries, follistatin is highly expressed by the granulosa cells (GC) of developing follicles [5][6][7]. The level of follistatin mRNA expression within the antral follicles increases as follicular maturation progresses and declines during the atretic process [5,8]. Follistatin has been shown to block all the actions of activin on GC, including the stimulation of FSH receptor expression, inhibin 420 A. Pierre et al…”