Influence of mutations affecting gonadotropin production or responsiveness on expression of inhibin subunit mRNA and protein in the mouse ovary

Abstract

Measurement of inhibins A and B in the serum of normal cyclic rodents has implicated FSH in the regulation of these peptides within the ovary. To extend these observations we have used a panel of mutant mice carrying mutations which affect either the production of, or the ability to respond to, FSH and LH. As a consequence, the females are infertile and show different degrees of follicular development. The aim of this study was to measure inhibin gene transcription in the ovaries of these mutant females together with inhibin protein levels in ovaries and serum and to relate these to follicular development within the ovary. Comparison was made with a pool of normal/heterozygous females. In hpg females where lack of GnRH production results in the absence of gonadotropin synthesis, in FSHb knockout (FSHbKO) females where disruption of the gene encoding FSHb results in the absence of FSH production, and in FSH receptor knockout (FSHRKO) females which are unable to respond to circulating FSH, follicular development remains at the pre-antral stage in these three mutants. Only in the hpg females were common inhibin a subunit mRNA levels significantly lower than normal. In these three mutants, however, mRNA levels for both the bA and bB subunits were extremely low compared with normal mice. At the protein level, neither inhibin A nor B was detected in the serum of these three mutants; however inhibin B, albeit at very low levels, was detectable within the ovaries. These observations confirm a major role for FSH in the control of transcription of the bA and bB genes but suggest that the constitutive transcription of the alpha subunit is less dependent on FSH. In contrast, in LH receptor knockout (LuRKO) female mice inhibin bA subunit mRNA levels were similar to those measured in normal/heterozygous females but levels of inhibin a and bB subunit mRNAs were significantly higher than in the normal group. This was reflected in significantly higher inhibin B protein levels in ovaries and serum. An inability to respond to LH combined with high circulating levels of FSH leads to a high proportion of antral follicles in LuRKO females, with granulosa cells constituting the major cell type within the ovary. The high percentage of antral granulosa cells is likely to account for the significantly higher levels of inhibin B production in these ovaries.

Follicle-stimulating hormone increases primordial follicle reserve in mature female hypogonadal mice

“…Likewise, elevated circulating inhibin A in tg-FSH hpg mice exhibiting antral follicle development, relative to non-tg hpg controls with antral arrest, agrees with the reported rise of inhibin A expression in secondary and antral follicles (Meunier et al 1988, Wang et al 2005. Inhibin A detection in 71% of tg-FSH (LH-deficient) hpg females in this study was similar to the 63% of LHR-null females expressing detectable inhibin A found by Hirst et al (2004). Overall, these findings support recent studies showing increased serum inhibins B and A in FSH-treated hpg females to be associated with antral follicles, although higher inhibin A requires LH activity and the presence of preovulatory follicles (Wang et al 2005).…”

“…Overall, these findings support recent studies showing increased serum inhibins B and A in FSH-treated hpg females to be associated with antral follicles, although higher inhibin A requires LH activity and the presence of preovulatory follicles (Wang et al 2005). The tg-FSH hpg ovary without LH stimulation would be expected to resemble ovaries in mice lacking functional LH-beta or receptor genes (Lei et al 2001, Zhang et al 2001, Ma et al 2004, which previously provided valuable comparisons for testicular development (Zhang et al 2001, Allan et al 2004, Hirst et al 2004. Indeed, arrested antral follicle development was observed in all these models exhibiting isolated FSH activity.…”

The ovarian response to standard gonadotrophin stimulation depends on FSHR, SHBG and CYP19 gene synergism

“…The role of FSHR in the local regulation of ovarian function has been highlighted, studying female FSHR-knockout mice. These mice are characterized by smaller ovaries, atrophic uterus and imperforate vagina [20] probably due to the lack of circulating biologically active estrogen, while their elevated serum and pituitary FSH concentrations lead to follicular arrest at the primordial, primary and preantral stages [21,22]. In the current study, the combined FSHR/SHBG/ CYP19 genotype analysis revealed increased follicle/oocytes numbers in Thr307Thr/Asn680Asn carriers compared to Ala307Ala/Ser680Ser carriers.…”

Pituitary Gonadotrophic Hormone Synthesis, Secretion, Subunit Gene Expression and Cell Structure in Normal and Follicle‐Stimulating Hormone β Knockout, Follicle‐Stimulating Hormone Receptor Knockout, Luteinising Hormone Receptor Knockout, Hypogonadal and Ovariectomised Female Mice

“…In the absence of FSH stimulation, follicles do not acquire LH receptors and are unable to convert thecal supplies of androgens to oestrogen. Ovarian concentrations of inhibins A and B have been found to be significantly lower in FSHβKO and FSHRKO mice compared to normal female mice and, in turn, feedback regulation of FSH is impaired.…”