Mark Cranfield

The physiological mechanisms controlling ovulation rate in mammals involve a complex exchange of endocrine signals between the pituitary gland and the ovary, and a localized exchange of intraovarian hormones between the oocyte and its adjacent somatic cells. The discoveries in sheep of mutations in bone morphogenetic protein 15 (BMP15) and bone morphogenetic protein receptor type IB (BMPR-IB) together with recent findings on the physiological effects of growth differentiation factor 9 (GDF9) and BMP15 on follicular development and ovulation rate highlight some important differences in the way in which the oocyte may function in mammals with different ovulation rate phenotypes. In sheep, BMP15 and GDF9 have each been shown to be essential for the early and later stages of follicular development. In addition, ovulation rate is sensitive to changes in the dose of either of these two oocyte-derived growth factors. These findings are in contrast to those reported for mice in which CDF9, but not BMP15, is essential for follicular development. The evidence to date is consistent with the hypothesis that the oocyte plays a central role in regulating key events in the process of follicular development and hence, is important in determining ovulation rate. Moreover, it appears that the mechanisms that the oocyte uses to control these processes differ between species with low and high ovulation rate phenotypes. © 2003 Society for Reproduction and Fertility

Summary: Background and objective  Recent studies have found anti‐Müllerian hormone (AMH) to be a potentially important marker for the assessment of ovarian reserve and prediction of the success of in vitro fertilization (IVF) treatment. The objectives of this study were to develop a sensitive and specific assay for AMH and to evaluate the potential application of the assay. This assay will be then available to our collaborators in the UK and overseas.Design  Samples obtained as part of another prospective cross‐sectional study from infertility patients and another prospective longitudinal study from pregnant women were used in this study to measure AMH using a new double‐antibody enzyme‐linked immunosorbent assay (ELISA).Patients and measurements  AMH levels were evaluated in (i) serum and seminal fluid from males (normal and male factor infertility males), (ii) serum and follicular fluid from females (normal and female with unexplained infertility) and (iii) serum, amniotic fluid (AF) and coelomic fluid (CF) from pregnant women. AMH levels in the samples were measured by a newly developed ELISA.Result  The assay had a detection limit of < 0·078 ng/ml. High recoveries of spiked recombinant protein were observed from male and female sera and also from follicular, seminal, coelomic and amniotic fluids. The intra‐ and interassay coefficients of variation (CVs) were 3·6% and 4·0%, respectively. Serially diluted human samples gave dose–response curves parallel to the standard curve. Immunoreactivity was stable to sample storage at room temperature for several days and to multiple cycles of freezing and thawing. In seminal fluid, the AMH concentrations in a group of men with male factor infertility were insignificantly different from those in fertile men. By contrast, serum AMH concentrations were lower in the male factor infertility group than the normal group of patients. Women with unexplained infertility had similar concentrations of AMH in serum and follicular fluid compared to controls. Pregnant women had higher concentrations of AMH in the circulation in early pregnancy compared with nonpregnant women, suggesting a foeto‐placental contribution and a possible biological role for this molecule in early pregnancy.Conclusion  We have developed a sensitive and specific assay for AMH. Serum AMH in men with male factor infertility is lower than in normal men. Levels of AMH in pregnancy are higher than normal menstrual cycle levels suggesting a foeto‐placental contribution.

The mRNA expression of two activin growth factor subunits (βA- and βC-activin), activin receptor subunits (ActRIIA, ActRIIB) and the activin-binding protein follistatin, and peptide expression of βA-activin and βC-activin subunits, were examined in regenerating rat liver after partial hepatectomy (PHx). Liver samples were collected from adult, male Sprague–Dawley rats, 12–240 h (n=3–5 rats per time point) after PHx or from sham-operated controls at the same time points. Hepatocyte mitosis and apoptosis were assessed histologically and by in situ cell death detection. RT and PCR were used to assess relative gene expression. βA- and βC-activin peptide immunoreactivity was assessed in liver and serum samples by western blotting, whereas cellular expression was investigated by immunohistochemistry, using specific monoclonal antibodies. βA- and βC-activin mRNA dropped to < 50% of sham control values 12 h after PHx and remained at this level until 168 h post-PHx, when βA-activin expression increased to three times sham control values and βC-activin mRNA returned to pre-PHx levels. A peak in follistatin expression was observed 24–48 h post-PHx, coincident with an increase in hepatocyte mitosis. No changes were observed in ActRIIA mRNA, whereas ActRIIB expression paralleled that of βA-activin mRNA. βC-activin immunoreactive homo- and heterodimers were observed in regenerating liver and serum. Mitotic hepatocytes frequently contained βC-activin immunoreactivity, whereas apoptotic hepatocytes were often immunoreactive for βA-activin. We conclude that βA- and βC-activin subunit proteins are autocrine growth regulators in regenerating liver and when expressed independently lead to hepatocyte apoptosis or mitosis in a subset of hepatocytes.

Paracrine factors secreted by oocytes play a pivotal role in promoting early ovarian follicle growth and in defining a morphogenic gradient in antral

Anti‐Müllerian hormone (AMH) is a member of the transforming growth factor‐β superfamily, which plays an important role in both ovarian primordial follicle recruitment and dominant follicle selection in mice. However, the role of AMH in folliculogenesis in humans has not been investigated in detail. In the present study, AMH expression was assessed using immunohistochemistry in ovarian sections, obtained from healthy regularly cycling women. To this end, a novel monoclonal antibody to human AMH was developed. AMH expression was not observed in primordial follicles, whereas 74% of the primary follicles showed at least a weak signal in the granulosa cells. The highest level of AMH expression was present in the granulosa cells of secondary, preantral and small antral follicles ≤4 mm in diameter. In larger (4–8 mm) antral follicles, AMH expression gradually disappeared. In conclusion, in the human AMH expression follows a similar pattern as compared to the mouse and rat, suggesting an important role of AMH in folliculogenesis.

Activins are formed by dimerization of β-subunits and, as members of the TGF-β superfamily, have diverse roles as potent growth and differentiation factors. As the biological function of the activin C homodimer (βC-βC) is unknown, we sought to compare activin A (βA-βA), B (βB-βB), and C homodimer bioactivities and to investigate the consequences of activin βC-subunit overexpression in prostate tumor cells. Exogenous activin A and B homodimers inhibited cell growth and activated activin-responsive promoters. In contrast, the activin C homodimer was unable to elicit these responses. We previously showed that the activin βC-subunit heterodimerized with activin βAin vitro to form activin AC. Therefore, we hypothesize that the activin βC-subunit regulates the levels of bioactive activin A by the formation of activin AC heterodimers. To test this hypothesis, we measured activin AC heterodimer production using a novel specific two-site ELISA that we developed for this purpose. In the PC3 human prostate tumor cell line, activin βC-subunit overexpression increased activin AC heterodimer levels, concomitantly reduced activin A levels, and decreased activin signaling. Overall, these data are consistent with a role for the activin βC-subunit as a regulatory mechanism to reduce activin A secretion via intracellular heterodimerization.

The TGF beta family member growth differentiation factor-9 (GDF-9) is an oocyte-derived factor that is essential for mammalian ovarian folliculogenesis. GDF-9 mRNAs have been shown to be expressed in the human ovarian follicle from the primary follicle stage onward, and recombinant GDF-9 has been shown to promote human ovarian follicle growth in vitro. In this study with primary cultures of human granulosa-luteal (hGL) cells, we investigated whether recombinant GDF-9 activates components of the Smad signaling pathways known to be differentially activated by TGF beta and the bone morphogenetic proteins (BMPs). As with TGF beta, GDF-9 treatment caused the phosphorylation of endogenous 53-kDa proteins detected in Western blots with antiphospho-Smad2 antibodies (alpha PS2). However, unlike BMP-2, GDF-9 did not activate the phosphorylation of antiphospho-Smad1 antibody (alphaPS1)-immunoreactive proteins in hGL cells. Infection of hGL cells with an adenovirus expressing Smad2 (Ad-Smad2) confirmed that GDF-9 activates specifically phosphorylation of the Smad2 protein. Infection of hGL cells with Ad-Smad7, which expresses the inhibitory Smad7 protein, suppressed the levels of both GDF-9-induced endogenous and adenoviral alpha PS2-reactive proteins. Furthermore, GDF-9 increased the steady state levels of inhibin beta(B)-subunit mRNAs in hGL cells and strongly stimulated the secretion of dimeric inhibin B. Again, Ad-Smad7 blocked GDF-9-stimulated inhibin B production in a concentration-dependent manner. We identify here for the first time distinct molecular components of the GDF-9 signaling pathway in the human ovary. Our data suggest that GDF-9 mediates its effect through the pathway commonly activated by TGF beta and activin, but not that activated by many BMPs. The results are also consistent with the suggestion that in addition to endocrine control of inhibin production by gonadotropins, a local paracrine control of inhibin production is likely to occur via oocyte-derived factors in the human ovary.