Serum GDF9 and BMP15 as potential markers of ovarian function in women with and without polycystic ovary syndrome.

OBJECTIVE: Growth differentiation factor-9 (GDF9) and bone morphogenetic protein-15 (BMP15) are critical paracrine regulators of female fertility and are predominantly expressed by oocytes. However, it is unknown if serum concentrations reflect changes in ovarian function and/or reproductive endocrine disorders. This study aimed to determine if serum GDF9/BMP15 are associated with ovarian, pituitary, oestrogenic, androgenic and metabolic characteristics and the ovarian pathologies, polycystic ovarian morphology (PCOM) and polycystic ovary syndrome (PCOS). DESIGN: Women aged 21-45 years (n = 381) were included from a cross-sectional study at the National University Hospital, Singapore. PATIENTS: Participants were volunteers and patients with possible PCOS. MEASUREMENTS: Anthropometric measurements, transvaginal ultrasound scans and serum sampling were performed and a questionnairecompleted. Serum GDF9 and BMP15 concentrations were matched with menstrual cycle length, ovarian protein and steroid hormone production, pituitary hormone production and metabolic assessments in women with PCOM or PCOS and those with neither (control). RESULTS: Serum GDF9 and BMP15 were detectable in 40% and 41% of women, respectively and were positively correlated with each other (r = 0.08, p = 0.003). GDF9, but not BMP15, was positively correlated with ovarian volume (p = 0.02) and antral follicle count (AFC) (p = 0.004), but not with anti-Müllerian hormone (p = 0.05). However, serum GDF9 and BMP15 concentrations were not significantly different between control, PCOM and PCOS women, nor associated with androgenic or metabolic PCOS features. However, the relationship between GDF9 and AFC differed between control, PCOM and PCOS women (p = 0.02). CONCLUSIONS: Serum GDF9 and BMP15 concentrations somewhat reflect ovarian but not androgenic or metabolic characteristics of PCOS, with increased GDF9 reflecting high AFC as seen in PCOM/PCOS.

Oocyte-Secreted Serum Biomarkers GDF9 and BMP15 in Women with Endometriosis.

Oocyte-secreted growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) are critical paracrine regulators of female fertility. Recent studies demonstrated that serum concentrations are associated with the number of oocytes retrieved during IVF, and therefore potential clinical use as biomarkers. However, it is unknown if the presence of endometriosis affects serum GDF9 or BMP15. An exploratory case-control study was prospectively performed on 60 women who underwent laparoscopy between April 2017 and August 2018 at two hospitals. GDF9 and BMP15 were measured by validated immunoassays in pre-operative serum samples. Data were analysed relative to laparoscopic assessment of endometriosis and staging. There were 35 women with confirmed laparoscopic diagnosis of endometriosis and 25 controls with no evidence of endometriosis at laparoscopy. GDF9 was detectable in 40% of controls and 48% of cases. There was no difference in median GDF9 concentrations between controls (20.0 pg/ml, range 20.0-2504 pg/ml) and cases (20.0 pg/ml, range 20.0-2963 pg/ml). BMP15 was detectable in 48% of controls and 58% of cases, with no difference in median concentrations between controls (26.5 pg/ml, range 24.0-1499 pg/ml) and cases (24.0 pg/ml, range 24.0-796 pg/ml). Furthermore, there were no significant differences in the proportion of detectable samples or concentrations of GDF9 or BMP15 with differing severities of endometriosis. In conclusion, serum concentrations of oocyte-secreted factors, GDF9 and BMP15 did not differ between control patients and patients with endometriosis. For clinical application in reproductive medicine, GDF9 and BMP15 serum biomarker quantitation is unlikely to be aberrant in the presence of endometriosis.

Interactions between serum FSH, inhibin B and antral follicle count in the decline of serum AMH during the menstrual cycle in late reproductive age.

Objective: To investigate the hormonal interrelationships during the menstrual cycle in women of late reproductive age with suppressed serum AMH and antral follicle count (AFC). Methods: Serum hormones (AMH, FSH, LH, estradiol, progesterone, inhibin A, inhibin B), AFC (2-10 mm) and AMH/AFC ratio (an estimate of AMH/follicle) were assessed every 2-3 days across the menstrual cycle in 26 healthy ovulatory women aged 18-50 years. Results: An 11-fold fall in AMH/AFC was observed in women aged ≥45 years compared to those 18-45 years (P < .001). Although women ≥45 years exhibited normal menstrual cycle patterns of serum estradiol, progesterone, LH and inhibin A, FSH was elevated (P < .001) and inhibin B suppressed (P < .001) compared to the younger group. Overall FSH was inversely correlated (r = .55, P < .05) and AMH directly correlated (r = .88, P < .01) with AFC; however, these relationships were curvilinear and more pronounced when AFC was low. Inhibin B was directly linearly correlated (r = .70, P < .01) with AFC across both high and low AMH/follicle groups. Conclusions: It is hypothesized that the marked fall in AMH/follicle in late reproductive age is attributed to the change in the hormonal interplay between the pituitary and ovary. The fall in AFC leads to a decrease in inhibin B and a concomitant increase in FSH by a recognized feedback mechanism. It is postulated the elevated FSH suppresses AMH either directly or indirectly through oocyte-specific growth factors leading to a marked fall in AMH/follicle. We propose that pituitary-ovarian and intra-ovarian regulatory systems underpin the accelerated fall in AMH/follicle during the transition to menopause.

Exploratory analysis of serum concentrations of oocyte biomarkers growth differentiation factor 9 and bone morphogenetic protein 15 in ovulatory women across the menstrual cycle.

OBJECTIVE: To characterize and evaluate the variation in serum concentrations of oocyte-secreted growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) throughout the menstrual cycle in women from young to advanced reproductive ages. DESIGN: Cross-sectional, observational, and exploratory study. SETTING: Multicenter university-based clinical practices and laboratories. PATIENT(S): Serum was collected every 1-3 days throughout the menstrual cycle from 3 cohorts of healthy, ovulatory women: menses to late luteal phase (21-29 years of age; n = 16; University of Otago) and across one interovulatory interval (18-35 years of age; n = 10; and 45-50 years of age; n = 15; University of Saskatchewan). INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): To detect the changes in serum GDF9 and BMP15 across the cycle, mean concentration and variance were statistically modeled using a generalized additive model of location, shape and scale (GAMLSS). Follicle-stimulating hormone, luteinizing hormone, estradiol, progesterone, and anti-Müllerian hormone were also assessed. RESULT(S): GDF9 and BMP15 were detectable in 54% and 73% of women and varied 236-fold and 52-fold between women, respectively. Across the menstrual cycle, there were minimal changes in GDF9 or BMP15 within a woman for all cohorts, with no significant differences detected in the modeled mean concentrations. However, modeled variances were highest in the luteal phases of all women for BMP15 immediately after ovulation, regardless of age. CONCLUSION(S): Serial changes in GDF9 or BMP15 concentrations across the cycle were not statistically detected and are likewise similar across the reproductive lifespan. Further research is required to fully elucidate the utility of these oocyte biomarkers at diagnosing fertility potential and/or disease.

Serum Concentrations of Oocyte-Secreted Factors BMP15 and GDF9 During IVF and in Women With Reproductive Pathologies.

Oocyte-secreted factors bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) are critical for folliculogenesis and fertility. This study developed ELISAs for the measurement of BMP15 and GDF9 in serum and investigated their usefulness as biomarkers of female reproductive function. Serum samples were obtained from women undergoing infertility treatments (n = 154) and from perimenopausal and postmenopausal women (n = 28). Serum concentrations of BMP15 and GDF9 were analyzed in women relative to age, anti-Müllerian hormone, number of oocytes retrieved, and polycystic ovary syndrome (PCOS) after superovulation for in vitro fertilization. BMP15 and GDF9 immunoassays were validated for specificity, sensitivity (24 and 26 pg/mL, respectively), and reproducibility. BMP15 and GDF9 were detectable in 61% and 29% of women, respectively. BMP15 and GDF9 varied 64-fold and 15-fold, respectively, between women, but they did not change within subjects following ovarian stimulation with gonadotropins. Serum GDF9 concentration, but not BMP15 concentration, was associated with oocyte number retrieved in patients without PCOS (P = 0.018). GDF9 and BMP15 associations with oocyte number differed significantly (P < 0.05) with PCOS status. GDF9 concentrations were lower in poor responders (women with fewer than four oocytes retrieved or with cancelled cycles; P = 0.020). Serum BMP15, but not GDF9, was lower in women >55 years of age, compared with women of reproductive age (P < 0.01). This study develops and validates immunoassays to quantitate BMP15 and GDF9 in human serum and to correlate concentrations with female reproductive potential. Although assay sensitivities require improvement, this study demonstrates the diagnostic potential of oocyte-secreted BMP15 and GDF9 as serum biomarkers in reproductive medicine.

Cumulin and FSH Cooperate to Regulate Inhibin B and Activin B Production by Human Granulosa-Lutein Cells In Vitro.

The oocyte-secreted factors bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) interact functionally, and it is hypothesized that this interaction may be mediated by formation of a GDF9:BMP15 heterodimer termed cumulin. GDF9 and BMP15 regulate folliculogenesis and ovulation rate and have been shown to regulate inhibin and activin, local regulators of folliculogenesis. The objective of this study was to determine whether cumulin regulates granulosa cell inhibin and activin production and whether this requires cooperation with FSH. Human granulosa-lutein (hGL) cells collected from patients undergoing in vitro fertilization were cultured with or without FSH with various forms of recombinant cumulin (native and cysteine mutants, with or without the prodomains), and cysteine mutant GDF9 or BMP15. Messenger RNA expression of the subunits of inhibins/activins (INHA, INHBA, INHBB) and secretion of inhibin A, inhibin B, and activin B were measured. Mature forms and proforms of cumulin stimulated comparable INHBB mRNA expression and secretion of inhibin B and activin B, whereas GDF9 or BMP15 exhibited no effect. Cumulin, but not GDF9 or BMP15, interacted synergistically with FSH to increase INHBB mRNA and inhibin B expression. FSH markedly stimulated INHA, which encodes the α subunit of inhibin A/B, and suppressed activin B. Cumulin with or without FSH did not significantly alter inhibin A. Together these data demonstrate that cumulin, but not GDF9 or BMP15, exerts paracrine control of FSH-induced regulation of inhibin B and activin B. The prodomains of cumulin may have a minimal role in its actions on granulosa cells.

A Novel, More Efficient Approach to Generate Bioactive Inhibins.

Gonadal-derived inhibins are essential factors in mammalian reproduction, negatively regulating pituitary production of FSH. Interestingly, declines in inhibin levels across the menopause transition correlate with not only an increase in FSH but also a rapid decrease in bone mass. Therefore, inhibins have been touted as potential therapeutics for osteoporosis in postmenopausal women. However, as heterodimeric proteins of α- and ß- (ßA or ßB)-subunits, inhibins are difficult to produce recombinantly, are poorly processed to their mature bioactive forms, and their expression is always accompanied by production of activins (ß-subunit homodimers), the proteins they antagonize. In this study, we developed the methodology to circumvent most of these issues. Initially, the cleavage sites between the pro- and mature domains of the α- and ßA-subunits were modified to ensure complete processing. These modifications led to a marked increase (9-fold) in the levels of bioactive inhibin A and a striking decrease (12.5-fold) in mature activin A production. Next, a single point mutation (M418A) was incorporated into the ßA-subunit, which reduced residual activin activity approximately 100-fold and, in so doing, increased inhibin bioactivity 8-fold. Finally, we showed that inhibin A noncovalently associated with its prodomain was more potent (∼20-fold) than mature inhibin A in specific in vitro bioassays, indicating an important role of the prodomain in inhibin bioactivity. In conclusion, the production of potent inhibin analogs in the virtual absence of activin activity will greatly facilitate the investigation of the therapeutic potential of these gonadal hormones on bone and other tissues.

Inhibin Biosynthesis and Activity Are Limited by a Prodomain-Derived Peptide.

Gonadal-derived inhibin A and B are essential factors in mammalian reproduction, negatively regulating pituitary production of FSH. Inhibins are synthesized as heterodimers of α- and ß-subunits, each comprising an N-terminal pro- and C-terminal mature domain. After dimerization, the inhibin α- and ß-subunit prodomains are enzymatically cleaved from the mature domains at consensus RXXR sites (site1). Interestingly, the inhibin α-subunit is a unique TGF-ß ligand, comprising a second cleavage site (site2) within its prodomain. Cleavage at site2 in the inhibin α-subunit prodomain releases a 43-amino acid proα-peptide. We aimed to determine the influence of the proα-peptide on inhibin synthesis and bioactivity. Blocking proα-peptide release by silencing cleavage site2 (Arg56-Arg61) inhibited both inhibin A and B synthesis. Ligand blot analysis and solid-phase binding assays indicated that the proα-peptide binds specifically to a mature 30-kDa inhibin (mean Kd 86 nM) but was unable to bind related activins. The proα-peptide suppressed inhibin A and B bioactivity in primary rat pituitary cell cultures. Mechanistically, the proα-peptide blocked inhibin A binding to its coreceptor, betaglycan (IC50 131 nM), and the subsequent sequestration of the activin type II receptor (IC50 156 nM), which underscores inhibin's biological activity. Based on the sequential mutations across the inhibin α-subunit, the proα-peptide binding site was localized to residues Arg341-Thr354, corresponding directly to the betaglycan binding region. Together our findings indicate that the proα-peptide limits the synthesis and bioactivity of inhibins.

Detection of serum antimüllerian hormone in women approaching menopause using sensitive antimüllerian hormone enzyme-linked immunosorbent assays.

OBJECTIVE: Current antimüllerian hormone (AMH) immunoassays are insufficiently sensitive to detect circulating AMH levels in ovulatory women approaching menopause. The aim of this study was to detect serum AMH levels across the menstrual cycle with age, using two new AMH enzyme-linked immunosorbent assay (ELISA) kits with increased sensitivity and differing specificity. METHODS: Serum AMH levels were determined every 2 to 3 days across the interovulatory interval of menstrual cycles among women of early-mid reproductive age (18-35 y; n = 10) and late reproductive age (45-55 y; n = 17). Two highly sensitive AMH ELISAs (designated 24/32 and 24/37) with differing sensitivities were developed and applied to sera using a recombinant human pro-mature AMH preparation as reference. A third AMH ELISA (Gen II AMH ELISA kit; Beckman Coulter, Brea, CA) used was directed on mature-pro regions of AMH. RESULTS: AMH levels in all cycles were detectable with the 24/32 and 24/37 AMH ELISAs. AMH levels across the menstrual cycle were highly correlated (r = 0.98) between the 24/32 and 24/37 AMH ELISAs and the Gen II AMH ELISA (r = 0.94), but with large intracycle variations observed in older women. In late reproductive age, more than 95% of AMH values were detectable with the 24/32 and 24/37 AMH ELISAs, whereas only 36% of AMH values were detectable with the Gen II AMH ELISA. AMH levels were detected in cycles with lower antral follicle count and at a later age using the 24/32 and 24/37 AMH ELISAs compared with the Gen II AMH ELISA. AMH level correlated with antral follicle count in younger women, but not in older women. CONCLUSIONS: The new 24/32 and 24/37 AMH ELISAs have the sensitivity to monitor ovarian follicle profiles in late reproductive age.

Aberrant GDF9 expression and activation are associated with common human ovarian disorders.

CONTEXT: Growth differentiation factor 9 (GDF9) is a central regulator of folliculogenesis and ovulation rate. Fourteen mutations in human (h) GDF9 have been reported in women with premature ovarian failure or polycystic ovarian syndrome as well as in mothers of dizygotic twins, implicating GDF9 in the etiology of these conditions. We sought to determine how these mutations alter the biological activity of hGDF9. OBJECTIVE: The objective of the study was to determine whether aberrant GDF9 expression or activation is associated with common ovarian disorders. DESIGN: Homology modeling was used to predict the location of individual mutations within structurally important regions of the pro domains and mature domains of hGDF9. Each hGDF9 variant was generated by site-directed mutagenesis, expressed from human embryonic kidney 293T cells and assessed as to whether it resulted in defective production or the enhanced activation of mature hGDF9 in an in vitro granulosa cell proliferation bioassay. RESULTS: Mutations observed in mothers of dizygotic twins (P103S and P374L) completely abrogated GDF9 expression, suggesting that women heterozygous for these mutations would have a 50% reduction in GDF9 levels. Comparable declines in GDF9 in ewes result in a 2-fold increase in ovulation rate and fecundity. Remarkably, three prodomain mutations associated with premature ovarian failure (S186Y, V216M, and T238A) all resulted in the activation of hGDF9. Mechanistically, these mutations reduced the affinity of the prodomain for mature hGDF9, allowing the growth factor to more readily access its signaling receptors. CONCLUSIONS: Together these findings indicate that alterations to hGDF9 synthesis and activity can contribute to the most common ovarian pathologies.

The perimenopausal woman: endocrinology and management.

This review focuses on the endocrine and physiological features of the transition to menopause, known as the menopausal transition or the perimenopause. The updated 2011 Stages of Reproductive Aging workshop (STRAW) system is presented with a discussion of the new subdivisions within stages -3 (late reproductive age) and +1 (postmenopause) and incorporation of FSH and other biomarkers in the supportive criteria. Ovarian follicle reserve and ovarian follicle dynamics are also discussed in terms of the changes that occur with reproductive aging, and the dramatic effect these changes have on the hypothalamic-pituitary-gonadal feedback system. Topics include the disruption of normal ovulatory function and related hormone secretion patterns, abnormal uterine bleeding, and the changes that occur in bone and the cardiovascular system. The review concludes with a discussion of management strategies. This article is part of a Special Issue entitled 'Menopause'.

Use of detergent-based buffers allows detection of precursor inhibin forms in an immunoassay format.

Inhibin ELISAs are used in monitoring aspects of reproductive function, however these assays are based on the measurements of the mature 30kDa inhibin forms and not precursor forms. In conventional ELISA formats, the 105kDa unprocessed 'Pro-inhibin' forms are immunologically inactive, but the immunoactivity can be recovered in the presence of detergents. The immunoactivity of Pro-inhibin forms was assessed in the presence of a range of detergents utilising antibodies to the α-, ßA- and ßB-subunits of inhibin. In contrast to mature forms, unprocessed inhibin forms showed a 10-40 fold increase in inhibin A and total inhibin immunoactivities under optimised detergent (0.5% SDS/2% Triton X-100) conditions. The suppressed immunoactivity of the Pro-inhibin forms in these immunoassays was attributed to steric hindrance by the respective ßA- and α-subunit prodomains. This study details a detergent-based immunoassay that allows detection of previously undetectable precursor inhibin forms.

Proteomics of the human endometrium and uterine fluid: a pathway to biomarker discovery.

Failure of the endometrium to achieve receptivity results in infertility, and it is also a rate-limiting step in in vitro fertilization (IVF) success. The microenvironments provided by the endometrium during the receptive phase and that support implantation are highly complex and constantly changing as implantation progresses. Although a number of gene array studies have defined mRNA changes across the cycle, with infertility, and in IVF cycles, these have not generally been informative due in part to the subsequent regulation of transcription and posttranslational modifications of the proteins. State-of-the-art proteomic technologies now enable analysis of changes in the endometrium and its secretome related to cycle phase and associated with infertility. These techniques include two-dimensional differential in-gel electrophoresis, isobaric tags for relative and absolute quantitation, and multiplex analyses of selected panels of markers. Subsequent definition of cellular location, timing of production of identified proteins, and their regulation by steroid hormones and blastocyst-derived factors provide indications of their functions and their relationship to the establishment of pregnancy. Proteins discovered by proteomic analyses and fully evaluated will provide the differentiative profiles necessary to inform clinical practice and serve as an end point for optimizing stimulation cycles in IVF clinics as well as more clearly defining the molecular mechanisms underlying successful implantation.

Inhibins and activins in blood: predictors of female reproductive health?

Inhibins A and B are gonadal factors which are important in fertility. Their use as predictors of female reproductive health has centred on their application to ovarian cancer, Anorexia Nervosa, Down Syndrome and preeclampsia. Inhibin B also provides an index of the endocrine feedback relationship between the ovary and pituitary particularly when the ovarian follicle reserve is low. These applications are relevant in monitoring the onset of the menopause transition, ovarian recovery following chemotherapy and disturbances in pubertal development. Currently, these applications have only found widespread use in Down Syndrome and ovarian cancer. Activins, on the other hand, appear to have a limited application.

Hemochromatosis and ovarian cancer.

Evaluation of: Gannon PO, Medelci S, Le Page C et al. Impact of hemochromatosis gene (HFE) mutations on epithelial ovarian cancer risk and prognosis. Int. J. Cancer 128(10), 2326-2334 (2011). The frequency of two mutations (C282Y and D62H) of the hemochromatosis gene were investigated in women with ovarian cancer. A single allele mutation of the C282Y but not the H63D gene product was detected in 8-9% of women with benign ovarian tumors (n = 124) and ovarian cancers (n = 360) compared with 2.5% for controls (n = 80) representing a 4.9-fold increase in risk. With high-grade serous ovarian cancers (n = 179), the survival rate of women with a single allele C282Y mutation was reduced from 39 to 19 months. These results implicate mutations of the hemochromatosis gene in the generation and severity of ovarian cancers, which may have prognostic value.

Generation of a specific activin antagonist by modification of the activin A propeptide.

Elevated activin A levels in inhibin-deficient mice promote the development of gonadal tumors and induce cachexia by reducing muscle, liver, stomach, and fat mass. Because activin A is an important regulator of tissue growth, inhibiting the actions of this TGFß family ligand may halt or reverse pathology in diseased tissues. In this study, we modified the activin A propeptide to generate a specific activin antagonist. Propeptides mediate the synthesis and secretion of all TGFß ligands and, for some family members (e.g. TGFß1), bind the mature growth factor with high enough affinity to confer latency. By linking the C-terminal region of the TGFß1 propeptide to the N-terminal region of the activin A propeptide, we generated a chimeric molecule [activin/TGFß1 propeptide (AT propeptide)] with increased affinity for activin A. The AT propeptide was 30-fold more potent than the activin A propeptide at suppressing activin-induced FSH release by LßT2 pituitary gonadotrope cells. Binding of the AT propeptide to activin A shields the type II receptor binding site, thereby reducing Smad2 phosphorylation and downstream signaling. In comparison with the commonly used activin antagonists, follistatin (IC(50) 0.42 nM), soluble activin type II receptor A-Fc (IC(50) 0.47 nM), and soluble activin type II receptor B-Fc (IC(50) 0.91 nM), the AT propeptide (IC(50) 2.6 nM) was slightly less potent. However, it was more specific, inhibiting activin A and activin B (IC(50) 10.26 nM) but not the closely related ligands, myostatin and growth differentiation factor-11. As such, the AT propeptide represents the first specific activin antagonist, and it should be an effective reagent for blocking activin actions in vivo.

The synthesis and secretion of inhibins.

Inhibin A and B, dimeric glycoproteins comprising an α- and ß((A/B))-subunit, negatively regulate follicle stimulating hormone (FSH) synthesis by the pituitary. The expression of α- and ß-subunits within Sertoli cells of the testis and granulosa cells of the ovary is controlled by a range of transcription factors, including CREB, SP-1, Smads, and GATA factors. The inhibin α- and ß-subunits are synthesized as precursor molecules consisting of an N-terminal propeptide and a C-terminal mature domain. Recently, we showed that hydrophobic residues within the propeptides of the α- and ß-subunits interact noncovalently with their mature domains, maintaining the molecules in a conformation competent for dimerization. Dimeric precursors are cleaved by proprotein convertases and mature inhibins are secreted from the cell noncovalently associated with their propeptides. Propeptides may increase the half-life of inhibin A and B in circulation, but they are readily displaced in the presence of the high-affinity receptors, betaglycan, and ActRII.

Feedback regulation by inhibins A and B of the pituitary secretion of follicle-stimulating hormone.

Inhibins A and B are gonadal factors that negatively regulate FSH synthesis by the anterior pituitary. Across the menstrual cycle, women show a strong inverse correlation between circulating FSH and inhibin B, estradiol, and anti-Mullerian hormone (AMH), but not with inhibin A. Estradiol is believed to provide a tonic inhibitory effect while the inhibitory role of AMH is unknown. In human males, inhibin B is the primary testicular factor regulating FSH with limited effects by gonadal steroids. In vitro and in vivo studies in rats indicate that inhibin B is more biologically active than inhibin A but showed a lower affinity for the activin type II receptors and the co-receptor, betaglycan, suggesting an alternative mechanism. While this review reinforces the important role inhibin plays in regulating FSH, the observed differences in mode of action of inhibins A and B and their interplay with other gonadal factors are still poorly understood.

Hearing facial identities: brain correlates of face--voice integration in person identification.

Audiovisual integration (AVI) is a well-known aspect of speech perception, but integration of facial and vocal information is also important for speaker recognition. We recently demonstrated AVI in the recognition of familiar (but not unfamiliar) speakers. Specifically, systematic behavioural benefits and costs in recognizing a familiar voice occur when the voice is combined with a time-synchronised articulating face of corresponding or noncorresponding speaker identity, respectively (Schweinberger et al., 2007; Robertson and Schweinberger, 2010). Here we report an experiment assessing event-related brain potentials (ERPs) in this novel paradigm, while participants recognized familiar speakers presented in (1) Voice only, (2) voice with identity-corresponding and (3) noncorresponding time-synchronised speaking faces, as well as (4) Face only conditions. Audiovisual speaker identity correspondence influenced only later ERPs around 250-600 msec, with increased negativity for noncorresponding identities at central electrodes. Strikingly, when compared with the ERPs from both unimodal conditions, both audiovisual conditions led to a much earlier onset of frontocentral negativity, with maximal differences around 50-80 msec. Moreover, audiovisual stimuli elicited larger N170 responses than Face only stimuli. These findings suggest that the perception of a voice and a time-synchronised articulating face triggers remarkably early and mandatory mechanisms of audiovisual processing, although the correspondence or discrepancy in audiovisual speaker identity may only be computed ∼200msec later.