Functional analysis of rare anti-Müllerian hormone protein-altering variants identified in women with PCOS

Recently, rare heterozygous AMH protein-altering variants were identified in women with polycystic ovary syndrome (PCOS), causing reduced anti-Müllerian hormone (AMH) signaling. However, the exact functional mechanism remains unknown. Here, we analyzed the processing, secretion, and signaling of these AMH variants. Functional analysis of six PCOS-specific AMH variants (V12G, P151S, P270S, P352S, P362S, H506Q) and one control-specific variant (A519V) was performed in the mouse granulosa cell-line KK-1. Human (h) AMH-151S and hAMH-506Q have ∼90% decreased AMH signaling compared to wild-type (wt) AMH signaling. Coexpression of hAMH-151S or hAMH-506Q with wt-hAMH dose-dependently inhibited wt-hAMH signaling. Western blotting revealed that hAMH-151S and hAMH-506Q proteins were detected in the cell lysate but not in the supernatant. Confocal microscopy showed that HEK293 cells expressing hAMH-151S and hAMH-506Q had higher cellular AMH protein levels with endoplasmic reticulum (ER) retention compared to cells expressing wt-hAMH. Using two AMH ELISA kits, hAMH-151S was detected in the cell lysate, while only very low levels were detected in the supernatant. Both hAMH-362S and hAMH-519V were detectable using the automated AMH ELISA but showed severely reduced immunoactivity in the manual ELISA. Surprisingly, hAMH-506Q was undetectable in both the cell lysate and supernatant using either ELISA. However, in PCOS cases, heterozygous carriers of the P151S and H506Q variants still had detectable AMH in both assays. Thus, P151S and H506Q disrupt normal processing and secretion of AMH, causing ER retention. Additionally, AMH variants can impair the AMH immunoactivity. An AMH variant may be considered when serum AMH levels are relatively low in PCOS cases.

Loss of Anti-Müllerian Hormone Signaling in Mice Affects Trabecular Bone Mass in a Sex- and Age-Dependent Manner

Ovariectomy-induced osteoporosis in mice results from an abrupt loss of ovarian sex steroids. Anti-Müllerian hormone knockout (AMHKO) mice show a gradual but accelerated ovarian aging, and therefore may better resemble osteoporosis following natural menopause. To study the impact of AMH signaling deficiency on bone, we compared trabecular and cortical bone parameters in 2-, 4-, 10-, and 16-month-old male and female wild-type (WT), AMHKO, and AMH type II receptor knockout (MRKI) mice using micro computed tomography (microCT). Goldner's staining was performed to confirm the observed bone phenotype. Both male and female AMHKO and MRKI mice showed age-dependent loss of trabecular bone (P < 0.001). However, reproductive-aged female AMHKO and MRKI mice had higher BV/TV compared with WT (P < 0.001), coinciding with increased growing follicle numbers (P < 0.05) and increased estrus inhibin B levels (AMHKO: P < 0.001; MRKI: P < 0.05) but normal inhibin A, estrogen, and progesterone levels. In aged female AMHKO and MRKI mice BV/TV did not differ from WT mice due to greater trabecular bone loss between 10 and 16 months compared with WT mice. At these ages, AMHKO and MRKI mice had reduced growing follicle numbers (P < 0.05) and reduced inhibin B levels (P < 0.001). At age 10 months, female MRKI mice had increased cortical bone parameters compared with WT mice (P < 0.01). Bone parameters of male AMHKO and MRKI mice did not differ from male WT mice. In conclusion, AMH signaling deficiency results in a sex- and age-dependent effect on predominantly trabecular bone. Our results further suggest that reproductive hormones beyond estrogen may contribute to bone homeostasis.

Ghrelin deficiency sex-dependently affects food intake, locomotor activity, and adipose and hepatic gene expression in a binge-eating mouse model

Binge-eating disorder is the most prevalent eating disorder diagnosed, affecting three times more women than men. Ghrelin stimulates appetite and reward signaling, and loss of its receptor reduces binge-eating behavior in male mice. Here, we examined the influence of ghrelin itself on binge-eating behavior in both male and female mice. Five-wk-old wild-type (WT) and ghrelin-deficient (Ghrl^-/-) mice were housed individually in indirect calorimetry cages for 9 wks. Binge-like eating was induced by giving mice ad libitum chow, but time-restricted access to a Western-style diet (WD; 2 h access, 3 days/wk) in the light phase (BE); control groups received ad libitum chow (CO), or ad libitum access to both diets (CW). All groups of BE mice showed binge-eating behavior, eating up to 60% of their 24-h intake during the WD access period. Subsequent dark phase chow intake was decreased in Ghrl^-/- mice and remained decreased in Ghrl^-/- females on nonbinge days. Also, nonbinge day locomotor activity was lower in Ghrl^-/- than in WT BE females. Upon euthanasia, Ghrl^-/- BE mice weighed less and had a lower lean body mass percentage than WT BE mice. In BE and CW groups, ghrelin and sex altered the expression of genes involved in lipid processing, thermogenesis, and aging in white adipose tissue and livers. We conclude that, although ghrelin deficiency does not hamper the development of binge-like eating, it sex-dependently alters food intake timing, locomotor activity, and metabolism. These results add to the growing body of evidence that ghrelin signaling is sexually dimorphic.NEW & NOTEWORTHY Ghrelin, a peptide hormone secreted from the gut, is involved in hunger and reward signaling, which are altered in binge-eating disorder. Although sex differences have been described in both binge-eating and ghrelin signaling, this interaction has not been fully elucidated. Here, we show that ghrelin deficiency affects the behavior and metabolism of mice in a binge-like eating paradigm, and that the sex of the mice impacts the magnitude and direction of these effects.

OUP accepted manuscript

STUDY QUESTION

Do polymorphisms in the anti-Müllerian hormone (AMH) promoter have an effect on AMH levels in patients with polycystic ovary syndrome (PCOS)?

SUMMARY ANSWER

We have identified a novel AMH promoter polymorphism rs10406324 that is associated with lower serum AMH levels and is suggested to play a role in the mechanism of regulation of AMH gene expression in women.

WHAT IS KNOWN ALREADY

Follicle number is positively correlated with serum AMH levels, reflected by elevated AMH levels in women with PCOS. In addition, it is suggested that AMH production per follicle is higher in women with PCOS than in normo-ovulatory women, implying an altered regulation of AMH in PCOS.

STUDY DESIGN, SIZE, DURATION

A discovery cohort of 655 PCOS women of Northern European ancestry and both an internal and external validation PCOS cohort (n = 458 and n = 321, respectively) were included in this study. Summary-level data of an AMH genome-wide association study meta-analysis including 7049 normo-ovulatory women was included as a control cohort. A genetic approach was taken through association analysis and in silico analysis of the associated variants in the AMH promoter. In vitro analysis was performed to investigate the functional mechanisms.

PARTICIPANTS/MATERIALS, SETTING, METHODS

All common two-allelic single-nucleotide polymorphisms (SNPs) in the region Chr19:2 245 353–2 250 827 bp (Build 37) were selected for the analysis. Linear regression analyses were performed to determine the association between SNPs in the AMH promoter region and serum AMH levels. For the in silico analysis, the webtools ‘HaploReg’ v4.1 for ENCODE prediction weight matrices and ‘atSNP’ were used. In vitro analysis was performed using KK1 cells, a mouse granulosa cell line and COV434 cells, a human granulosa tumor cell line. Cells were transfected with the reference or the variant human AMH promoter reporter construct together with several transcription factors (TFs). Dual-Glo^® Luciferase Assay was performed to measure the luciferase activity.

MAIN RESULTS AND THE ROLE OF CHANCE

Polymorphism rs10406324 was significantly associated with serum AMH levels in all three PCOS cohorts. Carriers of the minor allele G had significantly lower log-transformed serum AMH levels compared to non-carriers (P = 8.58 × 10⁻⁸, P = 1.35 × 10⁻³ and P = 1.24 × 10⁻³, respectively). This result was validated in a subsequent meta-analysis (P = 3.24 × 10⁻¹²). Interestingly, rs10406324 was not associated with follicle count, nor with other clinical traits. Also, in normo-ovulatory women, the minor allele of this variant was associated with lower serum AMH levels (P = 1.04 × 10⁻⁵). These findings suggest that polymorphism rs10406324 plays a role in the regulation of AMH expression, irrespective of clinical background. In silico analysis suggested a decreased binding affinity of the TFs steroidogenenic factor 1, estrogen-related receptor alpha and glucocorticoid receptor to the minor allele G variant, however in vitro analysis did not show a difference in promoter activity between the A and G allele.

LIMITATIONS, REASONS FOR CAUTION

Functional analyses were performed in a mouse and a human granulosa cell line using an AMH promoter reporter construct. This may have limited assessment of the impact of the polymorphism on higher order chromatin structures. Human granulosa cells generated from induced pluripotent stem cells, combined with gene editing, may provide a method to elucidate the exact mechanism behind the decrease in serum AMH levels in carriers of the −210 G allele. We acknowledge that the lack of follicle number in the external validation and the control cohort is a limitation of the paper. Although we observed that the association between rs10406324 and AMH levels was independent of follicle number in our discovery and internal validation PCOS cohorts, we cannot fully rule out that the observed effects on serum AMH levels are, in part, caused by differences in follicle number.

WIDER IMPLICATIONS OF THE FINDINGS

These results suggest that variations in serum AMH levels are not only caused by differences in follicle number but also by genetic factors. Therefore, the genetic context should be taken into consideration when assessing serum AMH levels in women. This may have clinical consequences when serum AMH levels are used as a marker for the polycystic ovarian morphology phenotype.

STUDY FUNDING/COMPETING INTEREST(S)

No external funding was used. J.S.E.L. has received consultancy fees from the following companies: Ferring, Roche Diagnostics and Ansh Labs and has received travel reimbursement from Ferring. J.A.V. has received royalties from AMH assays, paid to the institute/lab with no personal financial gain. The other authors declare no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Sex and Genotype Dependent Effects of a Restricted Access Diet in Ghrelin-Deficient Mice

Ghrelin, a peptide hormone secreted by the stomach, stimulates both appetite and reward signalling. Its deletion in mice results in poor recovery from metabolic challenges, like starvation, but does not affect food intake or body weight. While sex differences in appetite and feeding behavior have been reported, little is known about the role of ghrelin herein. To investigate this, we used a metabolic cage system to continuously monitor responses of ghrelin-deficient (GKO) and wildtype (WT) mice to three different diets. Male and female mice (5 weeks old) were housed individually in a Promethion system (Sable Systems, USA) and provided one of three diets for 9 weeks: RA, continuous chow with restricted access to a Western-style diet (WD; 2h access, 3d/week) in the light phase; CA, continuous access to both diets; CC, continuous chow. Glucose tolerance was assessed at week 7 by IPGTT; food intake (kcal/g bodyweight), energy expenditure and locomotor activity at week 8; body weight and body composition (EchoMRI, USA) at week 9. On access days, RA mice ate up to 60% of their 24h intake during the WD access period. Following WD access GKO RA mice ate less chow than WT RA mice. Intriguingly, this compensatory reduction in food intake by GKO mice occurred at different times for males and females. GKO RA males ate 45% less chow in the dark phase immediately after WD access (p &lt; 0.001). In contrast, this reduction in food intake (30% less) did not occur until the following, non-access, day in GKO RA females (genotype-sex: p &lt; 0.05). Depending on diet, GKO mice showed differential regulation of energy expenditure in the light phase. Energy expenditure was 6–17% higher in GKO than WT mice in the RA group on access days and in the CA group. On non-access days, however, GKO mice in the RA group expended 13% less energy than WT RA mice (p &lt; 0.005). Regardless of diet, locomotor activity in females was greater than in males (p &lt; 0.001). However, GKO females in the RA and CC groups showed a marked 30% reduction in locomotor activity compared to WTs (genotype-sex: p &lt; 0.05). After nine weeks, neither sex nor genotype effects were seen in body weight gain and composition of RA animals. CA females gained 17% more body weight and had a 6.1% higher fat percentage than CA males (both p &lt; 0.001). In the CC group body weight gain did not differ, but GKO females had 3.1% more fat than WT females (genotype-sex: p &lt; 0.01). Glucose tolerance (AUC) was similar in all groups. In conclusion, we demonstrated that ghrelin deficiency changes the response to the three diets in a sex-dependent manner. Especially, restricted access to WD differentially affected food intake timing and locomotor activity of male and female GKO mice. These results add to the growing body of evidence that ghrelin signalling is sexually dimorphic.

Loss of anti-Müllerian hormone (AMH) immunoactivity due to a homozygous AMH gene variant rs10417628 in a woman with classical polycystic ovary syndrome (PCOS)

Anti-Müllerian hormone (AMH) is produced by granulosa cells of pre-antral and small antral ovarian follicles. In polycystic ovary syndrome (PCOS), higher levels of serum AMH are usually encountered due to the ample presence of small antral follicles and a high AMH production per follicular unit which have led to the proposal of AMH as a serum diagnostic marker for PCOS or as a surrogate for polycystic ovarian morphology (PCOM). However, heterozygous coding mutations of the AMH gene with decreased in vitro bioactivity have been described in some women with PCOS. Such mutation carriers have a trend toward reduced serum AMH levels compared to noncarriers, although both types of women with PCOS have similar circulating gonadotropin and testosterone (T) levels. This report describes a normal-weight woman with PCOS by NIH criteria with severely reduced AMH levels (index woman with PCOS). Our objective was to examine the molecular basis for her reduced serum AMH levels and to compare her endocrine characteristics to similar-weight women with PCOS and detectable AMH levels. Twenty normoandrogenic ovulatory (control) and 13 age- and BMI-matched women with PCOS (19-35 years; 19-25 kg/m2) underwent transvaginal sonography and serum hormone measures including gonadotropins, sex hormone-binding globulin, total and free T, androstenedione, dehydroepiandrosterone sulfate, estrone, estradiol and AMH. The latter was measured by ELISA (Pico-AMH: Ansh Labs, Webster, TX, USA). Women with PCOS and detectable AMH had higher serum AMH (10.82 (6.74-13.40) ng/ml, median (interquartile range)), total and free T (total T: 55.5 (49.5-62.5) ng/dl; free T: 5.65 (4.75-6.6) pg/ml) levels and greater total antral follicle count (AFC) (46 (39-59) follicles) than controls (AMH: 4.03 (2.47-6.11) ng/ml; total T: 30 (24.5-34.5) ng/dl; free T: 2.2 (1.8-2.45) pg/ml; AFC 16 (14.5-21.5) follicles, P < 0.05, all values), along with a trend toward LH hypersecretion (P = 0.06). The index woman with PCOS had severely reduced serum AMH levels (∼0.1 ng/ml), although she also had a typical NIH-defined PCOS phenotype resembling that of the other women with PCOS and elevated AMH levels. All women with PCOS, including the index woman with PCOS, exhibited LH hypersecretion, hyperandrogenism, reduced serum estrogen/androgen ratios and PCOM. A homozygous Ala515Val variant (rs10417628) in the mature region of AMH was identified in the index woman with PCOS. Recombinant hAMH-515Val displayed normal processing and bioactivity, yet had severely reduced immunoactivity when measured by the commercial pico-AMH ELISA assay by Ansh Labs. In conclusion, homozygous AMH variant rs10417628 may severely impair serum AMH immunoactivity without affecting its bioactivity or PCOS phenotypic expression. Variants in AMH can interfere with serum AMH immunoactivity without affecting the phenotype in PCOS. This observation can be accompanied by discordance between AMH immunoactivity and bioactivity.

Sex difference in the mouse BAT transcriptome reveals a role of progesterone

Brown adipose tissue (BAT) is a metabolically active organ that exhibits sex-differential features, that is, being generally more abundant and active in females than in males. Although sex steroids, particularly estrogens, have been shown to regulate BAT thermogenic function, the underlying molecular mechanisms contributing to sexual dimorphism in basal BAT activity have not been elucidated. Therefore, we assessed the transcriptome of interscapular BAT of male and female C57BL/6J mice by RNA sequencing and identified 295 genes showing ≥2-fold differential expression (adjusted P < 0.05). In silico functional annotation clustering suggested an enrichment of genes encoding proteins involved in cell-cell contact, interaction, and adhesion. Ovariectomy reduced the expression of these genes in female BAT toward a male pattern whereas orchiectomy had marginal effects on the transcriptional pattern, indicating a prominent role of female gonadal hormones in this sex-differential expression pattern. Progesterone was identified as a possible upstream regulator of the sex-differentially expressed genes. Studying the direct effects of progesterone in vitro in primary adipocytes showed that progesterone significantly altered the transcription of several of the identified genes, possibly via the glucocorticoid receptor. In conclusion, this study reveals a sexually dimorphic transcription profile in murine BAT at general housing conditions and demonstrates a role for progesterone in the regulation of the interscapular BAT transcriptome.

SUN-008 Loss of Antimullerian Hormone Immunoreactivity Due to a Homozygous AMH Gene Mutation Rs10417628 in a Woman with Classical Polycystic Ovary Syndrome

Anti-Müllerian hormone (AMH), an inhibitor of primordial/small antral follicle development and Leydig cell androgen synthesis in mice, could exaggerate the polycystic ovary syndrome (PCOS) phenotype, given reports of PCOS-specific AMH loss-of-function mutations (1–3). This report describes a normal-weight PCOS woman with severely reduced AMH levels (index PCOS woman). It examines the molecular basis for her reduced serum AMH levels and also compares her endocrine characteristics to similar-weight PCOS women with detectable AMH. Twenty normo-androgenic ovulatory (control) and 13 age- and body mass index-matched PCOS women (19–35 years; 19–25 kg/m²) underwent transvaginal sonography and serum hormone measures. Wilcoxon rank-sum test compared clinical features of control and PCOS women with detectable AMH, which were then individually ranked by magnitude in all PCOS women. DNA analysis was performed by PCR amplification with direct gene sequencing. The identified mutation was introduced in hAMH-expression plasmids for functional analysis of AMH processing in HEK293 cells by Western blot and ELISA (pico-AMH assay, Ansh Labs, Webster, TX), and for bioactivity in KK-1/AMHR2 cells using a luciferase reporter. Unpaired t-test compared AMH-induced luciferase activity between wild type and mutant AMH. A homozygous AMH gene mutation rs10417628 involving a single base pair substitution in exon 5 (NG_012190.1:g.7705C>T, p.(Ala515Val)) was identified in the index PCOS woman. PCOS women with detectable AMH had higher serum AMH (10.82 [6.74–13.40] ng/mL, Median [IQR]), total/free testosterone (T) (total T: 55.5 [49.5–62.5] ng/dL; fT: 5.65 [4.75–6.6] pg/mL) levels and greater total antral follicle numbers (AFNs) (46 [39–59] follicles) than controls (AMH: 4.03 [2.47–6.11] ng/ml; total T: 30 [24.5–34.5] ng/dL; fT: 2.2 [1.8–2.45] pg/mL; AFNs 16 [14.5–21.5] follicles, P<0.05, all values), along with a trend toward LH hypersecretion (P=0.06). The index PCOS woman with the lowest AMH levels (0.1 ng/ml) did not have the highest serum total T/fT (total T: 89 ng/dL; fT: 7 pg/mL,) or LH levels nor the greatest AFN (43 follicles). In vitro analysis of cells expressing hAMH-⁵¹⁵Val or hAMH-⁵¹⁵Ala showed that hAMH^515-Val, in contrast to hAMH^515-Ala, was undetectable and severely reduced in the pico-AMH assay in cell lysates and supernatants, respectively. AMH protein processing and AMH-induced luciferase activity, however, did not differ between hAMH⁵¹⁵Val and hAMH⁵¹⁵Ala. Thus, homozygous AMH mutation rs10417628 in a PCOS woman can impair serum AMH immunoreactivity without affecting AMH bioactivity, perhaps because of conformational changes from the mutation that only interfere with its immunodetection but not its function. References: 1. Teixeira J, et al. Endocrinology 1999;140:4732 2. Gorsic LK et al. JCEM 2019;104:2855 3. Broekmans FJ, et al. Trends Endocrinol Metab 2008;19:340

Bone morphogenetic proteins and the polycystic ovary syndrome

Background

Polycystic Ovary Syndrome (PCOS) is defined by two out of the following three criteria being met: oligo- or anovulation, hyperandrogenism, and polycystic ovaries. Affected women are often obese and insulin resistant. Although the etiology is still unknown, members of the Transforming Growth Factor β (TGFβ) family, including Bone Morphogenetic Proteins (BMPs) and anti-Müllerian hormone (AMH), have been implicated to play a role. In this pilot study we aimed to measure serum BMP levels in PCOS patients.

Methods

Twenty patients, fulfilling the definition of PCOS according to the Rotterdam Criteria, were randomly selected. Serum BMP2, -4, -6 and −7 levels were measured using commercially available BMP2, BMP4, BMP6 and BMP7 immunoassays.

Results

Serum BMP2, serum BMP4 and serum BMP6 levels were undetectable. Three patients had detectable serum BMP7 levels, albeit at the lower limit of the standard curve.

Conclusions

BMP levels were undetectable in almost all patients. This suggests that with the current sensitivity of the BMP assays, measurement of serum BMP levels is not suitable as a diagnostic tool for PCOS.

Reproductive and metabolic phenotype of a mouse model of PCOS

Polycystic ovary syndrome (PCOS), the most common endocrine disorder in women in their reproductive age, is characterized by both reproductive and metabolic features. Recent studies in human, nonhuman primates, and sheep suggest that hyperandrogenism plays an important role in the development of PCOS. We investigated whether chronic dihydrotestosterone (DHT) exposure in mice reproduces both features of PCOS. Such a model would allow us to study the mechanism of association between the reproductive and metabolic features in transgenic mice. In this study, prepubertal female mice received a 90 d continuous release pellet containing the nonaromatizable androgen DHT or vehicle. At the end of the treatment period, DHT-treated mice were in continuous anestrous, their ovaries contained an increased number of atretic follicles, with the majority of atretic antral follicles having a cyst-like structure. Chronic DHT-exposed mice had significantly higher body weights (21%) than vehicle-treated mice. In addition, fat depots of DHT-treated mice displayed an increased number of enlarged adipocytes (P < 0.003). Leptin levels were elevated (P < 0.013), adiponectin levels were diminished (P < 0.001), and DHT-treated mice were glucose intolerant (P < 0.001). In conclusion, a mouse model of PCOS has been developed showing reproductive and metabolic characteristics associated with PCOS in women.

Female mice carrying a ubiquitin promoter-Insl3 transgene have descended ovaries and inguinal hernias but normal fertility

Mouse knockout studies have indicated that Insl3 is involved in development of the gubernaculum in males, which is essential for normal testicular descent. To determine further the functions of Insl3 we have generated transgenic (TG) mice ubiquitously expressing Insl3. In these mice low levels of transgenic Insl3 mRNA are expressed in all tissues analyzed. In the TG females the ovaries descend to the base of the abdominal cavity during the fetal period, as a consequence of the formation of male-like gubernaculum structures. Furthermore, the gubernacular structures developed express androgen receptor, identically to the corresponding structures in males. At adult age the ligaments formed connect the uterine horns to the inguinal region of the abdomen. Ligaments are also formed between the lower and upper parts of the uterine horns, and these ligaments force the uterus to form a coiled structure. However, the TG females retain their reproductive functions, indicating that neither the location of the ovaries nor the macroscopic structure of the uterus is vital for reproduction. In addition, Insl3 expression causes inguinal hernia in females, suggesting that a combination of estrogen and Insl3 action disrupts proper development of the muscular and connective tissue structures of the abdomen. The lack of a phenotype in other tissues indicates that gubernaculum formation is the most sensitive biological response as regards Insl3.

Hormonal control of gubernaculum development during testis descent: gubernaculum outgrowth in vitro requires both insulin-like factor and androgen

The gubernaculum connects the gonad to the inguinoscrotal region and is involved in testis descent. It rapidly develops in the male fetus, whereas development in the female fetus is lacking. Possible factors involved in gubernaculum development are androgens, anti-Müllerian hormone (AMH), and insulin-like factor (Insl3). Sexual dimorphism in gubernaculum development correlated with the mitotic activity of cells in the gubernacular bulbs from male and female fetuses. Androgen receptor expression was restricted to the mesenchymal core of the gubernacular bulb, whereas skeletal muscle was detected in its outer layer. In an organ culture system devised to further study gubernaculum development in vitro, morphology of gubernacular explants grown in the presence of testes was comparable with that of gubernacula developed in vivo. Testicular tissue or medium containing R1881, a synthetic androgen, had a growth stimulatory effect on gubernacular explants compared with ovarian tissue or basal medium only. Moreover, Amh-/-, Amh+/-, and Insl3+/- testes stimulated the growth of gubernacular explants to the same extent as control testes. Insl3-/- testes, however, did not produce such an activity. This study reveals an essential role for both androgen and Insl3 in the gubernaculum outgrowth during transabdominal testis descent.

Involvement of insulin-like factor 3 (Insl3) in diethylstilbestrol-induced cryptorchidism

Recently, it has been shown that targeted inactivation of the Insl3 gene in male mice results in cryptorchidism. The Insl3 gene encodes insulin-like factor 3 (Insl3), which is expressed in fetal Leydig cells. The testicular factor Insl3 appears to play an important role in the transabdominal phase of testis descent, which involves development of the gubernaculum. Other studies have demonstrated that in utero exposure to diethylstilbestrol (DES), a synthetic estrogen, can lead to cryptorchidism both in humans and in animal models. The present study was undertaken to investigate whether prenatal DES-exposure might interfere with testicular Insl3 mRNA expression. Furthermore, the effect of DES on steroidogenic factor 1 (SF-1) mRNA expression level was determined, since it has been shown that SF-1 plays an essential role in transcriptional activation of the Insl3 gene promoter. Timed pregnant mice were treated with DES (100 microg/kg body weight) or vehicle alone on days E9 (gestational day 9) through E17. Control and DES-exposed mouse fetuses were collected at E16, E17 and E18, when transabdominal testis descent is taking place. Lack of gubernaculum development in DES-exposed animals was confirmed by histological analyses at E17. Expression of Insl3 and SF-1 mRNAs was studied in testes of control and DES-exposed fetuses at E16 and E18 by RNase protection assay. Prenatal DES-exposure resulted in a three-fold decrease in Insl3 mRNA expression level (P<0.005), at both E16 and E18. In contrast, DES treatment had no effect on the expression of SF-1 mRNA. These results support our hypothesis that DES may interfere with gubernaculum development by altering Insl3 mRNA expression, providing a possible mechanism by which DES may cause cryptorchidism.

Effect of prenatal exposure to diethylstilbestrol on Müllerian duct development in fetal male mice

The clinical use of diethylstilbestrol (DES) by pregnant women has resulted in an increased incidence of genital carcinoma in the daughters born from these pregnancies. Also, in the so-called DES-sons abnormalities were found, mainly, the presence of Müllerian duct remnants, which indicates that fetal exposure to DES may have an effect on male sex differentiation. Fetal regression of the Müllerian ducts is under testicular control through anti-Müllerian hormone (AMH). In male mice, treated in utero with DES, the Müllerian ducts do not regress completely, although DES-exposed testes do produce AMH. We hypothesized that incomplete regression in DES-exposed males is caused by a diminished sensitivity of the Müllerian ducts to AMH. Therefore, the effect of DES on temporal aspects of Müllerian duct regression and AMH type II receptor (AMHRII) messenger RNA (mRNA) expression in male mouse fetuses was studied. It was observed that Müllerian duct regression was incomplete at E19 (19 days post coitum), upon DES administration during pregnancy from E9 through E16. Furthermore, analysis of earlier time points of fetal development revealed that the DES treatment had clearly delayed the onset of Müllerian duct formation by approximately 2 days; in untreated fetuses, Müllerian duct formation was complete by E13, whereas fully formed Müllerian ducts were not observed in DES-treated male fetuses until E15. Using in situ hybridization, no change in the localization of AMH and AMHRII mRNA expression was observed in DES-exposed male fetuses. The mRNA expression was quantified using ribonuclease protection assay, showing an increased expression level of AMH and AMHRII mRNAs at E 13 in DES-exposed male fetuses. Furthermore, the mRNA expression levels of Hoxa 11 and steroidogenic factor-1 (SF-1) were determined as a marker for fetal development. Prenatal DES exposure had no effect on Hoxa 11 mRNA expression, indicating that DES did not exert an overall effect on the rate of fetal development. In DES-exposed male fetuses, SF-1 showed a similar increase in mRNA expression as AMH, in agreement with the observations that the AMH gene promoter requires an intact SF-1 DNA binding site for time- and cell-specific expression, although an effect of DES on SF-1 expression in other tissues, such as the adrenal and pituitary gland, cannot be excluded. However, the increased expression levels of AMH and AMHRII mRNAs do not directly explain the decreased sensitivity of the Müllerian ducts to AMH. Therefore, it is concluded that prenatal DES exposure of male mice delays the onset of Müllerian duct development, which may result in an asynchrony in the timing of Müllerian duct formation, with respect to the critical period of Müllerian duct regression, leading to persistence of Müllerian duct remnants in male mice.

Androgen action during male sex differentiation includes suppression of cranial suspensory ligament development

The cranial suspensory ligament is located on the border of the cranial (mesonephric) mesentery in adult female mammals, which runs between the cranial pole of the internal genitalia and the dorsal abdominal wall. Absence of the cranial suspensory ligament in male mammals depends upon exposure of its primordium to fetal testicular androgens and is a prerequisite for testis descent. Female rats were exposed to 5alpha-dihydrotestosterone propionate at different stages of genital development, and cranial suspensory ligament development was studied in neonatal and in adult animals. Androgens suppressed cranial suspensory ligament development when exposure started during the early stages of genital development, until day 19 postconception (pc). Androgen receptor expression was immunohistochemically detected in the cranial mesentery of both sexes from day 16 pc onwards. A decrease of androgen receptor expression in female fetuses from day 18 pc onwards coincided with the appearance of a differentiated cranial suspensory ligament, as evidenced by the expression of two cell differentiation markers: alpha-smooth muscle (alpha-SM) actin and desmin. alpha-SM actin was located on the outer border of the cranial mesentery of both sexes at day 17 pc, and expression increased only in female fetuses. On day 19 pc, desmin expression was also detectable in the a-SM actin-positive cells. Proliferation and apoptosis indices of cells in the cranial mesentery, as analysed by 5'-bromodeoxyuridine incorporation and by detection of DNA strand breaks (TUNEL method) respectively, did not show any difference between the sexes, neither on day 17 nor on day 18 pc. Since primordial cells of the cranial suspensory ligament highly express the androgen receptor during the period of gestation when androgens can suppress cranial suspensory development, altered morphogenesis of these cells may be a direct consequence of androgen action.

Inhibin interferes with activin signaling at the level of the activin receptor complex in Chinese hamster ovary cells

To gain more insight in the mechanism of action of inhibin, we studied the effect of inhibin on activin signaling in Chinese hamster ovary cells. Inhibin specifically counteracted activin-induced expression of a plasminogen activator inhibitor 1 promoter element (3TP) and of the junB gene, but was ineffective when the responses were induced by transforming growth factor-beta. This indicates that inhibin acts only on the activin-specific part of these signaling cascades. Using a constitutively active activin type IB receptor we determined whether inhibin acted at the level of the activin-receptor complex or downstream of it. The mutant activin receptor stimulated the expression of the 3TP promoter in the absence of activin. This stimulation was insensitive to inhibin, indicating that inhibin acts exclusively at or upstream of this activin type I receptor. In addition, competition studies using labeled activin showed that inhibin displaced activin from the activin type II receptors, especially from the activin type IIB receptor, but not from the type I receptors. In conclusion, these data show that in Chinese hamster ovary cells inhibin acts directly at the activin receptor complex, most likely through displacement of activin from the activin type II receptor.

Structure and chromosomal localization of the human anti-müllerian hormone type II receptor gene

Using the rat anti-müllerian hormone type II receptor (AMHRII) cDNA as a probe, two overlapping lambda phage clones containing the AMHRII gene were isolated from a human genomic library. Sequence analysis of the exons was performed and the exon/intron boundaries were determined. The coding region was found to consist of 11 exons, divided over 8 kb. The genomic structure resembles that of the related activin type II receptor gene. The AMHRII gene was mapped to human chromosome 12q12-q13. The results reported are essential for identification of AMHRII gene alterations in patients with persistent müllerian duct syndrome.