Overexpression of mouse follistatin causes reproductive defects in transgenic mice

Activin C antagonizes activin A in vitro and overexpression leads to pathologies in vivo

Activin A is a potent growth and differentiation factor whose synthesis and bioactivity are tightly regulated. Both follistatin binding and inhibin subunit heterodimerization block access to the activin receptor and/or receptor activation. We postulated that the activin-beta(C) subunit provides another mechanism regulating activin bioactivity. To test our hypothesis, we examined the biological effects of activin C and produced mice that overexpress activin-beta(C). Activin C reduced activin A bioactivity in vitro; in LNCaP cells, activin C abrogated both activin A-induced Smad signaling and growth inhibition, and in LbetaT2 cells, activin C antagonized activin A-mediated activity of an follicle-stimulating hormone-beta promoter. Transgenic mice that overexpress activin-betaC exhibited disease in testis, liver, and prostate. Male infertility was caused by both reduced sperm production and impaired sperm motility. The livers of the transgenic mice were enlarged because of an imbalance between hepatocyte proliferation and apoptosis. Transgenic prostates showed evidence of hypertrophy and epithelial cell hyperplasia. Additionally, there was decreased evidence of nuclear Smad-2 localization in the testis, liver, and prostate, indicating that overexpression of activin-beta(C) antagonized Smad signaling in vivo. Underlying the significance of these findings, human testis, liver, and prostate cancers expressed increased activin-betaC immunoreactivity. This study provides evidence that activin-beta(C) is an antagonist of activin A and supplies an impetus to examine its role in development and disease.

Changes in ovarian follistatin levels during the oestrous cycle in sheep may serve as an intraovarian regulator

The expression and concentration of follistatin and activin change during oestrous cycle suggesting their involvement in the regulation of follicular development. The aim of this study was to determine the level, source and potential role of follistatin in the sheep ovary. Follistatin in ovarian venous blood, measured by radioimmunoassay, remained at its low level from follicular phase (day -1 and 0) to mid-luteal phase (days 11-13) phase but were significantly elevated during the late luteal phase (days 14 and 15) when corpora lutea underwent regression. Western blot analyses of follicular fluid at day 15 of the cycle showed two strong bands at 42 and 45 kDa and weakly stained bands at 39 and 31 kDa. At day 0, these bands became weaker and the 39 kDa band became undetectable. However, there were no differences in follistatin concentrations between ovaries with and without functional corpus luteum (CL) during the whole luteal phase. In addition, although the ovaries of Booroola ewes normally contain more corpora lutea than those of normal merino ewes, follistatin concentrations in both jugular and ovarian venous blood were similar in Booroola and normal merino ewes. It is concluded that the secretion of follistatin from the ovary is not related to the formation of CL or high ovulation rate of Booroola ewes. The elevation in follistatin concentration in follicular fluid and ovarian blood during late luteal phase may indicate a dual role of follistatin in the luteolysis of existing CL and development of new follicle cohort.

Differential antagonism of activin, myostatin and growth and differentiation factor 11 by wild-type and mutant follistatin

Follistatin binds and neutralizes members of the TGFbeta superfamily including activin, myostatin, and growth and differentiation factor 11 (GDF11). Crystal structure analysis of the follistatin-activin complex revealed extensive contacts between follistatin domain (FSD)-2 and activin that was critical for the high-affinity interaction. However, it remained unknown whether follistatin residues involved with myostatin and GDF11 binding were distinct from those involved with activin binding. If so, this would allow development of myostatin antagonists that would not inhibit activin actions, a desirable feature for development of myostatin antagonists for treatment of muscle-wasting disorders. We tested this hypothesis with our panel of point and domain swapping follistatin mutants using competitive binding analyses and in vitro bioassays. Our results demonstrate that activin binding and neutralization are mediated primarily by FSD2, whereas myostatin binding is more dependent on FSD1, such that deletion of FSD2 or adding an extra FSD1 in place of FSD2 creates myostatin antagonists with vastly reduced activin antagonism. However, these mutants also bind GDF11, indicating that further analysis is required for creation of myostatin antagonists that will not affect GDF11 activity that could potentially elicit GDF11-induced side effects in vivo.

Activin in the brain modulates anxiety-related behavior and adult neurogenesis

Activin, a member of the transforming growth factor-beta superfamily, is an endocrine hormone that regulates differentiation and proliferation of a wide variety of cells. In the brain, activin protects neurons from ischemic damage. In this study, we demonstrate that activin modulates anxiety-related behavior by analyzing ACM4 and FSM transgenic mice in which activin and follistatin (which antagonizes the activin signal), respectively, were overexpressed in a forebrain-specific manner under the control of the alphaCaMKII promoter. Behavioral analyses revealed that FSM mice exhibited enhanced anxiety compared to wild-type littermates, while ACM4 mice showed reduced anxiety. Importantly, survival of newly formed neurons in the subgranular zone of adult hippocampus was significantly decreased in FSM mice, which was partially rescued in ACM4/FSM double transgenic mice. Our findings demonstrate that the level of activin in the adult brain bi-directionally influences anxiety-related behavior. These results further suggest that decreases in postnatal neurogenesis caused by activin inhibition affect an anxiety-related behavior in adulthood. Activin and its signaling pathway may represent novel therapeutic targets for anxiety disorder as well as ischemic brain injury.

Fetal and early postnatal environmental exposures and reproductive health effects in the female

This short review presents current research into the role of the environment in normal female reproductive function and pathogenesis, specifically focusing on the ovary and uterus.

Cytokine knockouts in reproduction: the use of gene ablation to dissect roles of cytokines in reproductive biology

Cytokines play many diverse and important roles in reproductive biology, and dissecting the complex interactions between these proteins and the different reproductive organs is a difficult task. One approach is to use gene ablation, or 'knockout', to analyse the effect of deletion of a single cytokine on mouse reproductive function. This review summarizes the essential roles of cytokines in reproductive biology that have been revealed by gene knockout studies, including development and regulation of the hypothalamo-pituitary-gondal axis, ovarian folliculogenesis, implantation and immune system modulation during pregnancy. However, successful utilization of this approach must consider the caveats associated with gene ablation studies, e.g. embryonic lethality, systemic effects of cytokine ablation on local reproductive processes and the limited exposure to pathogens in mice housed in laboratory conditions. New sophisticated technology that temporally or spatially regulates gene ablation can overcome some of these limitations. Discoveries on the roles of cytokines in reproductive function uncovered by gene ablation studies can now be applied to improve in vitro fertilization for infertile couples and in the development of contraceptive therapies.

The adrenal and polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is one of the most common endocrine disorders characterized by androgen excess, oligo-ovulation and polycystic ovaries. Although ovaries are the main source of increased androgens in the syndrome, between 20 and 30% of patients with PCOS have adrenal androgen (AA) excess, detectable primarily by elevated dehydroepiandrosterone sulfate (DHEAS) levels. Patients with PCOS demonstrate a generalized hypersecretion of adrenocortical products, basally and in response to ACTH stimulation. The mechanisms of these abnormalities are unclear although AA excess in PCOS is likely a complex trait, modulated by both intrinsic and acquired factors. To date, no specific genetic defects have been identified. The production of AAs in response to ACTH appears to be closely related to altered factors regulating glucose-mediated glucose disposal, increased peripheral metabolism of cortisol, and to a less extent to the effects of extra-adrenal androgens, insulin resistance, hyperinsulinemia or obesity. Finally, DHEAS levels and the response of AAs to ACTH are relatively constant over time and are closely correlated between PCOS patients and their siblings suggesting that this abnormality is an inherited trait in PCOS.

Transgenic expression of a myostatin inhibitor derived from follistatin increases skeletal muscle mass and ameliorates dystrophic pathology in mdx mice

Myostatin is a potent negative regulator of skeletal muscle growth. Therefore, myostatin inhibition offers a novel therapeutic strategy for muscular dystrophy by restoring skeletal muscle mass and suppressing the progression of muscle degeneration. The known myostatin inhibitors include myostatin propeptide, follistatin, follistatin-related proteins, and myostatin antibodies. Although follistatin shows potent myostatin-inhibiting activities, it also acts as an efficient inhibitor of activins. Because activins are involved in multiple functions in various organs, their blockade by follistatin would affect multiple tissues other than skeletal muscles. In the present study, we report the characterization of a myostatin inhibitor derived from follistatin, which does not affect activin signaling. The dissociation constants (K(d)) of follistatin to activin and myostatin are 1.72 nM and 12.3 nM, respectively. By contrast, the dissociation constants (K(d)) of a follistatin-derived myostatin inhibitor, designated FS I-I, to activin and myostatin are 64.3 microM and 46.8 nM, respectively. Transgenic mice expressing FS I-I, under the control of a skeletal muscle-specific promoter showed increased skeletal muscle mass and strength. Hyperplasia and hypertrophy were both observed. We crossed FS I-I transgenic mice with mdx mice, a model for Duchenne muscular dystrophy. Notably, the skeletal muscles in the mdx/FS I-I mice showed enlargement and reduced cell infiltration. Muscle strength is also recovered in the mdx/FS I-I mice. These results indicate that myostatin blockade by FS I-I has a therapeutic potential for muscular dystrophy.

Neonatal exposure to estrogens suppresses activin expression and signaling in the mouse ovary

In the ovary, the steroid hormone estrogen and the TGF-beta superfamily member activin are both produced by granulosa cells and they both have intraovarian functions. Emerging evidence has indicated an interaction of these two signaling pathways. Based on the fact that estrogen and activin can impact early follicle formation and development, we hypothesize that estrogen treatment may alter activin signaling in the neonatal ovary. Therefore, this study was designed to examine the effect of neonatal diethylstilbestrol (DES) and estradiol (E(2)) exposure on the mRNA and protein levels of the key factors involved in activin signaling in the mouse ovary. CD-1 mouse pups were given daily injections of DES, E(2), or oil on postnatal d 1-5, and ovaries and sera were collected on d 19. Neonatal DES or E(2) exposure decreased the number of small antral follicles, induced multioocytic follicle formation, and decreased activin beta-subunit mRNA and protein levels. Consistent with local loss of beta-subunit expression, the phosphorylation of Smad 2, a marker of activin-dependent signaling, was decreased in the estrogen-treated ovaries. The decreased beta-subunit expression resulted in a decrease in serum inhibin levels, with a corresponding increase in FSH. Estrogen also suppressed activin subunit gene promoter activities, suggesting a direct transcriptional effect. Overall, this study demonstrates that activin subunits are targets of estrogen action in the early mouse ovary.

The activin A-follistatin system: potent regulator of human extracellular matrix mineralization

Bone quality is an important determinant of osteoporosis, and proper osteoblast differentiation plays an important role in the control and maintenance of bone quality. We investigated the impact of activin signaling on human osteoblast differentiation, extracellular matrix formation, and mineralization. Activins belong to the transforming growth factor-beta superfamily and activin A treatment strongly inhibited mineralization in osteoblast cultures, whereas the activin antagonist follistatin increased mineralization. Osteoblasts produced activin A and follistatin in a differentiation-dependent manner, leading to autocrine regulation of extracellular matrix formation and mineralization. In addition, mineralization in a vascular smooth muscle cell-based model for pathological calcification was inhibited. Comparative activin A and follistatin gene expression profiling showed that activin signaling changes the expression of a specific range of extracellular matrix proteins prior to the onset of mineralization, leading to a matrix composition with reduced or no mineralizing capacity. These findings demonstrate the regulation of osteoblast differentiation and matrix mineralization by the activin A-follistatin system, providing the possibility to control bone quality as well as pathological calcifications such as atherosclerosis by using activin A, follistatin, or analogs thereof.

Polymorphism of the follistatin gene in polycystic ovary syndrome

Follistatin has been reported as a candidate gene for polycystic ovary syndrome (PCOS) from linkage and association studies. Acting to regulate the development of ovarian follicles and as an antagonist to aromatase activity, alterations in follistatin function or expression may result in key features of PCOS such as reduced serum FSH, impaired ovarian follicle development and augmented ovarian androgen production. We investigated polymorphisms in the FST gene to determine if genetic variation is associated with susceptibility to PCOS or key phenotypic features of PCOS patients in a case-control association study. One hundred and seventy-three PCOS patients of Caucasian descent (mean age 30.0 +/- 4.8 years), conforming to the NIH diagnostic criteria, were recruited from a clinical practice database and 107 normal ovulating women (mean age 38.8 +/- 13.4 years) were recruited from the general community as control subjects. Morphometric data, biochemistry and genomic DNA were collected from study subjects and genotyping was performed on seven Single nucleotide polymorphisms (SNPs) in the FST gene region. Allele frequencies of the SNPs were rs1423560 G/C (0.99/0.01), rs3797297 C/A (0.80/0.20), rs11745088 C/G (0.98/0.02), rs3203788 A/T (0.98/0.02) and rs1062809 G/C (1.00/-), rs1127760 A/T (0.98/0.02) and rs1127761 A/T (0.98/0.02), and these were not significantly different between the PCOS and control groups (P < 0.05). Statistical analysis revealed significant associations between the SNP rs3797297 and sex hormone-binding globulin (P = 0.04) and free androgen index (FAI) (P < 0.01). We conclude that FST is not a susceptibility locus for PCOS; however, the SNP rs3797297 from FST gene was associated with androgenic markers for PCOS and may be of importance in the hyperandrogenaemia of the disease.

Determination and stability of sex

How is the embryonic bipotential gonad regulated to produce either an ovary or a testis? In males, transient early activation of the Y chromosome Sry gene makes both germ cells and soma male. However, in females, available evidence suggests that the process of ovary sex determination may take place independently in the germline and somatic lineages. In addition, in contrast to testis, in ovary somatic cells, female-to-male gonadal sex reversal can occur at times throughout ovary development and maturation. We suggest that a single gene pathway, likely hinging on the Foxl2 transcription factor, both initiates and maintains sex differentiation in somatic cells of the mammalian ovary.

Activin modulates the transcriptional response of LbetaT2 cells to gonadotropin-releasing hormone and alters cellular proliferation

Both GnRH and activin are crucial for the correct function of pituitary gonadotrope cells. GnRH regulates LH and FSH synthesis and secretion and gonadotrope proliferation, whereas activin is essential for expression of FSH. Little is known, however, about the interplay of signaling downstream of these two hormones. In this study, we undertook expression profiling to determine how activin pretreatment alters the transcriptional response of LbetaT2 gonadotrope cells to GnRH stimulation. Activin treatment alone altered the transcriptional profile of 303 genes including inducing that of the 17beta-hydroxysteroid dehydrogenase B1 gene that converts estrone to 17beta-estradiol, altering the sensitivity of the cells to estrone. Furthermore, activin had a dramatic effect on the response of LbetaT2 cells to GnRH. Hierarchical clustering of 2453 GnRH-responsive genes identified groups of genes the response of which to GnRH was either enhanced or blunted after activin treatment. Mapping of these genes to gene ontology classifications or signaling pathways highlighted significant differences in the classes of altered genes. In the presence of activin, GnRH regulates genes in pathways controlling cell energetics, cytoskeletal rearrangements, organelle organization, and mitosis in the absence of activin, but genes controlling protein processing, cell differentiation, and secretion. Therefore, we demonstrated that activin enhanced GnRH induction of p38MAPK activity, caused GnRH-dependent phosphorylation of p53, and reduced the ability of GnRH to cause G1 arrest. Thus, although activin alone changes a modest number of transcripts, activin pretreatment dramatically alters the response to GnRH from an antiproliferative response to a more differentiated, synthetic response appropriate for a secretory cell.

Transforming growth factor beta1 regulates follistatin mRNA expression during in vitro bovine granulosa cell differentiation

In order to test the hypothesis that transforming growth factor beta (TGF-beta) acts by FS regulation on bovine granulosa cells in in vitro differentiation, we analyzed the effect of TGF-beta1 on follistatin mRNA expression in three differentiation states of bovine granulosa cells. We showed a positive regulation of FS mRNA after TGF-beta1 (1 ng/ml) treatment of freshly isolated granulosa cells from small-medium antral follicles (2-8 mm). This effect was abolished by the addition of exogenous follistatin (100 ng/ml), suggesting that this effect could be mediated by activin. Although these cells showed a similar effect on FS mRNA expression after treatment with activin-A, a soluble form of activin receptor type IIA was unable to inactivate the TGF-beta effect. When we tested the TGF-beta effect on FS mRNA in different granulosa cell states, TGF-beta1 regulation was associated with progesterone production only in freshly isolated cells. The amount of total activin-A produced by first passage cells (dedifferentiated cells), was ten times smaller than the one measured in a conditioned medium from freshly isolated cells (mature cells). The TGF-beta1-dependent FS mRNA expression persisted in first passage cells without changes with FS addition. On the other hand, the BGC-1 granulosa cell line (immature cells) produced large amounts of activin-A regulated by TGF-beta1 and an invariable steady state of FS mRNAs. In summary, our results showed that FS mRNA expression is regulated by TGF-beta1 independently of activin effects in differentiated granulosa cells.

Ovarian follicle development and transgenic mouse models

Ovarian follicle development is a complex process that begins with the establishment of what is thought to be a finite pool of primordial follicles and culminates in either the atretic degradation of the follicle or the release of a mature oocyte for fertilization. This review highlights the many advances made in understanding these events using transgenic mouse models. Specifically, this review describes the ovarian phenotypes of mice with genetic mutations that affect ovarian differentiation, primordial follicle formation, follicular growth, atresia, ovulation and corpus luteum (CL) formation. In addition, this review describes the phenotypes of mice with mutations in a variety of genes, which affect the hormones that regulate folliculogenesis. Because studies using transgenic animals have revealed a variety of reproductive abnormalities that resemble many reproductive disorders in women, it is likely that studies using transgenic mouse models will impact our understanding of ovarian function and fertility in women.

Contribution of Germ Cells to the Differentiation and Maturation of the Ovary: Insights from Models of Germ Cell Depletion

In mammals, the role played by germ cells in ovarian differentiation and folliculogenesis has been the focus of an increasing number of studies over the last decades. From these studies, it has emerged that bidirectional communication between germ cells and surrounding companion cells is required as soon as the initial assembly of follicles. Models of germ cell depletion that arise from both spontaneous and experimentally induced mutations as well as irradiation or chemical treatments have been helpful in deciphering the role played by germ cells from the onset of ovarian differentiation onward. This review reports current knowledge and proposes novel hypotheses that can be formulated from these models about the contribution of germ cells to ovarian differentiation and folliculogenesis. In particular, it promotes the idea that the influence of germ cells on companion somatic cells varies within both ovarian differentiation and folliculogenesis.

Sexually dimorphic regulation of inhibin beta B in establishing gonadal vasculature in mice

Sexually dimorphic differentiation of gonads is accomplished through balanced interactions between positive and negative regulators. One of the earliest features of gonadal differentiation is the divergent patterning of the vasculature. A male-specific coelomic vessel develops on the anterior to posterior of the XY gonad, whereas this vessel is absent in XX gonads. It is postulated that the testis-determining gene Sry controls formation of the coelomic vessel, but the exact molecular mechanism remains unknown. Here we reveal a novel role for inhibin beta B in establishing sex-specific gonad vasculature. In the testis, inhibin beta B contributes to proper formation of the coelomic vessel, a male-specific artery critical for testis development and, later in development, hormone transportation. On the other hand, in the ovary, inhibin beta B is repressed by WNT4 and its downstream target follistatin, leading to the absence of the coelomic vessel. When either Wnt4 or follistatin was inactivated, the coelomic vessel appeared ectopically in the XX ovary. However, when inhibin beta B was also removed in either the Wnt4-null or follistatin-null background, normal ovarian development was restored and no coelomic vessel was found. Our results indicate that the sex-specific formation of the coelomic vessel is established by positive components in the testis as well as an antagonizing pathway from the ovary. Inhibin beta B is strategically positioned at the intersection of these opposing pathways.

The mouse forkhead gene Foxc1 is required for primordial germ cell migration and antral follicle development

Foxc1 encodes a forkhead/winged helix transcription factor expressed in many embryonic tissues. Previous studies have investigated defects in the urogenital system of Foxc1 null mutants, but the mechanisms underlying the abnormal development of the gonad have not been explored. From earliest stages, the mutant ovaries are smaller than normal, with fewer germ cells and disorganized somatic issue. No bursa membrane is formed, and the oviduct remains uncoiled. Although germ cells are specified correctly, many of them do not migrate to the gonadal ridge, remaining trapped in the hindgut. Consequently, the number initially reaching the gonad is less than 25% of normal. Once in the ovary, germ cells proliferate normally, but the supporting somatic cells are not organized correctly. Since mutant embryos die at birth, further development was followed in ovaries grafted underneath the kidney capsule of ovariectomized females. Transplanted ovaries display normal folliculogenesis up to preantral stages. However, no follicles develop beyond early antral stages. Mutant follicles are often polyovulatory and have disrupted theca and granulosa cell layers. We conclude that alongside its previously known roles in kidney, cardiovascular and eye development, Foxc1 has essential functions during at least two stages of gonad development-germ cell migration and folliculogenesis.

Cytokines, chemokines and growth factors in endometrium related to implantation

The complexity of the events of embryo implantation and placentation is exemplified by the number and range of cytokines with demonstrated roles in these processes. Disturbance of the normal expression or action of these cytokines results in complete or partial failure of implantation and abnormal placental formation in mice or humans. Of known importance are members of the gp130 family such as interleukin-11 (IL-11) and leukaemia inhibitory factor (LIF), the transforming growth factor beta (TGFbeta) superfamily including the activins, the colony-stimulating factors (CSF), the IL-1 system and IL-15 system. New data are also emerging for roles for a number of chemokines (chemoattractive cytokines) both in recruiting specific cohorts of leukocytes to implantation sites and in trophoblast differentiation and trafficking. This review focuses on those cytokines and chemokines whose expression pattern in the human endometrium is consistent with a potential role in implantation and placentation and for which some relevant actions are known. It examines what is known of their regulation and action along with alterations in clinically relevant situations.

Identification of downregulated messenger RNAs in bovine granulosa cells of dominant follicles following stimulation with human chorionic gonadotropin

Molecular determinants and mechanisms involved in ovarian follicular growth, ovulation, and luteinization are not well understood. The objective of this study was to identify genes expressed in bovine granulosa cells (GC) of dominant follicles (DF) and downregulated after hCG-induced ovulation, using the suppression subtractive hybridization (SSH). GC were collected from DF at Day 5 of the estrous cycle and from ovulatory follicles (OF) obtained 23 h following injection of hCG. A subtracted cDNA library (DF-OF) was generated and screened using unsubtracted (DF, OF) and subtracted (DF-OF, OF-DF) cDNAs as complex (32)P-probes. A total of 32 nonredundant cDNAs were identified: 23 cDNAs matched with sequences of known biological function and 9 cDNAs with complete or partial sequences of undefined biological function. Detection of genes known to be downregulated during the periovulatory period in the bovine species, such as CPD, CYP11A1, CYP19A1, FSHR, LRP8/ ApoER2, and SERPINE2, validated the physiological model and analytical techniques used. For a subset of genes, such as ARFGAP3, CYP11A1, CYP19A1, FSHR, FST, GJA1, IDH3, INHBA, LHCGR, LHCGR lacking exon 10, PRC1, PRG1, RPA2, SCD, and TRIB2, gene expression profiles were compared by virtual Northern blot or reverse transcriptase-polymerase chain reaction from follicles obtained at different developmental stages. Results confirmed a downregulation of the respective mRNAs in GC of OF compared with that of DF. We conclude that we have identified novel genes that are downregulated by hCG in bovine GC of DF during the periovulatory period, which may contribute to follicular growth, ovulation, and/or luteinization.

The molecular-genetic basis of functional hyperandrogenism and the polycystic ovary syndrome

The genetic mechanisms underlying functional hyperandrogenism and the polycystic ovary syndrome (PCOS) remain largely unknown. Given the large number of genetic variants found in association with these disorders, the emerging picture is that of a complex multigenic trait in which environmental influences play an important role in the expression of the hyperandrogenic phenotype. Among others, genomic variants in genes related to the regulation of androgen biosynthesis and function, insulin resistance, and the metabolic syndrome, and proinflammatory genotypes may be involved in the genetic predisposition to functional hyperandrogenism and PCOS. The elucidation of the molecular genetic basis of these disorders has been burdened by the heterogeneity in the diagnostic criteria used to define PCOS, the limited sample size of the studies conducted to date, and the lack of precision in the identification of ethnic and environmental factors that trigger the development of hyperandrogenic disorders. Progress in this area requires adequately sized multicenter collaborative studies after standardization of the diagnostic criteria used to classify hyperandrogenic patients, in whom modifying environmental factors such as ethnicity, diet, and lifestyle are identified with precision. In addition to classic molecular genetic techniques such as linkage analysis in the form of a whole-genome scan and large case-control studies, promising genomic and proteomic approaches will be paramount to our understanding of the pathogenesis of functional hyperandrogenism and PCOS, allowing a more precise prevention, diagnosis, and treatment of these prevalent disorders.

Changes in circulating and testicular levels of inhibin A and B and activin A during postnatal development in the rat

This study describes the testicular levels of inhibin/activin subunits by Northern analysis and in situ hybridization and serum and testicular levels of inhibins A and B and activin A by enzyme linked immunosorbent assays (ELISA) during postnatal development in the rat. We show that serum inhibin A levels are less than 4 pg/ml throughout postnatal life. Serum inhibin B levels peak at 572 +/- 119 pg/ml (mean +/- se) at d 40 post partum (pp) before falling to 182 +/- 35 pg/ml in mature males. Serum activin A decreases from 294 +/- 29 pg/ml at d 6 to 132 +/- 27 pg/ml at maturity. Within the testis, inhibin A levels fall from 0.330 +/- 0.108 ng/g at d 15 to less than 0.004 ng/g at maturity. Inhibin B levels peak at 43.9 +/- 4.2 ng/g at d 6 before falling to 1.6 +/- 0.13 ng/g at maturity. Testicular activin A levels fall from 18.6 +/- 2.2 ng/g at d 6 to 0.094 +/- 0.013 ng/g at maturity. Northern profiles of testicular inhibin/activin subunits correlate with immunoreactive levels demonstrated by ELISA. In situ hybridization suggests that beta(A) and beta(B) subunit expression is largely restricted to the seminiferous tubule, particularly Sertoli cells, spermatogonia, and primary spermatocytes. These data support the view that inhibin B is the major inhibin in the male rat and that levels relate to Sertoli cell number and activity. Furthermore, the demonstration of high local concentrations of activin A during the period of Sertoli cell proliferation and the onset of spermatogenesis support its proposed role because a modulator of testicular development and function.

The bone morphogenetic protein system in mammalian reproduction

Using molecular, cellular, and genetic approaches, recent studies examining the role of the bone morphogenetic protein (BMP) family of growth factors in the reproductive system have led to significant breakthroughs in our understanding of mammalian reproduction and fertility. Gene expression studies have revealed that key components of the BMP system (ligands, receptors, signaling molecules, and binding proteins) exhibit coordinated spatial and temporal expression patterns in fundamental cell types throughout the reproductive system. Availability of recombinant BMPs has enabled functional studies that have demonstrated important biological activities of BMPs in controlling cellular proliferation, differentiation, and apoptosis in reproductive tissues. The physiological importance of the BMP system for mammalian reproduction has been further highlighted by the elucidation of the aberrant reproductive phenotypes of animals with naturally occurring mutations or targeted deletions of certain BMP family genes. Collectively, these studies have established the concept that the BMP system plays a crucial role in fertility in female and male mammals. The purpose of this article is to review the evidence underpinning the importance of the BMP system in mammalian reproduction.

Stage-specific and tissue-specific expression characteristics of differentially expressed genes during mouse spermatogenesis

Spermatogenesis occurs in successive mitotic, meiotic, and post-meiotic phase, and involves a number of unique processes including meiosis and dramatic morphological changes. The unique differentiation mechanisms of spermatogenesis suggest the existence of germ-cell-specific molecules. The most straight forward strategy to elucidate differentiation mechanisms is to identify and characterize differentiation-specific molecules and their associated genes in germ cells. However, only a few genes specifically involved in spermatogenesis have been studied. In the present study, six different types of spermatogenic cells (primitive type A spermatogonia, type B spermatogonia, preleptotene spermatocytes, pachytene spermatocytes, round spermatids, and elongating spermatids) were isolated from Balb/c mice testes using velocity sedimentation and Atlas cDNA arrays containing 1,176 known mouse genes were used to determine the gene expression profiles of the spermatogenic cells. The expression of 260 genes were detected in six different stages of spermatogenic cells and a number of genes showed differential expression. The 23 differentially expressed genes were further analysed by reverse transcription polymerase chain reaction (RT-PCR) for their stage-specific and tissue-specific expression characteristics. Based on the results of RT-PCR, six genes highly express in both primitive type A and type B spermatogonia, four genes up-regulate in type B spermatogonia, two genes up-regulate in spermatocytes, two genes up-regulate in spermatids, three genes express constantly from primitive A spermatogonia to elongating spermatids, two genes express constantly from primitive A spermatogonia to round spermatids, two genes do not change in their expression during spermatogenesis, two genes can be detected highly in adult testis, but are undetectable in spermatogenic cells. The tissue-specific expression characteristics of the 23 genes showed that some of them specifically expressed in testes or other tissues. These data provide new information for further studies into spermatogenesis-related genes and may lead to the identification of genes with potential relevance to the differentiation of spermatogenic cells. In addition, some of these genes could be considered to be used as the molecular markers for different stages of spermatogenic cells.

Granulosa cell-specific inactivation of follistatin causes female fertility defects

Follistatin plays an important role in female physiology by regulating FSH levels through blocking activin actions. Failure to regulate FSH has been implicated as a potential cause of premature ovarian failure. Premature ovarian failure is characterized by amenorrhea, infertility, and elevated gonadotropin levels in women under the age of 40. Because follistatin is essential for postnatal viability, we designed a cre/loxP conditional knockout system to render the follistatin gene null specifically in the granulosa cells of the postnatal ovary using Amhr2cre transgenic mice. The follistatin conditional knockout females develop fertility defects, including reduced litter number and litter sizes and, in the most severe case, infertility. Reduced numbers of ovarian follicles, ovulation and fertilization defects, elevated levels of serum FSH and LH, and reduced levels of testosterone were observed in these mice. These findings demonstrate that compromising granulosa cell follistatin function leads to findings similar to those characterized in premature ovarian failure. Follistatin conditional knockouts may therefore be a useful model with which to further study this human syndrome. These studies are the first report of a granulosa cell-specific deletion of a gene in the postnatal ovary and have important implications for future endeavors to generate ovary-specific knockout mouse models.

Adenovirus-mediated overexpression of follistatin enlarges intact liver of adult rats

Under normal physiologic conditions, liver size is under strict regulatory control. Activin, a member of the transforming growth factor beta (TGF-beta) superfamily, is expressed in the intact adult liver and is an inhibitor of hepatocyte growth. However, the exact role played by endogenous activin in maintaining the size of a normal adult liver has yet to be completely examined in vivo. Here, we report the development of an adenoviral vector (AdexCAFS288) that expressed human follistatin-288, which binds to activin and neutralizes its biologic activities. AdexCAGFP, a control virus, expressed green fluorescent protein. AdexCAFS288 effectively expressed follistatin-288, as measured both in HepG2 cell lysate and conditioned medium and blocked activin signaling and its biologic functions in vitro. Intraperitoneal injection of AdexCAFS288 in vivo resulted in significant liver growth (146% of control) in intact liver of adult male rats 12 days following treatment without significant dysfunctions. The increase in liver size was attributed to increased hepatocyte proliferation, as monitored by the mitotic index. Furthermore, there was a significant correlation between serum follistatin levels and liver weight. In conclusion, our results suggest that activin plays a critical role in maintaining optimal liver size and implicates the endogenous activin system as a therapeutic target in the treatment of liver disease.

Hypogonadotropic hypogonadism due to loss of function of the KiSS1-derived peptide receptor GPR54

Hypogonadotropic hypogonadism is defined as a deficiency of the pituitary secretion of follicle-stimulating hormone and luteinizing hormone, which results in the impairment of pubertal maturation and of reproductive function. In the absence of pituitary or hypothalamic anatomical lesions and of anosmia (Kallmann syndrome), hypogonadotropic hypogonadism is referred to as isolated hypogonadotropic hypogonadism (IHH). A limited number of IHH cases are due to loss-of-function mutations of the gonadotropin-releasing hormone receptor. To identify additional gene defects leading to IHH, a large consanguineous family with five affected siblings and with a normal gonadotropin-releasing hormone receptor coding sequence was studied. Homozygosity whole-genome mapping allowed the localization of a new locus within the short arm of chromosome 19 (19p13). Sequencing of several genes localized within this region showed that all affected siblings of the family carried a homozygous deletion of 155 nucleotides in the GPR54 gene. This deletion encompassed the splicing acceptor site of intron 4-exon 5 junction and part of exon 5. The deletion was absent or present on only one allele in unaffected family members. GPR54 has been initially identified as an orphan G protein-coupled receptor with 40% homology to galanin receptors. Recently, a 54-aa peptide derived from the KiSS1 protein was identified as a ligand of GPR54. The present study shows that loss of function of GPR54 is a cause of IHH, and it identifies GPR54 and possibly KiSS1 protein-derived peptide as playing a major and previously unsuspected role in the physiology of the gonadotropic axis.

Overexpression of human chorionic gonadotropin causes multiple reproductive defects in transgenic mice

Human CG is a pregnancy marker secreted by the placenta, and it utilizes the same receptors as does LH. Human CG is a heterodimer, and its subunits are expressed in tissues other than placenta. Similarly, LH/hCG receptors are also expressed in multiple tissues; however, the physiological significance of this expression is unknown. Free hCGbeta is efficiently secreted in vitro in transfected cells and is highly expressed in many human cancers; however, the biological effects of free hCGbeta in vivo are unknown. To study in vivo consequences of elevated levels of free hCGbeta and hCG dimer in both male and female reproductive physiology, we used mouse metallothionein 1 promoter to generate multiple lines of transgenic mice that overexpressed either one or both subunits of hCG. Although mice expressing the glycoprotein hormone alpha subunit are normal and fertile, both male and female transgenic mice overexpressing only the hormone-specific hCGbeta subunit are infertile. The hCGbeta subunit-expressing transgenic female mice progressively develop cystic ovaries, whereas the male transgenic mice are infertile but otherwise are not phenotypically discernible. In contrast, both the male and female transgenic mice coexpressing high levels of the hCG subunits (i.e., the hCG dimer) demonstrate multiple reproductive defects. The male transgenic mice have Leydig cell hyperplasia, very high levels of serum testosterone, reduced testis size, and dramatically enlarged seminal vesicles and are infertile and display overly aggressive behavior when caged with females. The female transgenic mice are also infertile, have elevated levels of serum estradiol, and progressively develop hemorrhagic and cystic ovaries with thecal layer enlargement and stromal cell proliferation and degenerating kidneys. These results suggest that the in vivo biological effects of ectopically expressed free hCGbeta subunit are distinct from those of the hCG dimer and are gender specific. These transgenic mice are useful models for studying the biology of free hCGbeta subunit, for further analyzing the gain of function effects of hCG during early Leydig cell development, and for studying the roles of hCG in ovarian and kidney pathophysiology and function.

Control of pelage hair follicle development and cycling by complex interactions between follistatin and activin

Members of the transforming growth factor beta/bone morphogenetic protein (TGF-beta/BMP) family are involved in the control of hair follicle (HF) morphogenesis and cycling. The activities of several members of this family activins and BMP-2, -4, -7, and -11) are controlled by antagonists such as follistatin. Because follistatin-deficient mice show abnormalities in vibrissae development, we explored the role of follistatin and activin in pelage HF development and cycling. We show here that during HF development follistatin mRNA was prominently expressed by hair matrix and outer root sheath keratinocytes as well as by interfollicular epidermal cells, whereas activin betaA mRNA was mainly expressed in dermal papilla cells. Compared with age-matched wild-type controls, both follistatin knockout mice and activin betaA transgenic mice showed a significant retardation of HF morphogenesis. Treatment of wild-type embryonic skin explants with follistatin protein stimulated HF development. This effect was inhibited by addition of recombinant activin A protein. Activin betaA transgenic mice demonstrated retardation of catagen entry, down-regulation of BMP-2, and up-regulation of expression of its antagonist matrix GLA protein. These observations suggest that follistatin and activin interaction plays an important role in both HF development and cycling, possibly in part by regulating expression of BMP-2 and its antagonist.

The spatiotemporal expression pattern of the bone morphogenetic protein family in rat ovary cell types during the estrous cycle

In the mammalian ovary, great interest in the expression and function of the bone morphogenetic protein (BMP) family has been recently generated from evidence of their critical role in determining folliculogenesis and female fertility. Despite extensive work, there is a need to understand the cellular sites of expression of these important regulatory molecules, and how their gene expression changes within the basic ovary cell types through the cycle. Here we have performed a detailed in situ hybridization analysis of the spatial and temporal expression patterns of the BMP ligands (BMP-2, -3, -3b, -4, -6, -7, -15), receptors (BMPR-IA, -IB, -II), and BMP antagonist, follistatin, in rat ovaries over the normal estrous cycle. We have found that: i) all of the mRNAs are expressed in a cell-specific manner in the major classes of ovary cell types (oocyte, granulosa, theca interstitial, theca externa, corpora lutea, secondary interstitial, vascular and ovary surface epithelium); and ii) most undergo dynamic changes during follicular and corpora luteal morphogenesis and histogenesis. The general principle to emerge from these studies is that the developmental programs of folliculogenesis (recruitment, selection, atresia), ovulation, and luteogenesis (luteinization, luteolysis) are accompanied by rather dramatic spatial and temporal changes in the expression patterns of these BMP genes. These results lead us to hypothesize previously unanticipated roles for the BMP family in determining fundamental developmental events that ensure the proper timing and developmental events required for the generation of the estrous cycle.

Genetic engineering to study testicular tumorigenesis

In humans, Sertoli cell tumors account for approximately 4% of all testicular tumors, and 20% of these are malignant. The mechanisms underlying Sertoli cell tumorigenesis remain largely unknown. Using gene knockout technology, we previously generated mutant mice lacking the alpha subunit of inhibin dimers. The inhibin alpha-null male mice develop testicular Sertoli cell tumors with 100% penetrance. These tumors develop as early as 4 weeks of age and cause a cachexia-like wasting syndrome. Castrated inhibin alpha knockout mice develop sex steroidogenic adrenal cortical tumors. These studies have identified inhibins as secreted tumor suppressors with specificity for the gonads and adrenal glands. It had been suggested that endocrine factors play roles in Sertoli cell tumorigenesis by altering cell cycle machinery of the Sertoli cells. To test the potential of these factors to function as modifiers of Sertoli cell tumorigenesis, we have employed a genetic intercross strategy, breeding inhibin a mutant mice with mutant mice deficient in endocrine signaling factors including gonadotropin releasing hormone (hypogonadal, hpg mice), follicle stimulating hormone, anti-Miillerian hormone (AMH), activin receptor type II, or androgen receptor (testicular feminization, tfm mice), or mice overexpressing follistatin. We are also investigating the effects of loss of critical cell cycle regulators, such as cyclin dependent kinase inhibitor p27, on Sertoli cell tumorigenesis in inhibin alpha knockout males. These studies clearly demonstrate the roles of these factors as modifiers of the Sertoli cell tumorigenesis. Activin signaling through activin receptor type II is responsible for the cachexia-like syndrome observed in the inhibin a knockout mice with tumors. The gonadotropin hormones are essential for testicular tumor development, but elevated FSH levels are not sufficient to cause Sertoli cell tumors. Absence of FSH, lack of androgen receptor, or overexpression of follistatin slows the tumor growth and minimizes the cachexia symptoms, thus prolonging the life span of these double mutant mice. In contrast, absence of AMH or p27 causes earlier onset and more aggressive development of testicular tumor, with an earlier death of double mutant mice. We are currently investigating roles of estrogen signaling pathways, and other cell cycle regulators, in tumor development in the inhibin alpha knockout mice by generating mice with double or triple mutations. Genetic engineering in mouse models provides a powerful tool to study the mechanisms of testicular tumorigenesis and define the important genetic modifiers in vivo.

Genetic analysis of the mammalian transforming growth factor-beta superfamily

Members of the TGF-beta superfamily, which includes TGF-betas, growth differentiation factors, bone morphogenetic proteins, activins, inhibins, and glial cell line-derived neurotrophic factor, are synthesized as prepropeptide precursors and then processed and secreted as homodimers or heterodimers. Most ligands of the family signal through transmembrane serine/threonine kinase receptors and SMAD proteins to regulate cellular functions. Many studies have reported the characterization of knockout and knock-in transgenic mice as well as humans or other mammals with naturally occurring genetic mutations in superfamily members or their regulatory proteins. These investigations have revealed that TGF-beta superfamily ligands, receptors, SMADs, and upstream and downstream regulators function in diverse developmental and physiological pathways. This review attempts to collate and integrate the extensive body of in vivo mammalian studies produced over the last decade.

Extracellular regulation of BMP signaling in vertebrates: a cocktail of modulators

The transforming growth factor-beta (TGF-beta) superfamily contains a variety of growth factors which all share common sequence elements and structural motifs. These proteins are known to exert a wide spectrum of biological responses on a large variety of cell types in both vertebrates and invertebrates. Many of them have important functions during embryonic development in pattern formation and tissue specification, and in adult tissues, they are involved in processes such as wound healing, bone repair, and bone remodeling. The family is divided into two general branches: the BMP/GDF and the TGF-beta/Activin/Nodal branches, whose members have diverse, often complementary effects. It is obvious that an orchestered regulation of different actions of these proteins is necessary for proper functioning. The TGF-beta family members act by binding extracellularly to a complex of serine/threonine kinase receptors, which consequently activate Smad molecules by phosphorylation. These Smads translocate to the nucleus, where they modulate transcription of specific genes. Three levels by which this signaling pathway is regulated could be distinguished. First, a control mechanism exists in the intracellular space, where inhibitory Smads and Smurfs prevent further signaling and activation of target genes. Second, at the membrane site, the pseudoreceptor BAMBI/Nma is able to inhibit further signaling within the cells. Finally, a range of extracellular mediators are identified which modulate the functioning of members of the TGF-beta superfamily. Here, we review the insights in the extracellular regulation of members of the BMP subfamily of secreted growth factors with a major emphasis on vertebrate BMP modulation.

Smad4 overexpression causes germ cell ablation and leydig cell hyperplasia in transgenic mice

Members of the transforming growth factor-beta (TGF-beta) superfamily play a variety of important roles in testicular development and function. The tumor suppressor gene, Smad4, is a common mediator of TGF-beta, activin, and bone morphogenetic protein-mediated signaling pathways. To investigate the role of the Smad4 gene during testicular development and function, transgenic mice were generated using a Flag-tagged Smad4 gene driven by 180-bp fragment of the Mullerian inhibiting substance upstream promoter sequence. Three Smad4 transgenic founders (A, B, and G) were detected by Southern blot analysis; line B showed the highest expression of the Smad4 transgene and was further studied. The fertility in F1 generation (B) and F2 generation (BB) of the Smad4 transgenic mice was not impaired. However, in the F3 generation (B2x) all animals were impacted by the overexpression of the Smad4 transgene and two kinds of phenotypes were observed. In one group animals were completely infertile, while in the other group animals were fertile and sired the normal number of pups/litter. These groups are designated as infertile and fertile in the text. Histological evaluation of the testes from the infertile group showed variable degrees of Leydig cell hyperplasia, apoptosis of germ cells, spermatogenic arrest, seminiferous tubule degeneration, and infertility. In the fertile group, there was no apparent change in the histology of the testis except for a slight increase in the number of Leydig cells. Serum follicle-stimulating hormone levels in the adult animals of both groups of Smad4 transgenic male mice were not significantly different from normal littermates; however, testosterone levels in both groups were significantly (P < 0.05) increased. These results suggest that overexpression of Smad4 leads to testicular abnormalities and infertility supporting the hypothesis that the TGF-beta signaling pathways are carefully orchestrated during testicular development. In the absence of normal levels of Smad4 testicular function is compromised.

Activins, inhibins, and follistatins: from endocrinology to signaling. A paradigm for the new millennium

It has been 70 years since the name inhibin was used to describe a gonadal factor that negatively regulated pituitary hormone secretion. The majority of this period was required to achieve purification and definitive characterization of inhibin, an event closely followed by identification and characterization of activin and follistatin (FS). In contrast, the last 15-20 years saw a virtual explosion of information regarding the biochemistry, physiology, and biosynthesis of these proteins, as well as identification of activin receptors, and a unique mechanism for FS action-the nearly irreversible binding and neutralization of activin. Many of these discoveries have been previously summarized; therefore, this review will cover the period from the mid 1990s to present, with particular emphasis on emerging themes and recent advances. As the field has matured, recent efforts have focused more on human studies, so the endocrinology of inhibin, activin, and FS in the human is summarized first. Another area receiving significant recent attention is local actions of activin and its regulation by both FS and inhibin. Because activin and FS are produced in many tissues, we chose to focus on a few particular examples with the most extensive experimental support, the pituitary and the developing follicle, although nonreproductive actions of activin and FS are also discussed. At the cellular level, it now seems that activin acts largely as an autocrine and/or paracrine growth factor, similar to other members of the transforming growh factor beta superfamily. As we discuss in the next section, its actions are regulated extracellularly by both inhibin and FS. In the final section, intracellular mediators and modulators of activin signaling are reviewed in detail. Many of these are shared with other transforming growh factor beta superfamily members as well as unrelated molecules, and in a number of cases, their physiological relevance to activin signal propagation remains to be elucidated. Nevertheless, taken together, recent findings suggest that it may be more appropriate to consider a new paradigm for inhibin, activin, and FS in which activin signaling is regulated extracellularly by both inhibin and FS whereas a number of intracellular proteins act to modulate cellular responses to these activin signals. It is therefore the balance between activin and all of its modulators, rather than the actions of any one component, that determines the final biological outcome. As technology and model systems become more sophisticated in the next few years, it should become possible to test this concept directly to more clearly define the role of activin, inhibin, and FS in reproductive physiology.

Overexpression of Smad7 results in severe pathological alterations in multiple epithelial tissues

Biochemical studies have shown that Smad7 blocks signal transduction of transforming growth factor beta (TGFbeta); however, its in vivo functions are largely unknown. To determine the functions of Smad7, we have expressed Smad7 in transgenic mice, utilizing a keratin K5 promoter (K5.Smad7). K5.Smad7 mice exhibited pathological changes in multiple tissues and died within 10 days after birth. These mice were born with open eyelids and corneal defects, significantly delayed and aberrant hair follicle morphogenesis, and hyperproliferation in the epidermis and other stratified epithelia. Furthermore, K5.Smad7 mice developed severe thymic atrophy and massive thymocyte death, suggesting that Smad signaling in thymic epithelia is essential for thymocyte survival. Interestingly, in addition to a reduction in Smad phosphorylation, the protein levels of the receptors for TGFbeta, activin and bone morphogenetic protein were significantly decreased in the affected tissues of K5.Smad7 mice. Our study provides evidence that Smad7 is a potent in vivo inhibitor for signal transduction of the TGFbeta superfamily during development and maintenance of homeostasis of multiple epithelial tissues.

Genomic organization and promoter analysis of mouse follistatin-related gene (FLRG)

Follistatin (FS) is well characterized as an activin-binding protein. Recently, a novel follistatin-like protein called follistatin-related gene (FLRG) that has a similar domain organization to that of follistatin has been identified. Like follistatins, FLRG binds activins and bone morphogenetic proteins (BMPs). To study the regulation of FLRG expression, we have analyzed the genomic organization and promoter of the mouse FLRG gene. The mouse FLRG gene consists of five exons, and each encodes discrete functional regions. The overall genomic structure of FLRG is similar to that of FS except that the FLRG gene is missing one exon that codes a third FS domain found in FS. The promoter that covers 2.5 kbp and is linked to a luciferase reporter construct is active in human cervical carcinoma HeLa cells as well as in human embryonic kidney (HEK293) cells. Deletion analysis of the promoter regions indicates that a proximal 550 base pairs are enough for basal FLRG promoter activity in the cell lines. FLRG promoter activity is significantly augmented by phorbol 12-myristate 13-acetate (PMA) treatment, but not by cAMP stimulation. By contrast, FS promoter is activatable either by cAMP or PMA. Thus, although FS and FLRG are structurally and functionally related, their modes of regulation by external stimuli are different.

Effect of adenovirus-mediated overexpression of follistatin and extracellular domain of activin receptor type II on gonadotropin secretion in vitro and in vivo

Activins are dimeric proteins that stimulate the synthesis and secretion of pituitary FSH by interacting with two classes of receptors, type I and type II, to initiate their intracellular signaling cascade. The extracellular domain of type II activin receptor (ActRII-ECD) contains all structural determinants sufficient for high affinity ligand binding. A soluble recombinant ActRII-ECD has been reported to attenuate FSH secretion from cultured rat anterior pituitary cells in response to exogenous activin A or endogenous activin B. Follistatin is a binding protein that acts as an extracellular factor to bind and inactivate activin. We constructed adenoviral vectors able to mediate expression of follistatin 288 (AdexCAFS288) and ActRII-ECD (AdexCAECD) and tested their biological activities both in vitro and in vivo. The data show that adenovirus-mediated overexpression of either ActRII-ECD or follistatin was able to attenuate FSH secretion by cultured rat anterior pituitary cells. However, AdexCAFS288 overexpression of follistatin was more effective than adenovirus-mediated overexpression of ActRII-ECD. In vivo, a single ip injection of AdexCAFS288 induced the expression of high levels of follistatin and resulted in the suppression of serum FSH levels in castrated male rats for up to 12 d postinjection. Infection with AdexCAFS288 had no effect on LH secretion in vitro or in vivo, demonstrating its selectivity. In conclusion, the results demonstrate the effectiveness of adenovirus-mediated overexpression of follistatin and ActRII-ECD to regulate FSH secretion and the potential of using this strategy as a tool to further define the critical role of activin/inhibin/follistatin circuitry in the modulation of the reproductive system.

Follistatin inhibits the function of the oocyte-derived factor BMP-15

Recent studies have highlighted the importance of a novel oocyte-derived growth factor, bone morphogenetic protein-15 (BMP-15) in the regulation of proliferation and differentiation of granulosa cells in the ovary. Namely, BMP-15 stimulates granulosa cell mitosis and inhibits follicle-stimulating hormone (FSH) receptor mRNA expression in granulosa cell, thereby playing a critical role in the elaborate mechanism controlling ovarian folliculogenesis. At present, however, nothing is known about molecules which may regulate the biological activity of BMP-15. Here we demonstrate evidence that follistatin can form an inactive complex with BMP-15, through which follistatin inhibits BMP-15 bioactivities. The binding of follistatin to BMP-15 was directly demonstrated by a surface plasmon resonance biosensor, and the ability of follistatin to inhibit BMP-15 functions was determined by established BMP-15 bioassays using primary rat granulosa cells. Specifically, follistatin attenuated BMP-15 stimulation of granulosa cell proliferation and reversed BMP-15 inhibition of FSH receptor mRNA expression leading to the suppression of FSH-induced progesterone synthesis. This is the first demonstration of the biochemical interaction and biological antagonism of follistatin and BMP-15, which may be involved in the complex yet well-controlled mechanism of the regulation of follicle growth and development.

Mutant laboratory mice with abnormalities in hair follicle morphogenesis, cycling, and/or structure: annotated tables

Numerous transgenic, targeted mutagenesis (so-called knockouts), conditional (so-called "gene switch") and spontaneous mutant mice develop abnormal hair phenotypes. The number of mice that exhibit such abnormalities is increasing exponentially as genetic engineering methods become routine. Since defined abnormalities in hair follicle morphogenesis, cycling and/or structure in such mutant mice provide important clues to the as yet poorly understood functional roles of many gene products, it is useful to summarize and classify these mutant mice according to their hair phenotype. This review provides a corresponding, annotated table of mutant mice with hair abnormalities, classifying the latter into 6 categories, 1) abnormally low number of hair follicles, 2) disorders of hair morphogenesis, 3) of hair follicle cycling, 4) of hair follicle structure 5) of sebaceous gland structure, and 6) hair growth disorders as a consequence of immunological abnormalities. This annotated table should serve as a useful source of reference for anyone who is interested in the molecular controls of hair growth, for investigators who are looking for mouse models to explore or compare the functional activities of their gene of interest, and for comparing the hair phenotype of newly generated mouse mutants with existing ones.

Follistatin and activin A serum concentrations in obese and non-obese patients with polycystic ovary syndrome

BACKGROUND

Activin promotes ovarian follicular development, inhibits androgen production and increases FSH and insulin secretion. Follistatin, an activin-binding protein, neutralizes activin bioactivity. Therefore, a decrease in the ratio of activin/follistatin might encourage characteristic features of polycystic ovary syndrome (PCOS). We investigated whether women with PCOS showed disordered follistatin and/or activin serum concentrations.

METHODS

The study group included 24 obese and 20 non-obese (body mass index vertical line and <27 kg/m2 respectively) clomiphene-failure PCOS patients. The control group included 16 obese and 46 non-obese patients with normal ovulatory cycles. Blood samples were obtained from the patients on day 3-5 of a progesterone-induced or spontaneous cycle and were assayed for LH, FSH, testosterone, 17-hydroxy-progesterone, androstenedione, follistatin, activin A, fasting glucose and insulin.

RESULTS

Follistatin concentrations were comparable between obese and non-obese PCOS patients (mean +/- SE; 1171 +/- 103 and 1045 +/- 159 pg/ml respectively) and significantly higher than their respective controls (628 +/- 61 and 592 +/- 49 pg/ml, P < 0.0001 and P < 0.02 respectively). Activin A concentrations were comparable between the four groups (590 +/- 35, 513 +/- 74, 661 +/- 87 and 595 +/- 43 pg/ml in obese and non-obese PCOS and controls respectively). Stepwise regression analyses for relationships between follistatin or activin A levels and all other variables indicated that follistatin was significantly and independently positively affected by PCOS (P < 0.0001), age (P < 0.02), androstenedione (P < 0.03) and weight (P < 0.05). Activin A was significantly and independently negatively affected by PCOS (P < 0.003) and FSH (P < 0.03), and positively affected by weight (P < 0.009) and androstenedione (P < 0.02).

CONCLUSIONS

Serum follistatin is increased in PCOS patients, regardless of obesity. PCOS is the most significant variable that relates to high follistatin and low activin A serum concentration. A high follistatin/activin ratio could well contribute to the pathophysiology of PCOS.

Impaired wound healing in transgenic mice overexpressing the activin antagonist follistatin in the epidermis

Recently, we demonstrated a strong upregulation of activin expression after skin injury. Furthermore, overexpression of this transforming growth factor beta family member in the skin of transgenic mice caused dermal fibrosis, epidermal hyperthickening and enhanced wound repair. However, the role of endogenous activin in wound healing has not been determined. To address this question we overexpressed the soluble activin antagonist follistatin in the epidermis of transgenic mice. These animals were born with open eyes, and the adult mice had larger ears, longer tails and reduced body weight compared with non-transgenic littermates. Their skin was characterized by a mild dermal and epidermal atrophy. After injury, a severe delay in wound healing was observed. In particular, granulation tissue formation was significantly reduced, leading to a major reduction in wound breaking strength. The wounds, however, finally healed, and the resulting scar area was smaller than in control animals. These results implicate an important function of endogenous activin in the control of wound repair and scar formation.

Intracellular and extracellular control of activin function by novel regulatory molecules

Activin signal transduction is regulated through multiple mechanisms. We have identified novel regulatory proteins that control activin functions either intracellularly or extracellularly. As intracellular molecules, PSD-95/Dlg/ZO-1 (PDZ) proteins that specifically associate with activin type II receptors (ActRIIs) were identified. We have named the molecules as activin receptor-interacting proteins (ARIPs). ARIP1 has two WW domains and five PDZ domains, associates not only with ActRIIs but also with Smads, and controls activin functions intracellularly in neuronal cells. Another ARIP we have found has only one PDZ domain, and is likely to be involved in intracellular trafficking and sorting of activin receptor complexes in the cell. As an extracellular regulatory protein, we have identified a novel follistatin-like protein, named follistatin-related gene (FLRG). Like follistatins, FLRG binds activins and bone morphogenetic proteins (BMPs) and controls their functions extracellularly. The mode of association of follistatin and FLRG with activins and their expression patterns are different, suggesting the distinct functions of follistatin and FLRG in vivo.

Circulating follistatin concentrations are higher and activin concentrations are lower in polycystic ovarian syndrome

Familial polycystic ovarian syndrome (PCOS) has been proposed to be linked to a site near the follistatin gene. We studied the concentrations of circulating follistatin, activin A and inhibin B in well-characterized subjects with PCOS (n = 108) and controls without PCOS (n = 20). Mean (+/- SEM) concentrations of follistatin were higher (P < 0.05) in PCOS (0.27 +/- 0.03 ng/ml) than controls (0.15 +/- 0.02 ng/ml) and activin A were lower (P < 0.05) in PCOS (0.20 +/- 0.01ng/ml) than controls (0.24 +/- 0.02 ng/ml). Inhibin B concentrations were not different between the two groups: PCOS (0.06 +/- 0.01ng/ml), and controls (0.06 +/- 0.01ng/ml). It is proposed that higher concentrations of follistatin with lower concentrations of activin A may relate to follicular development not proceeding beyond 8-10 mm and may be partly responsible for the lack of pre-ovular follicle development in PCOS.

Actions of activins, inhibins and follistatins: implications in anterior pituitary function

1. The anterior pituitary is well documented to be under the control of central and peripheral factors that dynamically interact to affect cell-specific modulation of pituitary functions. However, it is becoming increasingly evident that these extrinsic factors work in concert with a variety of local products that exert autocrine/paracrine control on pituitary cells. 2. These factors modulate the activity of their target pituitary cells by altering the synthesis and secretion of cell-specific hormones and by exerting control on the growth and differentiation of cells of this tissue. Included in the list of growth factors and bioactive peptides known to be products of pituitary cells are the activins, possibly inhibins and follistatins. 3. These protein factors play an important role in the local modulation of several pituitary cell types and are crucial for the maintenance of normal follicle-stimulating hormone production and, thus, reproductive function and fertility.

Identification and characterization of a novel follistatin-like protein as a binding protein for the TGF-beta family

Follistatin is an activin-binding protein that prevents activin from binding to its receptors and neutralizes its activity. Follistatin also binds bone morphogenetic proteins (BMPs). In this study, we report the identification of a novel follistatin-like protein from mouse. The mouse cDNA encodes a 256-residue precursor and most likely a mouse homologue of human FLRG, which was found at the breakpoint of the chromosomal rearrangement in a B-cell line. Whereas follistatin has three follistatin domains, which are presumed to be growth factor binding motifs, FLRG possesses only two follistatin domains. Northern blotting revealed that mRNAs for FLRG were abundantly expressed in heart, lung, kidney, and testis in mouse. The recombinant mouse FLRG proteins were found to have binding activity for both activin and bone morphogenetic protein-2. Like follistatin, FLRG has higher affinity for activin than for BMP-2. The FLRG protein inhibited activin-induced and BMP-2-induced transcriptional responses in a dose-dependent manner. Glutathione S-transferase fusion proteins encoding various regions of FLRG were produced and studied. Ligand blotting using (125)I-activin revealed that the COOH-terminal region containing the second follistatin domain was able to bind activin. Our finding implies that cellular signaling by activin and BMPs is tightly regulated by multiple members of the follistatin family.

Association of AccI polymorphism in the follicle-stimulating hormone beta gene with polycystic ovary syndrome

OBJECTIVE

To search for FSH beta-subunit gene mutations in patients with polycystic ovary syndrome (PCOS) and determine the association between the mutations and the syndrome.

DESIGN

Clinical and molecular studies.

SETTING

Clinics and laboratories of the National University Hospital Obstetrics and Gynecology Department in Singapore.

PATIENT(S)

One hundred thirty-five patients with PCOS and 105 normal control subjects.

INTERVENTION(S)

Exons two and three were screened for mutations by single-stranded conformational polymorphism and DNA sequencing.

MAIN OUTCOME MEASURE(S)

Polymerase chain reaction followed by restriction enzyme analysis.

RESULT(S)

No missense mutation was found in the functional units of the FSHbeta gene in patients with PCOS, but a thymine-cytosine substitution in exon 3 (codon 76, TAT to TAC) was identified. The nucleotide change led to creation of an AccI digestion site. The distribution pattern of AccI polymorphism in the patients was significantly different from that in the control group, and the occurrence of homozygous carriers was significantly higher in patients (12.6%) than in the control group (3.8%). The frequency of polymorphism and prevalence of homozygosity were significantly higher in patients with PCOS with obesity (0.50% and 31.0%, respectively) than in those with menstrual disorders only (0.366% and 8.5%, respectively), which correlated with significantly higher androgen levels in the obese patients.

CONCLUSION(S)

The AccI polymorphism in FSHbeta gene may be associated with PCOS in some women, especially those with obesity.