Stage-specific expression of Smad2 and Smad3 during folliculogenesis

Endometrial cell-derived conditioned medium in combination with platelet-rich plasma promotes the development of mouse ovarian follicles

Fertility preservation is one of the most important issues in assisted reproductive technology. Previous studies have shown that cytokines and growth factors can improve follicle growth. The endometrial stromal cells secrete various factors that are involved in maintaining the integrity of uterine and epithelial secretory function. The platelet-rich plasma contains a large assembly of platelets suspended in plasma that successfully improves the viability and growth of various cell lines. This work aimed to investigate the influences of conditioned medium (CM) and platelet-rich plasma (PRP) on the development of ovarian follicles in infertile mice due to cyclophosphamide (CYC) exposure. In this study, 65 healthy BALB/c female mice (∼28-30 g and 6-8 weeks old) in five groups were studied. Immunohistochemistry (IHC) was used to detect growth differentiation factor 9 (GDF9)-positive cells. The mRNA expression levels of SMAD1, SMAD2, and BMP15 was assessed using reverse transcription-polymerase chain reaction (RT-PCR) method. The expression levels of SMAD1, GDF9, BMP15, and SMAD2 in the CM+PRP group was significantly more than in the CM and PRP groups. In addition, live birth occurred in the CM+PRP group. Treatment with CM+PRP in infertile mice due to Cy exposure increased fertility and live-birth rate. In general, our study suggested that the CM and PRP combination could improve the growth of mice ovarian follicles in vivo.

Expression and Polymorphisms of SMAD1, SMAD2 and SMAD3 Genes and Their Association with Litter Size in Tibetan Sheep (Ovis aries)

SMAD1, SMAD2, and SMAD3 are important transcription factors downstream of the TGF-β/SMAD signaling pathway that mediates several physiological processes. In the current study, we used cloning sequencing, RT-qPCR, bioinformatics methods and iMLDR technology to clone the coding region of Tibetan sheep genes, analyze the protein structure and detect the tissue expression characteristics of Tibetan sheep genes, and detect the polymorphisms of 433 Tibetan sheep and analyze their correlation with litter size. The results showed that the ORFs of the SMAD1, SMAD2 and SMAD3 genes were 1398 bp, 1404 bp and 1278 bp, respectively, and encoded 465, 467 and 425 amino acids, respectively. The SMAD1, SMAD2, and SMAD3 proteins were all unstable hydrophilic mixed proteins. SMAD1, SMAD2 and SMAD3 were widely expressed in Tibetan sheep tissues, and all were highly expressed in the uterus, spleen, ovary and lung tissues. Litter sizes of the genotype CC in the SMAD1 gene g.10729C>T locus were significantly higher than that of CT (p < 0.05). In the SMAD3 gene g.21447C>T locus, the genotype TT individuals showed a higher litter size than the CC and CT genotype individuals (p < 0.05). These results preliminarily demonstrated that SMAD1, SMAD2 and SMAD3 were the major candidate genes that affected litter size traits in Tibetan sheep and could be used as a molecular genetic marker for early auxiliary selection for improving reproductive traits during sheep breeding.

Therapeutic Mechanism and Clinical Observation of Traditional Chinese Medicine Combined with Interventional Recanalization for Tubal Infertility

To observe the clinical effect of traditional Chinese medicine (TCM) combined with interventional recanalization therapy in the treatment of tubal obstructive infertility, first, different treatment approaches were used on rabbits, and transmission electron microscopy (TEM) indicated that interventional recanalization combined with TCM can significantly ameliorate the pathological condition of the fallopian tube after treatment. Moreover, ELISA disclosed that the treatment could significantly reduce the levels of interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) and increase the expression of interleukin-10 (IL-10), which demonstrated that TCM therapy can help against inflammation of the fallopian tubes. PCR array analysis revealed that BMP4, BMPR1A, SMAD2, SMAD3, SMAD4, and KLF10 expressions were upregulated, and SMAD7 expression was downregulated, proving that combined treatment could influence gene expression in the TGF-β family and further regulate the secretion of proteins in SMADs. In addition, a clinical study recorded the fallopian tube patency rate of 165 patients after 12 months. The recanalization rates in the two groups were 81.9% and 53.1%, with the higher rates in the combined medicine enema group. All these findings implied that interventional recanalization combined with TCM preparation has a stronger effect. The mechanism probably involves effects on the expression of genes in the TGF-β/SMAD and BMP/SMAD signaling pathways, with simultaneous regulation of inflammatory factors, thereby improving the ovarian environment and increasing pregnancy rates.

Homozygous mutation of foxh1 arrests oogenesis causing infertility in female Nile tilapia†

Foxh1, a member of fox gene family, was first characterized as a transcriptional partner in the formation of the Smad protein complex. Recent studies have shown foxh1 is highly expressed in the cytoplasm of oocytes in both tilapia and mouse. However, its function in oogenesis remains unexplored. In the present study, foxh1-/- tilapia was created by CRISPR/Cas9. At 180 dah (days after hatching), the foxh1-/- XX fish showed oogenesis arrest and a significantly lower GSI. The transition of oocytes from phase II to phase III and follicle cells from one to two layers was blocked, resulting in infertility of the mutant. Transcriptomic analysis revealed that expression of genes involved in estrogen synthesis and oocyte growth were altered in the foxh1-/- ovaries. Loss of foxh1 resulted in significantly decreased Cyp19a1a and increased Cyp11b2 expression, consistent with significantly lower concentrations of serum estradiol-17β (E2) and higher concentrations of 11-ketotestosterone (11-KT). Moreover, administration of E2 rescued the phenotypes of foxh1-/- XX fish, as indicated by the appearance of phase III and IV oocytes and absence of Cyp11b2 expression. Taken together, these results suggest that foxh1 functions in the oocytes to regulate oogenesis by promoting cyp19a1a expression, and therefore estrogen production. Disruption of foxh1 may block the estrogen synthesis and oocyte growth, leading to the arrest of oogenesis and thus infertility in tilapia.

Granulosa cell genes that regulate ovarian follicle development beyond the antral stage: The role of estrogen receptor β

Follicle development beyond the preantral stage is dependent on gonadotropins. FSH signaling is crucial for the advancement of preantral follicles to the antral stage, and LH signaling is essential for further maturation of preovulatory follicles. Estrogen is intricately tied to gonadotropin signaling during the advanced stages of folliculogenesis. We observed that Erβ^null ovarian follicles fail to develop beyond the antral stage, even after exogenous gonadotropin stimulation. As ERβ is primarily expressed in the granulosa cells (GCs), we explored the gonadotropin-regulated GC genes that induce maturation of antral follicles. Synchronized follicle development was induced by administration of exogenous gonadotropins to wildtype 4-wk-old female rats. The GC transcriptome was analyzed via RNA-sequencing before and after gonadotropin stimulation. An Erβ^null mutant model that fails to show follicle maturation was also included in order to identify the ERβ-regulated genes involved at this step. We observed that specific groups of genes were differentially expressed in response to PMSG or hCG administration in wildtype rats. While some of the PMSG or hCG-induced genes showed a similar expression pattern in Erβ^null GCs, a subset of PMSG- or hCG-induced genes showed a differential expression pattern in Erβ^null GCs. These latter ERβ-regulated genes included previously known FSH or LH target genes including Lhcgr, Cyp11a1, Cyp19a1, Pgr, Runx2, Egfr, Kiss1, and Ptgs2, which are involved in follicle development, oocyte maturation, and ovulation. We also identified novel ERβ-regulated genes including Jaml, Galnt6, Znf750, Dusp9, Wnt16, and Mageb16 that failed to respond to gonadotropin stimulation in Erβ^null GCs. Our findings indicate that the gonadotropin-induced spatiotemporal pattern of gene expression is essential for ovarian follicle maturation beyond the antral stage. However, expression of a subset of those gonadotropin-induced genes is dependent on transcriptional regulation by ERβ.

A First Insight into the Gonad Transcriptome of Hong Kong Catfish (Clarias fuscus)

Hong Kong catfish (Clarias fuscus) exhibit sexual dimorphism, particularly in body size. Due to the fast growth rate of males, the sexual size dimorphism of Hong Kong catfish has become an economically important trait. However, limited knowledge is known about the molecular mechanisms of sex determination and sex differentiation in this species. In this study, a first de novo transcriptome sequencing analysis of testes and ovaries was performed to identify sex-biased genes in Hong Kong catfish. The results showed that a total of 290,291 circular consensus sequences (CCSs) were obtained, from which 248,408 full-length non-chimeric (FLNC) reads were generated. After non-redundant analysis, a total of 37,305 unigenes were predicted, in which 34,342 unigenes were annotated with multiple public databases. Comparative transcriptomic analysis identified 5750 testis-biased differentially expressed genes (DEGs) and 6991 ovary-biased DEGs. The enrichment analysis showed that DEGs were classified into 783 Gene Ontology (GO) terms and 16 Kyoto Encyclopedia of Gene and Genome (KEGG) pathways. Many DEGs were involved with sex-related GO terms and KEGG pathways, such as oocyte maturation, androgen secretion, gonadal development and steroid biosynthesis pathways. In addition, the expression levels of 23 unigenes were confirmed to validate the transcriptomic data by quantitative real-time polymerase chain reaction (qRT-PCR). This is the first investigation into the transcriptome of Hong Kong catfish testes and ovaries. This study provides an important molecular basis for the sex determination and sex control breeding of Hong Kong catfish.

miR-130a-3p regulates steroid hormone synthesis in goat ovarian granulosa cells by targeting the PMEPA1 gene

MicroRNAs (miRNAs) are key epigenomic regulators of proliferation, differentiation, and secretion in cells involved in follicular development. We here studied the functional role of one such molecule, miR-130a-3p, in goat ovarian granulosa cells (GCs). High expression of this miRNA was evident in goat GCs by fluorescence in situ hybridization and suppressed estradiol and progesterone secretion from these cells, as determined by ELISA. miR-130a-3p was predicted to have a binding site for the 3' UTR of the prostate transmembrane protein androgen induced 1 gene (PMEPA1), and this was verified by a dual-luciferase reporter assay. PMEPA1 mRNA and protein expression were both found to be regulated by miR-130a-3p in GCs. Moreover, the overexpression or knockdown of PMEPA1 enhanced or suppressed estradiol and progesterone secretion from these cells, respectively. Furthermore, the secretion of estradiol and progesterone did not change significantly after the offsetting of PMEPA1 overexpression in GCs by miR-130a-3p. In summary, our present data indicate that miR-130a-3p inhibits the secretion of estradiol and progesterone in GCs by targeting PMEPA1. Our study thus provides seminal data and important new insights into the regulation of reproductive mechanisms in the nanny goat and other female mammals.

Loss of dmrt1 restores zebrafish female fates in the absence of cyp19a1a but not rbpms2a/b

Sex determination and differentiation is a complex process regulated by multiple factors, including factors from the germline or surrounding somatic tissue. In zebrafish, sex-determination involves establishment of a bipotential ovary that undergoes sex-specific differentiation and maintenance to form the functional adult gonad. However, the relationships among these factors are not fully understood. Here, we identify potential Rbpms2 targets and apply genetic epistasis experiments to decipher the genetic hierarchy of regulators of sex-specific differentiation. We provide genetic evidence that the crucial female factor rbpms2 is epistatic to the male factor dmrt1 in terms of adult sex. Moreover, the role of Rbpms2 in promoting female fates extends beyond repression of Dmrt1, as Rbpms2 is essential for female differentiation even in the absence of Dmrt1. In contrast, female fates can be restored in mutants lacking both cyp19a1a and dmrt1, and prolonged in bmp15 mutants in the absence of dmrt1. Taken together, this work indicates that cyp19a1a-mediated suppression of dmrt1 establishes a bipotential ovary and initiates female fate acquisition. Then, after female fate specification, Cyp19a1a regulates subsequent oocyte maturation and sustains female fates independently of Dmrt1 repression.

Expression and regulation of Smad2 by gonadotropins in the protogynous hermaphroditic ricefield eel (Monopterus albus)

Smad2, a receptor-activated Smad, plays a critical role in regulating gametogenesis. In this study, a smad2 homologue was identified and sequenced from ricefield eel ovary cDNA, and its mRNA and protein expression levels were analysed during oocyte development. The cDNA sequence of ricefield eel smad2 consisted of 1863 bp encoding a 467-amino acid protein that had high sequence homology with Smad proteins in other teleosts, especially in Poeciliopsis prolifica. The results of real-time quantitative PCR (RT-qPCR) analysis revealed that smad2 is expressed in the ovary during gonad development, increased continuously until the early vitellogenic stage in the ovaries, and then decreased with ovary maturation. Smad2 protein immunoreactivity was localized in the cytoplasm of follicular cells, oogonia, and primary growth stage oocytes. In vitro experiments revealed that follicle-stimulating hormone (FSH) and human chorionic gonadotropin (hCG) promoted smad2 expression in ovary tissue in a time- and dose-dependent manner, respectively. In summary, Smad2 plays a potentially vital role in ricefield eel ovary development.

Transforming growth factor-β is involved in maintaining oocyte meiotic arrest by promoting natriuretic peptide type C expression in mouse granulosa cells

Natriuretic peptide type C (NPPC) secreted by mural granulosa cells (MGCs) maintains oocyte meiotic arrest via the activation of guanylyl cyclase-linked natriuretic peptide receptor 2 (NPR2). Here, we investigated the effect of transforming growth factor (TGF)-β on NPPC expression in MGCs and oocyte maturation. TGF-β ligands (TGFB1 and TGFB3, but not TGFB2) and receptors (TGFBR1 and TGFBR2) were predominantly expressed in MGCs. The activation of the follicle-stimulating hormone (FSH) receptor by FSH/equine chorionic gonadotropin (eCG) increased the levels of TGFB1, TGFBR2, and TGF-β downstream SMAD proteins in MGCs, which were decreased following the activation of the luteinizing hormone (LH) receptor by human chorionic gonadotropin (hCG). TGF-β significantly increased the gene and protein levels of NPPC in cultured MGCs through SMAD3 binding to Nppc promoter regions. In the presence of FSH, TGF-β further increased NPPC levels and inhibited oocyte meiotic resumption of cumulus-oocyte complexes (COCs). Moreover, Tgfbr2-specific depletion in granulosa cells using Fshr-Cre mice reduced NPPC mRNA and protein levels, resulting in the weak maintenance of oocyte meiotic arrest within large antral follicles. Tgfbr2 depletion also impaired follicle development, ovulation, and female fertility. Taken together, TGF-β-promoted NPPC in MGCs is involved in maintaining oocyte meiotic arrest. FSH and LH could regulate NPPC levels in MGCs via TGF-β and then control the process of oocyte meiosis.

Expressions of Transforming Growth Factor β1 Signaling Cytokines in Aortic Dissection

Objective

To demonstrate the underlying mechanisms of aortic dissection compared to those of coronary artery disease in terms of the transforming growth factor-beta (TGF-β) signaling pathway.

Methods

Twenty consecutive aortic dissection patients and 20 consecutive coronary artery disease patients undergoing a surgical treatment in this hospital were enrolled into this study. The aortic tissues were sampled and the TGF-β₁ and its receptor TGF-β receptor I (TβRI) were detected by Western blotting assay.

Results

TGF-β₁ and TβRI were positively expressed in the aortic tissues in both groups by Western blotting assay. The expressions of the two proteins were significantly higher in the aortic tissue of patients with aortic dissection than in those with coronary artery disease. The quantitative analyses of the relative gray scales of the proteins disclosed close correlations between the expressions of TGF-β1 and TβRI in both the study and control group patients.

Conclusions

The aortic remodeling of aortic dissection might differ from that of coronary artery atherosclerosis concerning the nature, mechanism, mode, and activities of TGF-β signaling pathway. The development of aortic dissection could be associated with a significantly enhanced function of TGF-β₁/Smad signaling transduction as a result of aortic remodeling incorporating both vascular injury and repair.

Activin A in Mammalian Physiology

Activins are dimeric glycoproteins belonging to the transforming growth factor beta superfamily and resulting from the assembly of two beta subunits, which may also be combined with alpha subunits to form inhibins. Activins were discovered in 1986 following the isolation of inhibins from porcine follicular fluid, and were characterized as ovarian hormones that stimulate follicle stimulating hormone (FSH) release by the pituitary gland. In particular, activin A was shown to be the isoform of greater physiological importance in humans. The current understanding of activin A surpasses the reproductive system and allows its classification as a hormone, a growth factor, and a cytokine. In more than 30 yr of intense research, activin A was localized in female and male reproductive organs but also in other organs and systems as diverse as the brain, liver, lung, bone, and gut. Moreover, its roles include embryonic differentiation, trophoblast invasion of the uterine wall in early pregnancy, and fetal/neonate brain protection in hypoxic conditions. It is now recognized that activin A overexpression may be either cytostatic or mitogenic, depending on the cell type, with important implications for tumor biology. Activin A also regulates bone formation and regeneration, enhances joint inflammation in rheumatoid arthritis, and triggers pathogenic mechanisms in the respiratory system. In this 30-yr review, we analyze the evidence for physiological roles of activin A and the potential use of activin agonists and antagonists as therapeutic agents.

Nuclear exclusion of SMAD2/3 in granulosa cells is associated with primordial follicle activation in the mouse ovary

Maintenance and activation of the limited supply of primordial follicles in the ovary are important determinants of reproductive lifespan. Currently, the molecular programme that maintains the primordial phenotype and the early events associated with follicle activation are not well defined. Here, we have systematically analysed these events using microscopy and detailed image analysis. Using the immature mouse ovary as a model, we demonstrate that the onset of granulosa cell (GC) proliferation results in increased packing density on the oocyte surface and consequent GC cuboidalization. These events precede oocyte growth and nuclear translocation of FOXO3a, a transcription factor important in follicle activation. Immunolabelling of the TGFβ signalling mediators and transcription factors SMAD2/3 revealed a striking expression pattern specific to GCs of small follicles. SMAD2/3 were expressed in the nuclei of primordial GCs but were mostly excluded in early growing follicles. In activated follicles, GC nuclei lacking SMAD2/3 generally expressed Ki67. These findings suggest that the first phenotypic changes during follicle activation are observed in GCs, and that TGFβ signalling is fundamental for regulating GC arrest and the onset of proliferation.

Serine threonine kinase receptor associated protein regulates early follicle development in the mouse ovary

The molecular mechanisms involved in regulating the development of small, gonadotrophin-independent follicles are poorly understood; however, many studies have highlighted an essential role for TGFB ligands. Canonical TGFB signalling is dependent upon intracellular SMAD proteins that regulate transcription. STRAP has been identified in other tissues as an inhibitor of the TGFB–SMAD signalling pathway. Therefore, in this study we aimed to determine the expression and role of STRAP in the context of early follicle development. Using qPCR, Strap, Smad3 and Smad7 revealed similar expression profiles in immature ovaries from mice aged 4–16 days containing different populations of early growing follicles. STRAP and SMAD2/3 proteins co-localised in granulosa cells of small follicles using immunofluorescence. Using an established culture model, neonatal mouse ovary fragments with a high density of small non-growing follicles were used to examine the effects of Strap knockdown using siRNA and STRAP protein inhibition by immuno-neutralisation. Both interventions caused a reduction in the proportion of small, non-growing follicles and an increase in the proportion and size of growing follicles in comparison to untreated controls, suggesting inhibition of STRAP facilitates follicle activation. Recombinant STRAP protein had no effect on small, non-growing follicles, but increased the mean oocyte size of growing follicles in the neonatal ovary model and also promoted the growth of isolated preantral follicles in vitro. Overall findings indicate STRAP is expressed in the mouse ovary and is capable of regulating development of small follicles in a stage-dependent manner.

Expression and distribution of forkhead activin signal transducer 2 (FAST2) during follicle development in mouse ovaries and pre-implantation embryos

Xenopus forkhead activin signal transducer 1 (xFAST 1) was first characterized in Xenopus as the transcriptional partner for Smad proteins. FAST2, which is the xFAST 1 homologues in mouse, is expressed during early developmental stages of the organism. However, the function of FAST2 in mouse ovaries and pre-implantation embryos is unclear. Therefore, we investigated its expression during these processes. In postnatal mice, FAST2 was expressed in oocytes and thecal cells from postnatal day (PD) 1 to PD 21. In gonadotropin-induced immature mice, FAST2 was expressed in oocytes, thecal cells and newly formed corpora lutea (CLs), but was expressed at a lower level in degenerated CLs. Similar results were observed upon western blot analyses. In meloxicam-treated immature mice, ovulation was inhibited and FAST2 was expressed in thecal cells, luteinized granulosa cells and entrapped oocytes. Immunofluorescence results showed that FAST2 was expressed in the cytoplasm and nucleus but not the nucleolus from the zygote to 8-cell embryo stage, after which it was localized to the cytoplasm of the morulae and inner cell mass of the blastocysts. Taken together, these observations suggest that FAST2 is expressed in a cell-specific manner during ovarian follicle development, ovulation, luteinization and early embryonic development, and that FAST2 might play important roles in these physiological processes.

Cooperative Effects of FOXL2 with the Members of TGF-β Superfamily on FSH Receptor mRNA Expression and Granulosa Cell Proliferation from Hen Prehierarchical Follicles

Forkhead box L2 (FOXL2) is a member of the forkhead nuclear factor 3 gene family and plays an essential role in ovarian growth and maturation in mammals. However, its potential effects and regulative mechanism in development of chicken ovarian prehierarchical follicles remain unexplored. In this study, the cooperative effects of FOXL2 with activin A, growth differentiation factor-9 (GDF9) and follistatin, three members of the transforming growth factor beta (TGF-β) superfamily that were previously suggested to exert a critical role in follicle development was investigated. We demonstrated herein, using in-situ hybridization, Northern blot and immunohistochemical analyses of oocytes and granulosa cells in various sizes of prehierarchical follicles that both FOXL2 transcripts and FOXL2 proteins are predominantly expressed in a highly similar expression pattern to that of GDF9 gene. In addition, the FOXL2 transcript was found at lower levels in theca cells in the absence of GDF9. Furthermore, culture of granulosa cells (GCs) from the prehierarchical follicles (6–8 mm) in conditioned medium revealed that in the pcDNA3.0-FOXL2 transfected GCs, there was a more dramatic increase in FSHR mRNA expression after treatment with activin A (10 ng/ml) or GDF9 (100 ng/ml) for 24 h which caused a stimulatory effect on the GC proliferation. In contrast, a significant decrease of FSHR mRNA was detected after treatment with follistatin (50 ng/ml) and resulted in an inhibitory effect on the cell proliferation. The results of this suggested that FOXL2 plays a bidirectional modulating role involved in the intracellular FSHR transcription and GC proliferation via an autocrine regulatory mechanism in a positive or negative manner through cooperation with activin A and/or GDF9, and follistatin in the hen follicle development. This cooperative action may be mediated by the examined Smad signals and simultaneously implicated in modulation of the StAR, CCND2, and CYP11A1 expression.

Activin A expression in esophageal carcinoma and its association with tumor aggressiveness and differentiation

The aim of the present study was to investigate the expression of activin A in esophageal carcinoma and its association with tumor differentiation and metastasis. A total of 57 esophageal carcinoma patients and 36 controls were included in the current study. The mRNA and protein expression levels of activin A in esophageal tumors or normal esophageal tissues were determined by reverse transcription-quantitative polymerase chain reaction and immunohistochemical analysis. In addition, the association of activin A expression with esophageal carcinoma differentiation, metastasis and recurrence postoperatively was analyzed. The mRNA and protein expression levels of activin A in esophageal carcinoma were significantly higher compared with those in normal esophageal tissues (P<0.05). The expression of activin A was higher in poorly-/moderately-differentiated esophageal tumor tissues compared with that of well-differentiated or control tissues (P<0.05). Furthermore, the expression of activin A in poorly-differentiated esophageal tumor tissues was higher compared with that of moderately-differentiated tissues (P<0.05). A positive correlation was also observed between differentiation degree and activin A expression. The expression of activin A was higher in patients with lymph node metastasis compared with those without metastasis (P<0.05). The cumulative survival rate of patients with a high expression of activin A at 1, 2 and 3 years postoperatively was significantly decreased compared with that of patients with a lower expression of activin A (P<0.05); by contrast, the cumulative recurrence rate was significantly higher in patients with a lower activin A expression (P<0.05). In conclusion, abnormal expression of activin A was detected in esophageal tumor tissues, which was correlated with the tumor differentiation, metastasis, survival and recurrence. In conclusion, activin A may be used as an auxiliary index in the diagnosis and prognosis of clinical esophageal carcinoma.

Expression and localization of Smad2 and Smad4 proteins in the porcine ovary

The objective of the present study was to investigate the temporal and spatial expression of Smad2 and Smad4 proteins, the downstream signaling molecules of the transforming growth factor beta (TGF-β) superfamily, in the porcine ovary. Cellular localization of Smad2 and Smad4 proteins was examined using immunohistochemistry. The specificity of the antibodies was examined using Western blot assay. Western blot analyses demonstrated that 52kDa Smad2 and 60kDa Smad4 proteins were expressed in the porcine ovary. Immunohistochemistry revealed that Smad2 and Smad4 were widely expressed in the porcine ovary, mainly localized in the oocyte, granulosa and thecal cells at different stages of folliculogenesis. Within the primordial and primary follicles, Smad2 and Smad4 showed strong staining in oocytes and follicular cells. In the antral follicle, strong staining was observed in oocytes, granulosa and theca cells. These findings suggest that Smad2 and Smad4 may be a key regulator of follicular development and growth of oocytes in the porcine ovary.

Evidence supporting a functional requirement of SMAD4 for bovine preimplantation embryonic development: a potential link to embryotrophic actions of follistatin

Transforming growth factor beta (TGFbeta) superfamily signaling controls various aspects of female fertility. However, the functional roles of the TGFbeta-superfamily cognate signal transduction pathway components (e.g., SMAD2/3, SMAD4, SMAD1/5/8) in early embryonic development are not completely understood. We have previously demonstrated pronounced embryotrophic actions of the TGFbeta superfamily member-binding protein, follistatin, on oocyte competence in cattle. Given that SMAD4 is a common SMAD required for both SMAD2/3- and SMAD1/5/8-signaling pathways, the objectives of the present studies were to determine the temporal expression and functional role of SMAD4 in bovine early embryogenesis and whether embryotrophic actions of follistatin are SMAD4 dependent. SMAD4 mRNA is increased in bovine oocytes during meiotic maturation, is maximal in 2-cell stage embryos, remains elevated through the 8-cell stage, and is decreased and remains low through the blastocyst stage. Ablation of SMAD4 via small interfering RNA microinjection of zygotes reduced proportions of embryos cleaving early and development to the 8- to 16-cell and blastocyst stages. Stimulatory effects of follistatin on early cleavage, but not on development to 8- to 16-cell and blastocyst stages, were observed in SMAD4-depleted embryos. Therefore, results suggest SMAD4 is obligatory for early embryonic development in cattle, and embryotrophic actions of follistatin on development to 8- to 16-cell and blastocyst stages are SMAD4 dependent.

SMAD3 regulates the diverse functions of rat granulosa cells relating to the FSHR/PKA signaling pathway

The function of Smad3, a downstream signaling protein of the transforming growth factor β (TGFβ) pathway, in ovarian follicle development remains to be elucidated. The effects of Smad3 on ovarian granulosa cells (GCs) in rat were studied. Female rats (21 days of age Sprague-Dawley) received i.p. injections of pregnant mare serum gonadotropin, and GCs were harvested for primary culture 48 h later. These cells were engineered to overexpress or knockdown Smad3, which were validated by immunohistochemistry and western blot. The expression of proliferating cell nuclear antigen (PCNA), cyclin D2, TGFβ receptor II (TGFβRII), protein kinase A (PKA), and FSH receptor (FSHR) was also detected by western blotting. Cell cycle and apoptosis of GCs were assayed by flow cytometry. The level of estrogen secreted by GCs was detected by ELISA. Smad3 overexpression promoted estrogen production and proliferation while inhibiting apoptosis of GCs. Reduction in Smad3 by RNAi resulted in reduced estrogen production and proliferation and increased apoptosis of GCs. Manipulation of Smad3 expression also resulted in changes in FSHR and PKA expression, suggesting that the effects of Smad3 on follicle development are related to FSHR-mediated cAMP signaling.

SMAD7 antagonizes key TGFβ superfamily signaling in mouse granulosa cells in vitro

Transforming growth factor β (TGFβ) superfamily signaling is essential for female reproduction. Dysregulation of the TGFβ signaling pathway can cause reproductive diseases. SMA and MAD (mothers against decapentaplegic) (SMAD) proteins are downstream signaling transducers of the TGFβ superfamily. SMAD7 is an inhibitory SMAD that regulates TGFβ signalingin vitro. However, the function of SMAD7 in the ovary remains poorly defined. To determine the signaling preference and potential role of SMAD7 in the ovary, we herein examined the expression, regulation, and function of SMAD7 in mouse granulosa cells. We showed that SMAD7 was expressed in granulosa cells and subject to regulation by intraovarian growth factors from the TGFβ superfamily. TGFB1 (TGFβ1), bone morphogenetic protein 4, and oocyte-derived growth differentiation factor 9 (GDF9) were capable of inducingSmad7expression, suggesting a modulatory role of SMAD7 in a negative feedback loop. Using a small interfering RNA approach, we further demonstrated that SMAD7 was a negative regulator of TGFB1. Moreover, we revealed a link between SMAD7 and GDF9-mediated oocyte paracrine signaling, an essential component of oocyte–granulosa cell communication and folliculogenesis. Collectively, our results suggest that SMAD7 may function during follicular development via preferentially antagonizing and/or fine-tuning essential TGFβ superfamily signaling, which is involved in the regulation of oocyte–somatic cell interaction and granulosa cell function.

Granulosa cell tumor mutant FOXL2C134W suppresses GDF-9 and activin A-induced follistatin transcription in primary granulosa cells

A single somatic FOXL2 mutation (FOXL2(C134W)) was identified in almost all granulosa cell tumor (GCT) patients. In the pituitary, FOXL2 and Smad3 coordinately regulate activin stimulation of follistatin transcription. We explored whether a similar regulation occurs in the ovary, and whether FOXL2(C134W) has altered activity. We show that in primary granulosa cells, GDF-9 and activin increase Smad3-mediated follistatin transcription. In contrast to findings in the pituitary, FOXL2 negatively regulates GDF-9 and activin-stimulated follistatin transcription in the ovary. Knockdown of endogenous FOXL2 confirmed this inhibitory role. FOXL2(C134W) displayed enhanced inhibitory activity, completely ablating GDF-9 and activin-induced follistatin transcription. GDF-9 and activin activity was lost when either the smad binding element or the forkhead binding element were mutated, indicating that both sites are required for Smad3 actions. This study highlights that FOXL2 negatively regulates follistatin expression within the ovary, and that the pathogenesis of FOXL2(C134W) may involve an altered interaction with Smad3.

Activin stimulates CYP19A gene expression in human ovarian granulosa cell-like KGN cells via the Smad2 signaling pathway

Activin, a transforming growth factor β family member, has a wide range of physiological roles during embryonic development and organogenesis. In the ovary, activin, secreted from ovarian granulosa cells, not only acts on the pituitary gland to regulate the gonadotropin secretion from the pituitary gland in an endocrine manner but also acts on granulosa cells in a paracrine/autocrine manner to regulate folliculogenesis. Previously, we showed that activin signals through activin type IB receptor (ActRIB) and up-regulates follicle-stimulating hormone receptor expression and P450 aromatase activity in human ovarian granulose cell-like KGN cells. In the current study, we demonstrate the direct involvement of Smad2 as a downstream signal mediator of ActRIB in the transcriptional regulation of the P450 aromatase gene (CYP19A) in KGN cells. Upon activin stimulation, Smad2 activation and an increase in P450 aromatase messenger RNA (mRNA) were observed in KGN cells. Interestingly, Smad2 phosphorylation correlated well with the increase in P450 aromatase mRNA. Reciprocally, knockdown of Smad2 mRNA in KGN cells led to a decrease in the P450 aromatase mRNA expression, suggesting that Smad2 regulates CYP19A gene expression. Further analysis of CYP19A promoter activity revealed that the 5' upstream region between -2069 and -1271bp is required for the activation by Smad2. Finally, we provide compelling evidence that Smad2 shows follicular stage-specific expression, which is high in granulosa cells of preantral or early antral follicles in mice. Our results suggest that activin signaling through the ActRIB-Smad2 pathway plays a pivotal role in CYP19A expression and thus in follicular development.

Intra-ovarian roles of activins and inhibins

Granulosa cells are the main ovarian source of inhibins, activins and activin-binding protein (follistatin) while germ (oogonia, oocytes) and somatic (theca, granulosa, luteal) cells express activin receptors, signaling components and inhibin co-receptor (betaglycan). Activins are implicated in various intra-ovarian roles including germ cell survival and primordial follicle assembly; follicle growth from preantral to mid-antral stages; suppression of thecal androgen production; promotion of granulosa cell proliferation, FSHR and CYP19A1 expression; enhancement of oocyte developmental competence; retardation of follicle luteinization and/or atresia and involvement in luteolysis. Inhibins (primarily inhibin A) are produced in greatest amounts by preovulatory follicles (and corpus luteum in primates) and suppress FSH secretion through endocrine negative feedback. Together with follistatin, inhibins act locally to oppose auto-/paracrine activin (and BMP) signaling thus modulating many of the above processes. The balance between activin-inhibin shifts during follicle development with activin signalling prevailing at earlier stages but declining as inhibin and betaglycan expression rise.

Smad7 is a transforming growth factor-beta-inducible mediator of apoptosis in granulosa cells

OBJECTIVE

To determine the functional role of Smad7 in granulosa cells.

DESIGN

Granulosa cell culture and molecular biological techniques were used to investigate regulation and function of Smad7.

SETTING

Research laboratory.

ANIMAL(S)

C57bl/j hybrid mouse.

INTERVENTION(S)

Primary mouse granulosa cells were isolated and grown in culture for all messenger RNA expression experiments. Smad7 promoter constructs were evaluated with a luciferase reporter system in SIGC cells to determine sites activating Smad7 expression.

MAIN OUTCOME MEASURE(S)

Overexpression (Smad7 complementary DNA) and downregulation (Smad7 small interfering RNA) of Smad7 in primary mouse granulosa cells were used to evaluate the functional role of Smad7 in granulosa cells.

RESULT(S)

Smad7 expression was upregulated by treatment with transforming growth factor-β (TGF-β) but not activin or activation of the cyclic adenosine monophosphate pathway. The promoter of Smad7 was activated by TGF-β. Truncation of the promoter or mutation of the Smad response element at -141 eliminated TGF-β activation of the promoter. Smad3 was not specifically required for TGF-β-stimulated expression of Smad7, though activation of the TGFBR1 receptor was. When Smad7 was overexpressed in granulosa cells, apoptosis was markedly increased. When Smad7 expression was reduced with small interfering RNA, then the TGF-β-induced apoptosis was blocked.

CONCLUSION(S)

Smad7 mediates apoptosis induced by TGF-β in mouse granulosa cells, suggesting that dysregulation of Smad7 could impair folliculogenesis.

Induction of Ski Protein Expression upon Luteinization in Rat Granulosa Cells

Ski protein is implicated in proliferation/differentiation in a variety of cells. We had previously reported that Ski protein is present in granulosa cells of atretic follicles, but not in preovulatory follicles, suggesting that Ski has a role in apoptosis of granulosa cells. The alternative fate of granulosa cells other than apoptosis is to differentiate to luteal cells; however, it is unknown whether Ski is expressed and has a role in granulosa cells undergoing luteinization. Thus, the aim of the present study was to locate Ski protein in the rat ovary during luteinizationto predict the possible role of Ski. In order to examine the expression pattern of Ski protein along with the progress of luteinization, follicular growth was induced by administration of equine chorionic gonadtropin to immature female rats, and luteinization was induced by human chorionic gonadtropin treatment to mimic luteinizing hormone (LH) surge. While no Ski-positive granulosa cells were present in preovulatory follicle, Ski protein expression was induced in response to LH surge, and was maintained after the formation of the corpus luteum (CL). Though Ski protein is absent in granulosa cells of preovulatory follicle, its mRNA (c-Ski) was expressed and the level was unchanged even after LH surge. Taken together, these results demonstrated that Ski protein expression is induced in granulosa cells upon luteinization, and suggests that its expression is regulated post-transcriptionally.

The relationship between Evi-1 expression and mouse ovarian follicular development

The ecotropic viral integration site-1 (Evi-1) is a transcription factor with two sets of zinc finger domains. It is an important regulator of the transforming growth factor beta superfamily. In the present study, we investigated the spatiotemporal expression patterns of Evi-1 using immunohistochemistry in ovaries from neonatal mice, gonadotropin-induced immature mice and mice in estrous cycle. Positive staining for Evi-1 was detected in the cytoplasm of oocytes. In postnatal mice, a high level of Evi-1 immunostaining was found from day 1 to 6, an intermediate level from day 10 to 16 and a low level on day 23. After gonadotropin treatment, Evi-1 was mainly expressed in small follicles and exhibited a very low level in large antral follicles. During the estrous cycle, the expression of Evi-1 was higher in diestrus and estrus than in proestrus and metestrus. Real-time PCR was performed to examine the relationship between Evi-1 mRNA and ovulation related genes (Ptgs2, Tnfaip6, Has2, Cd44, C1qbp). At 4 h after hCG treatment, Evi-1 mRNA was down-regulated whereas ovulation related genes were up-regulated. Overall, the results indicate that Evi-1 is expressed in a stage-specific manner during ovarian follicular development and may be involved in early follicle development.

Induction of Ski protein expression upon luteinization in rat granulosa cells without a change in its mRNA expression

The Ski protein is implicated in the proliferation/differentiation of a variety of cells. We previously reported that the Ski protein is present in granulosa cells of atretic follicles, but not in preovulatory follicles, suggesting that Ski has a role in apoptosis of granulosa cells. However, granulosa cells cannot only undergo apoptosis but can alternatively differentiate into luteal cells. It is unknown whether Ski is expressed and has a role in granulosa cells undergoing luteinization. Thus, the aim of the present study was to determine the localization of the Ski protein in the rat ovary during luteinization to examine if Ski might play a role in this process. In order to examine the Ski protein expression during the progression of luteinization, follicular growth was induced in immature female rats by administration of equine chorionic gonadotropin, and luteinization was induced by human chorionic gonadotropin treatment to mimic the luteinizing hormone (LH) surge. While no Ski-positive granulosa cells were present in the preovulatory follicle, Ski protein expression was induced in response to the LH surge and was maintained after formation of the corpus luteum (CL). Although the Ski protein is absent from the granulosa cells of the preovulatory follicle, its mRNA (c-ski) was expressed, and the level of c-ski mRNA was unchanged even after the LH surge. The combined results demonstrated that Ski protein expression is induced in granulosa cells upon luteinization, and suggested that its expression is regulated posttranscriptionally.

Relative expression of genes encoding SMAD signal transduction factors in human granulosa cells is correlated with oocyte quality

PURPOSE

To determine the expression of SMAD transcripts in human granulosa cells.

METHODS

Luteinized mural granulosa cells were harvested from forty women undergoing oocyte retrieval, and RNAs were isolated. SMAD expression levels were determined by polymerase chain reaction (PCR) and quantitative real-time PCR (q-RTPCR).

RESULTS

SMAD1-7 and 9 are expressed in human granulosa cells, with SMAD2, 3 and 4 showing the highest expression levels. Peak estradiol (E2) levels correlated with the number of oocytes retrieved during IVF. Oocyte number showed no correlation with SMAD expression levels or ratios. Fertilization rates also did not correlate with the expression levels of individual SMADs, but did correlate with higher SMAD4:SMAD3 ratios (p = 0.0062) and trended with SMAD4:SMAD2 (p = 0.0698).

CONCLUSIONS

SMAD transcripts are differently expressed in human granulosa cells, where they may mediate TGF-beta superfamily signaling during folliculogenesis and ovulation. Further, the relative expression ratios of SMAD2, 3 and 4 may differentially affect fertilization rate.

Smad3-dependent signaling underlies the TGF-β1-mediated enhancement in astrocytic iNOS expression

We previously demonstrated that transforming growth factor-beta1 (TGF-beta1), while having no effect alone, enhances nitric oxide (NO) production in primary, purified mouse astrocytes induced by lipopolysaccharide (LPS) plus interferon-gamma (IFN-gamma), by recruiting a latent population of astrocytes to respond, thereby enhancing the total number of cells that express Nos2. In this investigation, we evaluated the molecular signaling pathway by which this occurs. We found that purified murine primary astrocytes express mRNA for TGFbetaRII as well as the TGFbetaRI subunit activin-like kinase 5 (ALK5), but not ALK1. Immunofluorescence microscopy confirmed the expression of TGFbetaRII and ALK5 protein in astrocytes. Consistent with ALK5 signaling, Smad3 accumulated in the nucleus of astrocytes as early as 30 min after TGF-beta1 (3 ng/mL) treatment and persisted upto 32 hr after TGF-beta1 administration. Addition of ALK5 inhibitors prevented TGF-beta1-mediated Smad3 nuclear accumulation and NO production when given prior to the Nos2 induction stimuli, but not after. Finally, astrocyte cultures derived from Smad3 null mutant mice did not exhibit a TGF-beta1-mediated increase in iNOS expression. Overall, this data suggests that ALK5 signaling and Smad3 nuclear accumulation is required for optimal enhancement of LPS plus IFNgamma-induced NO production in astrocytes by TGF-beta1.

Smad1-Smad5 ovarian conditional knockout mice develop a disease profile similar to the juvenile form of human granulosa cell tumors

Granulosa cell tumors (GCTs) of the ovary are rare sex cord stromal tumors. Although generally indolent, GCTs recur, and if not diagnosed and treated in early stages, survival rates are significantly shortened. Very little is known regarding GCT etiology. Because of the low incidence of cases and lack of standard diagnostics, mouse models for granulosa cell tumors are a valuable tool for studying GCTs and provide models for developing diagnostic and treatment strategies. We recently developed a novel mouse model of metastatic granulosa cell tumors by genetic deletion of the bone morphogenetic protein signaling transcription factors (SMADs) in granulosa cells of the ovary. Histological and serum hormone analyses reveal that this mouse model most closely resembles the juvenile form of GCT. We further analyzed samples of human juvenile GCT (JGCT) for expression of anti-Müllerian hormone and activation of two major signaling pathways: TGFbeta/SMAD2/3 and wingless-related mouse mammary tumor virus integration site (Wnt)/beta-catenin. The TGFbeta family is active in mouse Smad1-Smad5 double knockout tumors, and here we show that this pathway, but not the beta-catenin pathway, is activated in samples of human JGCT. These data suggest that the SMAD family, possibly through disruption of SMAD1/5 or activation of SMAD2/3 may contribute to the pathogenesis of JGCT in humans.

Molecular mechanisms underlying the activation of mammalian primordial follicles

In humans and other mammalian species, the pool of resting primordial follicles serves as the source of developing follicles and fertilizable ova for the entire length of female reproductive life. One question that has intrigued biologists is: what are the mechanisms controlling the activation of dormant primordial follicles. Studies from previous decades have laid a solid, but yet incomplete, foundation. In recent years, molecular mechanisms underlying follicular activation have become more evident, mainly through the use of genetically modified mouse models. As hypothesized in the 1990s, the pool of primordial follicles is now known to be maintained in a dormant state by various forms of inhibitory machinery, which are provided by several inhibitory signals and molecules. Several recently reported mutant mouse models have shown that a synergistic and coordinated suppression of follicular activation provided by multiple inhibitory molecules is necessary to preserve the dormant follicular pool. Loss of function of any of the inhibitory molecules for follicular activation, including PTEN (phosphatase and tensin homolog deleted on chromosome 10), Foxo3a, p27, and Foxl2, leads to premature and irreversible activation of the primordial follicle pool. Such global activation of the primordial follicle pool leads to the exhaustion of the resting follicle reserve, resulting in premature ovarian failure in mice. In this review, we summarize both historical and recent results on mammalian primordial follicular activation and focus on the up-to-date knowledge of molecular networks controlling this important physiological event. We believe that information obtained from mutant mouse models may also reflect the molecular machinery responsible for follicular activation in humans. These advances may provide a better understanding of human ovarian physiology and pathophysiology for future clinical applications.

Smad3 is required for normal follicular follicle-stimulating hormone responsiveness in the mouse

Follicle-stimulating hormone (FSH) is the major regulator of folliculogenesis, but other factors modulate its action, including members of the transforming growth factor (TGF) beta family. The intersection of signal transduction pathways that integrate the follicular response to FSH remains to be elucidated. Herein, we investigated the role of Smad3, a critical molecule mediating the intracellular TGFbeta family proteins, in follicle development and the expression of FSH receptors. We found that gonadotropin stimulation could not induce normal ovulation in Smad3-deficient mice. Moreover, FSH could not stimulate early follicle growth in Smad3-deficient mice in in vivo or in vitro systems. Cultured granulosa cells from Smad3-deficient animals had reduced cell division rates following FSH treatment compared with granulosa cells derived from the ovaries of wild-type (WT) mice. Whole ovaries and isolated granulosa cells from Smad3-deficient animals had lower basal expression of FSH receptor (Fshr), aromatase (Cyp19a1), and cyclin D2 (Ccnd2) mRNA compared with WT mice. Follicle-stimulating hormone treatment of granulosa cells from WT ovaries upregulated Fshr, Cyp19a1, and Ccnd2 expression. However, FSH did not increase these mRNAs in Smad3-deficient granulosa cells. When Smad3 was introduced into Smad3-deficient granulosa cells with adenovirus vectors, FSH responsiveness was restored, and FSH was able to upregulate Fshr expression. Furthermore, SMAD3 interacts with a palindromic SMAD binding element in the Fshr promoter, and TGFB can activate promoter constructs containing this element. Collectively, these observations establish an essential role for Smad3 in regulating the response of ovarian follicles to FSH.

Existence of the lymphatic system in the primate corpus luteum

To date, there have been no detailed studies on the lymphatic system in the primate corpus luteum (CL); early reports suggested that the presence of this "secondary circulation" in luteal tissue is species-dependant. Therefore, studies were designed to determine if (a) lymphatic vessels exist, and (b) recently discovered lymphangiogenic factors and their receptor are expressed in the macaque CL during the menstrual cycle. Immunohistochemistry (IHC) detected the lymphatic endothelial cell marker, lymphatic vessel endothelial hyaluronan receptor 1 (LYVE1), in some endothelial cells and vessels within the ovarian stroma and theca layer of preovulatory follicles and in the CL. Dual fluorescent IHC demonstrated that LYVE1 co-localized with another lymphatic endothelial cell marker D2-40, but a blood vascular endothelial cell marker (von Willebrand Factor, VWF) was in different cells. The numbers and staining intensity of LYVE1-positive cells in the CL appeared to increase from early to mid luteal phase, and remained elevated thereafter. RT-PCR detected cDNA fragments for mRNAs encoding VEGFC, FIGF, and their receptor FLT4 in CL. Real-time PCR analyses revealed similar patterns of VEGFC and FLT4 expression during the luteal lifespan; mRNA levels increased (p < 0.05) from early to mid luteal phase and decreased (p < 0.05) by late luteal phase. In contrast, FIGF levels were elevated initially, declined (p < 0.05) at mid luteal phase, and then increased (p < 0.05) to very late luteal phase. The data strongly suggest that lymphatic vessels are present in the primate CL, and that the VEGFC/FIGF-FLT4 system regulates lymphangiogenesis and luteal structure-function during the menstrual cycle.

Loss of Runx3 affects ovulation and estrogen-induced endometrial cell proliferation in female mice

Runx3 is a transcription factor that belongs to the Runx family. We studied the function of Runx3 in the mouse ovary and uterus using the Runx3 knockout (Runx3(-/-)) mouse. Ovaries were collected from 8-week-old wild type (wt) and Runx3(-/-) mice. Histological studies showed that follicles were present at various developmental stages in the Runx3(-/-) and wt mouse ovaries. The numbers of primary, preantral and antral follicles in the Runx3(-/-) mice were significantly less than those in the wt mice while the number of primordial follicles in the Runx3(-/-) mice was not significantly different from that in the wt mice. Corpora lutea were not detected in the Runx3(-/-) mouse ovary. Gonadotropin treatment in immature female mice induced ovulation in Runx3(-/-) mice as well as in wt mice, indicating that ovaries of Runx3(-/-) mice respond to gonadotropin treatment as those in wt mouse ovaries. This suggests that failure of ovulation is due to dysfunction of regulatory mechanism of gonadotropin secretion. In addition, the uteri of Runx3(-/-) mice were atrophic, showed thin epithelial layers compared with those of the wt mice, and did not respond to estrogen in terms of DNA replication in endometrial epithelial cells. These results suggest that Runx3 takes part in the regulation of reproductive functions.

Redundant roles of SMAD2 and SMAD3 in ovarian granulosa cells in vivo

Transforming growth factor beta (TGF-beta) superfamily members are critical in maintaining cell growth and differentiation in the ovary. Although signaling of activins, TGF-betas, growth differentiation factor 9, and nodal converge preferentially to SMAD2 and SMAD3, the in vivo functions and redundancy of these SMADs in the ovary and female reproduction remain largely unidentified. To circumvent the deleterious phenotypic aspects of ubiquitous deletion of Smad2 and Smad3, a conditional knockout strategy was formulated to selectively inactivate Smad2, Smad3, or both Smad2 and Smad3 in ovarian granulosa cells. While granulosa cell ablation of individual Smad2 or Smad3 caused insignificant changes in female fertility, deletion of both Smad2 and Smad3 led to dramatically reduced female fertility and fecundity. These defects were associated with the disruption of multiple ovarian processes, including follicular development, ovulation, and cumulus cell expansion. Furthermore, the impaired expansion of cumulus cells may be partially associated with altered cumulus expansion-related transcripts that are regulated by SMAD2/3 signaling. Our results indicate that SMAD2 and SMAD3 function redundantly in vivo to maintain normal female fertility and further support the involvement of an intraovarian SMAD2/3 pathway in mediating oocyte-produced signals essential for coordinating key events of the ovulatory process.

Activin signals via SMAD2/3 between germ and somatic cells in the human fetal ovary and regulates kit ligand expression

Ovarian germ cell survival is dependent upon the formation of primordial follicles, which occurs during fetal life in the human. Activin contributes to germ cell proliferation and survival at this time. SMADs2 and 3 are central elements in the activin signalling pathway and thus indicate sites of activin action. We have investigated the expression and localisation of SMADs2 and 3 in the fetal ovary between 14 and 20 weeks gestation, i.e. preceding and during primordial follicle formation. SMAD3 mRNA expression increased 1.9 fold (P=0.02). SMAD2 and 3 proteins were localised by immunofluorescence to the nuclei of three distinct populations of somatic cells: (a) stromal cells between clusters of germ cells; (b) some somatic cells intermingled with activin beta A-expressing germ cells; (c) pre-granulosa cells surrounding primordial follicles. Germ cells did not express SMAD2 or 3. Activin A increased and follistatin decreased phosphorylation of SMAD2/3 in vitro, and activin increased SMAD2 and decreased KITLG mRNA expression. It therefore appears that somatic cells are the targets for activin signalling in the developing ovary. The effects of activin on germ cells are indirect and include mediation by the kit ligand/c-Kit pathway, rather than being an autocrine germ cell effect.

Visualizing Smad1/4 signaling response to bone morphogenetic protein-4 activation by FRET biosensors

Smad proteins are the major signal transducers for the Transforming Growth Factor superfamily of cytokines and their serine/threonine kinase receptors. Smads mediate the signal from the membrane into the nucleus. Bone Morphogenetic Protein-4 stimulates phosphorylation of Smad1, which interacts with Smad4. This complex translocates into the nucleus and regulates transcription of target genes. Here, we report our development of cellular fluorescence biosensors for direct visualization of Smad signaling in live mammalian cells. Fluorescence resonance energy transfer between cyan and yellow fluorescent proteins fused to the Smad1 and Smad4 proteins was used to unravel the temporal aspects of BMP/Smad signaling. A rate-limiting delay of 2-5 min occurred between BMP activation and Smad1 activity. A similar delay was observed in the Smad1/Smad4 complexation. Further experimentation indicated that the delay is dependent on the MH1 domain and linker of Smad1. These results give new insights into the dynamics of the BMP receptor -Smad1/4 signaling process and provide a new tool for studying Smads.

Role and regulation of nodal/activin receptor-like kinase 7 signaling pathway in the control of ovarian follicular atresia

Although the role of the TGF beta superfamily members in the regulation of ovarian folliculogenesis has been extensively studied, their involvement in follicular atresia is not well understood. In the present study, we have demonstrated for the first time that Nodal, a member of the TGF beta superfamily, is involved in promoting follicular atresia as evidenced by the following: 1) colocalization of Nodal and its type I receptor Activin receptor-like kinase 7 (ALK7) proteins in the granulosa cells was only observed in atretic antral follicles, whereas they were present in theca cells and granulosa cells of healthy follicles, respectively; 2) addition of recombinant Nodal or overexpression of Nodal by adenoviral infection induced apoptosis of otherwise healthy granulosa cells; 3) constitutively active ALK7 (ALK7-ca) overexpression mimicked the function of Nodal in the induction of granulosa cell apoptosis. Furthermore, overexpression of Nodal or ALK7-ca increased phosphorylation and nuclear translocation of Smad2, decreased X-linked inhibitor of apoptotic proteins (Xiap) expression at both mRNA and protein level and phospho-Akt content, as well as triggered mitochondrial release of death proteins Smac/DIABLO, Omi/HtrA2, and cytochrome c in the granulosa cells. Dominant-negative Smad2 significantly attenuated ALK7-ca-induced down-regulation of Xiap and thus rescued granulosa cells from undergoing apoptosis. In addition, whereas up-regulation of Xiap significantly attenuated ALK7-ca-induced apoptosis, down-regulation of Xiap sensitized granulosa cells to ALK7-ca-induced apoptosis. Furthermore, ALK7-ca-induced apoptosis was significantly attenuated by forced expression of activated Akt, and Akt rescued granulosa cells from undergoing apoptosis via proteasome-mediated ALK7 degradation. Taken together, Nodal plays an atretogenic role in the ovary where it induces granulosa cell apoptosis through activation of Smad2, down-regulation of the key survival molecules Xiap and phospho-Akt, as well as the activation of mitochondrial death pathway.

Smad signalling in the ovary

It has now been a decade since the first discovery of the intracellular Smad proteins, the downstream signalling molecules of one of the most important growth factor families in the animal kingdom, the transforming growth factor beta (TGF-beta) superfamily. In the ovary, several TGF-beta superfamily members are expressed by the oocyte, granulosa and thecal cells at different stages of folliculogenesis, and they signal mainly through two different Smad pathways in an autocrine/paracrine manner. Defects in the upstream signalling cascade molecules, the ligands and receptors, are known to have adverse effects on ovarian organogenesis and folliculogenesis, but the role of the individual Smad proteins in the proper function of the ovary is just beginning to be understood for example through the use of Smad knockout models. Although most of the different Smad knockouts are embryonic lethal, it is known, however, that in Smad1 and Smad5 knockout mice primordial germ cell development is impaired and that Smad3 deficient mice harbouring a deletion in exon 8 exhibit impaired folliculogenesis and reduced fertility. In this minireview we discuss the role of Smad structure and function in the ovarian context.

Genomic analyses facilitate identification of receptors and signalling pathways for growth differentiation factor 9 and related orphan bone morphogenetic protein/growth differentiation factor ligands

Recent advances in genomic sequencing allow a new paradigm in hormonal research, and a comparative genomic approach facilitates the identification of receptors and signalling mechanisms for orphan ligands of the transforming growth factor beta (TGFbeta) superfamily. Instead of purifying growth differentiation factor 9 (GDF9) receptor proteins for identification, we hypothesized that GDF9, like other ligands in the TGFbeta family, activates type II and type I serine/threonine kinase receptors. Because searches of the human genome for genes with sequence homology to known serine/threonine kinase receptors failed to reveal uncharacterized receptor genes, GDF9 likely interacts with the known type II and type I activin receptor-like kinase (ALK) receptors in granulosa cells. We found that co-treatment with the bone morphogenetic protein (BMP) type II receptor (BMPRII) ectodomain blocks GDF9 activity. Likewise, in a GDF9-non-responsive cell line, overexpression of ALK5, but none of the other six type I receptors, conferred GDF9 responsiveness. The roles of BMPRII and ALK5 as receptors for GDF9 were validated in granulosa cells using gene "knock-down" approaches. Furthermore, we demonstrated the roles of BMPRII, ALK3 and ALK6 as the receptors for the orphan ligands GDF6, GDF7 and BMP10. Thus, evolutionary tracing of polypeptide ligands, receptors and downstream signalling molecules in their respective 'subgenomes' facilitates a new approach for hormonal research.

Transforming growth factor B1 stimulated DNA synthesis in the granulosa cells of preantral follicles: negative interaction with epidermal growth factor

EGF or TGFB1 alone stimulates but together attenuate granulosa cell DNA synthesis. Intact preantral follicles from hamsters were cultured with TGFB1, EGF, or both to reveal the mechanisms of such unique regulation. Follicular CCND2 (also known as cyclin D2), CDKN1B (also known as p27(kip1)), and the involvement of appropriate signaling intermediaries and kinases were examined. TGFB1, acting via SMAD2 and SMAD3, antagonized the degradation of CCND2 protein by blocking its phosphorylation. In contrast, TGFB1 supported CDKN1B degradation by involving MAPK14 (also known as p38 Map Kinase) and PKC, resulting in CDK4 activation and DNA synthesis. EGF via MAPK3/1 maintained functional levels of CCND2 through CCND2 synthesis as well as degradation. EGF and TGFB1 together inhibited CDK4 activation and DNA synthesis. EGF attenuated TGFB1 stimulated phosphorylation of SMAD3, TGFB1-induced activation of MAPK14 and PKC, and TGFB1 suppression of CCND2 degradation. In contrast, TGFB1 suppressed EGF-induced increase in CCND2 mRNA levels. The final outcome was CCND2 degradation without replenishment and decreased activities of MAPK14 and PKC leading to suppression of CDK4 activation. The results indicate that each growth factor involves a separate mechanism to maintain an effective level of CCND2 in granulosa cells for the activation of CDK4 and induction of DNA synthesis. However, their simultaneous action is inhibitory to follicular DNA synthesis because they counteract each other's activity by interfering at specific sites. Because both EGF and TGFB1 are present in granulosa cells, this mechanism may explain how their effects are temporally modulated for granulosa cell proliferation and folliculogenesis.

The role of proteins of the transforming growth factor-beta superfamily in the intraovarian regulation of follicular development

Ovarian follicular development occurs in a hierarchical manner with each follicle having a unique biochemical composition at any moment in time. It has long been understood that a precise coordination between the growth and maturation of the oocyte and adjacent follicular cells (i.e. somatic cells) is essential in order to produce an oocyte that is fully competent to undergo fertilization and embryo development. In addition to the critical endocrine signalling pathways between the hypothalamus, pituitary and ovary, it is now evident that the oocyte itself is important in influencing the microenvironment of the developing follicle by regulating, via paracrine and autocrine mechanisms, its own maturation as well as somatic cell proliferation, differentiation and ovulation rate. Several of the key oocyte-derived regulating factors are members of the transforming growth factor-beta (TGF-beta) superfamily and to date the best understood are growth differentiation factor 9 (GDF9), bone morphogenetic protein 15 (BMP15) and BMP6. Significant species differences appear to exist in the relative importance of these growth factors and much remains to be elucidated about their roles in the human ovary. More information on the roles of these factors during ovarian follicular development is likely to advance new therapeutic applications for management of fertility as well as our understanding of how better to assess oocyte quality.

Induction of cyclin D2 in rat granulosa cells requires FSH-dependent relief from FOXO1 repression coupled with positive signals from Smad

Ovarian follicles undergo exponential growth in response to follicle-stimulating hormone (FSH), largely as a result of the proliferation of granulosa cells (GCs). In vitro under serum-free conditions, rat GCs differentiate in response to FSH but do not proliferate unless activin is also present. In the presence of FSH plus activin, GCs exhibit enhanced expression of cyclin D2 as well as inhibin-alpha, aromatase, steroidogenic factor-1 (SF-1), cholesterol side chain (SCC), and epiregulin. In this report we sought to identify the signaling pathways by which FSH and activin promote GC proliferation and differentiation. Our results show that these responses are associated with prolonged Akt phosphorylation relative to time-matched controls and are dependent on phosphatidylinositol 3-kinase (PI 3-kinase) and Smad2/3 signaling, based on the ability of the PI 3-kinase inhibitor LY294002 or infection with adenoviral dominant negative Smad3 (DN-Smad3) mutant to attenuate induction of cyclin D2, inhibin-alpha, aromatase, SCC, SF-1, and epiregulin. The DN-Smad3 mutant also abolished prolonged Akt phosphorylation stimulated by FSH plus activin 24 h post-treatment. Infection with the adenoviral constitutively active forkhead box-containing protein, O subfamily (FOXO)1 mutant suppressed induction of cyclin D2, aromatase, inhibin-alpha, SF-1, and epiregulin. Transient transfections of GCs with constitutively active FOXO1 mutant also suppressed cyclin D2, inhibin-alpha, and epiregulin promoter-reporter activities. Chromatin immunoprecipitation results demonstrate in vivo the association of FOXO1 with the cyclin D2 promoter in untreated GCs and release of FOXO1 from the cyclin D2 promoter upon addition of FSH plus activin. These results suggest that proliferation and differentiation of GCs in response to FSH plus activin requires both removal of FOXO1-dependent repression and positive signaling from Smad2/3.

Ovarian Follicle Development Requires Smad3

Smad3 is an important mediator of the TGFβ signaling pathway. Interestingly, Smad3-deficient (Smad3−/−) mice have reduced fertility compared with wild-type (WT) mice. To better understand the molecular mechanisms underlying the reduced fertility in Smad3−/− animals, this work tested the hypothesis that Smad3 deficiency interferes with three critical aspects of folliculogenesis: growth, atresia, and differentiation. Growth was assessed by comparing the size of follicles, expression of proliferating cell nuclear antigen, and expression of cell cycle genes in Smad3−/− and WT mice. Atresia was assessed by comparing the incidence of atresia and expression of bcl-2 genes involved in cell death and cell survival in Smad3−/− and WT mice. Differentiation was assessed by comparing the expression of FSH receptor (FSHR), estrogen receptor (ER) α, ERβ, and inhibin α-, βA-, and βB-subunits in Smad3−/− and WT mice. Because growth, atresia, and differentiation are regulated by hormones, estradiol, FSH, and LH levels were compared in Smad3−/− and WT mice. Moreover, because alterations in folliculogenesis can affect the ability of mice to ovulate, the number of corpora lutea and ovulated eggs in response to gonadotropin treatments were compared in Smad3−/− and WT animals. The results indicate that Smad3 deficiency slows follicle growth, which is characterized by small follicle diameters, low levels of proliferating cell nuclear antigen, and low expression of cell cycle genes (cyclin-dependent kinase 4 and cyclin D2). Smad3 deficiency also causes atretic follicles, degenerated oocytes, and low expression of bcl-2. Furthermore, Smad3 deficiency affects follicular differentiation as evidenced by decreased expression of ERβ, increased expression of ERα, and decreased expression of inhibin α-subunits. Smad3 deficiency causes low estradiol and high FSH levels. Finally, Smad3−/− ovaries have no corpora lutea, and they do not ovulate after ovulatory induction with exogenous gonadotropins. Collectively, these data provide the first evidence that reduced fertility in Smad3−/− mice is due to impaired folliculogenesis, associated with altered expression of genes that control cell cycle progression, cell survival, and cell differentiation. The findings that Smad3−/− follicles have impaired growth, increased atresia, and altered differentiation in the presence of high FSH levels, normal expression of FSHR, and lower expression of cyclin D2, suggest a possible interaction between Smad3 and FSH signaling downstream of FSHR in the mouse ovary.