Follicle-stimulating hormone synthesis and fertility depend on SMAD4 and FOXL2

A comprehensive transcriptomic view on the role of SMAD4 gene by RNAi-mediated knockdown in porcine follicular granulosa cells

As a key mediator of the transforming growth factor-beta (TGF-β) signaling pathway, which plays a pivotal role in regulating mammalian reproductive performance, Sma- and Mad-related protein 4 (SMAD4) is closely associated with the development of ovarian follicular. However, current knowledge of the genome-wide view on the role of SMAD4 gene in mammalian follicular granulosa cells (GCs) is still largely unknown. In the present study, RNA-Seq was performed to investigate the effects of SMAD4 knockdown by RNA interference (SMAD4-siRNA) in porcine follicular GCs. A total of 1025 differentially expressed genes (DEGs), including 530 upregulated genes and 495 downregulated genes, were identified in SMAD4-siRNA treated GCs compared with that treated with NC-siRNA. Furthermore, functional enrichment analysis indicated that upregulated DEGs in SMAD4-siRNA treated cells were mainly enriched in cell-cycle related processes, interferon signaling pathway, and immune system process, while downregulated DEGs in SMAD4-siRNA treated cells were mainly involved in extracellular matrix organization/disassembly, pathogenesis, and cell adhesion. In particular, cell cycle and TGF-β signaling pathway were discovered as the canonical pathways changed under SMAD4-silencing. Taken together, our data reveals SMAD4 knockdown alters the expression of numerous genes involved in key biological processes of the development of follicular GCs and provides a novel global clue of the role of SMAD4 gene in porcine follicular GCs, thus improving our understanding of regulatory mechanisms of SMAD4 gene in follicular development.

Molecular Plasticity of Male and Female Murine Gonadotropes Revealed by mRNA Sequencing

Gonadotropes in the anterior pituitary gland are of particular importance within the hypothalamic-pituitary-gonadal axis because they provide a means of communication and thus a functional link between the brain and the gonads. Recent results indicate that female gonadotropes may be organized in the form of a network that shows plasticity and adapts to the altered endocrine conditions of different physiological states. However, little is known about functional changes on the molecular level within gonadotropes during these different conditions. In this study we capitalize on a binary genetic strategy in order to fluorescently label murine gonadotrope cells. Using this mouse model allows to produce an enriched gonadotrope population using fluorescence activated cell sorting to perform mRNA sequencing. By using this strategy, we analyze and compare the expression profile of murine gonadotropes in different genders and developmental and hormonal stages. We find that gonadotropes taken from juvenile males and females, from cycling females at diestrus and at proestrus, from lactating females, and from adult males each have unique gene expression patterns with approximately 100 to approximately 500 genes expressed only in one particular stage. We also demonstrate extensive gene-expression profile changes with up to approximately 2200 differentially expressed genes when comparing female and male development, juveniles and adults, and cycling females. Differentially expressed genes were significantly enriched in the GnRH signaling, calcium signaling, and MAPK signaling pathways by Kyoto Encyclopedia of Genes and Genomes analysis. Our data provide an unprecedented molecular view of the primary gonadotropes and reveal a high degree of molecular plasticity within the gonadotrope population.

GnRH Pulse Frequency Control of Fshb Gene Expression Is Mediated via ERK1/2 Regulation of ICER

The pulsatile release of GnRH regulates the synthesis and secretion of pituitary FSH and LH. Two transcription factors, cAMP-response element-binding protein (CREB) and inducible cAMP early repressor (ICER), have been implicated in the regulation of rat Fshb gene expression. We previously showed that the protein kinase A pathway mediates GnRH-stimulated CREB activation. We hypothesized that CREB and ICER are activated by distinct signaling pathways in response to pulsatile GnRH to modulate Fshb gene expression, which is preferentially stimulated at low vs high pulse frequencies. In the LβT2 gonadotrope-derived cell line, GnRH stimulation increased ICER mRNA and protein. Blockade of ERK activation with mitogen-activated protein kinase kinase I/II (MEKI/II) inhibitors significantly attenuated GnRH induction of ICER mRNA and protein, whereas protein kinase C, calcium/calmodulin-dependent protein kinase II, and protein kinase A inhibitors had minimal effects. GnRH also stimulated ICER in primary mouse pituitary cultures, attenuated similarly by a MEKI/II inhibitor. In a perifusion paradigm, MEKI/II inhibition in LβT2 cells stimulated with pulsatile GnRH abrogated ICER induction at high GnRH pulse frequencies, with minimal effect at low frequencies. MEKI/II inhibition reduced GnRH stimulation of Fshb at high and low pulse frequencies, suggesting that the ERK pathway has additional effects on GnRH regulation of Fshb, beyond those mediated by ICER. Indeed, induction of the activating protein 1 proteins, cFos and cJun, positive modulators of Fshb transcription, by pulsatile GnRH was also abrogated by inhibition of the MEK/ERK signaling pathway. Collectively, these studies indicate that the signaling pathways mediating GnRH activation of CREB and ICER are distinct, contributing to the decoding of the pulsatile GnRH to regulate FSHβ expression.

Fshb-iCre mice are efficient and specific Cre deleters for the gonadotrope lineage

Genetic analysis of development and function of the gonadotrope cell lineage within mouse anterior pituitary has been greatly facilitated by at least three currently available Cre strains in which Cre was either knocked into the Gnrhr locus or expressed as a transgene from Cga and Lhb promoters. However, in each case there are some limitations including CRE expression in thyrotropes within pituitary or ectopic expression outside of pituitary, for example in some populations of neurons or gonads. Hence, these Cre strains often pose problems with regard to undesirable deletion of alleles in non-gonadotrope cells, fertility and germline transmission of mutant alleles. Here, we describe generation and characterization of a new Fshb-iCre deleter strain using 4.7 kb of ovine Fshb promoter regulatory sequences driving iCre expression exclusively in the gonadotrope lineage within anterior pituitary. Fshb-iCre mice develop normally, display no ectopic CRE expression in gonads and are fertile. When crossed onto a loxP recombination-mediated red to green color switch reporter mouse genetic background, in vivo CRE recombinase activity is detectable in gonadotropes at more than 95% efficiency and the GFP-tagged gonadotropes readily purified by fluorescence activated cell sorting. We demonstrate the applicability of this Fshb-iCre deleter strain in a mouse model in which Dicer is efficiently and selectively deleted in gonadotropes. We further show that loss of DICER-dependent miRNAs in gonadotropes leads to profound suppression of gonadotropins resulting in male and female infertility. Thus, Fshb-iCre mice serve as a new genetic tool to efficiently manipulate gonadotrope-specific gene expression in vivo.

Aetiological coding sequence variants in non-syndromic premature ovarian failure: From genetic linkage analysis to next generation sequencing

Premature ovarian failure (POF) is a frequent pathology affecting 1-1.5% of women under 40 years old. Despite advances in diagnosing and treating human infertility, POF is still classified as being idiopathic in 50-80% of cases, strongly suggesting a genetic origin for the disease. Different types of autosomal and X-linked genetic anomalies can originate the phenotype in syndromic and non-syndromic POF cases. Particular interest has been focused on research into non-syndromic POF causative coding variants during the past two decades. This has been based on the assumption that amino acid substitutions might modify the intrinsic physicochemical properties of functional proteins, thereby inducing pathological phenotypes. In this case, a restricted number of mutations might originate the disease. However, like other complex pathologies, POF might result from synergistic/compensatory effects caused by several low-to-mildly drastic mutations which have frequently been classified as non-functional SNPs. Indeed, reproductive phenotypes can be considered as quantitative traits resulting from the subtle interaction of many genes. Although numerous sequencing projects have involved candidate genes, only a few coding mutations explaining a low percentage of cases have been described. Such apparent failure to identify aetiological coding sequence variations might have been due to the inherent molecular complexity of mammalian reproduction and to the difficulty of simultaneously analysing large genomic regions by Sanger sequencing. The purpose of this review is to present the molecular and cellular effects caused by non-synonymous mutations which have been formally associated, by functional tests, with the aetiology of hypergonadotropic non-syndromic POF. Considerations have also been included regarding the polygenic nature of reproduction and POF, as well as future approaches for identifying novel aetiological genes based on next generation sequencing (NGS).

Gene variants associated with age at menopause are also associated with polycystic ovary syndrome, gonadotrophins and ovarian volume

STUDY QUESTION

Is there a relationship between the genetic risk for polycystic ovary syndrome (PCOS) and genetic variants that influence timing of menopause?

SUMMARY ANSWER

The genetic risk score, which sums the contribution of variants at all menopause loci, was associated with PCOS.

WHAT IS ALREADY KNOWN

Ovarian parameters and anti-Mullerian hormone levels suggest that women with PCOS should have a later age at menopause.

STUDY DESIGN, SIZE, DURATION

The study was a case-control examination of genetic variants associated with age at menopause in a discovery cohort of women with PCOS (n = 485) and controls (n = 407) from Boston recruited from 2003 to 2012. Replication was performed in women from Greece (cases, n = 884 and controls, n = 311).

PARTICIPANTS/MATERIALS, SETTINGS, METHODS

PCOS was defined by the National Institutes of Health criteria in Boston and Greece (n = 783), with additional subjects fulfilling the Rotterdam criteria (hyperandrogenism, polycystic ovary morphology and regular menses) in Greece (n = 101). Controls in Boston and Greece had regular menstrual cycles and no hyperandrogenism. Allele frequencies for variants previously associated with age at menopause were examined in PCOS cases and controls, along with the relationship to quantitative traits.

MAIN RESULTS AND ROLE OF CHANCE

The variant rs11668344-G was associated with decreased risk of PCOS (odds ratio: 0.77 [0.59-0.93]; P = 0.004). There was a strong relationship between the late menopause allele rs12294104-T and increased LH levels (β ± SE; 0.26 ± 0.06; P = 5.2 × 10(-5)) and the LH:FSH ratio (0.28 ± 0.06; P = 2.7 × 10(-6)). The minor allele at rs10852344-T was associated with smaller ovarian volume (-0.16 ± 0.05; P = 0.0012). A genetic risk score calculated from 16 independent variants associated with age at menopause was also associated with PCOS (P < 0.02), LH and the LH:FSH ratio (both P < 0.05).

LIMITATIONS, REASONS FOR CAUTION

The variant rs11668344 was not associated with PCOS in the Greek cohort, but results exhibited the same direction of effect as the Boston cohort. However, it is possible that the individual association was a false positive in the Boston cohort.

WIDER IMPLICATIONS OF THE FINDINGS

The study demonstrates that gene variants known to influence age at menopause are also associated with risk for PCOS. Further, our data suggest that the relationship between age at menopause and PCOS may be explained, at least in part, by effects on LH levels and follicle number. The data point to opposing influences of the genetic variants on both menopausal age and PCOS.

STUDY FUNDING/COMPETING INTERESTS

The project was supported by award number R01HD065029 from the Eunice Kennedy Shriver National Institute of Child Health & Human Development, award number 1 UL1 RR025758, Harvard Clinical and Translational Science Center, from the National Center for Research Resources and award 1-10-CT-57 from the American Diabetes Association. C.K.W. is a consultant for Takeda Pharmaceuticals.

TRIAL REGISTRATION NUMBER

NCT00166569.

Maximal expression of Foxl2 in pituitary gonadotropes requires ovarian hormones

Gonadotropin-releasing hormone (GnRH) and activin regulate synthesis of FSH and ultimately fertility. Recent in vivo studies cast SMAD4 and FOXL2 as master transcriptional mediators of activin signaling that act together and independently of GnRH to regulate Fshb gene expression and female fertility. Ovarian hormones regulate GnRH and its receptor (GNRHR) through negative and positive feedback loops. In contrast, the role of ovarian hormones in regulating activin, activin receptors, and components of the activin signaling pathway, including SMAD4 and FOXL2, remains understudied. The widespread distribution of activin and many of its signaling intermediates complicates analysis of the effects of ovarian hormones on their synthesis in gonadotropes, one of five pituitary cell types. We circumvented this complication by using a transgenic model that allows isolation of polyribosomes selectively from gonadotropes of intact females and ovariectomized females treated with or without a GnRH antagonist. This paradigm allows assessment of ovarian hormonal feedback and distinguishes responses that are either independent or dependent on GnRH. Surprisingly, our results indicate that Foxl2 levels in gonadotropes decline significantly in the absence of ovarian input and independently of GnRH. Expression of the genes encoding other members of the activin signaling pathway are unaffected by loss of ovarian hormonal feedback, highlighting their selective effect on Foxl2. Expression of Gnrhr, a known target of FOXL2, also declines upon ovariectomy consistent with reduced expression of Foxl2 and loss of ovarian hormones. In contrast, Fshb mRNA increases dramatically post-ovariectomy due to increased compensatory input from GnRH. Together these data suggest that ovarian hormones regulate expression of Foxl2 thereby expanding the number of genes controlled by the hypothalamic-pituitary-gonadal axis that ultimately dictate reproductive fitness.

Minireview: Activin Signaling in Gonadotropes: What Does the FOX say… to the SMAD?

The activins were discovered and named based on their abilities to stimulate FSH secretion and FSHβ (Fshb) subunit expression by pituitary gonadotrope cells. According to subsequent in vitro observations, activins also stimulate the transcription of the GnRH receptor (Gnrhr) and the activin antagonist, follistatin (Fst). Thus, not only do activins stimulate FSH directly, they have the potential to regulate both FSH and LH indirectly by modulating gonadotrope sensitivity to hypothalamic GnRH. Moreover, activins may negatively regulate their own actions by stimulating the production of one of their principal antagonists. Here, we describe our current understanding of the mechanisms through which activins regulate Fshb, Gnrhr, and Fst transcription in vitro. The activin signaling molecules SMAD3 and SMAD4 appear to partner with the winged-helix/forkhead transcription factor, forkhead box L2 (FOXL2), to regulate expression of all 3 genes. However, in vivo data paint a different picture. Although conditional deletion of Foxl2 and/or Smad4 in murine gonadotropes produces impairments in FSH synthesis and secretion as well as in pituitary Fst expression, Gnrhr mRNA levels are either unperturbed or increased in these animals. Surprisingly, gonadotrope-specific deletion of Smad3 alone or with Smad2 does not impair FSH production or fertility; however, mice harboring these mutations may express a DNA binding-deficient, but otherwise functional, SMAD3 protein. Collectively, the available data firmly establish roles for FOXL2 and SMAD4 in Fshb and Fst expression in gonadotrope cells, whereas SMAD3's role requires further investigation. Gnrhr expression, in contrast, appears to be FOXL2, SMAD4, and, perhaps, activin independent in vivo.

Genetic regulation of murine pituitary development

Significant progress has been made recently in unravelling the embryonic events leading to pituitary morphogenesis, both in vivo and in vitro. This includes dissection of the molecular mechanisms controlling patterning of the ventral diencephalon that regulate formation of the pituitary anlagen or Rathke's pouch. There is also a better characterisation of processes that underlie maintenance of pituitary progenitors, specification of endocrine lineages and the three-dimensional organisation of newly differentiated endocrine cells. Furthermore, a population of adult pituitary stem cells (SCs), originating from embryonic progenitors, have been described and shown to have not only regenerative potential, but also the capacity to induce tumour formation. Finally, the successful recapitulation in vitro of embryonic events leading to generation of endocrine cells from embryonic SCs, and their subsequent transplantation, represents exciting advances towards the use of regenerative medicine to treat endocrine deficits. In this review, an up-to-date description of pituitary morphogenesis will be provided and discussed with particular reference to pituitary SC studies.

Gonadotrope-specific deletion of Dicer results in severely suppressed gonadotropins and fertility defects

Pituitary gonadotropins follicle-stimulating hormone and luteinizing hormone are heterodimeric glycoproteins expressed in gonadotropes. They act on gonads and promote their development and functions including steroidogenesis and gametogenesis. Although transcriptional regulation of gonadotropin subunits has been well studied, the post-transcriptional regulation of gonadotropin subunits is not well understood. To test if microRNAs regulate the hormone-specific gonadotropin β subunits in vivo, we deleted Dicer in gonadotropes by a Cre-lox genetic approach. We found that many of the DICER-dependent microRNAs, predicted in silico to bind gonadotropin β subunit mRNAs, were suppressed in purified gonadotropes of mutant mice. Loss of DICER-dependent microRNAs in gonadotropes resulted in profound suppression of gonadotropin-β subunit proteins and, consequently, the heterodimeric hormone secretion. In addition to suppression of basal levels, interestingly, the post-gonadectomy-induced rise in pituitary gonadotropin synthesis and secretion were both abolished in mutants, indicating a defective gonadal negative feedback control. Furthermore, mutants lacking Dicer in gonadotropes displayed severely reduced fertility and were rescued with exogenous hormones confirming that the fertility defects were secondary to suppressed gonadotropins. Our studies reveal that DICER-dependent microRNAs are essential for gonadotropin homeostasis and fertility in mice. Our studies also implicate microRNAs in gonadal feedback control of gonadotropin synthesis and secretion. Thus, DICER-dependent microRNAs confer a new layer of transcriptional and post-transcriptional regulation in gonadotropes to orchestrate the hypothalamus-pituitary-gonadal axis physiology.

Constitutively active FOXO1 diminishes activin induction of Fshb transcription in immortalized gonadotropes

In the present study, we investigate whether the FOXO1 transcription factor modulates activin signaling in pituitary gonadotropes. Our studies show that overexpression of constitutively active FOXO1 decreases activin induction of murine Fshb gene expression in immortalized LβT2 cells. We demonstrate that FOXO1 suppression of activin induction maps to the −304/−95 region of the Fshb promoter containing multiple activin response elements and that the suppression requires the FOXO1 DNA-binding domain (DBD). FOXO1 binds weakly to the −125/−91 region of the Fshb promoter in a gel-shift assay. Since this region of the promoter contains a composite SMAD/FOXL2 binding element necessary for activin induction of Fshb transcription, it is possible that FOXO1 DNA binding interferes with SMAD and/or FOXL2 function. In addition, our studies demonstrate that FOXO1 directly interacts with SMAD3/4 but not SMAD2 in a FOXO1 DBD-dependent manner. Moreover, we show that SMAD3/4 induction of Fshb-luc and activin induction of a multimerized SMAD-binding element-luc are suppressed by FOXO1 in a DBD-dependent manner. These results suggest that FOXO1 binding to the proximal Fshb promoter as well as FOXO1 interaction with SMAD3/4 proteins may result in decreased activin induction of Fshb in gonadotropes.