Conditional Deletion of FOXL2 and SMAD4 in Gonadotropes of Adult Mice Causes Isolated FSH Deficiency

A Point Mutation in an Otherwise Dispensable Upstream Fshb Enhancer Moderately Impairs Fertility in Female Mice

Follicle-stimulating hormone (FSH) is necessary for fertility in both sexes as a regulator of gametogenesis and hormone synthesis. Humans with loss-of-function mutations within the gene encoding the FSH beta subunit (FSHB) are infertile. Similarly, female Fshb knock-out mice are infertile and fail to ovulate, and males are subfertile. We recently reported the discovery and characterization of an upstream enhancer of FSHB located 26 Kb upstream of the transcriptional start site in humans (-17 Kb in mouse) that also amplifies activin and gonadotropin-releasing hormone induction of FSHB. Notably, the upstream enhancer contains a polymorphic, fertility-associated site in humans, rs11031006 (G/A), and the minor allele (A) increased enhancer activity in vitro as compared to the major allele (G), likely by increasing the affinity of an SF1 binding element. To investigate the role of the novel enhancer and rs11031006 variant in vivo, we created mouse models to assess deletion of the upstream enhancer and the impact of the G>A point mutation at the rs11031006-equivalent base. A full characterization of the -17 Kb enhancer deletion model revealed no apparent differences in fertility or serum FSH/LH levels, nor did a larger deletion that also included an additional putative regulatory element. In contrast, female mice homozygous for the mutated A allele at the rs11031006-equivalent position had fewer litters over a 120-day fertility assay, abnormal estrous cycling at 10 months, and reduced pituitary Lhb transcript abundance. Overall, while the mouse -17 Kb Fshb enhancer is dispensable for fertility, the rs11031006-equivalent G>A mutation results in subfertility in females.

Unveiling the role of FOXL2 in female differentiation and disease: a comprehensive review†

Ovarian differentiation relies on the accurate and orderly expression of numerous related genes. Forkhead box protein L2 (FOXL2) is one of the earliest ovarian differentiation markers and transcription factors. In sex determination, FOXL2 maintains the differentiation of the female pathway by inhibiting male differentiation genes, including SOX9 and SF1. In addition, FOXL2 promotes the synthesis of follicle-stimulating hormone and anti-Müllerian hormone to support follicle development. Mutations in FOXL2 are associated with numerous female reproductive diseases. A comprehensive and in-depth study of FOXL2 provides novel strategies for the diagnosis and treatment of such diseases. This review discusses the mechanism of FOXL2 in female sex differentiation and maintenance, hormone synthesis, and disease occurrence and reveals the role of FOXL2 as a central factor in female sex development and fertility maintenance. This review will serve as a reference for identifying novel targets of other regulatory factors interacting with FOXL2 in female sex determination and follicle development and for the diagnosis and treatment of female reproductive diseases.

Smad4 and FoxH1 potentially interact to regulate cyp19a1a promoter in the ovary of ricefield eel (Monopterus albus)

BACKGROUND

Cyp19a1a is a key enzyme in the pathway that converts androgens into estrogen and is regulated by TGF-β signaling. Smad4 and FoxH1 are downstream effectors of TGF-β signaling and may play important roles in ovarian development in M. albus.

METHODS

We investigated the expression pattern of the Smad4 and FoxH1 using qRT‒PCR and immunofluorescence, then tested the changes of smad4 and foxh1 by qRT‒PCR after ovary incubation with FSH in vitro, and analysed the regulation of cyp19a1a transcription by Smad4 and FoxH1 by dual-luciferase reporter assays.

RESULTS

We found that Smad4 encoded a putative protein of 449 amino acids and harbored the three conserved domains typical of this protein family. Smad4 and foxh1 exhibited similar expression patterns during ovarian development and after FSH incubation, with Pearson's coefficients of 0.873 and 0.63-0.81, respectively. Furthermore, Smad4, FoxH1 and Cyp19a1a colocalized in the granulosa cells and theca cells of ovaries during the mid-to-late vitellogenic stage. Smad4 repressed cyp19a1a activity via SBE1 (- 1372/-1364) and SBE2 (- 415/-407) in the cyp19a1a promoter, whereas mutating SBE1 or SBE2 restored cyp19a1a promoter activity. Co-overexpression of Smad4 and FoxH1 significantly reduced cyp19a1a promoter activity.

CONCLUSIONS

This study provides new insights into the potential functions of transcription factors Smad4 and FoxH1 in ovarian development and the transcriptional regulation mechanism of cyp19a1a in M. albus, which will reveal Smad4/FoxH1-mediated TGF-β signaling in reproduction and the regulation of the cyp19a1a. Aromatase, encoded by cyp19a1a, is involved in ovarian development and plays an important role in the quality of eggs, as well the sex ratio, of the teleost fish, M. albus. The research on the transcriptional regulation of cyp19a1a has contributed to the understanding of its role in ovarian development. In previous study, it was shown that FoxH1 inhibits cyp19a1a transcription. In the present study, Smad4 was confirmed as a cyp19a1a transcriptional repressor and Smad4 may also coordinate with FoxH1 to repress cyp19a1a transcription. At present, we provide a new perspective for the transcriptional regulation of cyp19a1a by transcription factors Smad4 and FoxH1 in teleost fish ovary. In the future, the regulatory networks of Smad4 and FoxH1 will be further studied and the gene editing technology will be applied to screen specific regulatory factors of cyp191a1a gene, so as to alter the female cycle and modulate the sex ratio of the eggs production.

SMAD4 promotes somatic-germline contact during murine oocyte growth

Development of the mammalian oocyte requires physical contact with the surrounding granulosa cells of the follicle, which provide it with essential nutrients and regulatory signals. This contact is achieved through specialized filopodia, termed transzonal projections (TZPs), that extend from the granulosa cells to the oocyte surface. Transforming growth factor (TGFβ) family ligands produced by the oocyte increase the number of TZPs, but how they do so is unknown. Using an inducible Cre recombinase strategy together with expression of green fluorescent protein to verify Cre activity in individual cells, we examined the effect of depleting the canonical TGFβ mediator, SMAD4, in mouse granulosa cells. We observed a 20-50% decrease in the total number of TZPs in SMAD4-depleted granulosa cell-oocyte complexes, and a 50% decrease in the number of newly generated TZPs when the granulosa cells were reaggregated with wild-type oocytes. Three-dimensional image analysis revealed that TZPs of SMAD4-depleted cells were longer than controls and more frequently oriented towards the oocyte. Strikingly, the transmembrane proteins, N-cadherin and Notch2, were reduced by 50% in SMAD4-depleted cells. SMAD4 may thus modulate a network of cell adhesion proteins that stabilize the attachment of TZPs to the oocyte, thereby amplifying signalling between the two cell types.

Comparative genomic survey and functional analysis of DKKL1 during spermatogenesis in the Chinese soft-shelled turtle (Pelodiscus sinensis)

A feature of the Chinese soft-shelled turtle (Pelodiscus sinensis) is seasonal spermatogenesis; however, the underlying molecular mechanism is not well clarified. Here, we firstly cloned and characterized P. sinensis DKKL1, and then performed comparative genomic studies, expression analysis, and functional validation. P. sinensis DKKL1 had 2 putative N-glycosylation sites and 16 phosphorylation sites. DKKL1 also had classic transmembrane structures that were extracellularly localized. DKKL1's genetic distance was close to turtles, followed by amphibians and mammals, but its genetic distance was far from fishes. DKKL1 genes from different species shared distinct genomic characteristics. Meanwhile, they were also relatively conserved among themselves, at least from the perspective of classes. Notably, the transcription factors associated with spermatogenesis were also identified, containing CTCF, EWSR1, and FOXL2. DKKL1 exhibited sexually dimorphic expression only in adult gonads, which was significantly higher than that in other somatic tissues (P < 0.001), and was barely expressed in embryonic gonads. DKKL1 transcripts showed a strong signal in sperm, while faint signals were detected in other male germ cells. DKKL1 in adult testes progressively increased per month (P < 0.05), displaying a seasonal expression trait. DKKL1 was significantly downregulated in testes cells after the sex hormones (17β-estradiol and 17α-methyltestosterone) and Wnt/β-catenin inhibitor treatment (P < 0.05). Likewise, the Wnt/β-catenin inhibitor treatment dramatically repressed CTCF, EWSR1, and FOXL2 expression. Conversely, they were markedly upregulated after the 17β-estradiol and 17α-methyltestosterone treatment, suggesting that the three transcription factors might bind to different promoter regions, thereby negatively regulating DKKL1 transcription in response to the changes in the estrogen and androgen pathways, and positively controlling DKKL1 transcription in answer to the alterations in the Wnt/β-catenin pathway. Knockdown of DKKL1 significantly reduced the relative expression of HMGB2 and SPATS1 (P < 0.01), suggesting that it may be involved in seasonal spermatogenesis of P. sinensis through a positive regulatory interaction with these two genes. Overall, our findings provide novel insights into the genome evolution and potential functions of seasonal spermatogenesis of P. sinensis DKKL1.

Selected Genetic Factors Associated with Primary Ovarian Insufficiency

Primary ovarian insufficiency (POI) is a heterogeneous disease resulting from non-functional ovaries in women before the age of 40. It is characterized by primary amenorrhea or secondary amenorrhea. As regards its etiology, although many POI cases are idiopathic, menopausal age is a heritable trait and genetic factors play an important role in all POI cases with known causes, accounting for approximately 20% to 25% of cases. This paper reviews the selected genetic causes implicated in POI and examines their pathogenic mechanisms to show the crucial role of genetic effects on POI. The genetic factors that can be found in POI cases include chromosomal abnormalities (e.g., X chromosomal aneuploidies, structural X chromosomal abnormalities, X-autosome translocations, and autosomal variations), single gene mutations (e.g., newborn ovary homeobox gene (NOBOX), folliculogenesis specific bHLH transcription factor (FIGLA), follicle-stimulating hormone receptor (FSHR), forkhead box L2 (FOXL2), bone morphogenetic protein 15 (BMP15), etc., as well as defects in mitochondrial functions and non-coding RNAs (small ncRNAs and long ncRNAs). These findings are beneficial for doctors to diagnose idiopathic POI cases and predict the risk of POI in women.

Revisiting the gonadotropic regulation of mammalian spermatogenesis: evolving lessons during the past decade

Spermatogenesis is a multi-step process of male germ cell (Gc) division and differentiation which occurs in the seminiferous tubules of the testes under the regulation of gonadotropins - Follicle Stimulating Hormone (FSH) and Luteinising hormone (LH). It is a highly coordinated event regulated by the surrounding somatic testicular cells such as the Sertoli cells (Sc), Leydig cells (Lc), and Peritubular myoid cells (PTc). FSH targets Sc and supports the expansion and differentiation of pre-meiotic Gc, whereas, LH operates via Lc to produce Testosterone (T), the testicular androgen. T acts on all somatic cells e.g.- Lc, PTc and Sc, and promotes the blood-testis barrier (BTB) formation, completion of Gc meiosis, and spermiation. Studies with hypophysectomised or chemically ablated animal models and hypogonadal (hpg) mice supplemented with gonadotropins to genetically manipulated mouse models have revealed the selective and synergistic role(s) of hormones in regulating male fertility. We here have briefly summarized the present concept of hormonal control of spermatogenesis in rodents and primates. We also have highlighted some of the key critical questions yet to be answered in the field of male reproductive health which might have potential implications for infertility and contraceptive research in the future.

Transcription factor GATA2 may potentiate follicle-stimulating hormone production in mice via induction of the BMP antagonist gremlin in gonadotrope cells

Mammalian reproduction depends on the gonadotropins, follicle-stimulating hormone (FSH), and luteinizing hormone, which are secreted by pituitary gonadotrope cells. The zinc-finger transcription factor GATA2 was previously implicated in FSH production in male mice; however, its mechanisms of action and role in females were not determined. To directly address GATA2 function in gonadotropes, we generated and analyzed gonadotrope-specific Gata2 KO mice using the Cre-lox system. We found that while conditional KO (cKO) males exhibited ∼50% reductions in serum FSH levels and pituitary FSHβ subunit (Fshb) expression relative to controls, FSH production was apparently normal in cKO females. In addition, RNA-seq analysis of purified gonadotropes from control and cKO males revealed a profound decrease in expression of gremlin (Grem1), a bone morphogenetic protein (BMP) antagonist. We show Grem1 was expressed in gonadotropes, but not other cell lineages, in the adult male mouse pituitary. Furthermore, Gata2, Grem1, and Fshb mRNA levels were significantly higher in the pituitaries of WT males relative to females but decreased in males treated with estradiol and increased following ovariectomy in control but not cKO females. Finally, we found that recombinant gremlin stimulated Fshb expression in pituitary cultures from WT mice. Collectively, the data suggest that GATA2 promotes Grem1 expression in gonadotropes and that the gremlin protein potentiates FSH production. The mechanisms of gremlin action have not yet been established but may involve attenuation of BMP binding to activin type II receptors in gonadotropes, facilitating induction of Fshb transcription by activins or related ligands.

Deletion of Gαq/11 or Gαs Proteins in Gonadotropes Differentially Affects Gonadotropin Production and Secretion in Mice

Gonadotropin-releasing hormone (GnRH) regulates gonadal function via its stimulatory effects on gonadotropin production by pituitary gonadotrope cells. GnRH is released from the hypothalamus in pulses and GnRH pulse frequency differentially regulates follicle-stimulating hormone (FSH) and luteinizing hormone (LH) synthesis and secretion. The GnRH receptor (GnRHR) is a G protein-coupled receptor that canonically activates Gα q/11-dependent signaling on ligand binding. However, the receptor can also couple to Gα s and in vitro data suggest that toggling between different G proteins may contribute to GnRH pulse frequency decoding. For example, as we show here, knockdown of Gα s impairs GnRH-stimulated FSH synthesis at low- but not high-pulse frequency in a model gonadotrope-derived cell line. We next used a Cre-lox conditional knockout approach to interrogate the relative roles of Gα q/11 and Gα s proteins in gonadotrope function in mice. Gonadotrope-specific Gα q/11 knockouts exhibit hypogonadotropic hypogonadism and infertility, akin to the phenotypes seen in GnRH- or GnRHR-deficient mice. In contrast, under standard conditions, gonadotrope-specific Gα s knockouts produce gonadotropins at normal levels and are fertile. However, the LH surge amplitude is blunted in Gα s knockout females and postgonadectomy increases in FSH and LH are reduced both in males and females. These data suggest that GnRH may signal principally via Gα q/11 to stimulate gonadotropin production, but that Gα s plays important roles in gonadotrope function in vivo when GnRH secretion is enhanced.

Addition of a carboxy terminal tail to the normally tailless gonadotropin-releasing hormone receptor impairs fertility in female mice

Gonadotropin-releasing hormone (GnRH) is the primary neuropeptide controlling reproduction in vertebrates. GnRH stimulates follicle-stimulating hormone (FSH) and luteinizing hormone (LH) synthesis via a G-protein-coupled receptor, GnRHR, in the pituitary gland. In mammals, GnRHR lacks a C-terminal cytosolic tail (Ctail) and does not exhibit homologous desensitization. This might be an evolutionary adaptation that enables LH surge generation and ovulation. To test this idea, we fused the chicken GnRHR Ctail to the endogenous murine GnRHR in a transgenic model. The LH surge was blunted, but not blocked in these mice. In contrast, they showed reductions in FSH production, ovarian follicle development, and fertility. Addition of the Ctail altered the nature of agonist-induced calcium signaling required for normal FSH production. The loss of the GnRHR Ctail during mammalian evolution is unlikely to have conferred a selective advantage by enabling the LH surge. The adaptive significance of this specialization remains to be determined.

Gonadotrope-specific deletion of the BMP type 2 receptor does not affect reproductive physiology in mice†‡

Activins selectively stimulate follicle-stimulating hormone (FSH) secretion by pituitary gonadotrope cells. More recently, other members of the TGFbeta superfamily, the bone morphogenetic proteins (BMPs), were reported to regulate FSH synthesis. Activins and BMPs independently and synergistically stimulate transcription of the FSHbeta subunit (Fshb) gene in immortalized gonadotrope-like cells. Both ligands can signal via the activin receptor type IIA (ACVR2A) to regulate FSH synthesis in vitro. In vivo, global Acvr2a knockout mice exhibit a 60% reduction in circulating FSH relative to wild-type animals, suggesting that activins, BMPs, or related ligands might signal through additional type II receptors to regulate FSH in vivo. Although the leading candidates are ACVR2B and the BMP type II receptor (BMPR2), only the latter mediates activin or BMP2 induction of Fshb transcription in vitro. Here, we generated mice carrying a loss of function mutation in Bmpr2 specifically in gonadotropes. Puberty onset, estrous cyclicity, and reproductive organ weights were similar between control and conditional knockout females. Serum FSH and luteinizing hormone (LH) and pituitary expression of Fshb and the LHbeta subunit (Lhb) were similarly unaffected by the gene deletion in both sexes. These results suggest that BMPR2 might not play a necessary role in FSH synthesis or secretion in vivo or that another type II receptor, such as ACVR2A, can fully compensate for its absence. These data also further contribute to the emerging concept that BMPs may not be physiological regulators of FSH in vivo.

Distal Enhancer Potentiates Activin- and GnRH-Induced Transcription of FSHB

FSH is critical for fertility. Transcription of FSHB, the gene encoding the beta subunit, is rate-limiting in FSH production and is regulated by both GnRH and activin. Activin signals through SMAD transcription factors. Although the mechanisms and importance of activin signaling in mouse Fshb transcription are well-established, activin regulation of human FSHB is less well understood. We previously reported a novel enhancer of FSHB that contains a fertility-associated single nucleotide polymorphism (rs10031006) and requires a region resembling a full (8 base-pair) SMAD binding element (SBE). Here, we investigated the role of the putative SBE within the enhancer in activin and GnRH regulation of FSHB. In mouse gonadotrope-derived LβT2 cells, the upstream enhancer potentiated activin induction of both the human and mouse FSHB proximal promoters and conferred activin responsiveness to a minimal promoter. Activin induction of the enhancer required the SBE and was blocked by the inhibitory SMAD7, confirming involvement of the classical SMAD signaling pathway. GnRH induction of FSHB was also potentiated by the enhancer and dependent on the SBE, consistent with known activin/GnRH synergy regulating FSHB transcription. In DNA pull-down, the enhancer SBE bound SMAD4, and chromatin immunoprecipitation demonstrated SMAD4 enrichment at the enhancer in native chromatin. Combined activin/GnRH treatment elevated levels of the active transcriptional histone marker, histone 3 lysine 27 acetylation, at the enhancer. Overall, this study indicates that the enhancer is directly targeted by activin signaling and identifies a novel, evolutionarily conserved mechanism by which activin and GnRH can regulate FSHB transcription.

Development of a Highly Sensitive ELISA for Measurement of FSH in Serum, Plasma, and Whole Blood in Mice

Follicle-stimulating hormone (FSH) regulates gonadal function and fertility. Measurement of FSH in bodily fluids and tissues is possible with radioimmunoassays and enzyme-linked immunosorbent assays (ELISAs). Recently, several novel assays were developed to measure pituitary hormones including growth hormone, prolactin, and luteinizing hormone in mice from small sample volumes. Here, we describe a novel and sensitive ELISA that enables the accurate measurement of FSH in serum, plasma, and whole blood from female and male mice. The assay can also be used to measure FSH in murine pituitary lysates and cell culture media. In summary, the new methodology described here will enable investigators to measure FSH from a variety of biological samples in mice accurately, at low cost, and in their own laboratories.

Single cell ATAC-Seq reveals cell type-specific transcriptional regulation and unique chromatin accessibility in human spermatogenesis

During human spermatogenesis, germ cells undergo dynamic changes in chromatin organization/re-packaging and in transcriptomes. In order to better understand the underlying mechanism(s), scATAC-Seq of 5376 testicular cells from 3 normal men were performed. Data were analyzed in parallel with the scRNA-Seq data of human testicular cells. Ten germ cell types associated with spermatogenesis and 6 testicular somatic cell types were identified, along with 142 024 peaks located in promoter, genebody and CpG Island. We had examined chromatin accessibility of all chromosomes, with chromosomes 19 and 17 emerged as the leading chromosomes that displayed high chromatin accessibility. In accessible chromatin regions, transcription factor (TF)-binding sites were identified and specific motifs with high frequencies at different spermatogenesis stages were detected, including CTCF, BORIS, NFY, DMRT6, EN1, ISL1 and GLI3. Two most notable observations were noted. First, TLE3 was specifically expressed in differentiating spermatogonia. Second, PFN4 was found to be involved in actin cytoskeletal organization during meiosis. More important, unique regions upstream of PFN4 and TLE3 were shown to display high accessibility, illustrating their significance in supporting human spermatogenesis.

Increased FOXL2 expression alters uterine structures and functions†

The transcription factor forkhead box L2 (FOXL2) regulates sex differentiation and reproductive function. Elevated levels of this transcription factor have been observed in the diseases of the uterus, such as endometriosis. However, the impact of elevated FOXL2 expression on uterine physiology remains unknown. In order to determine the consequences of altered FOXL2 in the female reproductive axis, we generated mice with over-expression of FOXL2 (FOXL2OE) by crossing Foxl2LsL/+ with the Progesterone receptor Pgrcre model. FOXL2OE uterus showed severe morphological abnormality including abnormal epithelial stratification, blunted adenogenesis, increased endometrial fibrosis, and disrupted myometrial morphology. In contrast, increasing FOXL2 levels specifically in uterine epithelium by crossing the Foxl2LsL/+ with the lactoferrin Ltficre mice resulted in the eFOXL2OE mice with uterine epithelial stratification but without defects in endometrial fibrosis and adenogenesis, demonstrating a role of the endometrial stroma in the uterine abnormalities of the FOXL2OE mice. Transcriptomic analysis of 12 weeks old Pgrcre and FOXL2OE uterus at diestrus stage showed multiple signaling pathways related with cellular matrix, wnt/β-catenin, and altered cell cycle. Furthermore, we found FOXL2OE mice were sterile. The infertility was caused in part by a disruption of the hypophyseal ovarian axis resulting in an anovulatory phenotype. The FOXL2OE mice failed to show decidual responses during artificial decidualization in ovariectomized mice demonstrating the uterine contribution to the infertility phenotype. These data support that aberrantly increased FOXL2 expressions in the female reproductive tract can disrupt ovarian and uterine functions.

Murine FSH Production Depends on the Activin Type II Receptors ACVR2A and ACVR2B

Activins are selective regulators of FSH production by pituitary gonadotrope cells. In a gonadotrope-like cell line, LβT2, activins stimulate FSH via the activin type IIA receptor (ACVR2A) and/or bone morphogenetic protein type II receptor (BMPR2). Consistent with these observations, FSH is greatly reduced, though still present, in global Acvr2a knockout mice. In contrast, FSH production is unaltered in gonadotrope-specific Bmpr2 knockout mice. In light of these results, we questioned whether an additional type II receptor might mediate the actions of activins or related TGF-β ligands in gonadotropes. We focused on the activin type IIB receptor (ACVR2B), even though it does not mediate activin actions in LβT2 cells. Using a Cre-lox strategy, we ablated Acvr2a and/or Acvr2b in murine gonadotropes. The resulting conditional knockout (cKO) animals were compared with littermate controls. Acvr2a cKO (cKO-A) females were subfertile (~70% reduced litter size), cKO-A males were hypogonadal, and both sexes showed marked decreases in serum FSH levels compared with controls. Acvr2b cKO (cKO-B) females were subfertile (~20% reduced litter size), cKO-B males had a moderate decrease in testicular weight, but only males showed a significant decrease in serum FSH levels relative to controls. Simultaneous deletion of both Acvr2a and Acvr2b in gonadotropes led to profound hypogonadism and FSH deficiency in both sexes; females were acyclic and sterile. Collectively, these data demonstrate that ACVR2A and ACVR2B are the critical type II receptors through which activins or related TGF-β ligands induce FSH production in mice in vivo.

Human Follicle-Stimulating Hormone ß Subunit Expression Depends on FOXL2 and SMAD4

Follicle-stimulating hormone (FSH), an essential regulator of mammalian fertility, is synthesized by pituitary gonadotrope cells in response to activins. In mice, activins signal via SMAD3, SMAD4, and FOXL2 to regulate transcription of the FSHβ subunit (Fshb) gene. Gonadotrope-specific deletion of Foxl2, alone or in combination with Smad4, renders mice FSH-deficient. Whether human FSHB expression is similarly regulated is not known. Here, we used a combination of transgenic and conditional knockout mouse strains to assess the roles of activins, FOXL2, and SMAD4 in regulation of the human FSHB gene. First, we cultured pituitaries from mice harboring a human FSHB transgene (hFSHB mice) and measured both murine Fshb and human FSHB messenger ribonucleic acid (mRNA) expression in response to exogenous activins or two antagonists of endogenous activin-like signaling (follistatin-288 and SB431542). Both murine Fshb and human FSHB expression were stimulated by activins and reduced by the inhibitors. Next, we analyzed human FSHB expression in hFSHB mice carrying floxed Foxl2 and Smad4 alleles. Cre-mediated ablation of FOXL2 and SMAD4 strongly reduced basal and activin-stimulated murine Fshb and human FSHB expression in cultured pituitaries. Finally, the hFSHB transgene was previously shown to rescue FSH production and fertility in Fshb knockout mice. However, gonadotrope-specific Foxl2/Smad4 knockout females carrying the hFSHB transgene have significantly reduced murine Fshb and human FSHB pituitary mRNA levels and are hypogonadal. Collectively, these data suggest that similar to Fshb regulation in mice, FOXL2 and SMAD4 play essential roles in human FSHB expression.

Addition of an N-Terminal Poly-Glutamate Fusion Tag Improves Solubility and Production of Recombinant TAT-Cre Recombinase in Escherichia coli

Cre recombinase is widely used to manipulate DNA sequences for both in vitro and in vivo research. Attachment of a trans-activator of transcription (TAT) sequence to Cre allows TATCre to penetrate the cell membrane, and the addition of a nuclear localization signal (NLS) helps the enzyme to translocate into the nucleus. Since the yield of recombinant TAT-Cre is limited by formation of inclusion bodies, we hypothesized that the positively charged arginine-rich TAT sequence causes the inclusion body formation, whereas its neutralization by the addition of a negatively charged sequence improves solubility of the protein. To prove this, we neutralized the positively charged TAT sequence by proximally attaching a negatively charged poly-glutamate (E12) sequence. We found that the E12 tag improved the solubility and yield of E12-TAT-NLS-Cre (E12-TAT-Cre) compared with those of TAT-NLS-Cre (TATCre) when expressed in E. coli. Furthermore, the growth of cells expressing E12-TAT-Cre was increased compared with that of the cells expressing TAT-Cre. Efficacy of the purified TATCre was confirmed by a recombination test on a floxed plasmid in a cell-free system and 293 FT cells. Taken together, our results suggest that attachment of the E12 sequence to TAT-Cre improves its solubility during expression in E. coli (possibly by neutralizing the ionic-charge effects of the TAT sequence) and consequently increases the yield. This method can be applied to the production of transducible proteins for research and therapeutic purposes.

Rationale and Roadmap for Developing Panels of Hotspot Cancer Driver Gene Mutations as Biomarkers of Cancer Risk

Cancer driver mutations (CDMs) are necessary and causal for carcinogenesis and have advantages as reporters of carcinogenic risk. However, little progress has been made toward developing measurements of CDMs as biomarkers for use in cancer risk assessment. Impediments for using a CDM-based metric to inform cancer risk include the complexity and stochastic nature of carcinogenesis, technical difficulty in quantifying low-frequency CDMs, and lack of established relationships between cancer driver mutant fractions and tumor incidence. Through literature review and database analyses, this review identifies the most promising targets to investigate as biomarkers of cancer risk. Mutational hotspots were discerned within the 20 most mutated genes across the 10 deadliest cancers. Forty genes were identified that encompass 108 mutational hotspot codons overrepresented in the COSMIC database; 424 different mutations within these hotspot codons account for approximately 63,000 tumors and their prevalence across tumor types is described. The review summarizes literature on the prevalence of CDMs in normal tissues and suggests such mutations are direct and indirect substrates for chemical carcinogenesis, which occurs in a spatially stochastic manner. Evidence that hotspot CDMs (hCDMs) frequently occur as tumor subpopulations is presented, indicating COSMIC data may underestimate mutation prevalence. Analyses of online databases show that genes containing hCDMs are enriched in functions related to intercellular communication. In its totality, the review provides a roadmap for the development of tissue-specific, CDM-based biomarkers of carcinogenic potential, comprised of batteries of hCDMs and can be measured by error-correct next-generation sequencing. Environ. Mol. Mutagen. 61:152-175, 2020. Published 2019. This article is a U.S. Government work and is in the public domain in the USA. Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.

A Tale of Two Proteins: Betaglycan, IGSF1, and the Continuing Search for the Inhibin B Receptor

Inhibins are gonadal hormones that suppress follicle-stimulating hormone (FSH) synthesis by pituitary gonadotrope cells. The structurally related activins stimulate FSH by signaling through complexes of type I and type II receptors. Two models of inhibin action were proposed in 2000. First, inhibins function as competitive receptor antagonists, binding activin type II receptors with high affinity in the presence of the TGF-β type III coreceptor, betaglycan. Second, immunoglobulin superfamily, member 1 (IGSF1, then called p120) was proposed to mediate inhibin B antagonism of activin signaling via its type I receptor. These ideas have been challenged over the past few years. Rather than playing a role in inhibin action, IGSF1 is involved in the central control of the thyroid gland. Betaglycan binds inhibin A and inhibin B with high affinity, but only functions as an obligate inhibin A coreceptor in murine gonadotropes. There is likely to be a distinct, but currently unidentified coreceptor for inhibin B.

TGF-β Superfamily Regulation of Follicle-Stimulating Hormone Synthesis by Gonadotrope Cells: Is There a Role for Bone Morphogenetic Proteins?

Bone morphogenetic proteins (BMPs) are pleiotropic ligands in the TGF-β superfamily. In the early to mid-2000s, several BMPs, including BMP2, were shown to regulate FSH synthesis alone and in synergy with activins in immortalized gonadotrope-like cell lines and primary pituitary cultures. Activins are also TGF-β family members, which were identified and named based on their abilities to stimulate FSH production selectively. Mechanistic analyses suggested that BMP2 promoted expression of the FSHβ subunit gene (Fshb) via at least two nonmutually exclusive mechanisms. First, BMP2 stimulated the production of the inhibitor of DNA-binding proteins 1, 2, and 3 (Id1, Id2, and Id3), which potentiated the stimulatory actions of homolog of Drosophila mothers against decapentaplegic 3 (SMAD3) on the Fshb promoter. SMAD3 is an intracellular signaling protein that canonically mediates the actions of activins and is an essential regulator of Fshb production in vitro and in vivo. Second, BMP2 was shown to activate SMAD3-dependent signaling via its canonical type IA receptor, BMPR1A (also known as ALK3). This was a surprising result, as ALK3 conventionally activates distinct SMAD proteins. Although these initial results were compelling, they were challenged by contemporaneous and subsequent observations. For example, inhibitors of BMP signaling did not specifically impair FSH production in cultured pituitary cells. Of perhaps greater significance, mice lacking ALK3 in gonadotrope cells produced FSH normally. Therefore, the physiological role of BMPs in FSH synthesis in vivo is presently uncertain.

HDAC inhibitors impair Fshb subunit expression in murine gonadotrope cells

Fertility is dependent on follicle-stimulating hormone (FSH), a product of gonadotrope cells of the anterior pituitary gland. Hypothalamic gonadotropin-releasing hormone (GnRH) and intra-pituitary activins are regarded as the primary drivers of FSH synthesis and secretion. Both stimulate expression of the FSH beta subunit gene (Fshb), although the underlying mechanisms of GnRH action are poorly described relative to those of the activins. There is currently no consensus on how GnRH regulates Fshb transcription, as results vary across species and between in vivo and in vitro approaches. One of the more fully developed models suggests that the murine Fshb promoter is tonically repressed by histone deacetylases (HDACs) and that GnRH relieves this repression, at least in immortalized murine gonadotrope-like cells (LβT2 and αT3-1). In contrast, we observed that the class I/II HDAC inhibitor trichostatin A (TSA) robustly inhibited basal, activin A-, and GnRH-induced Fshb mRNA expression in LβT2 cells and in primary murine pituitary cultures. Similar results were obtained with the class I specific HDAC inhibitor, entinostat, whereas two class II-specific inhibitors, MC1568 and TMP269, had no effects on Fshb expression. Collectively, these data suggest that class I HDACs are positive, not negative, regulators of Fshb expression in vitro and that, contrary to earlier reports, GnRH may not stimulate Fshb by inhibiting HDAC-mediated repression of the gene.