FSHβ links photoperiodic signaling to seasonal reproduction in Japanese quail

Annual cycles in daylength provide an initial predictive environmental cue that plants and animals use to time seasonal biology. Seasonal changes in photoperiodic information acts to entrain endogenous programs in physiology to optimize an animal's fitness. Attempts to identify the neural and molecular substrates of photoperiodic time measurement in birds have, to date, focused on blunt changes in light exposure during a restricted period of photoinducibility. The objectives of these studies were first to characterize a molecular seasonal clock in Japanese quail and second, to identify the key transcripts involved in endogenously generated interval timing that underlies photosensitivity in birds. We hypothesized that the mediobasal hypothalamus (MBH) provides the neuroendocrine control of photoperiod-induced changes in reproductive physiology, and that the pars distalis of the pituitary gland contains an endogenous internal timer for the short photoperiod-dependent development of reproductive photosensitivity. Here, we report distinct seasonal waveforms of transcript expression in the MBH, and pituitary gland and discovered the patterns were not synchronized across tissues. Follicle-stimulating hormone-β (FSHβ) expression increased during the simulated spring equinox, prior to photoinduced increases in prolactin, thyrotropin-stimulating hormone-β, and testicular growth. Diurnal analyses of transcript expression showed sustained elevated levels of FSHβ under conditions of the spring equinox, compared to autumnal equinox, short (<12L) and long (>12L) photoperiods. FSHβ expression increased in quail held in non-stimulatory short photoperiod, indicative of the initiation of an endogenously programmed interval timer. These data identify that FSHβ establishes a state of photosensitivity for the external coincidence timing of seasonal physiology. The independent regulation of FSHβ expression provides an alternative pathway through which other supplementary environmental cues, such as temperature, can fine tune seasonal reproductive maturation and involution.

Reproductive physiology in young men is cumulatively affected by FSH-action modulating genetic variants: FSHR -29G/A and c.2039 A/G, FSHB -211G/T

Follicle-Stimulating Hormone Receptor (FSHR) -29G/A polymorphism (rs1394205) was reported to modulate gene expression and reproductive parameters in women, but data in men is limited. We aimed to bring evidence to the effect of FSHR -29G/A variants in men. In Baltic young male cohort (n = 982; Estonians, Latvians, Lithuanians; aged 20.2±2.0 years), the FSHR -29 A-allele was significantly associated with higher serum FSH (linear regression: effect 0.27 IU/L; P = 0.0019, resistant to Bonferroni correction for multiple testing) and showed a non-significant trend for association with higher LH (0.19 IU/L) and total testosterone (0.93 nmol/L), but reduced Inhibin B (−7.84 pg/mL) and total testes volume (effect −1.00 mL). Next, we extended the study and tested the effect of FSHR gene haplotypes determined by the allelic combination of FSHR -29G/A and a well-studied variant c.2039 A/G (Asn680Ser, exon 10). Among the FSHR -29A/2039G haplotype carriers (A-Ser; haplotype-based linear regression), this genetic effect was enhanced for FSH (effect 0.40 IU/L), Inhibin B (−16.57 pg/mL) and total testes volume (−2.34 mL). Finally, we estimated the total contribution of three known FSH-action modulating SNPs (FSHB -211G/T; FSHR -29G/A, c.2039 A/G) to phenotypic variance in reproductive parameters among young men. The major FSH-action modulating SNPs explained together 2.3%, 1.4%, 1.0 and 1.1% of the measured variance in serum FSH, Inhibin B, testosterone and total testes volume, respectively. In contrast to the young male cohort, neither FSHR -29G/A nor FSHR haplotypes appeared to systematically modulate the reproductive physiology of oligozoospermic idiopathic infertile patients (n = 641, Estonians; aged 31.5±6.0 years). In summary, this is the first study showing the significant effect of FSHR -29G/A on male serum FSH level. To account for the genetic effect of known common polymorphisms modulating FSH-action, we suggest haplotype-based analysis of FSHR SNPs (FSHR -29G/A, c.2039 A/G) in combination with FSHB -211G/T testing.

Mechanisms in endocrinology: Genetics of FSH action: a 2014-and-beyond view

OBJECTIVE

To assess the pharmacogenetic potential of FSH for infertility treatment.

DESIGN

Review of the literature and genomic databases.

METHODS

Single-nucleotide polymorphism (SNP) assessed: rs6166 (c.2039A>G, p.N680S), rs6165 (c.919A>G, p.T307A), rs1394205 (c.-29G>A) in FSHR, and rs10835638 (c.-211G>T) in FSHB. Literature search via PubMed. Blast analysis of genomic information available in the NCBI nucleotide database. Comparison of allele frequency and haplotype distribution using the http://spsmart.cesga.estool.

RESULTS

All these SNPs appear first in Homo, result in reduced FSH action, and are present with variable frequencies and combinations worldwide. Stringent clinical studies demonstrate that the FSHR genotype influences serum FSH levels and gonadal response in both sexes. Serum FSH levels depend on the -211G>T SNP, influencing transcriptional activity of the FSHB promoter. Genotypes reducing FSH action are overrepresented in infertile subjects.

CONCLUSIONS

Although the clinical relevance of the FSHR polymorphisms alone is limited, the combination of FSHR and FSHB genotypes has a much stronger impact than either one alone in both sexes. About 20% of people are carriers of the alleles associated with lower serum FSH levels/reduced FSHR expression or activity, possibly less favorable for reproduction. Prospective studies need to investigate whether stratification of infertile patients according to their FSHR-FSHB genotypes improves clinical efficacy of FSH treatment compared with the current, naïve approach. A relative enrichment of less favorable FSHR-FSHB genotypes may be related to changes in human reproductive strategies and be a marker of some health-related advantage at the cost of reduced fertility.

Differentiation of mouse embryonic stem cells into gonadotrope-like cells in vitro

OBJECTIVE

This research was conducted to investigate the potential of mouse embryonic stem (ES) cells to differentiate in vitro into gonadotropes.

METHODS

Undifferentiated ES cells were maintained on mitomycin C-inactivated fibroblasts in the presence of leukemia inhibitory factor (LIF). By a 5-day hanging drop culture devoid of them, ES cells were induced to form multidifferentiated structures called embryoid bodies (EBs). Reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting, and immunocytochemistry were used to analyze gene expression of gonadotrope markers in EBs at different time points during the culture.

RESULTS

Homeo box gene expressed in ES cells (Hesx1), LIM homeobox protein 3 (Lhx3), paired like homeodomain factor 1 (Prop1), GATA binding protein 2 (GATA2), follicle-stimulating hormone beta (FSHbeta), and luteinizing hormone beta (LHbeta) mRNAs were detected at day 6 EBs and maintained throughout the culture to day 56. FSHbeta and LHbeta proteins were expressed in EBs from day 6 onward. Immunofluorescent labeling of FSHbeta and LHbeta showed that specific staining was restricted to the cytoplasm of some differentiated EB cells. With the prolongation of EB culture, the number of positive cells increased significantly. Both monohormonal and bihormonal cells were present, mainly in clusters within EBs and sparsely distributed among the outermost cells surrounding the EBs.

CONCLUSION

These results indicate that mouse ES cells can give rise to mature gonadotrope-like cells in EBs. It also shows that EBs may serve as a novel model system to study the development and function of gonadotropes.

Mechanisms for pulsatile regulation of the gonadotropin subunit genes by GNRH1

The frequency of gonadotropin-releasing hormone (GNRH1, or GnRH) pulses secreted from the hypothalamus determine the ratios of the gonadotropin subunit genes luteinizing hormone beta (Lhb), follicle-stimulating hormone beta (Fshb) and the common alpha-glycoprotein subunit gene (Cga) transcribed in the anterior pituitaries of mammals. Fshb is preferentially transcribed at slower GNRH1 pulse frequencies, whereas Lhb and Cga are preferentially transcribed at more rapid pulse frequencies. Producing the gonadotropins in the correct proportions is critical for normal fertility. Currently, there is no definitive explanation for how GNRH1 pulses differentially activate gonadotropin subunit gene transcription. Several pathways may contribute to this regulation. For example, GNRH1-regulated GNRH1-receptor concentrations may lead to variable signaling pathway activation. Several signaling pathways are activated by GnRH, including mitogen-activated protein kinase, protein kinase C, calcium influx, and calcium-calmodulin kinase, and these may be preferentially regulated under certain conditions. In addition, some signaling proteins feed back to downregulate their own levels. Other arms of gonadotroph signaling appear to be regulated by synthesis, modification, and degradation of either transcription factors or regulatory proteins. Finally, the dynamic binding of proteins to the chromatin, and how that might be regulated by chromatin-modifying proteins, is addressed. Oscillations in expression, modification, and chromatin binding of the proteins involved in gonadotropin gene expression are likely a link between GNRH1 pulsatility and differential gonadotropin transcription.

Isolation and characterization of the follicle-stimulating hormone beta subunit gene and 5' flanking region of the Chinook salmon

In this study we have isolated the follicle-stimulating hormone beta subunit gene from the Chinook salmon (csFSHbeta). This gene encodes for a protein that is highly similar to those isolated from other salmonids and shares all of the structural constraints seen in mammalian gonadotropins, including twelve conserved cysteines and a putative N-linked glycosylation site. The organization of the gene follows the conserved pattern regarding the numbers and positions of the introns, although the csFSHbeta gene contains a particularly large 6.2-kb first intron due to the inclusion of several transposon-like elements. Isolation of 1.2 kb of the 5' flanking region of the csFSHbeta gene and subsequent analysis in silico have revealed a number of putative elements which appear highly conserved in teleost FSHbeta gene promoters and are thus likely involved in basal and hormone-induced transcriptional regulation. The functionality of this 1.2-kb fragment in driving expression of a reporter gene and its response to GnRH was shown in gonadotropes, while the overexpression of AP-1 factors, Sf-1, estrogen receptor or Smad1 revealed that the promoter is responsive to these transcription factors. Our current study has opened the way for future analysis to verify the role of these factors in mediating hormonally induced transcription of this gene.

Regulation of the rat follicle-stimulating hormone beta-subunit promoter by activin

FSH is controlled by a variety of positive and negative stimuli, and the unique FSHbeta-subunit is a major target for this regulation. Activin is a key modulator of FSHbeta transcription and hormone secretion. The signal transduction pathway leading to FSH expression was previously unknown. Here, we show that the transcription factors Smad3 and Smad4 mediate activin-stimulated activity of the rat FSHbeta promoter in a pituitary-derived cell line, LbetaT2. Cells were transiently transfected with the rat FSHbeta promoter fused to a luciferase reporter gene (-338rFSHbeta-Luc), and a minimal activin-responsive region was identified. Transfection of Smad3, but not the highly related Smad2, led to a ligand-independent stimulation of the FSHbeta promoter activity. As expected, activin caused an additional increase of luciferase expression, which was blocked by cotreatment with follistatin. Although Smad4 alone had no effect on FSHbeta transcription, it significantly augmented Smad3 and activin-mediated stimulation of the promoter. A palindromic consensus Smad-binding element in the proximal promoter was found to bind Smad4, and elimination of the region resulted in a loss of activin-mediated FSHbeta transcription. The activin signaling pathway is conserved in a number of cells, but FSHbeta expression is restricted to gonadotropes. A pituitary-specific transcription factor necessary for activin-dependent induction of the FSHbeta promoter has been identified that permits FSHbeta expression in nongonadotrope cells. Pitx2 is a member of Pitx subfamily of bicoid-related homeodomain factors that is required for pituitary development and is present in the adult pituitary. This factor was transfected into LbetaT2 cells, where it caused up-regulation of basal and activin-mediated FSHbeta promoter activity. Furthermore, cotransfection of Pitx2c with Smad3 in kidney-derived TSA cells resulted in activin-regulated FSHbeta response, suggesting its important role in tissue-restricted regulation of FSHbeta by activin. A Pitx2c binding site was identified within the proximal promoter, and elimination of this region also resulted in a loss of activin-regulated FSHbeta promoter activity. Taken together, these studies suggest that the regulation of FSHbeta is dependent on activin-mediated signaling factors in concert with pituitary-derived nuclear regulatory proteins.

Failure of normal Leydig cell development in follicle-stimulating hormone (FSH) receptor-deficient mice, but not FSHbeta-deficient mice: role for constitutive FSH receptor activity

Previous studies have suggested that FSH may be involved in regulation of Leydig cell function. We have examined this directly using two mouse models with null mutations in either the FSH beta-subunit (FSHbetaKO mice) or the FSH receptor (FSHRKO mice). Circulating LH levels were normal in adult FSHbetaKO mice, but were significantly increased in FSHRKO mice. Intratesticular testosterone levels increased normally in FSHbetaKO mice from birth to adulthood, whereas testosterone levels in FSHRKO mice failed to increase normally after puberty and were significantly reduced in adult animals. This was associated with reduced levels of mRNA encoding cytochrome P450 side-chain cleavage, 3beta-hydroxysteroid dehydrogenase type VI, and steroidogenic acute regulatory protein in FSHRKO mice. Leydig cell number was normal in FSHbetaKO mice during development, but in FSHRKO mice Leydig cell number increased slowly after puberty and was significantly reduced in the adult animal. Transfection studies showed that the FSHR exhibits constitutive activity in the absence of agonist stimulation. The results indicate, therefore, that Sertoli cells regulate the development of Leydig cell number and that constitutive activity within the FSHR is sufficient to stimulate this process. The presence of the hormone itself is not required when circulating LH levels are adequate.