Identification of a novel OCT1 binding site that is necessary for the elaboration of pulses of rat GnRH promoter activity

POU6F2 mutation in humans with pubertal failure alters GnRH transcript expression

Idiopathic hypogonadotropic hypogonadism (IHH) is characterized by the absence of pubertal development and subsequent impaired fertility often due to gonadotropin-releasing hormone (GnRH) deficits. Exome sequencing of two independent cohorts of IHH patients identified 12 rare missense variants in POU6F2 in 15 patients. POU6F2 encodes two distinct isoforms. In the adult mouse, expression of both isoform1 and isoform2 was detected in the brain, pituitary, and gonads. However, only isoform1 was detected in mouse primary GnRH cells and three immortalized GnRH cell lines, two mouse and one human. To date, the function of isoform2 has been verified as a transcription factor, while the function of isoform1 has been unknown. In the present report, bioinformatics and cell assays on a human-derived GnRH cell line reveal a novel function for isoform1, demonstrating it can act as a transcriptional regulator, decreasing GNRH1 expression. In addition, the impact of the two most prevalent POU6F2 variants, identified in five IHH patients, that were located at/or close to the DNA-binding domain was examined. Notably, one of these mutations prevented the repression of GnRH transcripts by isoform1. Normally, GnRH transcription increases as GnRH cells mature as they near migrate into the brain. Augmentation earlier during development can disrupt normal GnRH cell migration, consistent with some POU6F2 variants contributing to the IHH pathogenesis.

Genetic mechanisms mediating kisspeptin regulation of GnRH gene expression

Kisspeptins (Kiss) have been shown to be key components in the regulation of gonadotropin-releasing hormone (GnRH) secretion. In vitro studies have demonstrated an increase in GnRH gene expression by Kiss suggesting regulation of GnRH at both the secretory and pretranslational levels. Here, we define genetic mechanisms that mediate Kiss action on target gene expression. In vitro, sequential deletions of the mouse GnRH (mGnRH) gene promoter fused to the luciferase (LUC) reporter gene localized at kisspeptin-response element (KsRE) between -3446 and -2806 bp of the mGnRH gene. In vivo, transgenic mice bearing sequential deletions of the mGnRH gene promoter linked to the LUC reporter localized an identical KsRE. To define the mechanism of regulation, Kiss was first shown to induce nucleosome-depleted DNA within the KsRE, and a potential binding site for the transcription factor, Otx-2, was revealed. Furthermore, increased Otx-2 mRNA, protein, and binding to the KsRE after Kiss treatment were demonstrated. In conclusion, this work identified elements in GnRH-neuronal cell lines and in transgenic mice that mediate positive regulation of GnRH by Kiss. In addition, we show for the first time that Otx-2 is regulated by Kiss, and plays a role in mediating the transcriptional response of mGnRH gene.

Long range regulation of human FXN gene expression

BACKGROUND

Friedreich ataxia (FRDA) is the most common form of hereditary ataxia characterized by the presence of a GAA trinucleotide repeat expansion within the first intron of the FXN gene. The expansion inhibits FXN gene expression resulting in an insufficiency of frataxin protein.

METHODOLOGY/PRINCIPAL FINDING

In this study, computational analyses were performed on the 21.3 kb region upstream of exon 1 of the human FXN gene and orthologs from other species in order to identify conserved non-coding DNA sequences with potential regulatory functions. The conserved non-coding regions identified were individually analyzed in two complementing assay systems, a conventional luciferase reporter system and a novel Bacterial Artificial Chromosome (BAC)-based genomic reporter. The BAC system allows the evaluation of gene expression to be made in the context of its entire genomic locus and preserves the normal location and spacing of many regulatory elements which may be positioned over large distances from the initiation codon of the gene.

CONCLUSIONS/SIGNIFICANCE

The two approaches were used to identify a region of 17 bp located approximately 4.9 kb upstream of the first exon of the FXN gene that plays an important role in FXN gene expression. Modulation of FXN gene expression was found to be mediated by the action of the Oct-1 transcription factor at this site. A better understanding of cis-acting regulatory elements that control FXN gene expression has the potential to develop new strategies for the upregulation of the FXN gene as a therapy for FRDA.

The gonadotropin-releasing hormone cell-specific element is required for normal puberty and estrous cyclicity

Appropriate tissue-specific gene expression of gonadotropin-releasing hormone (GnRH) is critical for pubertal development and maintenance of reproductive competence. In these studies, a common element in the mouse GnRH (mGnRH) promoter, between -2806 and -2078 bp, is shown to mediate differential regulation of hypothalamic and ovarian mGnRH expression. To further characterize this region, we generated a knock-out mouse (GREKO(-/-)) with a deletion of the mGnRH promoter fragment between -2806 and -2078 bp. GnRH mRNA expression in the brain of GREKO(-/-) was less than the expression in wild-type mice; however, immunohistochemical analysis revealed no difference between the numbers of GnRH neurons among groups. GnRH mRNA expression in the ovary was fivefold higher in GREKO(-/-). The immunohistochemical staining for GnRH in the ovary increased in surface epithelial and granulosa cells and also in the corpora lutea of GREKO(-/-) mice. The reproductive phenotype revealed that the mean day of vaginal opening was delayed, and additionally, there was a significant decrease in the length of proestrus and diestrus-metestrus phases of the estrous cycle, resulting in a shortened estrous cycle in GREKO(-/-) mice. This work supports the hypothesis that the region of the GnRH promoter contained between -2806 and -2078 bp acts as a cell-specific enhancer in the GnRH neuron and as a repressor in the ovary. Deletion of this region in vivo implicates the GnRH promoter in mediating pubertal development and periodic reproductive cycling, and forms the foundation to define the nuclear proteins important for puberty and estrous cycling in mammals.

Epigenetic changes coincide with in vitro primate GnRH neuronal maturation

Cellular and molecular mechanisms underlying pulsatile GnRH release are not well understood. In the present study, we examined the developmental changes in intracellular calcium dynamics, peptide release, gene expression, and DNA methylation in cultured GnRH neurons derived from the nasal placode of rhesus monkeys. We found that GnRH neurons were functionally immature, exhibiting little fluctuation in intracellular calcium ([Ca(2+)](i)) and sparse pulses of GnRH peptide release in the first 12 d in vitro (div). By 14-18 div, GnRH neurons exhibited periodic [Ca(2+)](i) oscillations, synchronizing at approximately 60-min intervals and GnRH pulses occurred at approximately 60-min intervals. Interestingly, the total GnRH peptide release further increased after 18 div. Measurement of GnRH mRNA and gene CpG methylation status at 0, 14, and 20 div indicated that mRNA levels significantly (P < 0.05) increased between 14 and 20 div, just as maximal decapeptide release was observed. By bisulfite sequencing across a 5' CpG island of the GnRH gene, we further found that methylation at eight of 14 CpG sites significantly (P < 0.05) decreased between 0 and 20 div. These data indicate that epigenetic differentiation occurs during GnRH neuronal development and suggest that increased GnRH gene expression and decreased CpG methylation status are molecular phenotypes of mature GnRH neurons. To our knowledge, this is the first report that developmental DNA demethylation occurs in postmitotic neurons toward a stable neuronal phenotype.

Calcium influx and DREAM protein are required for GnRH gene expression pulse activity

Recent evidence using GT1-7 cells indicates that GnRH pulsatility depends on exocytotic-release and gene transcription events. To determine whether calcium or DREAM may play a role in linking these processes, we used an L-type Ca(2+)-blocker (nimodipine) and found that not only GnRH gene expression (GnRH-GE) pulse activity was abolished but also that binding of proteins to OCT1BS-a (essential site for GnRH-GE pulses) was reduced. We further found that only EF-hand forms of DREAM were expressed in GT1-7 and that DREAM was part of the complex binding to OCT1BS-a. Finally, microinjection of DREAM antibody into cells abolished GnRH-GE pulses demonstrating its importance in pulsatility. These results reveal that calcium and DREAM may bridge cytoplasmic and nuclear events enabling temporal coordination of intermittent activity. Expression of DREAM in various cell types coupled with the universal role of calcium raise the possibility that these factors may play similar role in other secretory cells.