An investigation into pituitary gonadotrophic hormone synthesis, secretion, subunit gene expression and cell structure in normal and mutant male mice

TP63 gain-of-function mutations cause premature ovarian insufficiency by inducing oocyte apoptosis

The transcription factor p63 guards genome integrity in the female germline, and its mutations have been reported in patients with premature ovarian insufficiency (POI). However, the precise contribution of the TP63 gene to the pathogenesis of POI needs to be further determined. Here, in 1,030 Chinese patients with POI, we identified 6 heterozygous mutations of the TP63 gene that impaired the C-terminal transactivation-inhibitory domain (TID) of the TAp63α protein and resulted in tetramer formation and constitutive activation of the mutant proteins. The mutant proteins induced cell apoptosis by increasing the expression of apoptosis-inducing factors in vitro. We next introduced a premature stop codon and selectively deleted the TID of TAp63α in mice and observed rapid depletion of the p63+/ΔTID mouse oocytes through apoptosis after birth. Finally, to further verify the pathogenicity of the mutation p.R647C in the TID that was present in 3 patients, we generated p63+/R647C mice and also found accelerated oocyte loss, but to a lesser degree than in the p63+/ΔTID mice. Together, these findings show that TID-related variants causing constitutive activation of TAp63α lead to POI by inducing oocyte apoptosis, which will facilitate the genetic diagnosis of POI in patients and provide a potential therapeutic target for extending female fertility.

Sexually Dimorphic Regulation of Gonadotrope Cell Hyperplasia in Medaka Pituitary via Mitosis and Transdifferentiation

The 2 pituitary gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), regulate the reproductive function in all vertebrates. While many studies have investigated the regulation of gonadotropin production and release by sex steroid feedback, its role on the regulation of gonadotrope cell number remains unclear. Using medaka as a model and an optimized protocol to restore physiological sex steroids levels following gonadectomy, we show that gonadal sex steroids not only decrease fshb transcript levels, but also Fsh cell number in both sexes. We then investigated the origin of Fsh cell hyperplasia induced by gonadectomy. In both sexes, bromodeoxyuridine incubation shows that this is achieved via Fsh cell mitosis. In situ hybridization reveals that new Fsh cells also originate from transdifferentiating Tsh cells in females, but not in males. Both phenomena are inhibited by sex steroid supplementation via feeding. In males (but not females), gonadectomy (without recovery with sex steroid supplementation) also reduces sox2 transcript levels and Sox2-immunopositive population size, suggesting that Sox2 progenitors may be recruited to produce new Fsh cells. Opposite to Fsh cells, gonadectomy decreases lhb levels in both sexes, and levels are not restored by sex steroid supplementation. In addition, the regulation of Lh cell number also seems to be sex dependent. Removal of gonadal sex steroids stimulates Lh cell mitosis in male (like Fsh cells) but not in females. To conclude, our study provides the first evidence on sexually dimorphic mechanisms used in the fish pituitary to remodel gonadotrope populations in response to sex steroids.

FSH regulates RA signaling to commit spermatogonia into differentiation pathway and meiosis

BACKGROUND

Spermatogenesis is a complex process that is controlled by interactions between germ cells and somatic cells. The commitment of undifferentiated spermatogonia to differentiating spermatogonia and normal spermatogenesis requires the action of gonadotropins. Additionally, numerous studies revealed the role of retinoic acid signaling in induction of germ cell differentiation and meiosis entry.

MAIN TEXT

Recent studies have shown that expression of several RA signaling molecules including Rdh10, Aldh1a2, Crabp1/2 are influenced by changes in gonadotropin levels. Components of signaling pathways that are regulated by FSH signaling such as GDNF, Sohlh1/2, c-Kit, DMRT, BMP4 and NRGs along with transcription factors that are important for proliferation and differentiation of spermatogonia are also affected by retinoic acid signaling.

CONCLUSION

According to all studies that demonstrate the interface between FSH and RA signaling, we suggest that RA may trigger spermatogonia differentiation and initiation of meiosis through regulation by FSH signaling in testis. Therefore, to the best of our knowledge, this is the first time that the correlation between FSH and RA signaling in spermatogenesis is highlighted.

Effects of sevoflurane on reproductive function of male rats and its main mechanism of action

Objective: To study the effects of sevoflurane on reproductive function and its main mechanism of action in male rats.Materials and methods: Forty adult male Sprague-Dawley rats were divided into 4 groups and exposed to 0, 50, 300 and 1800 ppm of sevoflurane, respectively. After 15 days, the serum levels of sex hormones and inflammatory factors were detected using enzyme-linked immunosorbent assay. Left testis was taken for conventional histopathological examination and TUNEL staining. Right testis was used for sperm production and daily sperm count were evaluated daily. Johnsen score was used to categorize the spermatogenesis. The expression of related genes in the hypothalamic-pituitary-gonadal axis were analyzed by quantitative real time polymerase chain reaction (qRT-PCR).Results: Exposure to sevoflurane increased the levels of serum follicle-stimulating hormone (FSH), luteinizing hormone (LH), tumor necrosis factor-α (TNF-α), and monocyte chemoattractant protein 1 (MCP-1), decreased the content of serum testosterone (T), reduced the concentration of testicular sperm, the production of daily sperm and Johnsen score, and damaged vas deferens in a dose dependent manner. In addition, chronic exposure to sevoflurane down-regulated transcription of gonadotropin-releasing hormone (GnRH) and kisspeptin (Kiss)-1 as well as its receptor GPR54 in hypothalamus, attenuated GnRH receptor and LH-β mRNA levels, but increased FSH-β mRNA in pituitary gland, and enhanced mRNA of LH receptor and FSH receptor, but decreased INH-α and INH-βA mRNA levels in testes.Discussion and conclusions: Sevoflurane induces disorders of spermatogenesis and causes testicular injury. The underlying mechanism may be related to the imbalance of sex hormones in the hypothalamic-pituitary-gonadal axis.

Phenotypic dissection of the mouse Ren1d knockout by complementation with human renin

Normal renin synthesis and secretion is important for the maintenance of juxtaglomerular apparatus architecture. Mice lacking a functional Ren1d gene are devoid of renal juxtaglomerular cell granules and exhibit an altered macula densa morphology. Due to the species-specificity of renin activity, transgenic mice are ideal models for experimentally investigating and manipulating expression patterns of the human renin gene in a native cellular environment without confounding renin–angiotensin system interactions. A 55-kb transgene encompassing the human renin locus was crossed onto the mouse Ren1d-null background, restoring granulation in juxtaglomerular cells. Correct processing of human renin in dense core granules was confirmed by immunogold labeling. After stimulation of the renin–angiotensin system, juxtaglomerular cells contained rhomboid protogranules with paracrystalline contents, dilated rough endoplasmic reticulum, and electron-lucent granular structures. However, complementation of Ren1d^−/− mice with human renin was unable to rescue the abnormality seen in macula densa structure. The juxtaglomerular apparatus was still able to respond to tubuloglomerular feedback in isolated perfused juxtaglomerular apparatus preparations, although minor differences in glomerular tuft contractility and macula densa cell calcium handling were observed. This study reveals that the human renin protein is able to complement the mouse Ren1d^−/− non-granulated defect and suggests that granulopoiesis requires a structural motif that is conserved between the mouse Ren1d and human renin proteins. It also suggests that the altered macula densa phenotype is related to the activity of the renin-1d enzyme in a local juxtaglomerular renin–angiotensin system.

Unacylated ghrelin promotes adipogenesis in rodent bone marrow via ghrelin O-acyl transferase and GHS-R1a activity: evidence for target cell-induced acylation

Despite being unable to activate the cognate ghrelin receptor (GHS-R), unacylated ghrelin (UAG) possesses a unique activity spectrum that includes promoting bone marrow adipogenesis. Since a receptor mediating this action has not been identified, we re-appraised the potential interaction of UAG with GHS-R in the regulation of bone marrow adiposity. Surprisingly, the adipogenic effects of intra-bone marrow (ibm)-infused acylated ghrelin (AG) and UAG were abolished in male GHS-R-null mice. Gas chromatography showed that isolated tibial marrow adipocytes contain the medium-chain fatty acids utilised in the acylation of UAG, including octanoic acid. Additionally, immunohistochemistry and immunogold electron microscopy revealed that tibial marrow adipocytes show prominent expression of the UAG-activating enzyme ghrelin O-acyl transferase (GOAT), which is located in the membranes of lipid trafficking vesicles and in the plasma membrane. Finally, the adipogenic effect of ibm-infused UAG was completely abolished in GOAT-KO mice. Thus, the adipogenic action of exogenous UAG in tibial marrow is dependent upon acylation by GOAT and activation of GHS-R. This suggests that UAG is subject to target cell-mediated activation – a novel mechanism for manipulating hormone activity.

Zebrafish mesonephric renin cells are functionally conserved and comprise two distinct morphological populations

Zebrafish provide an excellent model in which to assess the role of the renin-angiotensin system in renal development, injury, and repair. In contrast to mammals, zebrafish kidney organogenesis terminates with the mesonephros. Despite this, the basic functional structure of the nephron is conserved across vertebrates. The relevance of teleosts for studies relating to the regulation of the renin-angiotensin system was established by assessing the phenotype and functional regulation of renin-expressing cells in zebrafish. Transgenic fluorescent reporters for renin (ren), smooth muscle actin (acta2), and platelet-derived growth factor receptor-beta (pdgfrb) were studied to determine the phenotype and secretory ultrastructure of perivascular renin-expressing cells. Whole kidney ren transcription responded to altered salinity, pharmacological renin-angiotensin system inhibition, and renal injury. Mesonephric ren-expressing cells occupied niches at the preglomerular arteries and afferent arterioles, forming intermittent epithelioid-like multicellular clusters exhibiting a granular secretory ultrastructure. In contrast, renin cells of the efferent arterioles were thin bodied and lacked secretory granules. Renin cells expressed the perivascular cell markers acta2 and pdgfrb Transcriptional responses of ren to physiological challenge support the presence of a functional renin-angiotensin system and are consistent with the production of active renin. The reparative capability of the zebrafish kidney was harnessed to demonstrate that ren transcription is a marker for renal injury and repair. Our studies demonstrate substantive conservation of renin regulation across vertebrates, and ultrastructural studies of renin cells reveal at least two distinct morphologies of mesonephric perivascular ren-expressing cells.

Gene Expression in Mouse Thyrotrope Adenoma: Transcription Elongation Factor Stimulates Proliferation

Thyrotrope hyperplasia and hypertrophy are common responses to primary hypothyroidism. To understand the genetic regulation of these processes, we studied gene expression changes in the pituitaries of Cga(-/-) mice, which are deficient in the common α-subunit of TSH, LH, and FSH. These mice have thyrotrope hypertrophy and hyperplasia and develop thyrotrope adenoma. We report that cell proliferation is increased, but the expression of most stem cell markers is unchanged. The α-subunit is required for secretion of the glycoprotein hormone β-subunits, and mutants exhibit elevated expression of many genes involved in the unfolded protein response, consistent with dilation and stress of the endoplasmic reticulum. Mutants have elevated expression of transcription factors that are important in thyrotrope function, such as Gata2 and Islet 1, and those that stimulate proliferation, including Nupr1, E2f1, and Etv5. We characterized the expression and function of a novel, overexpressed gene, transcription elongation factor A (SII)-like 5 (Tceal5). Stable expression of Tceal5 in a pituitary progenitor cell line is sufficient to increase cell proliferation. Thus, Tceal5 may act as a proto-oncogene. This study provides a rich resource for comparing pituitary transcriptomes and an analysis of gene expression networks.

Spatially coordinated dynamic gene transcription in living pituitary tissue

Transcription at individual genes in single cells is often pulsatile and stochastic. A key question emerges regarding how this behaviour contributes to tissue phenotype, but it has been a challenge to quantitatively analyse this in living cells over time, as opposed to studying snap-shots of gene expression state. We have used imaging of reporter gene expression to track transcription in living pituitary tissue. We integrated live-cell imaging data with statistical modelling for quantitative real-time estimation of the timing of switching between transcriptional states across a whole tissue. Multiple levels of transcription rate were identified, indicating that gene expression is not a simple binary 'on-off' process. Immature tissue displayed shorter durations of high-expressing states than the adult. In adult pituitary tissue, direct cell contacts involving gap junctions allowed local spatial coordination of prolactin gene expression. Our findings identify how heterogeneous transcriptional dynamics of single cells may contribute to overall tissue behaviour.

Pituitary gonadotrophic hormone synthesis, secretion, subunit gene expression and cell structure in normal and follicle-stimulating hormone β knockout, follicle-stimulating hormone receptor knockout, luteinising hormone receptor knockout, hypogonadal and ovariectomised female mice

To investigate the relationship between gonadotroph function and ultrastructure, we have compared, in parallel in female mice, the effects of several different mutations that perturb the hypothalamic-pituitary-gonadal axis. Specifically, serum and pituitary gonadotrophin concentrations, gonadotrophin gene expression, gonadotroph structure and number were measured. Follicle-stimulating hormone β knockout (FSHβKO), follicle-stimulating hormone receptor knockout (FSHRKO), luteinising hormone receptor knockout (LuRKO), hypogonadal (hpg) and ovariectomised mice were compared with control wild-type or heterozygote female mice. Serum levels of LH were elevated in FSHβKO and FSHRKO compared to heterozygote females, reflecting the likely decreased oestrogen production in KO females, as demonstrated by the threadlike uteri and acyclicity. As expected, there was no detectable FSH in the serum or pituitary and an absence of expression of the FSHβ subunit gene in FSHβKO mice. However, there was a significant increase in expression of the FSHβ and LHβ subunit genes in FSHRKO female mice. The morphology of FSHβKO and FSHRKO gonadotrophs was not significantly different from the control, except that secretory granules in FSHRKO gonadotrophs were larger in diameter. In LuRKO and ovariectomised mice, stimulation of LHβ and FSHβ mRNA, as well as serum protein concentrations, were reflected in subcellular changes in gonadotroph morphology, including more dilated rough endoplasmic reticula and fewer, larger secretory granules. In the gonadotophin-releasing hormone deficient hpg mouse, gonadotrophin mRNA and protein levels were significantly lower than in control mice and gonadotrophs were correspondingly smaller with less abundant endoplasmic reticula and reduced numbers of secretory granules. In summary, major differences in pituitary content and serum concentrations of the gonadotrophins LH and FSH were found between control and mutant female mice. These changes were associated with changes in expression of the gonadotrophin subunit genes and were reflected in the cellular structure and secretory granule appearance within the gonadotroph cells.

Endocrine control of spermatogenesis: Role of FSH and LH/ testosterone

Evaluation of testicular functions (production of sperm and androgens) is an important aspect of preclinical safety assessment and testicular toxicity is comparatively far more common than ovarian toxicity. This chapter focuses (1) on the histological sequelae of disturbed reproductive endocrinology in rat, dog and nonhuman primates and (2) provides a review of our current understanding of the roles of gonadotropins and androgens. The response of the rodent testis to endocrine disturbances is clearly different from that of dog and primates with different germ cell types and spermatogenic stages being affected initially and also that the end-stage spermatogenic involution is more pronounced in dog and primates compared to rodents. Luteinizing hormone (LH)/testosterone and follicle-stimulating hormone (FSH) are the pivotal endocrine factors controlling testicular functions. The relative importance of either hormone is somewhat different between rodents and primates. Generally, however, both LH/testosterone and FSH are necessary for quantitatively normal spermatogenesis, at least in non-seasonal species.