Gonadotropin inhibitory hormone (GnIH) as a regulator of gonadotropes

Brain RFamide Neuropeptides in Stress-Related Psychopathologies

The RFamide peptide family is a group of proteins that share a common C-terminal arginine-phenylalanine-amide motif. To date, the family comprises five groups in mammals: neuropeptide FF, LPXRFamides/RFamide-related peptides, prolactin releasing peptide, QRFP, and kisspeptins. Different RFamide peptides have their own cognate receptors and are produced by different cell populations, although they all can also bind to neuropeptide FF receptors with different affinities. RFamide peptides function in the brain as neuropeptides regulating key aspects of homeostasis such as energy balance, reproduction, and cardiovascular function. Furthermore, they are involved in the organization of the stress response including modulation of pain. Considering the interaction between stress and various parameters of homeostasis, the role of RFamide peptides may be critical in the development of stress-related neuropathologies. This review will therefore focus on the role of RFamide peptides as possible key hubs in stress and stress-related psychopathologies. The neurotransmitter coexpression profile of RFamide-producing cells is also discussed, highlighting its potential functional significance. The development of novel pharmaceutical agents for the treatment of stress-related disorders is an ongoing need. Thus, the importance of RFamide research is underlined by the emergence of peptidergic and G-protein coupled receptor-based therapeutic targets in the pharmaceutical industry.

Rfamide-related peptide-3(RFRP-3) receptor gene is expressed in mouse ovarian granulosa cells: Potential role of RFRP-3 in steroidogenesis and apoptosis

RFRP-3 is a functional ortholog of avian GnIH and regulates reproductive activities in the gonads of animals. However, the role of RFRP-3 in the function of ovarian granulosa cells in mice remains unclear. First, we detected the expression of the RFRP-3 receptor (GPR147) in the ovarian granulosa cells of mice. Second, the effect of RFRP-3 treatment on estradiol and progesterone secretions from granulosa cells was tested by ELISA. Meanwhile, the expression of genes and proteins regulating steroid hormone synthesis was respectively examined by qPCR and western blot. Furthermore, the effect of RFRP-3 treatment on the apoptosis of granulosa cells was analyzed. The results revealed that the GPR147 protein (a RFRP-3 receptor) was expressed in the ovarian granulosa cells of mice. Low and medium doses RFRP-3 treatment significantly reduced progesterone secretion in the granulosa cells (P < 0.05), while RFRP-3 suppressed p450scc, 3β-HSD, StAR, and FSHR expression in a non-dose-dependent manner. Moreover, RFRP-3 treatment might induce the apoptosis of granulosa cells. Additionally, low doses RFRP-3 significantly reduced p-ERK1/2 protein expression (P < 0.05) in the ovarian granulosa cells. We here, for the first time, confirmed that GPR147 was expressed in the ovarian granulosa cells of mice. Our findings suggested that and RFRP-3 regulates the granulosa cell function through the ERK signaling pathway, which will lay the foundation for uncovering molecular mechanisms by which RFRP-3 regulates follicle development in future.

Recombinant HBsAg-S and RFRP-3 DNA vaccine promotes reproduction hormone secretion in sheep

RF-amide related peptides (RFRP) have been proposed as critical regulators of gonadotropin secretion in mammals. This study was designed to construct a DNA vaccine and investigate the effect of vaccine encoding RFRP-3 on reproduction physiology in ewe. A recombinant vaccine was constructed using two copies of the RFRP-3 gene and HBsAg-S that generate a fusion protein to induce an immunology response. Results showed this recombinant vaccine could produce a significant antibody titer in the treated animals (P < 0.05). The specific RFRP-3 antibody response induced by the vaccine was detected at week 2 with a peak at week 6 after the initial immunization. Furthermore, we found that ewes inoculated with pVAX-tPA-HBsAg-S-2RFRP-asd vaccine significantly raised the concentration of GnRH, LH and E₂ in serum compared to the control group. LH and E2 concentration in the treated ewes (Group T) was significantly higher than that in control ewes (Group C) at weeks 10, 12 and 14 after the initial immunization, respectively (P < 0.05). Therefore, RFRP-3 can be used as a target for DNA immunization to promote reproductive hormone secretion in ewes and RFRP-3 gene immunization might be a candidate tool to regulate mammal reproduction.

Expression of genes for Kisspeptin (KISS1), Neurokinin B (TAC3), Prodynorphin (PDYN), and gonadotropin inhibitory hormone (RFRP) across natural puberty in ewes

Expression of particular genes in hypothami of ewes was measured across the natural pubertal transition by in situ hybridization. The ewes were allocated to three groups (n = 4); prepubertal, postpubertal and postpubertally gonadectomized (GDX). Prepubertal sheep were euthanized at 20 weeks of age and postpubertal animals at 32 weeks. GDX sheep were also euthanized at 32 weeks, 1 week after surgery. Expression of KISS1, TAC3, PDYN in the arcuate nucleus (ARC), RFRP in the dorsomedial hypothalamus and GNRH1 in the preoptic area was quantified on a cellular basis. KISS1R expression by GNRH1 cells was quantified by double-label in situ hybridization. Across puberty, detectable KISS1 cell number increased in the caudal ARC and whilst PDYN cell numbers were low, numbers increased in the rostral ARC. TAC3 expression did not change but RFRP expression/cell was reduced across puberty. There was no change across puberty in the number of GNRH1 cells that expressed the kisspeptin receptor (KISS1R). GDX shortly after puberty did not increase expression of any of the genes of interest. We conclude that KISS1 expression in the ARC increases during puberty in ewes and this may be a causative factor in the pubertal activation of the reproductive axis. A reduction in expression of RFRP may be a factor in the onset of puberty, removing negative tone on GNRH1 cells. The lack of changes in expression of genes following GDX suggest that the effects of gonadal hormones may differ in young and mature animals.

Dynamic Changes of RFRP3/GPR147 in the Precocious Puberty Model Female Rats

BACKGROUND

Pubertal development is a complex physiological process regulated by the neuroendocrine system and hypothalamic-pituitary-gonadal axis. Sexual precocity is a common childhood endocrine disease.The pathogenesis of sexual precocity has not been fully elucidated. RFRP3/GPRl47 signal pathway is able to inhibit the reproductive capability in avians and mammals, probably by acting on the GnRH neuron and pituitary to regulate gonadotrophin synthesis and release. However, little is known about the role of RFRP3 in puberty development and sexual precocity.

OBJECTIVE

To observe the dynamic changes of RFamide related peptide 3/G proteincoupled receptor 147 (RFRP3/GPR147) in hypothalamic during puberty development and explore their role in precocious puberty based on a female rat model.

METHODS

The Sprague-Dawley female rats were randomly divided into three groups, normal, vehicle, and precocious puberty model. At 5 days old, the rat model with precocious puberty was prepared by subcutaneously injecting a mixture of danazoldissolved ethanol and glycol. At different day-age (15, 25, 30, 35, and 40 days), the levels of estradiol(E2), follicle-stimulating hormone(FSH), and luteinizing hormone (LH) in the peripheral blood were detected by the enzyme-linked immunosorbent assay, the messenger ribonucleic acid (mRNA) expressions of RFRP3, gonadotropin releasing hormone and GPR147 were examined by real-time polymerase chain reaction(R-T PCR). RFRP3 positive cells were observed using Immunofluorescence confocal microscopy.

RESULTS

At 25 and 30 days, the levels of sex hormones and the uterus coefficients were significantly higher in the precocious puberty model group than those in the normal and vehicle groups. The ovarian morphological development in the precocious puberty model rats was significantly earlier than those in the normal and vehicle groups. The mRNA expressions of RFRP3/GPR147 and GnRH in the precocious puberty model group gradually increased and peaked at 25 days. The different day-age and the interaction have significant statistical significance on the expression of RFRP3 mRNA, while the levels of RFRP3 mRNA in the model group and vehicle groups have no significant statistical significance. There was statistical significance between the model group and vehicle groups in different day-age on the expression of GPR147 mRNA.The expression of hypothalamic RFRP3/GPR147 mRNA and RFRP3 positive cells gradually decreased with puberty onset. At 35 days, the levels of RFRP3 mRNA and GPR147 mRNA were significantly lower in the precocious puberty model group than those in the vehicle groups. Meanwhile, the levels of LH in the precocious puberty model rats reached its peak at this age. In the vehicle group, the levels of RFRP3 mRNA and serum LH were gradually increased and LH nearly peaked at 35 day-age. Subsequently, it gradually decreased and reached the lowest level at 35 day-age. The expression of RFRP3 mRNA and LH were positively correlated.

CONCLUSION

The findings suggested that RFRP3/GPR147 signaling pathway may be involved in the pathogenesis of sexual precocity by regulating puberty development and sexual maturity in rats.

Regulation of LH secretion by RFRP-3 - From the hypothalamus to the pituitary

RFamide-related peptides (RFRPs) have long been identified as inhibitors of the hypothalamus-pituitary-gonad axis in mammals. However, less progress has been made in the detailed roles of RFRPs in the control of LH secretion. Recent studies have suggested that RFRP-3 neurons in the hypothalamus can regulate the secretion of LH at different levels, including kisspeptin neurons, GnRH neurons, and the pituitary. Additionally, conflicting results regarding the effects of RFRP-3 on these levels exist. In this review, we collect the latest evidence related to the effects of RFRP-3 neurons in regulating LH secretion by acting on kisspeptin neurons, GnRH neurons, and the pituitary and discuss the potential role of the timely reduction of RFRP-3 signaling in the modulation of the preovulatory LH surge.

Multiple signaling pathways convey central and peripheral signals to regulate pituitary function: Lessons from human and non-human primate models

The anterior pituitary gland is a key organ involved in the control of multiple physiological functions including growth, reproduction, metabolism and stress. These functions are controlled by five distinct hormone-producing pituitary cell types that produce growth hormone (somatotropes), prolactin (lactotropes), adrenocorticotropin (corticotropes), thyrotropin (thyrotropes) and follicle stimulating hormone/luteinizing hormone (gonadotropes). Classically, the synthesis and release of pituitary hormones was thought to be primarily regulated by central (neuroendocrine) signals. However, it is now becoming apparent that factors produced by pituitary hormone targets (endocrine and non-endocrine organs) can feedback directly to the pituitary to adjust pituitary hormone synthesis and release. Therefore, pituitary cells serve as sensors to integrate central and peripheral signals in order to fine-tune whole-body homeostasis, although it is clear that pituitary cell regulation is species-, age- and sex-dependent. The purpose of this review is to provide a comprehensive, general overview of our current knowledge of both central and peripheral regulators of pituitary cell function and associated intracellular mechanisms, focusing on human and non-human primates.

Metabolic Impact on the Hypothalamic Kisspeptin-Kiss1r Signaling Pathway

A large body of data has established the hypothalamic kisspeptin (KP) and its receptor, KISS1R, as major players in the activation of the neuroendocrine reproductive axis at the time of puberty and maintenance of reproductive capacity in the adult. Due to its strategic location, this ligand-receptor pair acts as an integrator of cues from gonadal steroids as well as of circadian and seasonal variation-related information on the reproductive axis. Besides these cues, the activity of the hypothalamic KP signaling is very sensitive to the current metabolic status of the body. In conditions of energy imbalance, either positive or negative, a number of alterations in the hypothalamic KP signaling pathway have been documented in different mammalian models including nonhuman primates and human. Deficiency of metabolic fuels during fasting causes a marked reduction of Kiss1 gene transcript levels in the hypothalamus and, hence, decreases the output of KP-containing neurons. Food intake or exogenous supply of metabolic cues, such as leptin, reverses metabolic insufficiency-related changes in the hypothalamic KP signaling. Likewise, alterations in Kiss1 expression have also been reported in other situations of energy imbalance like diabetes and obesity. Information related to the body's current metabolic status reaches to KP neurons both directly as well as indirectly via a complex network of other neurons. In this review article, we have provided an updated summary of the available literature on the regulation of the hypothalamic KP-Kiss1r signaling by metabolic cues. In particular, the potential mechanisms of metabolic impact on the hypothalamic KP-Kiss1r signaling, in light of available evidence, are discussed.

Molecular characterization and expression profiles of LPXRFa at the brain-pituitary-gonad axis of half-smooth tongue sole (Cynoglossus semilaevis) during ovarian maturation

Gonadotropin-inhibitory hormone (GnIH) has been characterized by its ability to inhibit either basal or gonadotropin-releasing hormone (GnRH)-induced gonadotropin synthesis and release in birds and mammals. However, the physiological role of GnIH on the reproductive axis in fish remains inconclusive, with most studies focusing on the orders Cypriniformes and Perciformes. To gain insight into the role of GnIH in the regulation of reproduction in the order Pleuronectiformes, we first cloned the LPXRFa gene, the piscine ortholog of GnIH, in the half-smooth tongue sole. The full-length cDNA of LPXRFa was 918bp in size with an open reading frame (ORF) of 585bp that encoded a 194 amino acids preprohormone with a calculated molecular mass and isoelectric point of 21.73kDa and 6.52, respectively. The LPXRFa precursor encoded two putative peptide sequences that included -MPMRF or -MPQRF motifs at the C-terminal. Tissue distribution analysis showed that LPXRFa transcripts could be detected at high levels in the brains of both sexes and to a lesser extent in the ovary, heart and stomach of females, while a noteworthy expression was observed in the kidney and muscle of males. Furthermore, the expression patterns of LPXRFa mRNA during ovarian maturation were also investigated. In the brain, the mRNA expression of LPXRFa increased significantly at stage III, declined at stage V and reached a maximum at stage VI. In the pituitary, the levels of LPXRFa mRNA remained stable during ovarian maturation and increased significantly to the top level at stage V and then declined back to basal levels. In contrast, the ovarian LPXRFa mRNA levels declined sharply at stage III and remained depressed over the course of ovarian maturation. Taken together, our results provide further evidence for the existence of LPXRFa in the order Pleuronectiformes and suggest its possible involvement in the regulation of reproduction in the female tongue sole.

RFamide-related Peptide-3 and the Trade-off between Reproductive and Ingestive Behavior

Ingestive and sex behaviors are important for individual survival and reproductive success, but when environmental energy availability is limited, individuals of many different species make a trade-off, forfeiting sex for ingestive behavior. For example, food-deprived female Syrian hamsters (Mesocricetus auratus) forego vaginal scent marking and lordosis (sex behaviors) in favor of foraging, hoarding, and eating food (ingestive behavior). Reproductive processes tend to be energetically costly, and individual survival requires homeostasis in metabolic energy. Thus, during energetic challenges, the chances of survival are enhanced by decreasing the energy expended on reproductive processes. The entire hypothalamic-pituitary-gonadal (HPG) system is inhibited by severe energetic challenges, but comparatively little is known about the effects of mild energetic challenges. We hypothesized that (1) a trade-off is made between sex and ingestive behavior even when the level of food restriction is insufficient to inhibit the HPG system; (2) mild energetic challenges force a trade-off between appetitive ingestive and sex behaviors, but not consummatory versions of the same behaviors; and (3) the trade-off is orchestrated by ovarian steroid modulation of RFamide-related peptide 3 (RFRP-3). In other species, RFRP-3, an ortholog of avian gonadotropin-inhibitory hormone, is implicated in control of behavior in response to energetic challenges and stressful stimuli. In support of our three hypotheses, there is a "dose-response" effect of food restriction and re-feeding on the activation of RFRP-3-immunoreactive cells in the dorsomedial hypothalamus and on appetitive behaviors (food hoarding and sexual motivation), but not on consummatory behaviors (food intake and lordosis), with no significant effect on circulating levels of estradiol or progesterone. The effect of food restriction on the activation of RFRP-3 cells is modulated at the time of estrus in gonadally-intact females and in ovariectomized females treated with progesterone alone or with estradiol plus progesterone. Intracerebral treatment with RFRP-3 results in significant decreases in sexual motivation and results in significant but small increases in food hoarding in hamsters fed ad libitum. These and other results are consistent with the idea that ovarian steroids and RFRP-3 are part of a system that orchestrates trade-offs in appetitive behaviors in environments where energy availability fluctuates.

Molecular identification of StAR and 3βHSD1 and characterization in response to GnIH stimulation in protogynous hermaphroditic grouper (Epinephelus coioides)

Gonadal steroids are critical factors in reproduction and sex reverse process. StAR (steroidogenic acute regulatory protein), transferring the cholesterol from the outer mitochondrial membrane to the inner membrane, is the rate-limiting factor of steroidogenesis. 3βHSD (3β-hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase), converting Δ5-steroids into Δ4-steroids, is an important oxidoreductase in steroidogenesis. In the present study, StAR and 3βHSD1 were cloned and characterized from protogynous orange-spotted grouper. StAR cDNA contains an 861bp open reading frame (ORF), encoding a predicted protein of 286 amino acids, and the ORF of 3βHSD1 was 1125bp, encoding a predicted protein of 374 amino acids. The transcript of StAR was mainly expressed in gonad, while 3βHSD1 mRNA was predominantly detected in brain and gonad. In the previous study, we found the expression of GnIH mRNA level in male, as well as in 17 alpha-methyltestosterone (MT)-induced male fish was significantly higher than in female fish, this indicating that GnIH/GnIHR signaling might be involved in the regulation of sex reversal and male maintenance. In order to figure out the function of GnIH in steroidogenesis, the expression of StAR and 3βHSD1 regulated by GnIH was examined. In vitro study showed that treatment of cultured ovary fragments with gGnIH peptides significantly stimulated the expression of StAR and 3βHSD1. In addition, the mRNA levels of StAR and 3βHSD1 were significantly increased after intraperitoneal injection (i.p.) with gGnIH peptides. Moreover, during MT-induced sex change from female to male, the levels of StAR mRNA significantly increased by 5.2, 24.8 and 353.5 folds, and that of 3βHSD1 mRNA by 3.5, 32.5 and 55.4 folds at the 2nd, 4th and 6th week after MT implantation, respectively. Collectively, our results indicate that GnIH may be involved in the regulation of sex reversal or male maintenance by stimulating the expression of StAR and 3βHSD1 in protogynous grouper.

Dynamic Regulation of Hypothalamic DMXL2, KISS1, and RFRP Expression During Postnatal Development in Non-Human Primates

The neurobiological mechanism of puberty onset in primates is currently only partly understood. A recent study reported an important role of Dmx-like 2 (DMXL2), a gene encoding rabconnectin-3α vesicular protein, in human subjects with mental retardation and neuroendocrine impairment of reproduction. To further characterize the potential role of DMXL2 in the regulation of reproduction, we analyzed the expression of DMXL2 in hypothalami of newborn, infantile, juvenile, pubertal, and postpubertal female and male common marmoset monkeys. Additionally, as the relative hypothalamic levels of gonadotropin-inhibitory hormone (GnIH) transcript during postnatal development are unknown in primates, we also quantified messenger RNA (mRNA) levels of RFRP, a gene encoding GnIH. Moreover, the transcript levels of kisspeptin, a well-known regulator of the hypothalamic neurohormonal axis controlling reproduction, were also checked. Transcript and protein levels of DMXL2 and Kiss1 transcript levels increase from the newborn to the infantile and from the juvenile (prepubertal) to the pubertal and the postpubertal period. We also noted a clear upsurge in RFRP transcript levels in the prepubertal period. In conclusion, the hypothalamic expressions of Kiss1 and DMXL2 mRNA increase during infantile, pubertal, and adult stages compared to newborn and juvenile stages in common marmoset monkeys. In contrast, the expression of RFRP mRNA upsurges in juvenile monkeys. Further mechanistic studies are needed to characterize the potential inhibitory role of the GnIH-GPR147 signaling in the prepubertal period and the role of DMXL2 in the molecular cascade regulating the neuroendocrine reproductive axis in primates.

The ecological and physiological bases of variation in the phenology of gonad growth in an urban and desert songbird

Birds often adjust to urban areas by advancing the timing (phenology) of vernal gonad growth. However, the ecological and physiological bases of this adjustment are unclear. We tested whether the habitat-related disparity in gonad growth phenology of male Abert's towhees, Melozone aberti, is due to greater food availability in urban areas of Phoenix, Arizona USA or, alternatively, a habitat-related difference in the phenology of key food types. To better understand the physiological mechanism underlying variation in gonad growth phenology, we compared the activity of the reproductive system at all levels of hypothalamo-pituitary-gonadal (HPG) axis. We found no habitat-associated difference in food availability (ground arthropod biomass), but, in contrast to the seasonal growth of leaves on desert trees, the leaf foliage of urban trees was already developed at the beginning of our study. Multiple estimates of energetic status did not significantly differ between the non-urban and urban towhees during three years that differed in the habitat-related disparity in gonad growth and winter precipitation levels. Thus, our results provide no support for the hypothesis that greater food abundance in urban areas of Phoenix drives the habitat-related disparity in gonad growth phenology in Abert's towhees. By contrast, they suggest that differences in the predictability and magnitude of change in food availability between urban and desert areas of Phoenix contribute to the observed habitat-related disparity in gonad growth. Endocrine responsiveness of the gonads may contribute to this phenomenon as desert - but not urban - towhees had a marked plasma testosterone response to GnRH challenge.

Gonadotrophin-Inhibitory Hormone in the Cichlid Fish Cichlasoma dimerus: Structure, Brain Distribution and Differential Effects on the Secretion of Gonadotrophins and Growth Hormone

The role of gonadotrophin-inhibitory hormone (GnIH) in the inhibition of the reproductive axis has been well-established in birds and mammals. However, its role in other vertebrates, such as the teleost fish, remains controversial. In this context, the present study aimed to evaluate whether GnIH modulates the release of gonadotrophins and growth hormone (GH) in the cichlid fish Cichlasoma dimerus. First, we partially sequenced the precursor polypeptide for GnIH and identified three putative GnIH peptides. Next, we analysed the expression of this precursor polypeptide via a polymerase chain reaction in the reproductive axis of both sexes. We found a high expression of the polypeptide in the hypothalamus and gonads of males. Immunocytochemistry allowed the observation of GnIH-immunoreactive somata in the nucleus posterioris periventricularis and the nucleus olfacto-retinalis, with no differences between the sexes. GnIH-immunoreactive fibres were present in all brain regions, with a high density in the nucleus lateralis tuberis and at both sides of the third ventricle. Finally, we performed in vitro studies on intact pituitary cultures to evaluate the effect of two doses (10(-6)  m and 10(-8)  m) of synthetic C. dimerus (cd-) LPQRFa-1 and LPQRFa-2 on the release of gonadotrophins and GH. We observed that cd-LPQRFa-1 decreased β-luteinising hormone (LH) and β-follicle-stimulating hormone (FSH) and also increased GH release to the culture medium. The release of β-FSH was increased only when it was stimulated with the higher cd-LPQRFa-2 dose. The results of the present study indicate that cd-LPQRFa-1, the cichlid fish GnIH, inhibits β-LH and β-FSH release and stimulates GH release in intact pituitary cultures of C. dimerus. The results also show that cd-LPQRF-2 could act as an β-FSH-releasing factor in this fish species.

Differential response of GnIH in the brain and gonads following acute stress in a songbird

Gonadotropin-inhibitory hormone (GnIH) acts to inhibit reproduction at all levels of the hypothalamo-pituitary-gonad axis. GnIH expression and/or immunoreactivity in the hypothalamus increase with acute stress in some birds and mammals, and thus may be involved in stress-induced reproductive inhibition. Much is known about GnIH and stress in seasonal and continuous breeders, but far less is known about these interactions in opportunistic breeders. For opportunistically breeding animals, reproductive readiness is closely associated with unpredictable environmental cues, and thus the GnIH system may be more sensitive to stress. To test this, we collected tissues from zebra finches immediately following capture or after 60 min of restraint. Restraint significantly increased plasma corticosterone in males and females but, contrary to studies on other species, restrained birds had significantly fewer GnIH immunoreactive (GnIH-ir) cell bodies than control birds. GnIH-ir cell number did not differ between the sexes. Stressed females had lower mRNA expression of the beta subunit of follicle stimulating hormone (FSHβ) in the pituitary, suggesting that the reduction in observed GnIH immunoreactivity in females may have been due to increased GnIH release in response to acute stress. GnIH expression increased in the testes, but not the ovaries, of restrained animals. Our data suggest that although GnIH responsiveness to stress appears to be conserved across species, specific tissue response and direction of GnIH regulation is not. Variation in the GnIH response to stress between species might be the result of ecological adaptations or other species differences in the response of the GnIH system to stress.

Genomic structure and promoter functional analysis of GnRH3 gene in large yellow croaker (Larimichthys crocea)

Gonadotropin-releasing hormone III (GnRH3) is considered to be a key neurohormone in fish reproduction control. In the present study, the cDNA and genomic sequences of GnRH3 were cloned and characterized from large yellow croaker Larimichthys crocea. The cDNA encoded a protein of 99 amino acids with four functional motifs. The full-length genome sequence was composed of 3797 nucleotides, including four exons and three introns. Higher identities of amino acid sequences and conserved exon-intron organizations were found between LcGnRH3 and other GnRH3 genes. In addition, some special features of the sequences were detected in partial species. For example, two specific residues (V and A) were found in the family Sciaenidae, and the unique 75-72 bp type of the open reading frame 2 and 3 existed in the family Cyprinidae. Analysis of the 2576 bp promoter fragment of LcGnRH3 showed a number of transcription factor binding sites, such as AP1, CREB, GATA-1, HSF, FOXA2, and FOXL1. Promoter functional analysis using an EGFP reporter fusion in zebrafish larvae presented positive signals in the brain, including the olfactory region, the terminal nerve ganglion, the telencephalon, and the hypothalamus. The expression pattern was generally consistent with the endogenous GnRH3 GFP-expressing transgenic zebrafish lines, but the details were different. These results indicate that the structure and function of LcGnRH3 are generally similar to the other teleost GnRH3 genes, but there exist some distinctions among them.

Molecular identification of GnIH/GnIHR signal and its reproductive function in protogynous hermaphroditic orange-spotted grouper (Epinephelus coioides)

Gonadotropin-inhibitory hormone (GnIH) and its receptor (GnIHR) play an important role in reproduction regulation in birds, mammals and some teleost species. In protogynous hermaphroditic orange-spotted grouper (Epinephelus coioides), the GnIH/GnIHR signaling pathway and its reproductive function have not been addressed yet. In this study, GnIH and GnIHR in orange-spotted grouper were characterized. gGnIH possessed three putative peptides (gGnIH-I, -II, -III), while gGnIHR showed the characteristics of G protein-coupled receptor and was clustered with GPR147. Functional assays demonstrated that three synthetic gGnIH peptides significantly decreased the forskolin-induced CRE promoter activity, but only gGnIH-I could significantly decrease SRE promoter activity in COS-7 cells transfected with gGnIHR. During the process of ovarian differentiation and development, gGnIH mRNA level in hypothalamus was low at the gonadal primordium stage with gonia, then increased significantly at the early differentiated gonad with primary growth oocytes, while decreased significantly at the developing gonads with cortical-alveolus and vitellogenic stage oocytes. During MT-induced sex reversal, gGnIH mRNA level in hypothalamus increased significantly when the fish completely reversed from female to male. However, gGnIHR mRNA level in pituitary decreased significantly in intersex and completely reversed male fish. Intraperitoneal injection (i.p.) of three gGnIH peptides significantly decreased GnRH1 mRNA levels in hypothalamus, and gGnIH-II significantly inhibited synthesis of LHβ in pituitary. In summary, we firstly identified the GnIH/GnIHR signal in protogynous orange-spotted grouper, which might be involved in the regulation of the reproductive function of sex differentiation, gonadal development and sex reversal via regulating the synthesis of both GnRH and GtH.

The involvement of gonadotropin inhibitory hormone and kisspeptin in the metabolic regulation of reproduction

Recently, kisspeptin (KP) and gonadotropin inhibitory hormone (GnIH), two counteracting neuropeptides, have been acknowledged as significant regulators of reproductive function. KP stimulates reproduction while GnIH inhibits it. These two neuropeptides seem to be pivotal for the modulation of reproductive activity in response to internal and external cues. It is well-documented that the current metabolic status of the body is closely linked to its reproductive output. However, how reproductive function is regulated by the body's energy status is less clear. Recent studies have suggested an active participation of hypothalamic KP and GnIH in the modulation of reproductive function according to available metabolic cues. Expression of KISS1, the KP encoding gene, is decreased while expression of RFRP (NPVF), the gene encoding GnIH, is increased in metabolic deficiency conditions. The lower levels of KP, as suggested by a decrease in KISS1 gene mRNA expression, during metabolic deficiency can be corrected by administration of exogenous KP, which leads to an increase in reproductive hormone levels. Likewise, administration of RF9, a GnIH receptor antagonist, can reverse the inhibitory effect of fasting on testosterone in monkeys. Together, it is likely that the integrated function of both these hypothalamic neuropeptides works as a reproductive output regulator in response to a change in metabolic status. In this review, we have summarized literature from nonprimate and primate studies that demonstrate the involvement of KP and GnIH in the metabolic regulation of reproduction.

Food availability, energetic constraints and reproductive development in a wild seasonally breeding songbird

In many organisms, food availability is a proximate cue that synchronizes seasonal development of the reproductive system with optimal environmental conditions. Growth of the gonads and secondary sexual characteristics is orchestrated by the hypothalamic–pituitary–gonadal (HPG) axis. However, our understanding of the physiological mechanisms by which food availability modulates activity of the HPG axis is limited.

It is thought that many factors, including energetic status, modulate seasonal reproductive activation. We tested the hypothesis that food availability modulates the activity of the HPG axis in a songbird. Specifically, we food‐restricted captive adult male Abert's Towhees Melozone aberti for 2 or 4 weeks during photoinduced reproductive development. A third group (control) received ad libitum food throughout. We measured multiple aspects of the reproductive system including endocrine activity of all three levels of the HPG axis [i.e. hypothalamic gonadotropin‐releasing hormone‐I (GnRH‐I), plasma luteinizing hormone (LH) and testosterone (T)], and gonad morphology. Furthermore, because gonadotropin‐inhibitory hormone (GnIH) and neuropeptide Y (NPY; a potent orexigenic peptide) potentially integrate information on food availability into seasonal reproductive development, we also measured the brain levels of these peptides.

At the hypothalamic level, we detected no effect of food restriction on immunoreactive (ir) GnRH‐I, but the duration of food restriction was inversely related to the size of ir‐GnIH perikarya. Furthermore, the number of ir‐NPY cells was higher in food‐restricted than control birds. Food restriction did not influence photoinduced testicular growth, but decreased plasma LH and T, and width of the cloacal protuberance, an androgen‐sensitive secondary sexual characteristic. Returning birds to ad libitum food availability had no effect on plasma LH or T, but caused the cloacal protuberance to rapidly increase in size to that of ad libitum‐fed birds.

Our results support the tenet that food availability modulates photoinduced reproductive activation. However, they also suggest that this modulation is complex and depends upon the level of the HPG axis considered. At the hypothalamic level, our results are consistent with a role for the GnIH and NPY systems in integrating information on energetic status. There also appears to be a role for endocrine function at the anterior pituitary gland and testicular levels in modulating reproductive development in the light of energetic status and independently of testicular growth.

Mutational analysis of the genes encoding RFamide-related peptide-3, the human orthologue of gonadotrophin-inhibitory hormone, and its receptor (GPR147) in patients with gonadotrophin-releasing hormone-dependent pubertal disorders

RFamide-related peptide-3 (RFRP-3), the orthologue of avian gonadotrophin-inhibitory hormone, and its receptor GPR147 have been recently identified in the human hypothalamus, and their roles in the regulation of reproductive axis has been studied. The present study aimed to investigate whether the presence of variants in the genes encoding human RFRP-3 (NPVF gene) and its receptor, GPR147 (NPFFR1 gene), is associated with the occurrence of gonadotrophin-releasing hormone-dependent pubertal disorders. Seventy-eight patients with idiopathic central precocious puberty (CPP) and 51 with normosmic isolated hypogonadotrophic hypogonadism (nIHH) were investigated. Fifty healthy subjects comprised the control group. The coding sequences of the NPVF and NPFFR1 genes were amplified and sequenced. Odds ratios (OR) were used to estimate the likelihood of CPP or nIHH in the presence of the described polymorphisms. All such polymorphisms have already been registered in the National Center for Biotechnology Information database. A three-nucleotide in frame deletion was identified in the NPVF gene (p.I71_K72), with a smaller proportion in the CPP (5%) compared to the nIHH (15%) group (P = 0.06). This results in the deletion of the isoleucine at position 71, adjacent to lysine at an endoproteolytic cleavage site of the precursor peptide. This polymorphism was associated with a lower risk of CPP (OR = 0.33; 95% confidence interval = 0.08-0.88); interestingly, only two men with nIHH were homozygotes for this variant. A total of five missense polymorphisms were found in the NPFFR1 gene, which encodes GPR147, with similar frequencies among groups and no association with pubertal timing. Our data suggest that RFRP-3/GPR147 may play secondary, modulatory roles on the regulation of pubertal development; a restraining modulatory effect of the NPVF p.I71_K72 variant on the activation of the gonadotrophic axis cannot be ruled out and deserves further investigation.

At the crossroads of physiology and ecology: food supply and the timing of avian reproduction

This article is part of a Special Issue “Energy Balance”. The decision of when to breed is crucial to the reproductive success and fitness of seasonally breeding birds. The availability of food for adults prior to breeding has long been thought to play a critical role in timing the initiation of seasonal reproductive events, in particular laying. However, unequivocal evidence for such a role remains limited and the physiological mechanisms by which an increase in food availability results in seasonal activation of the reproductive system are largely speculative. This lack of mechanistic information partly reflects a lack of integration of ecological and physiological approaches to study seasonal reproduction. Indeed, most work pertaining to the role of food availability for adults on the timing of avian reproduction has been ecological and has focused almost exclusively on female traits associated with reproductive timing (e.g., lay date and clutch size). By contrast, most work on the physiological bases of the relationship between food availability and the timing of reproduction has investigated male traits associated with reproductive development (e.g., reproductive hormones and gonadal development). To advance our understanding of these topics, we review the role of proximate factors including food availability, social factors, and ambient temperature in the control of breeding decisions, and discuss the role of three potential candidates (leptin, glucocorticoids, and GnIH-neuropeptide Y) that may mediate the effects of food availability on these decisions. We emphasize that future progress in this area is heavily contingent upon the use of physiology-based approaches and their integration into current ecological frameworks.