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Ishwar S. Parhar - One of the best experts on this subject based on the ideXlab platform.
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Single-Cell Gene Profiling Reveals Social Status-Dependent Modulation of Nuclear Hormone Receptors in GnRH Neurons in a Male Cichlid Fish.
International journal of molecular sciences, 2020Co-Authors: Satoshi Ogawa, Ishwar S. ParharAbstract:Gonadotropin-releasing hormone (GnRH) is essential for the initiation and maintenance of reproductive functions in vertebrates. To date, three distinct paralogue lineages, GnRH1, GnRH2, and GnRH3, have been identified with different functions and regulatory mechanisms. Among them, hypothalamic GnRH1 neurons are classically known as the hypophysiotropic form that is regulated by estrogen feedback. However, the mechanism of action underlying the estrogen-dependent regulation of GnRH1 has been debated, mainly due to the coexpression of low levels of estrogen receptor (ER) genes. In addition, the role of sex steroids in the modulation of GnRH2 and GnRH3 neurons has not been fully elucidated. Using single-cell real-time PCR, we revealed the expression of genes for estrogen, androgen, glucocorticoid, thyroid, and xenobiotic receptors in GnRH1, GnRH2, and GnRH3 neurons in the male Nile tilapia Oreochromis niloticus. We further quantified expression levels of estrogen receptor genes (ERα, ERβ, and ERγ) in three GnRH neuron types in male tilapia of two different social statuses (dominant and subordinate) at the single cell level. In dominant males, GnRH1 mRNA levels were positively proportional to ERγ mRNA levels, while in subordinate males, GnRH2 mRNA levels were positively proportional to ERβ mRNA levels. These results indicate that variations in the expression of nuclear receptors (and possibly steroid sensitivities) among individual GnRH cells may facilitate different physiological processes, such as the promotion of reproductive activities through GnRH1 neurons, and the inhibition of feeding and sexual behaviors through GnRH2 neurons.
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Expression of neuropeptide Y and gonadotropin-releasing hormone gene types in the brain of female Nile tilapia (Oreochromis niloticus) during mouthbrooding and food restriction.
Peptides, 2018Co-Authors: Kalpana Das, Takashi Kitahashi, Satoshi Ogawa, Ishwar S. ParharAbstract:A cichlid fish, the Nile tilapia (Oreochromis niloticus), is a maternal mouthbrooder, which exhibits minimum energy expenditure and slower ovarian cycles during mouthbrooding. The objective of this study was to observe changes in the gene expression of key neuropeptides involved in the control of appetite and reproduction, including neuropeptide Y a (NPYa), reproductive neuropeptides: gonadotropin-releasing hormone (GnRH1, GnRH2 and GnRH3) and kisspeptin (Kiss2) during mouthbrooding (4- and 12-days), 12-days of food restriction and 12-days of food restriction followed by refeeding. The food restriction regime showed a significant increase in npya mRNA levels in the telencephalon. However, there were no significant alterations in npya mRNA levels during mouthbrooding. gnrh1 mRNA levels were significantly lower in mouthbrooding female as compared with females with food restriction. gnrh3 mRNA levels were also significantly lower in female with 12-days of mouthbrooding, 12-days of food restriction followed by 12-days of refeeding when compared with controls. There were no significant differences in GnRH2 and kiss2 mRNA levels between groups under different feeding regimes. No significant changes were observed in mRNA levels of receptors for peripheral metabolic signaling molecules: ghrelin (GHS-R1a and GHS-R1b) and leptin (Lep-R). These results suggested that unaffected npya mRNA levels in the telencephalon might contribute to suppression of appetite in mouthbrooding female tilapia. Furthermore, lower gnrh1 and gnrh3 mRNA levels may influence the suppression of reproductive functions such as progression of ovarian cycle and reproductive behaviours, while GnRH2 and Kiss2 may not play a significant roles in reproduction under food restriction condition.
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Early-life stress changes expression of GnRH and kisspeptin genes and DNA methylation of GnRH3 promoter in the adult zebrafish brain.
General and comparative endocrinology, 2015Co-Authors: Yee Min Khor, Tomoko Soga, Ishwar S. ParharAbstract:Early-life stress can cause long-term effects in the adulthood such as alterations in behaviour, brain functions and reproduction. DNA methylation is a mechanism of epigenetic change caused by early-life stress. Dexamethasone (DEX) was administered to zebrafish larvae to study its effect on reproductive dysfunction. The level of GnRH2, GnRH3, Kiss1 and Kiss2 mRNAs were measured between different doses of DEX treatment groups in adult zebrafish. Kiss1 and GnRH2 expression were increased in the 200mg/L DEX treated while Kiss2 and GnRH3 mRNA levels were up-regulated in the 2mg/L DEX-treated zebrafish. The up-regulation may be related to programming effect of DEX in the zebrafish larvae, causing overcompensation mechanism to increase the mRNA levels. Furthermore, DEX treatment caused negative impact on the development and maturation of the testes, in particular spermatogenesis. Therefore, immature gonadal development may cause positive feedback by increasing GnRH and Kiss. This indicates that DEX can alter the regulation of GnRH2, GnRH3, Kiss1 and Kiss2 in adult zebrafish, which affects maturation of gonads. Computer analysis of 1.5 kb region upstream of the 5' UTR of Kiss1, Kiss2, GnRH2 and GnRH3 promoter showed that there are putative binding sites of glucocorticoid response element and transcription factors involved in stress response. GnRH3 promoter analysed from pre-optic area, ventral telencephalon and ventral olfactory bulb showed higher methylation at CpG residues located on -1410, -1377 and -1355 between control and 2mg/L DEX-treated groups. Hence, early-life DEX treatment can alter methylation of GnRH3 gene promoter, which subsequently affects gene regulation and reproductive functions.
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Diurnal and circadian oscillations in expression of kisspeptin, kisspeptin receptor and gonadotrophin-releasing hormone 2 genes in the grass puffer, a semilunar-synchronised spawner.
Journal of neuroendocrinology, 2014Co-Authors: Hironori Ando, Satoshi Ogawa, Shahjahan, Taro Ikegami, Hiroyuki Doi, Atsuhiko Hattori, Ishwar S. ParharAbstract:In seasonally breeding animals, the circadian and photoperiodic regulation of neuroendocrine system is important for precisely-timed reproduction. Kisspeptin, encoded by the Kiss1 gene, acts as a principal positive regulator of the reproductive axis by stimulating gonadotrophin-releasing hormone (GnRH) neurone activity in vertebrates. However, the precise mechanisms underlying the cyclic regulation of the kisspeptin neuroendocrine system remain largely unknown. The grass puffer, Takifugu niphobles, exhibits a unique spawning rhythm: spawning occurs 1.5-2 h before high tide on the day of spring tide every 2 weeks, and the spawning rhythm is connected to circadian and lunar-/tide-related clock mechanisms. The grass puffer has only one kisspeptin gene (kiss2), which is expressed in a single neural population in the preoptic area (POA), and has one kisspeptin receptor gene (kiss2r), which is expressed in the POA and the nucleus dorsomedialis thalami. Both kiss2 and kiss2r show diurnal variations in expression levels, with a peak at Zeitgeber time (ZT) 6 (middle of day time) under the light/dark conditions. They also show circadian expression with a peak at circadian time 15 (beginning of subjective night-time) under constant darkness. The synchronous and diurnal oscillations of kiss2 and kiss2r expression suggest that the action of Kiss2 in the diencephalon is highly dependent on time. Moreover, midbrain GnRH2 gene (GnRH2) but not GnRH1 or GnRH3 genes show a unique semidiurnal oscillation with two peaks at ZT6 and ZT18 within a day. The cyclic expression of kiss2, kiss2r and GnRH2 may be important in the control of the precisely-timed diurnal and semilunar spawning rhythm of the grass puffer, possibly through the circadian clock and melatonin, which may transmit the photoperiodic information of daylight and moonlight to the reproductive neuroendocrine centre in the hypothalamus.
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Cloning and functional expression of novel cholesterol transporters ABCG1 and ABCG4 in gonadotropin-releasing hormone neurons of the tilapia
Neuroscience, 2011Co-Authors: Yen Phang, Tomoko Soga, Takashi Kitahashi, Ishwar S. ParharAbstract:In addition to reproduction, gonadotropin-releasing hormone (GnRH) has been postulated to control cholesterol metabolism via cholesterol transport, which is carried out partly by the members of ATP-binding cassette (ABC) transporters G1 (ABCG1) and G4 (ABCG4). However, there is yet to be evidence demonstrating the relationship between these transporters with reference to GnRH neurons. In the present study, we cloned two ABCG1 messenger RNA (mRNA) variants and one ABCG4 mRNA and examined their expression in the brain including GnRH neurons (GnRH1, GnRH2, and GnRH3) in the cichlid tilapia (Oreochromis niloticus). Comparison of nucleotide sequences of the tilapia ABCG1 and ABCG4 with that of other fish species showed that both of these genes are evolutionarily conserved among fishes. ABCG1 and ABCG4 were shown to have high mRNA expressions in the CNS, pituitary, and gonads. In the brain, real-time polymerase chain reaction (PCR) showed that ABCG4 mRNA was higher than ABCG1a in all brain regions including the olfactory bulb (ABCG1=13.34, ABCG4=6796.35; P
Nancy M. Sherwood - One of the best experts on this subject based on the ideXlab platform.
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Endocrinology of zebrafish: A small fish with a large gene pool
Fish Physiology, 2010Co-Authors: Ellen R. Busby, Graeme J. Roch, Nancy M. SherwoodAbstract:Publisher Summary This chapter discusses the endocrinology of zebrafish. The endocrinology of zebrafish comprising the reproductive, stress, growth, and thyroidal systems is supported by a full cascade of neurohormones, pituitary hormones, and peripheral hormones including steroids comparable to human forms with duplicate genes in some cases. Zebrafish possess two forms of gonadotropin-releasing hormone (Gnrh) compared to most other teleosts with three forms. However, zebrafish have GnRH2, which is identical to one of the human forms (GnRH2), and Gnrh3, which is unique to teleost fishes, but 80% identical to the other human form (GNRH1). The vertebrate stress axis involves a signaling chain of several hormones and receptors. The primary stress response is initiated when corticotropin-releasing hormone (CRH) is secreted by hypothalamic neurons to bind its receptor in the anterior pituitary on the surface of corticotrope cells. This is followed by the release of adrenocorticotropic hormone (ACTH), a post-translational product of pro-opiomelanocortin (POMC). Zebrafish, like other teleosts, have a thyroid axis similar to that of mammals and amphibians, with a few unique variations. Thyrotropin releasing hormone (Trh) is detected throughout the zebrafish brain with a wider distribution than in other teleosts or mammals, suggesting possible additional functions in zebrafish. Zebrafish possess all of the major hormonal components found in mammals necessary to maintain osmotic balance. The best characterized zebrafish osmoregulatory neuropeptides are isotocin (It) and arginine vasotocin (Avt), the fish orthologs of mammalian oxytocin and arginine vasopressin, respectively.
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Amphioxus: beginning of vertebrate and end of invertebrate type GnRH receptor lineage.
Endocrinology, 2009Co-Authors: Javier A Tello, Nancy M. SherwoodAbstract:In vertebrates, activation of the GnRH receptor is necessary to initiate the reproductive cascade. However, little is known about the characteristics of GnRH receptors before the vertebrates evolved. Recently genome sequencing was completed for amphioxus, Branchiostoma floridae. To understand the GnRH receptors (GnRHR) from this most basal chordate, which is also classified as an invertebrate, we cloned and characterized four GnRHR cDNAs encoded in the amphioxus genome. We found that incubation of GnRH1 (mammalian GnRH) and GnRH2 (chicken GnRH II) with COS7 cells heterologously expressing the amphioxus GnRHRs caused potent intracellular inositol phosphate turnover in two of the receptors. One of the two receptors displayed a clear preference for GnRH1 over GnRH2, a characteristic not previously seen outside the type I mammalian GnRHRs. Phylogenetic analysis grouped the four receptors into two paralogous pairs, with one pair grouping basally with the vertebrate GnRH receptors and the other grouping with the octopus GnRHR-like sequence and the related receptor for insect adipokinetic hormone. Pharmacological studies showed that octopus GnRH-like peptide and adipokinetic hormone induced potent inositol phosphate turnover in one of these other two amphioxus receptors. These data demonstrate the functional conservation of two distinct types of GnRH receptors at the base of chordates. We propose that one receptor type led to vertebrate GnRHRs, whereas the other type, related to the mollusk GnRHR-like receptor, was lost in the vertebrate lineage. This is the first report to suggest that distinct invertebrate and vertebrate GnRHRs are present simultaneously in a basal chordate, amphioxus.
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Four functional GnRH receptors in zebrafish: analysis of structure, signaling, synteny and phylogeny.
Integrative and comparative biology, 2008Co-Authors: Javier A Tello, Jean Rivier, Nancy M. SherwoodAbstract:Reproduction in all vertebrates requires the brain hormone gonadotropin-releasing hormone (GnRH) to activate a cascade of events leading to gametogenesis. All vertebrates studied to date have one to three forms of GnRH in specific but different neurons in the brain. In addition, at least one type of GnRH receptor is present in each vertebrate for activation of specific physiological events within a target cell. Humans possess two types of GnRH (GnRH1 and GnRH2) but only one functional GnRH receptor. Zebrafish, Danio rerio, also have two types of GnRH (GnRH2 and GnRH3), although in contrast to humans, zebrafish appear to have four different GnRH receptors in their genome. To characterize the biological significance of multiple GnRH receptors within a single species, we cloned four GnRH receptor cDNAs from zebrafish and compared their structures, expression, and cell physiology. The zebrafish receptors are 7-transmembrane G-protein coupled receptors with amino-acid sequence identities ranging from 45 to 71% among the four receptors. High sequence similarity was observed among the seven helices of zebrafish GnRHRs compared with the human GnRHR, the green monkey type II GnRHR, and the two goldfish GnRHRs. Also, key amino acids for putative ligand binding, disulfide bond formation, N-glycosylation, and G-protein coupling were present in the extracellular and intracellular domains. The four zebrafish receptors were expressed in a variety of tissues including the brain, eye, and gonads. In an inositol phosphate assay, each receptor was functional as shown by its response to physiological doses of native GnRH peptides; two receptors showed selectivity between GnRH2 and GnRH3. Each of the four receptor genes was mapped to distinct chromosomes. Our phylogenetic and syntenic analysis segregated the four zebrafish GnRH receptors into two distinct phylogenetic groups that are separate gene lineages conserved throughout vertebrate evolution. We suggest the maintenance of four functional GnRH receptors in zebrafish compared with only one in humans may depend either on subfunctionalization or neofunctionalization in fish compared with mammalian GnRH receptors. The differences in structure, location, and response to GnRH forms strongly suggests that the four zebrafish GnRH receptors have novel functions in addition to the conventional activation of the pituitary gland in the reproductive axis.
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A role for GnRH in early brain regionalization and eye development in zebrafish.
Molecular and cellular endocrinology, 2006Co-Authors: Louise Page, Nancy M. SherwoodAbstract:Gonadotropin-releasing hormone (GnRH) is a highly conserved peptide that is expressed early in brain development in vertebrates. In zebrafish, we detected GnRH mRNA within 2h post fertilization by RT-PCR. To determine if GnRH is involved in development, we used gene knockdown techniques to block translation of GnRH2 or gnrh3 mRNA after which the expression patterns for gene markers were examined at 24h post fertilization with in situ hybridization. First, loss of either GnRH2 or GnRH3 affected regionalization of the brain as shown by a change in expression of fgf8 or pax2.1 genes in the midbrain-hindbrain boundary or diencephalon-midbrain boundary. Second, lack of GnRH2 and/or GnRH3 altered gene markers expressed in the formation of the eye cup (pax2.1, pax6.1, mab21l2 and meis1.1) or eye stalk (fgf8 and pax2.1). Third, knockdown of GnRH2 affected the size and shape of the midbrain and expression of gene markers therein. Results from assays with the TUNEL method and caspase-3 and -9 activity showed the brain and eye changes were unlikely to result from secondary apoptotic cell death before 24h post fertilization. These experiments suggest that GnRH loss-of-function affects early brain and eye formation during development.
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Developmental role of GnRH and PACAP in a zebrafish model.
General and comparative endocrinology, 2005Co-Authors: Nancy M. SherwoodAbstract:GnRH is expressed early in development long before reproduction begins. To determine whether GnRH has a role in development, gene knockdown with morpholinos was used in one-cell zebrafish embryos to block translation of gnrh mRNA into protein. Gene knockdown of GnRH2, gnrh3 or both at the one-cell stage resulted in a high percentage of embryos at 24-48 h with a defective mid-hindbrain boundary and underdeveloped eyes; a small percentage of embryos at 72 h had a defective heart. In similar studies on GHRH-PACAP, gene knockdown resulted in a smaller brain and eyes, but a normal-appearing heart. The evidence supports a role for the three neuropeptides in early development.
Stacia A Sower - One of the best experts on this subject based on the ideXlab platform.
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Identification and expression of GnRH2 and GnRH3 in the black sea bass (Centropristis striata), a hermaphroditic teleost
Fish Physiology and Biochemistry, 2015Co-Authors: Scott J. Morin, Wayne A. Decatur, Timothy S. Breton, Timothy J. Marquis, Mary K. Hayes, David L. Berlinsky, Stacia A SowerAbstract:We cloned two cDNAs for two gonadotropin-releasing hormones, GnRH2 (chicken GnRH-II) and GnRH3 (salmon GnRH), respectively, from the black sea bass ( Centropristis striata ). Black sea bass are protogynous hermaphroditic teleosts that change from females to males between 2 and 5 years of age. Similar to other GnRH precursors, the precursors of black sea bass GnRH2 and GnRH23 consisted of a signal peptide, decapeptide, a downstream processing site, and a GnRH-associated peptide. Our analyses failed to identify GnRH1. GnRH3 precursor transcript was more widely distributed in a variety of tissues compared with GnRH2. Further examination of GnRH expression and gonadal histology was done in black sea bass from three different size groups: small (11.4–44.1 g), medium (179.4–352.2 g) and large (393.8–607.3 g). Interestingly, GnRH3 expression occurred only in the pituitaries of males in the small and medium groups compared with expression of GnRH2. Future functional studies of the sea bass GnRHs will be valuable in elucidating the potential underlying neuroendocrine mechanisms of black sea bass reproduction and may ultimately contribute to management advances in this commercially important fish.
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Brain aromatase (cyp19a1b) and gonadotropin releasing hormone (GnRH2 and gnrh3) expression during reproductive development and sex change in black sea bass (Centropristis striata)
Comparative biochemistry and physiology. Part A Molecular & integrative physiology, 2014Co-Authors: Timothy S. Breton, Stacia A Sower, Matthew A. Dimaggio, David L. BerlinskyAbstract:Teleost fish exhibit diverse reproductive strategies, and some species are capable of changing sex. The influence of many endocrine factors, such as gonadal steroids and neuropeptides, has been studied in relation to sex change, but comparatively less research has focused on gene expression changes within the brain in temperate grouper species with non-haremic social structures. The purpose of the present study was to investigate gonadotropin releasing hormone (GnRH) and brain aromatase (cyp19a1b) gene expression patterns during reproductive development and sex change in protogynous (female to male) black sea bass (Centropristis striata). Partial cDNA fragments for cyp19a1b and eef1a (a reference gene) were identified, and included with known GnRH2 and gnrh3 sequences in real time quantitative PCR. Elevated cyp19a1b expression was evident in the olfactory bulbs, telencephalon, optic tectum, and hypothalamus/midbrain region during vitellogenic growth, which may indicate changes in the brain related to neurogenesis or sexual behavior. In contrast, GnRH2 and gnrh3 expression levels were largely similar among gonadal states, and all three genes exhibited stable expression during sex change. Although sex change in black sea bass is not associated with dramatic changes in GnRH or cyp19a1b gene expression among brain regions, these genes may mediate processes at other levels, such as within individual hypothalamic nuclei, or through changes in neuron size, that warrant further research.
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Insight from the lamprey genome: glimpsing early vertebrate development via neuroendocrine-associated genes and shared synteny of gonadotropin-releasing hormone (GnRH).
General and comparative endocrinology, 2013Co-Authors: Wayne A. Decatur, Jeffrey A. Hall, J. Joshua Smith, Stacia A SowerAbstract:Abstract Study of the ancient lineage of jawless vertebrates is key to understanding the origins of vertebrate biology. The establishment of the neuroendocrine system with the hypothalamic–pituitary axis at its crux is of particular interest. Key neuroendocrine hormones in this system include the pivotal gonadotropin-releasing hormones (GnRHs) responsible for controlling reproduction via the pituitary. Previous data incorporating several lines of evidence showed all known vertebrate GnRHs were grouped into four paralogous lineages: GnRH1, 2, 3 and 4; with proposed evolutionary paths. Using the currently available lamprey genome assembly, we searched genes of the neuroendocrine system and summarize here the details representing the state of the current lamprey genome assembly. Additionally, we have analyzed in greater detail the evolutionary history of the GnRHs based on the information of the genomic neighborhood of the paralogs in lamprey as compared to other gnathostomes. Significantly, the current evidence suggests that two genome duplication events (both 1R and 2R) that generated the different fish and tetrapod paralogs took place before the divergence of the ancestral agnathans and gnathostome lineages. Syntenic analysis supports this evidence in that the previously-classified type IV GnRHs in lamprey (lGnRH-I and -III) share a common ancestry with GnRH2 and 3, and thus are no longer considered type IV GnRHs. Given the single amino acid difference between lGnRH-II and GnRH2 we propose that a GnRH2-like gene existed before the lamprey/gnathostome split giving rise to lGnRH-II and GnRH2. Furthermore, paralogous type 3 genes (lGnRH-I/III and GnRH3) evolved divergent structure/function in lamprey and gnathostome lineages.
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Revisiting the evolution of gonadotropin-releasing hormones and their receptors in vertebrates: secrets hidden in genomes.
General and Comparative Endocrinology, 2011Co-Authors: Dong-kyu Kim, Eun Bee Cho, Mi Jin Moon, Sumi Park, Jong-ik Hwang, Olivier Kah, Stacia A Sower, Hubert Vaudry, Jae Young SeongAbstract:Gonadotropin-releasing hormone (GnRH) and its G protein-coupled receptor, GnRHR, play a pivotal role in the control of reproduction in vertebrates. To date, many GnRH and GnRHR genes have been identified in a large variety of vertebrate species using conventional biochemical and molecular biological tools in combination with bioinformatic tools. Phylogenetic approaches, primarily based on amino acid sequence identity, make it possible to classify these multiple GnRHs and GnRHRs into several lineages. Four vertebrate GnRH lineages GnRH1, GnRH2, GnRH3, and GnRH4 (for lamprey) are well established. Four vertebrate GnRHR lineages have also been proposed-three for nonmammalian GnRHRs and mammalian GnRHR2 as well as one for mammalian GnRHR1. However, these phylogenetic analyses cannot fully explain the evolutionary origins of each lineage and the relationships among the lineages. Rapid and vast accumulation of genome sequence information for many vertebrate species, together with advances in bioinformatic tools, has allowed large-scale genome comparison to explore the origin and relationship of gene families of interest. The present review discusses the evolutionary mechanism of vertebrate GnRHs and GnRHRs based on extensive genome comparison. In this article, we focus only on vertebrate genomes because of the difficulty in comparing invertebrate and vertebrate genomes due to their marked divergence.
José Antonio Muñoz-cueto - One of the best experts on this subject based on the ideXlab platform.
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Morphological relationship between GnIH and GnRH neurons in the brain of the neotropical cichlid fish Cichlasoma dimerus
General and comparative endocrinology, 2018Co-Authors: María Paula Di Yorio, José Antonio Muñoz-cueto, Daniela Pérez I. Sirkin, Gustavo M. Somoza, Tomás Horacio Delgadin, Kazuyoshi Tsutsui, Paula G. VissioAbstract:Abstract Reproduction is regulated by the hypothalamic-pituitary-gonadal axis. The first neuropeptide identified that regulates this function was the decapeptide gonadotropin-releasing hormone (GnRH). Nowadays, in gnatostomates, a number of GnRH variants have been identified and classified into three different types: GnRH1, GnRH2, and GnRH3. Almost 30 years later, a new peptide that inhibits gonadotropin synthesis and secretion was discovered and thus named as gonadotropin-inhibitory hormone (GnIH). In avians and mammals, the interaction and regulation between GnRH and GnIH neurons has been widely studied; however, in other vertebrate groups there is little information about the relationship between these neurons. In previous works, three GnRH variants and a GnIH propeptide were characterized in Cichlasoma dimerus, and it was demonstrated that GnIH inhibited gonadotropins release in this species. Because no innervation was detected at the pituitary level, we speculate that GnIH would inhibit gonadotropins via GnRH. Thus, the aim of the present study was to evaluate the anatomical relationship between neurons expressing GnIH and the three GnRH variants by double labelling confocal immunofluorescence in adults of C. dimerus. Our results showed no apparent contacts between GnIH and GnRH1, fiber to fiber interactions between GnIH and GnRH2, and co-localization of GnIH and GnRH3 variant in neurons of the nucleus olfacto-retinalis. In conclusion, whether GnIH regulates the expression or secretion of GnRH1 in this species, an indirect modulation seems more plausible. Moreover, the present results suggest an interaction between GnIH and GnRH2 systems. Finally, new clues were provided to investigate the role of nucleus olfacto-retinalis cells and putative GnIH and GnRH3 interactions in the modulation of the reproductive network in teleost fish.
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Effects of pinealectomy on the neuroendocrine reproductive system and locomotor activity in male European sea bass, Dicentrarchus labrax.
Comparative biochemistry and physiology. Part A Molecular & integrative physiology, 2017Co-Authors: Mairi Cowan, José A. Paullada-salmerón, José Fernando López-olmeda, Francisco Javier Sánchez-vázquez, José Antonio Muñoz-cuetoAbstract:The seasonally changing photoperiod controls the timing of reproduction in most fish species, however, the transduction of this photoperiodic information to the reproductive axis is still unclear. This study explored the potential role of two candidate neuropeptide systems, gonadotropin-inhibitory hormone (Gnih) and kisspeptin, as mediators between the pineal organ (a principle transducer of photoperiodic information) and reproductive axis in male European sea bass, Dicentrarchus labrax. Two seven-day experiments of pinealectomy (Px) were performed, in March (end of reproductive season) and August (resting season). Effects of Px and season on the brain expression of gnih (sbgnih) and its receptor (sbgnihr), kisspeptins (kiss1, kiss2) and their receptors (kissr2, kissr3) and gonadotropin-releasing hormone (gnrh1, GnRH2, gnrh3) and the main brain receptor (gnrhr-II-2b) genes, plasma melatonin levels and locomotor activity rhythms were examined. Results showed that Px reduced night-time plasma melatonin levels. Gene expression analyses demonstrated a sensitivity of the Gnih system to Px in March, with a reduction in sbgnih in the mid-hindbrain, a region with bilateral connections to the pineal organ. In August, kiss2 levels increased in Px animals but not in controls. Significant differences in expression were observed for diencephalic sbgnih, sbgnihr, kissr3 and tegmental GnRH2 between seasons. Recordings of locomotor activity following surgery revealed a change from light-synchronised to free-running rhythmic behavior. Altogether, the Gnih and Kiss2 sensitivity to Px and seasonal differences observed for Gnih and its receptor, GnRH2, and the receptor for Kiss2 (Kissr3), suggested they could be mediators involved in the relay between environment and seasonal reproduction.
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Gonadotropin Inhibitory Hormone Down-Regulates the Brain-Pituitary Reproductive Axis of Male European Sea Bass (Dicentrarchus labrax)
Biology of reproduction, 2016Co-Authors: José A. Paullada-salmerón, Mairi Cowan, María Aliaga-guerrero, Francesca Morano, Silvia Zanuy, José Antonio Muñoz-cuetoAbstract:Gonadotropin-inhibitory hormone (GnIH) inhibits gonadotropin synthesis and release from the pituitary of birds and mammals. However, the physiological role of orthologous GnIH peptides on the reproductive axis of fish is still uncertain, and their actions on the main neuroendocrine systems controlling reproduction (i.e., GnRHs, kisspeptins) have received little attention. In a recent study performed in the European sea bass, we cloned a cDNA encoding a precursor polypeptide that contained C-terminal MPMRFamide (sbGnIH-1) and MPQRFamide (sbGnIH-2) peptide sequences, developed a specific antiserum against sbGnIH-2, and characterized its central and pituitary GnIH projections in this species. In this study, we analyzed the effects of intracerebroventricular injection of sbGnIH-1 and sbGnIH-2 on brain and pituitary expression of reproductive hormone genes (gnrh1, GnRH2, gnrh3, kiss1, kiss2, gnih, lhbeta, fshbeta), and their receptors (gnrhr II-1a, gnrhr II-2b, kiss1r, kiss2r, and gnihr) as well as on plasma Fsh and Lh levels. In addition, we determined the effects of GnIH on pituitary somatotropin (Gh) expression. The results obtained revealed the inhibitory role of sbGnIH-2 on brain GnRH2, kiss1, kiss2, kiss1r, gnih, and gnihr transcripts and on pituitary fshbeta, lhbeta, gh, and gnrhr-II-1a expression, whereas sbGnIH-1 only down-regulated brain gnrh1 expression. However, at different doses, central administration of both sbGnIH-1 and sbGnIH-2 decreased Lh plasma levels. Our work represents the first study reporting the effects of centrally administered GnIH in fish and provides evidence of the differential actions of sbGnIH-1 and sbGnIH-2 on the reproductive axis of sea bass, the main inhibitory role being exerted by the sbGnIH-2 peptide.
Yonathan Zohar - One of the best experts on this subject based on the ideXlab platform.
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GnRH2 maintains reproduction in fasting zebrafish through dynamic neuronal projection changes and regulation of gonadotropin synthesis, oogenesis, and reproductive behaviors
Scientific Reports, 2021Co-Authors: Miranda Marvel, Berta Levavi-sivan, Ten Tsao Wong, Nilli Zmora, Yonathan ZoharAbstract:Restricted food intake, either from lack of food sources or endogenous fasting, during reproductive periods is a widespread phenomenon across the animal kingdom. Considering previous studies show the canonical upstream regulator of reproduction in vertebrates, the hypothalamic Gonadotropin-releasing hormone (Gnrh), is inhibited in some fasting animals, we sought to understand the neuroendocrine control of reproduction in fasted states. Here, we explore the roles of the midbrain neuropeptide, GnRH2, in inducing reproduction via its pituitary prevalence, gonadotropin synthesis, gametogenesis, and reproductive outputs in the zebrafish model undergoing different feeding regimes. We discovered a fasting-induced four-fold increase in length and abundance of GnRH2 neuronal projections to the pituitary and in close proximity to gonadotropes, whereas the hypothalamic Gnrh3 neurons are reduced by six-fold in length. Subsequently, we analyzed the functional roles of GnRH2 by comparing reproductive parameters of a GnRH2-depleted model, GnRH2 ^−/−, to wild-type zebrafish undergoing different feeding conditions. We found that GnRH2 depletion in fasted states compromises spawning success, with associated decreases in gonadotropin production, oogenesis, fecundity, and male courting behavior. GnRH2 neurons do not compensate in other circumstances by which Gnrh3 is depleted, such as in gnrh3 ^−/− zebrafish, implying that GnRH2 acts to induce reproduction specifically in fasted zebrafish.
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Knockout of GnRH2 in zebrafish (Danio rerio) reveals its roles in regulating feeding behavior and oocyte quality.
General and comparative endocrinology, 2019Co-Authors: Miranda Marvel, Olivia Smith Spicer, Ten Tsao Wong, Nilli Zmora, Yonathan ZoharAbstract:Abstract Many studies on Gnrh1, and the teleost Gnrh3, have elucidated the roles of these peptides in reproductive regulation. However, the role of the midbrain population of Gnrh, GnRH2, has long been a mystery, despite its ubiquitous conservation in all jawed vertebrates except rodents. Previous behavioral studies in sparrows, musk shrews, mice, zebrafish, and goldfish show that GnRH2 administrations both increase spawning behaviors and decrease feeding behaviors, suggesting a role of this peptide in metabolism regulation along with the canonical role in regulating reproduction. In order to more deeply explore the roles of GnRH2, we used a cyprinid teleost, zebrafish, which has 2 forms of Gnrh, GnRH2 and Gnrh3, to generate a knockout zebrafish line which contains a frameshift mutation and subsequent disruption of the coding for the functional GnRH2 peptide. We examined differences in reproduction, feeding, growth, and mobility in this line, and discovered major differences in feeding and growth parameters, suggesting that GnRH2 is a potent anorexigen in zebrafish. Additionally, there were no differences in mobility except for increased distances swam during feeding periods. There were no major differences in reproductive success, however, female GnRH2−/− zebrafish exhibited smaller oocytes and increased embryo mortality, indicating slightly decreased oocyte quality. Additionally, there were changes in the expression levels of many feeding, growth, and reproductive neuropeptides in GnRH2−/− zebrafish. Taken together, these findings suggest a role for GnRH2 in controlling satiation in zebrafish along with a minor role in maintaining optimal oocyte quality in females.
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Knockout of the Gnrh genes in zebrafish: effects on reproduction and potential compensation by reproductive and feeding-related neuropeptides
Biology of reproduction, 2018Co-Authors: Miranda Marvel, Olivia Smith Spicer, Ten Tsao Wong, Nilli Zmora, Yonathan ZoharAbstract:Gonadotropin-releasing hormone (GNRH) is known as a pivotal upstream regulator of reproduction in vertebrates. However, reproduction is not compromised in the hypophysiotropic Gnrh3 knockout line in zebrafish (gnrh3-/-). In order to determine if GnRH2, the only other Gnrh isoform in zebrafish brains, is compensating for the loss of Gnrh3, we generated a double Gnrh knockout zebrafish line. Surprisingly, the loss of both Gnrh isoforms resulted in no major impact on reproduction, indicating that a compensatory response, outside of the Gnrh system, was evoked. A plethora of factors acting along the reproductive hypothalamus-pituitary axis were evaluated as possible compensators based on neuroanatomical and differential gene expression studies. In addition, we also examined the involvement of feeding factors in the brain as potential compensators for GnRH2, which has known anorexigenic effects. We found that the double knockout fish exhibited upregulation of several genes in the brain, specifically gonadotropin-inhibitory hormone (gnih), secretogranin 2 (scg2), tachykinin 3a (tac3a), and pituitary adenylate cyclase-activating peptide 1 (pacap1), and downregulation of agouti-related peptide 1 (agrp1), indicating the compensation occurs outside of Gnrh cells and therefore is a noncell autonomous response to the loss of Gnrh. While the differential expression of gnih and agrp1 in the double knockout line was confined to the periventricular nucleus and hypothalamus, respectively, the upregulation of scg2 corresponded with a broader neuronal redistribution in the lateral hypothalamus and hindbrain. In conclusion, our results demonstrate the existence of a redundant reproductive regulatory system that comes into play when GnRH2 and Gnrh3 are lost.
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Comprehensive Analysis of GnRH2 Neuronal Projections in Zebrafish
Scientific Reports, 2014Co-Authors: Wei Xia, Nilli Zmora, Olivia Smith, Yonathan ZoharAbstract:The presence and conservation of GnRH2 across vertebrate species suggest important biological roles. However, the function of GnRH2 remains unclear. A good research model for GnRH2 functional studies is still lacking largely due to the absence of GnRH2 in the widely used mouse model. Hence, we used the zebrafish, for which powerful genetic tools are available and developed a transgenic (Tg) line expressing enhanced green fluorescence protein (eGFP). The high sensitivity of eGFP, which can diffuse throughout the neuron, enables us to document the complete projectome of GnRH2 neurons at different developmental stages. Fine projection structures were observed without sacrificing the fish. Crossed with the GnRH3:tdTomato Tg line, the GnRH2:eGFP Tg line provides us with an opportunity to visualize the entire GnRH system simultaneously in one organism. This work will provide a framework to understand the function of the highly-conserved GnRH2 system.