Characterization of the cDNAs encoding three GnRH forms in the pejerrey fish Odontesthes bonariensis (Atheriniformes) and the evolution of GnRH precursors

Presence of GnRH3 in sturgeon and the roles of GnRH1 and GnRH2 on the regulation of LH/FSH in mature female sterlet Acipenser ruthenus in vitro

Three forms of gonadotropin-releasing hormones (GnRHs), ArGnRH1, ArGnRH2, and ArGnRH3, were identified in sterlet. Compared with their orthologue, ArGnRH1 and ArGnRH2 have conserved core decapeptide but show low identity in the signal peptide and the rest of the sequences. The existence of the GnRH3 paralogue of sturgeon was predicted for the first time with TBLASTN by using the amino acid sequences of catshark and whale shark GnRH3 precursor as queries against the whole genome and transcript data of sterlet. The predicted ArGnRH3 cDNA sequence was composed of three exons containing all the elements of the GnRH family. The successful molecular cloning of GnRH3 from sterlets verified its expression in the brain of sturgeons. The analysis of the ArGnRH3 amino acid sequence revealed a completely conserved decapeptide sequence that shows 100% identity with the sequence of teleosts and differs in one amino acid with that of the cartilaginous fish (catshark and whale shark) at the 5th position. The structure of the phylogenetic tree showed that a total of 52 vertebrate GnRH sequences were clustered into three main clades corresponding to GnRH1, GnRH2, and GnRH3. The ArGnRH3 sequence is the oldest GnRH3 identified in teleosts. The tissue distribution analysis showed that ArGnRH1 was expressed in all the 13 examined tissues of females and in most of the tested tissues of male fish, with the highest expression in the pituitary and hypothalamus. ArGnRH2 is only expressed in the pituitary, hypothalamus, and gonads of both female and male sterlets. ArGnRH3 mRNA could be detected in the pituitary, hypothalamus, and gonad in both female and male fish. It is also present in the spleen, head kidney, and gill in female fish and in kidney and heart in male fish. However, the ArGnRH3 only showed weak expression in all the positive tissues. ArGnRH1 and ArGnRH2 active decapeptides were synthesized to investigate their roles on the regulation of LH/FSH using a mixed brain cell line from a sexually mature female sterlet. The results showed that ArGnRH1 and ArGnRH2 exerted different effects on the gene expression and release of gonadotropins. ArGnRH1 promoted the expression of fshβ significantly around 48 h, and the expression was suppressed when the treatment time was extended to 72 h. ArGnRH1 had no significant effects on the level of either mRNA or secreted lh in any of the tested treatment length or concentrations. Moreover, ArGnRH1 did not stimulate the activity of gonadotropins in the maturation stage of female sturgeons. ArGnRH2 promoted the expression of fshβ at 24 h and 48 h and increased mRNA level of lhβ at 6 h and 48 h, accompanied by the significant secretion of LH at 72 h, although the high mRNA level of fsh did not correlate with the secretion of FSH in ArGnRH2-treated groups. In conclusion, ArGnRH2 plays an important role in the maturation stage of female sterlets. Therefore, ArGnRH2 has the potential to induce ovulation and spermiation in sturgeons.

A half century of fish gonadotropin-releasing hormones: Breaking paradigms

The field of fish gonadotropin-releasing hormones (GnRHs) is also celebrating its 50th anniversary this year. This review provides a chronological history of fish GnRH biology over the past five decades. It demonstrates how discoveries in fish regarding GnRH and GnRH receptor multiplicity, dynamic interactions between GnRH neurons, and additional neuroendocrine factors acting alongside GnRH, amongst others, have driven a paradigm shift in our understanding of GnRH systems and functions in vertebrates, including mammals. The role of technological innovations in enabling scientific discoveries is portrayed, as well as how fundamental research in fish GnRH led to translational outcomes in aquaculture. The interchange between fish and mammalian GnRH research is discussed, as is the value and utility of using fish models for advancing GnRH biology. Current challenges and future perspectives are presented, with the hope of expanding the dialogue and collaborations within the neuroendocrinology scientific community at large, capitalizing on diversifying model animals and the use of comparative strategies.

Molecular cloning, immunological characterization, and expression analysis of gonadotropin-releasing hormone (GnRH) in the brain of the Chinese alligator during different stages of reproductive cycle

The neurohormone gonadotropin-releasing hormone (GnRH) plays an essential role in the control of reproductive functions in vertebrates. However, the full-length complementary DNA (cDNA) encoding the GnRHs precursor and it role in the reproductive cycles regulating has not been illustrated in crocodilian species. In the present study, full-length cDNAs encoding GnRH1 forms, its predominant localization within brain and peripheral tissues, and GnRH1 peptide concentrations in the hypothalamus and pituitary in relation to seasonal gonadal development of Chinese alligator were investigated. The cDNA of GnRH1 is consisted of 282 bp open reading frame encoding 93 amino acids. The deduced amino acid sequence of alligator GnRH1 contains several conserved regions and shows a closer genetic relationship to the avian species than to other reptile species. The GnRH1 immunopositive cells were not only detected widely in cerebrum, diencephalon, medulla oblongata but also observed in peripheral tissues, these widespread distribution characteristics indicated that GnRH1 possibly possess the multi-functionality in Chinese Alligator. GnRH1 peptide concentration within hypothalamus were observed be the highest in RP group (P < 0.05), in association with an peak value in GSI and emerging of late vitellogenic follicles in the ovary. Taken together, our results suggested that GnRH1 was predominantly involved in the vitellogenesis process of seasonal gonadal development of Chinese Alligator.

Distribution and expression of GnRH 1, kiss receptor 2, and estradiol α and ß receptors in the anterior brain of females of Chirostoma humboldtianum

Reproduction in vertebrates is a complex process regulated by many hormones, and by paracrine factors and their receptors. This study aimed to examine the expression of pjGonadotropin-releasing hormone (GnRH 1), the kisspeptin receptor 2 (kissr2), and estradiol receptors α and β (ER α and ER β) during different stages of the sexual cycle and their distribution within the anterior brain of females of Chirostoma humboldtianum. Among these molecules, the kissr2 showed the maximal variation in expression, while GnRH 1 showed minimal variation of expression, and ERβ and ERα had intermediate variation of expression. The distribution of these molecules in the anterior brain was consistent with their levels of expression; kissr2 was widely distributed throughout the telencephalon and diencephalon, while ER and GnRH 1 showed more restricted distributions. No coexpression of kissr2 and ER in GnRH 1ergic neurons, suggesting that regulation of this GnRH variant is indirectly mediated by kisspeptin and estradiol.

Characterization of the gonadotropin-releasing hormone system in the Neotropical teleost, Steindachneridion parahybae during the annual reproductive cycle in captivity

This study evaluated by immunohistochemical and Western blot methods, the distribution of two distinct gonadotropin-releasing hormones (GnRHs), corresponding to catfish GnRH (cfGnRH or GnRH1) and chicken-II GnRH (cGnRH-II or GnRH2), in Steindachneridion parahybae females in captivity, focusing these analyses on the reproductive cycle by semi-quantification of optical density (OD). Further, we found that the GnRH neuronal systems co-localized with their respective GnRH-associated peptides (GAPs). A group of neurons immunoreactive (ir) to GnRH1 were identified along the ventral region of the olfactory bulb (vOB) in the telencephalon (vTel) and in the main areas of the diencephalon (especially the medial basal hypothalamus, HBM), including fibers extending into the pituitary gland. In contrast, GnRH2 neurons were confined to the midbrain tegmentum, close to the ventricular surface, without projections to the pituitary gland. Moreover, a cfGAP (GnRH1)-specific band (9 kDa) was identified in the brain and pituitary gland, while a cGAP-II (GnRH2)-specific band (26 kDa) was observed only in the brain extract. During the reproductive cycle, GnRH1-ir presented greater OD values at the vitellogenic and regression stages than at the previtellogenic stage and after artificially induced to spawn. Larger GnRH2-ir neurons were observed during the reproductive cycle, but a higher OD was identified only in the regression stage compared with the other maturation stages. Finally, GnRH1 axons were found to be directed towards the pituitary, and this GnRH type, which is probably the hypophysiotropic form, can contribute to the reproductive dysfunction that occurs in S. parahybae females in captivity, whereas GnRH2 may act as a neuromodulator and/or neurotransmitter.

Kisspeptins and their receptors in the brain-pituitary-gonadal axis of Odonthestes bonariensis: Their relationship with gametogenesis along the reproductive cycle

In vertebrates, the reproduction is controlled by the brain-pituitary-gonadal (BPG) axis and kisspeptin has emerged as a key player of this axis. In this study, we analyzed changes in the expression levels of kiss1, kiss2, and their receptors, kissr2 and kissr3 during gametogenesis in the BPG axis of feral Odontesthes bonariensis. In females, levels of brain kiss1 showed an increase at final maturation (Fm), while kiss2 levels were shown to be high at primary growth (Pg) stage, with no differences in the expression of their receptors. In the pituitary, kiss1 and kiss2 peaked at the cortical alveoli (Ca) stage, and kissr3 at initial vitellogenesis. In parallel, there was an increase of kiss1, kissr2 and kissr3 in the ovary during the Ca stage and both receptors again at Fm stage. In males, the four genes were highly expressed in the brain at the arrested (A) stage. In the pituitary, kiss2 peaked at spermatogonial (SG) and spermatocytary (SC) stages; while kissr3 reached a peak at the spermiogenic stage (SP). In testes, kiss1 and kiss2 significantly increased during the SG and SC stages; meanwhile, kissr2 increased at SG and SC, whereas kissr3 levels were significantly high at SC and SP stages. Taken together these results showed that the kisspeptin system in pejerrey is expressed in the three levels of the BPG axis with different expression profiles during the gonadal cycle. These findings pointed that kisspeptins have different roles in gametogenesis in this species.

Characterization of Gnrh/Gnih elements in the olfacto-retinal system and ovary during zebrafish ovarian maturation

Gonadotropin releasing hormone (GnRH) is one of the key players of brain-pituitary-gonad axis, exerting overall control over vertebrate reproduction. In zebrafish, two variants were characterized and named as Gnrh2 and Gnrh3. In this species, Gnrh3, the hypohysiotropic form, is expressed by neurons of the olfactory-retinal system, where it is related with food detection, intra/interspecific recognition, visual acuity and retinal processing modulation. Previous studies have reported the presence of Gnrh receptors in the zebrafish retina, but not yet in the zebrafish olfactory epithelium. The current study analyzed the presence of gnrh2 and gnrh3, their receptors (gnrhr 1,2,3 and 4) and gnih (gonadotropin inhibitory hormone) transcripts, as well as the Gnrh3 protein in the olfactory epithelium (OE), olfactory bulb (OB), retina and ovary during zebrafish ovarian maturation. We found an increase of gnrh receptors transcripts in the OE at the final stages of ovarian maturation. In the OE, Gnrh3 protein was detected in the olfactory receptor neurons cilia and in the olfactory nerve fibers. Interestingly, in the OB, we found an inverse expression pattern between gnih and gnrh3. In the retina, gnrhr4 mRNA was found in the nuclei of amacrine, bipolar, and ganglion cells next to Gnrh3 positive fibers. In the ovary, gnrh3, gnrhr2 and gnrhr4 transcripts were found in perinucleolar oocytes, while gnih in oocytes at the cortical alveolus stage. Our results suggested that Gnrh/Gnih elements are involved in the neuromodulation of the sensorial system particularly at the final stages of maturation, playing also a paracrine role in the ovary.

Conservation of Three-Dimensional Helix-Loop-Helix Structure through the Vertebrate Lineage Reopens the Cold Case of Gonadotropin-Releasing Hormone-Associated Peptide

GnRH-associated peptide (GAP) is the C-terminal portion of the gonadotropin-releasing hormone (GnRH) preprohormone. Although it was reported in mammals that GAP may act as a prolactin-inhibiting factor and can be co-secreted with GnRH into the hypophyseal portal blood, GAP has been practically out of the research circuit for about 20 years. Comparative studies highlighted the low conservation of GAP primary amino acid sequences among vertebrates, contributing to consider that this peptide only participates in the folding or carrying process of GnRH. Considering that the three-dimensional (3D) structure of a protein may define its function, the aim of this study was to evaluate if GAP sequences and 3D structures are conserved in the vertebrate lineage. GAP sequences from various vertebrates were retrieved from databases. Analysis of primary amino acid sequence identity and similarity, molecular phylogeny, and prediction of 3D structures were performed. Amino acid sequence comparison and phylogeny analyses confirmed the large variation of GAP sequences throughout vertebrate radiation. In contrast, prediction of the 3D structure revealed a striking conservation of the 3D structure of GAP1 (GAP associated with the hypophysiotropic type 1 GnRH), despite low amino acid sequence conservation. This GAP1 peptide presented a typical helix-loop-helix (HLH) structure in all the vertebrate species analyzed. This HLH structure could also be predicted for GAP2 in some but not all vertebrate species and in none of the GAP3 analyzed. These results allowed us to infer that selective pressures have maintained GAP1 HLH structure throughout the vertebrate lineage. The conservation of the HLH motif, known to confer biological activity to various proteins, suggests that GAP1 peptides may exert some hypophysiotropic biological functions across vertebrate radiation.

Characterization and transcriptional profiles of Engraulis encrasicolus' GnRH forms

The European anchovy Engraulis encrasicolus, a member of the Clupeiformes order, holds a great biological and economical importance. In the past, this species was mostly investigated with the aim of assessing its reproductive biology, trophic ecology, population dynamics and the relations existing with the physical environment. At present days, though, an almost complete lack of information afflicts its neuroendocrinology and reproductive physiology. The hypothalamic-pituitary-gonadal (HPG) axis at its highest levels was herein investigated. In this study, the gonadotropin-releasing hormone (GnRH), a neuropeptide underlying many reproduction-related processes, the most critical of which is the stimulation of gonadotropin synthesis and secretion from the pituitary gland, was cloned. Three forms (salmon GnRH, chicken-II GnRH and the species-specific type) were characterized in their full-length open-reading frames and, in accordance with other Clupeiformes species, the distinctive one was found to be the herring-type GnRH. We qualitatively and semiquantitatively evaluated the localizations of expressions and the temporal transcription patterns of the three GnRH forms in male and female specimens throughout their reproductive cycle as well as described their phylogeny with regard to teleost GnRH lineages, and, specifically, to other Clupeiformes species.

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.

Characterization of Schizothorax prenanti cgnrhII gene: fasting affects cgnrhII expression

In this study, the role of chicken gonadotropin-releasing hormone II (cgnrhII) in feeding regulation was investigated in Schizothorax prenanti. First, the full-length S. prenanti cgnrhII cDNA consisted of 693 bp with an open reading frame of 261 bp encoding a protein of 86 amino acids. Next, cgnrhII was widely expressed in the central and peripheral tissues. Last, there were significant changes in cgnrhII mRNA expression in the fasted group compared to the fed group in the S. prenanti hypothalamus during 24 h fasting (P < 0.05). Furthermore, the cgnrhII gene expression presented a significant decrease in the fasted group compared with the fed group (P < 0.05) on days 3, 5 and 7, after re-feeding, there was no significant changes in cgnrhII mRNA expression level between refed and fed group on day 9 (P > 0.05). Thus, the results suggest that cGnRH II expression is influenced by fasting and the gene may be involved in feeding regulation in S. prenanti.

Identification and distribution of three gonadotropin-releasing hormone (GnRH) isoforms in the brain of a clupeiform fish, Engraulis japonicus

To gain a better understanding of the reproductive endocrinology of a primitive order clupeiform fish (Japanese anchovy, Engraulis japonicus), cDNAs encoding three gonadotropin-releasing hormone (GnRH) isoforms were isolated from the brain, and their distribution was analyzed using insitu hybridization (ISH). The three GnRH isoforms include GnRH1 (herring GnRH), GnRH2 (chicken GnRH-ll) and GnRH3 (salmon GnRH), and their full-length cDNAs encode 88, 86, and 89 deduced amino acids (aa), respectively. Alignment analysis of Japanese anchovy GnRH isoforms showed lower identities with other teleost fish. The major population of GnRH1 neurons was localized in the ventral telencephalon (VT) and nucleus preopticus (NPO) of the preoptic area (POA) with minor population in the anterior olfactory bulb (OB). GnRH2 neurons were restricted to the midbrain tegmentum (MT), specific to the nucleus of the medial longitudinal fasciculus (nMLF). GnRH3 neurons were localized in the olfactory nerve (ON), ventral OB, and transitional area between OB and ON. Interestingly, GnRH1 neurons were also localized in the olfactory bulb, in addition to its major population in the preoptic area. These results indicate the differential distribution of three GnRH isoforms expressed in the brain of the Japanese anchovy.

Melanin-concentrating hormone (MCH) and gonadotropin-releasing hormones (GnRH) in Atlantic cod, Gadus morhua: tissue distributions, early ontogeny and effects of fasting

Melanin-concentrating hormone (MCH) is classically known for its role in regulating teleost fish skin color change for environmental adaptation. Recent evidence suggests that MCH also has appetite-stimulating properties. The gonadotropin-releasing hormone (GnRH) peptide family has dual roles in endocrine control of reproduction and energy status in fish. Atlantic cod (Gadus morhua) are a commercially important aquaculture species inhabiting the shores of Atlantic Canada. In this study, we examine MCH and GnRH transcript expression profiles during early development as well as in central and peripheral tissues and quantify juvenile Atlantic cod MCH and GnRH hypothalamic mRNA expressions following food deprivation. MCH and GnRH3 cDNAs are maternally deposited into cod eggs, while MCH has variable expression throughout early development. GnRH2 and GnRH3 mRNAs "turn-on" during mid-segmentation once the brain is fully developed. For both MCH and GnRH, highest expression appears during the exogenous feeding stages, perhaps supporting their functions as appetite regulators during early development. MCH and GnRH transcripts are found in brain regions related to appetite regulation (telencephalon/preoptic area, optic tectum/thalamus, hypothalamus), as well as the pituitary gland and the stomach, suggesting a peripheral function in food intake regulation. Atlantic cod MCH mRNA is upregulated during fasting, while GnRH2 and GnRH3 transcripts do not appear to be influenced by food deprivation. In conclusion, MCH might be involved in stimulating food intake in juvenile Atlantic cod, while GnRHs may play a more significant role in appetite regulation during early development.

Two novel gonadotropin-releasing hormones (GnRHs) from the urochordate ascidian, Halocynthia roretzi: implications for the origin of vertebrate GnRH isoforms

Three forms of gonadotropin-releasing hormone (GnRH) are found in vertebrates; these differ in amino acid sequence, localization, distribution, and embryological origin. We used northern blot analysis, and in situ hybridization to detect GnRH transcripts in various tissues in the large ascidian Halocynthia roretzi. We cloned a cDNA encoding two novel GnRHs, termed tGnRH-10 and tGnRH-11, from H. roretzi, with deduced amino acid sequences of QHWSYGFSPG and QHWSYGFLPG, respectively. Both GnRHs are highly similar to those of teleosts and tetrapods. For example, the tGnRH-10 sequence is 90% identical to seabream GnRH1, and tGnRH-11 is 90% identical to salmon GnRH3. The primary structure of the deduced preprotein is similar to that of chordate GnRHs and consists of a signal peptide, two decapeptides, up- and downstream processing sequences (containing lysine and arginine), and a GnRH-associated peptide. The transcripts of the H. roretzi GnRH gene were expressed in all tissues examined. Comparison of the signal peptide of the lamprey GnRH-II precursor with those of three forms from representative vertebrates revealed homology to GnRH2 precursors. These novel ascidian GnRHs offer a new perspective on the origin of vertebrate GnRH subtypes. We hypothesize that gnathostome GnRH2 was derived only from lamprey GnRH-II and that ancestral gnathostome GnRH, which produces neurons that originate in peripheral organs, gave rise to vertebrate GnRH1 and GnRH3 through whole-genome duplication.

Gonadotrophin-releasing hormone in winter flounder (Pseudopleuronectes americanus): molecular characterization, distribution and effects of fasting

Gonadotrophin-releasing hormone (GnRH) is primarily related to reproductive processes in vertebrates. However other physiological roles, including functions in food intake regulation and energy status, have been demonstrated for GnRH in animals. The ten amino acid active peptide is relatively conserved throughout chordates, more specifically in fish species. Teleosts generally have at least two variants of GnRH present in their genomes. GnRH2 (commonly termed chicken-GnRH) is common to all fish, whereas other prevalent forms include GnRH1 and/or GnRH3 (also known as salmon-GnRH). The mRNAs of all three forms were identified in winter flounder (Pseudopleuronectes americanus). Winter flounder GnRH1 appears to be ubiquitously and strongly expressed throughout the brain. GnRH2 mRNA is highly expressed in the optic tectum/thalamus. Finally, GnRH3 mRNA is expressed throughout the brain, but not in the pituitary, with apparent highest expression in the telencephalon/preoptic area. Flounder GnRH1 mRNA is found in most peripheral tissues examined, including the foregut, midgut and gonads. GnRH2 mRNA appears to be expressed throughout the periphery, with apparent highest transcript expression in male gonads. Finally, winter flounder GnRH3 transcript is found at low levels in the skin, heart, and gonads. The effect of fasting on the expression of each of the three isoforms was assessed. Fasting reduces GnRH2 and GnRH3 mRNA expression in the optic tectum/thalamus and hypothalamus, and telencephalon/preoptic area, respectively, compared with fed fish. GnRH1 mRNA expression does not appear to be altered by feeding status. GnRH mRNAs do not seem to regulate food intake peripherally through the gut based on our preliminary findings. Our preliminary results suggest that the GnRH system could play a central role in food intake regulation of winter flounder.

Expression profiles of three types of GnRH during sex-change in the protandrous cinnamon clownfish, Amphiprion melanopus: Effects of exogenous GnRHs

Gonadotropin-releasing hormones (GnRHs) play pivotal roles in the control of reproduction and gonadal maturation in teleost fish. Fish have multiple GnRH genes that encode structurally distinct peptides. We identified salmon GnRH (sGnRH), seabream GnRH (sbGnRH), and chicken GnRH-II (cGnRH-II) by cDNA cloning in cinnamon clownfish (Amphiprion melanopus) using reverse transcription-PCR (RT-PCR) and rapid amplification of cDNA ends-PCR (RACE-PCR). Gene identity was confirmed by sequence alignment and subsequent phylogenetic analyses. We also investigated GnRH mRNA expression in the gonads by quantitative real time-PCR (Q-PCR), and measured plasma estradiol-17β (E(2)) levels in immature fish following treatment with the three molecular forms of GnRHs. The expression levels of sGnRH, sbGnRH, and cGnRH-II mRNA were higher in mature testes and ovaries, as compared to the levels in gonads at earlier stages of maturity. The levels of the three prepro-GnRH mRNA species and the plasma E(2) levels increased after injection of the three GnRH variants. These findings support the hypothesis that GnRH peptides play important roles in the regulation of the hypothalamic-pituitary-gonadal axis and are probably involved in paracrine control of gonadal development and sex change in cinnamon clownfish.

Clonagem e avaliação da expressão gênica do sbGnRH em machos juvenis e adultos de linguado, Paralichthys orbignyanus

Este estudo buscou clonar o cDNA do sbGnRH, identificar sua expressão em diferentes tecidos do linguado, bem como avaliar possíveis diferenças no RNA mensageiro (RNAm) desse gene no cérebro de linguados machos juvenis e adultos. Por meio da RT-PCR, demonstrou-se pela primeira vez, a clonagem da região codificadora do sbGnRH contendo 297 nucleotídeos do cérebro do linguado. A expressão do sbGnRH foi detectada em vários tecidos periféricos. Foram detectados níveis mais elevados de RNAm do sbGnRH no hipotálamo dos animais adultos. Estes resultados sugerem que o sbGnRH está envolvido na puberdade do linguado.

Evolution of the gonadotropin-releasing hormone (GnRH) gene family in relation to vertebrate tetraploidizations

The neuropeptide gonadotropin-releasing hormone (GnRH) plays an important role in the control of reproductive functions. Vertebrates possess multiple GnRH isoforms that are classified into three main groups, namely GnRH1, GnRH2 and GnRH3. In the present study, we show that the chromosomal organization of the three GnRH loci is very well conserved among gnathostome species. We analyzed genes belonging to several other multigenic families that are present in the vicinity of GnRH genes. Five of them were seen to occur in four chromosomal regions that clearly form a paralogon. Moreover, we show that the homologous regions in the amphioxus genome are present on a single locus. Taken together, these observations indicate that GnRH1, GnRH2 and GnRH3 genes represent three paralogous genes that resulted from the two rounds of tetraploidization that took place early in vertebrate evolution. They confirm that the GnRH3 gene which is currently known only in teleost has most likely been lost in the tetrapod lineage. Finally, they suggest the existence of a fourth GnRH gene, named GnRH4. Whether the GnRH4 gene still exists in extant vertebrates is currently unknown. A search for this putative gene would be particularly useful in basal groups such as agnathans and cartilaginous fish.

Molecular characterization, tissue distribution, and mRNA expression profiles of two Kiss genes in the adult male and female chub mackerel (Scomber japonicus) during different gonadal stages

Kisspeptins, encoded by the Kiss1 gene, have emerged as key modulators of reproduction in mammals. In contrast to the placental mammals, some teleosts express two Kiss genes, Kiss1 and Kiss2. In the present study, full-length cDNAs of Kiss1 and Kiss2 in the chub mackerel were cloned and sequenced. Chub mackerel Kiss1 and Kiss2 cDNAs encode 105 and 123 amino acids, respectively. A comparison of the deduced amino acid sequences of chub mackerel Kiss1 and Kiss2 with those of other vertebrate species showed a high degree of conservation only in the kisspeptin-10 region (Kp-10). The Kp-10 of chub mackerel Kiss1 (YNFNSFGLRY) and Kiss2 (FNFNPFGLRF) showed variations at three amino acids. Tissue distribution analysis using quantitative real-time PCR (qRT-PCR) revealed that the Kiss1 and Kiss2 transcripts were expressed in different tissues of adult chub mackerel. In addition, their levels in the adipose tissue exhibited sexually dimorphic expression. Further, to have a basic understanding on the involvement of Kiss1 and Kiss2 in the seasonal gonadal development, their relative mRNA expression profiles in the brain, pituitary, and gonads at different gonadal stages were analyzed using qRT-PCR. Kiss1 and Kiss2 levels in the brain showed a differential expression profile between male and female fish. In males, Kiss1 and Kiss2 levels gradually decreased from the immature stage to spermiation and reached a minimal level during the post-spawning period. In contrast, Kiss1 levels in the brain of females did not vary significantly among the different gonadal stages. However, Kiss2 levels fluctuated as that of males, gradually declining from the immature stage to the post-spawning period. The pituitary Kiss1 levels did not show significant fluctuations. However, Kiss1 levels in the gonads were highly elevated during spermiation and late vitellogenesis compared to the immature and post-spawning period. These results suggest the possible involvement of two Kiss genes in the brain and Kiss1 in the gonads of chub mackerel during seasonal gonadal development.

Molecular cloning and brain distribution of three types of gonadotropin-releasing hormone from mummichog Fundulus heteroclitus

Complementary DNAs encoding gonadotropin-releasing hormone (GnRH) precursors were cloned from the mummichog Fundulus heteroclitus brain, showing that this species has three GnRH forms, i.e. medaka Oryzias latipes GnRH (mdGnRH), chicken GnRH-II (cGnRH-II) and Atlantic salmon Salmo salar GnRH (sGnRH). The F. heteroclitus prepro GnRHs have common structural architectures of vertebrate GnRHs, consisting of the signal peptide, 10 amino acids of mature peptide, GKR sequence and GnRH-associated peptide (GAP). Phylogenetic analysis of fish prepro GnRHs showed that F. heteroclitus mdGnRH is a homologue of sbGnRHs and mdGnRHs of other acanthopterygian. Quantitative real-time PCR revealed that mdGnRH was abundantly expressed in the olfactory bulb and in olfactory lobe areas and is expressed in the pituitary. The cGnRH-II was mainly expressed in the midbrain and interbrain areas, and the sGnRH was expressed not only in the olfactory bulb but also in other regions of the brain. These results suggest that the mdGnRH is involved in the stimulation of gonadotrophs in the pituitary, whereas cGnRH-II and sGnRH are involved in neurotransmission and neuromodulation.

mRNA expression of GnRH variants and receptors in the brain, pituitary and ovaries of pejerrey (Odontesthes bonariensis) in relation to the reproductive status

The present study examined the differential mRNA expression levels of three forms of GnRH (sGnRH, pjGnRH and cGnRH-II) and two forms of GnRH receptor (pjGnRH-R I and pjGnRH-R II) in the brain, pituitary, and ovaries of pejerrey in relation to the reproductive status. The analysis revealed the presence of significant amounts of mRNA of the three GnRH forms while the ovaries showed only two (sGnRH and pjGnRH). The GnRH receptor II was found ubiquitously in the brain, pituitary, and ovaries while the form I was detected only in the brain. The levels of pjGnRH mRNA in the brain and pjGnRH-R II in the pituitary gland varied in correlation with the ovarian condition. However, brain sGnRH and pjGnRH-R I mRNA levels reached a maximum during early stages of ovarian development. In contrast, the brain levels of cGnRH-II mRNA showed no variation. The present study also shows a good correlation of ovarian sGnRH and pjGnRH-R II mRNA levels with the reproductive condition, suggesting that these molecules are may be involved in the regulation of pejerrey ovarian function.

Effects of light and temperature conditions on the expression of GnRH and GtH genes and levels of plasma steroids in Odontesthes bonariensis females

In this study we examined the endocrine mediation between environmental factors (temperature and photoperiod) and the brain-pituitary-gonadal axis in females of pejerrey Odontesthes bonariensis. Changes in the expression of brain gonadotropin-releasing hormones (GnRHs) and gonadotropin (GtH) subunit [follicle stimulating-beta (FSH-beta), luteinizing hormone-beta (LH-beta), glycoprotein hormone-alpha (GPH-alpha)] genes, plasma gonadal steroids [estradiol (E(2)) and testosterone (T)], gonadal histology, and gonadosomatic index (GSI) in adult females exposed to combinations of short-day (8 h) or long-day (16 h) photoperiods and low (12 degrees C) or high (20 degrees C) temperatures after winter conditions (8 h light, 12 degrees C) were analyzed. Pejerrey females kept under the short photoperiod had low GSIs, and their ovaries contained only previtellogenic oocytes regardless of the experimental temperature. In contrast, females exposed to the long photoperiod had high GSIs and ovaries with vitellogenic oocytes at both temperatures. These fish also showed a significantly higher expression of sGnRH, pjGnRH, cGnRH-II (the three different GnRH variants found to date in the pejerrey brain), FSH-beta, LH-beta and GPH-alpha genes and plasma E(2 )levels than those at the shorter photoperiod. No significant changes were observed in plasma T levels. Based on these results, we concluded that the increase in day length but not that of temperature triggers the maturation of pejerrey females after the winter period of gonadal rest and that this occurs by an integrated stimulation of the various components of the brain-pituitary-gonad axis.

Molecular characterization and expression of three GnRH forms mRNA during gonad sex-change process, and effect of GnRHa on GTH subunits mRNA in the protandrous black porgy (Acanthopagrus schlegeli)

Gonadotropin-releasing hormone (GnRH) plays a pivotal role in control of reproduction and gonadal maturation in teleost fish. To investigate the action GnRH in black porgy (Acanthopagrus schlegeli), we examined the mRNA expression of GTH subunits (GTHalpha, FSHbeta, and LHbeta) in the pituitary as well as plasma estradiol-17beta (E(2)) level following treatment with a GnRH analog (GnRHa) in immature fish. The expression levels of GTH subunits mRNA and plasma E(2) level were increased after GnRHa injection. We were also able to identify three GnRH forms: salmon GnRH (sGnRH), seabream GnRH (sbGnRH) and chicken GnRH-II (cGnRH-II) by cDNA cloning in the ovary of the black porgy. Black porgy gonadal development is divided into seven stages, involving sex change from male to female (immature testis, mature testis, testicular portion of mostly testis, ovarian portion of mostly testis, testicular portion of mostly ovary, ovarian portion of mostly ovary, and mature ovary). In the present study, we investigated the expression pattern of three GnRH molecular forms in the black porgy gonads at different stages of gonadal development by quantitative polymerase chain reaction (QPCR). The mRNA expressions of sGnRH, sbGnRH and cGnRH-II were found to be higher in mature testis and ovary, compared to gonads at different stages of maturity. The findings support the hypothesis that the three forms of GnRH play important roles in the regulation of hypothalamic-pituitary-gonadal axis, and are likely involved also in gonadal development and sex change in black porgy.

Molecular cloning, expression pattern, and immunocytochemical localization of a gonadotropin-releasing hormone-like molecule in the gastropod mollusk, Aplysia californica

Successful reproduction in vertebrates depends upon the actions of gonadotropin-releasing hormone (GnRH). Despite the wide presence of GnRH in Phylum Chordata, GnRH has not been isolated in protostomes other than the common octopus. To provide information on the evolution of this critical hormone, we isolated the full-length cDNA of a GnRH-like molecule from the central nervous system of a gastropod mollusk, the sea hare Aplysia californica. The open reading frame of this cDNA encodes a protein of 147 amino acids. The molecular architecture of the deduced protein is highly homologous to that reported for the prepro-octopus GnRH (oct-GnRH) and consists of a putative signal peptide, a GnRH dodecapeptide, a downstream processing site, and a GnRH-associated peptide (GAP). The deduced amino acid sequence of the Aplysia GnRH (ap-GnRH) is QNYHFSNGWYAG and differs from oct-GnRH by only two amino acids. The transcript for ap-GnRH is widely expressed in the central nervous system (CNS), the ovotestis, and the atrial gland, an exocrine gland. Immunocytochemistry (ICC) using an antiserum against oct-GnRH detected immunoreactive neurons in all CNS ganglia examined, and the staining was abolished by the preadsorption of the antiserum with synthetic ap-GnRH. In sum, ap-GnRH sequence is the first gastropod GnRH-like molecule to be elucidated. Further, it represents one of the only two GnRH-like molecules found outside Phylum Chordata. These data refute the possibility that oct-GnRH arose singly in cephalopods by convergent evolution and provide valuable support for an ancient origin of GnRH during metazoan evolution.

Identification and analysis of a prepro-chicken gonadotropin releasing hormone II (preprocGnRH-II) precursor in the Asian seabass, Lates calcarifer, based on an EST-based assessment of its brain transcriptome

Using a novel library of 5637 expressed sequence tags (ESTs) from the brain tissue of the Asian seabass (Lates calcarifer), we first characterized the brain transcriptome for this economically important species. The ESTs generated from the brain of L. calcarifer yielded 2410 unique transcripts (UTs) which comprise of 982 consensi and 1428 singletons. Based on database similarity, 1005 UTs (41.7%) can be assigned putative functions and were grouped into 12 functional categories related to the brain function. Amongst others, we have identified genes that are putatively involved in energy metabolism, ion pumps and channels, synapse related genes, neurotransmitter and its receptors, stress induced genes and hormone related genes. Subsequently we selected a putative preprocGnRH-II precursor for further characterization. The complete cDNA sequence of the gene obtained was found to code for an 85-amino acid polypeptide that significantly matched preprocGnRH-II precursor sequences from other vertebrates, and possesses structural characteristics that are similar to that of other species, consisting of a signal peptide (23 residues), a GnRH decapeptide (10 residues), an amidation/proteolytic-processing signal (glycine-lysine-argine) and a GnRH associated peptide (GAP) (49 residues). Phylogenetic analysis showed that this putative L. calcarifer preprocGnRH-II sequence is a member of the subcohort Euteleostei and divergent from the sequences of the subcohort Otocephalan. These findings provide compelling evidence that the putative L. calcarifer preprocGnRH-II precursor obtained in this study is orthologous to that of other vertebrates. The functional prediction of this preprocGnRH-II precursor sequence through in silico analyses emphasizes the effectiveness of the EST approach in gene identification in L. calcarifer.