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

Characterization of Kiss/Kissr system and expression profiling through developmental stages indicate kiss1 to be the active isotype in Clarias magur

Kisspeptin (Kiss) and kisspeptin receptor (Kissr) system is a key regulator of GnRH expression in several vertebrates. The Indian catfish, Clarias magur, is popular in the Indian sub-continent, and a neo-type of the Asian catfish, C. batrachus. Catfish breeding is constrained as males do not release milt captivity with/without stimulation. Magur Kiss/Kissr system comprising of kiss1, kiss2, kissr1, and kissr2 genes was characterized for the first time. Full-length mRNA was sequenced using RACE PCR. Neighbor-joining tree of predicted proteins shows one clade of teleost orthologs. Magur whole genome (NCBI GenBank) has single copies of each gene, though yet unannotated/misannotated. Anomalies in the nomenclature of earlier sequences in GenBank were noted. Relative gene expression was profiled during various ontogenic stages, in six tissues including brain and gonads at maturity, and also in brains and gonads of premature and spent fish. Expression of gnrh1, gnrhr1, and gnrhr2 was estimated concomitantly. The kiss1 was the first to be twofold upregulated (P < 0.05) at 12 h post fertilization. Kiss/Kissr genes expressed primarily in the brain, ovary, and testis. Though kiss2 was 10 times higher than kiss1, only kiss1 showed significant modulation across stages and appears to be the active isotype that regulates GnRH in magur.

Regulatory Effects of the Kiss1 Gene in the Testis on Puberty and Reproduction in Hezuo and Landrance Boars

Kisspeptin, a neuropeptide encoded by the Kiss1 gene, combines with its receptor Kiss1R to regulate the onset of puberty and male fertility by the hypothalamic-pituitary-gonadal axis. However, little is known regarding the expression signatures and molecular functions of Kiss1 in the testis. H&E staining revealed that well-arranged spermatogonia, spermatocytes, round and elongated spermatids, and spermatozoa, were observed in 4-, 6-, and 8-month-old testes compared to 1- and 3-month-old testes of Hezuo pigs; however, these were not observed in Landrance until 6 months. The diameter, perimeter, and cross-sectional area of seminiferous tubules and the perimeter and area of the tubular lumen increased gradually with age in both pigs. Still, Hezuo pigs grew faster than Landrance. The cloning results suggested that the Hezuo pigs' Kiss1 CDS region is 417 bp in length, encodes 138 amino acids, and is highly conserved in the kisspeptin-10 region. qRT-PCR and Western blot indicated that the expression trends of Kiss1 mRNA and protein were essentially identical, with higher expression levels at post-pubertal stages. Immunohistochemistry demonstrated that the Kiss1 protein was mainly located in Leydig cells and post-pubertal spermatogenic cells, ranging from round spermatids to spermatozoa. These studies suggest that Kiss1 is an essential regulator in the onset of puberty and spermatogenesis of boars.

Cloning, Expression Analysis and SNP Screening of the kiss1 Gene in Male Schizothorax biddulphi

Schizothorax biddulphi is an endemic fish distributed only in southern Xinjiang, China. Due to overfishing, water conservancy facilities, and other factors, as well as inherent biological limitations, resource recovery is quite difficult. For endangered fish with slow growth, late sexual maturity, and insufficient natural population supplementation, large-scale artificial reproduction and breeding are important for restoring resources. Therefore, it is urgent to optimize the reproductive regulation methods of the fish. The kiss1 gene is a key regulator of the reproductive regulation cascade, and identifying and analyzing the role of kiss1 are important for further elucidating the reproductive mechanism of S. biddulphi. To understand the characteristics of the kiss1 of S. biddulphi, the full-length cDNA sequence of kiss1 was obtained in this study, and its tissue expression specificity and association with phenotypic traits were analyzed in male fish. The full-length cDNA sequence of kiss1 in S. biddulphi was 658 bp, with an ORF of 327 bp, and encoded a 108-amino acid, unstable protein. Homology results indicated that kiss1 was highly conserved. qPCR showed kiss1 expression in different tissues in male S. biddulphi, with the highest expression in the gonads, followed by muscle, and significantly lower expression in the swim bladder, pituitary gland, heart, hypothalamus, gill, fin, liver, eye, and mid-kidney. qPCR revealed three SNP loci in the exonic region of kiss1. The c.3G>T locus was significantly correlated (p < 0.05) with gonad mass and the maturation coefficient in S. biddulphi. These results will help uncover the reproductive endocrinology network of S. biddulphi, improve artificial breeding technology for fish, and unveil new directions for breeding excellent strains of S. biddulphi and molecular marker-assisted breeding.

Sexually dimorphic distribution of kiss1 and kiss2 in the brain of yellowtail clownfish, Amphiprion clarkii

Kisspeptin system was shown to be a key factor in mediating social stress and reproduction. Yellowtail clownfish, Amphiprion clarkii, is a hermaphrodite fish, whose sex determination and gonadal development are affected by the social status of individuals. The yellowtail clownfish is a fantastic animal model to explore sex determination, but the social status and precise distribution of kiss mRNAs in the brain of this species are unknown. Hererin, a novel in situ hybridization technique, RNAscope, was used to investigate the distribution of kiss1 and kiss2 expressions in the brain of yellowtail clownfish. The coronal planes of brain showed that the kiss1 signal was mainly present in dorsal habenular nucleus (NHd) and kiss2 mRNA was widely expressed in telencephalon, midbrain, and hypothalamus, especially in dorsal part of the nucleus of the lateral recess (NRLd). Additionally, kiss1 and kiss2 signals have sexually dimorphic distribution. The kiss1 mRNA was distributed in NHd, the telencephalon, and lateral part of the diffuse nucleus of the inferior lobe (NDLIl) of females but in NHd and NDLIl of males. kiss2 signals were stronger in females than that in males. The distribution of kiss1 and kiss2 neurons in NHd of habenula and NRLd of hypothalamus may suggest that kiss genes associate environmental signaling and reproductive function in yellowtail clownfish.

Overview and New Insights Into the Diversity, Evolution, Role, and Regulation of Kisspeptins and Their Receptors in Teleost Fish

In the last two decades, kisspeptin (Kiss) has been identified as an important player in the regulation of reproduction and other physiological functions in vertebrates, including several fish species. To date, two ligands (Kiss1, Kiss2) and three kisspeptin receptors (Kissr1, Kissr2, Kissr3) have been identified in teleosts, likely due to whole-genome duplication and loss of genes that occurred early in teleost evolution. Recent results in zebrafish and medaka mutants have challenged the notion that the kisspeptin system is essential for reproduction in fish, in marked contrast to the situation in mammals. In this context, this review focuses on the role of kisspeptins at three levels of the reproductive, brain-pituitary-gonadal (BPG) axis in fish. In addition, this review compiled information on factors controlling the Kiss/Kissr system, such as photoperiod, temperature, nutritional status, sex steroids, neuropeptides, and others. In this article, we summarize the available information on the molecular diversity and evolution, tissue expression and neuroanatomical distribution, functional significance, signaling pathways, and gene regulation of Kiss and Kissr in teleost fishes. Of particular note are recent advances in understanding flatfish kisspeptin systems, which require further study to reveal their structural and functional diversity.

New Evidence for the Existence of Two Kiss/Kissr Systems in a Flatfish Species, the Turbot (Scophthalmus maximus), and Stimulatory Effects on Gonadotropin Gene Expression

Seasonal reproduction is generally controlled by the hypothalamus-pituitary-gonadal (HPG) axis in fish. Previous studies have demonstrated that the kisspeptin (Kiss)/kisspeptin receptor (Kissr) system, a positive regulator of the HPG axis, mediates the responses to environmental cues. Turbot (Scophthalmus maximus), a representative species of Pleuronectiformes, is one of the most commercially important fish species cultured in Europe and North China. However, the mechanisms by which the Kiss/Kissr system regulates the reproductive axis of turbot according to seasonal changes, especially photoperiod, have not been clearly characterized. In the current study, the cDNA sequences of kiss2/kissr2, along with kiss1/kissr3 which was thought to be lost in flatfish species, were cloned and functionally characterized. The kiss1, kiss2, and kissr3 transcripts were highly detected in the brain and gonad, while kissr2 mRNA was only abundantly expressed in the brain. Moreover, kiss/kissr mRNAs were further examined in various brain areas of both sexes. The kiss1, kissr2, kissr3 mRNAs were highly expressed in the mesencephalon, while a substantial degree of kiss2 transcripts were observed in the hypothalamus. During annual reproductive cycle, both kiss and kissr transcript levels declined significantly from the immature to mature stages and increased at the degeneration stage in the brains of both sexes, especially in the mesencephalon and hypothalamus. The ovarian kiss1, kiss2, and kissr2 mRNA levels were highest at the vitellogenic stage (mature stage), while expression of kissr3 was highest at the immature stage. The testicular kiss and kissr transcripts were highest in the immature and degeneration stages, and lowest at the mature stage. In addition, intraperitoneal injection of Kiss1-10 and Kiss2-10 significantly stimulated mRNA levels of pituitary lhβ, fhsβ, and gthα. In summary, two Kiss/Kissr systems were firstly proven in a flatfish species of turbot, and it has a positive involvement in controlling the reproduction of the Kiss/Kissr system in turbot. The results will provide preliminary information regarding how the Kiss/Kissr system controls seasonal reproduction in turbot broodstock.

Seasonal expression and distribution of kisspeptin1 (kiss1) in the ovary and testis of freshwater catfish, Clarias batrachus: A putative role in steroidogenesis

The central role of kisspeptin (kiss) in mammalian reproduction is well established; however, its intra-gonadal role is poorly addressed. Moreover, studies investigating intra-gonadal role of kiss in fish reproduction are scanty, contradictory and inconclusive. The expression of kiss1 mRNA has been detected in the fish brain, and functionally attributed to the regulation of reproduction, feeding and behavior. The kiss1 mRNA has also been demonstrated in tissues other than the brain in some studies, but its cellular distribution and role at the tissue level have not been adequately addressed in fish. Therefore, an attempt was made in the present study to localize kiss1 in gonadal cells of the freshwater catfish, Clarias batrachus. This study reports the presence of kiss1 in the theca cells and granulosa cells of the ovarian oocytes and interstitial cells in the testis of the catfish. The role of kiss1 in the ovary and testis of the catfish was also investigated using kiss1 receptor (kiss1r) antagonist (p234). The p234 treatment decreased the production of 17β-estradiol in ovary and testosterone in the testis by lowering the activities of 3β-hydroxysteroid dehydrogenase and 17β-hydroxysteroid dehydrogenase under both, in vivo as well as in vitro conditions. The p234 treatment also arrested the progression of oogenesis, as evident from the low number of advancing/advanced oocytes in the treated ovary in comparison to the control ovary. It also reduced the area and perimeter of the seminiferous tubules in the treated catfish testis. Thus, our findings suggest that kiss is involved in the regulation of gonadal steroidogenesis, independent of known endocrine/ autocrine/ paracine regulators, and thereby it accelerates gametogenic processes in the freshwater catfish.

Characterization of kiss2/kissr2 system in largemouth bass (Micropterus salmoides) and Kiss2-10 peptide regulation of the hypothalamic-pituitary-gonadal axis

The kisspeptin system, which lies upstream of the hypothalamic-pituitary-gonadal (HPG) axis, is believed to function as a regulator of reproduction in teleosts. In this study, we isolated and characterized kiss2 and its receptor kissr2 in largemouth bass (Micropterus salmoides). The complete coding sequences of kiss2 and kissr2 were 375 and 1134 bp long and encoded precursor proteins 124 and 377 amino acid long, respectively. Real-time PCR showed that kiss2 and kissr2 were primarily expressed in the HPG axis. The expression profile of kiss2 and kissr2 varied with gonadal development, with the highest and lowest expression levels being detected during the immature and final maturation stages, respectively. Intraperitoneal injection of exogenous Kiss2-10 peptide increased the transcript levels of gnrh3, kissr2, fshβ, lhβ, ar, and er2 within 24 h (p < 0.05), as well as plasma levels of 17β-estradiol and testosterone. Histological analysis indicated that chronic administration of exogenous Kiss2-10 peptide accelerated vitellogenesis in females and spermatogenesis in males. Further, in situ hybridization revealed that kiss2 is expressed in the ooplasm and vitelline envelope of oocytes and the spermatocytes of testes. In addition, experiments using gonad tissue primary cell cultures indicated that exogenous Kiss2-10 peptide stimulates the expression of reproduction-related genes. Collectively, our findings indicate that the kiss2/kissr2 system in largemouth bass is involved in regulating gonadal development through the HPG axis.

Hormonal and neuroendocrine control of reproductive function in teleost fish

Reproduction is one of the important physiological events for the maintenance of the species. Hormonal and neuroendocrine regulation of teleost requires multiple and complex interactions along the hypothalamic-pituitary-gonad (HPG) axis. Within this axis, gonadotropin-releasing hormone (GnRH) regulates the synthesis and release of gonadotropins, follicle-stimulating hormone (FSH), and luteinizing hormone (LH). Steroidogenesis drives reproduction function in which the development and differentiation of gonads. In recent years, new neuropeptides have become the focus of reproductive physiology research as they are involved in the different regulatory mechanisms of these species' growth, metabolism, and reproduction. However, especially in fish, the role of these neuropeptides in the control of reproductive function is not well studied. The study of hormonal and neuroendocrine events that regulate reproduction is crucial for the development and success of aquaculture.

Gametogenic and steroidogenic action of kisspeptin-10 in the Asian catfish, Clarias batrachus: Putative underlying mechanistic cascade

Unlike mammals, two kisspeptins genes encoding, kiss1 and kiss2 are detected in fishes with highly varied and contradictory difference in their reproductive activities. The present study was undertaken to examine the direct action of kisspeptin-10 and its role in gonadal activities in the gonadally quiescent Asian catfish using native mammalian kisspeptin decapeptide (KP-10) involving in vivo and in vitro approaches. The in vivo KP-10 treatment caused precocious onset of gametogenesis and its rapid progression, as was evident from the appearance of advanced stages of ovarian follicles in ovary, and advanced germ cells (spermatocytes/ spermatids) in the testis of the treated Clarias batrachus in comparison to the control gonads. It also elevated the steroid levels in gonads of the catfish in vivo and in vitro conditions. Simultaneously, it increased the expressions of key steroidogenic enzymes like 3β-HSD, 17β-HSD, and StAR protein, responsible for transfer of cholesterol from outer to inner membrane of the mitochondria of steroidogenic cells. Concurrently, it augmented the activities of 3β-HSD and 17β-HSD in the ovarian explants. The expressions of MAPK component (pERK1/2 and ERK1/2) were also up-regulated by KP-10 in gonadal explants. Thus, the data suggest that kisspeptin-10 stimulates gametogenesis by enhancing gonadal steroid production. The study also describes the putative mechanistic cascade of steroidogenic actions of kisspeptin-10 in the catfish so much so in teleost fish. The study also suggests that, kisspeptin may act locally to regulate gonadal activities in an autocrine/paracine manner, independent of known extra-gonadal factors in the catfish.

In silico analysis of kiss2, expression studies and protein-protein interaction with gonadotropin-releasing hormone 2 (GnRH2) and luteinizing hormone beta (LHβ) in Heteropneustes fossilis

Kisspeptins, encoded by the kiss genes, are neuropeptides that regulate the onset of puberty, maturation of gonads, and fertility in higher vertebrates including fishes. The gene ontology suggests that kisspeptin plays an important role not only in reproduction but also in cell signaling, immune response and metabolic processes, and to decipher protein-protein interactions, computational approach has been favored. The present investigation focuses on the detailed structural analysis and molecular docking of kiss2 gene using in silico tools. A putative kiss2 protein of 113 amino acids was encoded by an open reading frame of 342 bp kiss2 gene. The protein is of 13.12 kDa with isoelectric point of 9.45. The secondary structure of the protein indicates more than 50% random coils, followed by 34% of alpha helix and 13% extended strand. The protein was found to be extracellular and secretory in nature. Since, protein-protein interactions play a very crucial role in every cellular process and due to unavailability of crystal structure of our protein of interest in fishes computational approach has been employed. The 3D PDB modeling and the molecular docking of kiss2, Gonadotropin-releasing hormone 2 (GnRH2) and luteinizing hormone beta (LHβ) proteins in fishes have been demonstrated applying protein-docking approach. Molecular interactions of kiss2 protein were the highest with kisspeptin receptor 2 and lowest for the neuropeptide FF-amide peptide precursor protein. Expression of kiss2 transcripts, mainly in the brain and ovary of H. fossilis, supports its hypothalamic-pituitary-gonadal axis signaling and reproductive function. Further, changes in expression patterns of kiss2 mRNA during different developmental stages, indicate its potential role in embryonic development also. The present study conclusively reveals interaction of kiss2 with other neuropeptides. Prediction of binding structures and identification of key residues in protein-protein interaction illustrate direct interaction among these proteins, playing a cardinal role in neuroendocrine regulation of reproduction in catfish. Communicated by Ramaswamy H. Sarma.

Kiss2 but not kiss1 is involved in the regulation of social stress on the gonad development in yellowtail clownfish, Amphiprion clarkii

The yellowtail clownfish (Amphiprion clarkii) is a hermaphrodite fish, whose sex differentiation and gonad development are closely related to its social status. The kisspeptin/KissR system is regarded as a key factor mediating social stress on reproductive regulation. In order to understand the effects of social rank stress on the yellowtail clownfish gonadal differentiation, full-length cDNAs of two paralogous genes encoding kisspeptin (kiss1 and kiss2) and KissR (kissr2 and kissr3) were cloned and characterized. The results of real-time PCR showed that kiss1 was primarily expressed in the hypothalamus, and kiss2/kissr2 were abundantly expressed in the liver, while kissr3 was almost exclusively concentrated in the cerebellum and pituitary. Moreover, both Kiss1-10 and Kiss2-10 peptides could initiate downstream signaling pathways by interacting with cognate receptors expressed in eukaryotic cells. Among the three social status groups, the mRNA levels of kiss2 in the hypothalamus and pituitary as well as kissr2 in the pituitary were significantly higher in subordinate individuals (nonbreeders) than dominate individuals (females and males); while the mRNA levels of kissr3 in the hypothalamus and gonad were low in subordinate individuals. Furthermore, the plasma estradiol (E₂) and testosterone (T) levels were higher in subordinate than dominate individuals. This study shows that kiss2 is involved in the regulation of social stress on the gonad development in the yellowtail clownfish, but not kiss1.

Kisspeptin2 regulates hormone expression in female zebrafish (Danio rerio) pituitary

Kisspeptin2 is a neuropeptide widely found in the brain and multiple peripheral tissues in the zebrafish. The pituitary is the center of synthesis and secretes various endocrine hormones. However, Kiss2 innervation in the zebrafish pituitary is unknown. In this study, the organization of Kiss2 cells and structures in the zebrafish pituitary by promoter-driving mCherry-labeling Kiss2 neurons were investigated. Kiss2 neurons in the hypothalamus do not project into the pituitary. Kiss2 cells are found in the female pituitary. Unidentified Kiss2 cells and extensions are located in the proximal pars distalis (PPD), similar to the distribution of Gnrh3 fibers. Kiss2 structures reside alongside Gnrh3 fibers. No Kiss2 structures are found in the male pituitary. The transcriptional expression of the kisspeptin receptor kiss1rb is detected in both female and male pituitaries. In situ hybridization shows that kiss1rb-positive cells are located in the PPD and pars intermedia (PI). In vitro Kiss2-10 treatment stimulates Akt and Erk phosphorylation and significantly induces lhβ, fshβ, and prl1 mRNA expression in the female pituitary. The results in this study suggest that Kiss2 and Kiss1rb may form an independent paracrine or autocrine system in the female zebrafish pituitary. Kiss2 and Kiss1rb signaling regulates the expression of pituitary hormones.

Identification of kisspeptin2 cDNA in the catfish Heteropneustes fossilis: Expression profile, in situ localization and steroid modulation

Kisspeptin (Kiss) is considered an upstream regulator of gonadotropin-releasing hormone in mammals but its role in non-mammalian vertebrates is not unequivocally established. In the catfish Heteropneustes fossilis, a 605 bp long cDNA was identified from the brain by cloning as well as by retrieving from the catfish transcriptome database. The open reading frame (ORF, 93-405 bp) codes for a 113 amino acids long precursor protein. Homology and phylogenetic analyses showed that the predicted protein belongs to the vertebrate Kiss2 type with a high degree of conservation in the Kiss2-10 region (FNFNPFGLRF). The kiss2 transcripts were expressed highly in the brain and gonads in a dimorphic manner with a female bias. In the brain, kiss2 transcripts showed regional differences with higher expression in the medulla oblongata and forebrain regions. The kiss2 transcripts showed significant seasonal variations with the highest expression in the brain in spawning phase and in the gonads in prespawning phase. The kiss2 transcripts were localized in the brain (nucleus preopticus, habenular nucleus, nucleus recessus posterioris, nucleus recessus lateralis) and stratum periventriculare (radial glial cells) of optic tectum, pituitary and ovary (follicular layer and germinal vesicle). Ovariectomy (1, 2, 3 and 4 weeks) decreased brain kiss2 mRNA levels and a single injection of estradiol-17β (E₂; 0.5 μg/g body weight) in 3- week ovariectomized (OVX) and sham operated fish resulted in an increase in the transcript levels after 24 h. The E₂ receptor antagonist Tamoxifen (TMX) produced biphasic effects on the kiss2 expression in the dose- response study. TMX inhibited the expression in the OVX fish, but elicited a stimulatory effect in the OVX + E₂-treated fish. Testosterone (T) decreased, and progesterone (P₄) inhibited (resting phase) or stimulated (prespawning phase) the transcript level in 3-week OVX fish. In the 3-week sham groups, E₂ increased, and TMX, T and P₄ inhibited the kiss2 transcript levels. The results suggest that Kiss2 is an important regulator of the brain- pituitary- gonadal- endocrine axis, and in habenular and optic tectum functions.

Annual patterns of ocular melatonin level in the female grass puffer, Takifugu alboplumbeus: possible involvement in seasonal reproductive response

The aim of this study was to investigate the expression patterns of ocular melatonin in the annual reproductive cycle of the female grass puffer. Spawning season of the female grass puffer is from June to July in Jeju, South Korea. Time-resolved fluoroimmunoassay revealed that levels of ocular melatonin, which show an annual change, peaked in May (spawning season). Additionally, expression of reproductive-related genes also showed annual patterns: GnRH1 peaked in August, GnRH2 peaked in February, GnRH3, Kiss2, and LPXRFa peaked in November. These results suggest that ocular melatonin may be related to the annual reproductive cycle in the grass puffer. To better understand the photic regulation of AANAT1a mRNA in the retina, we observed the nocturnal pattern of ocular melatonin levels daily, which shows a nocturnal pattern in both short photoperiod (SD) and long photoperiod (LD) conditions. In the brain, AANAT2 mRNA also shows a nocturnal pattern in both SD and LD; however, the time of peak expression of AANAT2 mRNA was unchanged in both conditions. Following intraperitoneal injection of melatonin for 2 weeks, expression of GnRH2 and LPXRFa mRNA in the brain significantly increased, while that of Kiss2 mRNA was decreased, suggesting that melatonin has a reproduction-related effect. Furthermore, under SD and LD conditions for 14 weeks, the gonadosomatic index more increased and the maturity of the ovary progressed under LD compared with those under SD, suggesting that the SD photoperiodic signal inactivated ovarian development. These results indicate that the ocular melatonin may have a possible role in the reproductive endocrinology of the grass puffer.

Leptin stimulates gonadotropin release and ovarian development in marine teleost chub mackerel

Leptin transmits information about energy stored in the periphery to the reproductive axis and is an essential signal for puberty initiation in mammals; however, to date, few studies have focused on the direct effects of leptin stimulation on reproductive factors in fish. This study demonstrated the effect of leptin stimulation on important reproductive factors and ovarian development in the marine teleost chub mackerel (Scomber japonicus). We prepared recombinant leptin and conducted functional analyses through in vitro bioassays using primary pituitary cells, long-term leptin treatment administered to pre-pubertal females, and intracerebroventricular (ICV) administration. The results showed that leptin stimulation strongly induced gonadotropin (follicle-stimulating hormone: FSH and luteinizing hormone: LH) secretion from pituitary cells collected from pre-pubertal females, and that long-term leptin treatment significantly promoted ovarian development and triggered pubertal onset. Furthermore, ICV administration of leptin did not affect kisspeptin gene expression but significantly upregulated gonadotropin-releasing hormone 1 (gnrh1), fshb and lhb gene expression in sexually immature females. These results strongly suggest leptin as an important signal for reproductive-axis activation in chub mackerel.

Alanine scanning and characterization of core peptides in Scombridae fish family for construction of Kiss1 super analog

Chronic Kiss1 administration strongly promotes gonadal development in immature chub mackerel (cm) (Scomber japonicus). Here, we performed an Alanine scanning (Ala-scanning) of Kiss1 to determine its key residues. Additionally, we examined functional peptides from 16 Scombridae species to develop maturation-inducing super-analogs that can be used universally in Scombridae species. In the Ala-scanning of Kiss1-15 (QDMSSYNFNSFGLRY), substitution of Gln¹ and Asp² did not affect agonistic activity. This suggests that peptides could be downsized. Furthermore, it is possible that Phe⁸ can be substituted by unnatural amino acids that are difficult to degrade. In molecular cloning, only Scomber showed a 16-residue form as a putative mature peptide. The other genera, did not have a His residue at the N-terminal, which indicated that the functional peptide was 15 residues and the second and third residues from the N-terminal showed variation between interspecies. Next, we examined the binding affinity of various synthetic Kiss1 core peptides in Scombridae interspecies using an SRE-Luc reporter system. We cloned Kiss1 receptors (KissR1) from bluefin tuna (bft) (Thunnus orientalis) and Japanese Spanish mackerel (jsm) (Scomberomorus niphonius) for the first time. In binding affinity with cmKissR1, bftKissR1, and jsmKissR1, the species specificity of the second residue from the N-terminus in each ligand could be ignored, but the difference in the third residue strongly affected receptor binding. Scombridae species possess the same Kiss1 system but the structure of the functional peptide might be species-specific.

The mRNA expression patterns of kisspeptins, GnRHs, and gonadotropins in the brain and pituitary gland of a tropical damselfish, Chrysiptera cyanea, during the reproductive cycle

The sapphire devil (Chrysiptera cyanea) is a tropical damselfish that undergoes active reproduction under long-day conditions. To elucidate the physiological regulation of the brain-pituitary-gonadal axis in female sapphire devil, we cloned and characterized the genes of two kisspeptins (kiss1 and kiss2), three gonadotropin-releasing hormones (gnrh1, gnrh2, gnrh3), and the β-subunit of two gonadotropins (fshβ and lhβ) and investigated the gene expression changes during ovarian development. Quantitative polymerase chain reaction analyses in various brain parts revealed high expression levels of kiss1, kiss2, and gnrh2 in the diencephalon; gnrh2 and gnrh3 in the telencephalon; and fshβ and lhβ in the pituitary. In situ hybridization (ISH) analyses revealed positive signals of kiss1 in the dorsal and ventral habenular nucleus and of kiss2 in the dorsal and ventral parts of the nucleus of the lateral recess. This analysis showed gnrh1 expression in the preoptic area (POA), suggesting that GnRH1 plays a stimulating role in the secretion of gonadotropins from the pituitary of the sapphire devil. High transcription levels of kiss1, kiss2, gnrh1, gnrh2, fshβ, and lhβ were observed in the brain during the late vitellogenic stage, suggesting their involvement in the physiological processes of vitellogenesis. Immersion of fish in estradiol-17β (E2)-containing seawater resulted in increased expression of kiss2 and gnrh1 in their brains. This study showed that kiss-expressing neurons in the diencephalon are influenced by E2, leading to upregulation of gnrh1 in the POA and of fshβ and lhβ in the pituitary during vitellogenesis.

Transcription pattern of reproduction relevant genes along the brain-pituitary-gonad axis of female, male and intersex thicklip grey mullets, Chelon labrosus, from a polluted harbor

The reproductive cycle of teleost fishes is regulated by the brain-pituitary-gonad (BPG) axis. The transcription profile of genes involved in the reproduction signalling in the BPG-axis differs in females and males during the gametogenic cycle. Impacts of endocrine disrupting chemicals on these signalling pathways in fish are known, but the participation of the BPG-axis in the development of the intersex condition is not well understood. Intersex thicklip grey mullets (Chelon labrosus) have been identified in several estuaries from the SE Bay of Biscay, revealing the presence of feminizing contaminants in the area. In previous studies, transcription patterns of genes related with steroidogenesis and gamete growth have been shown to differ among female, male and intersex mullets. However, many components of the reproduction control have not been studied yet. The aim of this study was to assess the transcription levels of target BPG-axis genes in female, male and intersex mullets captured in the polluted harbour of Pasaia, during their gametogenic cycle. After histologically examining the gonads, the transcription levels of previously sequenced target genes were measured by qPCR: kiss2, gpr54 and gnrh1 in brain, fshβ and lhβ in pituitary and fshr and lhr in gonads. In both females and males, brain genes were most transcribed in early gametogenesis, proving their relevance in the onset of both oogenesis and spermatogenesis. Pituitary gonadotropins in females showed upregulation as oogenesis progressed, reaching the highest transcription levels at vitellogenic stage, while in males transcript levels were constant during spermatogenesis. Transcription levels of gonadotropin receptors showed different patterns in ovaries and testes, suggesting differing function in relation to gametogenesis and maturation. Intersex mullets showed transcription levels of brain target genes similar to those observed in females at cortical alveoli stage and to those in mid spermatogenic males. In intersex testes the transcription pattern of gonadotropin receptor fshr was downregulated in comparison to non-intersex testes.

Hypothalamic- and pituitary-derived growth and reproductive hormones and the control of energy balance in fish

Most endocrine systems in the body are influenced by the hypothalamic-pituitary axis. Within this axis, the hypothalamus delivers precise signals to the pituitary gland, which in turn releases hormones that directly affect target tissues including the liver, thyroid gland, adrenal glands and gonads. This action modulates the release of additional hormones from the sites of action, regulating key physiological processes, including growth, metabolism, stress and reproduction. Pituitary hormones are released by five distinct hormone-producing cell types: somatotropes (which produce growth hormone), thyrotropes (thyrotropin), corticotropes (adrenocorticotropin), lactotropes (prolactin) and gonadotropes (follicle stimulating hormone and luteinizing hormone), each modulated by specific hypothalamic signals. This careful and distinct organization of the hypothalamo-pituitary axis has been classically associated with the existence of many lineal axes (e.g., the hypothalamic-pituitary-gonadal axis) in charge of the control of the different physiological processes. While this traditional concept is valid, it is becoming apparent that hormones produced by the hypothalamo-pituitary axis have diverse effects. For instance, gonadotropin-releasing hormone II has been associated with a suppressive effect on food intake in fish. Likewise, growth hormone has been shown to influence appetite, swimming activity and aggressive behavior in fish. This review will focus on the hypothalamic and pituitary hormones classically involved in regulating growth and reproduction, and will attempt to provide a general overview of the current knowledge on their actions on energy balance and appetite in fish. It will also give a brief perspective of the role of some of these peptides in integrating feeding, metabolism, growth and reproduction.

The Kiss2/GPR54 system stimulates the reproductive axis in male black porgy, Acanthopagrus schlegelii

Although it is well established that the Kiss1/GPR54 system stimulates the reproductive axis in mammals, its functional roles, especially in male reproduction of non-mammalian species, is less clear. In this study, we have isolated the full-length kiss2 and gpr54 cDNAs from black porgy (Acanthopagrus schlegelii). The Kiss2 precursor expressed from kiss2 comprises 124 amino acids and contains a highly conserved 10-amino acid sequence, Kiss2-10 (FNFNPFGLRF). GPR54 comprises 375 amino acid residues and contains distinct characteristics of G protein-coupled receptors. Real-time PCR analysis indicated that kiss2 and gpr54 were expressed highly in the brain regions. Moreover, intraperitoneal injection of porgy Kiss2-10 could stimulate genes expression of the gpr54, gnrh1, gnrh3, fshβ, lhβ, p450c17, star, and ar, and the serum testerone level in male black porgy. Our findings demonstrate that the Kisspeptin stimulates the male reproductive axis in black porgy.

Feedback regulation of 17β-estradiol on two kisspeptin genes in the Dabry's sturgeon (Acipenser dabryanus)

In tetrapods, kisspeptins are a group of peptides that play essential roles in the regulation of the Gonadotropin-releasing hormone secretion, and may participate in the feedback regulation of sex steroids as well. In this study, two kiss paralogs, designated as dskiss1 and dskiss2 were identified in Acipenser dabryanus. The full-length cDNA sequences of dskiss1 and dskiss2 are 1265 and 744 base pairs (bp), encoding 130 and 146 amino acids, respectively. Multiple sequence alignment indicated that both Kiss1 and Kiss2 decapeptides were highly conserved among vertebrates. Besides, Kiss1 of Dabry's sturgeon shared closer evolutionary relationship with the holostean species spotted gar (Lepisosteus oculatus), while Kiss2 of Acipenser dabryanus was conservatively grouped with the early sarcopterygian coelacanth (Latimeria chalumnae) in the phylogenetic analysis. Tissue distribution analysis showed that dskiss1 transcribed exclusively in the brain, whereas dskiss2 exhibited wider tissue distribution including brain, testis and ovary. Furthermore, male Dabry's sturgeons were intraperitoneally injected with 17β-estradiol (E2) and the effect of E2 on hypothalamus kiss and its receptors kissr mRNA levels was evaluated by relative real-time PCR. The transcription levels of dskiss2 and dskissr1 were significantly increased by E2 injection (P < .05). However, the mRNA levels of dskiss1 and dskissr2 were not changed in E2-treated group compared to the control group. These results indicate that E2 exerts positive feedback effects through dskiss2/dskissr1 in male Dabry's sturgeon.

Kiss1 hexadecapeptide directly regulates gonadotropin-releasing hormone 1 in the scombroid fish, chub mackerel

Here we report that the Kiss1 hexadecapeptide (Kiss1-16) directly regulates the functional form of gonadotropin-releasing hormone (GnRH) in the preoptic area (POA) of a scombroid fish model. In this study, we analyzed the localization of two kisspeptin (kiss1 and kiss2) neurons and two kisspeptin receptors (kissr1 and kissr2) in the brain of adult chub mackerel using in situ hybridization to determine whether the kisspeptin receptors co-localize with GnRH1 neurons. The kiss1- and kiss2-expressing neurons were mainly localized in the nucleus recessus lateralis (NRL) and the nucleus of the posterior recess (NRP) in the hypothalamus. Kissr1 was present in the anterior POA and the habenular nucleus. Kissr2 was widely distributed, including in the POA, lateral tuberal nucleus, NRL, and NRP. Notably, GnRH1 was expressed in neurons in the POA, and these neurons co-expressed kissr1. In contrast, kissr2 was expressed abundantly in the vicinity of GnRH1 neurons, but their co-expression did not seem to occur. We also characterized the endogenous mature form of the Kiss1 peptide. An in vitro reporter gene assay clearly showed that Kiss1-16 (HQDMSSYNFNSFGLRY-NH2) was more potent at receptor activation than Kiss1 pentadecapeptide (Kiss1-15), which is the form of Kiss1 found in other fish species. This study strongly suggests that kisspeptin signaling, especially Kiss1 signaling, is important for regulating reproduction in scombroid fish.

The Roles of Kisspeptin System in the Reproductive Physiology of Fish With Special Reference to Chub Mackerel Studies as Main Axis

Kisspeptin, a novel neuropeptide product of the Kiss1 gene, activates the G protein-coupled membrane receptor G protein-coupled receptor 54 (now termed Kiss1r). Over the last 15 years, the importance of the kisspeptin system has been the subject of much debate in the mammalian research field. At the heart of the debate is whether kisspeptin is an absolute upstream regulator of gonadotropin-releasing hormone secretion, as it has been proposed to be the master molecule in reproductive events and plays a special role not only during puberty but also in adulthood. The teleostean kisspeptin system was first documented in 2004. Although there have been a number of kisspeptin studies in various fish species, the role of kisspeptin in reproduction remains a subject of controversy and has not been widely recognized. There is an extensive literature on the physiological and endocrinological bases of gametogenesis in fish, largely derived from studying small, model fish species, and reports on non-model species are limited. The reason for this discrepancy is the technical difficulty inherent in developing rigorous experimental systems in many farmed fish species. We have already established methods for the full life-cycle breeding of a commercially important marine fish, the chub mackerel (cm), and are interested in understanding the reproductive function of kisspeptins from various perspectives. Based on a series of experiments clarifying the role of the brain-pituitary-gonad axis in modulating reproduction in cm, we theorize that the kisspeptin system plays an important role in the reproduction of this scombroid species. In this review article, we provide an overview of kisspeptin studies in cm, which substantially aids in elucidating the role of kisspeptins in fish reproduction.

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.

Molecular characterization and functional analysis of pituitary GnRH receptor in a commercial scombroid fish, chub mackerel (Scomber japonicus)

The gonadotropin-releasing hormone (GnRH) is essential during pubertal onset, for its regulation of the synthesis and release of pituitary gonadotropins. Its action is mediated by GnRH receptors (GnRHRs) in the pituitary gonadotrophs. Our previous study demonstrated that the chub mackerel brain expresses three GnRH forms (gnrh1, gnrh2, and gnrh3), and that only GnRH1 neurons innervate anterior pituitary regions. Furthermore, chub mackerel gnrh1 mRNA exhibited a significant increase at pubertal onset. The present study aimed to isolate the functional GnRHR form involved in chub mackerel puberty. The open reading frame of our cloned receptor encodes 428 amino acids and contains seven transmembrane domains. Phylogenetic analysis also indicated clustering with other teleost-type IIB GnRHRs, mainly those involved in reproduction. Reporter gene assay results showed that all four synthetic peptides (GnRH1, GnRH2, GnRH3, and GnRH analogue) bind to the cloned receptor. Three deduced GnRH ligands stimulated luteinizing hormone (LH) release from cultured pituitary cells in vitro. Receptor gene expression was mainly detected in the pituitary and showed an increasing trend in the developing gonadal stages of both sexes during the pubertal process; this process was synchronous with previous studies of follicle-stimulating hormone beta (fshβ) and lhβ gene expression in chub mackerel. These results suggest that the cloned receptor is likely involved in the regulation of pubertal onset in this species. Therefore, we have designated the receptor cmGnRHR1.

Characterization of kiss2 and kissr2 genes and the regulation of kisspeptin on the HPG axis in Cynoglossus semilaevis

Reproduction allows organisms to produce offspring. Animals shift from immature juveniles into mature adults and become capable of sexual reproduction during puberty, which culminates in the first spermiation and sperm hydration or ovulation. Reproduction is closely related to the precise control of the hypothalamic-pituitary-gonadal (HPG) axis. Kisspeptin peptides are considered as the important regulator of HPG axis in mammalian. However, the current understanding of kisspeptin in flatfish is not comprehensive. In this study, we cloned and analyzed the kiss2 and kissr2 genes in Cynoglossus semilaevis. Interesting alternative splicing in the 5'-untranslated regions (UTR) of the Cskissr2 gene was found. The expression profiles of Cskiss2 and Cskissr2 showed relative high messenger RNA (mRNA) levels at the late gastrula stage during embryonic development, at total length = 40 mm during early gonadal differentiation, and in the brains and gonads of all investigated tissues. These results suggested that the kisspeptin system participated in embryogenesis and in the regulation of gonadal differentiation and development. Considering that the control and regulatory mechanisms of kisspeptin in the central reproductive axis are still unclear, we documented that the intramuscular injection of kisspeptin caused different sGnRH and cGnRH mRNA levels in a dose- and tissue-dependent manner. The mRNA expressions of FSH and LH were stimulated in the ovary and were inhibited in the testis under the kisspeptin treatments. These results provided foundations for understanding the roles of kisspeptin in the neuroendocrine system in fish. The manipulation of the kisspeptin system may provide new opportunities to control the gonadal development and even reproduction in fish.

Two vitellogenins in the loliginid squid Uroteuthis edulis: Identification and specific expression in ovarian follicles

Vitellogenenesis is a physiological process common in oviparous animals. The molecular profile, modifications, and utilization of vitellogenin (VTG), a precursor of yolk protein, have been characterized in various taxa to understand oogenesis within different modes of reproduction. Hormonal regulation of VTGs has been investigated in invertebrates, such as insects and crustaceans; conversely, little is known for cephalopods. In this study, we isolated two VTG genes (ue-VTG1 and ue-VTG2) from the loliginid swordtip squid, Uroteuthis edulis, via a comprehensive survey of a transcriptome database and subsequent cDNA cloning. Structural analysis of the two ue-VTGs revealed their unique features, namely the absence of two domains usually found in VTGs from other organisms: the von Willebrand factor D domain (vWD) and the domain of unknown function 1943 (DUF1943). Levels of ue-VTG1 and ue-VTG2 transcripts in the ovary, specifically in follicular cells, increased during the late-vitellogenic phase, suggesting that yolk accumulation progresses via paracrine interactions involving follicular cells and oocytes. N-terminal amino acid sequencing of biochemically purified yolk protein revealed its origins from these two VTGs, indicating that both are functional precursors of yolk protein. These results provide information that is essential to understanding the physiological pathway of yolk synthesis, accumulation, and storage in loliginid squids.

Genetic analysis of the reproductive axis in fish using genome-editing nucleases

Reproduction in fish is controlled by the brain-pituitary-gonad reproductive axis. Although genes of the reproductive axis are conserved from fish to humans, their in vivo functions are less clear in fish. Mutant lines of the reproductive axis have been systematically investigated in zebrafish and medaka using recently developed genome-editing nucleases. Here, we review recent progress in the genetic analysis of the reproductive axis in fish as well as the opportunities and challenges of applying genome-editing nucleases in fisheries.

Photoperiod regulate gonad development via kisspeptin/kissr in hypothalamus and saccus vasculosus of Atlantic salmon (Salmo salar)

Atlantic salmon exhibit seasonal reproduction. However, the mechanisms governing this are still unclear. Generally speaking, kisspeptin has been recognized as a regulator of reproduction. Here, we report a relationship between kisspeptin, GnRH and photoperiod in Atlantic salmon. The results demonstrated that the expression of the Atlantic salmon kisspeptin-receptor (skissr) was not always consistent with the expression pattern of Atlantic salmon GnRH3 (sGnRH3) during all developmental processes. Kisspeptin may exert its influence primarily in the early and later stages of gonad development by promoting the secretion of sGnRH3. Meanwhile, the expression levels of kissr were higher in fish with gonads at stage II and stage V under the long-day photoperiod regime than under the short-day regime. In addition, both skissr and sGnRH3 were also expressed in the saccus vasculosus (SV), an organ only found in fish. The SV might be a seasonal sensor regulating reproduction in addition to the hypothalamus (Hyp).

Eel Kisspeptins: Identification, Functional Activity, and Inhibition on both Pituitary LH and GnRH Receptor Expression

The European eel (Anguilla anguilla) presents a blockade of sexual maturation at a prepubertal stage due to a deficient production of gonadotropins. We previously initiated, in the eel, the investigation of the kisspeptin system, one of the major gatekeepers of puberty in mammals, and we predicted the sequence of two Kiss genes. In the present study, we cloned and sequenced Kiss1 and Kiss2 cDNAs from the eel brain. The tissue distributions of Kiss1 and Kiss2 transcripts, as investigated by quantitative real-time PCR, showed that both genes are primarily expressed in the eel brain and pituitary. The two 10-residue long sequences characteristic of kisspeptin, eel Kp1(10) and Kp2(10), as well as two longer sequences, predicted as mature peptides, eel Kp1(15) and Kp2(12), were synthesized and functionally analyzed. Using rat Kiss1 receptor-transfected Chinese hamster ovary cells, we found that the four synthesized eel peptides were able to induce [Ca²⁺]_i responses, indicating their ability to bind mammalian KissR-1 and to activate second messenger pathways. In primary culture of eel pituitary cells, all four peptides were able to specifically and dose-dependently inhibit lhβ expression, without any effect on fshβ, confirming our previous data with heterologous kisspeptins. Furthermore, in this eel in vitro system, all four peptides inhibited the expression of the type 2 GnRH receptor (gnrh-r2). Our data revealed a dual inhibitory effect of homologous kisspeptins on both pituitary lhβ and gnrh-r2 expression in the European eel.

Kisspeptin2 stimulates the HPG axis in immature Nile tilapia (Oreochromis niloticus)

It has been suggested that kisspeptin influences reproduction and onset of puberty in fishes. Unlike mammals, which produce only one kisspeptin (Kiss1), some teleosts have two, Kiss1 and Kiss2, both thought to be involved in the stimulation of gonadotropin (GTH) secretion. In Nile tilapia (Oreochromis niloticus), however, only Kiss2 has been identified so far. The effect of Kiss2 on GTH release varies significantly depending on species and reproductive stage. Furthermore, its physiological function in this species is not clearly defined. In this study, kiss2 gene expression profiles were examined using quantitative real-time PCR (qRT-PCR) in the brain, pituitary, and gonads of Nile tilapia at different reproductive stages (male: immature, pre-spermiation, post-spermiation; female: immature, pre-spawning, post-spawning). The kiss2 mRNA expression profiles of the brain, pituitary, and gonads of both sexes shared a similar pattern their expression was significantly higher at the immature stage than at the mature or post-spawning stages, implying it is involved in early gonadal maturation in this species. To investigate the effect of kisspeptin on the hypothalamus-pituitary-gonad (HPG) axis in vivo, synthetic kisspeptin2 (FNYNPLSLRF) was injected into immature male and female tilapia intraperitoneally (i.p.) at a dose of 200pmol/g body weight. The results showed that synthetic Kiss2 administration increased the expression of GnRH I, fshβ and lhβ mRNA in the brain and increased 17β-estradiol (E₂) and 11-ketotestosterone (11-KT) levels in the plasma. These results suggest that Kiss2 stimulates the expression of GnRH and GTH genes in immature Nile tilapia.

Identification and characterization of kiss2 and kissr2 homologs in Paralichthys olivaceus

The role of kisspeptin in puberty onset has been extensively investigated by neuroendocrinologists in the past decade. In the present study, we first cloned and analyzed Pokiss2 and Pokissr2 genes in Paralichthys olivaceus, a Pleuronectiformes fish. By 5'/3' rapid amplification of cDNA ends (RACE), the P. olivaceus kiss2 gene (Pokiss2) and two isoforms of the P. olivaceus kissr2 gene (Pokissr2) transcripts were cloned. During development, Pokissr2 was maternally inherited but Pokiss2 was not, and their expression reached maximum and minimum levels, respectively, when the gonads began to develop. Analysis of tissue distribution revealed that Pokiss2 and Pokissr2 transcripts were predominantly expressed in the brain and gonads, with expression levels in females higher than those in males. Moreover, Pokiss2 and Pokissr2 both showed significantly higher expression in brains and gonads during puberty. In situ hybridization of the ovary at pre-vitellogenesis stage and testis at spermatogonial proliferation stage revealed that both Pokiss2 and Pokissr2 were expressed in spermatocyte, oocytes, and some somatic cells. Our results also showed significantly stronger Pokiss2 expression in the area of the third ventricle of females than males and no Pokissr2 expression in this region in both sexes. These results lay a strong foundation for understanding the role of kisspeptin in neuroendocrine system in teleosts, in particular in Pleuronectiformes.

Molecular characterization of kisspeptin gene and effect of nano-encapsulted kisspeptin-10 on reproductive maturation in Catla catla

Kisspeptin, a member of the RF-amide-related peptide family, has emerged recently as an essential gatekeeper of various reproductive processes via its ability to activate kisspeptin receptors at puberty. In this study, the kiss1 gene and its receptor kiss1rb were cloned and characterized from the brain of Catla catla. Further, the effects of kissppetin-10 (K-10) and chitosan-encapsulated K-10 nanoparticles (CK-10) on gene expression were assessed. The full-length complementary DNA sequence of kiss1 is 754 bp with an open reading frame of 351 bp that encodes a putative protein of 116 amino acids. The kiss1rb complementary DNA is 1,280 bp long and contains a 5'-untranslated region of 30 bp, 3'-untranslated region of 149 bp, and an open reading frame (open reading frame) of 1,101 bp. The expression patterns of kiss1 and kiss1rb messenger RNA (mRNA) in basal tissues revealed that they are mainly expressed in the brain, pituitary gland, and gonads. CK-10 nanoparticles with a particle size of 125 nm and a zeta potential of 36.45 mV were synthesized and compared with K-10. Chitosan nanoparticles showed 60% entrapment efficiency for K-10. The mRNA expression of reproductive genes (GnRH, LH, and FSH) in fish injected with K-10 declined after 6 h, whereas those injected with CK-10 showed controlled and a sustained surge of mRNA expression of these genes with a peak at 12 h. Histologic examination of ovaries indicated a pronounced effect of CK-10 on maturation and gonadal development. The study reports that this sustained release delivery system will help in increasing the half-life of K-10 and other therapeutic protein drugs in the biological system. Besides, the nanoformulation developed in the present study may be useful for developing therapies against various reproductive dysfunctions in vertebrates.

Molecular characterization of the gonadal kisspeptin system: Cloning, tissue distribution, gene expression analysis and localization in sablefish (Anoplopoma fimbria)

The kisspeptin system plays pivotal roles in the regulation of vertebrate reproduction. Classically, kisspeptin produced in the brain stimulates brain gonadotropin-releasing hormone signaling, which in turn activates the pituitary-gonad axis. Expression of the kisspeptin system has also been documented in peripheral tissues, including gonads of mammals and fishes. However, the fish gonadal kisspeptin system remained uncharacterized. Herein we report identification and characterization of four kisspeptin system mRNAs (kisspeptin 1 (kiss1), kiss2, and G protein-coupled receptor 54-1 (gpr54-1) and gpr54-2) in sablefish, Anoplopoma fimbria. Sablefish predicted protein sequences were highly similar to those of other marine teleosts, but less so to freshwater teleosts. Tissue distribution analyses revealed that all four kisspeptin-system transcripts were expressed in both brain and gonad. However, kiss2 was the predominant transcript in the gonads and the only transcript detected in ovulated eggs. Ontogenetic analysis of kiss2 expression in juvenile sablefish gonads demonstrated that levels were low during sex differentiation but increased with fish size and gonadal development. Dramatic increases in kiss2 mRNA occurred during primary oocyte growth, while levels remained relatively low in testes. In situ hybridization revealed that kiss2 mRNA was localized to cytoplasm of perinucleolus stage oocytes, suggesting it could play a local role in oogenesis or could be synthesized and stored within oocytes as maternal mRNA. This represents the first study to focus on the gonadal kisspeptin system in fishes and provides important tools for further investigation of both the gonadal and brain kisspeptin systems in sablefish.

Expression changes of mRNAs encoding kisspeptins and their receptors and gonadotropin-releasing hormones during early development and gonadal sex differentiation periods in the brain of chub mackerel (Scomber japonicus)

In recent years, brain kisspeptin system has been shown to be involved in diverse reproductive function, including sexual differentiation in vertebrates. Our previous reports demonstrated that the chub mackerel (Scomber japonicus) brain expresses two kisspeptin (kiss1, kiss2), two kisspeptin receptor (kissr1, kissr2) and three gonadotropin-releasing hormone (gnrh1, gnrh2, gnrh3) genes. In the present study, using quantitative real-time PCR (qRT-PCR) assays, we analysed expression changes of these genes during early development (0-30dphs) and gonadal sex differentiation periods (37-60dphs). Absolute expression level of kiss-kissr-gnrh in the whole head was higher between 0 and 15dphs, in comparison to later developmental periods. Histological analyses revealed presence of sexually differentiated males and females with testicular and ovarian features at 37, 45, and 60dphs. In both males and females, kiss2, kissr1, and kissr2 levels were higher at 37dph, in comparison to 45 and 60dphs, with kiss1 showing no significant differences. Levels of all three gnrh mRNAs were higher at 45dph, in comparison to 60dph. Changes in the expression level of kiss-kissr-gnrh mRNAs in different brain regions of sexually differentiated males and females indicated differences in their regional distribution. These results suggest possible involvement of Kiss-KissR-GnRH systems during early development and gonadal sex differentiation in the chub mackerel.

Possible Involvement of Photoperiodic Regulation in Reproductive Endocrine System of Female Olive Flounder Paralichthys olivaceus

This study investigated possible involvement of photoperiodic regulation in reproductive endocrine system of female olive flounder. To investigate the influence on brain-pituitary axis in endocrine system by regulating photoperiod, compared expression level of Kisspeptin and sbGnRH mRNA in brain and FSH-β, LH-β and GH mRNA in pituitary before and after spawning. Photoperiod was treated natural photoperiod and long photoperiod (15L:9D) conditions from Aug. 2013 to Jun. 2014. Continuous long photoperiod treatment from Aug. (post-spawning phase) was inhibited gonadal development of female olive flounder. In natural photoperiod group, the Kiss2 expression level a significant declined in Mar. (spawning period). And also, FSH-β, LH-β and GH mRNA expression levels were increasing at this period. However, in long photoperiod group, hypothalamic Kiss2, FSH-β, LH-β and GH mRNA expression levels did not show any significant fluctuation. These results suggest that expression of hypothalamic Kiss2, GtH and GH in the pituitary would change in response to photoperiod and their possible involvement of photoperiodic regulation in reproductive endocrine system of the BPG axis.

Characterisation of kisspeptin system genes in an ovoviviparous teleost: Sebastes schlegeli

Kisspeptins are neuropeptides that play important roles in the reproduction and the onset of puberty in vertebrate by activating their receptor, Kissr. In the present study, we first isolated kiss1 and kissr4 genes from an ovoviviparous fish, the black rockfish (Sebastes schlegeli) by homologue cloning. Phylogenetic analysis indicated that the kiss and kissr of S. schlegeli belonged to kiss1 and kissr4 respectively. Quantitative real-time PCR analysis showed that the kissr4 was expressed mainly in the brain and testis, while the kiss1 was expressed predominantly in the heart of both sexes. As for the different gonadal maturation stages the kiss1 showed different expression patterns in different tissues. During the early development stage, expression levels of the ligand and receptor genes showed similar increasing trends. The promoter region of kissr4 contained several putative transcription factor (TF) binding sites which may have the function of regulating kisspeptin system gene expression, providing potential targets for future in-depth investigation. These results together confirmed that the kisspeptin system in S. schlegeli may be involved in reproduction and other activities. Furthermore, our study laid the groundwork for further learning about the evolution and function of kisspeptin system in fish even vertebrate.

Possible Involvement of Photoperiodic Regulation in Reproductive Endocrine System of Female Olive Flounder Paralichthys olivaceus

This study investigated possible involvement of photoperiodic regulation in reproductive endocrine system of female olive flounder. To investigate the influence on brain-pituitary axis in endocrine system by regulating photoperiod, compared expression level of Kisspeptin and sbGnRH mRNA in brain and FSH-β, LH-β and GH mRNA in pituitary before and after spawning. Photoperiod was treated natural photoperiod and long photoperiod (15L:9D) conditions from Aug. 2013 to Jun. 2014. Continuous long photoperiod treatment from Aug. (post-spawning phase) was inhibited gonadal development of female olive flounder. In natural photoperiod group, the Kiss2 expression level a significant declined in Mar. (spawning period). And also, FSH-β, LH-β and GH mRNA expression levels were increasing at this period. However, in long photoperiod group, hypothalamic Kiss2, FSH-β, LH-β and GH mRNA expression levels did not show any significant fluctuation. These results suggest that expression of hypothalamic Kiss2, GtH and GH in the pituitary would change in response to photoperiod and their possible involvement of photoperiodic regulation in reproductive endocrine system of the BPG axis.

The kiss/kissr systems are dispensable for zebrafish reproduction: evidence from gene knockout studies

The kiss1/gpr54 signaling system is considered to be a critical regulator of reproduction in most vertebrates. However, this presumption has not been tested vigorously in nonmammalian vertebrates. Distinct from mammals, multiple kiss1/gpr54 paralogous genes (kiss/kissr) have been identified in nonmammalian vertebrates, raising the possibility of functional redundancy among these genes. In this study, we have systematically generated the zebrafish kiss1(-/-), kiss2(-/-), and kiss1(-/-);kiss2(-/-) mutant lines as well as the kissr1(-/-), kissr2(-/-), and kissr1(-/-);kissr2(-/-) mutant lines using transcription activator-like effector nucleases. We have demonstrated that spermatogenesis and folliculogenesis as well as reproductive capability are not impaired in all of these 6 mutant lines. Collectively, our results indicate that kiss/kissr signaling is not absolutely required for zebrafish reproduction, suggesting that the kiss/kissr systems play nonessential roles for reproduction in certain nonmammalian vertebrates. These findings also demonstrated that fish and mammals have evolved different strategies for neuroendocrine control of reproduction.

A platelet-activating factor (PAF) receptor deficiency exacerbates diet-induced obesity but PAF/PAF receptor signaling does not contribute to the development of obesity-induced chronic inflammation

Platelet-activating factor (PAF) is a well-known phospholipid that mediates acute inflammatory responses. In the present study, we investigated whether PAF/PAF receptor signaling contributed to chronic inflammation in the white adipose tissue (WAT) of PAF receptor-knockout (PAFR-KO) mice. Body and epididymal WAT weights were higher in PAFR-KO mice fed a high-fat diet (HFD) than in wild-type (WT) mice. TNF-α mRNA expression levels in epididymal WAT and the infiltration of CD11c-positive macrophages into epididymal WAT, which led to chronic inflammation, were also elevated in HFD-fed PAFR-KO mice. HFD-fed PAFR-KO mice had higher levels of fasting serum glucose than HFD-fed WT mice as well as impaired glucose tolerance. Although PAF receptor signaling up-regulated the expression of TNF-α and lipopolysaccharide induced the expression of acyl-CoA:lysophosphatidylcholine acyltransferase 2 (LPCAT2) mRNA in bone marrow-derived macrophages, no significant differences were observed in the expression of LPCAT2 mRNA and PAF levels in epididymal WAT between HFD-fed mice and normal diet-fed mice. In addition to our previous finding in which energy expenditure in PAF receptor (PAFR)-deficient mice was low due to impaired brown adipose tissue function, the present study demonstrated that PAF/PAF receptor signaling up-regulated the expression of Ucp1 mRNA, which is essential for cellular thermogenesis, in 3T3-L1 adipocytes. We concluded that the marked accumulation of abdominal fat due to HFD feeding led to more severe chronic inflammation in WAT, which is associated with glucose metabolism disorders, in PAFR-KO mice than in WT mice, and PAF/PAF receptor signaling may regulate energy expenditure and adiposity.