Molecular characterization of CART, AgRP, and MC4R genes and their expression with fasting and re-feeding in common carp (Cyprinus carpio)

Effects of fasting and environmental factors on appetite regulators in pond loach Misgurnus anguillicaudatus

The pond loach (Misgurnus anguillicaudatus) is an important aquaculture freshwater species, used as an ornamental fish, food source for humans and angling bait. Pond loaches are resistant to fasting and extreme environmental conditions, including temperature and low oxygen levels. Little is known about how these factors affect the feeding physiology and the endocrine regulation of feeding of loaches. In this study, we examined the effects of fasting, as well as increased temperature and decreased oxygen levels on food intake and transcript levels of appetite regulators. Fasted fish had lower blood glucose levels, and lower expression levels of intestine CCK and PYY, and brain CART1, but had higher levels of brain orexin and ghrelin than fed fish. Fish held at 30 °C had higher food intake, glucose levels, and mRNA levels of intestine CCK and PYY, and brain CART2, but lower brain orexin levels than fish at 20 °C. Fish held at low oxygen levels had a lower food intake, higher intestine CCKa and ghrelin, and brain orexin, CART2 and ghrelin mRNA expression levels than fish held at high O2 levels. Our results suggest that fasting and high temperatures increase the expression of orexigenic and anorexigenic factors respectively, whereas the increase in expression of both orexigenic and anorexigenic factors in low O2 environments might not be related to their role in feeding, but possibly to protection from tissue damage. The results of our study might shed new light on how pond loaches are able to cope with extreme environmental conditions such as low food availability, extreme temperatures and hypoxia.

Neuropeptide Y receptor Y8b (npy8br) regulates feeding and digestion in Japanese medaka (Oryzias latipes) larvae: evidence from gene knockout

Neuropeptide Y receptor Y8 (NPY8R) is a fish-specific receptor with two subtypes, NPY8AR and NPY8BR. Changes in expression levels during physiological processes or in vivo regulation after ventricular injection suggest that NPY8BR plays an important role in feeding regulation; this has been found in only a few fish, at present. In order to better understand the physiological function of npy8br, especially in digestion, we used clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) technology to generate npy8br-/- Japanese medaka (Oryzias latipes). We found that the deletion of npy8br in medaka larvae affected their feeding and digestion ability, ultimately affecting their growth. Specifically, npy8br deficiency in medaka larvae resulted in decreased feed intake and decreased expression levels of orexigenic genes (npy and agrp). npy8br-/- medaka larvae fed for 10 d (10th day of feeding) still had incompletely digested brine shrimp (Artemia nauplii) in the digestive tract 8 h after feeding, the messenger RNA (mRNA) expression levels of digestion-related genes (amy, lpl, ctra, and ctrb) were significantly decreased, and the activity of amylase, trypsin, and lipase also significantly decreased. The deletion of npy8br in medaka larvae inhibited the growth and significantly decreased the expression of growth-related genes (gh and igf1). Hematoxylin and eosin (H&E) sections of intestinal tissue showed that npy8br-/- medaka larvae had damaged intestine, thinned intestinal wall, and shortened intestinal villi. So far, this is the first npy8br gene knockout model established in fish and the first demonstration that npy8br plays an important role in digestion.

Effects of different acute stressors on the regulation of appetite genes in the carp (Cyprinus carpio L.) brain

Our understanding of the timing of stress responses and specific roles of different regulatory pathways that drive stress responses is incomplete. In particular, the regulation of appetite genes as a consequence of exposure to different stressors has not been studied in sufficient detail in fish. Therefore, a stress trial was conducted with koi carp, aiming at identifying typical effects of stress on regulation of appetite genes. The stressors tank manipulation, air exposure and feed rewarding were chosen. The responses to these stressors were evaluated 10, 30 and 60 min after the stressors were applied. Orexigenic and anorexigenic genes were investigated in four different brain regions (telencephalon, hypothalamus, optic tectum and rhombencephalon). The results show that, apart from the typical appetite regulation in the hypothalamus, the different brain regions also display pronounced responses of appetite genes to the different stressors. In addition, several genes in the serotonergic, dopaminergic and gaba-related pathways were investigated. These genes revealed that rearing in pairs of two and opening of the tank lid affected anorexigenic genes, such as cart and cck, which were not changed by air exposure or feed rewarding. Moreover, distress and eustress led to limited, but distinguishable gene expression pattern changes in the investigated brain regions.

Improved Growth and High Inheritance of Melanocortin-4 Receptor (mc4r) Mutation in CRISPR/Cas-9 Gene-Edited Channel Catfish, Ictalurus punctatus

Effects of CRISPR/Cas9 knockout of the melanocortin-4 receptor (mc4r) gene in channel catfish, Ictalurus punctatus, were investigated. Three sgRNAs targeting the channel catfish mc4r gene in conjunction with Cas9 protein were microinjected in embryos and mutation rate, inheritance, and growth were studied. Efficient mutagenesis was achieved as demonstrated by PCR, Surveyor® assay, and DNA sequencing. An overall mutation rate of 33% and 33% homozygosity/bi-allelism was achieved in 2017. Approximately 71% of progeny inherited the mutation. Growth was generally higher in MC4R mutants than controls (CNTRL) at all life stages and in both pond and tank environments. There was a positive relationship between zygosity and growth, with F₁ homozygous/bi-allelic mutants reaching market size 30% faster than F₁ heterozygotes in earthen ponds (p = 0.022). At the stocker stage (~ 50 g), MC4R × MC4R mutants generated in 2019 were 40% larger than the mean of combined CNTRL × CNTRL families (p = 0.005) and 54% larger than F₁ MC4R × CNTRL mutants (p = 0.001) indicating mutation may be recessive. With a high mutation rate and inheritance of the mutation as well as improved growth, the use of gene-edited MC4R channel catfish appears to be beneficial for application on commercial farms.

The neuropeptide Y receptor gene repository, phylogeny and comparative expression in allotetraploid common carp

NPY-family receptors belong to G protein-coupled receptors (GPCR), which lays a physiological foundation for the transmembrane transport of an endogenous appetite-stimulating factor neuropeptide Y and related peptides. In this study, we investigated the npyr genes in ten representative species, and twelve npyr genes were identified from allotetraploid C. carpio, the npyr gene number of C. carpio was twice the number of its subgenome B progenitor-like diploid Poropuntius huangchuchieni. Phylogenetic analysis showed that all npyr genes were divided into three subgroups, and they underwent strong purifying selection according to selection pressure analysis. Subsequently, synteny analysis showed that most npyr genes were evenly distributed on the homologous chromosomes of two subgenomes in allotetraploid C. carpio, in which npy1r and npy2r were tandem duplicated, respectively. In addition, the global expression of npyr genes during embryonic development in allotetraploid C. carpio suggested the potential function of npyr genes in immunity and reproduction. In adult tissues, npyr genes were mainly distributed in the brain, gonad, and skin, which displayed a similar expression pattern between the C. carpio B subgenome and P. huangchuchieni. In general, our research could provide reference information for future exploration of the NPY receptors and neuroendocrine system of allotetraploid C. carpio and vertebrates.

Mutations in melanocortin-4 receptor: From fish to men

Melanocortin-4 receptor (MC4R), expressed abundantly in the hypothalamus, is a critical regulator of energy homeostasis, including both food intake and energy expenditure. Shortly after the publication in 1997 of the Mc4r knockout phenotypes in mice, including increased food intake and severe obesity, the first mutations in MC4R were reported in humans in 1998. Studies in the subsequent two decades have established MC4R mutation as the most common monogenic form of obesity, especially in early-onset severe obesity. Studies in animals, from fish to mammals, have established the conserved physiological roles of MC4R in all vertebrates in regulating energy balance. Drug targeting MC4R has been recently approved for treating morbid genetic obesity. How the MC4R can be exploited for animal production is highly worthy of active investigation.

Protective Effect of Emblica officinalis in Cyprinus carpio against Hepatotoxicity Induced by Malachite Green: Ultrastructural and Molecular Analysis

Malachite green (MG) dye, besides coloring is used as an effective aquaculture therapeutic. The present study assesses the mitigating ability of Emblica officinalis (EO) fruit extract against the dye induced chronic (60 days) cyto-toxicity in Cyprinus carpio. For this, four experimental groups were maintained: group I—control, group II—MG, group III—EO (positive control), group IV—MG + EO. The study was made at three tiers: detailing structural anomalies using a light microscope and transmission electron microscope (TEM), biochemical estimation of antioxidant enzymes, and lipid peroxidation and molecular analysis of expression patterns of HSP70, and CYP1A genes. MG intoxication resulted in necrosis, cytoplasmic vacuolation, glycogen depletion, abundant macrophages, loss of cell integrity and prominent nuclear alterations. Significant (p < 0.05) inhibition in the activities of catalase (CAT), superoxide dismutase (SOD), glutathione-S-transferase (GST) and reduced glutathione (GSH), along with an elevation in malondialdehyde (MDA) levels, occurred after 60 days of MG exposure. CYP1A and HSP70 genes presented a significant change in their expression in MG treated fish. Whereas oral supplementation with EO significantly restored the histo-architecture, normalized the altered enzymatic activity, reduced the oxidative stress level and regulated the expression of HSP70 and CYP1A genes. Thus, it can be concluded that EO acted as an effective ameliorant against malachite green induced cyto-toxicity in Cyprinus carpio.

Food intake, growth, and expression of neuropeptides regulating appetite in clown anemonefish (Amphiprion ocellaris) exposed to predicted climate changes

The clown anemonefish (Amphiprion ocellaris) is a common model species in studies assessing the impact of climate changes on tropical coral fish physiology, metabolism, growth, and stress. However, the basic endocrine principles for the control of food intake and energy homeostasis, under normal and elevated sea temperatures, in this species remain unknown. In this work, we studied food intake and growth in clown anemonefish reared at different temperatures and with different food availability. We also analyzed expression of genes in the melanocortin system, which is believed to be involved in the control of appetite and feeding behavior. These were two paralogues of pomc: pomca and pomcb; two paralogs of agrp: agrp1 and agrp2; and one mc4r-like. Groups of juvenile clown anemonefish were exposed to four experimental treatments combining (orthogonal design) two rearing temperatures: 28 °C (T28; normal) and 32 °C (T32; high) and two feeding regimes: one (1 M; 08:00) or three (3 M; 08:00, 12:00, 15:00) meals per day, fed to satiety by hand. The results showed that high temperature (T32) did not affect the average growth rate but induced a stronger asymmetrical individual body weight of the fish within the population (tank). Lower feeding frequency (1 M) resulted in lower growth rates at both rearing temperatures. Fish reared at high temperature had higher total daily food intake, which correlated with a lower expression of pomca, supporting an anorexigenic role of this gene. High temperature combined with restricted feeding induced higher agrp1 levels and resulted in a higher food intake in the morning meal compared to the control. This supports an orexigenic role for agrp1. mRNA levels of agrp2 responded differently from agrp1, supporting different roles for the paralogues. Levels of mc4r-like inversely correlated with fish body weight, indicating a possible size/stage dependence of gene expression. In conclusion, our results indicate that the melanocortin system is involved in adjusting appetite and food intake of clown anemonefish in response to elevated temperature and low food availability.

MRAP2 Interaction with Melanocortin-4 Receptor in SnakeHead (Channa argus)

The melanocortin-4 receptor (MC4R) plays an important role in the regulation of food intake and energy expenditure. Melanocortin-2 receptor accessory protein 2 (MRAP2) modulates trafficking, ligand binding, and signaling of MC4R. The Northern snakehead (Channa argus) is an economically important freshwater fish native to East Asia. To explore potential interaction between snakehead MC4R and MRAP2, herein we cloned snakehead mc4r and mrap2. The snakehead mc4r consisted of a 984 bp open reading frame encoding a protein of 327 amino acids, while snakehead mrap2 contained a 693 bp open reading frame encoding a protein of 230 amino acids. Synteny analysis indicated that mc4r was highly conserved with similar gene arrangement, while mrap2 contained two isoforms in teleost with different gene orders. Snakehead mc4r was primarily expressed in the brain, whereas mrap2 was expressed in the brain and intestine. Snakehead mc4r and mrap2 expression was modulated by fasting and refeeding. Further pharmacological experiments showed that the cloned snakehead MC4R was functional, capable of binding to peptide agonists and increasing intracellular cAMP production in a dose-dependent manner. Snakehead MC4R exhibited high constitutive activity. MRAP2 significantly decreased basal and agonist-stimulated cAMP signaling. These findings suggest that snakehead MC4R might be involved in energy balance regulation by interacting with MRAP2. Further studies are needed to elucidate MC4R in regulating diverse physiological processes in snakehead.

The stage-specific long non-coding RNAs and mRNAs identification and analysis during early development of common carp, Cyprinus carpio

Cyprinus carpio is considered an alternative vertebrate fish model to zebrafish. However, systemic times-series research on the lncRNAs and mRNAs during early development of C. carpio has not been reported yet. This study provides the first long non-coding RNA (lncRNA)-mRNA expression profiles during six main early development stages (2 h post-fertilization hpf, 6 hpf, 12 hpf, 20 hpf, 64 hpf and 1 day post-hatching). A total of 51,979 lncRNAs were identified. We screened the top 10 abundance lncRNAs and mRNAs and stage-specific lncRNAs and mRNAs (specificity measure SPM > 0.9). We identified significant differentially expressed lncRNAs and mRNAs (|log2 (fold change)| ≥ 1 and false discovery rate FDR of <0.05). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis identified numerous signaling pathways. Additionally, the lncRNA-mRNA co-regulated network analysis of two lncRNAs (lncrps25 and malat1) and two mRNAs (mitf and troponin T) were investigated. Our results provide new insight into the role of lncRNAs and mRNAs, and would advance the understanding of lncRNA-mediated mechanisms in early development of fish.

The Melanocortin System in Atlantic Salmon (Salmo salar L.) and Its Role in Appetite Control

The melanocortin system is a key neuroendocrine network involved in the control of food intake and energy homeostasis in vertebrates. Within the hypothalamus, the system comprises two main distinct neuronal cell populations that express the neuropeptides proopiomelanocortin (POMC; anorexigenic) or agouti-related protein (AGRP; orexigenic). Both bind to the melanocortin-4 receptor (MC4R) in higher order neurons that control both food intake and energy expenditure. This system is relatively well-conserved among vertebrates. However, in Atlantic salmon (Salmo salar L.), the salmonid-specific fourth round whole-genome duplication led to the presence of several paralog genes which might result in divergent functions of the duplicated genes. In the current study, we report the first comprehensive comparative identification and characterization of Mc4r and extend the knowledge of Pomc and Agrp in appetite control in Atlantic salmon. In silico analysis revealed multiple paralogs for mc4r (a1, a2, b1, and b2) in the Atlantic salmon genome and confirmed the paralogs previously described for pomc (a1, a2, and b) and agrp (1 and 2). All Mc4r paralogs are relatively well-conserved with the human homolog, sharing at least 63% amino acid sequence identity. We analyzed the mRNA expression of mc4r, pomc, and agrp genes in eight brain regions of Atlantic salmon post-smolt under two feeding states: normally fed and fasted for 4 days. The mc4ra2 and b1 mRNAs were predominantly and equally abundant in the hypothalamus and telencephalon, the mc4rb2 in the hypothalamus, and a1 in the telencephalon. All pomc genes were highly expressed in the pituitary, followed by the hypothalamus and saccus vasculosus. The agrp genes showed a completely different expression pattern from each other, with prevalent expression of the agrp1 in the hypothalamus and agrp2 in the telencephalon. Fasting did not induce any significant changes in the mRNA level of mc4r, agrp, or pomc paralogs in the hypothalamus or in other highly expressed regions between fed and fasted states. The identification and wide distribution of multiple paralogs of mc4r, pomc, and agrp in Atlantic salmon brain provide new insights and give rise to new questions of the melanocortin system in the appetite regulation in Atlantic salmon.

The genetic polymorphisms of melanocortin-4 receptor gene are associated with carcass quality traits in a Chinese indigenous beef cattle breed

Melanocortin-4 receptor (MC4R) was considered as an essential modifiers in feelings intake, the regulation of metabolism and body weight. This study aimed at identifying polymorphisms in MC4R gene that might associate with carcass quality traits in Chinese indigenous beef cattle breed. qPCR analysis showed that the MC4R gene was widely expressed in various tissues, with predominantly expression levels in heart. Three single-nucleotide polymorphisms (SNPs) were identified, including a mutation (g.85A > G) in 5'untranslated regions (UTR) and two mutations (g.927C > T and g.1069C > G) in exon 1. Based on the χ² test, both g.927C > T and g.1069C > G loci fitted with Hardy-Weinberg equilibrium (P > .05). Population genetic analysis showed that except for g.85A > G, the other detected SNPs strongly affected the bovine back fat thickness and intramuscular fat content (P < .05). The individuals with Hap1/4 diplotypes (ACC-ATG) were highly significantly associated with carcass quality traits than the other diplotypes (P < .01 or P < .05). Results indicated that the bovine MC4R gene polymorphisms were implicated as genetic markers of potential importance in marker-assisted selection (MAS) strategies to improve carcass quality in Chinese Qinchuan cattle.

Metabolic control of teleost reproduction by leptin and its complements: Understanding current insights from mammals

Reproduction is expensive. Hence, reproductive physiology is sensitive to an array of endogenous signals that provide information on metabolic and nutritional sufficiency. Although metabolic gating of reproductive function in mammals, as evidenced by studies demonstrating delayed puberty and perturbed fertility, has long been understood to be a function of energy sufficiency, an understanding of the endocrine regulators of this relationship have emerged only within recent decades. Peripheral signals including leptin and cortisol have long been implicated in the physiological integration of metabolism and reproduction. Recent studies have begun to explore possible roles for these two hormones in the regulation of reproduction in teleost fishes, as well as a role for leptin as a catabolic stress hormone. In this review, we briefly explore the reproductive actions of leptin and cortisol in mammals and teleost fishes and possible role of both hormones as putative modulators of the reproductive axis during stress events.

Three forms of cocaine- and amphetamine-regulated transcript may be involved in food intake regulation in gibel carp (Carassius auratus gibelio)

In fish, as in mammals, several studies have demonstrated that the cocaine- and amphetamine-regulated transcript (CART) plays an important role in feeding. However, thus far, the function of CART in gibel carp (Carassius auratus gibelio) feeding regulation has not been reported. In our study, we first identified three forms of CART peptide precursors from gibel carp brain and named these CART-1, CART-2, and CART-3. The full-length cDNA sequences of CART-1, CART-2, and CART-3 were 616 bp, 705 bp, and 760 bp, respectively, encoding peptides of 118, 120, and 104 amino acid residues. We detected mRNA expression of CART-1, CART-2, and CART-3 in a wide range of peripheral and central tissues, with the highest expression detected in the brain. After a meal, mRNA expression of CART-1, CART-2, and CART-3 was significantly elevated, suggesting that CART-1, CART-2, and CART-3 may act as postprandial satiety signals. Moreover, mRNA expression of all three CART-1, CART-2, and CART-3 was significantly reduced during fasting and significantly elevated with refeeding. Our findings indicate that CART-1, CART-2, and CART-3 might function as a satiety factor in the gibel carp.

UCN3 suppresses food intake in coordination with CCK and the CCK2R in Siberian sturgeon (Acipenser baerii)

Urocortin-3 (UCN3) as a brain-gut peptide inhibits food intake of animal, but the underlying mechanism is not clear. To explore the appetite mechanism about the action of UCN3 in fish, intraperitoneal injection of UCN3 with CCK8, Lorglumide (CCK1R antagonist) or LY225910 (CCK2R antagonist) were conducted. Siberian sturgeon administrated with UCN3 and CCK8 showed a drastic reduction in food intake. The anorectic effect of UCN3 was significantly blocked by LY225910, but not affected by Lorglumide. Furthermore, LY225910 could effectively reverse appetite factor mRNA expressions, including cck, pyy, cart, npy, ucn3, apelin and nucb2 in the whole brain, stomach and intestinum valvula, but Lorglumide could only partially reverse these effects, suggesting the anorectic effect of UCN3 may be primarily mediated CCK2R in Siberian sturgeon. This study indicates for the first time in fish that UCN3 may inhibit food intake in coordination with CCK and CCK2R.

Nutrient Regulation of Endocrine Factors Influencing Feeding and Growth in Fish

Endocrine factors regulate food intake and growth, two interlinked physiological processes critical for the proper development of organisms. Somatic growth is mainly regulated by growth hormone (GH) and insulin-like growth factors I and II (IGF-I and IGF-II) that act on target tissues, including muscle, and bones. Peptidyl hormones produced from the brain and peripheral tissues regulate feeding to meet metabolic demands. The GH-IGF system and hormones regulating appetite are regulated by both internal (indicating the metabolic status of the organism) and external (environmental) signals. Among the external signals, the most notable are diet availability and diet composition. Macronutrients and micronutrients act on several hormone-producing tissues to regulate the synthesis and secretion of appetite-regulating hormones and hormones of the GH-IGF system, eventually modulating growth and food intake. A comprehensive understanding of how nutrients regulate hormones is essential to design diet formulations that better modulate endogenous factors for the benefit of aquaculture to increase yield. This review will discuss the current knowledge on nutritional regulation of hormones modulating growth and food intake in fish.

The Expression of agrp1, A Hypothalamic Appetite-Stimulating Neuropeptide, Reveals Hydrodynamic-Induced Starvation in a Larval Fish

Larval fish suffer dramatic mortality in the days following transition to autonomous feeding, with over 90% of larvae being eliminated within a period of few weeks. Recent work has shown that the hydrodynamic environment experienced by recently-hatched larvae impedes their feeding rates even under high prey densities. Here, we quantified starvation through early ontogeny in Sparus aurata larvae (8–18 days post-hatching; DPH) and tested whether the emerging ontogenetic pattern is consistent with that expected one based on the hydrodynamic environment that these larvae experience. We screened three candidate genes agrp1, npy, and hsp70, whose expression was previously shown to respond to starvation in fish. Of the three genes, agrp1 was identified as a suitable indicator for starvation. Localization of agrp1 mRNA by whole-mount in-situ hybridization confirmed that, in S. aurata larvae, agrp1 is expressed only in the hypothalamus. Quantification of agrp1 mRNA using real-time PCR revealed that the expression of this gene is elevated in starved compared to fed larvae, and in younger (8 DPH) compared to older larvae (18 DPH). Manipulating the water viscosity to simulate the hydrodynamic conditions during the onset of the critical period led to increased agrp1 expression. These findings suggest that the hydrodynamic constraints on larval feeding lead to the starvation of small larvae. Further, they provide a mechanistic explanation for the “safe harbor” hypothesis, which postulates that larvae should allocate resources toward rapid linear growth to escape detrimental effects of dwelling in an environment where viscous fluid forces dominate.

Cloning and effects of fasting on the brain expression levels of appetite-regulators and reproductive hormones in glass catfish (Kryptopterus vitreolus)

The regulation of feeding is a complex process that involves coordination between various signals. Feeding hormones can be described as orexigenic (stimulate food intake, e.g. orexin and neuropeptide Y - NPY) or anorexigenic (inhibit food intake, e.g. cocaine and amphetamine regulated transcript - CART). Reproduction and energy homeostasis are closely linked, as factors that affect appetite have also been shown to influence reproductive hormones and behaviors. Gonadotropin-releasing hormone (GnRH) is one of the most influential factors controlling reproduction. Although our understanding of the endocrine regulation of feeding and reproduction in fish is progressing, many gaps still remain, particularly in catfish. Glass catfish (Kryptopterus vitreolus) are freshwater fish known for their natural transparency. In this study, we isolated cDNA encoding reproductive hormones (GnRH1, GnRH2) and appetite regulators (orexin, NPY, and CART) from glass catfish and examined their distribution in various tissues. All peptides had wide distributions across various brain and peripheral tissues, except CART, which was only present in brain. In order to assess whether limited energy supply affects these peptides, we examined the effects of fasting on their brain mRNA expression levels. Fasting increased the expression of both the orexigenic (i.e. orexin and NPY) and anorexigenic (i.e. CART) hormones, and decreased expression levels of GnRH1, but did not affect GnRH2. Overall, our results suggest that fasting affects the expression of peptides involved in both feeding and reproduction, and provides new insights on the endocrine mechanisms that regulate feeding and reproduction in catfish.

One evidence of cocaine- and amphetamine-regulated transcript (CART) has the bidirectional effects on appetite in Siberian sturgeon (Acipenser baerii)

Cocaine- and amphetamine-regulated transcript (CART), discovered in 1995, with various biological functions, has received much attention recently due to its role in the regulation of appetite in mammals. However, the function of CART on the appetite control in fish species is still not very clear. In this study, Siberian sturgeon (Acipenser baerii Brandt) cart gene was cloned for the first time, and the cart mRNA levels in 11 feeding-related tissues was investigated. The Siberian sturgeon cart gene sequence was 1459 base pairs (bp), including a 3'-terminal untranslated region (3'-UTR) of 39 bp, a 5'-terminal untranslated region (5'-UTR) of 52 bp, and an open reading frame (ORF) of 348 bp encoding 115 amino acids. Siberian sturgeon cart gene has three exons and two introns including 341 bp intron 1 and 679 bp intron 2. The result of tissue distribution showed that cart was widely distributed in 11 tissues with the highest expression in the whole brain. The effects of periprandial (pre- and post-feeding), fasting, and re-feeding on cart mRNA abundance in the whole brain were assessed. Periprandial result showed the expression of cart mRNA in the whole brain significantly elevated after feeding for 3 h. However, fasting experiment showed that the level of cart significantly decreased after 1 day of fasting, but that significantly increased after 3-17 days of food deprivation and returned to the basic level after 3 days of re-feeding in the fishes which were fasted for 15 days. In conclusion, this study suggests that CART has the bidirectional effects on appetite, which acts as a satiety factor in short-term feeding regulation but as a starvation factor in long-term appetite regulation in Siberian sturgeon.

Effect of growth hormone overexpression on gastric evacuation rate in coho salmon

Growth hormone (GH) transgenic (T) coho salmon consistently show remarkably enhanced growth associated with increased appetite and food consumption compared to non-transgenic wild-type (NT) coho salmon. To improve understanding of the mechanism by which GH overexpression mediates food intake and digestion in T fish, feed intake and gastric evacuation rate (over 7 days) were measured in size-matched T and NT coho salmon. T fish displayed greatly enhanced feed intake levels (~ 2.5-fold), and more than 3-fold increase in gastric evacuation rates relative to NT coho salmon. Despite the differences in feed intake, no differences were noted in the time taken from first ingestion of food to stomach evacuation between genotypes. These results indicate that enhanced feed intake is coupled with an overall increased processing rate to enhance energy intake by T fish. To further investigate the molecular basis of these responses, we examined the messenger RNA (mRNA) levels of several genes in appetite- and gastric-regulation pathways (Agrp1, Bbs, Cart, Cck, Glp, Ghrelin, Grp, Leptin, Mc4r, Npy, and Pomc) by qPCR analyses in the brain (hypothalamus, preoptic area) and pituitary, and in peripheral tissues associated with digestion (liver, stomach, intestine, and adipose tissue). Significant increases in mRNA levels were found for Agrp1 in the preoptic area (POA) of the brain, and Grp and Pomc in pituitary for T coho salmon relative to NT. Mch and Npy showed significantly lower mRNA levels than NT fish in all brain tissues examined across all time-points after feeding. Mc4r and Cart for T showed significantly lower mRNA levels than NT in the POA and hypothalamus, respectively. In the case of peripheral tissues, T fish had lower mRNA levels of Glp and Leptin than NT fish in the intestine and adipose tissue, respectively. Grp, Cck, Bbs, Glp, and Leptin in stomach, adipose tissue, and/or intestine showed significant differences across the time-points after feeding, but Ghrelin showed no significant difference between T and NT fish in all tested tissues.

Distribution and female reproductive state differences in orexigenic and anorexigenic neurons in the brain of the mouth brooding African cichlid fish, Astatotilapia burtoni

Integration of reproduction and metabolism is necessary for species survival. While the neural circuits controlling energy homeostasis are well-characterized, the signals controlling the relay of nutritional information to the reproductive axis are less understood. The cichlid fish Astatotilapia burtoni is ideal for studying the neural regulation of feeding and reproduction because females cycle between a feeding gravid state and a period of forced starvation while they brood developing young inside their mouths. To test the hypothesis that candidate neuropeptide-containing neurons known to be involved in feeding and energy homeostasis in mammals show conserved distribution patterns, we performed immunohistochemistry and in situ hybridization to localize appetite-stimulating (neuropeptide Y, NPY; agouti-related protein, AGRP) and appetite-inhibiting (cocaine and amphetamine-regulated transcript, CART; pro-opiomelanocortin, pomc1a) neurons in the brain. NPY, AGRP, CART, and pomc1a somata showed distribution patterns similar to other teleosts, which included localization to the lateral tuberal nucleus (NLT), the putative homolog of the mammalian arcuate nucleus. Gravid females also had larger NPY and AGRP neurons in the NLT compared to brooding females, but brooding females had larger pomc1a neurons compared to gravid females. Hypothalamic agrp mRNA levels were also higher in gravid compared to brooding females. Thus, larger appetite-stimulating neurons (NPY, AGRP) likely promote feeding while females are gravid, while larger pomc1a neurons may act as a signal to inhibit food intake during mouth brooding. Collectively, our data suggest a potential role for NPY, AGRP, POMC, and CART in regulating energetic status in A. burtoni females during varying metabolic and reproductive demands.

Feedback from Arctic charr: Feed flavour stimulation and re-feeding after feed deprivation stimulate genes encoding both orexigenic and anorexigenic neuropeptides

Despite vast research attention, the knowledge about central mechanisms of appetite regulation in teleost remains inconclusive. A common strategy in studies on appetite regulating mechanisms is to measure the response to feed restriction or - deprivation, but responses vary between fish species and between experiments, and are also likely dependent on the degree of energy perturbation. The anadromous Arctic charr is an interesting model for studying appetite regulation as its feeding cycle comprises months of winter anorexia, and hyperphagia during summer. Here we studied how the gene expression of putative hypothalamic appetite regulators were affected by two days, one week and one month feed deprivation during summer, and subsequent re-feeding and exposure to feed flavour. Short-term feed deprivation caused only a minor reduction in condition factor and had no effect on hypothalamic gene expression. Long-term feed-deprivation caused a marked reduction in weight and condition factor which contrasted the increase in weight and condition factor seen in ad libitum fed controls. A marked energy perturbation by feed deprivation was also indicated by a lower hypothalamic expression of the genes encoding insulin-like growth factor 1 (IGF1) and IGF1 binding protein 5 in the feed deprived charr compared to fed controls. Surprisingly, long-term feed deprivation and energy perturbation did not induce changes in hypothalamic appetite regulators. Unexpectedly, re-feeding and exposure to feed flavour caused an increase in the expression of the genes encoding the orexigenic agouti-related peptide and the anorexigenic melanocortin receptor 4 and cocaine- and amphetamine-regulated transcript. Our study gives strong evidence for a role of these in appetite regulation in Arctic charr, but their mechanisms of action remain unknown. We suggest that changes in gene expression are more likely to be registered during transition phases, e.g. from fasting to feeding and upon stimulatory inputs such as feed flavour.

Appetite-Controlling Endocrine Systems in Teleosts

Mammalian studies have shaped our understanding of the endocrine control of appetite and body weight in vertebrates and provided the basic vertebrate model that involves central (brain) and peripheral signaling pathways as well as environmental cues. The hypothalamus has a crucial function in the control of food intake, but other parts of the brain are also involved. The description of a range of key neuropeptides and hormones as well as more details of their specific roles in appetite control continues to be in progress. Endocrine signals are based on hormones that can be divided into two groups: those that induce (orexigenic), and those that inhibit (anorexigenic) appetite and food consumption. Peripheral signals originate in the gastrointestinal tract, liver, adipose tissue, and other tissues and reach the hypothalamus through both endocrine and neuroendocrine actions. While many mammalian-like endocrine appetite-controlling networks and mechanisms have been described for some key model teleosts, mainly zebrafish and goldfish, very little knowledge exists on these systems in fishes as a group. Fishes represent over 30,000 species, and there is a large variability in their ecological niches and habitats as well as life history adaptations, transitions between life stages and feeding behaviors. In the context of food intake and appetite control, common adaptations to extended periods of starvation or periods of abundant food availability are of particular interest. This review summarizes the recent findings on endocrine appetite-controlling systems in fish, highlights their impact on growth and survival, and discusses the perspectives in this research field to shed light on the intriguing adaptations that exist in fish and their underlying mechanisms.

Characterization of appetite-regulating factors in platyfish, Xiphophorus maculatus (Cyprinodontiformes Poeciliidae)

The regulation of energy in fish, like most vertebrates, is a complex process that involves a number of brain and peripheral hormones. These signals include anorexigenic (e.g. cholecystokinin (CCK) and cocaine- and amphetamine-regulated transcript (CART)) as well as orexigenic (e.g. orexin and neuropeptide Y (NPY)) peptides. Platyfish, Xiphophorus maculatus, are freshwater viviparous fish for which little is known about the endocrine mechanisms regulating feeding. In order to elucidate the role of these peptides in the regulation of feeding of platyfish, we examined the effects of peripheral injections of CCK and orexin on feeding behavior and food intake. Injections of CCK decreased both food intake and searching behavior, while injections of orexin increased searching behavior but did not affect food consumption. In order to better characterize these peptides, we examined their mRNA tissue distribution and assessed the effects of a 10-day fast on their brain and intestine expressions in both males and females. CCK, CART, NPY and orexin all show widespread distributions in brain and several peripheral tissues, including intestine and gonads. Fasting induced decreases in both CCK and CART and an increase in orexin mRNA expressions in the brain and a decrease in CCK expression in the intestine, but did not affect either expressions of NPY. There were no significant sex-specific differences in either the behavioral responses to injections or the expression responses to fasting. The widespread distribution and the fasting-induced changes in expression of these peptides suggest that they might have several physiological roles in platyfish, including the regulation of feeding.

Molecular cloning, tissue distribution, and pharmacological characterization of melanocortin-4 receptor in grass carp (Ctenopharyngodon idella)

Melanocortin-4 receptor (MC4R) plays a pivotal role in the mediation of leptin action on food intake and energy expenditure in mammals. The MC4R has also been identified in several teleosts, and its importance in the regulation of fish energy homeostasis is emerging. We herein reported on the molecular cloning, tissue distribution, and pharmacological characterization of MC4R in grass carp (Ctenopharyngodon idella), an economically and ecologically important fish. We showed that grass carp MC4R (ciMC4R) consisted of a 981 bp open reading frame encoding a protein of 326 amino acids, highly homologous (>95%) to several teleost MC4Rs. Phylogenetic and synteny analysis further indicated ciMC4R was closely related to piscine MC4Rs. Using reverse transcription PCR, we found that mc4r messenger RNA was expressed in the brain as well as various peripheral tissues in grass carp. The pharmacological properties of ciMC4R were investigated using 4 agonists, including α-melanocyte stimulating hormone (α-MSH), β-MSH, [Nle⁴, D-Phe⁷]-MSH (NDP-MSH), and adrenocorticotropic hormone (ACTH). We showed that all 4 ligands could bind to ciMC4R and initiate dose-dependent intracellular cyclic adenosine monophosphate (cAMP) accumulation. Grass carp MC4R had the highest affinity for NDP-MSH. Both NDP-MSH and ACTH (1-24) exhibited higher potencies compared to the other 2 endogenous agonists. The ciMC4R was constitutively active, with significantly increased basal cAMP level compared with that of human MC4R (P < 0.01). The availability of ciMC4R and its pharmacologic characteristics provide a basis for future investigation of its functional roles in regulating diverse physiological processes and novel insights into understanding the mechanism of food habit transition in grass carp.

Novel hypophysiotropic AgRP2 neurons and pineal cells revealed by BAC transgenesis in zebrafish

The neuropeptide agouti-related protein (AgRP) is expressed in the arcuate nucleus of the mammalian hypothalamus and plays a key role in regulating food consumption and energy homeostasis. Fish express two agrp genes in the brain: agrp1, considered functionally homologous with the mammalian AgRP, and agrp2. The role of agrp2 and its relationship to agrp1 are not fully understood. Utilizing BAC transgenesis, we generated transgenic zebrafish in which agrp1- and agrp2-expressing cells can be visualized and manipulated. By characterizing these transgenic lines, we showed that agrp1-expressing neurons are located in the ventral periventricular hypothalamus (the equivalent of the mammalian arcuate nucleus), projecting throughout the hypothalamus and towards the preoptic area. The agrp2 gene was expressed in the pineal gland in a previously uncharacterized subgroup of cells. Additionally, agrp2 was expressed in a small group of neurons in the preoptic area that project directly towards the pituitary and form an interface with the pituitary vasculature, suggesting that preoptic AgRP2 neurons are hypophysiotropic. We showed that direct synaptic connection can exist between AgRP1 and AgRP2 neurons in the hypothalamus, suggesting communication and coordination between AgRP1 and AgRP2 neurons and, therefore, probably also between the processes they regulate.

Effect of long-term fasting and a subsequent meal on mRNA abundances of hypothalamic appetite regulators, central and peripheral leptin expression and plasma leptin levels in rainbow trout

Knowledge about neuroendocrine mechanisms regulating appetite in fish, including the role of leptin, is inconclusive. We investigated leptin mRNA abundance in various tissues, plasma leptin levels and the hypothalamic gene expression of putative orexigenic (neuropeptide Y and agouti-regulated peptide) and anorexigenic (melanocortin receptor, proopiomelanocortins (POMCs), cocaine- and amphetamine-regulated transcript and corticotropin-releasing factor) neuropeptides in relation to feeding status in rainbow trout (Oncorhynchus mykiss). Blood and tissues were first (Day 1) sampled from trout that had been fed or fasted for 4 months and the day after (Day 2) from fasted fish after they had been given a large meal, and their continuously fed counterparts. The fasted fish ate vigorously when they were presented a meal. There were no differences between fed, fasted and re-fed fish in hypothalamic neuropeptide transcript levels, except for pomca1 and pomcb, which were higher in fasted fish than in fed fish at Day 1, and which, for pomcb, decreased to the level in fed fish after the meal at Day 2. Plasma leptin levels did not differ between fasted, re-fed and fed fish. A higher leptina1 transcript level was seen in the belly flap of fasted fish than in fed fish, even after re-feeding on Day 2. The data do not reveal causative roles of the investigated brain neuropeptides, or leptin, in appetite regulation. It is suggested that the elevated pomc transcript levels provide a satiety signal that reduces energy expenditure during prolonged fasting. The increase in belly flap leptin transcript with fasting, which did not decrease upon re-feeding, indicates a tissue-specific role of leptin in long-term regulation of energy homeostasis.

The Neuroendocrine Regulation of Food Intake in Fish: A Review of Current Knowledge

Fish are the most diversified group of vertebrates and, although progress has been made in the past years, only relatively few fish species have been examined to date, with regards to the endocrine regulation of feeding in fish. In fish, as in mammals, feeding behavior is ultimately regulated by central effectors within feeding centers of the brain, which receive and process information from endocrine signals from both brain and peripheral tissues. Although basic endocrine mechanisms regulating feeding appear to be conserved among vertebrates, major physiological differences between fish and mammals and the diversity of fish, in particular in regard to feeding habits, digestive tract anatomy and physiology, suggest the existence of fish- and species-specific regulating mechanisms. This review provides an overview of hormones known to regulate food intake in fish, emphasizing on major hormones and the main fish groups studied to date.

Appetite regulating factors in pacu (Piaractus mesopotamicus): Tissue distribution and effects of food quantity and quality on gene expression

The pacu Piaractus mesopotamicus is an omnivorous fish considered a promising species for aquaculture. Little is known about the endocrine regulation of feeding in this species. In this study, transcripts for orexin, cocaine and amphetamine regulated transcript (CART), cholecystokinin (CCK) and leptin were isolated in pacu. Orexin, CCK and leptin have widespread mRNA distributions in brain and periphery, CART is limited to the brain. To examine the role of these peptides in the regulation of feeding and energy status, mRNA expression levels were compared between fed and fasted fish and around feeding time. Both orexin and CART brain expressions were affected by fasting and displayed periprandial changes, suggesting a role in both short- and long-term regulation of feeding. CCK intestinal expression decreased in fasted fish and displayed periprandial changes, suggesting CCK acts as a peripheral satiety factor. Leptin was not affected by fasting but displayed periprandial changes, suggesting a role as a short-term regulator. To examine if these peptides are affected by diet, brain and gut expressions were assessed in fish fed with different diets containing soy protein concentrate. Food intake, weight gain and expressions of orexin, CART, CCK and leptin were little affected by replacement of fish protein with soy protein, suggesting that pacu is able to tolerate and grow well with a diet rich in plant material. Overall, our results suggest that orexin, CART, CCK and leptin are involved in the physiology of feeding of pacu and that their expressions are little affected by plant-based diets.

Appetite regulating factors in dourado, Salminus brasiliensis: cDNA cloning and effects of fasting and feeding on gene expression

The dourado, Salminus brasiliensis (Cuvier, 1816) is a freshwater piscivorous Characin native to South American rivers. Owing to the high quality of its flesh and its fast growth, it is the object of both capture fisheries and fish farming. However, very little is known about the endocrine regulation of feeding and metabolism of dourado. In this study, cDNAs for orexin, CART and CCK were isolated in dourado, and their mRNA tissue distributions examined. In order to assess the role of these peptides in the regulation of feeding of dourado, the effects of fasting and feeding on mRNA expression levels of orexin, CART and CCK in the brain as well as CCK in the intestine were assessed. Whereas orexin and CCK have widespread mRNA distributions in the brain and peripheral organs, CART seems to be mostly limited to the brain. Orexin brain expression increased with fasting and displayed periprandial changes, suggesting it is involved in both long- and short-term regulation of feeding and appetite. CART and CCK hypothalamic expressions were not affected by fasting, but displayed periprandial changes with post-feeding decreases, suggesting roles in short-term satiation. CCK expression in the anterior intestine was not affected by fasting and did not display periprandial changes. Overall, our results suggest that orexin, CART and CCK are involved in the physiology of feeding of dourado.

Ya-fish (Schizothorax prenanti) spexin: identification, tissue distribution and mRNA expression responses to periprandial and fasting

Spexin (SPX) is a novel peptide which was known for its role in physiological homeostasis. A recent study has confirmed that SPX plays an important role in the feeding regulation. However, the reports about SPX are very limited. In the present study, we characterized the structure, distribution and mRNA expression responses to feeding status of SPX in Ya-fish (Schizothorax prenanti). The full-length cDNA of Ya-fish SPX was 1330 base pairs (bp), which encoded 106 amino acid residues. These residues contained a 31-amino acid signal peptide region and a 14-amino acid mature peptide. The sequence alignment demonstrated that the Ya-fish SPX showed high conservation with other species. Our data revealed that SPX was widely expressed in all test tissues. The highest expression of SPX mRNA was observed in Ya-fish forebrain. Compared with the Ya-fish SPX mRNA expression in the forebrain between the preprandial and postprandial groups, the fed group was prominently increased than unfed groups after a meal, while the unfed group at 1 and 3 h substantially decreased than preprandial groups (P < 0.01). In addition, SPX mRNA expression in forebrain was significantly decreased (P < 0.01) during fasting for a week and sharply increased (P < 0.01) after refeeding on the 7th day, and then return to normal level on the 9th day. These results point toward that SPX mRNA expression is regulated by metabolic status or feeding conditions in Ya-fish.

Appetite regulation in Schizothorax prenanti by three CART genes

In recent years, cocaine- and amphetamine-regulated transcript (CART) has received much attention as mediators of appetite regulation in mammals. However, the involvement of CART in the feeding behavior of teleosts has not been well understood. In this study, three distinct CARTs were cloned from the Schizothorax prenanti (S. prenanti). Real-time quantitative PCR were applied to characterize the tissue distribution and appetite regulatory effects of CARTs in S. prenanti. The S. prenanti CART-1, CART-2 and CART-3 full-length cDNA sequences were 597 bp, 694 bp and 749 bp in length, encoding the peptides of 125, 120 and 104 amino acid residues, respectively. All the S. prenanti CARTs consisted of three exons and two introns. Tissue distribution analysis showed that the high mRNA levels of S. prenanti CART-1 were observed in the telencephalon and eye, followed by the hypothalamus, myelencephalon, and mesencephalon. The S. prenanti CART-2 mRNA was mainly found in the mesencephalon, hypothalamus, telencephalon and myelencephalon. The S. prenanti CART-3 mRNA was widely distributed among the tissues, with the high levels in the hypothalamus and foregut. In the periprandial experiment, all three CARTs mRNA expressions in the hypothalamus were highly elevated after a meal, suggesting that CARTs are postprandial satiety signals. In the fasting experiment, all three CARTs mRNA expressions decreased after fasting and increased after refeeding, suggesting that CARTs might be involved in regulation of appetite in the S. prenanti.

Characterization of seven cocaine- and amphetamine-regulated transcripts (CARTs) differentially expressed in the brain and peripheral tissues of Solea senegalensis (Kaup)

CART (cocaine- and amphetamine-regulated transcript) is a peptide with neurotransmitter and neuroendocrine functions with several key roles, both centrally and peripherally. In mammals there is a single gene that produces two alternatively spliced variants in rat and a single transcript in human but in teleosts multiple genes have been found. In the present study we report the existence of seven transcripts in Senegalese sole and characterize their sequences and phylogenetic relationships, as well as their expression patterns in the brain and peripheral tissues, and in response to feeding. Both cart2a and cart4 showed a ubiquitous expression in the brain, while cart1a, cart1b and cart3a were similarly expressed and had higher transcript levels in the mesencephalon, followed by the diencephalon. On the other hand, cart2b showed a main expression in the olfactory bulbs, and cart3b was predominantly expressed in the spinal cord. The expression profile in peripheral tissues differed substantially between cart's, even between more recently duplicated genes. Collectively, all the tissues examined, except the muscle, express at least one of the different cart's, although the highest transcript levels were found in the brain, gonads (ovary and testis) and, in some cases, eye and kidney. Concerning the feeding response, only brain cart1a, cart2a and cart4 showed a significant postprandial regulation, although future studies are necessary to assess potential confounding effects of stress imposed by the force feeding technique employed. Senegalese sole exhibits the highest number of cart genes reported to date in a vertebrate species. Their differential expression patterns and feeding regulation suggest that multiple cart genes, resulting from at least 3 rounds of whole genome duplication, have been retained in fish genomes through subfunctionalization, or possibly even through neofunctionalization.

Effects of chronic growth hormone overexpression on appetite-regulating brain gene expression in coho salmon

Organisms must carefully regulate energy intake and expenditure to balance growth and trade-offs with other physiological processes. This regulation is influenced by key pathways controlling appetite, feeding behaviour and energy homeostasis. Growth hormone (GH) transgenesis provides a model where food intake can be elevated, and is associated with dramatic modifications of growth, metabolism, and feeding behaviour, particularly in fish. RNA-Seq and qPCR analyses were used to compare the expression of multiple genes important in appetite regulation within brain regions and the pituitary gland (PIT) of GH transgenic (fed fully to satiation or restricted to a wild-type ration throughout their lifetime) and wild-type coho salmon (Oncorhynchus kisutch). RNA-Seq results showed that differences in both genotype and ration levels resulted in differentially expressed genes associated with appetite regulation in transgenic fish, including elevated Agrp1 in hypothalamus (HYP) and reduced Mch in PIT. Altered mRNA levels for Agrp1, Npy, Gh, Ghr, Igf1, Mch and Pomc were also assessed using qPCR analysis. Levels of mRNA for Agrp1, Gh, and Ghr were higher in transgenic than wild-type fish in HYP and in the preoptic area (POA), with Agrp1 more than 7-fold higher in POA and 12-fold higher in HYP of transgenic salmon compared to wild-type fish. These data are consistent with the known roles of orexigenic factors on foraging behaviour acting via GH and through MC4R receptor-mediated signalling. Igf1 mRNA was elevated in fully-fed transgenic fish in HYP and POA, but not in ration-restricted fish, yet both of these types of transgenic animals have very pronounced feeding behaviour relative to wild-type fish, suggesting IGF1 is not playing a direct role in appetite stimulation acting via paracrine or autocrine mechanisms. The present findings provide new insights on mechanisms ruling altered appetite regulation in response to chronically elevated GH, and on potential pathways by which elevated feeding response is controlled, independently of food availability and growth.

Obestatin partially suppresses ghrelin stimulation of appetite in "high-responders" grass carp, Ctenopharyngodon idellus

Ghrelin and obestatin are two gastrointestinal peptides obtained by post-translational processing of a common precursor, preproghrelin. The effect of obestatin on food intake is still controversial. The aim of the present study was to investigate the effects of ghrelin and obestatin on food intake in grass carp, Ctenopharyngodon idellus. Fish received intraperitoneal (IP) injection of saline, ghrelin (100 ng g(-1)BW), obestatin-like (25 ng g(-1)BW) and ghrelin in combination with obestatin-like. Ghrelin stimulation of food intake varied considerably among individual fish with 70.8% eliciting a robust response. In these high-responders, food intake was significantly increased by IP ghrelin within 2 h. Co-administration of ghrelin and obestatin-like resulted in a decrease in food intake, indicating that obestatin was able to antagonize the effect of ghrelin. However, IP obestatin-like alone could not regulate food intake in grass carp. RT-PCR analysis demonstrated that IP ghrelin peptide led to a significant increase in mRNA abundance of NPY, Y8a and Y8b genes compared to saline injected fish, while in combination with obestatin-like peptide decreased ghrelin-induced gene expressions of these three genes. IP sole obestatin-like peptide did not modify the expression levels of NPY, Y8a, Y8b, CART and POMC compared to the control group. Therefore, IP administration of obestatin-like peptide, partially blocking the ghrelin-induced appetite, investigated the possible involvement of obestatin as a mediator of the ghrelin stimulatory action on food intake, at least in "high-responders" grass carp.

In vitro assessment of interactions between appetite-regulating peptides in brain of goldfish (Carassius auratus)

Orexins, apelin, melanin-concentrating hormone (MCH), neuropeptide Y (NPY) and cocaine and amphetamine regulated transcript (CART) are important appetite-regulating factors produced by the brain of both mammals and fish. These peptide systems and their target areas are widely distributed within the central nervous system. Although morphological connections between some of these systems have been demonstrated in the brain, little is known about the functional interactions between these systems, in particular in fish. In order to better understand the interactions between appetite-related peptides, the effects of in vitro treatments of hindbrain, forebrain and hypothalamus--a major feeding regulating area--fragments with MCH, apelin and orexin on the expression of MCH, apelin, orexin, CART (forms 1 and 2) and NPY were assessed. Overall, the apelin and orexin systems stimulate each other and stimulate the NPY system while inhibiting the CART system, which is consistent with the known orexigenic actions of these two peptides. The actions of MCH remain unclear: although it appears to interact positively with orexigenic systems--as it stimulates both the orexin and apelin systems and its expression is increased by apelin--it also increases the hypothalamic expression of CART2--but not CART1--an anorexigenic factor, and inhibits the NPY system in all brain regions examined. This study suggests that MCH, apelin, orexin, CART and NPY do influence each other within the brain of goldfish and that these interactions might differ in nature and strength according to the peptide form and the brain region considered.

Characterization, tissue distribution and regulation by fasting of the agouti family of peptides in the sea bass (Dicentrarchus labrax)

The melanocortin system is one of the most complex hormonal systems in vertebrates. Atypically, the signaling of melanocortin receptors is regulated by the binding of endogenous antagonists, named agouti-signaling protein (ASIP) and agouti-related protein (AGRP). Teleost specific genome duplication (TSGD) rendered new gene copies in teleost fish and up to four different genes of the agouti family of peptides have been characterized. In this paper, molecular cloning was used to characterize mRNA of the agouti family of peptides in sea bass. Four different genes were identified: AGRP1, ASIP1, AGRP2 and ASIP2. The AGRP1 gene is mainly expressed in the brain whereas ASIP1 is mainly expressed in the ventral skin. Both ASIP2 and AGRP2 are expressed in the brain and the pineal gland but also in some peripheral tissues. Immunocytochemical studies demonstrated that AGRP1 is exclusively expressed within the lateral tuberal nucleus, the homologue of the mammalian arcuate nucleus in fish. Long-term fasting (8-29 days) increased the hypothalamic expression of AGRP1 but depressed AGRP2 expression (15-29 days). In contrast, the hypothalamic expression of ASIP2 was upregulated during short-term fasting suggesting that this peptide could be involved in the short term regulation of food intake in the sea bass.

Appetite regulating peptides in red-bellied piranha, Pygocentrus nattereri: cloning, tissue distribution and effect of fasting on mRNA expression levels

cDNAs encoding the appetite regulating peptides apelin, cocaine and amphetamine regulated transcript (CART), cholecystokinin (CCK), peptide YY (PYY) and orexin were isolated in red-bellied piranha and their mRNA tissue and brain distributions examined. When compared to other fish, the sequences obtained for all peptides were most similar to that of other Characiforme fish, as well as to Cypriniformes. All peptides were widely expressed within the brain and in several peripheral tissues, including gastrointestinal tract. In order to assess the role of these peptides in the regulation of feeding of red-bellied piranha, we compared the brain mRNA expression levels of these peptides, as well as the gut mRNA expression of CCK and PYY, between fed and 7-day fasted fish. Within the brain, fasting induced a significant increase in both apelin and orexin mRNA expressions and a decrease in CART mRNA expression, but there where were no significant differences for either PYY or CCK brain mRNA expressions between fed and fasted fish. Within the intestine, PYY mRNA expression was lower in fasted fish compared to fed fish but there was no significant difference for CCK intestine mRNA expression between fed and fasted fish. Our results suggest that these peptides, perhaps with the exception of CCK, play a major role in the regulation of feeding of red-bellied piranha.

CART in the brain of vertebrates: circuits, functions and evolution

Cocaine- and amphetamine-regulated transcript peptide (CART) with its wide distribution in the brain of mammals has been the focus of considerable research in recent years. Last two decades have witnessed a steady rise in the information on the genes that encode this neuropeptide and regulation of its transcription and translation. CART is highly enriched in the hypothalamic nuclei and its relevance to energy homeostasis and neuroendocrine control has been understood in great details. However, the occurrence of this peptide in a range of diverse circuitries for sensory, motor, vegetative, limbic and higher cortical areas has been confounding. Evidence that CART peptide may have role in addiction, pain, reward, learning and memory, cognition, sleep, reproduction and development, modulation of behavior and regulation of autonomic nervous system are accumulating, but an integration has been missing. A steady stream of papers has been pointing at the therapeutic potentials of CART. The current review is an attempt at piecing together the fragments of available information, and seeks meaning out of the CART elements in their anatomical niche. We try to put together the CART containing neuronal circuitries that have been conclusively demonstrated as well as those which have been proposed, but need confirmation. With a view to finding out the evolutionary antecedents, we visit the CART systems in sub-mammalian vertebrates and seek the answer why the system is shaped the way it is. We enquire into the conservation of the CART system and appreciate its functional diversity across the phyla.

Molecular characterization, tissue distribution and feeding related changes of NUCB2A/nesfatin-1 in Ya-fish (Schizothorax prenanti)

The protein nucleobindin-2 (NUCB2) was identified over a decade ago and recently raised great interest as its derived peptide nesfatin-1 was shown to reduce food intake and body weight in rodents. However, the involvement of NUCB2 in feeding behavior has not well been studied in fish. In the present study, we characterized the structure, distribution, and meal responsive of NUCB2A/nesfatin-1 in Ya-fish (Schizothorax prenanti) for the first time. The full length cDNA of Ya-fish was 2140base pair (bp), which encoded a polypeptide of 487 amino acid residues including a 23 amino acid signal peptide. A high conservation in NUCB2 sequences was found in vertebrates, however the proposed propeptide cleavage site (Arg-Arg) conserved among other species is not present in Ya-fish NUCB2A sequence. Tissue distribution analysis revealed that Ya-fish NUCB2A mRNA was ubiquitously expressed in all test tissues, and abundant expression was detected in several regions including the hypothalamus, hepatopancreas, ovary and intestines. NUCB2A mRNA expression respond to feeding status change may vary and be tissue specific. NUCB2A mRNA levels significantly increased (P<0.05) in the hypothalamus and intestines after feeding and substantially decreased (P<0.01) during a week food deprivation in the hypothalamus. Meanwhile, NUCB2A mRNA in the hepatopancreas was significantly elevated (P<0.001) during food deprivation, and a similar increase was also found after short-time fasting. This points toward a potential hepatopancreas specific local role for NUCB2A in the regulation of metabolism during food deprivation. Collectively, these results provide the molecular and functional evidence to support potential anorectic and metabolic roles for NUCB2A in Ya-fish.

Increased food intake in growth hormone-transgenic common carp (Cyprinus carpio L.) may be mediated by upregulating Agouti-related protein (AgRP)

In fish, food intake and feeding behavior are crucial for survival, competition, growth and reproduction. Growth hormone (GH)-transgenic common carp exhibit an enhanced growth rate, increased food intake and higher feed conversion rate. However, the underlying molecular mechanisms of feeding regulation in GH-transgenic (TG) fish are not clear. In this study, we observed feeding behavior of TG and non-transgenic (NT) common carp, and analyzed the mRNA expression levels of NPY, AgRP I, orexin, POMC, CCK, and CART I in the hypothalamus and telencephalon after behavioral observation. We detected similar gene expression levels in the hypothalamus of TG and NT common carp, which had been cultured in the field at the same age. Furthermore, we tested the effects of GH on hypothalamus fragments in vitro to confirm our findings. We demonstrated that TG common carp displayed increased food intake and reduced food consumption time, which were associated with a marked increase in hypothalamic AgRP I mRNA expression. Our results suggest that elevated GH levels may influence food intake and feeding behavior by upregulating the hypothalamic orexigenic factor AgRP I in GH-transgenic common carp.

Gene amplification and functional diversification of melanocortin 4 receptor at an extremely polymorphic locus controlling sexual maturation in the platyfish

In two swordtail species of the genus Xiphophorus, the onset of puberty has been shown to be modulated at the P locus by sequence polymorphism and gene copy-number variation affecting the type 4 melanocortin hormone receptor Mc4r. The system works through the interaction of two allelic types, one encoding wild type and the other dominant-negative receptors. We have analyzed the structure and evolution of the P locus in the platyfish Xiphophorus maculatus, where as many as nine alleles of P determining the onset of sexual maturity in males and females, fecundity in females, and adult size in males are located on both the X and Y chromosomes in a region linked to the master sex-determining locus. In this species, mc4r has been amplified to up to 10 copies on both the X and Y chromosomes through recent large serial duplications. Subsequently, mc4r paralogues have diverged considerably into many different subtypes. Certain copies have acquired new untranslated regions through genomic rearrangements, and transposable element insertions and other mutations have accumulated in promoter regions, possibly explaining observed deviations from the classical mc4r transcriptional pattern. In the mc4r-coding sequence, in-frame insertions and deletions as well as nonsense and missense mutations have generated a high diversity of Mc4r-predicted proteins. Most of these variants are expressed in embryos, adults, and/or tumors. Functional receptor characterization demonstrated major divergence in pharmacological behavior for Mc4r receptors encoded by different copies of platyfish mc4r, with differences in constitutive activity as well as binding and stimulation by hormones. The high degree of allelic and copy-number variation observed between individuals can explain the high level of polymorphism for sexual maturation, fecundity, and body size in the platyfish: multiple combinations of Mc4r variants with different biochemical properties might interact to modulate the melanocortin signaling that regulates the hypothalamus-pituitary-gonadal axis.

The effects of amphetamine injections on feeding behavior and the brain expression of orexin, CART, tyrosine hydroxylase (TH) and thyrotropin releasing hormone (TRH) in goldfish (Carassius auratus)

In this study, the effects of peripheral (intraperitoneal) injections of D-amphetamine on feeding behavior were assessed in goldfish. Compared with the saline-injected group, amphetamine injections decreased food intake at doses ranging from 1 to 75 μg/g, but not 0.5 μg/g, but increased locomotor behavior, as indicated by the increased number of total feeding and non-feeding acts, at doses ranging from 2.5 to 25 μg/g. Amphetamine at high doses inhibited both food intake (at 25, 50 and 75 μg/g) and feeding behavior (at 75 μg/g). In the hypothalamus, the expression of orexin was down-regulated, and both CART 1 and CART 2 expressions were up-regulated in amphetamine-treated fish (50 μg/g) as compared to saline-injected fish, but amphetamine treatment had no effect on either hypothalamic TH or TRH expression. In the telencephalon, amphetamine treatment (50 μg/g) up-regulated CART 1, CART 2 and TH mRNA expressions but had no effect on either orexin or TRH. Our results suggest that, as in mammals, the orexin, CART and TH systems might be involved in amphetamine-induced feeding/locomotor responses in goldfish.

Changes in expression of appetite-regulating hormones in the cunner (Tautogolabrus adspersus) during short-term fasting and winter torpor

Feeding in vertebrates is controlled by a number of appetite stimulating (orexigenic, e.g., orexin and neuropeptide Y, NPY) and appetite suppressing (anorexigenic, e.g., cholecystokinin, CCK and cocaine- and amphetamine-regulated transcript, CART) hormones. Cunners (Tautogolabrus adspersus) survive the winter in shallow coastal waters by entering a torpor-like state, during which they forgo feeding. In order to better understand the mechanisms regulating appetite/fasting in these fish, quantitative real-time PCR was used to measure transcript expression levels of four appetite-regulating hormones: NPY, CART, orexin and CCK in the forebrain (hypothalamus and telencephalon) and CCK in the gut of fed, short-term summer fasted, and natural winter torpor cunners. Summer fasting induced a decrease in hypothalamic orexin levels and telencephalon NPY, CART and CCK mRNA levels. All brain hormone mRNA levels decreased during natural torpor as compared to fed summer fish. In the gut, CCK expression levels decreased during summer fasting. These results indicate that, in cunner, orexin, NPY, CART and CCK may play a role in appetite regulation and might mediate different physiological responses to short-term summer fasting and torpor-induced long-term fasting.

Characterization, tissue distribution and regulation of agouti-related protein (AgRP) in a cyprinid fish (Schizothorax prenanti)

Agouti-related protein (AgRP) is an important neuropeptide involved in the regulation of feeding in both mammals and fish. In this study, we have cloned the full-length cDNA sequence for AgRP in a cyprinid fish (Schizothorax prenanti). The AgRP gene, encoding 126-amino acids, was strongly expressed in the brain. The AgRP gene was detected in embryos at developmental stages. Further, its mRNA was detectable in unfertilized eggs. An experiment was conducted to determine the expression profile of AgRP during short-term and long-term fasting of the hypothalamus. The expression level of AgRP in unfed fish was significantly increased at 3 and 4h post-fasting than in fed fish but did not affect AgRP mRNA expression after 14 days fasting. Overall, our results suggest that AgRP is a conserved peptide that might be involved in the regulation of short-term feeding and other physiological function in Schizothorax prenanti.

A consensus linkage map provides insights on genome character and evolution in common carp (Cyprinus carpio L.)

Common carp (Cyprinus carpio L.) is cultured worldwide and is a major contributor to the world's aquaculture production. The common carp has a complex tetraploidized genome, which may historically experience additional whole genome duplication than most other Cyprinids. Fine maps for female and male carp were constructed using a mapping panel containing one F1 family with 190 progeny. A total of 1,025 polymorphic markers were used to construct genetic maps. For the female map, 559 microsatellite markers in 50 linkage groups cover 3,468 cM of the genome. For the male map, 383 markers in 49 linkage groups cover 1,811 cM of the genome. The consensus map was constructed by integrating the new map with two published linkage maps, containing 732 markers and spanning 3,278 cM in 50 linkage groups. The number of consensus linkage groups corresponds to the number of common carp chromosomes. A significant difference on sex recombinant rate was observed that the ratio of female and male recombination rates was 4.2:1. Comparative analysis was performed between linkage map of common carp and genome of zebrafish (Danio rerio), which revealed clear 2:1 relationship of common carp linkage groups and zebrafish chromosomes. The results provided evidence that common carp did experienced a specific whole genome duplication event comparing with most other Cyprinids. The consensus linkage map provides an important tool for genetic and genome study of common carp and facilitates genetic selection and breeding for common carp industry.