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

Towards a comprehensive understanding of the muscle proteome in Schizothorax labiatus: Insights from seasonal variations, metabolic responses, and reproductive signatures in the River Jhelum

Proteomics is a very advanced technique used for defining correlations, compositions and activities of hundreds of proteins from organisms as well as effectively used in identifying particular proteins with varying peptide lengths and amino acid counts. In the present study, an endeavour has been put forth to create muscle proteome expression of snow trout, Schizothorax labiatus. Liquid chromatography-mass spectrometry (LC-MS) using label free quantification (LFQ) technique has extensively been carried out to explore changes in protein metabolism and its composition to discriminate across species, clarify functions and pinpoint protein biomarkers from organisms. In LFQ technique, the abundances of proteins are determined based on the signal intensities of their corresponding peptides in mass spectrometry. The main benefit of using this method is that it doesn't require pre-labelling proteins with isotopic tags, which streamlines the experimental procedure and gets rid of any bias that might have been caused by the labelling process. LFQ techniques frequently offer a wider dynamic range, making it possible to detect and quantify proteins over a broad range of abundances obtained from the complex biological materials including fish muscle. The results of proteomic analysis could provide an insight in understanding about how various proteins are expressed in response to environmental challenges. For proteomic study, two different weight groups of S. labiatus were taken from River Jhelum based on biological, physiological and logistical factors. These groups corresponded to different life stages, such as younger size and adults/brooders in order to capture potential variations in the muscle proteome related to growth and development. The proteomic analysis of S. labiatus depicted that an overall of 220 proteins in male and 228 in female fish of group 1 were noted. However, when male and female S. labiatus were examined based on spectral count and peptide abundance using ProteinLynx Global Software, a total of 10 downregulated and 32 upregulated proteins were found. In group 2 of S. labiatus, a total of 249 proteins in male and 301 in female fish were documented. When the two genders of S. labiatus were likened to one another by LFQ technique, a total of 41 downregulated and 06 upregulated proteins were identified. The variability in the protein numbers between two fish weight groups reflected biological differences, influenced by factors such as age, developmental stages, physiological condition and reproductive activities. During the study, it was observed that S. labiatus exhibited downregulated levels of proteins that were involved in feeding and growth. The contributing factors to this manifestation could be explained by lower feeding and metabolic activity of fish and decreased food availability during winter in River Jhelum. Contrarily, the fish immune response proteins were found to be significantly over-expressed in S. labiatus, indicating that the environment was more likely to undergo increased microbial infection, pollution load and anthropogenic activities. In addition, it was also discovered that there was an upregulated expression of the reproductive proteins in S. labiatus, which could be linked to the fish's pre-spawning time as the fish used in this study was collected in the winter season which is the pre-spawning period of the fish. Therefore, the present study would be useful in obtaining new insights regarding the molecular makeup of species, methods of adaptation and reactions to environmental stresses. This information contributes to our understanding of basic science and may have applications in environmental monitoring, conservation and preservation of fish species.

Effects of Five Lipid Sources on Growth, Hematological Parameters, Immunity and Muscle Quality in Juvenile Largemouth Bass (Micropterus salmoides)

This study investigated the effects of fish oil (FO), soybean oil (SO), rapeseed oil (RO), peanut oil (PO) and lard oil (LO) on growth, immunity and muscle quality in juvenile largemouth bass. After 8 weeks, the results showed that FO and RO could increase weight gain and serum alkaline phosphatase and apelin values compared with LO (p < 0.05). Except lower crude lipid contents, higher amounts of n-3 polyunsaturated fatty acids (15.83% and 14.64%) were present in the dorsal muscle of the FO and RO groups. Meanwhile, FO and RO could heighten mRNA levels of immune defense molecules (lysozyme, hepcidin, and transforming growth factor β1) compared with PO (p < 0.05). While SO could increase potential inflammatory risk via rising counts of white blood cells, platelets, neutrophils and monocytes, and mRNA levels of interleukins (IL-1β, IL-8, IL-12 and IL-15), FO and RO could improve hardness, chewiness and springiness through increasing amounts of hydroxyproline, collagen and lysyl oxidase, and mRNA levels of collagen 1α2 and prolyl hydroxylase in the fish dorsal muscle. Moreover, FO and RO could improve firmness through increasing glycogen and glycogen synthase 1 levels when compared with LO (p < 0.05). Therefore, these results could provide dietary lipid source references during the feeding process of adult largemouth bass.

Metabolic rates, feed intake, appetite control, and gut transit of clownfish Amphiprion ocellaris exposed to increased temperature and limited feed availability

Episodes of elevated temperature, combined with lower feed availability, are among the predicted scenarios of climate change representing a challenge for coral reef fish. We investigated the response of clownfish (Amphiprion ocellaris) to a scenario in which it received a single meal to satiety after 48 h fasting at 32 °C (climate change scenario) and 28 °C (control). We analysed the metabolic rate (MR), feed intake, gut transit, and expression of selected brain neuropeptides and one receptor believed to be involved in appetite control. Fish at 32 °C ingested 17.9% less feed and had a faster gut transit than did fish at 28 °C. MR in the unfed fish was 31% higher at 32 °C compared to 28 °C. In the fed fish, postprandial MR at 28 °C was 30% higher compared to that of unfed fish, while at 32 °C it was only 15% higher. The expression of agrp1 did not differ between unfed and refed fish. The levels of both pomca and mc4r increased immediately after the meal and subsequently declined, suggesting a possible anorexic role for these genes. Notably, this pattern was accelerated in fish kept at 32 °C compared with that in fish kept at 28 °C. The dynamics of these changes in expression correspond to a faster gut transition of ingested feed at elevated temperatures. For both agrp2 and pomcb there was an increase in expression following feeding in fish maintained at 32 °C, which was not observed in fish kept at 28 °C. These results suggest that low feed availability and elevated temperature stimulate anorexigenic pathways in clownfish, resulting in significantly lower feed intake despite the temperature-induced increase in metabolic rate. This may be a mechanism to ameliorate the decrease in aerobic scope that results from higher temperatures.

Response of the thyroid axis and appetite-regulating peptides to fasting and overfeeding in goldfish (Carassius auratus)

The thyroid axis is a major regulator of metabolism and energy homeostasis in vertebrates. There is conclusive evidence in mammals for the involvement of the thyroid axis in the regulation of food intake, but in fish, this link is unclear. In order to assess the effects of nutritional status on the thyroid axis in goldfish, Carassius auratus, we examined brain and peripheral transcripts of genes associated with the thyroid axis [thyrotropin-releasing hormone (TRH), thyrotropin-releasing hormone receptors (TRH-R type 1 and 2), thyroid stimulating hormone beta (TSHβ), deiodinase enzymes (DIO2, DIO3) and UDP-glucoronsyltransferase (UGT)] and appetite regulators [neuropeptide Y (NPY), proopiomelanocortin (POMC), agouti-related peptide (AgRP) and cholecystokinin (CCK)] in fasted and overfed fish for 7 and 14 day periods. We show that the thyroid axis responds to overfeeding, with an increase of brain TRH and TSHβ mRNA expression after 14 days, suggesting that overfeeding might activate the thyroid axis. In fasted fish, hepatic DIO3 and UGT transcripts were downregulated from 7 to 14 days, suggesting a time-dependent inhibition of thyroid hormone degradation pathways. Nutritional status had no effect on circulating levels of thyroid hormone. Central appetite-regulating peptides exhibited temporal changes in mRNA expression, with decreased expression of the appetite-inhibiting peptide POMC from 7 to 14 days for both fasted and overfed fish, with no change in central NPY or AgRP, or intestinal CCK transcript expression. Compared to control fish, fasting increased AgRP mRNA expression at both 7 and 14 days, and POMC expression was higher than controls only at 7 days. Our results indicate that nutritional status time-dependently affects the thyroid axis and appetite regulators, although no clear correlation between thyroid physiology and appetite regulators could be established. Our study helps to fill a knowledge gap in current fish endocrinological research on the effects of energy balance on thyroid metabolism and function.

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.

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.

Hypothalamic agrp and pomc mRNA Responses to Gastrointestinal Fullness and Fasting in Atlantic Salmon (Salmo salar, L.)

The orexigenic agouti-related protein (AgRP) and the anorexigenic pro-opiomelanocortin (POMC) are crucial players in the control of feed intake in vertebrates, yet their role in teleosts has not been fully established. Triplicate groups of Atlantic salmon (Salmo salar) post smolts were subjected to (1) fasting for 3 days (fast) and (2) normal feeding (fed), resulting in a significant (p < 0.05) upregulation of hypothalamic agrp1 transcripts levels in the fast group. Moreover, the mRNA abundance of agrp1 was significantly (p < 0.05) correlated with the stomach dry weight content. Corresponding inverse patterns were observed for pomca2, albeit not statistically significant. No significant differences were found for the other paralogues, agrp2 and pomca1 and b, between fed and fast groups. The significant correlation between stomach fullness and agrp1 mRNA expression suggests a possible link between the stomach filling/distension and satiety signals. Our study indicates that hypothalamic agrp1 acts as an orexigenic signal in Atlantic salmon.

Transcriptional study of appetite regulating genes in the brain of zebrafish (Danio rerio) with impaired leptin signalling

The hormone leptin is a key regulator of body weight, food intake and metabolism. In mammals, leptin acts as an anorexigen and inhibits food intake centrally by affecting the appetite centres in the hypothalamus. In teleost fish, the regulatory connections between leptin and other appetite-regulating genes are largely unknown. In the present study, we used a zebrafish mutant with a loss of function leptin receptor to investigate brain expression patterns of 12 orexigenic and 24 anorexigenic genes under different feeding conditions (normal feeding, 7-day fasting, 2 and 6-hours refeeding). Expression patterns were compared to wild-type zebrafish, in order to identify leptin-dependent differentially expressed genes under different feeding conditions. We provide evidence that the transcription of certain orexigenic and anorexigenic genes is influenced by leptin signalling in the zebrafish brain. We found that the expression of orexigenic genes was not affected by impaired leptin signalling under normal feeding conditions; however, several orexigenic genes showed increased transcription during fasting and refeeding, including agrp, apln, galr1a and cnr1. This suggests an inhibitory effect of leptin signal on the transcription of these orexigenic genes during short-term fasting and refeeding in functional zebrafish. Most pronounced effects were observed in the group of anorexigenic genes, where the impairment of leptin signalling resulted in reduced gene expression in several genes, including cart family, crhb, gnrh2, mc4r, pomc and spx, in the control group. This suggests a stimulatory effect of leptin signal on the transcription of these anorexigenic genes under normal feeding condition. In addition, we found multiple gain and loss in expression correlations between the appetite-regulating genes, in zebrafish with impaired leptin signal, suggesting the presence of gene regulatory networks downstream of leptin signal in zebrafish brain. The results provide the first evidence for the effects of leptin signal on the transcription of various appetite-regulating genes in zebrafish brain, under different feeding conditions. Altogether, these transcriptional changes suggest an anorexigenic role for leptin signal, which is likely to be mediated through distinct set of appetite-regulating genes under different feeding conditions.

Effect of agmatine on food intake in mandarin fish (Siniperca chuatsi)

Agmatine, an endogenous biogenic amine, is considered to be a central neurotransmitter. And it plays an important role in mammal feeding behavior. However, there were few studies on the effect of agmatine on feeding behavior in fishes. Here, we investigated the impact of intracerebroventricular (ICV) injections of agmatine (1.25-20 nmol/fish) on food intake in mandarin fish (Siniperca chuatsi). At 1-h post-injection, food intake showed a significant decrease in agmatine-treated fishes compared with the saline treated. Furthermore, the food intake in agmatine treatment mostly did not differ from that in saline treatment at 4--24-h post-injection as well as the results of genes expression of neuropeptide Y (NPY), agouti-regulated peptide (AgRP), and anorexigenic melanocortin 4 receptor (MC4R). In accordance with the insulin level increasing in liver, the gene expression of insulin receptor substrate (IRS2) was significantly higher in agmatine treatment compared to saline treatment at 1-h post-injection. Thus, the anorexigenic effect of agmatine is likely to decrease NPY and AgRP expression levels and increase MC4R and IRS2 levels which was coupled with stimulation of insulin secretion. Although these initial findings are limited in dose, the data firstly provides evidence for the anorectic effects of agmatine in fish.

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.

Characterization, tissue distribution of apela and periprandial, fasting and refeeding changes of apela mRNA in Siberian sturgeon Acipenser baerii

Apela identified from zebrafish Danio rerio for the first time in 2013 is a novel endogenous peptide ligand for the apelin receptor. To study the role of apela in regulating fish feeding, the complementary (c) DNA sequence of apela of Siberian sturgeon Acipenser baerii was cloned for the first time. The apela cDNA fragment of 836 bp was obtained by cloning. The open reading frame (ORF) of apela was 165 bp encoding a 54 amino acid, including 22 amino acids signal peptide and two proteolytic sites. Phylogenetic tree analysis showed that A. baerii apela was clustered with mammalian and amphibian sequences. A. baerii apela messeger (m)RNA was widely distributed in 11 tissues related to feeding, with high expressions in brain, oesophagus and stomach, especially in the brain. The level of apela mRNA in brain increased significantly after feeding. On the first day of fasting, apela expression in brain was significantly lower than that of the fed group, but after fasting for 3-15 days, the expression of apela in A. baerii brain was significantly higher than that in the fed group. After refeeding apela mRNA expression was obviously reduced. These results suggest that apela plays a bidirectional role in feeding regulation of A. baerii, which may serve as a short-term satiation factor and a long-term hunger factor.

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.

The evidence of apelin has the bidirectional effects on feeding regulation in Siberian sturgeon (Acipenser baerii)

Apelin is a peptide, mainly produced in the brain, which participates in several physiologic effects. However, knowledge about the mechanism of appetite regulation in teleosts, including the role of apelin is not well understood. The aim of this study is to explore the effect of feeding status on the expression of apelin mRNA in the whole brain and the effects of injection of apelin on food intake in Siberian sturgeon (Acipenser baerii). In this study, we first cloned the apelin cDNA sequence of the Siberian sturgeon. We obtained a 1046-bp cDNA fragment, including a 237-bp open reading frame (ORF) that encoded 78 amino acids. Apelin was widely distributed in 11 tissues related to feeding regulation, with the highest expression in thewhole brain, followed by the spleen and trunk kidney. In addition, we measured the effects of periprandial (preprandial and postprandial) change, fasting and re-feeding on apelin mRNA expression in whole brain. The level of apelin mRNA was significantly decreased 1h after feeding. The results of the fasting experiment showed that the expression of apelin mRNA in the brain was significantly reduced after 1day of fasting but consistently increased throughout the 15-day food deprivation period. When the 15-day fasted fish were re-fed, apelin mRNA expression in the brain was significantly increased as compared to that of the control. These results suggest that apelin may play a bidirectional role in the regulation of food intake in the Siberian sturgeon. In order to further examine the effect of apelin on feeding regulation in Siberian sturgeons, acute and chronic intraperitoneal (i.p.) injection experiments were performed and food intakes were recorded. Results showed that acute i.p. injection of apelin-13 reduced food intake, however, chronic i.p. injection apelin-13 increased the food intake for 7days in Siberian sturgeons. In conclusion, our results show that apelin has a bidirectional effect on feeding regulation in Siberian sturgeons by acting as a satiety factor in short-term feeding regulation and a starvation factor in long-term feeding regulation.

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.

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.

Profiling of microRNAs in AML cells following overexpression or silencing of the VEGF gene

Acute myeloid leukemia (AML) is a disease of the hematopoietic progenitor cells associated with heterogeneous clonal proliferation. Vascular endothelial growth factor (VEGF) and its receptors play important roles in the regulation of angiogenesis during physiological and pathological processes. It is thought that AML cells have an autocrine VEGF pathway that contributes to the development and progression of AML. In addition, growing evidence has suggested that numerous microRNAs are involved in AML. The present study aimed to investigate the relationship between VEGF dysregulation and microRNA profiles in AML cells and patients. VEGF-overexpressing and VEGF-knockdown leukemia cells were constructed and changes in the patterns of microRNA expression were analyzed using a microRNA array. Subsequently, mononuclear cells from the blood of patients with AML showing high or low expression levels of VEGF were obtained and were used to assess the patterns of microRNA expression by reverse transcription-quantitative polymerase chain reaction. The results of the present study suggested that downregulation of VEGF markedly altered the profile of microRNAs in AML cells, while upregulation of VEGF did not. Examination of clinical samples from patients with AML showed that several microRNAs were closely associated with the expression level of VEGF, including miR-20a, miR-93, miR-16-5p, miR-17-5p, miR-124-5p and miR-17-3p. These results suggested that VEGF may be a pivotal protein that can both receive and initiate signals in leukemia cells.

Intraperitoneal injection urocortin-3 reduces the food intake of Siberian sturgeon (Acipenser baerii)

Urocortin-3 (UCN3), one of the corticotropin releasing factor (CRF) family peptides, which was discovered in 2001, has a variety of biological functions. However, the researches of UCN3 in fish were scarce. In order to understand whether UCN3 play a role in regulating food intake in fish, we first cloned the ucn3 cDNAs sequence of Siberian sturgeon (Acipenser baerii Brandt), and investigated the ucn3 mRNA levels in 11 tissues. The Siberian sturgeon ucn3 cDNA sequence was 1044bp, including an open reading frame (ORF) of 447bp that encoded 148 amino acids with a mature peptide of 40 amino acids, a 5'-terminal untranslated region (5'-UTR) of 162bp and a 3'-terminal untranslated region (3'-UTR) of 435bp. The result of tissue distribution showed that ucn3 widely distributed in 11 tissues with highest expression in brain. We also assessed the effects of periprandial (pre- and post-feeding), fasting and re-feeding on ucn3 mRNAs abundance in brain. The results showed the expression of ucn3 mRNA in brain was significantly elevated after feeding, decreased after fasting 17 days and increased after re-feeding. To further investigate the food intake role of UCN3 in Siberian sturgeon, we performed intraperitoneal (i.p.) injection of Siberian sturgeon UCN3 (SsUCN3) with three doses (60, 120 or 240ng/g) and recorded the food intake. Acute and chronic i.p. injection SsUCN3 reduced the food intake in a dose-dependent pattern. In conclusion, this study indicates that SsUCN3 acts as a satiety factor to inhibit the food intake of Siberian sturgeon.

Molecular characterization of melanin-concentrating hormone (MCH) in Schizothorax prenanti: cloning, tissue distribution and role in food intake regulation

Melanin-concentrating hormone (MCH) is a crucial neuropeptide involved in various biological functions in both mammals and fish. In this study, the full-length MCH cDNA was obtained from Schizothorax prenanti by rapid amplification of cDNA ends polymerase chain reaction. The full-length MCH cDNA contained 589 nucleotides including an open reading frame of 375 nucleotides encoding 256 amino acids. MCH mRNA was highly expressed in the brain by real-time quantitative PCR analysis. Within the brain, expression of MCH mRNA was preponderantly detected in the hypothalamus. In addition, the MCH mRNA expression in the S. prenanti hypothalamus of fed group was significantly decreased compared with the fasted group at 1 and 3 h post-feeding, respectively. Furthermore, the MCH gene expression presented significant increase in the hypothalamus of fasted group compared with the fed group during long-term fasting. After re-feeding, there was a dramatic decrease in MCH mRNA expression in the hypothalamus of S. prenanti. The results indicate that the expression of MCH is affected by feeding status. Taken together, our results suggest that MCH may be involved in food intake regulation in S. prenanti.

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.

Molecular and physiological evidences for the role in appetite regulation of apelin and its receptor APJ in Ya-fish (Schizothorax prenanti)

Apelin is a recently discovered peptide produced by several tissues with diverse physiological actions mediated by its receptor APJ. In order to better understand the role of apelin in the regulation of appetite in fish, we cloned the cDNAs encoding apelin and APJ, and investigated their mRNA distributions in Ya-fish (Schizothorax prenanti) tissues. We also assessed the effects of different nutritional status on apelin and APJ mRNAs abundance. Apelin and APJ mRNAs were ubiquitously expressed in all tissues tested, relatively high expression levels were detected in the heart, spleen, hypothalamus and kidney. Short-term fasting significant increased APJ mRNA expression, but no significant difference between fasted fish and fed control on 5- and 7-day. Meanwhile, apelin mRNA expression consistently increased during the 7-day food deprivation. In order to further characterize apelin in fish, we performed intraperitoneal (i.p.) injection of apelin-13 and examined food intake of the injected fish. Apelin injected at a dose of 100 ng/g body weight induced a significant increase in food intake compared to saline injected fish. Our results suggest that apelin acts as an orexigenic factor in Ya-fish. Their widespread distributions also suggest that apelin and APJ might play multiple physiological regulating roles in fish.

Schizothorax prenanti corticotropin-releasing hormone (CRH): molecular cloning, tissue expression, and the function of feeding regulation

Corticotropin-releasing hormone (CRH) is a potent mediator of endocrine, autonomic, behavioral, and immune responses to stress. For a better understanding of the structure and function of the CRH gene and to study its effect on feeding regulation in cyprinid fish, the cDNA of the CRH gene from the brain of Schizothorax prenanti was cloned and sequenced. The full-length CRH cDNA consisted of 1,046 bp with an open reading frame of 489 bp encoding a protein of 162 amino acids. Real-time quantitative PCR analyses revealed that CRH was widely expressed in central and peripheral tissues. In particular, high expression level of CRH was detected in brain. Furthermore, CRH mRNA expression was examined in different brain regions, especially high in hypothalamus. In addition, there was no significant change in CRH mRNA expression in fed group compared with the fasted group in the S. prenanti hypothalamus during short-term fasting. However, CRH gene expression presented significant decrease in the hypothalamus in fasted group compared with the fed group (P < 0.05) on day 7; thereafter, re-feeding could lead to a significant increase in CRH mRNA expression in fasted group on day 9. The results suggest that the CRH may play a critical role in feeding regulation in S. prenanti.

Characterization of Schizothorax prenanti cgnrhII gene: fasting affects cgnrhII expression

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

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.

Cloning, distribution and effects of fasting status of melanocortin 4 receptor (MC4R) in Schizothorax prenanti

Melanocortin 4 receptor (MC4R) has an important role in the regulation of energy homeostasis in both mammals and fish. In this study, MC4R was characterized in S. prenanti (Schizothorax prenanti) and designated as SpMC4R. SpMC4R cDNA is composed of 1004 nucleotides with a 978 nucleotide open reading frame encoding a protein of 326 amino acids. The SpMC4R contained predicted regions that were structural features of MCR subtypes of vertebrates. In addition, phylogenetic analyses suggested that S. prenanti MC4R was closely related to fish MC4Rs. The SpMC4R mRNA was detected in embryos at developmental stages. Further, its mRNA was detectable in unfertilized eggs. Using real-time RT-PCR, MC4R is widely expressed, with highest levels of expression in brain and ovary. An experiment was conducted to determine the expression profile of MC4R during short-term and long-term fasting of the brain. The expression level of MC4R in unfed fish was significantly increased at 6, 9 and 24h post-fasting (hpf) and 14days fasting than in fed fish, this suggests that MC4R is conserved peptide that might be involved in the regulation of food intake and other physiological function in S. prenanti.