Molecular cloning, tissue distribution, and effect of fasting and refeeding on the expression of neuropeptide Y in Channa argus

Tissue distribution of appetite regulation genes and their expression in the Amazon fish Colossoma macropomum exposed to climate change scenario

Climate change leads to an increase in water acidification and temperature, two environmental factors that can change fish appetite and metabolism, affecting fish population in both wild and aquaculture facilities. Therefore, our study tested if climate change affects gene expression levels of two appetite-regulating peptides - Neuropeptide Y (NPY) and Cholecystokinin (CCK) - in the brain of tambaqui, Colossoma macropomum. Additionally, we show the distribution of these genes throughout the body. Amino acid sequences of CCK and NPY of tambaqui showed high similarity with other Characiformes, with the closely related order Cypriniformes, and even with the more distantly related order Salmoniformes. High apparent levels of both peptides were expressed in all brain areas, while expression levels varied for peripheral tissues. NPY and CCK mRNA were detected in all peripheral tissues but cephalic kidney for CCK. As for the effects of climate change, we found that fish exposed to extreme climate scenario (800 ppm CO2 and 4.5 °C above current climate scenario) had higher expression levels of NPY and lower expression levels of CCK in the telencephalon. The extreme climate scenario also increased food intake, weight gain, and body length. These results suggest that the telencephalon is probably responsible for sensing the metabolic status of the organism and controlling feeding behavior through NPY, likely an orexigenic hormone, and CCK, which may act as an anorexigenic hormone. To our knowledge, this is the first study showing the effects of climate change on the endocrine regulation of appetite in an endemic and economically important fish from the Amazon. Our results can help us predict the impact of climate change on both wild and farmed fish populations, thus contributing to the elaboration of future policies regarding their conservation and sustainable use.

Neuropeptide Y in Spotted Scat (Scatophagus Argus), Characterization and Functional Analysis towards Feed Intake Regulation

Neuropeptide Y (Npy) is an intricate neuropeptide regulating numerous physiological processes. It is a highly conserved peptide known to improve feed intake in many vertebrates, including fishes. To enlighten the mechanism of Npy in spotted scat feed intake control, we cloned and identified the Npy cDNA sequence. We further examined its expression in some tissues and explored its expression effects at different time frames (hours and days). Here, we discovered that spotted scat Npy comprised a 300 bp open reading frame (ORF) and a 99 amino acid sequence. Npy was identified to be expressed in all tissues examined. Using in situ hybridization examination, we proved that npy has a wide expression in the brain of the spotted scat. Furthermore, the expression of npy in the hypothalamus significantly increased one hour after feeding (p < 0.05). Further, it was revealed that npy expression significantly increased in fish that were fasted for up to 5 days and significantly increased after refeeding from the 8th to the 10th day. This suggests that Npy is an orexigenic peptide, and hence, it increases food intake and growth in the spotted scat. Additionally, results from in vitro and in vivo experiments revealed that Npy locally interacts with other appetite-regulating peptides in the spotted scat hypothalamus. This research aimed to set a fundamental study in developing the feed intake regulation, improving growth and reproduction, which is significant to the aquaculture industry of the spotted scat.

Molecular cloning and tissue distribution of the leptin gene in gibel carp (Carassius auratus gibelio): Regulation by postprandial and long-term fasting treatment

Leptin is a multifunctional hormone that serves as a feeding regulator in mammals. However, the effect of leptin on fish remains unclear. We sequenced the leptin gene from gibel carp (Carassius auratus gibelio) and designated it gLEP. The length of the gLEP cDNA sequence was 562 bp, including an open reading frame (ORF) of 516 bp. The ORF putatively encodes a peptide of 171 amino acids, including a signal peptide of 20 amino acids. gLEP shared low primary amino acid sequence homology with leptin genes in vertebrates, whereas three-dimensional (3D) structural modeling revealed strong identity with the structures in other vertebrates. gLEP mRNA was widely distributed in all of the tissue that we examined, with the highest levels of expression in the hepatopancreas. Hepatopancreas gLEP mRNA expression levels showed no changes following postprandial treatment. However, hepatopancreas gLEP mRNA expression levels greatly decreased (P < 0.05) after fasting but substantially increased (P < 0.05) after refeeding in the long-term fasting treatment. In summary, these results indicate that leptin expression could be influenced by the regulation of food intake. These results provide the initial step toward elucidating the appetite regulatory systems associated with leptin in gibel carp.

Effects of starvation and refeeding on growth performance, appetite, growth hormone-insulin-like growth factor axis levels and digestive function of Acipenser dabryanus

The aim of this study was to explore the effects and mechanisms of different starvation treatments on the compensatory growth of Acipenser dabryanus. A total of 120 fish (60·532 (sem 0·284) g) were randomly assigned to four groups (fasting 0, 3, 7 or 14 d and then refed for 14 d). During fasting, middle body weight decreased significantly with prolonged starvation. The whole-body and muscle composition, serum biochemical indexes, visceral indexes and digestive enzyme activities had been effected with varying degrees of changes. The growth hormone (GH) level in serum was significantly increased in 14D; however, insulin-like growth factor-1 (IGF-1) showed the opposite trend. The neuropeptide Y (npy) mRNA level in brain was significantly improved in 7D; peptide YY (pyy) mRNA level in intestine was significantly decreased during fasting. After refeeding, the final body weight, percentage weight gain, specific growth rate, feed intake, feed efficiency and protein efficiency ratio showed no difference between 0D and 3D. The changes of whole-body and muscle composition, serum biochemical indexes, visceral indexes and digestive enzyme activities had taken place in varying degrees. GH levels in 3D and 7D were significantly higher than those in the 0D; the IGF-1 content decreased significantly during refeeding. There was no significant difference in npy and pyy mRNA levels. These results indicated that short-term fasting followed by refeeding resulted in full compensation and the physiological and biochemical effects on A. dabryanus were the lowest after 3 d of starvation and 14 d of refeeding. Additionally, compensation in A. dabryanus may be mediated by appetite genes and GH, and the degree of compensation is also affected by the duration of starvation.

Neuroendocrine Mechanisms Underlying Non-breeding Aggression: Common Strategies Between Birds and Fish

Aggression is an adaptive behavior that plays an important role in gaining access to limited resources. Aggression may occur uncoupled from reproduction, thus offering a valuable context to further understand its neural and hormonal regulation. This review focuses on the contributions from song sparrows (Melospiza melodia) and the weakly electric banded knifefish (Gymnotus omarorum). Together, these models offer clues about the underlying mechanisms of non-breeding aggression, especially the potential roles of neuropeptide Y (NPY) and brain-derived estrogens. The orexigenic NPY is well-conserved between birds and teleost fish, increases in response to low food intake, and influences sex steroid synthesis. In non-breeding M. melodia, NPY increases in the social behavior network, and NPY-Y1 receptor expression is upregulated in response to a territorial challenge. In G. omarorum, NPY is upregulated in the preoptic area of dominant, but not subordinate, individuals. We hypothesize that NPY may signal a seasonal decrease in food availability and promote non-breeding aggression. In both animal models, non-breeding aggression is estrogen-dependent but gonad-independent. In non-breeding M. melodia, neurosteroid synthesis rapidly increases in response to a territorial challenge. In G. omarorum, brain aromatase is upregulated in dominant but not subordinate fish. In both species, the dramatic decrease in food availability in the non-breeding season may promote non-breeding aggression, via changes in NPY and/or neurosteroid signaling.

Characterization of two kcnk3 genes in rabbitfish (Siganus canaliculatus): Molecular cloning, distribution patterns and their potential roles in fatty acids metabolism and osmoregulation

KCNK3 is a two-pore-domain (K_2P) potassium channel involved in maintaining ion homeostasis, mediating thermogenesis, controlling breath and modulating electrical membrane potential. Although the functions of this channel have been widely described in mammals, its roles in fishes are still rarely known. Here, we identified two kcnk3 genes from the euryhaline rabbitfish (Siganus canaliculatus), and their roles related to fatty acids metabolism and osmoregulation were investigated. The open reading frames of kcnk3a and kcnk3b were 1203 and 1176 bp in length, encoding 400 and 391 amino acids respectively. Multiple sequences alignment and phylogenetic analysis revealed that the two isotypes of kcnk3 were extensively presented in fishes. Quantitative real-time PCRs indicated that both genes were widely distributed in examined tissues but showed different patterns. kcnk3a primary distributed in adipose, eye, heart, and spleen tissues, while kcnk3b was mainly detectable in heart, kidney, muscle and spleen tissues. In vivo experiments showed that fish fed diets with fish oil as dietary lipid (rich in long chain polyunsaturated fatty acids, LC-PUFA) induced higher mRNA expression levels of kcnk3 genes in comparison with fish fed with plant oil diet at two different salinity environments (32 and 15‰). Meanwhile, the expression levels of kcnk3 genes were higher in seawater (32‰) than that in brackish water (15‰) when fishes were fed with both types of feeds. In vitro experiments with rabbitfish hepatocytes showed that LC-PUFA significantly improved hepatic kcnk3a expression level compared with treatment of linolenic acid. These results suggest that two kcnk3 genes are widely existed and they might be functionally related to fatty acids metabolism and osmoregulation in the rabbitfish.

Molecular characterization of two leptin genes and their transcriptional changes in response to fasting and refeeding in Northern snakehead (Channa argus)

Leptin has been proved to play critical roles in energy metabolism, body weight regulation, food intake, reproduction and immunity in mammals. However, its roles are still largely unclear in fish. Here, we report two leptin genes (lepA and lepB) from the Northern snakehead (Channa argus) and their transcriptions in response to different feeding status. The snakehead lepA is 781 bp in length and contains a 480 bp open reading frame (ORF) encoding a 159-aa protein, while the snakehead lepB is 553 bp in length and contains a 477 bp ORF encoding a 158-aa protein. Multi-sequences alignment, three-dimensional (3D) model prediction, syntenic and genomic comparison, and phylogenetic analysis confirm two leptin genes are widely existing in teleost. Tissue distribution revealed that the two leptin genes exhibit different patterns. In a post-prandial experiment, the hepatic lepA and brain lepB showed a similar transcription pattern. In a long-term (2-week) fasting and refeeding experiment, the hepatic lepA and brain lepB showed a similar transcription change pattern induced by food deprivation stimulation but differential changes after refeeding. These findings suggest snakehead lepA and lepB are differential both in tissue distribution and molecular functions, and they might play as an important regulator in energy metabolism and food intake in fish, respectively.

Characterization of two kcnk3 genes in Nile tilapia (Oreochromis niloticus): Molecular cloning, tissue distribution, and transcriptional changes in various salinity of seawater

As one important member of the two-pore-domain potassium channel (K_2P) family, potassium channel subfamily K member 3 (KCNK3) has been reported for thermogenesis regulation, energy homeostasis, membrane potential conduction, and pulmonary hypertension in mammals. However, its roles in fishes are far less examined and published. In the present study, we identified two kcnk3 genes (kcnk3a and kcnk3b) in an euryhaline fish, Nile tilapia (Oreochromis niloticus), by molecular cloning, genomic survey and laboratory experiments to investigate their potential roles for osmoregulation. We obtained full-length coding sequences of the kcnk3a and kcnk3b genes (1209 and 1173 bp), which encode 402 and 390 amino acids, respectively. Subsequent multiple sequence alignments, putative 3D-structure model prediction, genomic survey and phylogenetic analysis confirmed that two kcnk3 paralogs are widely presented in fish genomes. Interestingly, a DNA fragment inversion of a kcnk3a cluster was found in Cypriniforme in comparison with other fishes. Quantitative real-time PCRs demonstrated that both the tilapia kcnk3 genes were detected in all the examined tissues with a similar distribution pattern, and the highest transcriptions were observed in the heart. Meanwhile, both kcnk3 genes in the gill were proved to have a similar transcriptional change pattern in response to various salinity of seawater, implying that they might be involved in osmoregulation. Furthermore, three predicted transcription factors (arid3a, arid3b, and arid5a) of both kcnk3 genes also showed a similar pattern as their target genes in response to the various salinity, suggesting their potential positive regulatory roles. In summary, we for the first time characterized the two kcnk3 genes in Nile tilapia, and demonstrated their potential involvement in osmoregulation for this economically important fish.

Molecular cloning of two kcnk3 genes from the Northern snakehead (Channa argus) for quantification of their transcriptions in response to fasting and refeeding

Potassium channel subfamily K member 3 (KCNK3) has been reported to play important roles in membrane potential conduction, pulmonary hypertension and thermogenesis regulation in mammals. However, its roles remain largely unknown and scarce reports were seen in fish. In the present study, we for the first time identified two kcnk3 genes (kcnk3a and kcnk3b) from the carnivorous Northern snakehead (Channa argus) by molecular cloning and a genomic survey. Subsequently, their transcription changes in response to different feeding status were investigated. Full-length coding sequences of the kcnk3a and kcnk3b genes are 1203 and 1176 bp, encoding 400 and 391 amino acids, respectively. Multiple alignments, 3D-structure prediction and phylogenetic analysis further suggested that these kcnk3 genes may be highly conserved in vertebrates. Tissue distribution analysis by real-time PCR demonstrated that both the snakehead kcnk3s were widely transcribed in majority of the examined tissues but with different distribution patterns. In a short-term (24-h) fasting experiment, we observed that brain kcnk3a and kcnk3b genes showed totally opposite transcription patterns. In a long-term (2-week) fasting and refeeding experiment, we also observed differential change patterns for the brain kcnk3 genes. In summary, our findings suggest that the two kcnk3 genes are close while present different transcription responses to fasting and refeeding. They therefore can be potentially selected as novel target genes for improvement of production and quality of this economically important fish.

Role of Myeloperoxidase of northern snakehead (Channa argus) in Aeromonas veronii infection

Myeloperoxidase (MPO) is a ferrous lysosomal protein with many immune functions that belongs to the heme peroxidase enzyme. In this study, the functions of MPO in the northern snakehead (Channa argus) were investigated by cloning an MPO cDNA sequence with a full length of 3181 bp. Homology analysis showed that northern snakehead MPO gene had the highest (81%) homology with mandarin fish (Siniperca chuatsi). In healthy northern snakehead, the MPO gene was expressed in the head-kidney, kidney, heart, gill, spleen, liver, and muscles but not midgut. After the northern snakehead was infected with Aeromonas veronii, the MPO gene expression varied in different tissues with low level in spleen, liver, gill and muscle, fluctuated in kidney and head-kidney and showed high level in heart. The result indicated that MPO might play an important role in the antimicrobial immune response of the northern snakehead.

Cloning, expression profiling, and effects of fasting status on neuropeptide Y in Schizothorax davidi

To better comprehend the mechanism that neuropeptide Y (npy) regulates feeding in Schizothorax davidi, we cloned and identified the full-length cDNA sequence of the npy gene in this species using RACE technology. Subsequently, we explored the npy mRNA distribution in 18 tissues and investigated the expression of npy mRNA at postprandial and fasting stages. We found that the npy full-length cDNA sequence is 803 bp. Moreover, npy mRNAs extensively expressed in all detected tissues, with the highest expression in hypothalamus. In postprandial study, the expression of npy mRNA in the hypothalamus was significantly decreased after eating (p < 0.01). In addition, the expression of the npy gene was significantly increased on the fifth day after fasting (p < 0.05). However, after refeeding, the expression of the npy gene was decreased significantly on days 9, 11, and 14 (p < 0.01). Our research suggest that npy may have an orexigenic role in S. davidi. PRACTICAL APPLICATIONS: S. davidi, a coldwater fish native to China, has high economic value, and it has gained great popularity. To date, there is still no large-scale breeding of S. davidi in China. How to strengthen the production performance of S. davidi is a hot research area. Neuropeptide Y (NPY), a 36-amino-acid single-chain polypeptide, is one of the main appetite regulation factors. However, to date, no studies have reported on the biological function of npy in the feeding of S. davidi. In our study, we revealed that the trend of hypothalamic npy expression during the postprandial and fasting stages. The results suggested that npy might be an appetite-promoting factor in this species. Overall, we provide the theoretical basis for how to strengthen the production performance of S. davidi through appetite regulation.

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.

Complete mitochondrial genome of a kind of snakehead fish Channa siamensis and its phylogenetic consideration

The snakehead fish, Channa siamensis, belongs to the genus of Channa (perciformes: Channidae) and was first reported by Günther in 1861. Despite it has been described approximately for 15 decades, the genetic information is limited and the taxon status of this kind of fish is still unclear. The primary objective of this study is to get more genomic data and calculate the taxon location of this kind of fish. The next generation sequencing method was used to obtain the whole mitochondrial DNA information, and bioinformatic analysis was performed to investigate the evolutionary status and taxon location of C. siamensis. The circular mitochondrial DNA was 16,570 bp in length, and which showed typical piscine structure and arrangement. The overall nucleotide composition was 29.28% A, 24.72% T, 30.71% C, 15.29% G, with 54.1% AT, respectively. Phylogenetic analyses using concatenated amino acid and nucleotide sequences of the 13 protein-coding genes with two different methods (Maximum likelihood and Bayesian analysis) both highly supported C. siamensis belongs to the genus Channa and shows a close relationship with C. micropeltes. These data will provide more useful information for a better understanding of the mitochondrial genomic diversities and evolution in fish as well as novel genetic markers for studying population genetics and species identification.