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.

Characterization and evaluation of the tissue distribution of CRH, apelin, and GnRH2 reveal responses to feeding states in Schizothorax davidi.

Schizothorax davidi is a rare fish in Southwest China and is considered a promising species for aquaculture. Compared with other teleosts, little is known about the endocrine regulation of feeding in this species. In this study, we identified the CRH, apelin, and GnRH2 genes in S. davidi and assessed the effects of different energy statuses on CRH, apelin, and GnRH2 expression. Our results showed that the full-length cDNA sequences of CRH, apelin, and GnRH2 of S. davidi were 995, 905, and 669 bp long, respectively. Furthermore, CRH was mainly expressed in the hypothalamus, telencephalon, and myelencephalon; apelin was highly expressed in the spleen and heart; and GnRH2 mRNA was widely distributed in all examined tissues, with the highest level in the hypothalamus. Notably, the levels of CRH and GnRH2 increased in the hypothalamus at 1 h and 3 h post-feeding, while hypothalamic apelin levels decreased. Conversely, CRH and GnRH2 expression in the hypothalamus significantly decreased after fasting for 7 days and returned to the control levels after re-feeding for 3 or 5 days. In contrast, fasting increased apelin levels in the hypothalamus. Overall, this study suggests that CRH, apelin, and GnRH2 play critical roles in appetite regulation in S. davidi. These results provide an essential groundwork to elucidate the appetite regulatory systems in S. davidi as well as in other teleosts.

Effects of feeding status on nucb1 and nucb2A mRNA expression in the hypothalamus of Schizothorax davidi.

NUCB1 and NUCB2, two novel nucleobindins, have attracted extensive attention for their role in the appetite regulation in mammals. However, little is known about the appetite regulation of NUCB1 and NUCB2 in fish species. Therefore, we investigated the role of these peptides in the regulation of feeding in Schizothorax davidi (S. davidi). In this study, full-length cDNA sequences of nucb1 and nucb2A of S. davidi were obtained for the first time. Additionally, the tissue distribution and the effects of different energy status on nucb1 and nucb2A mRNAs abundance were assessed, showing that nucb1 and nucb2A are widely distributed in 18 detected tissues, with the highest expression in the cerebellum. The abundances of nucb1 and nucb2A increased in the hypothalamus at 1 h and 3 h post-feeding. Furthermore, fasting and re-feeding experiments showed that the expressions of nucb1 and nucb2A in hypothalamus significantly decreased after fasting for 7 days, and returned to the control level after re-feeding for 3 or 5 days. In conclusion, the present study suggests that both NUCB1 and NUCB2A are involved in the short-term and long-term appetite regulation, as an anorexigenic factor, in S. davidi. These results can provide a basis for further investigation into the appetite regulatory role of NUCB family in teleost.

NPY and NPY receptors in the central control of feeding and interactions with CART and MC4R in Siberian sturgeon.

Neuropeptide Y (NPY) is the most powerful central neuropeptide implicated in feeding regulation via its receptors. Understanding the role of NPY system is critical to elucidate animal feeding regulation. Unlike mammal, the possible mechanisms of NPY system in the food intake of teleost fish are mostly unknown. Therefore, we investigated the regulatory mechanism of NPY and NPY receptors in Siberian sturgeon. In this study, we cloned the cDNA encoding NPY, and assessed the effects of different energy status on npy mRNAs abundance. The expression of npy was decreased in the brain after feeding 1 and 3 h. Besides, the expression of npy was increased after fasting within 15 days, while exhibiting significant decrease after refeeding. In order to further characterize the role of NPY receptor in fish, we performed acute intraperitoneal (i.p.) injection of NPY Y1 and Y2 receptor agonists, which is [Leu 31, Pro 34] NPY and NPY13-36 respectively. The results showed that the food intake of Siberian sturgeon was increased within 30 mins after injection of both Y1 and Y2 receptor agonist. To explore the relationship between NPY, NPY receptors and another appetite peptides, we examined the level of npy, cocaine- and amphetamine-regulated transcript (cart) and melanocortin-4 receptor (mc4r) by injected Y1 and Y2 receptor agonist. The results suggested that cart expression was regulated by NPY which acts on Y1 receptor or Y2 receptor. While mc4r expression just was mediated by NPY and Y1 receptor.

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.

Molecular characterization and expression of toll-like receptor 5 genes from Pelteobagrus vachellii.

Toll-like receptor 5 (TLR5) is an important pathogen recognition receptor (PRR) that recognizes the flagellin protein of pathogenic bacteria and plays a fundamental role in activating the innate immune response. In this study, full-length pvTLR5m (membrane) and pvTLR5s (soluble) genes were cloned from darkbarbel catfish Pelteobagrus vachellii, and their expression and that of downstream genes were analyzed following exposure to the Aeromonas hydrophila pathogen. The 3009 bp pvTLR5m cDNA includes a 2652 bp open reading frame (ORF) encoding 884 amino acids. The 2422 bp pvTLR5s cDNA includes a 1944 bp ORF encoding a predicted protein of 648 amino acids. The genes are most closely related to TLR5m (75%) and TLR5s (69%) from Ictalurus punctatus, respectively, and both have a typical TLR structure. Both genes were constitutively expressed in all examined tissues, and most abundantly in the head kidney and spleen. Following pathogen challenge, pvTLR5m and pvTLR5s expression was increased significantly (P <0.05) and peaked at 24 and 12 h post-exposure in the liver, 24 and 12 h in the head kidney, and 48 and 24 h in the spleen, respectively. The downstream genes interleukin-1ß (IL-1ß), IL-12 and tumor necrosis factor-alpha (TNF-α) were significantly up-regulated following pathogen exposure in spleen, and the NF-kB inhibitor (IκB) was down-regulated. These findings indicated that pvTLR5 may play an important role in the immune responses to A. hydrophila. These results provide new insight to elucidate the immune signalling pathways of fish TLR.

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

Neuropeptide Y (NPY) is a 36 amino-acid amidated peptide of the pancreatic polypeptide (PP) family, which plays an important role in appetite regulation and energy expenditure in mammals. Although several teleost NPY have been identified, its roles remain unclear in fish. We herein reported on the molecular cloning, tissue distribution and the effect of fasting on the expression of NPY in Channa argus, and designated as CaNPY. It consisted of a 300 bp open reading frame predicted to encode a prepro-NPY of 99 amino acids. Sequence analysis revealed that CaNPY was highly conserved (>60%) with other vertebrate NPY. Phylogenetic analysis highly supported CaNPY was closely related to piscine NPY. In addition, except for muscle and spleen tissues, CaNPY was found to extensively expressed in all other detected tissues, with the highest level in brain. Futhermore, the CaNPY transcript was found to significantly increase after short-term and long-term food deprivation, and dramatically decrease following refeeding. These findings suggested that CaNPY might be involved in food intake regulation and it could be as a potential target locus to improve commercial production of this kind of fish.

Uncoupling protein 1 in snakehead (Channa argus): Cloning, tissue distribution, and its expression in response to fasting and refeeding.

In mammals, uncoupling protein 1 (UCP1) is well known for its thermogenic role in brown adipose tissue (BAT). However, the UCP1 physiological roles are still unclear in fish, although several teleost ucp1 genes have been identified. The aim of this study is to investigate the potential roles of fish UCP1 involved in food intake regulation and energy homeostasis. We herein report on the molecular cloning, tissue distribution and the effect of fasting and refeeding on the expression of ucp1 in Channa argus. UCP1 consisted of a 921 bp open reading frame predicted to encode 306 amino acids. Sequence analysis revealed that snakehead UCP1 was highly conserved (>80%) with teleost UCP1, but shared a lower identity (60-72%) with mammals. Phylogenetic analysis supported that snakehead UCP1 was closely related to piscine UCP1. In addition, ucp1 was found to extensively expressed in all detected tissues, with the highest level in liver. Futhermore, the hepatic ucp1 was found to significantly increased after short-term and long-term food deprivation, and dramatically increased following refeeding. These findings suggested that snakehead UCP1 might play important roles in food intake regulation and fatty acid metabolism in snakehead fish, and it could be as a potential target locus to improve commercial production of this kind of fish.

Transcriptome analysis of the spleen of the darkbarbel catfish Pelteobagrus vachellii in response to Aeromonas hydrophila infection.

Intensive aquaculture has increased the susceptibility of fish to Aeromonas hydrophila, and this has led to severe economic damage. There has been little study of the host defense mechanism against A. hydrophila infection in scaleless fish. Therefore, in the present study, the transcriptome profiles of the spleen of Pelteobagrus vachellii were examined after infection with A. hydrophila. In total, 37,730 unigenes from 322 KEGG pathways were identified. Following A. hydrophila infection, 27,803 differentially expressed genes were identified, including 13,934 upregulated and 13,869 downregulated genes. Significant enrichment analysis of these differentially expressed unigenes showed that the major immune pathways were involved, including toll-like receptor pathways, B-cell receptor signaling pathways, Fcγ receptor-mediated phagocytosis, complement and coagulation cascades, and natural killer cell-mediated cytotoxicity pathways. From these pathways, 59 key immune-related differentially expressed genes were selected: 53 genes that were upregulated, including those coding for complement components, interferons, and interleukins, and six DEGs that were downregulated, including inhibitor of nuclear factor kappa-B kinase. Finally, nine DEGs, which were randomly selected, were confirmed by qRT-PCR to be differentially expressed. The results indicated that complement components, interferons and Fcγ receptor-mediated phagocytosis played key role in the response to A. hydrophila infection in the spleen of P. vachellii, which may prove useful in the future for the development of therapeutic regimens.

Effect of ammonia-N and pathogen challenge on complement component 8α and 8ß expression in the darkbarbel catfish Pelteobagrus vachellii.

The complement components C8α and C8ß mediate the formation of the membrane attack complex (MAC) to resist pathogenic bacteria and play important roles in innate immunity. Full-length complement C8α (Pv-C8α) and C8ß (Pv-C8ß) cDNA were identified in the darkbarbel catfish Pelteobagrus vachellii, and their mRNA expression levels were analyzed after ammonia-N and pathogen treatment. The Pv-C8α gene contained 1983 bp, including a 1794-bp open reading frame (ORF) encoding 598 amino acids. The Pv-C8ß gene contained 1952 bp, including a 1761-bp ORF encoding 587 amino acids. Pv-C8α and Pv-C8ß had the highest amino acid identity with rainbow trout Oncorhynchus mykiss C8α (62%) and Japanese flounder Paralichthys olivaceus C8ß (83%), respectively. Sequence analysis indicated that both Pv-C8α and Pv-C8ß contained a thrombospondin type-1 (TSP1) domain, a low-density lipoprotein receptor class A (LDLR-A) domain, a membrane attack complex/perforin (MACPF) domain and an epidermal growth factor-like (EGF-like) domain. In addition, Pv-C8α and Pv-C8ß were mainly distributed in the liver, head kidney, spleen, and eggs. Under ammonia-N stress, the Pv-C8α and Pv-C8ß mRNA levels significantly decreased (P < 0.05), with minimum levels, respectively, attained at 24 and 48 h in the liver, 48 and 24 h in the head kidney, and 24 and 24 h in the spleen. After Aeromonas hydrophila challenge, the Pv-C8α and Pv-C8ß mRNA levels significantly increased (P < 0.05), with maximum levels, respectively, attained at 48 and 24 h in the liver, 24 and 48 h in the head kidney, and 48 and 48 h in the spleen. The present study indicated that Pv-C8α and Pv-C8ß exhibited important immune responses to infection and that ammonia-N in water decreased the immune responses of Pv-C8α and Pv-C8ß.

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.

Evidence that ghrelin may be associated with the food intake of gibel carp (Carassius auratus gibelio).

Ghrelin, a non-amidated peptide hormone, is a potent anorectic neuropeptide implicated in feeding regulation in mammals and non-mammalian vertebrates. However, the involvement of ghrelin in the feeding behavior of teleosts has not been well understood. To better understand the role of ghrelin in the regulation of appetite in fish, in this study, we cloned the cDNAs encoding ghrelin and investigated their mRNA distributions in gibel carp tissues. We also assessed the effects of different nutritional status on ghrelin mRNA abundance. Ghrelin mRNAs were ubiquitously expressed in ten tissues (intestine, liver, brain, mesonephron, head kidney, spleen, skin, heart, muscle, gill and pituitary gland), and relatively high expression levels were detected in the gut. Postprandial studies analysis revealed a significant postprandial decrease in ghrelin mRNA expression in the gut (1 and 3 h after the regular feeding time). In addition, ghrelin mRNA expression in the gut significantly increased at day 7 after fasting and declined sharply after refeeding, which suggested that ghrelin might be involved in the regulation of appetite in gibel carp. Overall, our result provides basis for further investigation into the regulation of feeding in gibel carp.

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.

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.

Leptin and cholecystokinin in Schizothorax prenanti: molecular cloning, tissue expression, and mRNA expression responses to periprandial changes and fasting.

In the present study, full-length cDNA sequences of leptin and cholecystokinin (CCK) were cloned from Schizothorax prenanti (S. prenanti), and applied real-time quantitative PCR to characterize the tissue distribution, and appetite regulatory effects of leptin and CCK in S. prenanti. The S. prenanti leptin and CCK full-length cDNA sequences were 1121 bp and 776 bp in length, encoding the peptide of 171 and 123 amino acid residues, respectively. Tissue distribution analysis showed that leptin mRNA was mainly expressed in the liver of S. prenanti. CCK was widely expressed, with the highest levels of expression in the hypothalamus, myelencephalon, telencephalon and foregut of S. prenanti. The CCK mRNA expression was highly elevated after feeding, whereas the leptin mRNA expression was not affected by single meal. These results suggested that CCK is a postprandial satiety signal in S. prenanti, but leptin might not be. In present study, leptin and CCK gene expression were both decreased after fasting and increased after refeeding, which suggested leptin and CCK might be involved in regulation of appetite in S. prenanti. This study provides an essential groundwork to further elucidate the appetite regulatory systems of leptin and CCK in S. prenanti as well as in other teleosts.

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.

Interspecific differences and ecological correlations between scale number and skin structure in freshwater fishes.

Fish skin is mainly composed of the epidermis, dermis, and its derivative scales. There is a wide diversity in scale number in fishes, but the diversity of skin structure lacks systematic histological comparison. This research aimed to improve our understanding of the functional relationship between the scale number and the skin structure in freshwater fishes and to determine which ecological factors affect the scale number and skin structure. First, we presented a method to quantify skin structure in fish and histologically quantified the skin structure of 54 freshwater fishes. Second, we collected the scale number and habitat information of 509 Cyprinidae fishes in China and explored which ecological factors were related to their scale number. Third, common carp and scaleless carp were used as models to study the effects of scale loss on swimming. We found a strong negative correlation between scale thickness and scale number. The main factor affecting the skin structure of fishes was the species' water column position, and the skin of benthic fishes was the most well-developed (thicker skin layers (dermis, epidermis) or more/larger goblet cells and club cells). The scale number was related to two factors, namely, temperature and water column position, and cold, benthic and pelagic adaptation may have contributed to increased scale numbers. Only in benthic fishes, the more well-developed their skin, the more scales. In common carp, scale loss did not affect its swimming performance. In summary, we suggest that there is a rich diversity of skin structure in freshwater fishes, and the scales of fish with well-developed skin tend to degenerate (greater number/smaller size/thinner, or even disappear), but the skin of fish with degenerated scales is not necessarily well developed.

Chromosomal genome of Triplophysa bleekeri provides insights into its evolution and environmental adaptation.

BACKGROUND: Intense stresses caused by high-altitude environments may result in noticeable genetic adaptions in native species. Studies of genetic adaptations to high elevations have been largely limited to terrestrial animals. How fish adapt to high-elevation environments is largely unknown. Triplophysa bleekeri, an endemic fish inhabiting high-altitude regions, is an excellent model to investigate the genetic mechanisms of adaptation to the local environment. Here, we assembled a chromosomal genome sequence of T. bleekeri, with a size of ∼628 Mb (contig and scaffold N50 of 3.1 and 22.9 Mb, respectively). We investigated the origin and environmental adaptation of T. bleekeri based on 21,198 protein-coding genes in the genome. RESULTS: Compared with fish species living at low altitudes, gene families associated with lipid metabolism and immune response were significantly expanded in the T. bleekeri genome. Genes involved in DNA repair exhibit positive selection for T. bleekeri, Triplophysa siluroides, and Triplophysa tibetana, indicating that adaptive convergence in Triplophysa species occurred at the positively selected genes. We also analyzed whole-genome variants among samples from 3 populations. The results showed that populations separated by geological and artificial barriers exhibited obvious differences in genetic structures, indicating that gene flow is restricted between populations. CONCLUSIONS: These results will help us expand our understanding of environmental adaptation and genetic diversity of T. bleekeri and provide valuable genetic resources for future studies on the evolution and conservation of high-altitude fish species such as T. bleekeri.

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.

Molecular characterization and expression of complement factor I in Pelteobagrus vachellii during Aeromonas hydrophila infection.

Complement factor I (CFI) is a novel regulatory serine protease that plays an important role in resistance to pathogen infection. In this study, the CFI gene of Pelteobagrus vachellii (Pv-CFI) was sequenced and characterized. The full-length cDNA of 2320 bp includes a 155 bp 5'-untranslated region (UTR), a 164 bp 3'-UTR, and a 2001 bp open reading frame (ORF) encoding a 667 amino acids. Multiple sequence alignment revealed five highly conserved domains with a typical modular architecture and identical active sites in vertebrates, indicating a conserved function. Pv-CFI mRNA was constitutively expressed in all examined tissues and most abundant in liver. During infection with Aeromonas hydrophila, Pv-CFI mRNA expression was significantly up-regulated in liver at 3-24 h, spleen at 3-48 h and head kidney at 3-48 h. The results suggest Pv-CFI plays an important role in resistance to pathogenic bacteria in P. vachellii.