Identification, tissue distribution, periprandial expression, and anorexigenic effect of spexin in Siberian sturgeon, Acipenser baeri.

Spexin (Spx), an endogenous peptide, is considered to be a neuropeptide. In a few fish and mammals, it has been proved to play a role in the regulation of animal feeding. However, the possible mechanisms of spexin regulating food intake are mostly blurry in vertebrates including Siberian sturgeon. In this study, firstly, the coding sequence of spexin cDNA was cloned and sequenced in Siberian sturgeon. Then, we detected that spexin mRNA was widely expressed in the hypothalamus, gastrointestinal tract, and liver, with the highest expression in the hypothalamus. The expression of spexin mRNA in the hypothalamus was significantly increased after food intake. At 1 h, 3 h, and 6 h after injection, the food intake in the spexin group (0.10, 0.30, and 0.90 µg/g BW) was significantly lower than that in the saline group. Moreover, compared with the saline group, the mRNA expression of anorectic nucb2, cart, ucn3, and pyy in the hypothalamus was significantly upregulated and orectic npy was significantly downregulated at 1 h after spexin injection; in the stomach, the mRNA expression of nucb2 and pyy was significantly upregulated. All in all, these results provide evidence for the anorexic effect of spexin on Siberian sturgeon.

Characterization, tissue distribution of resistin gene and the effect of fasting and refeeding on resistin mRNA expression in Siberian sturgeon (Acipenser baerii).

Resistin as an adipokine identified from rodents in 2001 is involved in many biological processes. However, little is known about this gene in fish. We cloned Siberian sturgeon (Acipenser baerii) resistin cDNA of 795 base pairs, encoding 107 amino acids, which showed 38-40% identity to human and rodents. Real-time quantitative PCR showed that the resistin gene was widely distributed in tissues of Siberian sturgeon, with the highest expression in liver. After fasting for 1, 3, 6 and 10 days, the expression of the resistin gene in the liver of Siberian sturgeon decreased significantly, and after refeeding on the 10 days of fasting the resistin mRNA expression increased rapidly, suggesting that resistin may play an important role in liver in response to starvation. Taken together, these results suggest that resistin may be involved in the regulation of energy homeostasis in liver.

Transcriptome analysis and the effects of polyunsaturated fatty acids on the immune responses of the critically endangered angtze sturgeon (Acipenser dabryanus).

The poor understanding of nutrition needed has become a significant obstruction to artificial conservation of Yangtze sturgeon (Acipenser dabryanus) and the relationship between ployunsaturated fatty acid nutrition and the immune response of Yangtze sturgeon is remains unclear. To explore this relationship, the immune response was determined by the activities of serum immune-related enzymes and the transcriptome pattern in the spleen after feeding different fat source diets for 7 weeks. In addition, the gene expression pattern after a lipopolysaccharide (LPS) challenge was investigated in the presence of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Long-term feeding of the fish oil diets increased the serum immune-related enzyme activities, including lysozyme, acid phosphatase, and alkaline phosphatase of Yangtze sturgeon. More than 653,999 transcripts with an N50 length of 1047 bp were obtained and a final set of 280,408 unigenes was generated. After annotating the unigenes, 3549 genes were assigned to the immune system and 2839 were identified to participate in the response to the different fat sources. A transcriptome assay showed the fish oil diets moderately upregulated immune-related signaling pathways in the spleen of Yangtze sturgeon, including NLR signaling, platelet activation, Fc gamma R-mediated phagocytosis, Th17 cell differentiation, and Th1 and Th2 cell differentiation. The quantitative polymerase chain reaction (qPCR) results of candidate genes for these pathways showed similar results. The LPS challenge study revealed that DHA and EPA moderately upregulated the candidate immune-related genes and modulated excessive activation of the immune pathway by the pathogen. This study confirmed the immunomodulatory function of unsaturated fatty acids in Yangtze sturgeon. This research will provide a reference for the preparation of artificial diets for Yangtze sturgeon.

Progress in understanding the roles of Urocortin3 (UCN3) in the control of appetite from studies using animal models.

Urocortin3 (UCN3), the newest member of corticotrophin releasing hormone (CRH) family polypeptides, is an anorexic factor discovered in 2001, which has a strong inhibitory effect on animal appetite regulation. UCN3 is widely distributed in various tissues of animals and has many biological functions. Based on the research progress of UCN3 on mammals and non-mammals, this paper summarized the discovery, tissue distribution, appetite regulation and mechanism of UCN3 in animals, in order to provide a reference for feeding regulation and growth in mammals and fish in further research and production.

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

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

Intraperitoneal injection of nesfatin-1 primarily through the CCK-CCK1R signal pathway affects expression of appetite factors to inhibit the food intake of Siberian sturgeon (Acipenser baerii).

Nesfatin-1 is an 82-amino acid protein derived from nucleobindin 2 (NUCB2), which could inhibit food intake in fish and mammals. However, the neuroendocrine mechanism of nesfatin-1 in animal appetite regulation is unclear. To explore the feeding mechanism of nesfatin-1 in Siberian sturgeon (Acipenser baerii), intraperitoneal injections of nesfatin-1 and sulfated cholecystokinin octapeptide (CCK8), Lorglumide (CCK1R selective antagonist), or LY 225,910 (CCK2R selective antagonist) were performed. Co-injection of nesfatin-1 and CCK8 synergistically significantly decreased the food intake in 1 h. Lorglumide reversed the anorectic effect of nesfatin-1, but LY 225,910 had no effect. Moreover, Lorglumide could also reverse the expressions of appetite factors including nucb2, cck, unc3, cart, apelin, pyy, and npy induced by nesfatin-1 in the brain, stomach, and liver, while LY 225,910 partially reversed these changes. These results indicate that nesfatin-1 inhibits the appetite of Siberian sturgeon mainly through the CCK-CCK1R signaling pathway.

The inhibitory effect of NUCB2/nesfatin-1 on appetite regulation of Siberian sturgeon (Acipenser baerii Brandt).

Since NUCB2 was discovered, the information about NUCB2/nesfatin-1 in appetite regulation in both mammals and teleost has been still limited. The present study aims to determine the effects of nesfatin-1 on food intake and to explore the appetite mechanism in Siberian sturgeon. In this study, nucb2 cDNA sequence of 1571 bp was obtained, and the mRNA expression of nucb2 was abundant in brain and liver. Levels of nucb2 were appreciably increased in brain after feeding 1 and 3 h, while significantly decreased within fasting 15 days. Except for fasting 1 day, the expression pattern of nucb2 in the liver was similar to the brain. Acute intraperitoneal (i.p.) injection of nesfatin-1 inhibited the food intake during 0-1 h in a dose-dependent manner and 50 or 100 ng/g BW nesfatin-1 significantly decreased the cumulative food intake during 3 h. The daily food intake and cumulative food intake were remarkably reduced post chronic (7 days) i.p. injection. Moreover, chronic i.p. injection of nesfatin-1 affected the expression of appetite factors including cart, apelin and pyy in the brain, stomach and liver with the consistent pattern of change, while the levels of cck, ucn3 and nucb2 in these have different patterns. This study demonstrates that nesfatin-1 acts as a satiety factor in reducing the short-term and long-term food intake of Siberian sturgeon. Therefore, the data suggesting nesfatin-1 inhibits the appetite through different signal pathways in the central and peripheral endocrine systems of Siberian sturgeon.

CCK reduces the food intake mainly through CCK1R in Siberian sturgeon (Acipenser baerii Brandt).

To explore the effect of CCK on food intake in Siberian sturgeon, cck cDNA sequence of 1005 bp was obtained, and cck mRNA possessed the highest expression in brain. The expressions of cck were significantly increased after feeding 1 and 3 h, while displaying significant decrease after fasting within 15 days in brain and duodenum. Re-feeding for 3 days induced cck level returned to basic level. Acute i.p. injection experiment showed 100 and 200 ng/g BW CCK8 inhibited the food intake in 0-1 h together with the cumulative food intake within 3 h. 7 days chronic i.p. injection of 100 and 200 ng/g BW CCK8, both daily food intake and cumulative food intake were significantly decreased. In addition, chronic i.p injection of CCK8 induced the expression of feeding related factors changes including cck, ucn3, cart, apelin, pyy and npy in respective organization. Moreover, as revealed by the results, Lorglumide, the CCK1R selective antagonist, effectively reversed the inhibitory effects of CCK8 on food intake and the levels of feeding related factors. On the other hand, LY 225910, the CCK2R selective antagonist, partially reversed these effects. These results indicate CCK is a satiety factor inhibits the feeding of Siberian sturgeon primarily through CCK1R.