Molecular characterization of a teleost-specific toll-like receptor 22 (tlr22) gene from yellow catfish (Pelteobagrus fulvidraco) and its transcriptional change in response to poly I:C and Aeromonas hydrophila stimuli.

Toll-like receptors (TLRs) are a class of pattern recognition receptors (PRRs) that can recognize pathogen-associated molecular patterns (PMPs) and play important roles in the innate immune system in vertebrates. In this study, we identified a teleost-specific tlr22 gene from yellow catfish (Pelteobagrus fulvidraco) and its immune roles in response to different pathogens were also determined. The open reading frame (ORF) of the tlr22 was 2892 bp in length, encoding a protein of 963 amino acids. Multiple protein sequences alignment, secondary and three-dimensional structure analyses revealed that TLR22 is highly conserved among different fish species. Phylogenetic analysis showed that the phylogenetic topology was divided into six families of TLR1, TLR3, TLR4, TLR5, TLR7 and TLR11, and TLR22 subfamily was clustered into TLR11 family. Meanwhile, synteny and gene structure comparisons revealed functional and evolutionary conservation of the tlr22 gene in teleosts. Furthermore, tlr22 gene was shown to be widely expressed in detected tissues except barbel and eye, with highest expression level in liver. The transcription of tlr22 was significantly increased in spleen, kidney, liver and gill tissues at different timepoints after Poly I:C infection, suggesting TLR22 plays critical roles in defensing virus invasion. Similarly, the transcription of tlr22 was also dramatically up-regulated in spleen, kidney and gill tissues with different patterns after Aeromonas hydrophila infection, indicating that TLR22 is also involved in resisting bacteria invasion. Our findings will provide a solid basis for the investigation the immune functions of tlr22 gene in teleosts, as well as provide useful information for disease control and treatment for yellow catfish.

Myo-inositol improves growth performance and regulates lipid metabolism of juvenile Chinese mitten crab (Eriocheir sinensis) fed different percentage of lipid.

This study evaluated the effects of dietary myo-inositol (MI) on growth performance, antioxidant status and lipid metabolism of juvenile Chinese mitten crab (Eriocheir sinensis) fed different percentage of lipid. Crabs (4·58 (sem 0·05) g) were fed four diets including a normal lipid diet (N, containing 7 % lipid and 0 mg/kg MI), N with MI supplementation (N + MI, containing 7 % lipid and 1600 mg/kg MI), a high lipid diet (H, containing 13 % lipid and 0 mg/kg MI) and H with MI supplementation (H + MI, containing 13 % lipid and 1600 mg/kg MI) for 8 weeks. The H + MI group showed higher weight gain and specific growth rate than those in the H group. The dietary MI could improve the lipid accumulations in the whole body, hepatopancreas and muscle as a result of feeding on the high dietary lipid (13 %) in crabs. Besides, the crabs fed the H + MI diets increased the activities of antioxidant enzymes but reduced the malondialdehyde content in hepatopancreas compared with those fed the H diets. Moreover, dietary MI enhanced the expression of genes involved in lipid oxidation and exportation, yet reduced lipid absorption and synthesis genes expression in the hepatopancreas of crabs fed the H diet, which might be related to the activation of inositol 1,4,5-trisphosphate receptor (IP3R)/calmodulin-dependent protein kinase kinase-ß (CaMKKß)/adenosine 5'-monophosphate-activated protein kinase (AMPK) signalling pathway. This study demonstrates that MI could increase lipid utilisation and reduce lipid deposition in the hepatopancreas of E. sinensis fed a high lipid diet through IP3R/CaMKKß/AMPK activation. This work provides new insights into the function of MI in the diet of crustaceans.

Gamma-aminobutyric acid regulates glucose homeostasis and enhances the hepatopancreas health of juvenile Chinese mitten crab (Eriocheir sinensis) under fasting stress.

The ability of immune defense and resistance to physiological stress is crucial to animal health and survival. This study investigated the regulation of γ-aminobutyric acid (GABA) on metabolic homeostasis and its enhancement of hepatopancreas health in juvenile Chinese mitten crab (Eriocheir sinensis) under food deprivation. Juvenile crabs of 400 individuals were divided into four treatment groups: a control group without injection, and injections with a phosphate-buffered saline solution, 100 µmol GABA/mL and 1000 µmol GABA/mL, respectively. Hypoglycemia was induced by fasting, whereas the GABA treatment regulated hemolymph glucose homeostasis. The quantitative real-time PCR (qRT-PCR) results showed that the GABA treatment significantly up-regulated the mRNA expression levels of crustacean hyperglycemic hormone (CHH) and pyruvate kinase (PK). In contrast, the expression of E. sinensis insulin-like peptide (EsILP) was significantly down-regulated in the cranial ganglia, thoracic ganglia and hepatopancreas. Moreover, acid phosphatase (ACP), alkaline phosphatase (AKP), aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities were significantly increased in the hepatopancreas by the GABA treatment. Furthermore, the hemocyanin content in serum was significantly increased with the GABA injection, and the glutathione (GSH) content, total superoxide dismutase (T-SOD) activity and catalase (CAT) activity in the hepatopancreas showed a similar increasing trend with the dose elevation of GABA. Therefore, these results indicate that GABA can effectively maintain the hemolymph glucose homeostasis by regulating the levels of glucose metabolism-related hormones and key enzymes to promote the degradation and utilization of hepatopancreas glycogen. Meanwhile, GABA can improve the hepatopancreas function and immune status of juvenile E. sinensis under fasting stress. The treatment with GABA may provide a clue to guide health management in crab farming.

Gamma-aminobutyric acid enhances hypoxia tolerance of juvenile Chinese mitten crab (Eriocheir sinensis) by regulating respiratory metabolism and alleviating neural excitotoxicity.

With climate change and intensive aquaculture development, environmental hypoxia in aquaculture water has become a common challenge for many aquatic species. Therefore, it is crucial to improve the hypoxic tolerance of animals through nutritional strategies. This study explored the positive role of dietary gamma-aminobutyric acid (GABA) supplementation in enhancing hypoxia tolerance of juvenile Eriocheir sinensis through respiratory regulation and alleviation of hypoxia-induced neural excitotoxicity. Acute hypoxia stress significantly up-regulated the mRNA expression level of hypoxia-inducible factor 1α, oxygen consumption rate and anaerobic respiratory metabolism-related enzyme activities. On the other hand, aerobic respiratory metabolism-related enzyme activities were significantly decreased. However, dietary GABA supplementation remodeled the respiratory metabolism pattern of juvenile crabs exposed to hypoxia stress. In addition, acute hypoxic stress significantly increased the contents of free glutamate and GABA in the nervous tissue. The expression levels of N-Methyl-d-aspartate-related receptor genes and calcium-dependent degradation enzyme-related genes were significantly up-regulated. Similarly, neuronal apoptosis rates, expression levels of apoptosis-related genes, and vesicular glutamate transporter genes were also significantly increased. The high-affinity neuronal glutamate transporter decreased significantly in the crabs exposed to hypoxia stress. However, dietary GABA supplementation could effectively prevent acute hypoxia stress-induced neural excitotoxicity. Furthermore, dietary GABA could significantly improve the redox status in vivo exposed to hypoxia stress. In conclusion, acute hypoxia stress can affect respiratory metabolism and redox state and induce neural excitotoxicity in juvenile E. sinensis. GABA supplementation could improve hypoxia tolerance through multiple physiological regulation pathways.

Impact of Dietary Vitamin D3 Supplementation on Growth, Molting, Antioxidant Capability, and Immunity of Juvenile Chinese Mitten Crabs (Eriocheir sinensis) by Metabolites and Vitamin D Receptor.

Vitamin D3 (vit-D3), as an indispensable and fat-soluble nutrient, is associated with skeletal mineralization and health in mammals. However, such associations have not been well studied in economically important crustaceans. Six levels of vit-D3 with isonitrogenous and isolipidic diets were used to feed Eriocheir sinensis. The range of optimal vit-D3 requirements is 5685.43-10,000 IU/kg based on growth. The crabs fed 9000 IU/kg vit-D3 showed the best growth performance. This vit-D3 dose significantly increased antioxidant capacity in the hepatopancreas and intestine and was optimal for molting and innate immunity via quantitative polymerase chain reaction analysis. Transcriptomics analyses indicate that vit-D3 could alter protein processing in the endoplasmic reticulum, steroid biosynthesis, and antigen processing and presentation. As shown by the enzyme-linked immunosorbent assay, vit-D3 could improve vitamin D receptor, retinoic acid receptor, and C-type lectins concentrations. The 1α,25-dihydroxy vit-D3 content in serum was significantly higher in 3000-9000 IU/kg vit-D3. The study suggests that dietary vit-D3 and its metabolites can regulate molting and innate immunity in crabs.

Characterization of MRF genes and their tissue distributions and analysis of the effects of starvation and refeeding on the expression of these genes in Acipenser dabryanus muscle.

The purpose of the study was to clone the sequences of myogenic regulatory factors in Acipenser dabryanus and explore the changes in their expression during starvation and refeeding in A. dabryanus muscle. One hundred twenty fish (60.532 ± 0.284 g) were randomly assigned to four groups (fasted for 0, 3, 7 or 14 d and then refed for 14 d). Our predictions showed that the coding sequences of myod1, myf5, myog and myf6 in A. dabryanus encoded 275, 248, 248 and 243 amino acids, respectively, and the expression of the four genes was the highest in muscle. During fasting, the expression of myod1 in muscle was significantly decreased in the 14 d group. The expressions of myf5 and myf6 were increased significantly at first and then decreased with prolonged starvation time. The expression of myog in the 14 d group was significantly decreased compared with other groups (P < 0.05). During refeeding, the highest values of myod1 and myf6 expression were found in the 3 d group (P < 0.05).The expressions of myf5 and myog in 0 d and 3 d group were significantly higher than those in 7 d and 14 d group (P < 0.05). These results indicate that myogenic regulatory factors (MRFs) play important roles in muscle growth and development in A. dabryanus. The inhibition of long-term starvation (14 d) on the expression of myogenic regulatory factors is probably one of the reasons why it can not achieve full compensation for growth.

Discovery of differentially expressed genes in the intestines of Pelteobagrus vachellii within a light/dark cycle.

In aquaculture, it is necessary to determine of the diurnal biological variations in the intestines to determine an appropriate feeding schedule. The present study aimed to examine the transcriptomes of the Pelteobagrus vachellii intestines at four time points (0 h, 6 h, 12 h, and 18 h) within a light/dark cycle. In comparison with the zeitgeber time 0 (ZT0) transcriptomes, we identified 37,842 unigenes with significant differential expression, including 6,638; 9,626; and 7,938 that genes upregulated, and 3,507; 4,703; and 5,412 genes that were down regulated at 4, 12, and 24 h respectively. The differentially expressed unigenes were subjected to enrichment analysis, which indicated the involvement of the major digestive pathways, including digestion of protein, lipid and carbohydrate, catabolic process (protein, carbohydrate and lipid), and circadian rhythm. We selected 73 key differentially expressed genes (DEGs) from among these pathways and identified DEGs that showed increased expression at night, including those encoding trypsin-3, chymotrypsinogen 2, amino acid transporter, maltase-glucoamylase, facilitated glucose transporter, lipase, phospholipase, fatty acid-binding protein, fatty acid synthase, long-chain fatty acid transport protein, and apolipoprotein. Moreover, DEGs involved of circadian rhythm were identified, including brain-muscle-Arnt-like 1 (BMAL1), cryptochrome-1, circadian locomoter output cycles protein kaput (CLOCK) and period circadian protein homolog 1-3. Finally, the expression levels of 12 unigenes were analyzed using quantitative real-time PCR, which were in accordance with RNA-sequencing analysis. In general, the expression of genes related to the digestion of proteins, lipids, and carbohydrates showed upregulated expression at night; however, the peak time of expression of transporters for different nutrition molecules showed more diversification within the light/dark cycle.