Characterization of Cdc2 kinase in the red claw crayfish (Cherax quadricarinatus): Evidence for its role in regulating oogenesis

Hepatopancreatic transcriptome analysis and humoral immune factor assays in red claw crayfish (Cherax quadricarinatus) provide insight into innate immunomodulation under Vibrio parahaemolyticus infection

Red claw crayfish (Cherax quadricarinatus) is an economically and nutritionally important specie. We aimed to assess the immunostimulatory response to C. quadricarinatus infection with Vibrio parahaemolyticus. After determining the LD50, we infected C. quadricarinatus and examined the differential expression profiles of hepatopancreas transcriptional genes, and observed the temporal changes of hepatopancreas pathological sections and serum immunoenzymatic activities at different time points to reveal the infection mechanism of V. parahaemolyticus and the immune detoxification mechanism of the organism. The results showed that V. parahaemolyticus infection with C. quadricarinatus caused hepatopancreas injury and the immune enzyme activity of the organism changed with time delay. Transcriptome analysis of 47,338 single genes obtained by RNA sequencing and de nove transcriptome assembly identified a total of 3678 differentially expressed genes (P < 0.05) in the expression profiles of susceptible and normal animals for comparative analysis, and 2516 differentially expressed genes (P < 0.05) in the expression profiles of asymptomatic (infection-resistant) and normal animals. GO and KEGG and analyses revealed immune-related pathways under V. parahaemolyticus infection, including Vibrio cholerae infection, phagosome, lysozyme, oxidative phosphorylation, antigen processing and presentation, apoptosis, and Toll-like receptor signaling, as well as significant differences in the expression patterns of related immune genes at different times (P < 0.05). These new experimental results reveal the molecular response of the hepatopancreas to V. parahaemolyticus infection and the corresponding adaptive mechanisms, thus further revealing the pathogenesis due to bacterial infection in the aquatic environment, and providing a reference for further understanding of microbial-host interactions in aquatic systems.

Cold stress regulates lipid metabolism via AMPK signalling in Cherax quadricarinatus

Lipids play an important role in protecting poikilotherms from cold stress, but relatively little is known about the regulation of lipid metabolism under cold stress, especially in crustaceans. In the present study, red-clawed crayfish Cherax quadricarinatus was employed as a model organism. Animals were divided into four temperature groups (25, 20, 15 and 9 °C) and treated for 4 weeks, with the 25 °C group serving as a control. The total lipid content in the hepatopancreas as well as the triglyceride, cholesterol and free fatty acid levels in the hemolymph were determined. Lipids stored in the hepatopancreas and hemolymph decreased with decreasing temperature, with changes in the 9 °C group most pronounced, indicating that lipids are the main energy source for crayfish at low temperatures. Furthermore, enzyme activity of lipase, fatty acid synthase, acetyl-CoA carboxylase, and lipoprotein esterase, and gene expression analysis of fatty acid synthase gene, acetyl-CoA carboxylase gene and carnitine palmitoyltransferase gene showed that the digestion, synthesis and oxidation of lipids in the hepatopancreas were inhibited under low temperature stress, but expression of sphingolipid delta-4 desaturase (DEGS) was increased, indicating an increase in the demand for highly unsaturated fatty acids at low temperatures. Analysis of the expression of genes related to the AMP-activated protein kinase (AMPK) signalling pathway revealed that the adiponectin receptor gene was rapidly upregulated at low temperatures, which may in turn activate the expression of the downstream AMPKα gene, thereby inhibiting lipid anabolism.

Effects of exposure to waterborne polystyrene microspheres on lipid metabolism in the hepatopancreas of juvenile redclaw crayfish, Cherax quadricarinatus

Previous research has identified microplastics as new environmental pollutants that are widely distributed in a variety of environments, including aquaculture environments. However, the potential hazard of microplastics to aquaculture animals, especially toward lipid metabolism involved with the survival and growth of aquatic animal, has not yet been investigated. In the present study, redclaw crayfish (Cherax quadricarinatus) were exposed to different concentrations of 200 nm-sized polystyrene microspheres (0, 0.5, and 5 mg/L) for 21 days, to investigate the effects of microplastics on lipid metabolism. After ingestion, the microplastics were distributed in the intestines and hepatopancreas, and appeared to inhibit the growth of Cherax quadricarinatus. Subsequently, the lipid levels in the hepatopancreas and hemolymph was detected, and found that after 21 days of exposure, the lipid content and free fatty acids in the hepatopancreas and hemolymph decreased significantly, and total cholesterol and triglycerides levels increased significantly in the hemolymph. This might have been caused by insufficient intake of exogenous fat. A significant decrease in lipase activity also supported this view. The activity of lipoprotein lipase related to lipolysis in the hepatopancreas increased significantly, while the activity of fatty acid synthase related to fat synthesis increased, and the activity of acetyl-CoA carboxylase decreased. These results indicated disturbed lipid metabolism in the hepatopancreas. The significant increase of lipid transport-related low-density lipoprotein indicated that the lipolytic capacity was higher than the lipid synthesis capacity. The expression levels of fatty acid metabolism-related genes FAD6 and FABP decreased significantly, indicating that the fatty acid utilization ability of hepatopancreas cells was inhibited, which was consistent with the results of enzyme activities. Thus, microplastics represent a potential hazard to redclaw crayfish, at least on lipid metabolism. This study provided basic data on the ecotoxicological effects of microplastics on crustaceans.

Effect of sub-chronic dietary L-selenomethionine exposure on reproductive performance of Red Swamp Crayfish, (Procambarus clarkii)

The effect of selenium (Se) on the reproductive system has been investigated in both humans and vertebrates, but few studies of female fertility and reproduction in invertebrate have been reported. This study is aimed to investigate the effect of SeMet on growth performance and reproductive system after crayfish were fed with graded levels of dietary SeMet (0, 1.49, 3.29, 10.02, 30.27 or 59.8 μg Se/g dry weight) for 60 days. Crayfish treated with the high levels of SeMet (10.02, 30.27 and 59.76 μg Se/g) exhibited decreasing FW and CL in both male and female. Interestingly, Se accumulation was higher in ovary than in other tissues, suggesting that ovary may serve as a target organ for Se accumulation. We found that dietary Se concentration of 10.02 μg Se/g significantly improved the spawning rate, promoted the synchronized spawning, and up-regulated the expressions of mRNA of cdc2 and vitellogenin, with significantly increased E2 and VTG concentrations in hemolymph of female crayfish. However, a marked decrease of the E2 contents and spawning rate was observed in the groups treated with 30.27 and 59.76 μg Se/g diets. In conclusion, the results of this study indicated that the Se had maximum accumulation in ovary, affecting the reproductive capacity by intervening the expression of cdc2 and vitellogenin in the reproductive system. The LOAEL to induce FW was observed in crayfish fed with 10.02 μg Se/g diet, and its value can cause toxicity within the range of natural concentration, so the addition of Se in the feed should be within 10.02 μg Se/g.

Molecular cloning, tissue expression and regulation of nutrition and temperature on Δ6 fatty acyl desaturase-like gene in the red claw crayfish (Cherax quadricarinatus)

Desaturase enzymes play an important role in the synthesis of unsaturated fatty acids. In this study, a complete cDNA sequence of a Δ6 desaturase-like gene was cloned from the hepatopancreas of the red claw crayfish, Cherax quadricarinatus. The full-length 1885 bp sequence comprises a 5' UTR of 254 bp, 3' UTR of 234 bp, and an open reading frame (ORF) of 1377 bp encoding a 458 amino acid polypeptide (GenBank accession no. MF497442). Bioinformatics analysis revealed three conserved histidine-rich regions, a cytochrome b5 domain at the N-terminus, and a haem binding site (HPGG) in the cytochrome b5 domain, all of which are typical of Δ6 desaturases. Quantitative real-time PCR demonstrated significantly higher expression in the hepatopancreas than other tissues. After feeding crayfish four formulated diets in which fish oil was replaced by 0, 33, 67, or 100% highly unsaturated soybean oil for 8 weeks, Δ6 desaturase-like mRNA expression and enzyme activity were higher than in the fish oil only group. Additionally, a 4-week low temperature treatment at 25, 20, 15, or 9 °C increased Δ6 desaturase mRNA expression and enzyme activity with decreasing water temperature. These results may help us better understand the biosynthesis of unsaturated fatty acids in C. quadricarinatus.