Immune response of peroxinectin of Chinese mitten crab Eriocheir sinensis to exterior stimulation

Molecular cloning and functional characterization of peroxinectin from red swamp crayfish, Procambarus clarkii

Peroxinectin, which has both peroxidase and cell adhesion activities, is crucial for invertebrate innate immune responses. In this study, we first cloned the full-length cDNA of Procambarus clarkii Peroxinectin (denoted as Pc-Px) and evaluated its immune roles. The Pc-Px cDNA had 2460 base pairs (bp) and 819 amino acid residues, including peroxidase domain and a putative integrin-binding motif. Pc-Px tissue expression was found to be ubiquitous in all examined tissues under normal physiological conditions. Pc-Px mRNA levels were highest in hemocytes, followed by gills and heart, and were lowest in the gut. The LPS, PGN, and Poly I:C treatment significantly up-regulated the transcript level of Pc-Px gene, but the expression trends were different after the microbials component treatments. Pc-Px knockdown using double-stranded RNA altered the transcription profiles of various immune-related genes in hepatopancreas of P. clarkii. Taken together, Pc-Px is an important component of immune system that likely to modulate immune function of P. clarkii via regulating immune-associated genes.

Role of peroxinectin in the antibacterial immune response of the Chinese mitten crab, Eriocheir sinensis

To elucidate the antibacterial role of peroxinectin (referred to as PXN) and its molecular mechanism in Chinese mitten crab Eriocheir sinensis, we analyzed the bacterial binding and removal of the peroxinectin recombinant protein in vitro and the interaction of peroxinectin with integrin and CuZn-SOD through GST-pulldown and bimolecular fluorescence complementation methods. Concurrently, the effect of peroxinectin interference on the expression of other immune-related genes was studied using RNA interference. The results showed that the recombinant peroxinectin protein could bind to Bacillus subtilis, Staphylococcus aureus, Aeromonas hydrophila, and Vibrio parahaemolyticus with different affinities in vitro and could eliminate Vibrio parahaemolyticus in vivo. The findings also indicated that peroxinectin could establish interactions with integrin and CuZn-SOD in vitro. Furthermore, 48 h after the injection of the peroxinectin gene siRNA in vivo, the expression of peroxinectin mRNA decreased significantly (P < 0.05), integrin mRNA expression decreased by 16.8%, and CuZn-SOD mRNA expression decreased by 62.84% (P < 0.01). The expression levels of Dorsal, GPx, GST, PPAF, and Relish (P < 0.01), as well as that of lectin (P < 0.001) were significantly decreased. When peroxinectin siRNA was injected in vivo for 48 h and Aeromonas hydrophila was injected into mitten crabs, the expression of immune-related genes significantly increased. All data indicate that the recombinant peroxinectin protein in Chinese mitten crabs can recognize and bind different bacteria and promote the elimination of Vibrio parahaemolyticus from the body. Furthermore, peroxinectin may establish interactions with integrin and CuZn-SOD to activate the expression of related immune genes to elicit responses to bacterial infections and achieve immune protection.

The functional characterization of peroxinectin in the defense of Fenneropenaeus penicillatus against pathogens

Peroxinectin with cell adhesion and peroxidase activities plays an important role in innate immune responses of invertebrate. In the study, the full-length cDNA of a peroxinectin homolog (FpPX) was identified from Fenneropenaeus penicillatus. The full-length cDNA of FpPX is 2573 bp long, with an open reading frame (ORF) encoding a putative protein of 780 amino acids, including a peroxidase domain and a KGD motif. FpPX shared 65-96% similarities with other crustaceans peroxinectin proteins. Real-time quantitative RT-PCR indicated that FpPX was constitutively expressed in gill, heart, hemocytes and muscle of F. penicillatus. The temporal expression patterns of FpPX mRNA were different in the various tissues after microbial challenge. FpPX expression levels were significantly upregulated in gill, hemocytes and muscle after white spot syndrome baculovirus (WSSV) or Vibrio alginolyticus injection. Conversely, FpPX expression in the heart maintained at a low level and showed no obvious changes at any of the tested time points. The results of RNAi experiment showed that silencing FpPX could inhibit prophenoloxidase expression in vivo, and lead to a significantly higher mortality of shrimps after WSSV or V. alginolyticus challenge, suggesting FpPX is required in defense against bacterial and viral pathogens. In conclusion, these data revealed that FpPX played an important role in immune response of F. penicillatus against pathogenic infection.

Isolation and characterization of a novel strain (YH01) of Micropterus salmoides rhabdovirus and expression of its glycoprotein by the baculovirus expression system

As one of the most important aquatic fish, Micropterus salmoides suffers lethal and epidemic disease caused by rhabdovirus at the juvenile stage. In this study, a new strain of M. salmoides rhabdovirus (MSRV) was isolated from Yuhang, Zhejiang Province, China, and named MSRV-YH01. The virus infected the grass carp ovary (GCO) cell line and displayed virion particles with atypical bullet shape, 300-500 nm in length and 100-200 nm in diameter under transmission electron microscopy. The complete genome sequence of this isolate was determined to include 11 526 nucleotides and to encode five classical structural proteins. The construction of the phylogenetic tree indicated that this new isolate is clustered into the Vesiculovirus genus and most closely related to the Siniperca chuatsi rhabdovirus. To explore the potential for a vaccine against MSRV, a glycoprotein (1-458 amino acid residues) of MSRV-YH01 was successfully amplified and cloned into the plasmid pFastBac1. The high-purity recombinant bacmid-glycoprotein was obtained from DH10Bac through screening and identification. Based on polymerase chain reaction (PCR), western blot, and immunofluorescence assay, recombinant virus, including the MSRV-YH01 glycoprotein gene, was produced by transfection of SF9 cells using the pFastBac1-gE2, and then repeatedly amplified to express the glycoprotein protein. We anticipate that this recombinant bacmid system could be used to challenge the silkworm and develop a corresponding oral vaccine for fish.

Arginine supplementation improves growth, antioxidant capacity, immunity and disease resistance of juvenile Chinese mitten crab, Eriocheir sinensis

To investigate the effects of arginine (Arg) on the growth, antioxidant capacity, immunity and disease resistance of juvenile Chinese mitten crab, three diets containing Arg levels at 1.72% (control), 2.73% and 3.72% were formulated and fed to Chinese mitten crab (0.22 ± 0.03 g) for eight weeks. The weight gain, ecdysterone and growth hormone in the serum, relative expression of insulin-like growth factor 2 in the hepatopancreas significantly increased in crabs fed the 2.73% and 3.72% Arg diets. The protein and lipid contents significantly increased in crabs fed the 3.72% Arg diet. The feed conversion ratios in crabs fed the diets with Arg additions were lower than in the control. Arg supplementation also enhanced the antioxidative capacity by increasing the activities of superoxide dismutase, catalase and the relative expression of Kelch-like ECH-associated protein 1 gene in the hepatopancreas, which subsequently decreased malondialdehyde content in the hepatopancreas. Besides, Arg also decreased nitric oxide content in the serum and the activity of nitric oxide synthetase in the hepatopancreas. The relative mRNA levels of crustin, relish, lysozyme and cryptocyanin genes were significantly upregulated by Arg supplementation. The activities of acid phosphatase and alkaline phosphatase in the serum significantly increased in crabs fed the 3.72% Arg diet than those in the control. Similarly, the relative mRNA levels of crustin, cryptocyanin and proPO genes were significantly upregulated in crabs fed the 2.73% Arg diet after lipopolysaccharide challenge, and in crabs fed the 3.72% Arg diet after the Poly (I:C) challenge. The crabs fed the 2.73% and 3.72% Arg diets had higher survival rate after bacterial infection than those fed the control diet. This study indicates that the addition of Arg to the diet at 2.7-3.7% can improve the growth, survival, antioxidant capacity, immunity and disease resistance in juvenile Chinese mitten crab.

Endocrine-disrupting chemicals impair the innate immune prophenoloxidase system in the intertidal mud crab, Macrophthalmus japonicus

Endocrine-disrupting chemicals (EDCs), xenobiotics that interfere with endogenous hormone function, have been studied for their impacts in aquatic environments. However, there is limited information about the potentially hazardous impact of bisphenol A (BPA) and di-(2-ethylhexyl) phthalate (DEHP) on the marine environment. The aim of this study was to investigate the effects of BPA and DEHP on the immune response of the intertidal mud crab, Macrophthalmus japonicus. In order to examine immunological responses involving the prophenoloxidase (proPO) system, mRNA transcript and activity levels of six immune-related genes, including lipopolysaccharide and β-1,3-glucan-binding protein (LGBP), proPO, phenoloxidase (PO), peroxinectin (PE), serine protease inhibitor (Serpin), and trypsin (Tryp), were assessed in M. japonicus hepatopancreas and gills exposed to BPA or DEHP. Expression of immune genes generally decreased in M. japonicus hepatopancreas and gills exposed to all concentrations of BPA by days 4 and 7. However, at day 1, expression of Serpin and Tryp genes was significantly increased in M. japonicus hepatopancreas and gills exposed to BPA. For DEHP exposure, all genes, with the exception of Serpin, were significantly downregulated in M. japonicus gills. In the hepatopancreas, gene expression of PO, proPO, and LGBP increased at day 1, and then decreased by day 7, while mRNA expression of Serpin and Tryp exhibited up-regulation over all exposure periods. In addition, PE gene expression was upregulated in hepatopancreas at day 7 in a dose-dependent manner. Taken together, these results indicated that the crab immune responses were perturbed by exposure to BPA, and, in particular, DEHP.

Hydroxymethylation of protein-encoding genes in the testes involved in precocious puberty of Eriocheir sinensis

To investigate the possible effects of epigenetic modification of testis protein-encoding genes on precocious puberty of Eriocheir sinensis, we used MeDIP-seq and hMeDIP-seq techniques to compare the methylation and hydroxymethylation of 263 E. sinensis protein-encoding genes known in the NCBI database in precocious testes with those in normally developing testes. The results showed that total methylation level of those genes was lower than their total hydroxymethylation level. Moreover, their total hydroxymethylation level in precocious testes was significantly lower than that in normal testes. In addition, no methylated genes had significant difference, but there were 37 different hydroxymethylated genes (DhMGs) in the precocious testes compared to the normal ones. Among the DhMGs, 21 were hypo-hydroxymethylated and 16 were hyper-hydroxymethylated. The hypo-hydroxymethylated DhMGs were associated with development, cell structural and cytoskeletal proteins, and response to stress. However, the hyper-hydroxymethylated DhMGs included immune-related genes, free radicals removement-related genes, protein folding-related genes, and so on. In addition, some DhMGs were hyper-hydroxymethylated while their homologous DhMGs were hypo-hydroxymethylated. The results of a qRT-PCR assay showed that the expression levels of 5 DhMGs randomly chosen presented a positive correlation with their hydroxymethylation levels. It can be seen that hydroxymethylation might regulate the expression of genes and be involved in precocious puberty to cause high mortality of crabs. Therefore, the hydroxymethylation level of DhMGs may be used as an evaluation index with economically meaningful growth and breeding traits.

Identification of immune-related genes in gills of Chinese mitten crabs (Eriocheir sinensis) during adaptation to air exposure stress

The Chinese mitten crab, Eriocheir sinensis, is the most important crab in China. Air exposure is regarded as one of the crucial restriction factors in the crab cultivation and transportation process. Numerous studies have shown that air exposure stress can cause many negative effects on aquatic farming animals. However, the molecular mechanisms of drying on Chinese mitten crabs are still poorly studied. In this study, gill reference transcriptome was assembled and differentially expressed gene (DGE) analysis was conducted between air exposure 16 h and normal dissolved oxygen of Chinese mitten crab. A total of 76075 transcripts were generated and 50800 unigenes with a mean length of 1090 bp and N50 length of 1584 bp were observed. Transcriptomic comparison revealed 352 DEGs between air exposure 16 h group and control group, including 122 up-regulated genes and 230 down-regulated genes. Gene ontology (GO) analysis revealed that these DEGs involved in 16 biological process subcategories, 8 cellular component subcategories and 6 molecular function subcategories. Further Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis annotated 352 DEGs to 85 pathways, and some pathways were regarded as related with immune system and diseases, such as phagosome, systemic lupus erythematosus, and alcoholism. Eight genes involved in multiple KEGG signaling pathways were validated by qRT-PCR. This study demonstrates the first gill transcriptomic analysis challenged with air exposure stress in Chinese mitten crab and provides valuable gene resources for understanding the crab gill immunity, which can provides insight into the immune response of crab against air exposure stress.

Histopathological effects of Pedunsaponin A on Pomacea canaliculata

Pedunsaponin A, a novel molluscicidal compound isolated from Pueraria peduncularis, exhibits strong toxicity against Pomacea canaliculata. To determine the mechanisms of Pedunsaponin A toxicity, its effects on the organs and hemocytes of P. canaliculata were examined in this study. The results showed that Pedunsaponin A had significant toxic effects on different organs of the snail, including the lungs, gills, mantle, siphon tube, ventricle, pericardial cavity, hepatopancreas, kidneys, and the major symptom of this toxicity was the loss of cilia in the lungs and gills. Additionally, in further studies on the effects of Pedunsaponin A treatment, we found that the hemocyte count was changed and hemocyte morphology was damaged, which was primarily reflected by cytoplasm leakage, nuclei deformation, and significant reductions in the number of ribosomes and granulocyte mitochondria. Based on these results and considering that blood vessels are distributed in the lungs and gills, we hypothesized that Pedunsaponin A would first destroy the cilia, which disrupt physiological activities such as respiration, excretion and feeding, and then enter the hemolymph through blood vessels, disrupt the normal function of the hemocytes and destroy the snail immune system, eventually resulting in the death of the snail.

Transcriptome analysis of mud crab (Scylla paramamosain) gills in response to Mud crab reovirus (MCRV)

Mud crab (Scylla paramamosain) is an economically important marine cultured species in China's coastal area. Mud crab reovirus (MCRV) is the most important pathogen of mud crab, resulting in large economic losses in crab farming. In this paper, next-generation sequencing technology and bioinformatics analysis are used to study transcriptome differences between MCRV-infected mud crab and normal control. A total of 104.3 million clean reads were obtained, including 52.7 million and 51.6 million clean reads from MCRV-infected (CA) and controlled (HA) mud crabs respectively. 81,901, 70,059 and 67,279 unigenes were gained respectively from HA reads, CA reads and HA&CA reads. A total of 32,547 unigenes from HA&CA reads called All-Unigenes were matched to at least one database among Nr, Nt, Swiss-prot, COG, GO and KEGG databases. Among these, 13,039, 20,260 and 11,866 unigenes belonged to the 3, 258 and 25 categories of GO, KEGG pathway, and COG databases, respectively. Solexa/Illumina's DGE platform was also used, and about 13,856 differentially expressed genes (DEGs), including 4444 significantly upregulated and 9412 downregulated DEGs were detected in diseased crabs compared with the control. KEGG pathway analysis revealed that DEGs were obviously enriched in the pathways related to different diseases or infections. This transcriptome analysis provided valuable information on gene functions associated with the response to MCRV in mud crab, as well as detail information for identifying novel genes in the absence of the mud crab genome database.

Effect of lipopolysaccharide on the hemocyte apoptosis of Eriocheir sinensis

In the present study, we investigated the possible toxicity mechanism of lipopolysaccharide (LPS) extracted from Gram-negative bacteria in Eriocheir sinensis hemocytes. Apoptotic hemocytes and reactive oxygen species (ROS) production induced by the LPS were monitored by the combination of flow cytometry and microscope observation. It was shown that LPS induced serious damage on the DNA and morphological changes in hemocytes, including cell shrinkage, fracture of nucleus membrane, margination, condensation and fragmentation of chromatin, and formation of apoptotic bodies indicating obvious hemocyte apoptosis. As compared with the control group, the apoptotic cell ratio increased to 30.61% and 39.01% after 1-h exposure and 57.72% and 75.01% after 2-h exposure to 1 and 10 μg/ml LPS, respectively (P<0.05). Significant outburst of ROS production was observed in LPS-treated hemocytes with approximately 176.6% of relative dichlorofluorescein mean fluorescence at 1-h exposure, followed by a drastic decline (P<0.05). These results indicated that LPS would induce oxidative stress on hemocytes from E. sinensis and cause ROS burst, DNA damage, and subsequently apoptosis. The process of ROS-mediated apoptosis might be one of the potential toxicity mechanisms of LPS on crustacean hemocytes.

Identification, characterization and expression analysis of ERK2 in Chinese mitten crab Eriocheir sinensis after challenge with LPS and Aeromonas hydrophila

Farming of Eriocheir sinensis was seriously threaten by the infection of opportunistic pathogens, especially the gram-negative bacterium. In this paper, we analyzed the sequence of extracellular signal-regulated kinases 2 (ERK2) of E. sinensis (EsERK2) and its expression levels after challenge with LPS and Aeromonas hydrophila in both in vivo and in vitro examination. The full-length cDNA sequence of EsERK2 was 2455 bp in size with an open reading frame (ORF) of 1095 bp, encoding the protein of 365 amino acids. It owned a predicted molecular mass of 42.4 kDa and a theoretical isoelectric point (pI) of 5.93. EsERK2 was distributed in all examined tissues including haemocyte, gonad, hepatopancreas, gill, muscle heart, stomach and intestine, but its expression level was significantly higher in hepatopancreas than it in other examined tissues. The expression level of EsERK2 increased significantly after LPS challenge at 2 h (P < 0.05), and then gradually increased and reached highest at 16 h. However, its expression level decreased significantly after A. hydrophila challenge at 4 h, and then gradually decreased till 24 h (P < 0.05), and returned to its initial value at 36 h. According to the immunofluorescence assay and western blotting assay, EsERK2 was found to be distributed mainly in cytoplasm of haemocyte, and its expression level showed a prominent boost in primary cultured haemocytes after challenge with LPS and A. hydrophila in vitro. These results indicated that the expression of EsERK2 was sensitive to the exterior stimulants and its encoding protein might be associated with the signaling transduction in response to exterior pathogens in E. sinensis.