Molecular cloning and characterisation of prophenoloxidase cDNA from haemocytes of the giant freshwater prawn, Macrobrachium rosenbergii, and its transcription in relation with the moult stage

Effects of cadmium on antioxidant and non-specific immunity of Macrobrachium nipponense

As a non-essential and toxic element, cadmium poses an important threat to aquatic organisms and human food safety. In this study, the effects of cadmium on antioxidant and non-specific immunity of Macrobrachium nipponense were studied from the physiological and biochemical indexes, histology and expression of related genes. These results showed that low concentrations (0.01, 0.02 mg/L) of cadmium have a positive effect on the non-specific immunity of M. nipponense, but high concentration (0.04 mg/L) of cadmium could inhibit or even damage the non-specific immunity of M. nipponense. The cadmium could induce oxidative stress in M. nipponense, and M. nipponense actived the antioxidant defense system to deal with oxidative stress, but high concentration (0.04 mg/L) of cadmium could inhibit the antioxidant defense system of M. nipponense, leading to oxidative damage, and may induce apoptosis in severe case. At the same time, the results of histology showed that cadmium can damage the structure of gill and hepatopancreas tissues of M. nipponense. This study provides theoretical data for evaluating the influences of heavy metal cadmium on M. nipponense and the toxic mechanism of heavy metal cadmium.

Dietary supplementation of host‐associated lactic acid bacteria modulates growth, metabolic activities, and immune‐related gene expression in giant freshwater prawn, Macrobrachium rosenbergii

The present study was carried out to evaluate the dietary effects of host‐associated lactic acid bacteria on growth performance, metabolic enzyme activities, and immune response of Macrobrachium rosenbergii juveniles. To formulate the test diets, a control (Con) diet was supplemented with a commercial probiotic and three host‐derived bacteria Enterococcus faecalis (EC), Lactococcus lactis I (LC‐I), and L. lactis II (LC‐II), which were previously isolated from the gastrointestinal tract of adult individuals of M. rosenbergii. Juvenile M. rosenbergii (0.65 ± 0.008 g) were randomly stocked at 20 individuals/100 L of fiberglass tanks with three replications for each test diet. After 50 days, juveniles fed the diets LC‐I and LC‐II showed significantly higher (p < .05) weight gain, specific growth rate, and the lowest feed conversion ratio. The analyses of glutamic oxaloacetate transaminase and glutamic pyruvate transaminase in muscle and hepatopancreas revealed significantly (p < .05) reduced values in LC‐I fed juveniles. The total hemocyte count and phenoloxidase activity were significantly increased (p < .05) in LC‐I and LC‐II fed juveniles. The relative mRNA expression patterns of immune‐related α2‐M, LGBP, ProPO, Cu, Zn‐SOD, TG, PE, AKP, and ACP genes were significantly (p < .05) upregulated in juveniles fed with LC‐I followed by the diet LC‐II. Finally, the study suggests that the growth performance and immune response of M. rosenbergii can be improved through supplementation of host‐associated L. lactis bacteria for its higher production.

Establishment of hematopoietic tissue primary cell cultures from the giant freshwater prawn Macrobrachium rosenbergii

The giant freshwater prawn Macrobrachium rosenbergii is one of the most important aquaculture species in Southeast Asia. In this study, in vitro culture of its hematopoietic tissue cells was achieved and characterized for use as a tool to study its pathogens that cause major farm losses. By transmission electron microscopy, the ultrastructure of the primary culture cells was similar to that of cells lining intact hematopoietic tissue lobes. Proliferating cell nuclear antigen (PCNA) (a marker for hematopoietic stem cell proliferation) was detected in some of the cultured cells by polymerase chain reaction (PCR) testing and flow cytometry. Using a specific staining method to detect phenoloxidase activity and using PCR to detect expression markers for semigranular and granular hemocytes (e.g., prophenoloxidase activating enzyme and prophenoloxidase) revealed that some of the primary cells were able to differentiate into mature hemocytes within 24 h. These results showed that some cells in the cultures were hematopoietic stem cells that could be used to study other interesting research topics (e.g. host pathogen interactions and development of an immortal hematopoietic stem cell line).

DNA damage, immunotoxicity, and neurotoxicity induced by deltamethrin on the freshwater crayfish, Procambarus clarkii

Pyrethroid pesticides are applied to both agricultural and aquacultural industries for pest control. However, information of their impact on the commercial important freshwater crayfish, Procambarus clarkii is scarce. Therefore, the present study aimed to characterize to effects of a commonly used pyrethroid pesticide, deltamethrin on DNA damage, immune response, and neurotoxicity in P. clarkii. Animals were exposed to 7, 14, and 28 ng/L of deltamethrin, which correspond to 1/8, 1/4, and 1/2 of the LC50 (96 hours) of this pyrethroid to P. clarkii. Significant increase of olive tail moment (OTM) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) was found after deltamethrin exposure in a dose-dependent way. Total hemocyte counts (THC) and activities of immune-related enzymes including acid phosphatase (ACP), lysozyme (LZM), and phenoloxidase (PO) were all decreased and significantly lower than control at concentration of 28 ng/L after 96 hours exposure. Acetylcholinesterase (AChE) activity, an indicator of neurotoxic effect was investigated and it was decreased significantly in muscles at 14 and 28 ng/L after 24 hours exposure. The level of intracellular reactive oxygen species (ROS) in hemocytes was also measured and the significant increase of ROS was found at 14 and 28 ng/L concentrations. The results revealed that deltamethrin induced DNA damage, immunotoxicity, and neurotoxicity in P. clarkii by excessive generation of ROS. Because of the dose-dependent responses of all parameters under exposure of deltamethrin at environmentally realistic concentrations, these parameters could be used as sensitive biomarkers for risk assessment of deltamethrin in aquaculture area.

Assessing the relevance of a multiplexed methodology for proteomic biomarker measurement in the invertebrate species Gammarus fossarum: A physiological and ecotoxicological study

Recently, a protein sequence database was built specifically for the sentinel non-model species Gammarus fossarum using a proteogenomics approach. A quantitative multiplexed targeted proteomics assay (using Selected Reaction Monitoring mass spectrometry) was then developed for a fast and simultaneous quantification of dozens of biomarker peptides specific of this freshwater sentinel crustacean species. In order to assess the relevance of this breakthrough methodology in ecotoxicology, the response patterns of a panel of 26 peptides reporting for 20 proteins from the Gammarus fossarum proteome with putative key functional roles (homeostasis, osmoregulation, nutrition, reproduction, molting,…) were recorded through male and female reproductive cycles and after exposure to environmental concentrations of cadmium and lead in laboratory-controlled conditions. Based on these results, we validated the implication of annotated vtg-like peptides in the oogenesis process, and the implication of Na⁺/K⁺ ATPase proteins in the molt cycle of organisms. Upon metal (cadmium and lead) contamination, peptides belonging to proteins annotated as involved in antioxidant and detoxification functions, immunity and molting were significantly down-regulated. Overall, this multiplex assay allowed gaining relevant insights upon disruption of different main functions in the sentinel species Gammarus fossarum. This breakthrough methodology in ecotoxicology offers a valid and high throughput alternative to currently used protocols, paving the way for future practical applications of proteogenomics-derived protein biomarkers in chemical risk assessment and environmental monitoring.

Copper-induced oxidative damage to the prophenoloxidase-activating system in the freshwater crayfish Procambarus clarkii

Previous studies have demonstrated copper-induced proteins damage in gill and hepatopancreas of the freshwater crayfish Procambarus clarkii, but little information is available about its effects on key component of the innate defense in haemolymph. In the present study, we evaluated the relationship between oxidative carbonylation and prophenoloxidase-activating system (proPO-AS) activity, by exposing P. clarkii to sub-lethal concentrations (1/50, 1/12, 1/6 and 1/3 of the 96 h LC50) Cu(2+) up to 96 h. Six biomarkers of oxidative stress, i.e. reactive oxygen species (ROS), superoxide dismutase (SOD), catalase (CAT), protein carbonyl (PC), malondialdehyde (MDA) and DNA-protein crosslinks (DPCs), and six indicators of immune status, i.e. total hemocyte counts (THCs), differential hemocyte counts (DHCs), hemocyanin (HC), prophenoloxidase (proPO), serine protease (SP) and phenoloxidase (PO), were determined in haemolymph. The results indicated that there was a significant increase (P < 0.05) in the levels of ROS, PC, MDA and DPCs accompanied by markedly decreased (P < 0.05) activities of proPO, SP, PO and HC in a dose and time dependent manner. The significant and positive correlations (P < 0.01) between ROS production and the formation of PC, MDA and DPCs were observed in crayfish at 96 h. There was a significant negative correlation (P < 0.01) between the levels of protein carbonyls and the activities of proPO and SP in hemocyte lysate supernatant and PO and HC in haemolymph. Carbonylated proteins may be recognized not merely as a specific signal in oxidative stress pathways but also as a "non-self" molecule in proPO-AS. In crayfish species, copper-catalyzed protein carbonylation may be one of the main mechanisms for immunity dysfunction in proPO-AS.

Immune indices and identical functions of two prophenoloxidases from the haemolymph of green tiger shrimp Penaeus semisulcatus and its antibiofilm activity

In the present study, we purified two prophenoloxidases (proPO) from haemolymph of green tiger shrimp, Penaeus semisulcatus by gel fermentation chromatography using blue Sepharose matrix. The two purified prophenoloxidase macromolecules are of about 76 and 75 kDa determined through SDS-PAGE and named as Penaeus semisulcatus prophenoloxidase I (PSproPO I) and Penaeus semisulcatus prophenoloxidase II (PSproPO II). It was further characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Circular Dichroism (CD) and High Performance Liquid Chromatography (HPLC) analysis. The purified PSproPO I and PSproPO II showed the strongest agglutination titre against human erythrocytes compared to goat RBC. The PSproPO I and PSproPO II showed phagocytic activity against yeast Saccharomyces cerevisiae and encapsulation activity against Sepharose CL 6B beads compared to CM Sepharose and Sodium alginate beads. The functional analysis of purified PSproPO I and PSproPO II showed enhanced PO activity when added with the triggering molecules such as pathogen associated molecular patterns (PAMPs), metals and chemicals. In addition, eluted fraction containing PSproPO I and PSproPO II showed antibiofilm activity against Gram positive and Gram negative bacteria. The above results concluded that no significant differences were found between the purified PSproPO I and PSproPO II immune indices and functions. This study might provide a sensitive platform to understand more about the critical roles of PSproPO I and PSproPO II in crustacean immune system.

The Involvement of Hemocyte Prophenoloxidase in the Shell-Hardening Process of the Blue Crab, Callinectes sapidus

Cuticular structures of arthropods undergo dramatic molt-related changes from being soft to becoming hard. The shell-hardening process of decapod crustaceans includes sclerotization and mineralization. Hemocyte PPO plays a central role in melanization and sclerotization particularly in wound healing in crustaceans. However, little is known about its role in the crustacean initial shell-hardening process. The earlier findings of the aggregation of heavily granulated hemocytes beneath the hypodermis during ecdysis imply that the hemocytes may be involved in the shell-hardening process. In order to determine if hemocytes and hemocyte PPO have a role in the shell-hardening of crustaceans, a knockdown study using specific CasPPO-hemo-dsRNA was carried out with juvenile blue crabs, Callinectes sapidus. Multiple injections of CasPPO-hemo-dsRNA reduce specifically the levels of CasPPO-hemo expression by 57% and PO activity by 54% in hemocyte lysate at the postmolt, while they have no effect on the total hemocyte numbers. Immunocytochemistry and flow cytometry analysis using a specific antiserum generated against CasPPO show granulocytes, semigranulocytes and hyaline cells as the cellular sources for PPO at the postmolt. Interestingly, the type of hemocytes, as the cellular sources of PPO, varies by molt stage. The granulocytes always contain PPO throughout the molt cycle. However, semigranulocytes and hyaline cells become CasPPO immune-positive only at early premolt and postmolt, indicating that PPO expression in these cells may be involved in the shell-hardening process of C. sapidus.

Oxidative damage of hepatopancreas induced by pollution depresses humoral immunity response in the freshwater crayfish Procambarus clarkii

Previous studies provide evidences for the possible oxidative damage of toxic environmental pollutants to tissue protein in fish and amphibian, but little information is available about their effects on immunity response in crustacean. In the present study, we evaluated the relationship between oxidative damage and immune response induced by both typical pollutants (viz. copper and beta-cypermethrin), by exposing the freshwater Procambarus clarkii to sub-lethal concentrations (1/40, 1/20, 1/10 and 1/5 of the 96 h LC50) up to 96 h. Five biomarkers of oxidative stress, i.e. reactive oxygen species (ROS), superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA) and protein carbonyl in hepatopancreas, and two immune factors, i.e. phenoloxidase (PO) and hemocyanin in haemolymph were determined. The results indicated that there was a significant increase (P < 0.05) in the contents of ROS, MDA and protein carbonyl accompanied by markedly decreased (P < 0.05) PO and hemocyanin levels in a dose and time dependent manner. The significant and positive correlation (P < 0.01) between protein carbonyls induction and MDA formation was observed in crayfish hepatopancreas at 96 h. The production of these protein carbonyls could significantly depress (P < 0.01) the levels of phenoloxidase and hemocyanin in hemolymph. Higher contents of ROS enhanced the risk of lipid peroxidation, protein carbonylation and immunosuppression of crayfish, and hepatopancreas might play an important role in immune system of crustaceans. Protein oxidation may be one of the main mechanisms for pollution-induced immunotoxicity in P. clarkii.

Comparison of protein expression profiles of the hepatopancreas in Fenneropenaeus chinensis challenged with heat-inactivated Vibrio anguillarum and white spot syndrome virus

Fenneropenaeus chinensis (Chinese shrimp) culture industry, like other Penaeidae culture, has been seriously affected by the shrimp diseases caused by bacteria and virus. To better understand the mechanism of immune response of shrimp to different pathogens, proteome research approach was utilized in this study. Firstly, the soluble hepatopancreas protein samples in adult Chinese shrimp among control, heat-inactivated Vibrio-challenged and white spot syndrome virus-infected groups were separated by 2-DE (pH range, 4-7; sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and pH range, 3-10; tricine-SDS-PAGE). Then the differentially expressed protein spots (≥1.5-fold or ≤0.67-fold averagely of controls) were analyzed by LC-ESI-MS/MS. Using Mascot online database searching algorithm and SEQUEST searching program, 48 and 49 differentially expressed protein spots were successfully identified in response to Vibrio and white spot syndrome virus infection, respectively. Based on these results, we discussed the mechanism of immune response of the shrimp and shed light on the differences between immune response of shrimp toward Vibrio and white spot syndrome virus. This study also set a basis for further analyses of some key genes in immune response of Chinese shrimp.

Cloning of prophenoloxidase from hemocytes of the blue crab, Callinectes sapidus and its expression and enzyme activity during the molt cycle

The arthropods cuticle undergoes dramatic morphological and biochemical changes from being soft to hardness through each molting process. Prophenoloxidase (PPO) known as a key enzyme in the arthropod innate immune system involved in the melanization reaction, has been related with the initial shell-hardening process, specifically in the sclerotization of the protein matrix in the new cuticle. Since hemocytes have been reported as the main PPO source in arthropods, the transport of hemocyte PPO into the newly laid, soft cuticle has been proposed for shell-hardening occurring during and immediately after ecdysis. In order to define the role of hemocyte PPO in the shell-hardening of crustaceans, the full-length cDNA sequence (2806 nt) of hemocytes PPO of the blue crab Callinectes sapidus (CasPPO-hemo) is isolated using degenerate PCR and 5'-3' RACE. CasPPO-hemo encodes a putative PPO (672 aa) showing three hemocyanin domains: N, M, and C in order and two copper binding sites (CuA & CuB). The sequence analysis identifies the putative CasPPO-hemo as zymogen which requires the cleavage at the N-terminus for its activation. Hemocyte extract (CasHLS) contains the PO, the activity of which depends on the in vitro activation of trypsin. The expression levels of CasPPO-hemo are kept constant during the molt cycle. The increase in the number of hemocytes at early premolt correlates with the elevated PO activity, while at late premolt, the increment in hemocyte numbers does not reflect on the PO activity. The functional importance of the changes in the levels of CasHLS-PO activity during molt cycle is discussed in relation to cuticle hardening process.

Beta-glucan: an ideal immunostimulant in aquaculture (a review)

The major hindrance in the development and sustainability of aquaculture industry is the occurrence of various diseases in the farming systems. Today, preventive and management measures are central concern to overcome such outbreak of diseases. Immunostimulants are considered as an effective tool for enhancing immune status of cultured organisms. Among different immunostimulants used in aquaculture practices, β-glucan is one of the promising immunostimulant, which is a homopolysaccharide of glucose molecule linked by the glycoside bond. It forms the major constituents of cell wall of some plants, fungi, bacteria, mushroom, yeast, and seaweeds. Major attention on β-glucan was captivated with the gain in knowledge on its receptors and the mechanism of action. The receptor present inside the animal body recognizes and binds to β-glucan, which in turn renders the animal with high resistance and enhanced immune response. This review highlights β-glucan as an immunostimulant, its effective dosages, and route of administration and furthermore provides an outline on role of β-glucan in enhancing growth, survival, and protection against infectious pathogens pertaining to fishes and shellfishes. Study also summarizes the effect of β-glucan on its receptors, recognition of proteins, immune-related enzymes, immune-related gene expression and their mechanisms of action.

Molecular and immunological responses of the giant freshwater prawn, Macrobrachium rosenbergii, to the organophosphorus insecticide, trichlorfon

Trichlorfon is an organophosphorus (OP) insecticide that is used as an agriculture pesticide to destroy insects, a human medicine to combat internal parasites, and an ectoparasiticide in the livestock and aquaculture industries, but which has caused aquatic toxicity in the prawn industry. The aim of this study was to investigate the effects of trichlorfon on molecular and enzymatic processes of the immunological response of the giant freshwater prawn, Macrobrachium rosenbergii, at 0, 0.2, and 0.4mgL(-1) with 0, 3, 6, 12, and 24h of exposure. The total hemocyte count (THC), respiratory bursts (RBs), phenoloxidase (PO) activity, and superoxide dismutase (SOD) activity were examined to evaluate immunological responses and oxidative stress. Results showed that THCs of the prawn exposed to trichlorfon at both concentrations (0.2 and 0.4mgL(-1)) had increased after 12 and 24h; SOD and PO activities had significantly increased at 3h, whereas production of RBs had dramatically increased as oxidative stress at each sampling time after exposure to trichlorfon compared to the control. A potential biomarker of OPs, acetylcholinesterase (AChE) revealed a significant decrease after exposure for 6h, and showed a time-dependent tendency. Immune gene expressions, including prophenoloxidase (proPO), the lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP), peroxinectin (PE), α2-macroglubulin (α2M), transglutaminase (TG), and copper, zinc (Cu,Zn)-SOD, of prawns exposed to trichlorfon at 0, 0.2, and 0.4mgL(-1) for 0, 6, and 24h were further evaluated. Expressions of all of the immune genes significantly decreased when prawns were exposed to 0.4mgL(-1) trichlorfon for 24h, and among them, an increase in SOD expression was seen after exposure to 0.4mgL(-1) for 6h. Prawns exposed to trichlorfon within 24h exhibited the decrease of circulating hemocytes, and also the induction of oxidative stress, which caused subsequent damage to DNA formation of immune genes. From these results, we concluded that immunological responses and immune gene expressions of prawn exposed to trichlorfon at 0.4mgL(-1) for 24h were perturbed, thus causing a deficiency in immunity and subsequent increased susceptibility to pathogen infections.

Transcriptome analysis on Chinese shrimp Fenneropenaeus chinensis during WSSV acute infection

Previous studies have discovered a lot of immune-related genes responding to white spot syndrome virus (WSSV) infection in crustacean. However, little information is available in relation to underlying mechanisms of host responses during the WSSV acute infection stage in naturally infected shrimp. In this study, we employed next-generation sequencing and bioinformatic techniques to observe the transcriptome differences of the shrimp between latent infection stage and acute infection stage. A total of 64,188,426 Illumina reads, including 31,685,758 reads from the latent infection group and 32,502,668 reads from the acute infection group, were generated and assembled into 46,676 unigenes (mean length: 676 bp; range: 200-15,094 bp). Approximately 24,000 peptides were predicted and classified based on homology searches, gene ontology, clusters of orthologous groups of proteins, and biological pathway mapping. Among which, 805 differentially expressed genes were identified and categorized into 11 groups based on their possible function. Genes in the Toll and IMD pathways, the Ras-activated endocytosis process, the RNA interference pathway, anti-lipopolysaccharide factors and many other genes, were found to be activated in shrimp from latent infection stage to acute infection stage. The anti-bacterially proPO-activating cascade was firstly uncovered to be probably participated in antiviral process. These genes contain not only members playing function in host defense against WSSV, but also genes utilized by WSSV for its rapid proliferation. In addition, the transcriptome data provides detail information for identifying novel genes in absence of the genome database of shrimp.

A novel effect of imidazole derivative KK-42 on increasing survival of Aeromonas hydrophila challenged prawn Macrobrachium nipponense

Imidazole derivative KK-42 is well known as the insect growth regulator. Here we find that KK-42 pretreatment could promote the survival of Macrobrachium nipponense infected with Aeromonas hydrophila, which is considered to be possibly related to the prophenoloxidase (proPO), a conserved copper-containing enzyme that plays an important role in defense against pathogens. In this study, a full-length of proPO gene from M. nipponense haemocytes, designated as MnproPO, was firstly cloned and characterized. The full-length cDNA contained 2428 bp with a 2013 bp open reading frame encoding a putative proPO protein of 671 amino acids with a predicted molecular mass of 76.5 kDa and pI of 7.31. It was predicted to possess all the expected features of proPO members, including two putative copper-binding sites with six histidine residues and a thiol ester-like motif. Sequence analysis showed that MnproPO exhibited the highest amino acid sequence similarity (93%) to a proPO of Macrobrachium rosenbergii. The gene was expressed highly in haemocytes and weakly in hepatopancreas. Real-time PCR analysis revealed that the MnproPO expression increased significantly at 3, 12 and 24 h after KK-42 treatment, the PO activity also importantly rose from 6 to 48 h in KK-42-treated prawns and reached the maximum at 24 h with a 2.3-fold higher than that in control group. Injection of A. hydrophila could stimulate the MnproPO transcription and PO activity whether or not the prawns were pretreated by KK-42, the mRNA level increased obviously only at 3 h and 6 h after the bacterium injection (challenged control), but increased constantly during the phase of experiment except at 6 h under the condition of KK-42 pretreatment (challenged treatment group). The change trend of PO activity was basically similar to that of MnproPO expression. Our present results demonstrate that the MnproPO expression as well as PO activity may be induced by KK-42, which is likely one of the molecular mechanisms of KK-42 acts for increasing survival of the prawn infected with A. hydrophila.

Nonspecific effect of double-stranded (ds) RNA on prophenoloxidase (proPO) expression in Penaeus monodo n

RNA interference-mediated silencing is an effective way of controlling white spot syndrome virus (WSSV). However, the effect of RNAi on the innate immune mechanism is not well understood. Prophenoloxidase (proPO) is an important component of the shrimp innate immunity. In the present study, nonspecific effect of two double-stranded (ds)RNA-expressing constructs, one targeting vp28 gene of WSSV (pCMV-VP28-LH) and another targeting green fluorescent protein (GFP) (pCMV-GFP-LH) on proPO2 gene expression, is investigated. mRNA expression levels of proPO2 in hemocytes of DNA construct-injected shrimp were estimated using real-time PCR with elongation factor 1-α as internal control. Empty vector (pcDNA)-injected shrimp were used as experimental control. In pCMV-VP28-LH-injected shrimp, proPO2 showed significant upregulation until 48 h post-injection (p.i.). Similarly, pCMV-GFP-LH-injected animals showed high levels of expression until 72 h p.i. WSSV-challenged animals, compared to pcDNA-injected control group, showed no significant change in expression of the gene until 24 h. However, an increased expression was noticed at 48 h p.i. Our results suggest that neither the plasmids nor the long hairpin RNA expressed by the constructs has any nonspecific silencing effect on the proPO2 expression. On the contrary, the consistent upregulation of proPO2 observed in shrimp injected with dsRNA at early time-points indicates the possibility of nonspecific protection against WSSV infection.

Molecular cloning of prophenoloxidase and the effects of dietary β-glucan and rutin on immune response in hemocytes of the fleshy shrimp, Fenneropenaeus chinensis

To investigate the effects of dietary β-glucan (0.5 or 1 g kg⁻¹ diet: 0.5-BG, 1-BG) and rutin (0.5 or 1 g kg⁻¹ diet: 0.5-RT, 1-RT) after 10 days in the absence of pathogen challenge on the immune response of Fenneropenaeus chinensis, we determined total hemocyte count (THC) and the expression of four immune-related genes in hemocytes: those for prophenoloxidase (proPO), peroxinectin (PX), lipopolysaccharide and/or β-glucan binding protein (LGBP), and c-type lectin (CL). As a prerequisite for subsequent experiments, cDNA encoding proPO of the fleshy shrimp, Fenneropenaeus chinensis (f-proPO) was obtained from hemocytes; it had a full length of 3023 bp, with an open reading frame (ORF) of 2061bp, a 105-bp 5'-untranslated region, and a 906-bp 3'-untranslated region containing the poly A signal. The THCs of shrimp fed β-glucan of 1 g kg⁻¹ diet, and rutin of 1 g kg⁻¹ diet were significantly higher than that of the control (P < 0.05). The expression of proPO mRNA was slightly downregulated and that of LGBP mRNA was upregulated (except in 1-RT). PX and CL mRNA remained constitutively expressed in all groups. Our results reveal that β-glucan and rutin dietary supplements have minimal effect on immune response in the absence of pathogen challenge.

The expression of prophenoloxidase mRNA in red swamp crayfish, Procambarus clarkii, when it was challenged

The expression of the prophenoloxidase (proPO) gene was investigated in nine tissues of red swamp crayfish Procambarus clarkii, by real-time PCR after challenges by CpG oligodeoxynucleotide (ODN), Aeromonas hydrophila and white spot syndrome virus (WSSV). The results can be summarized as follows: (i) the expression level of the proPO gene in haemocytes was highest among nine studied tissues before the challenge; (ii) the expression of proPO increased in all studied tissues after stimulation by CpG ODN and WSSV, and also increased in all tissues, except the ovary, after the A. hydrophila challenge; (iii) the whole expression profiles were different, suggesting that different immune mechanisms may exist for crayfish that are resistant to WSSV and A. hydrophila, although the expression in haemocytes was similar before and after the WSSV and A. hydrophila challenges.

A novel type of prophenoloxidase from the kuruma prawn Marsupenaeus japonicus contributes to the melanization of plasma in crustaceans

Melanization is one of the major immune responses in arthropods. Prophenoloxidases (proPOs) catalyze the oxidation of mono- or o-diphenols, a reaction that is the key initial step of melanin formation. Well-characterized proPOs from crustaceans are synthesized in haemocytes and are released into plasma in response to microbial attack. However, PO activity does exist in the plasma of haemolymph without pathogenic infections. Here, we demonstrate that a novel type of proPO contributes to such PO activity in the plasma fraction of haemolymph of crustaceans. The novel enzyme, which was purified from the plasma of the kuruma prawn (Marsupenaeus japonicus), possessed strong and specific monophenol and o-diphenol oxidation activity compared with that of known haemocyte-type proPO. Amino acid sequence analyses indicated that this enzyme was distinct from the known proPO. The cDNA sequence and deduced amino acid sequence of this enzyme has a putative binuclear copper center, and showed approximately 30% and 20% identity with the primary structures of reported proPO and haemocyanin sequences of the kuruma prawn, respectively. Reverse transcription PCR analysis showed that this enzyme was synthesized in the hepatopancreas rather than in haemocytes. Although the primary structure and enzymatic properties of this novel enzyme suggested that it is a phenoloxidase, its biogenesis, tissue distribution, and oligomeric state resemble those of haemocyanin, which belongs to the same protein family (type III copper protein). This novel proPO enzyme may share a role with the already characterized version, itself a major component of the innate immune system in crustaceans.

Identification and cloning of a transglutaminase from giant freshwater prawn, Macrobrachium rosenbergii, and its transcription during pathogen infection and moulting

Complementary (c)DNA encoding transglutaminase (TG) messenger (m)RNA of the giant freshwater prawn, Macrobrachium rosenbergii, was cloned from haemocytes by a reverse-transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) using oligonucleotide primers based on the TG sequence of the horseshoe crab, Tachypleus tridentatus; tiger shrimp, Penaeus monodon; kuruma shrimp, Marsupenaeus japonicus; and crayfish, Pacifastacus leniusculus. The 2722-bp cDNA contained an open reading frame (ORF) of 2334 bp, a 72-bp 5'-untranslated region (UTR), and a 316-bp 3'-UTR containing a stop codon and a poly A tail. The molecular mass of the deduced amino acid (aa) sequence (778 aa) was 86.67 kDa with an estimated pI of 5.4. The M. rosenbergii TG (abbreviated MrTG, accession no.: JF309296) contains a typical transglutaminase-like homologue, two putative integrin-binding motifs (RGD), ten glycosylation sites, and four calcium-binding sites; a catalytic triad is present as in arthropod TGs. Sequence comparison and a phylogenetic analysis revealed that shrimp TG can be separated into three subgroups, penaeid TG1, freshwater crustacean TG2 and marine crustacean TG2, and MrTG was more closely related to TG2 than to TG1. MrTG mRNA and TG activities were detected in all tested tissues of M. rosenbergii, with MrTG mainly being synthesised by haemocytes. There was a negative correlation between clotting time of haemolymph, and MrTG expression and TG activity of haemocytes in prawn injected with Lactococcus garvieae. The pattern of MrTG mRNA expression and TG activity in haemocytes exhibited a contrary tendency with clotting time of haemolymph during the moult stages. Those results indicate that cloned MrTG is involved in the defence response, and is probably the major functional TG for haemolymph coagulation in M. rosenbergii.

Molecular cloning and characterization of lipopolysaccharide- and beta-1,3-glucan-binding protein from the giant freshwater prawn Macrobrachium rosenbergii and its transcription in relation to foreign material injection and the molt stage

Lipopolysaccharide (LPS)- and beta-1,3-glucan-binding protein (LGBP) complementary (c)DNA was cloned from the hepatopancreas of the giant freshwater prawn Macrobrachium rosenbergii using oligonucleotide primers and a reverse-transcription polymerase chain reaction (RT-PCR). Both 3'- and 5'-regions were isolated by the rapid amplification of cDNA ends (RACE) method. Analysis of the nucleotide sequence revealed that the cDNA clone has an open reading frame of 1389 bp encoding a protein of 378 amino acids (aa) including a 15-aa signal peptide. The calculated molecular mass of the mature protein (363 aa) was 41.2 kDa with an estimated pI of 4.73. The M. rosenbergii LGBP sequence contains (1) three putative integrin-binding motifs, (2) a glucanase motif, (3) a putative N-glycosylation site, (4) four protein kinase C phosphorylation sites, (5) four casein kinase II phosphorylation sites, and (6) a putative recognition motif. Sequence comparison showed that the deduced amino acids of LGBP of M. rosenbergii had overall similarities of 60-71% to those of known crustacean LGBPs and beta-1,3-glucan-binding proteins (BGBPs). The LGBP of M. rosenbergii was mainly expressed in the hepatopancreas. The LGBP transcript of M. rosenbergii was downregulated in haemocytes, but was upregulated in the hepatopancreas when injected with LPS and poly:IC after 12 h. The LGBP messenger (m)RNA expression of prawns in the postmolt stage was significantly upregulated in haemocytes, but downregulated in the hepatopancreas, which revealed a complementary relationship between haemocytes and the hepatopancreas in the molt cycle.

Two prophenoloxidases are important for the survival of Vibrio harveyi challenged shrimp Penaeus monodon

Phenoloxidase (PO) plays an important role in arthropod melanization. Previously, a prophenoloxidase (PmproPO1) gene was cloned and characterized from the hemocytes of the black tiger shrimp, Penaeus monodon. In the present study, we report a novel proPO gene (PmproPO2) belonging to the proPO family identified from the P. monodon EST database (http://pmonodon.biotec.or.th). The full-length sequence of PmproPO2 consists of 2513bp encoding a predicted 689 amino acid residues with a calculated molecular mass and pI of 79.21kDa and 6.69, respectively. It is predicted to possess all the expected features of proPO members, including two putative tyrosinase copper-binding motifs with six histidine residues and a thiol ester-like motif, sharing 67% amino acid sequence identity with PmproPO1. Tissue distribution analyses revealed that the two proPO genes are primarily expressed in the hemocyte. Gene silencing of either PmproPO1 or PmproPO2 or both by RNA interference (RNAi) resulted in a significant decrease in the respective endogenous proPO mRNA level in hemocytes and a reduction of total PO enzyme activity by 75, 73 and 88%, respectively. Experimental infection of P. monodon with the pathogenic bacterium, Vibrio harveyi, revealed that PmproPO silenced shrimps were more susceptible to bacterial infection than the control GFP injected shrimps, and suggesting that the two proPOs are important components in the shrimp immune defense.

A novel prophenoloxidase 2 exists in shrimp hemocytes

The prophenoloxidase (proPO)-activating system in crustaceans and other arthropods is regarded as a constituent of the immune system and plays an important role in defense against pathogens. Hitherto in crustaceans, only one proPO gene per species has been identified. Here we report the identification of a novel proPO-2 (LvproPO-2) from the hemocytes of Litopenaeus vannamei, which shows 72% identity to proPO-1 (LvproPO-1) cloned previously. Northern blotting analysis and quantitative real-time PCR reveal that LvproPO-2 is mainly expressed in the hemocytes, and its expression is down-regulated in shrimp challenged with white spot syndrome virus (WSSV). Western blotting analysis shows that most LvproPO-2/LvPO-2 (L. vannamei phenoloxidase-2) exists in the hemocytes, but not in plasma of L. vannamei. LvproPO-2/LvPO-2 could be detected on the hemocyte surface and the nucleus of hemocytes by indirect immunofluorescence assay (IFA). These findings provide insight into the molecular biological basis for further studying on the defense mechanism of shrimp innate immunity, especially on the proPO-activating system and melanization cascade of shrimp.

Comparison of gene expression profiles of Fenneropenaeus chinensis challenged with WSSV and Vibrio

Microarray technique was used to analyze the gene expression profiles of shrimp when they were challenged by WSSV and heat-inactivated Vibrio anguillarum, respectively. At 6 h post challenge (HPC), a total of 806 clones showed differential expression profile in WSSV-challenged samples, but not in Vibrio-challenged samples. The genes coding energy metabolism enzyme and structure protein were the most downregulated elements in 6 h post WSSV-challenged (HPC-WSSV) tissues. However, a total of 155 clones showed differential expression in the Vibrio-challenged samples, but not in WSSV-challenged samples. Serine-type endopeptidase and lysosome-related genes were the most upregulated elements in tissues 6 h post Vibrio challenge (HPC-Vibrio). Totally, 188 clones showed differential expression in both 6 and 12 HPC-WSSV and HPC-Vibrio samples. Most of the differentially expressed genes (185/188) were downregulated in the samples of 12 HPC-WSSV, whereas upregulated in the samples at 6 and 12 HPC-Vibrio and 6 HPC-WSSV. The expression profiles of three differentially expressed genes identified in microarray hybridization were analyzed in hemocytes, lymphoid organ, and hepatopancreas of shrimp challenged by WSSV or Vibrio through real-time PCR. The results further confirmed the microarray hybridization results. The data will provide great help for us in understanding the immune mechanism of shrimp responding to WSSV or Vibrio.

A prophenoloxidase from the Chinese mitten crab Eriocheir sinensis: gene cloning, expression and activity analysis

Prophenoloxidase (proPO) is a conserved copper-containing enzyme that plays important roles in immune response of crustaceans and insects. In the present study, the full-length cDNA of a prophenoloxidase (designated EsproPO) was cloned from haemocytes of Chinese mitten crab Eriocheir sinensis by expressed sequence tag (EST) and PCR techniques. The isolated 3549bp full-length cDNA of EsproPO contained a 2040bp open reading frame (ORF) encoding a putative proPO protein of 679 amino acids, a 5'-untranslated region (UTR) of 68bp, and a long 3'-UTR of 1441bp. Two putative copper-binding sites, a proteolytic activation site, and a complement-like motif (GCGWPQHM) were identified in the deduced amino acid sequence of EsproPO. Homology analysis revealed that EsproPO was highly similar to other proPOs from crustaceans with identities from 52% to 68%. The conserved domains and motifs, and higher similarity with other proPOs suggested that EsproPO was a member of the proPO family. The mRNA expression of EsproPO and PO specific activities in the tissues of hepatopancreas, gill, gonad, muscle, heart, eye and haemocytes were measured by quantitative real-time PCR and colorimetric assay, respectively. The mRNA transcripts of EsproPO and PO specific activities could be detected in all the examined tissues with the highest level both in hepatopancreas. Three peaks of EsproPO mRNA expression were recorded at 2h, 12h and 48h in haemocytes of Chinese mitten crab post Vibrio anguillarum challenge, which was consistent with the temporal profile of PO specific activity. The mRNA expression pattern and the activity fluctuation of EsproPO post V. anguillarum stimulation indicated that it was potentially involved in the acute response against invading bacteria in Chinese mitten crab.

Pattern of nucleotide substitution and divergence of prophenoloxidase in decapods

Despite the unprecedented development in identification and characterization of prophenoloxidase (proPO) in commercially important decapods, little is known about the evolutionary relationship, rate of amino acid replacement and differential selection pressures operating on proPO of different species of decapods. Here we report the evolutionary relationship among these nine decapod species based on proPO gene and types of selective pressures operating on proPO codon sites. Our analyses revealed that all the nine decapod species shared a common ancestor. The mean percentage sequence divergence at proPO gene was 34.4+/-0.6%. Pairwise estimates of nonsynonymous to synonymous ratio (omega) for Homarus americanus-H. gammarus is greater than one, therefore indicating adaptive evolution (functional diversification) of proPO in these two species. In contrast, strong purifying selection (omega<1) was observed in all other species pairs. However, phylogenetically closely related decapods revealed relatively higher omega value (omega=0.15+/-0.3) than the distantly related species pairs (omega=0.0075+/-0.005). These discrepancies could be due to higher fixation probability of beneficial mutation in closely related species. Maximum likelihood-based codon substitution analyses revealed a strong purifying selection operating on most of the codon sites, therefore suggesting proPO is functionally constrained (purifying selection). Codon substitution analyses have also revealed the evidence of strong purifying selection in haemocyanin subunits of decapods.

Peroxinectin gene transcription of the giant freshwater prawn Macrobrachium rosenbergii under intrinsic, immunostimulant, and chemotherapeutant influences

Peroxinectin (PE) gene expressions were determined using real-time PCR in the giant freshwater prawn Macrobrachium rosenbergii based on moulting; prawns were fed diets containing different concentrations of sodium alginate, and were exposed to different concentrations of copper sulphate, benzalkonium chloride (BKC), and trichlorfon. Results showed that PE mRNA expression of prawns was the highest in stage A, significantly decreased in stage B, and reached the lowest level in stages D0/D1. The PE transcript was significantly higher in prawns fed the 1.0 gkg(-1) sodium alginate-containing diet than those fed the 2.0 gkg(-1) sodium alginate-containing diet and those fed the control diet. PE transcripts significantly decreased in prawns exposed to 0.1-0.4 mgL(-1) copper sulphate after 96 h, 0.3-1.0 mgL(-1) BKC after 96 h, and 0.2-0.4 mgL(-1) trichlorfon after 48 h. It was concluded that the status of PE gene expression was seriously affected by the moult cycle, immunostimulant, and chemotherapeutants.

Cloning and characterisation of a prophenoloxidase from the haemocytes of mud crab Scylla serrata

A prophenoloxidase (proPO) cDNA was cloned from the haemocytes of mud crab Scylla serrata using oligonucleotide primers and RT-PCR. Both 3'- and 5'-regions were isolated by rapid amplification of cDNA end (RACE) method. Analysis of the nucleotide sequence revealed that the cDNA clone has a full length of 2663bp, with an open reading frame of 2019bp, a 124-bp 5'-untranslated region, and a 520-bp 3'-untranslated region containing a poly A signal. It encodes a protein of 673 amino acids with a predicted molecular weight of 77.5kDa and with an estimated pI of 5.96. It contains two putative tyrosinase copper-binding motifs with six histidine residues (copper A, 185, 189, 211, and copper B, 346, 350, 386). The proPO has thiol-ester-like motif (GCGWPQHM), which showed similar structural features of proPOs from other decapod crustaceans. It also contains five possible glycosylation sites, and a conserved C-terminal region common to all known proPOs. Sequence comparison showed that the proPO-deduced amino acid of mud crab S. serrata has an overall similarity of 78%, 57%, 56%, 51-55%, 54%, 53%, 52%, 52%, and 52% to that of Dungeness crab Cancer magister, American lobster Homarus americanus, European lobster Homarus gammarus, kuruma prawn Marsupenaeus japonicus, crayfish Pacifastacus leniusculus, white shrimp Litopenaeus vannamei, tiger shrimp Penaeus monodon, green tiger shrimp Penaeus semisulcatus, and giant freshwater prawn Macrobrachium rosenbergii, respectively. The proPO was strongly expressed in haemocytes, but not in heart, eyestalk, gill, muscle, ovary, hepatopancreas, stomach, and intestine. The proPO transcript of mud crab S. serrata increased significantly in 12 and 24h post-lipopolysaccharide (LPS) injection, but returned to the original values in 72h post injection.