Characterization of white spot syndrome virus replication in in vitro-cultured haematopoietic stem cells of freshwater crayfish, Pacifastacus leniusculus

Insect cells of Spodoptera frugiperda support WSSV gene replication but not progeny virion assembly

The lacking of stable and susceptible cell lines has hampered research on pathogenic mechanism of crustacean white spot syndrome virus (WSSV). To look for the suitable cell line which can sustain WSSV infection, we performed the studies on WSSV infection in the Spodoptera frugiperda (Sf9) insect cells. In consistent with our previous study in vitro in crayfish hematopoietic tissue cells, the WSSV envelope was detached from nucleocapsid around 2 hpi in Sf9 cells, which was accompanied with the cytoplasmic transport of nucleocapsid toward the cell nucleus within 3 hpi. Furthermore, the expression profile of both gene and protein of WSSV was determined in Sf9 cells after viral infection, in which a viral immediate early gene IE1 and an envelope protein VP28 exhibited gradually increased presence from 3 to 24 hpi. Similarly, the significant increase of WSSV genome replication was found at 3-48 hpi in Sf9 cells after infection with WSSV, indicating that Sf9 cells supported WSSV genome replication. Unfortunately, no assembled progeny virion was observed at 24 and 48 hpi in Sf9 cell nuclei as determined by transmission electron microscope, suggesting that WSSV progeny could not be assembled in Sf9 cell line as the viral structural proteins could not be transported into cell nuclei. Collectively, these findings provide a cell model for comparative analysis of WSSV infection mechanism with crustacean cells.

Experimental Infection Models and Their Usefulness for White Spot Syndrome Virus (WSSV) Research in Shrimp

White spot syndrome virus (WSSV) is marked as one of the most economically devastating pathogens in shrimp aquaculture worldwide. Infection of cultured shrimp can lead to mass mortality (up to 100%). Although progress has been made, our understanding of WSSV's infection process and the virus-host-environment interaction is far from complete. This in turn hinders the development of effective mitigation strategies against WSSV. Infection models occupy a crucial first step in the research flow that tries to elucidate the infectious disease process to develop new antiviral treatments. Moreover, since the establishment of continuous shrimp cell lines is a work in progress, the development and use of standardized in vivo infection models that reflect the host-pathogen interaction in shrimp is a necessity. This review critically examines key aspects of in vivo WSSV infection model development that are often overlooked, such as standardization, (post)larval quality, inoculum type and choice of inoculation procedure, housing conditions, and shrimp welfare considerations. Furthermore, the usefulness of experimental infection models for different lines of WSSV research will be discussed with the aim to aid researchers when choosing a suitable model for their research needs.

Propagation of IHHNV (Infectious hypodermal and haematopoietic necrosis virus)/PstDVI and MBV (Monodon baculovirus)/PmNV in shrimp primary haemocyte culture

In vitro propagation of shrimp viruses IHHNV (Infectious hematopoietic hypodermal necrosis virus)/PstDV1 and MBV (Monodon baculovirus)/PmNV in the primary haemocyte culture was successfully be accomplished in the present study. The haemocytes were maintained in double-strength L15 medium with growth supplements and antibiotics. Cytopathic changes observed in the cells were detachment, slendering of cells, vacuolation, and rounding of the cells. Replication of viruses in the culture was confirmed through the expression of DNA polymerase, polyhedrin and lef 4 of MBV and capsid gene of IHHNV. Ultrathin sections of haemocytes observed through electron microscopy revealed scattered chromatin, virogenic stroma and presence of viruses and occlusion bodies (MBV). The study revealed that primary haemocyte culture could be used as a platform for the propagation of a variety of shrimp viruses.

Shrimp (Penaeus vannamei) survive white spot syndrome virus infection by behavioral fever

Both endotherms and ectotherms may raise their body temperature to limit pathogen infection. Endotherms do this by increasing their basal metabolism; this is called 'fever'. Ectotherms do this by migrating to warmer places; this is called 'behavioral fever'. White spot syndrome virus (WSSV) is the most lethal pathogen of cultured shrimp. This study examined the existence of behavioral fever in WSSV-infected Penaeus vannamei shrimp. Shrimp weighing 15 ± 0.5 g were inoculated intramuscularly with WSSV and kept in a four-compartment system (4-CS) with all the chambers at 27 °C or with a thermal gradient (27-29-31-33 °C). During the first 4 days post-inoculation, 94% of the WSSV-inoculated shrimp died in the 4-CS with a fixed temperature (27 °C), while only 28% died in the 4-CS with a temperature gradient. The inoculated animals clearly demonstrated a movement towards the warmer compartments, whereas this was not the case with the mock- and non-inoculated animals. With primary lymphoid organ cell cultures, it was demonstrated that the increase of temperature from 27-29 °C to 31-33 °C inhibits virus replication. It is concluded that behavioral fever is used by shrimp to elevate their temperature when infected with WSSV. Behavioral fever prevents WSSV infection and mortality.

Activity of bovine lactoferrin in resistance to white spot syndrome virus infection in shrimp

White spot syndrome virus (WSSV) is a notorious pathogen that has plagued shrimp farming worldwide for decades. To date, there are no known treatments that are effective against this virus. Lactoferrin (LF) is a protein with many bioactivities, including antiviral properties. In this study, the activities and mechanisms of bovine LF (bLF) against WSSV were analyzed. Our results showed that bLF treatment significantly reduced shrimp mortalities caused by WSSV infection. bLF was found to have the ability to bind to surfaces of both host cells and WSSV virions. These bindings may have been a result of bLF interactions with the host cellular chitin binding protein and F1 ATP synthase β subunit protein and the WSSV structural proteins VP28, VP110, VP150 and VP160B. bLF demonstrated potential for development as an anti-WSSV agent in shrimp culture. Furthermore, these reactionary proteins may play a role in WSSV infection.

Invasion and Propagation of White Spot Syndrome Virus: Hijacking of the Cytoskeleton, Intracellular Transport Machinery, and Nuclear Import Transporters

The pathogenesis of white spot syndrome virus (WSSV) is largely unclear. In this study, we found that actin nucleation and clathrin-mediated endocytosis were recruited for internalization of WSSV into crayfish hematopoietic tissue (Hpt) cells. This internalization was followed by intracellular transport of the invading virions via endocytic vesicles and endosomes. After envelope fusion within endosomes, the penetrated nucleocapsids were transported along microtubules toward the periphery of the nuclear pores. Furthermore, the nuclear transporter CqImportin α1/β1, via binding of ARM repeat domain within CqImportin α1 to the nuclear localization sequences (NLSs) of viral cargoes and binding of CqImportin β1 to the nucleoporins CqNup35/62 with the action of CqRan for docking to nuclear pores, was hijacked for both targeting of the incoming nucleocapsids toward the nuclear pores and import of the expressed viral structural proteins containing NLS into the cell nucleus. Intriguingly, dysfunction of CqImportin α1/β1 resulted in significant accumulation of incoming nucleocapsids on the periphery of the Hpt cell nucleus, leading to substantially decreased introduction of the viral genome into the nucleus and remarkably reduced nuclear import of expressed viral structural proteins with NLS; both of these effects were accompanied by significantly inhibited viral propagation. Accordingly, the survival rate of crayfish post-WSSV challenge was significantly increased after dysfunction of CqImportin α1/β1, also showing significantly reduced viral propagation, and was induced either by gene silencing or by pharmacological blockade via dietary administration of ivermectin per os. Collectively, our findings improve our understanding of WSSV pathogenesis and support future antiviral designing against WSSV. IMPORTANCE As one of the largest animal DNA viruses, white spot syndrome virus (WSSV) has been causing severe economical loss in aquaculture due to the limited knowledge on WSSV pathogenesis for an antiviral strategy. We demonstrate that the actin cytoskeleton, endocytic vesicles, endosomes, and microtubules are hijacked for WSSV invasion; importantly, the nuclear transporter CqImportin α1/β1 together with CqRan were recruited, via binding of CqImportin β1 to the nucleoporins CqNup35/62, for both the nuclear pore targeting of the incoming nucleocapsids and the nuclear import of expressed viral structural proteins containing the nuclear localization sequences (NLSs). This is the first report that NLSs from both viral structure proteins and host factor are elaborately recruited together to facilitate WSSV infection. Our findings provide a novel explanation for WSSV pathogenesis involving systemic hijacking of host factors, which can be used for antiviral targeting against WSSV disease, such as the blockade of CqImportin α1/β1 with ivermectin.

Transcriptome profiles of red swamp crayfish Procambarus clarkii hematopoietic tissue in response to WSSV challenge

The crayfish Procambarus clarkii could achieve a high cumulative mortality after WSSV infections. To better understand the immune response to WSSV in hematopoietic tissue, the present study investigated the immunological response of P. clarkii and analyzed the expression of some hematopoietic cytokines. After assembly, there was an average of 47,712,411 clean reads were obtained in control and treatment groups. A total of 35,945 unigenes were discovered with N50 length of 1554 bp. Under functional classification, enrichment, and pathway analysis using different database, there were about 257 differentially expressed genes (DEGs) identified, of which 139 were up-regulated and 118 were down-regulated. The GO function analysis of these DEGs were mostly participated in activation of immune response, complement activation, complement binding, negative regulation of humoral immune response and secretory granule membrane. Under KEGG analysis, these DEGs were involved in ECM-receptor interaction, HIF-1 signaling pathway, Glycolysis/Gluconeogenesis, Thyroid hormone signaling pathway and Glucagon signaling pathway. The real-time quantitative PCR (RT-qPCR) analysis of 9 selected genes confirmed the reliability of RNA-Seq results. The present research provide for the first time the transcriptomic profile of P. clarkii hematopoietic tissue in response to WSSV infection and reveals the astakines may play important roles in antiviral immune response. The results of the present study will further enrich the theoretical basis of the crayfish immune system and provide new ideas for disease prevention and control.

Cytology, function and dynamics of stem and progenitor cells in decapod crustaceans

Stem cells play key roles in development, tissue homeostasis, regeneration, ageing and diseases. Comprehensive reviews on stem cells are available for the determinately growing mammals and insects and some lower invertebrates like hydra but are rare for larger, indeterminately growing invertebrates that can live for many decades. This paper reviews the cytology, function and dynamics of stem and progenitor cells in the decapod crustaceans, a species-rich and ecologically and economically important animal group that includes mainly indeterminate growers but also some determinate growers. Further advantages of decapods for stem cell research are almost 1000-fold differences in body size and longevity, the regeneration of damaged appendages and the virtual absence of age-related diseases and tumours in the indeterminately growing species. The available data demonstrate that the Decapoda possess a remarkable variety of structurally and functionally different stem cells in embryos and larvae, and in the epidermis, musculature, haematopoietic tissue, heart, brain, hepatopancreas, olfactory sense organs and gonads of adults. Some of these seem to be rather continuously active over a lifetime but others are cyclically activated and silenced in periods of days, weeks and years, depending on the specific organ and function. Stem cell proliferation is triggered by signals related to development, moulting, feeding, reproduction, injury, infection, environmental enrichment and social status. Some regulatory pathways have already been identified, including the evolutionarily conserved GATA-binding and runt-domain transcription factors, the widespread neurotransmitter serotonin, the arthropod-specific hormone 20-hydroxyecdysone and the novel astakine growth factors. Knowledge of stem cells in decapods primarily refines our picture on the development, growth and maintenance of tissues and organs in this animal group. Cultured decapod stem cells have good potential for toxicity testing and virus research with practical relevance for aquaculture. Knowledge of stem cells in decapods also broadens our understanding of the evolution of stem cells and regeneration in the animal kingdom. The stem cells of long-lived, indeterminately growing decapods may hold the key to understanding how stem and progenitor cells function into old age without adverse side effects, possibly evoking new ideas for the development of anti-ageing and anti-cancer treatments in humans.

Immune properties of invertebrate phenoloxidases

Melanin production from different types of phenoloxidases (POs) confers immunity from a variety of pathogens ranging from viruses and microorganisms to parasites. The arthropod proPO expresses a variety of activities including cytokine, opsonin and microbiocidal activities independent of and even without melanin production. Proteolytic processing of proPO and its activating enzyme gives rise to several peptide fragments with a variety of separate activities in a process reminiscent of vertebrate complement system activation although proPO bears no sequence similarity to vertebrate complement factors. Pathogens influence proPO activation and thereby what types of immune effects that will be produced. An increasing number of specialised pathogens - from parasites to viruses - have been identified who can synthesise compounds specifically aimed at the proPO-system. In invertebrates outside the arthropods phylogenetically unrelated POs are participating in melanization reactions obviously aimed at intruders and/or aberrant tissues.

In vitro propagation of infectious myonecrosis virus in C6/36 mosquito cell line

Infectious myonecrosis (IMN) is an important shrimp viral disease caused by infectious myonecrosis virus (IMNV). Based on previous reports, an attempt was made to propagate IMNV in apparently healthy C6/36 subclone of Aedes albopictus cell line. The confirmatory assays such as RT-PCR, real-time PCR and bioassay revealed that C6/36 cells were found to be susceptible to IMNV and these cells could be used easily for isolation and propagation of IMNV. The results of real-time PCR assay showed that a lower C_T value of 22.25 in IMNV-infected cells was obtained on 10 day post-infection (d p.i.), whereas the higher C_T value of 35.21 was obtained in IMNV-infected cells on 2 d p.i. There is no significant difference between C_T values of IMNV production in vitro using C6/36 cell line and in vivo using shrimp. The IMNV propagated in C6/36 cells is capable of infecting shrimp and caused 100% mortality in shrimp. Clinical signs observed in shrimp injected with IMNV propagated in C6/36 cell line were found to be similar to naturally infected shrimp.

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).

'PmLyO-Sf9 - WSSV complex' could be a platform for elucidating the mechanism of viral entry, cellular apoptosis and replication impediments

White spot syndrome virus (WSSV) is the most devastating pathogen found in shrimp aquaculture. The lack of certified continuous/established cell lines from penaeid shrimp restricts in vitro studies on the viruses to bring out effective prophylactic and therapeutic measures. In this context, a novel hybrid cell line named, PmLyO-Sf9, consisting of shrimp and Sf9 genomes has been established and employed to study WSSV susceptibility and multiplication. The hybrid cells were exposed to the shrimp virus WSSV and cytopathic effects (CPE) such as (a) enlargement of cells, (b) cessation cell division, (c) granulation of cytoplasm, (d) rounding off of cells, shortening and disappearance of tail-like structures and (e) detachment from the flask. Expression of immediate early genes such as ie 1, dnapol, rr1, tk-tmk, and pk 1could be confirmed indicating that viral DNA replication in the PmLyO-Sf9 took place followed by the expression of late genes such as VP-28, VP-26, VP-15 and VP-19. Electron micrograph of WSSV infected cells demonstrated marginated dense zones in the nucleus with clumped chromatin, and the mid zone with virus-like particles. However, neither discrete virus particles nor the culture supernatant having infectivity could be observed suggesting that virions were not getting formed in the cells. This is the first report of the susceptibility of PmLyO-Sf9 to WSSV, and the 'PmLyO-Sf9 - WSSV Complex' formed, defined as the infected status of PmLyO-Sf9 with WSSV, could be of use for unraveling at molecular level the mechanism of viral entry, replication impediments and cellular apoptosis.

The shrimp microsporidian Enterocytozoon hepatopenaei (EHP): Biology, pathology, diagnostics and control

Disease is a major limiting factor in the global production of cultivated shrimp. The microsporidian parasite Enterocytozoon hepatopenaei (EHP) was formally characterized in 2009 as a rare infection of the black tiger shrimp Penaeus monodon. It remained relatively unstudied until mid-2010, after which infection with EHP became increasingly common in the Pacific whiteleg shrimp Penaeus vannamei, by then the most common shrimp species farmed in Asia. EHP infects the hepatopancreas of its host, causing hepatopancreatic microsporidiosis (HPM), a condition that has been associated with slow growth of the host in aquaculture settings. Unlike other infectious disease agents that have caused economic losses in global shrimp aquaculture, EHP has proven more challenging because too little is still known about its environmental reservoirs and modes of transmission during the industrial shrimp production process. This review summarizes our current knowledge of the EHP life cycle and the molecular strategies that it employs as an obligate intracellular parasite. It also provides an analysis of available and new methodologies for diagnosis since most of the current literature on EHP focuses on that topic. We summarize current knowledge of EHP infection and transmission dynamics and currently recommended, practical control measures that are being applied to limit its negative impact on shrimp cultivation. We also point out the major gaps in knowledge that urgently need to be bridged in order to improve control measures.

Environmental concentrations of sulfamethoxazole increase crayfish Pacifastacus leniusculus susceptibility to White Spot Syndrome Virus

Antibiotics used for humans and livestock are emerging as pollutants in aquatic environments. However, little is known about their effect on aquatic organisms, especially in crustaceans. In the present study, the freshwater crayfish Pacifastacus leniusculus was exposed during 21 days to environmental concentrations of sulfamethoxazole (SMX) (100 ng/L and 1 μg/L). Subsequently, the crayfish susceptibility to infection was evaluated by using White Spot Syndrome Virus (WSSV) challenge, a well-known crustacean pathogen. The median survival time of the infected crayfish exposed to 100 ng/L SMX was one day, whereas the control and the group exposed to 1 μg/L SMX survived for two and three days, respectively. In order to elucidate the effect of SMX upon the crayfish immune response, new sets of crayfish were exposed to the same SMX treatments to evaluate mRNA levels of immune-related genes which are expressed and present in hemocytes and intestine, and to perform total and differential hemocyte counts. These results show a significant down-regulation of the antimicrobial peptide (AMP) Crustin 3 in hemocytes from the 100 ng/L SMX group, as well as a significant up-regulation of the AMP Crustin 1 in intestines from the 1 μg/L SMX group. Semigranular and total hemocyte cell number were observed to be significantly lower after exposure to 100 ng/L SMX in comparison with the control group. The present study demonstrates that environmentally relevant SMX concentrations in the water at 100 ng/L led to an increased WSSV susceptibility, that may have been caused by a reduction of circulating hemocytes. Nevertheless, SMX concentrations of 1 μg/L could marginally and for a few days have an immunostimulatory effect.

Medium optimization and characterization of cell culture system from Penaeus vannamei for adaptation of white spot syndrome virus (WSSV)

The lack of shrimp cell lines and difficulty in establishing shrimp cell culture systems, with an appropriate medium is a major concern in the aquaculture sector. The present study attempts to address this issue by developing an in vitro cell culture system from various tissues (hemocytes, heart, lymphoid tissue, hepatopancreas, gill, eye stalk, and muscle) of Penaeus vannamei (P.vannamei) using commercially available L-15 medium. The cell culture medium was formulated using five different media such as HBSCM-1, HBSCM-2, HBSCM-3, HBSCM-4, and HBSCM-5 containing L-proline and glucose with fetal bovine serum (FBS) supplements. Among the different media used, the HBSCM-5 medium with supplements showed good attachment and proliferation of cells with fibroblast-like, epithelioid, round, and adherent cell morphology in hemocyte culture. The same medium was further screened using different tissues to enhance the cell growth. The hemocytes, heart, and lymphoid tissue cells were passaged five times and maintained up to 20 days. Hepatopancreas and gill cells initially showed good morphological features and survived for more than ten days following subculture cells. Eye stalks and muscle cells perished within five days and did not show any unique morphology. The primary hemocyte cells were subjected to species identification, using cytochrome oxidase subunit I (COI) gene. To assess the primary hemocyte cell culture, cells were used for in vitro propagation of white spot syndrome virus (WSSV) and confirmed by the conventional polymerase chain reaction (PCR). Similarly, the primary cells were treated with bacterial extracellular products (ECPs) from Vibrio parahaemolyticus and Vibrio harveyi, to evaluate the cytotoxicity.

The effect of temperature on white spot disease progression in a crustacean, Pacifastacus leniusculus

The effects of temperature on the progression of White Spot Disease (WSD) have been studied in the freshwater crayfish Pacifastacus leniusculus. In this study, we aimed to understand the reason for previously observed low mortalities with white spot syndrome virus (WSSV) infected crayfish at low temperatures. The susceptibility of freshwater crayfish to WSSV was studied at different temperatures. The mortality rate at 6 °C was zero, meanwhile the animals kept at 22 °C developed WSD symptoms and died in a few days after WSSV injections, however upon transfer of animals from 6 °C to 22 °C the mortality reached 100% indicating that the virus is not cleared at 6 °C. Moreover, the VP28 expression at 6 °C was significantly lower compared to animals kept at 22 °C. We injected animals with demecolcine, an inhibitor that arrests the cell cycle in metaphase, and observed a delayed mortality. Furthermore, the VP28 expression was found to be lower in these animals receiving both injections with WSSV and demecolcine since cell proliferation was inhibited by demecolcine. We quantified WSSV copy numbers and found that virus entry was blocked at 6 °C, but not in demecolcine treatments. We supported this result by quantifying the expression of a clip domain serine protease (PlcSP) which plays an important role for WSSV binding, and we found that the PlcSP expression was inhibited at 6 °C. Therefore, our hypothesis is that the WSSV needs proliferating cells to replicate, and an optimum temperature to enter the host hematopoietic stem cells successfully.

Development of a primary culture system for haematopoietic tissue cells from Cherax quadricarinatus and an exploration of transfection methods

Various known and unknown viral diseases can threaten crustacean aquaculture. To develop prophylactic and therapeutic strategies against viruses, crustacean cell lines are urgently needed for immunology and virology studies. However, there are currently no permanent crustacean cell lines available. In this study, we developed a new method for preparing crayfish plasma (CP) and found that CP enhanced the proliferative capacity of haematopoietic tissue (hpt) cells from Cherax quadricarinatus by an EdU (5-ethynyl-2'-deoxyuridine) assay. The optimal CP concentration for hpt cell culture and the optimal subculture method are discussed. To achieve efficient expression of a foreign gene in hpt cells cultured in vitro, different transfection methods and vectors were analysed. We found that Lipofectamine 2000 could be used to efficiently transfect a foreign vector into hpt cells and exhibited a lower level of cytotoxicity than the other methods tested, and transfection of pEGFP-N1/w249 and pDHsp70-EGFP-FLAG resulted in high EGFP expression. By transmission electron microscopy (TEM) and virus copy number analysis, we found that white spot syndrome virus (WSSV) could infect hpt cells and multiply efficiently. Our results implied that the crayfish hpt cell culture system we improved could be used as a replacement for immortal crustacean cell lines in viral infection studies. Our findings provide a solid foundation for future immortalization and gene function studies in crustacean cells.

Transfection of crayfish hematopoietic tissue cells

Transfection is a powerful tool useful for studying gene function. Establishing transfection methods that enable highly efficient DNA uptake has become increasingly important. The crayfish hematopoietic tissue (Hpt) cell cultures have been proven to be suitable for studies on immunity and cell differentiation in crustaceans including shrimps, but no efficient gene transfer and expression method is available for these cells. Here we report a novel and highly efficient DNA transfection system based on electroporation. This method depends on a recombinant plasmid with the promoter from white spot syndrome virus immediate-early gene wsv249. This plasmid could be introduced into primary cells and efficiently express foreign genes by electroporation. By optimizing different electroporation parameters, more than 30% transfection efficiency could be achieved with the relative viability of cells around 50%. This is the first report of gene introduction to crayfish Hpt cells and will be useful for the expanding our research on crustacean immunity.

An Ns1abp-like gene promotes white spot syndrome virus infection by interacting with the viral envelope protein VP28 in red claw crayfish Cherax quadricarinatus

Influenza A virus non-structural-1A binding protein (named as Ns1abp) was originally identified as a host protein from human that bound to the viral NS-1 protein. In our previous study, the expression of an Ns1abp-like gene (denoted as CqNs1abp-like gene) was found to be up-regulated in a transcriptome library from the haematopoietic tissue (Hpt) cells of red claw crayfish Cherax quadricarinatus post white spot syndrome virus (WSSV) infection. To elucidate the role of CqNs1abp-like gene involved in WSSV infection, we cloned the CqNs1abp-like gene in which the open reading frame was 2232 bp, encoding 743 amino acids with two typical domains of one BTB (Broad-Complex, Tramtrack and Bric a brac) domain at N-terminal and six Kelch domains at C-terminal. The gene expression profile showed that the mRNA transcript of CqNs1abp-like gene was widely expressed in all the tested tissues with highest expression in nerve, relatively high expression in Hpt and lowest expression in eyestalk. Importantly, both the WSSV entry and the viral replication were significantly reduced in Hpt cells after gene silencing of CqNs1abp-like gene. By using protein pull-down assay, we found that the recombinant BTB domain, six Kelch domains and CqNs1abp-like intact protein were all bound to the WSSV envelope protein VP28, respectively, in which the BTB domain showed slightly less binding affinity than that of the six Kelch domains or the recombinant intact protein. Besides, the WSSV entry into Hpt cells was clearly decreased when the virus was pre-incubated with the recombinant BTB domain, six Kelch domains, or the recombinant CqNs1abp-like intact protein, respectively, suggesting that the CqNs1abp-like gene was likely to function as a putative recognition molecular towards WSSV infection in a crustacean C. quadricarinatus. Taken together, these data shed new light on the mechanism of WSSV infection and a putatively novel target on anti-WSSV infection in crustacean farming.

Experimental inoculation of oriental river prawn Macrobrachium nipponense with white spot syndrome virus (WSSV)

The oriental river prawn Macrobrachium nipponense is an economically important species that is widely farmed in China. White spot syndrome virus (WSSV) is one of the most devastating pathogens of the cultured shrimp Litopenaeus vannamei, responsible for massive loss of its commercial products worldwide. We investigated the infectivity and pathogenicity of WSSV in adult M. nipponense using standardized conditions for L. vannamei. The median lethal dose of WSSV in adult M. nipponense was 103.84±0.06 copies g-1, which was about 1000-fold higher than in L. vannamei (100.59±0.22 copies g-1). WSSV was detected by 2-step PCR in the gills, hepatopancreas, muscle, stomach, heart, gut, nerve, integument, pereopod, eyestalk, testis, and ovary of experimentally infected dead M. nipponense. Lesions were observed histologically following WSSV injection, showing basophilic intranuclear inclusion bodies in the hepatopancreas and subsequently in the gills. The clearance of WSSV was observed in hepatopancreas and gills at 48 and 96 h post-inoculation, respectively. No histological lesions were detected in muscle from 0-96 h post-injection. The results show that the oriental river prawn M. nipponense can be infected by WSSV and the infections are self limiting over time; therefore, M. nipponense may serve as a useful model for studying resistance to WSSV.

CqToll participates in antiviral response against white spot syndrome virus via induction of anti-lipopolysaccharide factor in red claw crayfish Cherax quadricarinatus

It is well known that Tolls/Toll like receptors (TLRs), a family of pattern recognition receptors, play important roles in immune responses. Previously, we found that a Toll transcript was increased in a transcriptome library of haematopoietic tissue (Hpt) cells from the red claw crayfish Cherax quadricarinatus post white spot syndrome virus infection. In the present study, a full-length cDNA sequence of Toll receptor (named as CqToll) was identified with 3482 bp which contained an open reading frame of 3021 bp encoding 1006 amino acids. The predicted structure of CqToll protein was composed of three domains, including an extracellular domain of 19 leucine-rich repeats residues, a transmembrane domain and an intracellular domain of 138 amino acids. Tissue distribution analysis revealed that CqToll was expressed widely in various tissues determined from red claw crayfish with highest expression in haemocyte but lowest expression in eyestalk. Importantly, significant lower expression of the anti-lipopolysacchride factor (CqALF), an antiviral antimicrobial peptide (AMP) in crustaceans, but not CqCrustin was observed after gene silencing of CqToll in crayfish Hpt cell cultures, indicating that the CqALF was likely to be positively regulated via Toll pathway in red claw crayfish. Furthermore, the transcription of both an immediate early gene and a late envelope protein gene VP28 of WSSV were clearly enhanced in Hpt cells if silenced with CqToll, suggesting that the increase of WSSV replication was likely to be caused by the lower expression of the CqALF resulted from the loss-of-function of CqToll. Taken together, these data implied that CqToll might play a key role in anti-WSSV response via induction of CqALF in a crustacean C. quadricarinatus.

A Pacifastacus leniusculus serine protease interacts with WSSV

Serine proteases are involved in many critical physiological processes including virus spread and replication. In the present study, we identified a new clip-domain serine protease (PlcSP) in the crayfish Pacifastacus leniusculus hemocytes, which can interact with the White Spot Syndrome Virus (WSSV) envelope protein VP28. It was characterized by a classic clip domain with six strictly conserved Cys residues, and contained the conserved His-Asp-Ser (H-D-S) motif in the catalytic domain. Furthermore, signal peptide prediction revealed that it has a 16-residue secretion signal peptide. Tissue distribution showed that it was mainly located in P. leniusculus hemocytes, and its expression was increased in hemocytes upon WSSV challenge. In vitro knock down of PlcSP decreased both the expression of VP28 and the WSSV copy number in hematopoietic stem (HPT) cells. Accordingly, these data suggest that the new serine protease may be of importance for WSSV infection into hematopoietic cells.

Characterization and prevalence of a novel white spot syndrome viral genotype in naturally infected wild crayfish, Procambarus clarkii, in Shanghai, China

White spot syndrome virus (WSSV) infection is commonly detected by vp28-qPCR assay in wild crayfish, Procambarus clarkii, a widespread crustacean species in the aquatic environment in China. The virions of crayfish WSSV have been isolated and purified. Based on TEM observation, they exhibited morphological structures that are identical to known WSSV. In addition, the WSSV major envelope protein VP28 was observed based on Western blot analysis of the total structural proteins of crayfish WSSV. PCR amplification and sequencing analyses of variable regions of ORF14/15, ORF23/24 and ORF94, along with viral genomic sequencing and phylogenomic analysis, indicated that the crayfish WSSV, named WSSV-CN-Pc, represents a new WSSV genotype. Intramuscular injection bioassay revealed that WSSV-CN-Pc was as virulent as the WSSV Taiwan strain. The WSSV-CN-Pc exhibited characteristics of a dominant genotype, with high infection load (107-108 WSSV/mg) and high prevalence (91.7%, 110 of 120 crayfish samples) observed in the surveyed wild crayfish. WSSV-CN-Pc was also detected, with similar infection pattern as observed in crayfish, in farmed Litopenaeus vannamei shrimp that shared similar ecological niches with the sampled crayfish. Our results indicated that there was horizontal transmission of WSSV-CN-Pc between crayfish and shrimp in nature. Our findings also implicated that crayfish and shrimp farming should be integrated and managed with cautions in order to reduce the risk of spread and circulation of WSSV in the aquatic environment.

Identification of an anti-lipopolysacchride factor possessing both antiviral and antibacterial activity from the red claw crayfish Cherax quadricarinatus

It is well-known that anti-lipopolysacchride factors (ALFs) are involved in the recognition and elimination of invading pathogens. In this study, the full-length ALF cDNA sequence of the red claw crayfish Cherax quadricarinatus (termed CqALF) was cloned from a suppression subtractive hybridization library constructed using red claw crayfish hematopoietic tissue cell (Hpt cell) cultures following challenge with white spot syndrome virus (WSSV). The full-length cDNA sequence of CqALF was 863 bp, and the open reading frame encoded 123 amino acids with a signal peptide in the N-terminus and a conserved LPS-binding domain. Unlike most ALFs, which are highly expressed in haemocytes, high expression levels of CqALF were detected in epithelium, the stomach and eyestalks, while lower expression was detected in Hpt, nerves, the heart, muscle tissue, gonads, haemocytes, intestines, gills and the hepatopancreas. To further explore the biological activities of CqALF, mature recombinant CqALF protein (rCqALF) was expressed and purified using a eukaryotic expression system, and an antimicrobial activity test was carried out. rCqALF clearly exerted antiviral activity, as evidenced by the severe disruption of the envelope of intact WSSV virions following co-incubation of virions with rCqALF. Additionally, pre-incubation of WSSV with rCqALF resulted in both a significant reduction in WSSV replication in red claw crayfish Hpt cell cultures and an increased survival rate among animals. Furthermore, rCqALF was effective against both Gram-negative bacteria and Gram-positive bacteria, particularly Shigella flexneri and Staphylococcus aureus. A membrane integrity assay suggested that rCqALF was unlikely to disrupt bacterial membrane integrity compared to cecropin P1. Taken together, these data suggest that CqALF may play an important role in immune defence in the crustacean C. quadricarinatus.

Proteomic analysis by iTRAQ in red claw crayfish, Cherax quadricarinatus, hematopoietic tissue cells post white spot syndrome virus infection

To elucidate proteomic changes of Hpt cells from red claw crayfish, Cherax quadricarinatus, we have carried out isobaric tags for relative and absolute quantitation (iTRAQ) of cellular proteins at both early (1 hpi) and late stage (12 hpi) post white spot syndrome virus (WSSV) infection. Protein database search revealed 594 protein hits by Mascot, in which 17 and 30 proteins were present as differentially expressed proteins at early and late viral infection, respectively. Generally, these differentially expressed proteins include: 1) the metabolic process related proteins in glycolysis and glucogenesis, DNA replication, nucleotide/amino acid/fatty acid metabolism and protein biosynthesis; 2) the signal transduction related proteins like small GTPases, G-protein-alpha stimulatory subunit, proteins bearing PDZ- or 14-3-3-domains that help holding together and organize signaling complexes, casein kinase I and proteins of the MAP-kinase signal transduction pathway; 3) the immune defense related proteins such as α-2 macroglobulin, transglutaminase and trans-activation response RNA-binding protein 1. Taken together, these protein information shed new light on the host cellular response against WSSV infection in a crustacean cell culture.

Yellow head virus infection in black tiger shrimp reveals specific interaction with granule-containing hemocytes and crustinPm1 as a responsive protein

Yellow head virus (YHV) causes acute infections and mass mortality in black tiger shrimp culture. Our study aims to investigate molecular interaction between YHV and circulating hemocytes of Penaeus monodon at early infection. Total shrimp hemocytes were isolated by Percoll gradient centrifugation and identified by flow cytometric analysis. At least three types of hemocyte cells were identified as hyaline, semi-granular, and granular hemocytes. Experimental infection of YHV in shrimp culture demonstrated drastic changes in total and each hemocyte cell counts. Immunohistochemistry analysis demonstrated interaction and replication of YHV mainly with the granule-containing hemocytes and little to none in hyaline cell. These granule-containing hemocytes are proposed to be YHV targets providing the first line of defense to viral infection. Protein expression profiling of granule-containing hemocytes revealed several immune-responsive proteins including antimicrobial protein crustins (crustinPm1 and crustinPm4), alpha-2-macroglobulin, and kazal-type serine proteinase inhibitor. During an early phase of YHV infection at 6 hpi crustinPm1 illustrated a significant increase of mRNA and protein expression level in plasma. The results suggest that an antimicrobial crustinPm1 may participate in shrimp defense mechanism against YHV, especially on the granule-containing hemocytes.

Cellular and molecular markers in monitoring the fate of lymphoid cell culture from Penaeus monodon Fabricius (1798)

Lymphoid cell culture from penaeid shrimps has gained much acceptance as an in vitro platform to facilitate research on the development of prophylaxis, and therapeutic strategies against viruses and for cell line development. However, lymphoid cells can be used as platform for in vitro research, only if they are in metabolically and mitotically active state in vitro with unaltered cell surface receptors. Through this study, we addressed the response of lymphoid cells to a new microenvironment at cellular and molecular levels; including the study of mitotic events, DNA synthesis, expression profile of cell cycle genes, cytoskeleton organization, metabolic activity and viral susceptibility. The S-phase entry and synthesis of new DNA was recorded by immunoflourescent technique. Cdc2, CycA, CycB, EF-1α and BUB3 genes involved in cell cycle were studied in both the cells and tissue, of which EF-1α showed an elevated expression in cells in vitro (∼ 19.7%). Cytoskeleton network of the cell was examined by studying the organization of actin filaments. As the markers for metabolic status, mitochondrial dehydrogenase, protein synthesis and glucose assimilation by the cells were also assessed. Viral susceptibility of the cell was determined using WSSV to confirm the preservation of cellular receptors. This study envisages to strengthen the shrimp cell line research and to bring forth lymphoid cell culture system as a 'model' in vitro system for shrimp and crustaceans altogether.

White spot syndrome virus enters crayfish hematopoietic tissue cells via clathrin-mediated endocytosis

White spot syndrome virus (WSSV) is a major pathogen of aquacultured shrimp. However, the mechanism of its entry remains poorly understood. In this study, by analyzing the internalization of WSSV using crayfish hematopoietic tissue (HPT) cells, we showed that WSSV virions were engulfed by cell membrane invaginations sharing the features of clathrin-coated pits and then internalized into coated cytoplasmic vesicles. Further investigation indicated that WSSV internalization was significantly inhibited by chlorpromazine (CPZ) but not genistein. The internalized virions were colocalized with endogenous clathrin as well as transferrin which undergoes clathrin-dependent uptake. Preventing endosome acidification by ammonium chloride (NH4Cl) or chloroquine (CQ) dramatically reduced WSSV entry as well. Moreover, disturbance of dynamin activity or depletion of membrane cholesterol also blocked WSSV uptake. These data indicate that WSSV enters crayfish HPT cells via clathrin-mediated endocytosis in a pH-dependent manner, and membrane cholesterol as well as dynamin is critical for efficient viral entry.

Crayfish hematopoietic tissue cells but not hemocytes are permissive for white spot syndrome virus replication

Hemocytes are the major immune cells of crustaceans which are believed to be essential for the pathogenesis of white spot syndrome virus (WSSV) infection. Crayfish hemocytes and hematopoietic tissue (HPT) cells have been found to be susceptible to WSSV infection, but the procedure of WSSV infection to both cell types has not yet been carefully investigated. In this study, we analyzed the infection and proliferation of WSSV in crayfish hemocytes as well as HPT cells in detail through transmission electronic microscopy (TEM). The results showed that WSSV could enter both hemocytes and HPT cells through endocytosis, but the production of progeny virus was only achieved in HPT cells. Further investigation demonstrated that although WSSV could transcribe its genes in both cell types, viral genome replication and structural protein expression were unsuccessful in hemocytes, which may be responsible for the failure of progeny production. Therefore, we propose that both hemocytes and HPT cells are susceptible to WSSV infection but only HPT cells are permissive to WSSV replication. These findings will extend our knowledge of the interaction between WSSV and the host immune system.

Identification of genes involved in taura syndrome virus resistance in litopenaeus vannamei

Abstract The goal of the present research was to identify the genes that are differentially expressed between two lineages of Pacific white shrimp Litopenaeus vannamei displaying different susceptibilities to Taura syndrome virus (TSV) and to understand the molecular pathways involved in resistance to the disease. An oligonucleotide microarray was constructed and used to identify several genes that were differentially expressed in the two L. vannamei lineages following infection with TSV. Individual L. vannamei from either resistant or susceptible lineages were exposed via injection to TSV. Individuals were removed at 6 and 24 h postinfection, and gene expression was assessed with the in-house microarray. The microarray data resulted in the selection of a set of 397 genes that were altered by TSV exposure between the different lineages. Significantly differentially expressed genes were subjected to hierarchical clustering and revealed a lineage-dependent clustering at 24 h postinoculation, but not at 6 h postinoculation. Discriminant analysis resulted in the identification of a set of 11 genes that were able to correctly classify Pacific white shrimp as resistant or susceptible based on gene expression data. Received June 21, 2013; accepted October 24, 2013.

Recent advances in crayfish hematopoietic stem cell culture: a model for studies of hemocyte differentiation and immunity

Hematopoiesis is the process by which blood cells (hemocytes) mature and subsequently enter the circulation and we have developed a new technique to culture the hematopoietic progenitor cells in vitro. The reason for the successful culture was the isolation of a plasma protein that turned out to be a novel cytokine, astakine 1 (Ast1) containing a domain present in several vertebrates, so-called prokineticins. Now we have detected several astakines from other invertebrate species. Depending on our discovery of the cytokine Ast1 we have an opportunity to study in detail the differentiation of cells in the hematopoietic tissue of a crustacean, a tissue of evolutionary interest for studies of the connection between the vascular system and the nervous system. We have been able to isolate the entire hematopoietic tissue and for the first time detected a link between this tissue and the brain. We have further localized a proliferation center in the tissue and characterized its different parts. We have also used this system to isolate a new hematopoietic factor CHF that is important in the crossroad between apoptosis and hemocyte differentiation. Our technique for culture of crayfish hematopoietic stem cells provides a simple tool for studying the mechanism of hematopoiesis, but also enables detailed studies of immune defense reactions. Further, the culture system has been used for studies of viral defense and the system is suitable for gene silencing which allows functional characterization of different molecules involved in host defense as well as in hemocyte differentiation.

High efficacy of white spot syndrome virus replication in tissues of freshwater rice-field crab, Paratelphusa hydrodomous (Herbst)

An attempt was made to determine the replication efficiency of white spot syndrome virus (WSSV) of shrimp in different organs of freshwater rice-field crab, Paratelphusa hydrodomous (Herbst), using bioassay, PCR, RT-PCR, ELISA, Western blot and real-time PCR analyses, and also to use this crab instead of penaeid shrimp for the large-scale production of WSSV. This crab was found to be highly susceptible to WSSV by intramuscular injection. PCR and Western blot analyses confirmed the systemic WSSV infection in freshwater crab. The RT-PCR analysis revealed the expression of VP28 gene in different organs of infected crab. The indirect ELISA was used to quantify the VP28 protein in different organs of crab. It was found that there was a high concentration of VP28 protein in gill tissue, muscle, haemolymph and heart tissue. The copy number of WSSV in different organs of infected crab was quantified by real-time PCR, and the results revealed a steady increase in copy number in different organs of infected crab during the course of infection. The viral inoculum prepared from different organs of infected crab caused significant mortality in tiger prawn, Penaeus monodon (Fabricius). The results revealed that this crab can be used as an alternate host for WSSV replication and production.

Biology, Host Range, Pathogenesis and Diagnosis of White spot syndrome virus

White spot syndrome virus (WSSV) is the most serious viral pathogen of cultured shrimp. It is a highly virulent virus that can spread quickly and can cause up to 100 % mortality in 3-10 days. WSSV is a large enveloped double stranded DNA virus belonging to genus Whispovirus of the virus family Nimaviridae. It has a wide host range among crustaceans and mainly affects commercially cultivated marine shrimp species. The virus infects all age groups causing large scale mortalities and the foci of infection are tissues of ectodermal and mesodermal origin, such as gills, lymphoid organ and cuticular epithelium. The whole genome sequencing of WSSV from China, Thailand and Taiwan have revealed minor genetic differences among different strains. There are varying reports regarding the factors responsible for WSSV virulence which include the differences in variable number of tandem repeats, the genome size and presence or absence of different proteins. Aim of this review is to give current information on the status, host range, pathogenesis and diagnosis of WSSV infection.

Susceptibility of testicular cell cultures of crab, Scylla serrata (Forskal) to white spot syndrome virus

Testicular cell culture of crab, Scylla serrata (Forskal) was used to study the effects of White spot syndrome virus (WSSV). We are showing the susceptibility of cell culture of crabs to WSSV. The proliferating cell culture of testes were maintained for more than 4 months in a medium prepared from L15 and crab saline supplemented with epidermal growth factor. The cell cultures inoculated with different concentrations of virus showed distinct cytopathic effects such as change in cell appearance, shrinkage and cell lysis. WSSV infection of cultured cells was confirmed by Nested PCR technique. The incorporation of viral DNA in cultured cells was shown by RAPD profile generated using 10-mer primers. The controls that were not exposed to WSSV did not show cytopathic effects. This work shows the usefulness of proliferating testicular cell culture for studying WSSV infection using molecular tools. Thus, this report gains significance as it opens new vistas for diagnostics and drugs for WSSV.

A novel JNK from Litopenaeus vannamei involved in white spot syndrome virus infection

The c-Jun N-terminal kinase (JNK), a member of MAP kinases, is a serine/threonine-specific protein kinase which responds to extracellular stimuli and regulate various cellular activities. It is well documented in innate immune responses and reported to be involved in various viral infections of mammals. In present study, we cloned JNK homolog in a crustacean, Litopenaeus vannamei (designated as LvJNK) and studied its role in white spot syndrome virus (WSSV) infection. Sequence analysis displayed that LvJNK shared high similarity with other members of the JNK subfamily, including the conserved TPY motif and serine/threonine protein kinase (S_TKc) domain. Western blot analysis showed that the activation of LvJNK took place in WSSV infection. LvJnk silencing mediated by specific dsRNA in shrimps could significantly inhibit the proliferation of the virus. Moreover, inhibition of shrimp JNK signaling pathway by specific inhibitor resulted in the reduction of WSSV replication and the delay of WSSV gene transcription. These results indicate for the first time that shrimp JNK is activated in response to WSSV infection and WSSV could benefit from JNK activation. It may facilitate our understanding of the molecular mechanism of virus infection and provided a potential target for preventing the WSSV infection.

Lymphoid organ cell culture system from Penaeus monodon (Fabricius) as a platform for white spot syndrome virus and shrimp immune-related gene expression

Shrimp cell lines are yet to be reported and this restricts the prospects of investigating the associated viral pathogens, especially white spot syndrome virus (WSSV). In this context, development of primary cell cultures from lymphoid organs was standardized. Poly-l-lysine-coated culture vessels enhanced growth of lymphoid cells, while the application of vertebrate growth factors did not, except insulin-like growth factor-1 (IGF-1). Susceptibility of the lymphoid cells to WSSV was confirmed by immunofluoresence assay using monoclonal antibody against the 28 kDa envelope protein of WSSV. Expression of viral and immune-related genes in WSSV-infected lymphoid cultures could be demonstrated by RT-PCR. This emphasizes the utility of lymphoid primary cell culture as a platform for research in virus-cell interaction, virus morphogenesis, up and downregulation of shrimp immune-related genes, and also for the discovery of novel drugs to combat WSSV in shrimp culture.

Identification of differentially transcribed genes in shrimp Litopenaeus vannamei exposed to osmotic stress and challenged with WSSV virus

The effects of hyposmotic stress and white spot syndrome virus (WSSV) challenge in expression was studied in the marine shrimp Litopenaeus vannamei. Messenger RNA from gills of shrimp submitted to osmotic stress was isolated to identify genes differentially expressed through the suppressive subtractive hybridization (SSH) method. Two subtractive libraries forward and two reverse were constructed to identify up and down-regulated genes under these conditions. About 192 clones were sequenced, of which 46 genes were identified. These genes encode proteins corresponding to a wide range of biological roles, including defense, cell signaling, electron transfer, cell proliferation and differentiation, apoptosis, intermediary metabolism, cytoskeleton and digestion. Among the identified genes, 19 were up-regulated and 27 were down-regulated in the animals kept at a lower ion concentration. We evaluated the expression of eight genes by RT-qPCR in shrimp submitted to hyposmotic conditions with and without WSSV challenge. The SSH enabled the identification of genes that are influenced by hyposmotic stress. A significant up-regulation was observed in lectin-C, QM, TGF beta inducible nuclear protein 1, ciclophilin, malate dehydrogenase, mitochondrial ATP synthase F chain and ATP synthase subunit 9 precursor transcripts. However, the expression of these genes in L. vannamei was not affected by WSSV infection both at isosmotic and hyposmotic conditions.

Gene transfection and expression in the primary culture of crayfish hemocytes

Lack of efficient gene delivery and expression methods is the major obstacle for crustacean research in the cellular level. Here, we reported the construction of an expression vector with a strong promoter from shrimp white spot syndrome virus. This vector could efficiently express foreign genes in the primary culture of crayfish hemocytes with the transfection efficiency between 5 and 10% by electroporation. Our findings provide a method for in vitro gene functional study in primary crayfish cells.

Differential gene expression profile from haematopoietic tissue stem cells of red claw crayfish, Cherax quadricarinatus, in response to WSSV infection

White spot syndrome virus (WSSV) is one of the most important viral pathogens in crustaceans. During WSSV infection, multiple cell signaling cascades are activated, leading to the generation of antiviral molecules and initiation of programmed cell death of the virus infected cells. To gain novel insight into cell signaling mechanisms employed in WSSV infection, we have used suppression subtractive hybridization (SSH) to elucidate the cellular response to WSSV challenge at the gene level in red claw crayfish haematopoietic tissue (Hpt) stem cell cultures. Red claw crayfish Hpt cells were infected with WSSV for 1h (L1 library) and 12h (L12 library), respectively, after which the cell RNA was prepared for SSH using uninfected cells as drivers. By screening the L1 and L12 forward libraries, we have isolated the differentially expressed genes of crayfish Hpt cells upon WSSV infection. Among these genes, the level of many key molecules showed clearly up-regulated expression, including the genes involved in immune responses, cytoskeletal system, signal transduction molecules, stress, metabolism and homestasis related genes, and unknown genes in both L1 and L12 libraries. Importantly, of the 2123 clones screened, 176 novel genes were found the first time to be up-regulated in WSSV infection in crustaceans. To further confirm the up-regulation of differentially expressed genes, the semi-quantitative RT-PCR were performed to test twenty randomly selected genes, in which eight of the selected genes exhibited clear up-regulation upon WSSV infection in red claw crayfish Hpt cells, including DNA helicase B-like, multiprotein bridging factor 1, apoptosis-linked gene 2 and an unknown gene-L1635 from L1 library; coatomer gamma subunit, gabarap protein gene, tripartite motif-containing 32 and an unknown gene-L12-254 from L2 library, respectively. Taken together, as well as in immune and stress responses are regulated during WSSV infection of crayfish Hpt cells, our results also light the significance of cytoskeletal system, signal transduction and other unknown genes in the regulation of antiviral signals during WSSV infection.

Isolation and in vitro characterisation of prohaemocytes from the spider crab, Hyas araneus (L.)

A population of small, mostly undifferentiated, haemocytes were identified and enriched from the circulation of the spider crab, H. araneus, using a two-step density gradient separation procedure. Typically, these cells are spherical, ca. 8-12 μm diameter and have a high nucleus:cytoplasm ratio. Their number in the circulation increases significantly 24 h after a state of haemocytopenia has been created by withdrawal of 2 mL of haemolymph. The rise in the number of these cells at this time is consistent with a left shift phenomenon. A two-step separation procedure was developed to generate enriched populations of these small cells from the haemolymph and in vitro assays revealed that ca. 47% are BrdU-positive in vitro. By contrast BrdU uptake was not observed in the hyaline, semigranular or granular cells. The proliferative ability of the small cells, coupled with their close morphological resemblance to immature haemocytes reported from the haematopoietic tissue of other decapod species, leads us to conclude that these cells are prohaemocytes.

Multiplication of Taura syndrome virus in primary hemocyte culture of shrimp (Penaeus vannamei)

The propagation of Taura syndrome virus (TSV) in primary hemocyte culture of Pacific white shrimp (Penaeus vannamei) was investigated. Purified TSV was inoculated into a 24 h old primary hemocyte culture and the development of cytopathic effects was monitored. The cell morphology started changing within 6 h post-inoculation; TSV-infected hemocytes started shrinking and granular structures began to form on the cell surface. There was a gradual loss of cell viability and, by 48 h post-inoculation, most cells detached from the bottom of the 96 well microplate. The propagation of TSV during the 48 h time course studied was measured by real-time RT-PCR. TSV copy number reached the highest level by 12 h post-inoculation and then started to decrease. Using an anti-TSV polyclonal antibody, the 55 kDa VP1 capsid protein was detected by Western blot analysis. The data suggest that shrimp primary hemocyte culture supports TSV replication and could be used as a tool for the study of host-virus interactions in TSV pathogenesis.

Response to Dengue virus infections altered by cytokine-like substances from mosquito cell cultures

Background

With both shrimp and commercial insects such as honey bees, it is known that stable, persistent viral infections characterized by absence of disease can sometimes shift to overt disease states as a result of various stress triggers and that this can result in serious economic losses. The main research interest of our group is to understand the dynamics of stable viral infections in shrimp and how they can be destabilized by stress. Since there are no continuous cell lines for crustaceans, we have used a C6/36 mosquito cell line infected with Dengue virus to test hypotheses regarding these interactions. As a result, we accidentally discovered two new cytokine-like substances in 5 kDa extracts from supernatant solutions of acutely and persistently infected mosquito cells.

Results

Naïve C6/36 cells were exposed for 48 h to 5 kDa membrane filtrates prepared from the supernatant medium of stable C6/36 mosquito cell cultures persistently-infected with Dengue virus. Subsequent challenge of naïve cells with a virulent stock of Dengue virus 2 (DEN-2) and analysis by confocal immunofluorescence microscopy using anti-DEN-2 antibody revealed a dramatic reduction in the percentage of DEN-2 infected cells when compared to control cells. Similar filtrates prepared from C6/36 cells with acute DEN-2 infections were used to treat stable C6/36 mosquito cell cultures persistently-infected with Dengue virus. Confocal immunofluorescence microscopy revealed destabilization in the form of an apoptosis-like response. Proteinase K treatment removed the cell-altering activities indicating that they were caused by small polypeptides similar to those previously reported from insects.

Conclusions

This is the first report of cytokine-like substances that can alter the responses of mosquito cells to Dengue virus. This simple model system allows detailed molecular studies on insect cytokine production and on cytokine activity in a standard insect cell line.

A gC1qR prevents white spot syndrome virus replication in the freshwater crayfish Pacifastacus leniusculus

The gC1qR/p32 protein is a multiple receptor for several proteins and pathogens. We cloned a gC1qR homologue in a crustacean, Pacifastacus leniusculus, and analyzed the expression of P. leniusculus C1qR (PlgC1qR) in various tissues. The gC1qR/p32 transcript was significantly enhanced by white spot syndrome virus (WSSV) infection 6 h after viral infection both in vitro in a hematopoietic tissue cell culture (Hpt) and in vivo compared to appropriate controls. Moreover, PlgC1qR silencing in both the Hpt cell culture and live crayfish enhanced the WSSV replication. In addition, by making a recombinant PlgC1qR protein we could show that if this recombinant protein was injected in a crayfish, Pacifastacus leniusculus, followed by injection of WSSV, this significantly reduced viral replication in vivo. Furthermore, if the recombinant PlgC1qR was incubated with Hpt cells and then WSSV was added, this also reduced viral replication. These experiments clearly demonstrate that recombinant PlgC1qR reduce WSSV replication both in vivo and in vitro. The results from a far-Western overlay and glutathione S-transferase pull-down assays showed that PlgC1qR could bind to VP15, VP26, and VP28. Altogether, these results demonstrate a role for PlgC1qR in antiviral activity against WSSV.

Suitability of the clonal marbled crayfish for biogerontological research: a review and perspective, with remarks on some further crustaceans

This article examines the suitability of the parthenogenetic marbled crayfish for research on ageing and longevity. The marbled crayfish is an emerging laboratory model for development, epigenetics and toxicology that produces up to 400 genetically identical siblings per batch. It is easily cultured, has an adult size of 4-9 cm, a generation time of 6-7 months and a life span of 2-3 years. Experimental data and biological peculiarities like isogenicity, direct development, indeterminate growth, high regeneration capacity and negligible senescence suggest that the marbled crayfish is particularly suitable to investigate the dependency of ageing and longevity from non-genetic factors such as stochastic developmental variation, allocation of metabolic resources, damage and repair, caloric restriction and social stress. It is also well applicable to examine alterations of the epigenetic code with increasing age and to identify mechanisms that keep stem cells active until old age. As a representative of the sparsely investigated crustaceans and of animals with indeterminate growth and extended brood care the marbled crayfish may even contribute to evolutionary theories of ageing and longevity. Some relatives are recommended as substitutes for investigation of topics, for which the marbled crayfish is less suitable like genetics of ageing and achievement of life spans of decades under conditions of low food and low temperature. Research on ageing in the marbled crayfish and its relatives is of practical relevance for crustacean fisheries and aquaculture and may offer starting points for the development of novel anti-ageing interventions in humans.

White spot syndrome virus: an overview on an emergent concern

Viruses are ubiquitous and extremely abundant in the marine environment. One of such marine viruses, the white spot syndrome virus (WSSV), has emerged globally as one of the most prevalent, widespread and lethal for shrimp populations. However, at present there is no treatment available to interfere with the unrestrained occurrence and spread of the disease. The recent progress in molecular biology techniques has made it possible to obtain information on the factors, mechanisms and strategies used by this virus to infect and replicate in susceptible host cells. Yet, further research is still required to fully understand the basic nature of WSSV, its exact life cycle and mode of infection. This information will expand our knowledge and may contribute to developing effective prophylactic or therapeutic measures. This review provides a state-of-the-art overview of the topic, and emphasizes the current progress and future direction for the development of WSSV control strategies.