An improved method of cell culture system from eye stalk, hepatopancreas, muscle, ovary, and hemocytes of Penaeus vannamei

Immunofluorescence detection of Ecytonucleospora hepatopenaei (EHP) in Penaeus vannamei

Hepatopancreatic microsporidiosis (HPM), caused by the microsporidium Ecytonucleospora hepatopenaei (EHP) leads to retarded growth and enhanced susceptibility to other diseases in shrimp resulting in a major loss for the shrimp industry worldwide. It is little understood how EHP infects its host and hijacks its cellular machinery to replicate and exert clinical manifestations in infected shrimp. Since the initial record of HPM, histopathology and polymerase chain reaction (PCR)-based assays were developed for the detection of EHP to prevent spread of the disease. Availability of an antibody-based detection method would complement these existing diagnostic tools and be useful in studying EHP pathogenesis. We describe here an immunofluorescence assay (IFA) for detecting EHP using monoclonal antibodies (mAbs) that were originally developed against Cryptosporidium parvum, a coccidian parasite that infects calves (Bos taurus), other agriculturally important animals, and humans. Forty-one mAbs were screened and two mAbs, 3E2 and 3A12, were found to detect EHP successfully. The utility of these mAbs in detecting EHP was further assessed by testing 36 experimentally challenged EHP-infected shrimp (Penaeus vannamei). EHP-detection data from infected shrimp were compared by Hematoxylin and Eosin (H&E) histology, real-time PCR, and immunofluorescence. The data show IFA using mAbs 3E2 and 3A12 could successfully detect EHP and that the sensitivity of detection is comparable to H&E histology and quantitative PCR. Availability of mAbs that can detect EHP is expected to be immensely beneficial in HPM diagnosis. Since the pathobiology of C. parvum has been so widely studied, these cross-reactive mAbs may also aid in gaining some insight into EHP pathogenesis and disease.

Considerations for cultivated crustacean meat: potential cell sources, potential differentiation and immortalization strategies, and lessons from crustacean and other animal models

Cultivated crustacean meat (CCM) is a means to create highly valued shrimp, lobster, and crab products directly from stem cells, thus removing the need to farm or fish live animals. Conventional crustacean enterprises face increasing pressures in managing overfishing, pollution, and the warming climate, so CCM may provide a way to ensure sufficient supply as global demand for these products grows. To support the development of CCM, this review briefly details crustacean cell culture work to date, before addressing what is presently known about crustacean muscle development, particularly the molecular mechanisms involved, and how this might relate to recent work on cultivated meat production in vertebrate species. Recognizing the current lack of cell lines available to establish CCM cultures, we also consider primary stem cell sources that can be obtained non-lethally including tissues from limbs which are readily released and regrown, and putative stem cells in circulating hemolymph. Molecular approaches to inducing myogenic differentiation and immortalization of putative stem cells are also reviewed. Finally, we assess the current status of tools available to CCM researchers, particularly antibodies, and propose avenues to address existing shortfalls in order to see the field progress.

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.

An optimization of supplements and physical factors for growth of hemocytes culture from Penaeus vannamei (White shrimp) in selective medium

BACKGROUND

Standardization of cell culture medium plays a vital role in the development of primary or continuous cell line. Apart from the basal media, supplements in the medium and various physical factors promote the cell growth. With this context, the study was carried out to optimize the culture medium using various supplements and physical factors for the growth of hemocytes culture from Penaeus vannamei.

METHODS

Various concentrations of Fetal Bovine Serum (FBS; 1-25%), Shrimp Muscle Extract (SME; 1-25%) and basic Fibroblast Growth Factor (bFGF; 0.5-5 ng mL ^-1) were attempted to optimize the cell culture media for the development of primary hemocytes culture of P. vannamei. Various pH, temperature and osmolality was also screened to optimize the medium.

RESULTS

15% FBS was ideal for the healthy morphology of cells with rapid replication. SME supplementation at 5-20% supported the cell growth for 24 h but only 30% of cell viability was observed after 48 h. bFGF (0.5-5 ng mL^-1) enhanced cell growth in the medium with 15% FBS; The ideal pH level was examined by preparing the HBSCM-5 medium at pH between 6.8-8.0. Osmolality of 730 ± 20, pH of 7.2 and temperature of 28 °C resulted in the healthy cells with good morphology. NSW supplement supported the cell growth at low concentrations of salt; however, more than 2% salt concentrations cells did not form fibroblast-like morphology and instead a crystal-like morphology was observed.

CONCLUSION

The hemocytes culture were optimized for use as an in vitro cell culture system by testing cell growth on HBSCM-5 medium with various supplements, growth factors and physical parameters.

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.

The Development and Characterization of a Cell Culture System from Indian Mud Crabs Scylla serrata

Commercially available culture media and supplements were tested for their potential to produce primary cell cultures from tissues of Indian mud crabs Scylla serrata. Eight commercially available culture media from Sigma-Aldrich (Leibovitz's L-15, Medium 199, Grace's Insect Medium, Minimal Essential Medium, Dulbecco's Modified Eagle Medium, TC-100 Insect Medium, IPL-41 Insect Medium, and Roswell Park Memorial Institute) were examined. Three different supplements (amino acid and sugar [AS], crab muscle extract [CME], and natural seawater [NSW]) were also examined. The hemocyte culture appeared to grow well for a maximum period of 21 d in 2 × L-15 medium supplemented with AS and 15% fetal bovine serum (FBS). Partial amplification and sequencing of the cytochrome oxidase subunit I (COI) gene confirmed that the primary hemocytes originated from Indian mud crabs. The effects of four metals on hemocyte viability were evaluated using the MTT assay. Of the four metals examined (arsenic, lead, cobalt, and nickel), cobalt and nickel were more toxic to the crab cells than the other metals. Both acridine orange/ethidium bromide and Hoechst staining showed the presence of apoptosis and necrosis in metal-treated groups, which suggests that metals in an aquatic environment induce death of the Indian mud crab's hemocytes. The hemocyte primary cell culture was also used to study the cytotoxicity effect of bacterial extracellular products from Vibrio harveyi and white spot syndrome virus. This study demonstrates that hemocyte primary cell culture can be used as a tool to study viral and bacterial pathogenesis and to assess the cytotoxicity of pollutants present in aquatic environments.

Application of PEG-Covered Non-Biodegradable Polyelectrolyte Microcapsules in the Crustacean Circulatory System on the Example of the Amphipod Eulimnogammarus verrucosus

Layer-by-layer assembled microcapsules are promising carriers for the delivery of various pharmaceutical and sensing substances into specific organs of different animals, but their utility in vivo inside such an important group as crustaceans remains poorly explored. In the current study, we analyzed several significant aspects of the application of fluorescent microcapsules covered by polyethylene glycol (PEG) inside the crustacean circulatory system, using the example of the amphipod Eulimnogammarus verrucosus. In particular, we explored the distribution dynamics of visible microcapsules after injection into the main hemolymph vessel; analyzed the most significant features of E. verrucosus autofluorescence; monitored amphipod mortality and biochemical markers of stress response after microcapsule injection, as well as the healing of the injection wound; and finally, we studied the immune response to the microcapsules. The visibility of microcapsules decreased with time, however, the central hemolymph vessel was confirmed to be the most promising organ for detecting the spectral signal of implanted microencapsulated fluorescent probes. One million injected microcapsules (sufficient for detecting stable fluorescence during the first hours after injection) showed no toxicity for six weeks, but in vitro amphipod immune cells recognize the PEG-coated microcapsules as foreign bodies and try to isolate them by 12 h after contact.

Directed differentiation of granular cells from crayfish hematopoietic tissue cells

Hemocytes are the major immune cells of crustaceans. New hemocyte production is required throughout the life cycle of these animals to maintain a functional immune system. The mechanism of crustacean hematopoiesis has just begun to be understood and new methods are needed for the investigation of this process. Here we report the directed differentiation of granular cells (GCs) from the hematopoietic tissue (HPT) cells of Cherax quadricarinatus in vitro. We started by providing the cultured HPT cells with different additives to induce possible differentiation. We found that crayfish muscle extract greatly promoted the physical status of the cells and induced the formation of refractile cytoplasmic granules. The transcription of marker genes and the production of functional prophenoloxidase further confirmed the formation of mature GCs. In our experiments, young GCs usually started to develop in ∼2 weeks post induction and over 60% of the cells became mature within 3-4 weeks. This is the first time that the fully differentiation of crustacean hemocytes is accomplished in vitro. It provides a powerful tool for in-depth study of crustacean hematopoiesis.

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.

Hemocytes of the mud crab Scylla paramamosain: Cytometric, morphological characterization and involvement in immune responses

Hemocytes play essential roles in the innate immune system of crustaceans. Characterization of hemocytes from estuary mud crab Scylla paramamosain was performed by flow cytometry and morphological studies such as cytochemical staining and electron microscopy. The hemocyte subsets were further separated using a modified Percoll density gradient centrifugation method. Based on the morphological characteristics of the cells, three distinct categories of hemocytes were identified: granulocytes with abundant large granularity representing 5.27 ± 0.42%, semigranulocytes with small or less granularity representing 76.03 ± 3.34%, and hyalinocytes (18.70 ± 3.92%) which were almost no granularity. The total hemocyte cell count and the percentage of hemocyte subsets varied after pathogen infection, including Vibrio alginolyticus and the viral double-stranded RNA analog Poly (I:C). The phagocytic process is of fundamental importance for crustaceans' cellular immune response as well as development and survival. The results of the in vitro phagocytosis assays analyzed by flow cytometry demonstrated that granulocytes and semigranulocytes had significantly higher phagocytic ability than hyalinocytes. A primary culture system, L-15 medium supplemented with 5-10% fetal bovine serum, was developed to further investigate the immune function of hemocytes. Furthermore, adenovirus can be utilized to effectively transfer GFP gene into hemocytes. Overall, three hemocyte sub-populations of S. paramamosain were successfully discriminated, moreover, their response to pathogen infections, phagocytic activity and adenovirus mediated transfection were also investigated for the first time. This study may contribute to a better understanding of the innate immune system of estuary crabs.

Culture of neural cells of the eyestalk of a mangrove crab is optimized on poly-L-ornithine substrate

Although there is a considerable demand for cell culture protocols from invertebrates for both basic and applied research, few attempts have been made to culture neural cells of crustaceans. We describe an in vitro method that permits the proliferation, growth and characterization of neural cells from the visual system of an adult decapod crustacean. We explain the coating of the culture plates with different adhesive substrates, and the adaptation of the medium to maintain viable neural cells for up to 7 days. Scanning electron microscopy allowed us to monitor the conditioned culture medium to assess cell morphology and cell damage. We quantified cells in the different substrates and performed statistical analyses. Of the most commonly used substrates, poly-L-ornithine was found to be the best for maintaining neural cells for 7 days. We characterized glial cells and neurons, and observed cell proliferation using immunocytochemical reactions with specific markers. This protocol was designed to aid in conducting investigations of adult crustacean neural cells in culture. We believe that an advantage of this method is the potential for adaptation to neural cells from other arthropods and even other groups of invertebrates.

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.

Multifactorial interaction of growth factors on Penaeus monodon lymphoid cells and the impact of IGFs in DNA synthesis and metabolic activity in vitro

Development of continuous cell lines from shrimp is essential to investigate viral pathogens. Unfortunately, there is no valid cell line developed from crustaceans in general and shrimps in particular to address this issue. Lack of information on the requirements of cells in vitro limits the success of developing a cell line, where the microenvironment of a cell culture, provided by the growth medium, is of prime importance. Screening and optimization of growth medium components based on statistical experimental designs have been widely used for improving the efficacy of cell culture media. Accordingly, we applied Plackett-Burman design and response surface methodology to study multifactorial interactions between the growth factors in shrimp cell culture medium and to identify the most important ones for growth of lymphoid cell culture from Penaeus monodon. The statistical screening and optimization indicated that insulin like growth factor-I (IGF-I) and insulin like growth factor-II (IGF-II) at concentrations of 100 and 150 ng ml(-1), respectively, could significantly influence the metabolic activity and DNA synthesis of the lymphoid cells. An increase of 53 % metabolic activity and 24.8 % DNA synthesis could be obtained, which suggested that IGF-I and IGF-II had critical roles in metabolic activity and DNA synthesis of shrimp lymphoid cells.

Endocytic pathway is indicated for white spot syndrome virus (WSSV) entry in shrimp

The white spot syndrome virus (WSSV) has had a serious economic impact on the global shrimp aquaculture industry in the past two decades. Although research has clarified a lot about its genome and structure, the mechanism of how WSSV enters a cell is still unclear. In this study to determine this mechanism, primary cultured hemocytes were used as an experimental model to observe the process of WSSV entry because the stable shrimp cell lines for WSSV infection are lacking. After labeling virions and endosomes with fluorescent dyes followed by observation with a confocal microscope, the results show that the WSSV colocalizes with early endosomes. Hemocytes are further treated with different endocytic inhibitors, methyl-β-cyclodextrin (MβCD) and chlorpromazine (CPZ). WSSV still can be detected in the hemocytes treated with CPZ, but not in the hemocytes treated with MβCD. Thus, we conclude that WSSV adopts the caveolae-mediated endocytosis to enter the shrimp cell.

A novel medium for the development of in vitro cell culture system from Penaeus monodon

Lack of a valid shrimp cell line has been hampering the progress of research on shrimp viruses. One of the reasons identified was the absence of an appropriate medium which would satisfy the requirements of the cells in vitro. We report the first attempt to formulate an exclusive shrimp cell culture medium (SCCM) based on the haemolymph components of Penaeus monodon prepared in isosmotic seawater having 27 ‰ salinity. The SCCM is composed of 22 amino acids, 4 sugars, 6 vitamins, cholesterol, FBS, phenol red, three antibiotics, potassium dihydrogen phosphate and di-sodium hydrogen phosphate at pH 6.8-7.2. Osmolality was adjusted to 720 ± 10 mOsm kg(-1) and temperature of incubation was 25 ºC. The most appropriate composition was finally selected based on the extent of attachment of cells and their proliferation by visual observation. Metabolic activity of cultured cells was measured by MTT assay and compared with that in L-15 (2×), modified L-15 and Grace's insect medium, and found better performance in SCCM especially for lymphoid cells with 107 % increase in activity and 85 ± 9 days of longevity. The cells from ovary and lymphoid organs were passaged twice using the newly designed shrimp cell dissociation "cocktail".

Establishment of shrimp cell lines: perception and orientation

Development of continuous shrimp cell lines for effective investigation on shrimp viruses remains elusive with an arduous history of over 25 years. Despite presenting challenges to researchers in developing a cell line, the billion dollar aquaculture industry is under viral threat. Advances in molecular biology and various gene transfer technologies for immortalization of cells have resulted in the development of hundreds of cell lines from insects and mammals, but yet not a single cell line has been developed from shrimp and other marine invertebrates. Though improved growth and longevity of shrimp cells in vitro could be achieved by using modified growth media this did not make any leap to spontaneous transformation; probably due to the fact that shrimp cells inhibited neoplastic transformations. Oncogenic induction and immortalization are considered as the possible ways, and an exclusive medium for shrimp cell culture and an appropriate mode of transformation are crucial. In this review status of shrimp cell line development and its future orientation are discussed.

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.