Primary culture of lymphoid, nerve, and ovary cells from Penaeus stylirostris and Penaeus vannamei

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.

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.

Establishment of long-term ostracod epidermal culture

Primary crustacean cell culture was introduced in the 1960s, but to date limited cell lines have been established. Skogsbergia lerneri is a myodocopid ostracod, which has a body enclosed within a thin, durable, transparent bivalved carapace, through which the eye can see. The epidermal layer lines the inner surface of the carapace and is responsible for carapace synthesis. The purpose of the present study was to develop an in vitro epidermal tissue and cell culture method for S. lerneri. First, an optimal environment for the viability of this epidermal tissue was ascertained, while maintaining its cell proliferative capacity. Next, a microdissection technique to remove the epidermal layer for explant culture was established and finally, a cell dissociation method for epidermal cell culture was determined. Maintenance of sterility, cell viability and proliferation were key throughout these processes. This novel approach for viable S. lerneri epidermal tissue and cell culture augments our understanding of crustacean cell biology and the complex biosynthesis of the ostracod carapace. In addition, these techniques have great potential in the fields of biomaterial manufacture, the military and fisheries, for example, in vitro toxicity testing.

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.

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.

Na+/H+ exchanger (NHE) in Pacific white shrimp (Litopenaeus vannamei): Molecular cloning, transcriptional response to acidity stress, and physiological roles in pH homeostasis

Na⁺/H⁺ exchangers are the most common membrane proteins involved in the regulation of intracellular pH that concurrently transport Na⁺ into the cells and H⁺ out of the cells. In this study, the full-length cDNA of the Na⁺/H⁺ exchanger (NHE) from the Pacific white shrimp (Litopenaeus vannamei) was cloned. The LvNHE cDNA is 3167 bp long, contains a 5’-untranslated region (UTR) of 74 bp and a 3’-UTR of 456 bp and an open reading frame (ORF) of 2637 bp, coding for a protein of 878 amino acids with 11 putative transmembrane domains and a long cytoplasmic tail. LvNHE shows high sequence homology with mud crab NHE at the amino acid level. LvNHE mRNA was detected in the hepatopancreas, gill, eyestalk, skin, heart, intestine, muscle, brain and stomach, with the highest abundance in the intestine. In the shrimp intestinal fragment cultures exposed to gradually declining pH medium (from pH 8.0 to pH 6.4), the LvNHE mRNA expression was significantly stimulated, with the highest response when incubated in pH 7.0 medium for 6 h. To investigate the functional roles of LvNHE in pH regulation at the physiological and cellular levels, the LvNHE mRNA expression was silenced by siRNA knockdown. Upon low-pH challenge, the hemolymph pH was significantly reduced in the LvNHE mRNA knockdown shrimp. In addition, knockdown of LvNHE mRNA reduced the recovery capacity of intracellular pH in intestinal fragment cultures after acidification. Altogether, this study demonstrates the role of NHE in shrimp response to low pH stress and provides new insights into the acid/base homeostasis mechanisms of crustaceans.

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.

Emilia sonchifolia extract activity against white spot syndrome virus and yellow head virus in shrimp cell cultures

Emilia sonchifolia (L.) DC is a plant used in traditional medicine to treat several viral and bacterial diseases. The antiviral activities of selected Sephadex LH-20 column fractions and HPLC subfractions of an acetone extract of E. sonchifolia leaves were determined in shrimp Penaeus merguiensis primary lymphoid cells infected with either white spot syndrome virus (WSSV) or yellow head virus (YHV). WSSV and YHV replication was quantified using quantitative real-time PCR tests targeted to the VP19 and ORF1b gene transcripts, respectively. In lymphoid organ cells exposed to 100 µg ml⁻¹ of either the Sephadex fraction F14 or the HPLC F14 subfraction SF4, both fractions caused reduced replication, but YHV replication was reduced only by SF4. In the asthiazolyl blue mitochondrial enzyme activity assays to assess extract cytotoxicity, >60% of primary lymphoid organ cells remained viable following exposure to 100 µg ml⁻¹ of either F14 or SF4. GC-MS analysis of the HPLC F14 subfraction SF4 showed that it contained 2,4-di-tert-butylphenol. This study is the first to show that E. sonchifolia leaf extracts might be useful as bioactive agents to protect shrimp against viruses such as WSSV and YHV.

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.

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.

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.

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.

Development of cell line from the testicular tissues of crab Scylla serrata

This is the first report on development of a finite cell line from testicular tissues of crab, Scylla serrata. Both the explant and segregated tissues of testes yielded cells that could proliferate and grow. These cells ranged in size from 10 to 38 μm with distinct nuclei of varying shapes. The testicular cells survived and proliferated best in L-15-crab saline medium supplemented with epidermal growth factor (20 ng/mL) and glucose (1 mg/mL). The cell proliferation rate was assessed by Methyl tetrazolium assay in terms of change in optical density which clearly indicated a prominent increase in cell density. The testicular cells were subcultured at an interval of 4-6 days. These subcultured cells remained healthy and proliferated for 5 months with a minimum of ten subsequent passages. The finite cell line was characterized in terms of morphology, growth rate, lactate dehydrogenase release (for detecting health status) and 18S rRNA sequencing. This cell line could be a very useful tool for testing infections and replications of crustacean viruses. The present work provides a technique that could be extended for developing other crustacean cell lines.

Primary culture and characteristic morphologies of neurons from the cerebral ganglion of the mud crab, Scylla paramamosain

Crustacean neurons, obtained from the cerebral ganglion of the mud crab Scylla paramamosain, were successfully cultured in vitro. They maintained typical morphological characteristics and showed better outgrowth in modified Medium 199 (M199) medium than that in Liebowitz's L-15 medium. Fetal bovine serum (FBS), muscle extracts, and hemolymph of the mud crab S. paramamosain were added as supplements. Only 20% FBS could promote neuron outgrowth, while muscle extracts and hemolymph of S. paramamosain did not improve neuron outgrowth. For cell dissociation, both collagenase type I and trypsin worked well as determined by initial cell viability and following cell outgrowth potential. More than six kinds of cells with different morphological characteristics were identified in the neuron outgrowth. They were "small cells", "veilers", "branchers", "multipolar cells", "super-large cell", and "bipolar cells". Among all of the cells, bipolar cells were identified for the first time in crustacean neurons culture and they could live longer than other cells. The neurons could grow for more than a week before retraction and eventual degradation.

Application of nucleic-acid-based therapeutics for viral infections in shrimp aquaculture

Viral infections are one of the major reasons for the huge economic losses in shrimp farming. The control of viral diseases in shrimp remains a serious challenge for the shrimp aquacultural industry, with major pathogens, such as the white spot syndrome virus, yellow head virus, Taura syndrome virus, hepatopancreatic parvovirus, and baculoviruses, being geographically widespread. In the absence of a true adaptive immune response system in invertebrates such as shrimp, one of the alternative and more specific approaches to counteract viral infections in shrimp could be the use of molecular-based gene transfer technologies, such as RNA interference (RNAi). The RNAi mechanism is initiated by double-stranded RNAs (dsRNAs), which are fragmented into shorter 21-23 nucleotides of short interfering RNAs (siRNAs) by a type III endonuclease, the Dicer. RNAi, which is mediated by small interfering RNA (siRNA), results in the sequence-specific post-transcriptional silencing of a target gene. This gene-silencing mechanism is universally conserved and is a well-known phenomenon that exists in many eukaryotes, including invertebrates. It has been recently extended to shrimp as an important potential tool in viral disease prevention. RNAi technology shows considerable promise as a therapeutic approach and efficient strategy for shrimp virus control in the aquaculture industry. Further progress in understanding the mechanism of siRNAs at the molecular level, as well as strategies to achieve their tightly regulated, stable, prolonged and tissue-specific expression in an effective manner, will definitely revolutionize therapeutic approaches for counteracting viral diseases of shrimp. In the present review, the recent development and potential use of RNAi in combating shrimp viral infections is discussed.

Development of primary cell culture from Scylla serrata : Primary cell cultures from Scylla serrata

This paper reports for the first time, the Primary cell culture of hepatopancreas from edible crab Scylla serrata using crab saline, L-15 (Leibovitz), 1 x L-15 + crab saline, 2 x L-15 + crab saline, 3 x L-15 and citrate buffer without any serum. We could isolate and maintain E (Embryonalzellen), F (Fibrenzellen), B (Blasenzellen), R (Restzellen) and G (Granular cells). Upon seeding the hepatopancreatic E, F, B, and R cells showed different survival pattern over time than granular cells. A modified L-15 (3x) medium supported the best survival of hepatopancreatic E, F B, and R cells in in-vitro culture. However granular cells could be maintained for 184 days with L-15 (1x) + crab saline. Fetal bovine serum was not effective additive and hampered cell viability in present study.

Primary culture of hemocytes from the Caribbean spiny lobster, Panulirus argus, and their susceptibility to Panulirus argus Virus 1 (PaV1)

Primary cultures of hemocytes from the Caribbean spiny lobster Panulirus argus were developed for studies on the in vitro propagation of Panulirus argus Virus 1 (PaV1). A modified Leibovitz L-15 medium supported the best survival of hemocytes in in vitro primary cultures. However, degradation of the cultures occurred rapidly in the presence of granulocytes. A Percoll step gradient was used to separate hemocytes into three subpopulations enriched in hyalinocytes, semigranulocytes, and granulocytes, respectively. When cultured separately, hyalinocytes and semigranulocytes maintained higher viability ( approximately 80%) after 18 days incubation compared with granulocytes, which degraded over 2-3 days. Susceptibility of the cell types was investigated in challenge studies with PaV1. Hyalinocytes and semigranulocytes were susceptible to PaV1. Cytopathic effects (CPE) were observed as early as 12h post-inoculation, and as the infection progressed, CPE became more apparent, with cell debris and cellular exudates present in inoculated cultures. Cell lysis was noticeable within 24h of infection. The presence of virus within cells was further confirmed by in situ hybridization using a specific DNA probe. The probe gave a unique staining pattern to cells infected with PaV1 24-h post-inoculation. Cells in the control treatment were intact and negative to hybridization. This assay was further applied to the quantification of infectious virus in hemolymph using a 50% tissue culture infectious dose assay (TCID(50)) based on CPE. These tools will now allow the quantification of PaV1 using established culture-based methods.

Establishment, characterization and viral susceptibility of 3 new cell lines from snakehead, Channa striatus (Blooch)

Three cell lines were established from muscle (SHMS), heart (SHHT) and swim bladder (SHSB) of snakehead (Channa striatus). The cells grew initially at 25 degrees C in L15 medium supplemented with 20% fetal bovine serum and have been subcultured 13-18 times since their initiation on June 25, 2002. Growth of the snakehead cells was serum-dependent and plating efficiencies ranged from 22-29%. These snakehead cells grew well in RPMI 1640 and L-15 media, which are commonly used for cultivation of animal and mammalian cells and retained 95.9-96.6% cell viability following storage for 4 months in liquid nitrogen. Karyotyping indicated that these snakehead-derived cell lines remained diploid with a chromosome count of 44 at their early passage (passage 8-14). These cell lines were sensitive to CCV, VHSV, SVCV, IPN and SHRV; they were refractory to IHNV. These newly established cell lines are currently being used for the investigation of snakehead viral diseases in Hawaii and will be available for future isolation and study of snakehead viruses.

OVARIAN PRIMARY TISSUE CULTURE OF THE KURUMA SHRIMP MARSUPENAEUS JAPONICUS

Cell growth in ovarian primary culture of the kuruma shrimp, Marsupenaeus japonicus, was examined under various culture conditions. The best growth of ovarian cells was obtained in a culture system consisting of double strength of Leibovitz-15 medium supplemented with 10% fetal bovine serum, glucose (1 g/L), proline (0.1 g/L), TC-Yeastolate (1 g/L), and lactalbumin hydrolysate (1 g/L). The cells survived in this medium at 25 degrees C for 45 d. The epithelial-like cells predominated in 10-d-old cultures, covering >80% of the surface area on the bottom of flask. Cells in mitosis were often observed. Cell proliferation was monitored by incorporation of 5-bromo-2'-deoxyuridine (BrdU), an analog of thymidine. 5-Bromo-2'-deoxyuridine-associated cells accounted for 11.5 and 35.0% of cell populations at 2 and 24 h, respectively, after BrdU treatment. Our results provide an improved culture technique for ovarian tissue of the kuruma shrimp.

Lipopolysaccharide induces DNA-synthesis in a sub-population of hemocytes from the swimming crab, Liocarcinus depurator

The swimming crab, Liocarinus depurator, contains a small proportion of circulating blood cells which enter S-phase in vitro, as revealed by BrdU assay. These cells are enriched within the semigranular cell band produced by density gradient centrifugation on Percoll and their proportion is significantly higher in blood samples taken from crabs injected 3h previously with lipopolysaccharide (LPS). The occurrence of these cells does not persist as blood samples taken 12h post-injection show similar numbers of these cells to those from saline-treated and untreated controls. However, their appearance appears to be dose related; hemolymph from animals given 15 microg LPS per animal contains greater numbers than that from animals given LPS doses of 0.15 or 0.015 microg per animal. Estimation of the probable number of these cells per ml of the hemolymph, taking into account cell viability and changes in the size of the semigranular cell pool, indicates that they are very rare, comprising merely ca 0.06% of the total cell count. Notwithstanding, this still represents a baseline population in the region of 1.25 x 10(4) ml-1. More importantly, their number rises, approximately 11-fold to ca 14 x 10(4) ml-1 of hemolymph by 3h of injection of LPS. These results show that certain hemocytes from a brachyuran crab can synthesise DNA in vitro, and offers evidence that these cells constitute a rare but distinct sub-population of hemocytes that co-migrate with the semigranular cells during density gradient centrifugation. Since the cells received the stimulus to enter S-phase in vivo, the response must represent one of the mechanisms used by decapods to restore the hemocyte number in the circulation after non-self challenge.

Penaeid (Penaeus japonicus) lymphoid cells replicate by cell division in vitro

Penaeid cell culture has gained much attention as a potential model to facilitate researches on the characterization of the virus and to develop more sophisticated and improved diagnostic procedures for use in the aquaculture industry. However, to date, cell division processes of cultured penaeid cells have not been found, which is suggested as one of the reasons that block the establishment of the continuous penaeid cell lines. We reported here the cell division processes of cultured lymphoid cells of Penaeus japonicus. The culture medium used was based on M199 and was modified by supplementing saline components. Cultures were incubated at 25 degrees C, and 5% CO2 was supplemented. In primary cultured lymphoid cells, dividing cells in different shapes were found. Cell division processes of 12 dividing lymphoid cells were tracked. After cell division, their daughter cells turned into fibroblast-like or epithelioid cells. These results proved that the culture conditions used were suitable for lymphoid cells of I japonicus to proliferate in vitro and that cultured lymphoid cells still had the ability to carry out cell division. These findings would give light to the establishment of continuous penaeid cell lines and would also provide us with the knowledge of cell division processes of the penaeid.

Effect of low doses of ionizing radiation on cells cultured from the hematopoietic tissue of the Dublin Bay prawn, Nephrops norvegicus

Explant cultures from the hematopoietic tissue of the Dublin Bay prawn, Nephrops norvegicus, were exposed to low doses of (60)Co gamma radiation. Cells growing from the explants were examined 7 days after irradiation using light and transmission electron microscopy and were also tested for their ability to produce signals indicative of a bystander effect. The exposed cultures displayed pronounced damage and were orders of magnitude more sensitive than the data in the literature would suggest for arthropod cells. The cultures were also more sensitive than mammalian cells that were exposed to similar doses. Cellular abnormalities included damage to cytoplasmic organelles, particularly the cytoskeleton. Abnormal mitochondria were also prominent. At low doses (0.5 Gy), nuclear damage was not apparent in the cultures, but there was evidence of a dose-dependent increase in apoptosis. The irradiated cultures released a factor into the medium that was capable of inducing apoptosis and cell death in unirradiated fish and human cells. This bystander effect was of a similar magnitude to that reported for mammalian cell systems. It is suggested that these crustaceans may be highly sensitive to radiation, unlike terrestrial arthropods and certain other invertebrates, which are generally considered to be radioresistant.

Hemolymph analysis and evaluation of newly formulated media for culture of shrimp cells (Penaeus stylirostris)

Creation of a shrimp cell line has been an elusive goal. This failure may be due to the composition of the cell culture medium, which may be inadequate to support primary cultured cells. Shrimp hemolymph should contain the nutritional components needed to support cell growth and division. We report here the comprehensive biochemical analysis of hemolymph from the blue shrimp, Penaeus stylirostris (Litopenaeus stylirostris) (see Holthuis, L. B. Shrimps and prawns of the world, in: FAO species catalog. Vol. 1. Rome: Food and Agriculture Organization of the United Nations; 1980), for free amino acids (FAAs), carbohydrates, electrolytes, metals, pH, and osmolality. Levels of hemolymph components were compared to 2xL-15 with 20% fetal bovine serum, a commonly used culture medium for crustacean cells. The FAAs, taurine and proline, and the metals, strontium and zinc, were significantly higher in hemolymph than in the 2 x L-15 medium. In contrast, other FAAs were up to 50 times higher in the 2 x L-15 medium than in the hemolymph. To mimic more closely the hemolymph composition, we created two new media based on either the 0.2 x L-15 or the M199 medium. We compared the microscopic appearance of cells cultured in these media and evaluated deoxyribonucleic acid (DNA) and protein synthesis by 3H-thymidine uptake and 35S-methionine uptake assays. The ovary cells of P. stylirostris cultured in either of the new media formed monolayers, while the cells cultured in 2 x L-15 medium did not. Despite these differences, there was no evidence of sustained DNA or protein synthesis with any of the media. Future studies to establish a shrimp cell line should focus on analysis of the cell cycle and on overcoming the molecular blocks to cell division.

Primary cultures of heart cells from the scallop Pecten maximus (mollusca-bivalvia)

Primary cultures of Pecten maximus heart cells, isolated by an enzymatic procedure, were routinely obtained with a high level of reproducibility in a simple medium based on sterile seawater. Cells attached to the plastic substratum without the need to add a special factor. The number of adhering cells gradually increased with the time of culture. Two types of adhering cells were observed: epitheliallike cells and fibroblastlike cells, which were more numerous. The latter cells were identified as myocytes by electron microscopy and immunofluorescent staining. Results obtained by autoradiography, after incorporation of [14C]leucine, [3H]thymidine, and [14C]acetate, confirmed functional activity of the cells. These cultures were maintained viable in vitro during at least 1 mo.

Development of an in vitro quantal assay in primary cell cultures for a non-occluded baculo-like virus of penaeid shrimp

An in vitro quantal assay (TCID50) for a non-occluded baculo-like virus isolate from naturally infected Penaeus japonicus obtained from China and experimentally infected P. stylirostris was developed using primary shrimp lymphoid cell cultures in Primaria 24-well tissue culture plates. The virus caused cytopathogenic effect (CPE) in the cell cultures as early as 2 day post-infection (p.i.). Initially, the cells rounded up and finally detached from the culture vessel as the infection progressed. At the present time, there is no established quantitative in vitro cell culture protocol for the assay of this baculo-like virus which has been reported by our laboratory to be highly pathogenic for P. stylirostris and P. vannamei, the two species of penaeid shrimp commercially cultured in Hawaii and the Western hemisphere. This quantal assay thus provides a simple and convenient method for the detection and assay of infectious virus in cultured penaeid shrimp.

Viral pathogens of the penaeid shrimp

While significant advances that have been made in determining the role of viruses involved in various epizootics occurring in penned shrimp aquaculture, viral diseases will continue to plague the industry. A major obstacle to the study of these diseases is the lack of convenient and quantitative methodologies, such as in vitro cell culture systems to grow and study (characterize) the virus. A beginning has been made with the recent development of protocols for the consistent preparation of primary shrimp lymphoid cells, which were employed for the quanta1 assay of some of the shrimp viral pathogens. The primary cell lines have also been used to analyze the synthesis of viral proteins at the cellular level and to study viral pathogenesis. With the further successful development of additional primary cell lines from other shrimp tissues and the establishment of continuous diploid and transformed shrimp cell lines, this problem is being solved. The value of cell culture systems is becoming increasingly clear. They present several obvious advantages because (1) they are more cost effective, sensitive, and convenient than whole animals, particularly for rapid monitoring of infectivity, (2) they yield quantitatively reproducible results, and (3) viral growth kinetics, biochemical and genetic characteristics, and so on can be studied more easily. Their biggest potential use is in future molecular biology and genetic studies of shrimp viruses.