A novel heart-cell line from brown-marbled grouper Epinephelus fuscoguttatus and its susceptibility to iridovirus

A cell line derived from heart of rainbow trout is refractory to Tilapia lake virus

Cell lines are important in vitro models to answer biological mechanisms with less genetic variations. The present study was attempted to develop a cell line from rainbow trout, where we obtained a cell line from the heart, named "RBT-H." The cell line was authenticated using karyotyping and cytochrome c oxidase subunit I (COI) gene sequencing. The karyotype demonstrated diploid chromosome number (2n) as 62 and the sequence of partial COI gene was 99.84% similar to rainbow trout COI data set, both suggesting the origin of RBT-H from the rainbow trout. The heart cell line was mycoplasma-free and found to be refractory to infection with the Tilapia lake virus. The RBT-H cell line is deposited in the National Repository of Fish Cell Line (NRFC) at ICAR-NBFGR, Lucknow, India, with Accession no. NRFC0075 for maintenance and distribution to researchers on request for R&D.

Megalocytivirus and Other Members of the Family Iridoviridae in Finfish: A Review of the Etiology, Epidemiology, Diagnosis, Prevention and Control

Aquaculture has expanded to become the fastest growing food-producing sector in the world. However, its expansion has come under threat due to an increase in diseases caused by pathogens such as iridoviruses commonly found in aquatic environments used for fish farming. Of the seven members belonging to the family Iridoviridae, the three genera causing diseases in fish comprise ranaviruses, lymphocystiviruses and megalocytiviruses. These three genera are serious impediments to the expansion of global aquaculture because of their tropism for a wide range of farmed-fish species in which they cause high mortality. As economic losses caused by these iridoviruses in aquaculture continue to rise, the urgent need for effective control strategies increases. As a consequence, these viruses have attracted a lot of research interest in recent years. The functional role of some of the genes that form the structure of iridoviruses has not been elucidated. There is a lack of information on the predisposing factors leading to iridovirus infections in fish, an absence of information on the risk factors leading to disease outbreaks, and a lack of data on the chemical and physical properties of iridoviruses needed for the implementation of biosecurity control measures. Thus, the synopsis put forth herein provides an update of knowledge gathered from studies carried out so far aimed at addressing the aforesaid informational gaps. In summary, this review provides an update on the etiology of different iridoviruses infecting finfish and epidemiological factors leading to the occurrence of disease outbreaks. In addition, the review provides an update on the cell lines developed for virus isolation and culture, the diagnostic tools used for virus detection and characterization, the current advances in vaccine development and the use of biosecurity in the control of iridoviruses in aquaculture. Overall, we envision that the information put forth in this review will contribute to developing effective control strategies against iridovirus infections in aquaculture.

Megalocytiviruses in ornamental fish: A review

Iridoviruses, especially megalocytiviruses, are related to severe disease resulting in high economic losses in the aquaculture industry worldwide. The ornamental fish industry has been affected severely due to Megalocytivirus infections. Megalocytivirus is a DNA virus that has three genera; including red sea bream iridovirus, infectious spleen and kidney necrosis virus, and turbot reddish body iridovirus. Megalocytivirus causes non-specific clinical signs in ornamental fish. Cell culture, histology, immunofluorescence test, polymerase chain reaction (PCR) assay, and loop-mediated isothermal amplification assay have been used to diagnose megalocytiviruses. Risk factors such as temperature, transportation (export and import), and life stages of ornamental fish have been reported for the previous cases due to Megalocytivirus infections. In addition, other prevention and control methods also have been practiced in farms to prevent Megalocytivirus outbreaks. This is the first review of megalocytiviruses in ornamental fish since its first detection in 1989. This review discusses the occurrences of Megalocytivirus in ornamental fish, including the history, clinical signs, detection method, risk factors, and prevention measures.

New Protocol for Cell Culture to Obtain Mitotic Chromosomes in Fishes

Cell culture is an excellent alternative for the maintenance of cell lines and to obtain quality chromosome preparations of fishes. However, this methodology is still little employed, mainly because of the difficulty of standardization of cell cultures. In this study, we describe a methodology for the rapid acquisition of cell lineages and mitotic chromosomes for cytogenetic studies of fish species from muscle tissue cells. Our methodology is based on the use of a gelatin film, which provides better adhesion of a large number of cells and appropriate conditions for multiplication. The cells of Astyanax altiparanae, used as an experimental model, with fibroblast-like morphology, showed rapid cellular proliferation, resulting in a great number of cells. Chromosomal preparations of cultured cells showed the diploid number of the species, 2n = 50 chromosomes, in 80% of the cells examined, with chromosomes intact and distended. Cell populations were cryopreserved and after being recovered, these cells maintained their proliferative capacity. The development of this methodology represents an innovation for the fish cytogenetics area and it may bring a significant contribution to the conservation and study of several groups due to the difficulty of obtaining good-quality chromosome preparations.

Establishment and characterization of a brain-cell line from kelp grouper Epinephelus moara

A new brain-cell line, EMB, was developed from kelp grouper Epinephelus moara, a cultured marine fish. The EMB cells were subcultured for more than 60 passages. The cells were cultured in Leibovitz's L-15 medium (L15) supplemented with antibiotics, foetal bovine serum (FBS), 2-mercaptoethanol (2-ME) and basic fibroblast growth factor (bFGF). The cells could grow at 18-30° C, with the maximum growth between 24 and 30° C. The optimum FBS concentration for the cells growth ranged between 15 and 20%. Chromosome analysis indicated that the modal chromosome number was 48 in the cells at passage 45. After being transfected with pEGFP-N3 plasmid, the cells could successfully express green fluorescence protein (GFP), implying that this cell line can be used for transgenic studies. A significant cytopathic effect (CPE) was observed in the cells after infection with Singapore grouper iridovirus (SGIV) or red spotted grouper nervous necrosis virus (RGNNV) and the viral replication was confirmed by quantitative real-time PCR (qrt-PCR) assay, which suggested EMB's application potential for studies of SGIV and RGNNV.

Establishment and characterization of a kidney cell line from kelp grouper Epinephelus moara

A novel cell line, Epinephelus moara kidney cell line (EMK), was established from kidneys of kelp grouper E. moara. Cells were cultured at 24 °C in Leibovitz's L-15 medium (L15) supplemented with antibiotics, basic fibroblast growth factor (bFGF), foetal bovine serum (FBS) and 2-mercaptoethanol (2-ME). EMK cells, fibroblastic in morphology, proliferated to 100% confluency in 3-4 days and were subcultured for over 50 passages. The cells could grow from 18 to 30 °C, with optimal growth at 24 °C. Chromosome analysis indicated that the modal chromosome number was 48 in the cells at passage 42. Green fluorescent signals could be observed in EMK cells when the cells were transfected with pEGFP-N3 plasmid. Moreover, a significant cytopathic effect (CPE) was observed in the cells after infection with Singapore grouper iridovirus (SGIV) or nervous necrosis virus (NNV), and viral replication was confirmed by quantitative real-time PCR (qPCR). These results suggested the potential of the EMK cell line for studies of transgene and pathogenesis of SGIV and NNV.

Establishment of a hepatocyte line for studying biosynthesis of long-chain polyunsaturated fatty acids from a marine teleost, the white-spotted spinefoot Siganus canaliculatus

A hepatocyte line was established from the liver of white-spotted spinefoot Siganus canaliculatus to study the biosynthesis of long-chain polyunsaturated fatty acids (LC-PUFA). The cells from the line, designated S. canaliculatus hepatocyte line (SCHL), grew and multiplied well in Dulbecco's modified Eagle's medium (DMEM)-F12 medium supplemented with 20 mM 4-(2-hydroxyethyl) piperazine-1-ethanesulphonic acid (HEPES), 10% foetal bovine serum (FBS) and 0·5% rainbow trout Oncorhychus mykiss serum at 28° C, showing an epithelial-like morphology and the normal chromosome number of 48 (2n) and have been subcultured for over 60 passages. The identity of the hepatocytes was confirmed by periodic acid Schiff (PAS) staining. The mRNA expression of all genes encoding the key enzymes for LC-PUFA biosynthesis including two desaturases (Δ4 Fad and Δ6-Δ5 Fad) and two elongases (Elovl4 and Elovl5), were detected in all cells from passages 5 to 60 and their expression levels became stable after passage 35 and showed responses to various PUFA incubation. This is similar to the situation determined in the liver of S. canaliculatus that were fed diets containing different fatty acids. These results indicated that SCHL was successfully established and can provide an in vitro tool to investigate lipid metabolism and regulatory mechanisms of LC-PUFA biosynthesis in teleosts, especially marine species.

Characterization and viral susceptibility of a brain cell line from brown-marbled grouper Epinephelus fuscoguttatus (Forsskål) with persistent betanodavirus infection

A continuous cell line designated BMGB (brown-marbled grouper brain) was established from the brain tissues of the brown-marbled grouper Epinephelus fuscoguttatus and characterized. BMGB cells were identified as astroglial progenitor cells because they expressed glial fibrillary acidic protein and keratin and were persistently infected by betanodavirus, as confirmed through immunocytochemistry, polymerase chain reaction and immunoblot analyses. Because few intact virions were present in the BMGB cell culture fluid, the cytopathic effect (CPE) was not observed when the culture fluid was inoculated with GBC1 cells. However, BMGB cells displayed typical CPE after infection with additional betanodavirus, megalocytivirus and chum salmon reovirus. BMGB cells showed low myxovirus resistance (Mx) protein expression, which increased following betanodavirus and reovirus infection. Because the cells contained several unusual or degraded viral proteins, the persistent infection of betanodavirus in the BMGB cells may have resulted from a mechanism that destroys the viral proteins rather than the result of Mx protein expression. Despite the persistent betanodavirus infection, BMGB cells proliferated in a manner similar to other normal tropic fish cells and supported the propagation of several piscine viruses; however, the yield was lower than that of normal cells. The BMGB cells will be useful for investigating virus and host cell interaction.

Establishment and characterization of a gonad cell line from half-smooth tongue sole Cynoglossus semilaevis pseudomale

A new cell line was established from half-smooth tongue sole Cynoglossus semilaevis pseudomale gonad (CSPMG). Primary culture was initiated from gonad tissues pieces, and the CSPMG cells were cultured at 24 °C in Dulbecco's modified Eagle medium/F12 medium (1:1) (pH7.0), supplemented with 20 % fetal bovine serum, basic fibroblast growth factor, epidermal growth factor, insulin-like growth factor-I, 2-mercaptoethanol, penicillin and streptomycin. The cultured CSPMG cells, in fibroblast shape, proliferated to 100 % confluency 10 days later and had been subcultured to passage 109. Chromosome analyses indicated that the CSPMG cells exhibited chromosomal aneuploidy with a modal chromosome number of 42, which displayed the normal diploid karyotype of half-smooth tongue sole (2n = 42t, NF = 42). Reverse transcription polymerase chain reaction revealed CSPMG cells could express gonad somatic cell functional genes Sox9a, Wt1a and weakly germ cell marker gene Vasa, but not male specific gene Dmrt1. Transfection experiment demonstrated that CSPMG cells transfected with pEGFP-N3 plasmid and small RNA could express green and red fluorescence signals with high transfection efficiency. In conclusion, a continuous CSPMG cell line has been established successfully. The cell line might serve as a valuable tool for studies on the mechanism of sex determination, sex reversal and gonad development in flatfish.

Establishment and characterization of an ovarian cell line from half-smooth tongue sole Cynoglossus semilaevis

A new ovarian cell line, CSO, was established from half-smooth tongue sole Cynoglossus semilaevis. Primary culture of CSO cells was initiated from digestion of ovarian tissues pieces by trypsin solution and cultured at 24° C in Dulbecco's modified Eagle's medium-F12 medium (DMEM-F12, 1:1) (pH 7·0), supplemented with 20% foetal bovine serum, basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), insulin-like growth factor-I (IGF-I) and human chorionic gonadotropin (HCG). The cultured CSO cells, fibroblastic in morphology, proliferated to 100% confluency 3 days later and had been subcultured to passage 80. Chromosome analyses indicated that the CSO cells exhibited chromosomal aneuploidy with a modal chromosome number of 42 that displayed the normal diploid karyotype of C. semilaevis [2n = 42 t, fundamental number (NF ) = 42]. Reverse transcription polymerase chain reaction revealed that CSO cells could express ovarian somatic cell functional genes p450armo, foxl2 and sox9a but not ovary germ cell marker gene vasa and male-specific gene dmrt1. Transfection experiment demonstrated that CSO cells transfected with pEGFP-N3 plasmid could express green fluorescence protein (GFP) with higher transfection efficiency. The CSO cell line might serve as a valuable tool for studies on the mechanism of sex determination and oogenesis of ovary in flatfish.

Establishment of caudal fin cell lines from tropical ornamental fishes Puntius fasciatus and Pristolepis fasciata endemic to the Western Ghats of India

Two new cell lines, PFF and CFF were established from the caudal fin of the Puntius fasciatus, and Pristolepis fasciata respectively. Since their initiation, these cell lines (PFF and CFF) have been subcultured in L-15 medium with 10% fetal bovine serum for more than 35 passages at 28°C and both the cell lines were characterized. Karyotyping analysis of PFF and CFF cells at 25th passage indicated that the modal chromosome number was 2n=50 and 2n=48 respectively. The cell line was cryopreserved in liquid nitrogen at -196°C and could be recovered from storage after six months with good cell viability. Polymerase chain reaction amplification of the fragments of two mitochondrial genes, 16S rRNA and COI confirmed that the cell lines originated from the respective species. The bacterial extracellular products from Vibrio cholerae MTCC3904 and Aeromonas hydrophila were found to be toxic to PFF and CFF. Both the cells were resistant to the marine viral nervous necrosis virus (VNNV). No CPE could be found in both cell lines inoculated with the fish samples and cell culture supernatants were demonstrated free of SVC, iridovirus and KHV by molecular methods. These results indicated the absence of SVC, iridovirus and KHV in the ornamental fishes collected from the Western Ghats of India.

Viral susceptibility, transfection and growth of SPB--a fish neural progenitor cell line from the brain of snubnose pompano, Trachinotus blochii (Lacépède)

This study investigates the susceptibilities of the SPB cell line to fish viruses including giant seaperch iridovirus (GSIV-K1), red sea bream iridovirus (RSIV-Ku), grouper nervous necrosis virus (GNNV-K1), chum salmon reovirus (CSV) and eel herpesvirus (HVA). GSIV-K1, RSIV-Ku and CSV replicated well in SPB cells, with a significant cytopathic effect and virus production. However, the cells were HVA and GNNV refractory. To examine the ability of SPB cells to stably express foreign protein, expression vectors encoding GNNV B1 and B2 fused to enhanced green fluorescent protein (EGFP) and GSIV ORF35L fused to DsRed were constructed and introduced by transfection into SPB cells. Stable transfectants displayed different morphologies compared with SPB and with each other. EGFP-B1 was predominantly localized in the nuclei, EFPF-B2 was distributed throughout the cytoplasm and nucleus, and granular 35L-DsRed was localized with secreted vesicles. The expression of EFPF-B2 in SPB cells produced blebs on the surface, but the cells showing stable expression of EGFP, EGFP-B1 or 35L-DsRed showed normal morphologies. Results show the SPB cells and the transfected cells grow well at temperatures between 20 and 35 °C and with serum-dependent growth. SPB cells are suitable for studies on foreign protein expression and virology.