Development, characterization and application of a new epithelial cell line from caudal fin of Pangasianodon hypophthalmus (Sauvage 1878)

Development and Characterisation of an Immortal Cell Line From Largemouth Bass (Micropterus salmoides) for Viral Studies

Largemouth bass (Micropterus salmoides), a freshwater fish species, is cultivated widely across China. The industry has been greatly affected by various viral diseases. We generated a new immortal cell line from the fin of M. salmoides (MSF). It has been successfully maintained in continuous culture for over 80 passages. Cells multiply well at 28°C using Medium 199 or Leibovitz's L-15 supplemented with 10%-20% fetal bovine serum. MSF cells comprise a mass of epithelialoid cells. Chromosome analysis showed that ploidy at passage 55 was 2n = 58. Amplification and analysis of the sequence of cytochrome oxidase I gene ascertained the origin of MSF cells from M. salmoides. The cell line is devoid of contamination with mycoplasma. Successful transfection with a GFP reporter gene indicated that the MSF cell line can be a useful tool for further gene expression studies. MSF cells exhibited susceptibility to Largemouth bass ranavirus (LMBV), Infectious spleen and kidney necrosis virus (ISKNV), and Siniperca chuatsi rhabdovirus (SCRV). Transmission electron microscopy (TEM), and immunofluorescence confirmed that the MSF cell line showed high susceptibility to all the tested viruses. The titre values of MSF after infection with LMBV, ISKNV, and SCRV reached 107.4 TCID50/mL, 106.15 TCID50/mL, and 106.35 TCID50/mL at 7dpi, respectively. In conclusion, an immortal cell line derived from the fin tissue of M. salmoides was successfully developed and certain fish viruses can effectively propagated in the newly established MSF cell line that can be helpful for future gene manipulation and infectious viral mechanistic studies in the future.

Development and characterization of a cell line from the caudal fin of Schizothorax niger (Heckel, 1838) for in vitro toxicity testing

Here, we successfully grew the SNCF (Schizothorax niger caudal fin) cell line from the caudal fin explants of S. niger, an important cold-water fish of the Himalayas. The cells were successfully grown up to 22 passages by planting explant tissues in DMEM medium supplemented with FBS. We observed optimal cell growth at a concentration of 18% FBS. We observed the steady generation of cells from explants from days 2 to 5 of seeding, and obtained a complete monolayer at days 7-10. We tested various temperatures, including 10 °C, 13 °C, 16 °C, 19 °C, 22 °C, 25 °C, and 28 °C, and found that 22 °C was the optimal temperature for cell growth. We examined the response to various doses of epidermal growth factor (EGF) and fibroblast growth factor (FGF) (0, 2, 4, 6, 8, and 10 ng/mL) on cell colony growth at an optimal temperature of 22 °C. We characterized the cell line using karyotyping at the 14th and 20th passages. The cell line showed epithelial cell-like growth by morphology, which was confirmed by immunotyping. We further used the cell line to study the impact of three pesticides (chlorpyrifos, dimethoate, and endosulfan), and a fungicide (mancozeb) and bacterial extracellular product (ECP). The DAPI stain assay and MTT assay confirmed the pesticides toxic effects on the cells, revealing disintegration of the cell nuclei by the formation of micronuclei and LC50 concentrations. ECP treatment showed disruption of the monolayer within 0-36 hrs.

Application of Novel Gill Cell Line from Lates calcarifer for Recognizing Metals Using Probes

Lates calcarifer (Bloch) is a potential candidate fish species for culture in marine and brackishwater. A continuous gill cell line was derived from L. calcarifer by the explant culture method and has been passaged for 132 times, in Leibovitz's L-15 medium containing 10% fetal bovine serum (FBS) at 28 °C. The cells showed a rate of recovery between 90 and 95% after being successfully cryopreserved at various passage levels and formed monolayer in 2-3 days without any morphological changes. Immunophenotypic analysis of the SBG cell line revealed that they are of epithelial origin. Polymerase chain reaction assay using mitochondrial 12S rRNA primer specific to L. calcarifer was used to confirm the authenticity of the established gill cell line origin from seabass. The transfection efficiency was evaluated in Seabass Gill (SBG) cell line using pEGFP-N1 and Lipofectamine™ 3000. Transfection efficiency was found to be between 13 and 16%. The cytotoxicity of three different metal detecting probes was evaluated by MTT and Alamar blue assays to determine safe concentration. The result revealed that SBG cell line can be applied for recognition of metals using probes. The current study established, for the first time, a gill-derived cell line (SBG) from Lates calcarifer and its application for the detection of intracellular indium, mercury, and lutetium ions by specific fluorescent probes.

Establishment and characterization of a kidney cell line from hybrid snakehead (male Channa argus × female Channa maculata) and its susceptibility to hybrid snakehead rhabdovirus (HSHRV)

Hybrid snakehead (male Channa argus × female Channa maculata) is an emerging fish breed with increasing production levels. However, infection with hybrid snakehead rhabdovirus (HSHRV) critically affects hybrid snakehead farming. In this study, a fish cell line called CAMK, derived from the kidneys of hybrid snakehead, was established and characterized. CAMK cells exhibited the maximum growth rate at 28 °C in Leibovitz's-15 medium supplemented with 10% fetal bovine serum(FBS). Karyotyping revealed diploid chromosomes in 54% of the cells at the 50th passage (2n = 66), and 16S rRNA sequencing validated that CAMK cells originated fromhybrid snakehead, and the detection of kidney-specific antibodies suggested that it originated from kidney. .The culture was free from mycoplasma contamination, and the green fluorescent protein gene was effectively transfected into CAMK cells, indicating their potential use for in vitro gene expression investigations. Furthermore, qRT-PCR and immunofluorescence analysis revealed that HSHRV could replicate in CAMK cells, indicating that the cells were susceptible to the virus. Transmission electron microscopy revealed that the viral particles had bullet-like morphology. The replication efficiency of HSHRV was 107.33 TCID50/mL. Altogether, we successfully established and characterized a kidney cell line susceptible to the virus. These findings provide a valuable reference for further genetic and virological studies.

Establishment and characterization of a golden pompano (Trachinotus blochii) fin cell line for applications in marine fish pathogen immunology

Pompano fishes have been widely farmed worldwide. As a representative commercial marine species of the Carangidae family, the golden pompano (Trachinotus blochii) has gained significant popularity in China and worldwide. However, because of rapid growth and high-density aquaculture, the golden pompano has become seriously threatened by various diseases. Cell lines are the most cost-effective resource for in vitro studies and are widely used for physiological and pathological research owing to their accessibility and convenience. In this study, we established a novel immortal cell line, GPF (Golden pompano fin cells). GPF has been passaged over 69 generations for 10 months. The morphology, adhesion and extension processes of GPF were evaluated using light and electron microscopy. GPF cells were passaged every 3 days with L-15 containing 20 % fetal bovine serum (FBS) at 1:3. The optimum conditions for GPF growth were 28 °C and a 20 % FBS concentration. DNA sequencing of 18S rRNA and mitochondrial 16S rRNA confirmed that GPF was derived from the golden pompano. Chromosomal analysis revealed that the number pattern of GPF was 48 chromosomes. Transfection experiments demonstrated that GPF could be utilized to express foreign genes. Furthermore, heavy metals (Cd, Cu, and Fe) exhibited dose-dependent cytotoxicity against GPF. After polyinosinic-polycytidylic acid (poly I:C) treatment, transcription of the retinoic acid-inducible gene I-like receptor (RLR) pathway genes, including mda5, mita, tbk1, irf3, and irf7 increased, inducing the expression of interferon (IFN) and anti-viral proteins in GPF cells. In addition, lipopolysaccharide (LPS) stimulation up-regulated the expression of inflammation-related factors, including myd88, irak1, nfκb, il1β, il6, and cxcl10 expression. To the best of our knowledge, this is the first study on the immune response signaling pathways of the golden pompano using an established fin cell line. In this study, we describe a preliminary investigation of the GPF cell line immune response to poly I:C and LPS, and provide a more rapid and efficient experimental material for research on marine fish immunology.

A New Cell Line from the Brain of Red Hybrid Tilapia (Oreochromis spp.) for Tilapia Lake Virus Propagation

Tilapia lake virus (TiLV) presents a substantial threat to global tilapia production. Despite the development of numerous cell lines for TiLV isolation and propagation, none have been specifically derived from red hybrid tilapia (Oreochromis spp.). In this study, we successfully established a new cell line, RHTiB, from the red hybrid tilapia brain. RHTiB cells were cultured for 1.5 years through over 50 passages and demonstrated optimal growth at 25 °C in Leibovitz-15 medium supplemented with 10% fetal bovine serum at pH 7.4. Morphologically, RHTiB cells displayed a fibroblast-like appearance, and cytochrome oxidase I gene sequencing confirmed their origin from Oreochromis spp. Mycoplasma contamination testing yielded negative results. The revival rate of the cells post-cryopreservation was observed to be between 75 and 80% after 30 days. Chromosomal analysis at the 25th passage revealed a diploid count of 22 pairs (2n = 44). While no visible cytopathic effects were observed, both immunofluorescence microscopy and RT-qPCR analysis demonstrated successful TiLV propagation in the RHTiB cell line, with a maximum TiLV concentration of 107.82 ± 0.22 viral copies/400 ng cDNA after 9 days of incubation. The establishment of this species-specific cell line represents a valuable advancement in the diagnostic and isolation tools for viral diseases potentially impacting red hybrid tilapia.

Development and characterization of brain cell line from Trachinotus blochii and its application in virological and gene expression studies

A permanent cell line, SPB (Snubnose pompano brain) was established from Trachinotus blochii by the explant culture method. It has been sub-cultured more than 75 passages and showed optimal growth at 28°C using L-15 medium supplemented with 15% to 20% FBS. The SPB cells were cryopreserved at different passage levels for various applications. SPB cells were composed of fibroblastic and epithelial-like cells. The SPB cells were tested for mycoplasma contamination which was found to be negative. The origin of the SPB cell line from T. blochii was confirmed by amplification of the mitochondrial cytochrome oxidase I (COI) gene. The transfection efficiency of SPB cell line is 15% assessed by expression of green fluorescent protein using pEGFP-N1 plasmid. In addition, two CMV promotor plasmids pFNCPE42-DNA and pcDNAVP28 were transfected to SPB cells and it shows high expression levels of FNCP of fish nodavirus and VP28 protein of white spot syndrome virus by immunostaining. The SPB cells showed susceptibility to SJNNV and the infection was confirmed by RT-PCR, Western blot, ELISA, TCID50 and RT-qPCR. Experimental infection was carried out in T. blochii using SJNNV propagated in SPB cell line and found 100% mortality with clinical signs. The infection was confirmed by RT-PCR. The SPB cell line can be used for propagation of fish viral pathogens and production of the recombinant proteins.

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.

Fish cell line: depositories, web resources and future applications

Cell lines are important bioresources to study the key biological processes in the areas like virology, pathology, immunology, toxicology, biotechnology, endocrinology and developmental biology. Cell lines developed from fish organs are utilized as a model in vitro system in disease surveillance programs, pharmacology, drug screening and resolving cases of metabolic abnormalities. During last decade, there were consistent efforts made globally to develop new fish cell lines from different organs like brain, eye muscles, fin, gill, heart, kidney, liver, skin, spleen, swim bladder, testes, vertebra etc. This increased use and development of cell lines necessitated the establishment of cell line depositories to store/preserve them and assure their availability to the researchers. These depositories are a source of authenticated and characterized cell lines with set protocols for material transfer agreements, maintenance and shipping as well as logistics enabling cellular research. Hence, it is important to cryopreserve and maintain cell lines in depositories and make them available to the research community. The present article reviews the current status of the fish cell lines available in different depositories across the world, along with the prominent role of cell lines in conservation of life on land or below water.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-023-00601-2.

Development, characterization and in vitro applications of a thymus cell line from Pangasianodon hypophthalmus (Sauvage 1878)

Pangasianodon hypophthalmus is an economically important catfish species cultured in India. In the present study, a continuous cell line from the thymus of P. hypophthalmus (PHT) was established using the explant method and subcultured 52 times since development. PHT cells showed optimal growth in L-15 medium containing 20% fetal bovine serum at 28°C. The species of the cell line from striped catfish was confirmed through PCR amplification and sequencing of 16S, and COI genes. The cell line was found to be Mycoplasma free. The modal chromosome number of PHT cells was 60 (2n). Immunophenotyping using different antibodies showed the epithelial nature of the cells. Cytotoxicity of arsenic and mercury was assessed using Neutral red and MTT assay, which revealed reduced cell survival with an increase in toxicant concentration. Cells transfected successfully with the GFP reporter gene using lipofectamine reagent indicated the suitability of the cell line for expression studies. The cell line has been submitted to NRFC, Lucknow with accession no. NRFC-078 at ICAR-NBFGR, Lucknow. The developed cell line will have applications in suspected viral disease investigation, transgenic, and immunological studies.

Establishment and application of four long-term culture cell lines of the olive flounder Paralichthys olivaceus blastocysts

Four new embryonic cell lines derived from blastocysts of the olive flounder Paralichthys olivaceus, an important commercial marine fish, were established and characterized. They were designated as PoEFCI, PoEFCII, PoEFCIII, and PoEFCIV and were all fibroblastic cells. The cells were cultured in DMEM/F-12 medium supplemented with antibiotics, FBS, and growth factors at temperature of 25 °C and subcultured for >100 passages over 18 months. The origin of the cell lines was confirmed by examining the partial sequences of the cytochrome oxidase c subunit I (COI) gene of the flounder mitochondrial DNA (mtDNA). The four cell lines showed different growth curve patterns. According to the results of gene and protein expression and enzyme activity, the cell lines PoEFCI, PoEFCII, and PoEFC III could be pluripotent. The cells of all four cell lines were also successfully transfected with the green fluorescent protein (GFP) reporter gene, suggesting that they could be used to study gene function in the flounder or other fish. More importantly, PoEFCI-III were sensitive to chromium (Cr) and red sea bream Pagrus major iridovirus (RSIV), so they could be used as a powerful tool for the study of the toxicological investigation of heavy metals and RSIV in fish. Therefore, these cell lines would be useful for biotechnological and toxicological research on marine fish as an in vitro biological system.

Establishment and characterization of a continuous cell line from caudal fin of Labeo calbasu (Hamilton, 1822)

Labeo calbasu is an important food fish and candidate species for diversification of carp aquaculture. In the present study, we have established a continuous cell line, designated as L. calbasu fin (LCF), from caudal fin of L. calbasu using explant method. The cell line has been subcultured for over 73 passages and the LCF cells show optimal growth in Leibovitz's L-15 medium supplemented with 20% fetal bovine serum at a temperature of 28°C. In karyotype analysis, the modal chromosome number of LCF cells at 35th passage was found to be 50. The amplification and sequencing of partial fragments of mitochondrial genes, namely 16S rRNA and COI from LCF cells confirmed the origin of cell line from L. calbasu. The LCF cells could be successfully transfected with GFP reporter gene, indicating suitability of these cells for expression of foreign genes. Further, following inoculation with supernatant from Tilapia lake virus (TiLV) infected cell line, no cytopathic effects were observed in the LCF cells and cell pellet was negative for TiLV in RT-PCR, indicating that LCF cells were not susceptible to TiLV. The developed cell line has been submitted to National Repository of Fish Cell Lines being maintained at ICAR-National Bureau of Fish Genetic Resources, Lucknow (accession no. NRFC063). The newly developed LCF cell line would be helpful in investigating diseases affecting this candidate species particularly the ones suspected to be of viral etiology, and for cytotoxicity and transgenic studies.

Development and characterization of a new gill cell line from the striped catfish, Pangasianodon hypophthalmus (Sauvage, 1878)

Cell lines as an in vitro model developed from different target organs of fish find their use in virus susceptibility, cytotoxicity, gene expression studies. The striped catfish, Pangasianodon hypophthalmus, is one of the main species in aquaculture, especially in Southeast Asian countries like Thailand, Indonesia, China, India, Bangladesh, and Vietnam. The present study reports the development of a new permanent cell line from the gills of P. hypophthalmus designated as PHG and its application in toxicological research. Leibovitz's L-15 cell culture medium supplemented with 15% fetal bovine serum (FBS) was used to maintain cell line PHG. The morphology of the PHG cell line was observed fibroblastic-like. PHG cells grew well at varying temperatures ranging from 24 to 30 °C with an optimum temperature of 28 °C. The PHG cell line was characterized using a sequence of mitochondrial cytochrome C oxidase subunit I, which authenticated the species of origin of the cell line. The cell line was transfected with a pEGFP-C1 plasmid, and the transfection reporter gene was successfully expressed 48 h post-transfection with 9% transfection efficiency. The toxicity assessment of two organophosphate pesticides, chlorpyrifos, and malathion using the PHG cell line revealed that the two organophosphate pesticides were cytotoxic to the cell line at varying concentrations.

Tilapia lake virus: The story so far

Tilapia lake virus (TiLV) is a highly contagious pathogen that has detrimental effects on tilapia farming. This virus was discovered in 2014 and has received tremendous global attention from the aquaculture sector due to its association with high fish mortalities and its strong economic impact on the tilapia aquaculture industry. Currently, TiLV has been reported in 16 countries, and this number is continuing to rise due to improved diagnostic assays and surveillance activities around the world. In this review, we summarize the up-to-date knowledge of TiLV with regard to TiLV host species, the clinical signs of a TiLV infection, the affected tissues, pathogenesis and potential disease risk factors. We also describe the reported information concerning the virus itself: its morphology, genetic make-up and transmission pathways. We review the current methods for virus detection and potential control measures. We close the review of the TiLV story so far, by offering a commentary on the major TiLV research gaps, why these are delaying future TiLV research and why the TiLV field needs to come together and proceed as a more collaborative scientific community if there is any hope limiting the impact of this serious virus.