Characterization of a novel cell line from the caudal fin of koi carp Cyprinus carpio

Characterization of a novel brain cell line from Jian carp (Cyprinus carpio var. Jian)

Jian carp (Cyprinus carpio var. Jian) is an economically important cultured fish in China. Currently, it is facing threats from infectious diseases including koi herpesvirus (KHV). Here, we established a new cell line, designated CCB-J, derived from the brain tissue of the Jian carp. CCB-J cells grew well in Leibovitz's L-15 medium containing 20% fetal bovine serum at 25 °C and have been subcultured for more than 60 passages. At the 30th passage, analysis showed that the number of chromosomes was 100, which is identical to that of other carp variants. Sequencing of the 18S ribosomal DNA confirmed that CCB-J originated from Jian carp. After transfection with the pEGFP-N1 plasmid, green fluorescence was observed in CCB-J. The replication of KHV in CCB-J cells was confirmed by RT-PCR and transmission electron microscopy. The viral titers of KHV in CCB-J cells and CCB cells, which have been widely used in the study of KHV, reached 10^3.9 and 10^1.8 median tissue culture infectious dose (TCID₅₀/mL), respectively, within 14 days. The result of TaqMan PCR revealed that CCB-J cells were more sensitive to KHV than CCB cells. Meanwhile, a cytopathic effect (CPE) was also observed in the CCB-J cells in a shorter time post-infection compared with CCB cells. In summary, the CCB-J cell line will be a useful tool in the study of viral pathogenesis and vaccine research.

Development, characterization and virus susceptibility of a continuous cell line from the caudal fin of marbled eel (Anguilla marmorata)

A continuous cell line consisting mostly of epithelioid cells was established from the caudal fin of marbled eels (Anguilla marmorata) and designated as marbled eel caudal fin (MECF)-1. The cells multiplied well in Leibovitz's L-15 medium containing 2% to 15% foetal bovine serum at temperatures of 20°C to 35°C and were subcultured for >90 passages during a 5-year period from 2012 to 2017. Transcripts of ictacalcin, keratin 13, cd146, nestin, ncam1 and myod1 were demonstrated in the cells using reverse transcription polymerase chain reaction. The results indicated that MECF-1 was composed of epidermal and mesenchyme stem and progenitor cells including myoblasts. MECF-1 was susceptible to Japanese eel herpesvirus HVA980811, marbled eel polyoma-like virus (MEPyV), aquabirnavirus MEIPNV1310 and aquareovirus CSV. By contrast, MECF-1 was noted refractory to megalocytiviruses RSIV-Ku and GSIV-K1 infection. Moreover, the cells were resistant to betanodavirus infection. In conclusion, MECF-1 derived from marbled eel is suitable for studies on anguillid viruses and interaction with host cells.

Monitoring changing cellular characteristics during the development of a fin cell line from Cyprinus carpio

The establishment and in-depth characterization of a novel continuous cell line derived from fin tissue of common carp (Cyprinus carpio), CCApin, is reported. The cells of the cell line could be propagated in Leibovitz's L-15 medium containing 15% foetal calf serum and 0.5% carp serum for >150 passages during the last 24 months, with a stable fast growth. Furthermore, antibody staining indicated that cell types obtained in primary cultures, containing the epithelial stem-cell marker tumorprotein 63, were different from cells in long-term cell cultures, containing tight junction protein zona occludens 1 and cytokeratin 7. These observations suggest a switch of dominant cell types. Molecular analysis of gene expression profiles of caudal fin tissue and CCApin cells showed that genes relevant in epithelial cells but also in mesenchymal cells were expressed. However, during cultivation of CCApin a set of very steadily expressed, primarily mesenchymal genes like collagen 1 alpha 1, fibronectin or cadherin 2 was found. In summary, the long-term cell culture could be described as a stably growing epithelial population with some mesenchymal features. There are several application possibilities, especially for virus susceptibility studies, e.g. cyprinid herpesvirus-3 (CyHV-3). The study leads to a better understanding of molecular and physiological mechanisms of in vitro fish cell cultures.

Characterization and virus susceptibility of a continuous cell line derived from the brain of Aequidens rivulatus (Günther)

Cell cultures derived from the brain tissues of Aequidens rivulatus (Günther) have been characterized previously. In this study, a continuous cell line ARB8 was further established, and its growth characteristics, transcription and susceptibility to fish viruses-including chum salmon reovirus (CSV), marbled eel infectious pancreative necrosis virus (MEIPNV), grouper nervous necrosis virus (GNNV), giant seaperch iridovirus (GSIV), red seabream iridovirus (RSIV), koi herpesvirus (KHV), herpesvirus anguilla (HVA) and marbled eel polyoma-like virus (MEPyV)-were examined. ARB8 cells that showed epithelioid morphology and were passaged >80 times grew well at temperatures ranging from 25°C to 30°C in L-15 medium containing 5%-15% foetal bovine serum. The cells constitutively transcribed connexion 43, glutamine synthetase, nestin and nkx6-2, which are markers for neural progenitor cells. The cells were highly susceptible to CSV, MEIPNV, GSIV and RSIV and showed the typical cytopathic effect (CPE). However, the cells were resistant to GNNV, KHV, HVA and MEPyV because no significant CPE was noted after infection. Optimal temperatures for virus production ranged from 25°C to 30°C. The results revealed that the neural progenitor cell line ARB8 can potentially serve as a useful tool for investigating fish viruses and isolating new viruses in ornamental cichlid fishes.

Inoculation of cyprinid herpesvirus 3 (CyHV-3) on common carp brain cells-influence of process parameters on virus yield

Research of cyprinid herpesvirus 3 (CyHV-3) is focused on the infection mechanism and disease development in animals using genetic and immunological approaches to improve treatments and diagnostics. In contrast, only few tried to investigate the CyHV-3 replication behaviour in available cell cultures. Whereas, obtaining high virus yields by in vitro replication enables achieving of the mentioned above goals easier and more reliable. The following work presents an attempt to illuminate the KHV replication in common carp brain (CCB) cell cultures from the engineering point of view. The isolate KHV-TP30 was used testing the influence on process parameters, such as multiplicity of infection (MOI), time of infection (TOI) and time of harvest (TOH). Virus concentrations and infectivity at different time points of infection were examined using hydrolyzed probe qPCR (Gilad et al. 2004) and 50% tissue culture infectivity dose (TCID₅₀). The data obtained show that while the amount of the virus DNA remains constant after reaching its maximum, the infectivity of the virus decreases. Thus, especially, TOH can be crucial for generating a high-quality virus stock. Applying optimized parameters improved the infectivity of the harvested virus and reached a robust titre as high as 1.9 × 10⁸ TCID₅₀/mL. To our knowledge, so far, there is no information in the peer-reviewed literature showing comparably high virus titres. Such virus yields not only facilitate conduction of further studies, including stability tests of the virus stock under various supplementation or disinfection trails, but also provide enough virus material to perform more detailed examinations of the infection mechanism.

Isolation of a novel polyomavirus, related to Japanese eel endothelial cell-infecting virus, from marbled eels, Anguilla marmorata (Quoy & Gaimard)

Marbled eels, Anguilla marmorata (Quoy & Gaimard), cultured in Taiwan exhibited haemorrhage and mortality in January 2012. The severely diseased eels bled from the gills and showed congestion of the central venous sinus of the gill filaments and haemorrhage throughout the body similar to viral endothelial cell necrosis of eel. In this study, a novel polyomavirus (AmPyV) was isolated from the diseased eels using the AMPF cell line established from the pectoral fin of healthy marbled eels. AmPyV was found to encode a long T-antigen orthologous gene. Phylogenetic analysis showed that AmPyV was closely related to Japanese eel endothelial cell-infecting virus. PCR assays revealed AmPyV infection throughout the systemic organs. AmPyV proliferated in the AMPF, EK-1 and EO-2 cells at temperatures 25-30 °C, and the progeny virus yields were 10(7.0) , 10(7.4) and 10(7.7) TCID50  mL(-1) , respectively. The purified virions were icosahedral particles, 70-80 nm in diameter. No clinical signs or mortality was observed among the eels injected with the virus; however, the virus was reisolated from the brain, eyes, kidneys, fins and gills of infected eels 2 month after injection. Our results suggest that AmPyV exhibits a latent infection. Pathogen of the disease needs to study further.

Cyprinid Herpesvirus 3: An Archetype of Fish Alloherpesviruses

The order Herpesvirales encompasses viruses that share structural, genetic, and biological properties. However, members of this order infect hosts ranging from molluscs to humans. It is currently divided into three phylogenetically related families. The Alloherpesviridae family contains viruses infecting fish and amphibians. There are 12 alloherpesviruses described to date, 10 of which infect fish. Over the last decade, cyprinid herpesvirus 3 (CyHV-3) infecting common and koi carp has emerged as the archetype of fish alloherpesviruses. Since its first description in the late 1990s, this virus has induced important economic losses in common and koi carp worldwide. It has also had negative environmental implications by affecting wild carp populations. These negative impacts and the importance of the host species have stimulated studies aimed at developing diagnostic and prophylactic tools. Unexpectedly, the data generated by these applied studies have stimulated interest in CyHV-3 as a model for fundamental research. This review intends to provide a complete overview of the knowledge currently available on CyHV-3.

Stabilization of gene expression and cell morphology after explant recycling during fin explant culture in goldfish

The development of fin primary cell cultures for in vitro cellular and physiological studies is hampered by slow cell outgrowth, low proliferation rate, poor viability, and sparse cell characterization. Here, we investigated whether the recycling of fresh explants after a first conventional culture could improve physiological stability and sustainability of the culture. The recycled explants were able to give a supplementary cell culture showing faster outgrowth, cleaner cell layers and higher net cell production. The cells exhibited a highly stabilized profile for marker gene expression including a low cytokeratin 49 (epithelial marker) and a high collagen 1a1 (mesenchymal marker) expression. Added to the cell spindle-shaped morphology, motility behavior, and actin organization, this suggests that the cells bore stable mesenchymal characteristics. This contrast with the time-evolving expression pattern observed in the control fresh explants during the first 2 weeks of culture: a sharp decrease in cytokeratin 49 expression was concomitant with a gradual increase in col1a1. We surmise that such loss of epithelial features for the benefit of mesenchymal ones was triggered by an epithelial to mesenchymal transition (EMT) process or by way of a progressive population replacement process. Overall, our findings provide a comprehensive characterization of this new primary culture model bearing mesenchymal features and whose stability over culture time makes those cells good candidates for cell reprogramming prior to nuclear transfer, in a context of fish genome preservation.

Cell-penetrating peptide delivery of biologically active oct4 protein into cultured Takifugu rubripes spermary cells

Continuous cell culture of a puffer fish Takifugu rubripes has been established for efficient delivery of exogenous genes or proteins to cultured fish cells. Transcription factor oct4 was chosen for transduction into cultured fish cells because of its conserved structure and function between fish and mammals. In this work, the T. rubripes oct4 gene was cloned and expressed in Escherichia coli as a recombinant protein by introducing cell-penetrating peptide (CPP) poly-arginine (11R) and 6His-tag at the C-terminus. After purification, recombinant proteins were added to the growth medium and incubated with T. rubripes spermary cells. Recombinant proteins that crossed the cell membrane were detected in the cytoplasm and nucleus by western blot and immunofluorescent observation. The function of transduced oct4 as a transcription factor in fish cells was confirmed by driving green fluorescent protein expression in the pEGFP-1 reporter construct with the conserved specific oct4-binding sequence from mouse Mus musculus. Taken together, 11R can be an efficient CPP in delivering fusion proteins to cultured fish cells.