Establishment of a cell line with high transfection efficiency from zebrafish Danio rerio embryos and its susceptibility to fish viruses

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.

Transfection of Sponge Cells and Intracellular Localization of Cancer-Related MYC, RRAS2, and DRG1 Proteins

The determination of the protein's intracellular localization is essential for understanding its biological function. Protein localization studies are mainly performed on primary and secondary vertebrate cell lines for which most protocols have been optimized. In spite of experimental difficulties, studies on invertebrate cells, including basal Metazoa, have greatly advanced. In recent years, the interest in studying human diseases from an evolutionary perspective has significantly increased. Sponges, placed at the base of the animal tree, are simple animals without true tissues and organs but with a complex genome containing many genes whose human homologs have been implicated in human diseases, including cancer. Therefore, sponges are an innovative model for elucidating the fundamental role of the proteins involved in cancer. In this study, we overexpressed human cancer-related proteins and their sponge homologs in human cancer cells, human fibroblasts, and sponge cells. We demonstrated that human and sponge MYC proteins localize in the nucleus, the RRAS2 in the plasma membrane, the membranes of the endolysosomal vesicles, and the DRG1 in the cell's cytosol. Despite the very low transfection efficiency of sponge cells, we observed an identical localization of human proteins and their sponge homologs, indicating their similar cellular functions.

Establishment and characterization of a spinal cord tissue cell line from mandarin fish, Siniperca chuatsi and its susceptibility to several viruses

In this study, we established and characterized a continuous cell line from the spinal cord tissue of mandarin fish, Siniperca chuatsi and assessed its susceptibility to infectious spleen and kidney necrosis virus (ISKNV), Siniperca chuatsi ranavirus (SCRaV) and Siniperca chuatsi rhabdovirus (SCRV). The cell line, named SCC, has been successively cultured up to 40 passages. The optimal growing conditions of SCC cells were in Leibovitz's L-15 medium supplemented with 20% foetal bovine serum (FBS) at 28°C. Karyotype analysis demonstrated 48 normal diploid chromosomes in the cells. The identity of S. chuatsi origin of SCC cells was confirmed by partial sequencing of the 16S rRNA and cytochrome oxidase I (COI) genes. Infection susceptibility assessment showed that ISKNV, SCRIV and SCRV and can be stably produced and transmitted in SCC cells, and the replication efficiency of ISKNV, SCRaV and SCRV ranged from 10^7.4 to 10^9.6 TCID₅₀ /ml. In addition, transmission electron microscopy analysis of ISKNV, SCRAV and SCRV infected SCC cells showed numerous viral particles. In conclusion, the newly established SCC cells provide an important tool for isolation and production of viruses, as well as for molecular and cell biology 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.

Establishment and characterization of a liver cell line, ALL, derived from yellowfin sea bream, Acanthopagrus latus, and its application to fish virology

Yellowfin sea bream (Acanthopagrus latus) is an important economic fish, which is seriously threatened by various fish viruses. In this study, a cell line designated as ALL derived from the liver of yellowfin sea bream was developed and characterized. The cell line grew well in Dulbecco's modified Eagle's medium containing 10%-20% foetal bovine serum at 28°C. Amplification of the cytochrome B gene indicated that ALL cells originated from yellowfin sea bream. The modal chromosome number of ALL cells was 48. ALL cells were efficiently transfected with pEGFP-N3 plasmids, indicating the potential application of ALL cells in exogenous gene manipulation studies. ALL cells were susceptive to three main fish viruses, including viral haemorrhagic septicaemia virus (VHSV), red-spotted grouper nervous necrosis virus (RGNNV) and largemouth bass virus (LMBV). The replication of VHSV, RGNNV and LMBV in ALL cells was confirmed by quantitative real-time polymerase chain reaction, virus titre and transmission electron microscopy assays. Moreover, ALL cells could respond to VHSV, RGNNV and LMBV infections, as indicated by the differential expression of antiviral genes involving in the innate immune response. In conclusion, the newly established ALL cell line will be an excellent in vitro platform for the study of the virus-yellowfin sea bream interaction.

Establishment, characterization, and transfection potential of a new continuous fish cell line (CAM) derived from the muscle tissue of grass goldfish (Carassius auratus)

A new continuous fish cell line (CAM) has been successfully derived from the muscle tissues of grass goldfish, Carassius auratus. The primary cell cultures were initiated by incomplete trypsinization first and then explant culture in a Leibovitz-15 medium supplemented with 15% fetal bovine serum and 10% fish muscle extract. It was found that the CAM cells were very sensitive to trypsinization and needed to be sub-cultured at a low trypsin concentration of 0.0625% to be able to go through the crisis of spontaneous immortalization transformation, and afterward a total of five derivative cell strains were isolated from the original CAM cell line. This spontaneous immortalization transformation event was recorded successively at passages 44-47, beginning with a large-scale apoptosis and senescence and followed by mitosis arrest and re-activation, thus designated as cell strain CAM-44A, 44B, 45A, 44B, and 47A. Now both the CAM cell line and strains had been sub-cultured for more than 89 times and could be well cryopreserved in the growth medium containing 5% dimethylsulfoxide. Chromosome analysis and COI gene analysis had confirmed the grass goldfish origin of these CAM cells. Transfection potential analysis indicated that Lipofectamine LTX and Xfect were two suitable transfection reagents to be used in the gene delivery of CAM cells with a transfection efficiencies up to 11±6% and 8±3% in the CAM cell lines, respectively. Among the five cell strains, CAM-47A showed the highest transfection potential with a transfection efficiency up to 28 ± 5%. This work will provide a useful cell source for works on the cell-based artificial fish meat production and functional studies of fish myogenesis-related genes.

Establishment and characterization of a new cell line from the muscle of humpback grouper (Cromileptes altivelis)

The humpback grouper (Cromileptes altivelis) is a commercially important species of the family Epinephelidae. With the development in aquaculture industry, C. altivelis breeding has gradually increased in volumetric production, leading to the occurrence of various diseases. In this study, we established a new cell line (CAM) derived from the muscle tissue of C. altivelis. Our results showed that the optimal growth temperature and working concentration of fetal bovine serum (FBS) of CAM cells were 28 °C and 15%, respectively. DNA sequencing and comparative analysis of 18S rRNA gene sequence showed that CAM cell line was originated from C. altivelis. Chromosome analysis showed that the modal chromosome number of CAM cells was 48. After transfection using pEGFP-N3 plasmid, CAM cells exhibited high transfection efficiency, indicating that CAM cells could be used in foreign gene expression studies. Further, cytotoxicity analysis revealed that CAM cells were sensitive to Vibrio harveyi and Edwardsiella tarda. Moreover, the cytotoxicity of heavy metals (Hg, Cd, and Cu) to CAM cells was dose-dependent. This CAM cell line might be used as an ideal tool in vitro for analyzing and understanding the mechanisms of pathogenesis, host-pathogen interactions, and toxicity assay of heavy metals.

MiR-202-5p Inhibits RIG-I-Dependent Innate Immune Responses to RGNNV Infection by Targeting TRIM25 to Mediate RIG-I Ubiquitination

The RIG-I-like receptors (RLRs) signaling pathway is essential for inducing type I interferon (IFN) responses to viral infections. Meanwhile, it is also tightly regulated to prevent uncontrolled immune responses. Numerous studies have shown that microRNAs (miRNAs) are essential for the regulation of immune processes, however, the detailed molecular mechanism of miRNA regulating the RLRs signaling pathway remains to be elucidated. Here, our results showed that miR-202-5p was induced by red spotted grouper nervous necrosis virus (RGNNV) infection in zebrafish. Overexpression of miR-202-5p led to reduced expression of IFN 1 and its downstream antiviral genes, thus facilitating viral replication in vitro. In comparison, significantly enhanced levels of IFN 1 and antiviral genes and significantly low viral burden were observed in the miR-202-5p^-/- zebrafish compared to wild type zebrafish. Subsequently, zebrafish tripartite motif-containing protein 25 (zbTRIM25) was identified as a target of miR-202-5p in both zebrafish and humans. Ectopic expression of miR-202-5p suppressed zbTRIM25-mediated RLRs signaling pathway. Furthermore, we showed that miR-202-5p inhibited zbTRIM25-mediated zbRIG-I ubiquitination and activation of IFN production. In conclusion, we demonstrate that RGNNV-inducible miR-202-5p acts as a negative regulator of zbRIG-I-triggered antiviral innate response by targeting zbTRIM25. Our study reveals a novel mechanism for the evasion of the innate immune response controlled by RGNNV.

Zebrafish TRIM25 Promotes Innate Immune Response to RGNNV Infection by Targeting 2CARD and RD Regions of RIG-I for K63-Linked Ubiquitination

RIG-I-like receptors (RLRs) play important roles in response to virus infection by regulating host innate immune signaling pathways. Meanwhile, the RLR signaling pathway is also tightly regulated by host and virus to achieve the immune homeostasis between antiviral responses and virus survival. Here, we found that zebrafish TRIM25 (zbTRIM25) functioned as a positive regulator of RLR signaling pathway during red spotted grouper nervous necrosis virus (RGNNV) infection. Post-RGNNV infection, zbTRIM25 expression was obviously inhibited and ectopic expression of zbTRIM25 led to enhanced expression of RLR signaling pathway-related genes. Overexpression and knockdown analysis revealed that zbTRIM25 promoted zebrafish RIG-I (zbRIG-I)-mediated IFN signaling and inhibited RGNNV replication. Mechanistically, zbTRIM25 bound to zbRIG-I; in particular, the SPRY domain of zbTRIM25 interacted with the tandem caspase activation and recruitment domains (2CARD) and repressor domain (RD) regions of zbRIG-I. zbTRIM25 promoted the K63 polyubiquitination of 2CARD and RD regions of zbRIG-I. Furthermore, zbTRIM25-mediated zbRIG-I activation of IFN production was enhanced by K63-linked ubiquitin, indicating that zbTRIM25-mediated zbRIG-I polyubiquitination was essential for RIG-I-triggered IFN induction. In conclusion, these findings reveal a novel mechanism that zbTRIM25 positively regulates the innate immune response by targeting and promoting the K63-linked polyubiquitination of zbRIG-I.

Establishment and characterization of a fin tissue cell line derived from silver pomfret, Pampus argenteus

A cell line (PaF) derived from the fin tissue of silver pomfret (Pampus argenteus) was established and characterized in this study. The cell line has been subcultured for more than 50 times in Dulbecco's modified Eagle's medium (DMEM) containing 15% foetal bovine serum (FBS) since the initial primary culture. PaF cells grew well at temperatures from 24°C to 28°C in DMEM supplemented with 15% FBS. Partial amplification and sequence analysis of the cytochrome B gene indicated that PaF originated from silver pomfret. Cytogenetic analysis demonstrated that the modal chromosome number was 48. A significant cytopathic effect was observed in PaF cells during viral haemorrhagic septicaemia virus (VHSV) infection, and the VHSV replication was confirmed by qRT-PCR and viral titre assays. In contrast, PaF cells were resistant to red-spotted grouper nervous necrosis virus infection. Moreover, PaF cells could respond to VHSV and lipopolysaccharide treatments, as indicated by the expression of immune-related genes, TLR5 and TLR9. In conclusion, the establishment of PaF cell line will provide an appropriate in vitro tool for the study of mechanisms of pathogen-silver pomfret interaction.

Establishment of a cell line from egg of rare minnow Gobiocypris rarus for propagation of grass carp reovirus genotype II

The rare minnow, Gobiocypris rarus, is small experimental fish proven to be sensitive to Grass Carp Reovirus (GCRV) infection. In present study we established a new cell (GrE) from eggs of G. rarus. GrE cells grew well at 28 °C in M199 medium containing 10% fetal bovine serum, and has been subcultured for over 70 passages. Chromosome analysis indicated that 40% of the cells were diploid 2n = 66 while the chromosome number of the fish is 2n = 50. Viral replication in GrE cells was confirmed by transmission electron microscopy, immunofluorescence assays and virus titration experiments. GrE cells and Cyenopharyngodon idellus kidney cells were infected with two GCRV genotypes while the virus copies of GCRV II in GrE peaked at 2.25 × 10⁵ on 12th dpi. In vivo challenge experiments using GCRV I and II isolates at generations 1 and 20 indicated that GCRV II reproduce similar symptoms and histopathological changes of the disease in the rare minnow. These results indicated that GrE is permissive for GCRV genotype II propagation and can be used for pathogenesis studies and vaccine development of the predominant genotype of GCRV.