Derivation and characterization of new cell line from intestine of turbot (Scophthalmus maximus)

Establishment and characterization of SSI cell line from Sebastes schlegelii intestine for investigating the immune response to Pathogenic Bacteria

As a commercially valuable fish species, Sebastes schlegelii faces threats from pathogenic bacteria like Edwardsiella piscicida during aquaculture. The global host range of E. piscicida encompasses various species, yet its pathogenic mechanism remains incompletely elucidated. Cell lines offer invaluable in vitro resources for studying the pathogen pathogenicity. Here, we established and characterized a cell line derived from the intestinal tissue of the S. schlegelii, designated as SSI. SSI has undergone continuous subculturing for over 80 passages, demonstrating robust growth in DMEM supplemented with 10%-20% FBS and 20 μM HEPES at 24°C. Karyotype analysis and 18S rRNA amplification confirm its origin. SSI exhibits high transfection efficiency for exogenous DNA, making it suitable for gene expression and intestinal function analysis. E. piscicida infects SSI cells at low densities without inducing morphological changes within 6 h of infection, suggesting the potential of SSI as an in vitro model for studying E. piscicida pathogenicity. This cell line provides a valuable tool for investigating mucosal immunity and E. piscicida pathogenic mechanisms in marine fish.

Transfection, cytotoxicity, and cell cycle studies on the two newly developed and characterized humpback grouper (Cromileptes altivelis) fin cell lines

The development and characterization of two novel humpback grouper (Cromileptes altivelis) fin cell lines are described in this study. The CA1F3Ex and CA1F4Tr cell lines were developed by explant and trypsinization methods, respectively, in Leibovitz's L15 (L-15) medium supplemented with 20% FBS (fetal bovine serum) and subcultured over 150 times. Cell lines exhibited high stability, as evidenced by the high revival rate (85-95%) and good attachment while seeding after one year of cryostorage. They displayed good seeding (91%) and plating efficiencies (15-25%). The optimum temperature for growth was recorded at 28˚C. Serum requirement decreased with increased passage and lowered to 2% FBS beyond 30-35 passages. However, higher serum concentration (2-20%) caused a concurrent increase in cell growth. Both the cell lines were fibroblast-type, and immunotyping results showed strong reactivity towards the fibroblast marker. Chromosome analysis of these cell lines revealed aneuploidy, and the authenticity was confirmed by mitochondrial Cytochrome C Oxidase Subunit I (COI) genotyping analysis. Cell cycle studies were performed utilizing the flow cytometric technique. CA1F3Ex and CA1F4Tr cell lines showed high transfection efficiency with pEGFP-N1 plasmid using Lipofectamine and cytotoxicity towards heavy metals (Hg and Cd) was also studied. Hence, these continuous cell lines could be employed as in vitro models for aquatic toxicological and genetic manipulation studies.

Intestinal epithelial cells of Japanese flounder (Paralichthys olivaceus) as an in vitro model for studying intestine immune function based on transcriptome analysis

Japanese flounder (Paralichthys olivaceus) is an economically crucial marine species, but diseases like hemorrhagic septicemia caused by Edwardsiella tarda have resulted in significant economic losses. E. tarda infects various hosts, and its pathogenicity in fish is not fully understood. Lipopolysaccharides (LPS) are components of the outer membrane of Gram-negative bacteria and are representative of typical PAMP molecules that cause activation of the immune system. The PoIEC cell line is a newly established intestinal epithelial cell line from P. olivaceus. In order to investigate whether it can be used as an in vitro model for studying the pathogenesis of E. tarda and LPS stimulation, we conducted RNA-seq experiments for the PoIECs model of E. tarda infection and LPS stimulation. In this study, transcriptome sequencing was carried out in the PoIEC cell line after treatment with LPS and E. tarda. A total of 62.52G of high-quality data from transcriptome sequencing results were obtained in nine libraries, of which an average of 87.96% data could be aligned to the P. olivaceus genome. Data analysis showed that 283 and 414 differentially expressed genes (DEGs) in the LPS versus Control (LPS-vs-Con) and E. tarda versus Control groups (Et-vs-Con), respectively, of which 60 DEGs were shared in two comparation groups. The GO terms were predominantly enriched in the extracellular space, inflammatory response, and cytokine activity in the LPS-vs-Con group, whereas GO terms were predominantly enriched in nucleus and positive regulation of transcription by RNA polymerase II in the Et-vs-Con group. KEGG analysis revealed that three immune-related pathways were co-enriched in both comparison groups, including the Toll-like receptor signaling pathway, C-type lectin receptor signaling pathway, and Cytokine-cytokine receptor interaction. Five genes were randomly screened to confirm the validity and accuracy of the transcriptome data. These results suggest that PoIEC cell line can be an ideal in vitro model for studies of marine fish gut immunity and pathogenesis of Edwardsiellosis.

Genome-wide identification, evolution and expression analysis of tight junction gene family and the immune roles of claudin5 gene in turbot (Scophthalmus maximus L.)

Tight junction proteins (TJs) are important component proteins that maintaining the structure and function of TJs, connecting to each other to form a TJ complex between cells, maintaining the biological homeostasis of the internal environment. In this study, a total of 103 TJ genes were identified in turbot according to our whole-transcriptome database. Transmembrane TJs were divided into seven subfamilies, including claudin (CLDN), occludin (OCLD), tricellulin (MARVELD2), MARVEL domain containing 3 (MARVELD3), junctional adhesion molecules (JAM), immunoglobulin superfamily member 5 (IGSF5/JAM4), blood vessel epicardial substance (BVEs). Moreover, the majority of homologous pairs of TJ genes showed highly conserved alongside length, exon/intron number and motifs. As for phylogenetic analysis for 103 TJ genes, eight of them have undergone a positive selection and JAMB-like has undergone the most neutral evolution. The expression patterns of several TJ genes showed the lowest expression levels in blood, while the highest expression levels were detected in intestine, gill and skin, which all belong to mucosal tissues. Meanwhile, most examined TJ genes showed down-regulated expression patterns during bacterial infection, while several TJ genes exhibited up-regulated expression patterns at a later stage (24 h). At the same time, several potential candidate genes (such as CLDN-15, CLDN-3, CLDN-12, CLDN-5 and OCLD) were significantly down-regulated, which may indicate their important functions that involved in the regulation of bacterial infection. Currently, there is little research on CLDN5 in the intestine, but it is highly expressed in the intestine and has significant changes in intestinal expression after bacterial infection. Thus, we knocked down CLDN5 by the method of lentiviral infection. The result showed CLDN5 was related to cell migration (wound healing) and apoptosis, and the method of dualluciferasereporterassay showed that the functions of CLDN5 could be regulated by miR-24. The study of TJs may lead to a better understanding of the function of TJs in teleost.

The manipulation of cell suspensions from zebrafish intestinal mucosa contributes to understanding enteritis

Background

Although zebrafish are commonly used to study intestinal mucosal immunity, no dedicated procedure for isolating immune cells from zebrafish intestines is currently available. A speedy and simple operating approach for preparing cell suspension from mucosa has been devised to better understanding of intestinal cellular immunity in zebrafish.

Methods and results

The mucosal villi were separated away from the muscle layer by repeated blows. The complete deprivation of mucosa was done and evidenced by HE and qPCR results. Higher expression of both innate (mpeg1, mpx, and lck) and adaptive immune genes (zap70, blnk, foxp3a, and foxp3b) was revealed compared to cells obtained by typical mesh rubbing. The cytometric results also revealed that the tested operation group had a higher concentration and viability. Further, fluorescent-labelled immune cells from 3mo Tg(lyz:DsRED2), Tg(mpeg1:EGFP), Tg(Rag2:DsRED), and Tg(lck:EGFP), were isolated and evaluated for the proportion, and immune cells' type could be inferred from the expression of marker genes. The transcriptomic data demonstrated that the intestinal immune cell suspension made using the new technique was enriched in immune-related genes and pathways, including il17a/f, il22, cd59, and zap70, as well as pattern recognition receptor signaling and cytokine-cytokine receptor interaction. In addition, the low expression of DEG for the adherent and close junctions indicated less muscular contamination. Also, lower expression of gel-forming mucus-associated genes in the mucosal cell suspension was consistent with the current less viscous cell suspension. To apply and validate the developed manipulation, enteritis was induced by soybean meal diet, and immune cell suspensions were analyzed by flow cytometry and qPCR. The finding that in enteritis samples, there was inflammatory increase of neutrophils and macrophages, was in line with upregulated cytokines (il8 and il10) and cell markers (mpeg1 and mpx).

Conclusion

As a result, the current work created a realistic technique for studying intestinal immune cells in zebrafish. The immune cells acquired may aid in further research and knowledge of intestinal illness at the cellular level.