Galectins in turbot (Scophthalmus maximus L.): Characterization and expression profiling in mucosal tissues

Genome-wide characterization, phylogenetic and expression analysis of Galectin gene family in Golden pompano Trachinotus ovatus

Galectins (Gals) are a type of S-type lectin that are widespread and evolutionarily conserved among metazoans, and can act as pattern recognition receptors (PRRs) to recognize pathogen-associated molecular patterns (PAMPs). In this study, 10 Gals (ToGals) were identified in the Golden pompano (Trachinotus ovatus), and their conserved domains, motifs, and collinearity relationships were analyzed. The expression of ToGals was regulated following infection to Cryptocaryon irritans and Streptococcus agalactiae, indicating that ToGals participate in immune responses against microbial pathogens. Further analysis was conducted on one important member, Galectin-3, subcellular localization showing that ToGal-3like protein is expressed both in the nucleus and cytoplasm. Recombinant protein obtained through prokaryotic expression showed that rToGal-3like can agglutinate red blood cells of rabbit, carp and golden pompano and also agglutinate and kill Staphylococcus aureus, Bacillus subtilis, Vibrio vulnificus, S. agalactiae, Pseudomonas aeruginosa, and Aeromonas hydrophila. This study lays the foundation for further research on the immune roles of Gals in teleosts.

Single-cell atlas of rainbow trout peripheral blood leukocytes and profiling of their early response to infectious pancreatic necrosis virus

The recent development of single cell sequencing technologies has revolutionized the state-of-art of cell biology, allowing the simultaneous measurement of thousands of genes in single cells. This technology has been applied to study the transcriptome of single cells in homeostasis and also in response to pathogenic exposure, greatly increasing our knowledge of the immune response to infectious agents. Yet the number of these studies performed in aquacultured fish species is still very limited. Thus, in the current study, we have used the 10x Genomics single cell RNA sequencing technology to study the response of rainbow trout (Oncorhynchus mykiss) peripheral blood leukocytes (PBLs) to infectious pancreatic necrosis virus (IPNV), an important trout pathogen. The study allowed us to obtain a transcriptomic profile of 12 transcriptionally distinct leukocyte cell subpopulations that included four different subsets of B cells, T cells, monocytes, two populations of dendritic-like cells (DCs), hematopoietic progenitor cells, non-specific cytotoxic cells (NCC), neutrophils and thrombocytes. The transcriptional pattern of these leukocyte subpopulations was compared in PBL cultures that had been exposed in vitro to IPNV for 24 h and mock-infected cultures. Our results revealed that monocytes and neutrophils showed the highest number of upregulated protein-coding genes in response to IPNV. Interestingly, IgM+IgD+ and IgT+ B cells also upregulated an important number of genes to the virus, but a much fainter response was observed in ccl4 + or plasma-like cells (irf4 + cells). A substantial number of protein-coding genes and genes coding for ribosomal proteins were also transcriptionally upregulated in response to IPNV in T cells and thrombocytes. Interestingly, although genes coding for ribosomal proteins were regulated in all affected PBL subpopulations, the number of such genes transcriptionally regulated was higher in IgM+IgD+ and IgT+ B cells. A further analysis dissected which of the regulated genes were common and which were specific to the different cell clusters, identifying eight genes that were transcriptionally upregulated in all the affected groups. The data provided constitutes a comprehensive transcriptional perspective of how the different leukocyte populations present in blood respond to an early viral encounter in fish.

A review of soluble factors and receptors involved in fish skin immunity: The tip of the iceberg

The immune system of fish possesses soluble factors, receptors, pathways and cells very similar to those of the other vertebrates' immune system. Throughout evolutionary history, the exocrine secretions of organisms have accumulated a large reservoir of soluble factors that serve to protect organisms from microbial pathogens that could disrupt mucosal barrier homeostasis. In parallel, a diverse set of recognition molecules have been discovered that alert the organism to the presence of pathogens. The known functions of both the soluble factors and receptors mentioned above encompass critical aspects of host defense, such as pathogen binding and neutralization, opsonization, or modulation of inflammation if present. The molecules and receptors cooperate and are able to initiate the most appropriate immune response in an attempt to eliminate pathogens before host infection can begin. Furthermore, these recognition molecules, working in coordination with soluble defence factors, collaboratively erect a robust and perfectly coordinated defence system with complementary specificity, activity and tissue distribution. This intricate network constitutes an immensely effective defence mechanism for fish. In this context, the present review focuses on some of the main soluble factors and recognition molecules studied in the last decade in the skin mucosa of teleost fish. However, knowledge of these molecules is still very limited in all teleosts. Therefore, further studies are suggested throughout the review that would help to better understand the functions in which the proteins studied are involved.

Identification and functional characterization of caspases in turbot (Scophthalmus maximus) in response to bacterial infection

Apoptosis is the autonomous and orderly death of cells under genetic control to maintain the stability of the internal environment, and is a programmed cell death process with unique morphological and biochemical properties that is regulated by a variety of factors. Caspase gene family has a significant function in the process of apoptosis. However, the knowledge of caspases in turbot remains largely unknown. In present study, a total of nine turbot caspase genes were identified. The mRNA length of these caspase genes was ranged from 1149 bp (caspase-1) to 3216 bp (caspase-2), and the protein length was ranged from 281 aa (caspase-3a) to 507 aa (caspase-10). Phylogenetic analysis showed these caspase genes were divided into three subfamilies. The qRT-PCR results showed that turbot caspase genes were expressed in all the examined organs, especially the intestine, kidney, blood and gills. Meanwhile, we explored the expression patterns of caspase genes in the intestine, skin and gills after Vibrio anguillarum and Aeromonas salmonids infections. The results showed that caspase genes showed different expression patterns in mucosal tissues after bacterial infection, demonstrating the critical role of caspase genes in mucosal immune responses. In addition, protein-protein interaction analysis showed that caspase proteins interacted with immune molecules such as NLR, IL-1β, and birc. The results of interference and overexpression experiments showed that caspase-1 might play key roles in the regulation of the IL-1β production, but the detailed mechanism needs to be further studied. The results of this study provide valuable information for further study the roles of caspase genes in turbot, which could help us to further understand the inflammatory pathways in teleost.

Comprehensive identification and expression profiling of immune-related lncRNAs and their target genes in the intestine of turbot (Scophthalmus maximus L.) in response to Vibrio anguillarum infection

Long non-coding RNA (lncRNA) play vital regulatory roles in various biological processes. Intestine is one of the most sensitive organs to environmental and homeostatic disruptions for fish. However, systematic profiles of lncRNAs in the intestine of teleost in responses to pathogen infections is still limited. Turbot (Scophthalmus maximus L.), an important commercial fish species in China, has been suffering with Vibrio anguillarum infection, resulted in dramatic economic loss. Hereinto, the intestinal tissues of turbot were sampled at 0 h, 2 h, 12 h, and 48 h following V. anguillarum infection. The histopathological analysis revealed that the pathological trauma was mainly present in intestinal tunica mucosal epithelium. After high-throughput sequencing and bioinformatic analysis, a total of 9722 lncRNAs and 21,194 mRNAs were obtained, and the average length and exon number of lncRNAs were both less than those of mRNAs. Among which, a set of 158 lncRNAs and 226 mRNAs were differentially expressed (DE-lncRNAs and DEGs) in turbot intestine at three time points, related to many immune-related genes such as complement, interleukin, chemokine, lysosome, and macrophage, indicating their potential critical roles in immune responses. In addition, 2803 and 1803 GO terms were enriched for DEGs and co-expressed target genes of DE-lncRNAs, respectively. Moreover, 127 and 50 KEGG pathways including cell adhesion molecules (CAMs), phagosome, JAK-STAT signaling pathway, cytokine-cytokine receptor interaction, and intestinal immune network for IgA production, were enriched for DEGs and co-expressed target genes of DE-lncRNAs, respectively. Finally, qRT-PCR was conducted to confirm the reliability of sequencing data. The present study will set the foundation for the future exploration of lncRNA functions in teleost in response to bacterial infection.