Transcriptome analysis revealed multiple immune processes and energy metabolism pathways involved in the defense response of the large yellow croaker Larimichthys crocea against Pseudomonas plecoglossicida

The bacterial pathogen Pseudomonas plecoglossicida, its epidemiology, virulence factors, vaccine development, and host-pathogen interactions

OBJECTIVE

Pseudomoans plecoglossicida has been identified as a fish pathogen since 2000 and has caused serious infections in cultured Large Yellow Croakers Larimiththys crocea in coastal eastern China during recent years.

METHODS

Published literatures of this pathogen have been reviewed.

RESULT

Several strains with high genomic similarity have been isolated and identified; the bacteria induce natural infection at lower water temperatures (12.0-25.5°C) and induce numerous granulomas and nodules in the visceral organs of croakers. Researchers have investigated the epidemiology of P. plecoglossicida infection, identified major virulence factors, searched for pathogenic genes, analyzed host-pathogen interactions, and endeavored to develop efficient vaccines.

CONCLUSION

This paper provides an overview of these research advances to elucidate the virulence mechanisms of the pathogen and to promote vaccine development against infection.

Applying genetic technologies to combat infectious diseases in aquaculture

Disease and parasitism cause major welfare, environmental and economic concerns for global aquaculture. In this review, we examine the status and potential of technologies that exploit genetic variation in host resistance to tackle this problem. We argue that there is an urgent need to improve understanding of the genetic mechanisms involved, leading to the development of tools that can be applied to boost host resistance and reduce the disease burden. We draw on two pressing global disease problems as case studies-sea lice infestations in salmonids and white spot syndrome in shrimp. We review how the latest genetic technologies can be capitalised upon to determine the mechanisms underlying inter- and intra-species variation in pathogen/parasite resistance, and how the derived knowledge could be applied to boost disease resistance using selective breeding, gene editing and/or with targeted feed treatments and vaccines. Gene editing brings novel opportunities, but also implementation and dissemination challenges, and necessitates new protocols to integrate the technology into aquaculture breeding programmes. There is also an ongoing need to minimise risks of disease agents evolving to overcome genetic improvements to host resistance, and insights from epidemiological and evolutionary models of pathogen infestation in wild and cultured host populations are explored. Ethical issues around the different approaches for achieving genetic resistance are discussed. Application of genetic technologies and approaches has potential to improve fundamental knowledge of mechanisms affecting genetic resistance and provide effective pathways for implementation that could lead to more resistant aquaculture stocks, transforming global aquaculture.

Splenic protection network revealed by transcriptome analysis in inactivated vaccine-immunized flounder (Paralichthys olivaceus) against Edwardsiella tarda infection

The protective immune response produced by fish after vaccination is crucial for vaccine effectiveness. Our previous studies have shown inactivated vaccine against Edwardsiella tarda can induce immune response in flounder (Paralichthys olivaceus). To elucidate the protective immune response at the genetic level, in this study, flounder was immunized with inactivated E. tarda for 5 weeks, and then they were challenged with E. tarda. The spleen was dissected at 7th day post immunization, 1st and 7th day post challenge, respectively. Transcriptome analysis showed that average of 46 million clean reads were obtained per library, while percentage of clean reads being mapped to reference genome was more than 89% in all cases, which suggested good quality of samples. As for differentially expressed genes (DEGs) identification in inactivated E. tarda groups, at 7th day post immunization, 1422 DEGs were identified and significantly enriched in innate immune-related pathways, such as Phagosome, Cell adhesion molecules and NF-kappa B signaling pathway; At 1st post challenge day, 1210 DEGs were identified and enriched to Antigen processing and presentation and Cell adhesion molecules, indicating that the pathogen was rapidly recognized and delivered; At 7th post challenge day, 1929 DEGs were identified, belonged to Toll-like receptor signaling pathway, Antigen processing and presentation, Th1 and Th2 cell differentiation and Th17 cell differentiation. Compared to 7th post immunization day, 73 immune-associated DEGs were identified at 1st post challenge day. Protein-protein interaction networks analysis revealed 11 hub genes (TLR7, TLR3, CXCR4, IFIH1, TLR8 etc), associated with recognition of pathogens and activation of innate immunity; while for 7th post challenge day, 141 immune-associated DEGs were identified. 30 hub genes (IL6, STAT1, HSP90A.1, TLR7, IL12β etc) were associated with stimulation of lymphocyte differentiation and activation of cellular immunity. Ten immune-related genes were randomly selected for RT-qPCR validation at each time point. In conclusion, data revealed protection of flounder against E. tarda infection by inactivated vaccine is mediated via immediate recognition of pathogen and subsequently activation of cellular immunity. Results give new aspect for vaccine protection cascades, is good references for vaccine evaluation.

Transcriptome Analysis Reveals the Multiple Functions of pBD2 in IPEC-J2 Cells against E. coli

Defensins play an important role in fighting bacteria, and are a good candidate for bactericidal agents. However, the function and mechanism of defensins in regulating host responses against bacteria is unclear. In this study, transcriptome analysis was used to study the comprehensive functions of pBD2 in IPEC-J2 cells against E. coli. In total, 230 differentially expressed genes (DEGs) were identified in IPEC-J2 cells between the control and E. coli groups, and were found by KEGG analysis to be involved in many signaling pathways related to immunity. Furthermore, 812 DEGs were observed between E. coli and E. coli +pBD2 groups, involved in the ribosome, oxidative phosphorylation, and certain disease pathways. Among these, 94 overlapping DEGs were in the two DEG groups, and 85 DEGs were reverse expression, which is involved in microRNA in cancer, while PTEN and CDC6 were key genes according to PPI net analysis. The results of qRT-PCR verified those of RNA-seq. The results indicated that pBD2 plays an important role against E. coli by acting on the genes related to immune response, cell cycle, ribosomes, oxidative phosphorylation, etc. The results provide new insights into the potential function and mechanism of pBD2 against E. coli. Meanwhile, this study provides a certain theoretical basis for research and the development of novel peptide drugs.

UBE2G1 Is a Critical Component of Immune Response to the Infection of Pseudomonas Plecoglossicida in Large Yellow Croaker (Larimichthys crocea)

The large yellow croaker (Larimichthys crocea) is one of the most economically valuable mariculture fish in China. Infection of Pseudomonas plecoglossicida can cause an outbreak of “internal organ white-spot disease”, which seriously affects the aquaculture of the large yellow croaker. Ubiquitylation is closely related to the post-translation modification of proteins and plays a vital role in many hosts’ immune defense pathways, while the E2-binding enzyme is a key factor in ubiquitination. Our previous genome-wide association study found that the ubiquitin-binding enzyme E2G1 (designed LcUbe2g1) was one of the candidate genes related to disease resistance in large yellow croaker. In this study, we analyzed the molecular characteristics, function, and immune mechanism of the LcUbe2g1. The full-length cDNA is 812 bp, with an open reading frame of 513 bp, encoding 170 amino acid residues. The results of the RT-qPCR and immunohistochemistry analysis revealed that its transcription and translation were significantly activated by the infection of P. plecoglossicida in large yellow croaker. Immunocytochemistry experiments verified the co-localization of LcUBE2G1 and the ubiquitin proteins in the head kidney cells of large yellow croaker. Through GST pull-down, we found that LcUBE2G1 interacted with NEDD8 to co-regulate the ubiquitination process. The above results indicate that LcUBE2G1 is essential in the regulation of ubiquitination against P. plecoglossicida infection in large yellow croaker, which lays a foundation for further study on the resistance mechanism of internal organ white-spot disease.