ELAVL1a is an immunocompetent protein that protects zebrafish embryos from bacterial infection

Two novel antimicrobial peptides P33-57 and mP168-187 from zebrafish showing potent antibacterial activities

It is known that overuse or abuse of antibiotics has undoubtedly accelerated the global antibiotic resistance crisis, and long-time use of antibiotics may have adverse effects on the health of animal, human, and ecosystem. Therefore, it is necessary to find antibiotic alternatives that can be used in aquaculture and are non-toxic to the human. Here we clearly demonstrated that both the PH and FYVE domain of Plekhf2 in zebrafish have antibacterial properties and can interact with PGN in this study. Therefore, we screened four candidate peptides from the two domains. It was demonstrated that P152-172 and P168-187 had no obvious antibacterial activities, while P33-57 and mP168-187 had strong antibacterial activities, which may be used as antimicrobial peptides. Additionally, transmission electron microscopy experiment revealed that P33-57 and mP168-187 can destroy the cell wall of bacteria, thereby directly killing bacteria. Importantly, it was found that P33-57 and mP168-187 had no hemolysis to red blood cells and lacked cytotoxicity. In summary, P33-57 and mP168-187could be seen as antibacterial activity centers of PLEKHF2 and may be promising antimicrobial peptides to combat bacterial infections facing an antibiotic-resistance crisis.

Genomic organization, evolution and functional characterization of embryonic lethal abnormal vision like protein 1 (ELAVL1) in miiuy croaker (Miichthys miiuy)

Embryonic lethal vision-like protein 1 (ELAVL1), an AU-rich elements (AREs) binding protein involved in the regulation of inflammatory transcript stability, which has not been reported in fish. In this study, we identified the ELAVL1 gene in Miichthys miiuy (mmiELAVL1), and then analyzed its structure and evolution, furthermore described its expression pattern in miiuy croaker. The results showed that mmiELAVL1 and other vertebrate ELAVL1 genes all have three highly conserved RNA recognition motif (RRM) protein domains, and the structure and protein structure are evolutionarily conserved, indicating that their functions may also conservative. In healthy miiuy croaker, mmiELAVL1 was commonly expressed in the tested tissues, and mmiELAVL1 is mainly localized in the nucleus of kidney cells. In addition, mmiELAVL1 responds to poly(I:C) and SCRV stimulation and promotes antiviral genes, indicating its active role in immune process. In summary, this study will facilitate future studies on the role and underlying mechanisms of ELAVL1 in fish immune responses.

Identification and functional characterization of zebrafish ELAVL1b as a new member of antimicrobial protein

Previous studies have shown that ELAVL1 play multiple roles and may be associated with immune response. However, it remains largely unknown about the direct roles of ELAVL1 during a bacterial infection. After reporting the zebrafish ELAVL1a is a maternal immune factor that can protect zebrafish embryos from bacterial infection, here we studied the immune function of zebrafish ELAVL1b. In this study, we showed that zebrafish elavl1b was markedly up-regulated by LTA and LPS treatment, suggesting it may be involved in anti-infectious responses. We also showed that zebrafish recombinant ELAVL1b (rELAVL1b) could bind to both the Gram-positive and negative bacteria M. luteus and S. aureus, E. coli and A. hydrophila as well as their signature molecules LTA and LPS, hinting it may act as a pattern recognition receptor, capable of identifying pathogens. In addition, rELAVL1b could directly kill the Gram-positive and negative bacteria tested via inducing membrane depolarization and intracellular ROS production. Collectively, our results indicate that zebrafish ELAVL1b plays an immune-relevant role as a newly-characterized antimicrobial protein. This work also provides further information to understand the biological roles of ELAVL family and the innate immunity in vertebrates.

40S ribosomal protein S18 is a novel maternal peptidoglycan-binding protein that protects embryos of zebrafish from bacterial infections

Previous studies have shown that ribosomal proteins play important roles in ribosome assembly and protein translation, but other biological functions remain ill-defined. Here it is clearly demonstrated that RPS18 is a newly identified PGN-binding protein which is present abundantly in the eggs/embryos of zebrafish. Recombinant RPS18 not only identifies the bacterial signature molecule PGN, LPS, and LTA, and binds the bacteria as a pattern recognition receptor, but also kills the Gram-positive and Gram-negative bacteria as an antibacterial effector molecule. What is important is that, we reveal that microinjection of rRPS18 into early embryos significantly improved the resistance of the embryos against pathogenic Aeromonas hydrophila challenge, and co-injection of anti-RPS18 antibody could markedly reduced this improved bacterial resistance. In summary, these results indicate that RPS18 is a maternal immune factor that can protect the early embryos of zebrafish against pathogenic attacks. This work also provides another angle for understanding the biological functions of ribosomal proteins.