Identification and characterization of a novel PRR of fibrinogen-related protein in Apostichopus japonicus

The ARM repeat domain of hemocyanin interacts with MKK4 to modulate antimicrobial peptides expression

The mitogen-activated protein kinase (MAPK) intracellular signaling pathway mediates numerous biological processes, including antimicrobial immune response by inducing antimicrobial peptides (AMPs) production. Although MAPK signaling cascade proteins have been identified in penaeid shrimp, their modulation via the MKK4-p38-c-Jun cascade and effect on AMPs production is unknown. Here, we show that hemocyanin (PvHMC), antimicrobial peptides (anti-lipopolysaccharide factor, crustin, and penaeidins), and MKK4-p38-c-Jun cascade proteins are simultaneously induced by pathogens (Vibrio parahaemolyticus, Staphylococcus aureus, and white spot syndrome virus) in Penaeus vannamei. Intriguingly, knockdown of PvHMC with or without pathogen challenge attenuated the expression of MKK4-p38-c-Jun cascade proteins and their phosphorylation level, which consequently decreased AMPs expression. Further analysis revealed that PvHMC interacts via its armadillo (ARM) repeat domain with PvMKK4 to modulate the p38 MAPK signaling pathway. Thus, the ARM repeat domain enables penaeid shrimp hemocyanin to modulate AMPs expression during antimicrobial response by activating the p38 MAPK signaling pathway.

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Pathogens induce hemocyanin, MKK4-p38-c-Jun proteins, and antimicrobial peptide genes

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Hemocyanin modulates MKK4-p38-c-Jun cascade proteins to regulate AMPs gene expression

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Hemocyanin interacts with MKK4 to modulate p38 MAPK signaling in penaeid shrimp

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Deletion of the ARM repeat domain attenuates the interaction of hemocyanin with MKK4

Single-cell RNA-seq profiling of individual Biomphalaria glabrata immune cells with a focus on immunologically relevant transcripts

The immune cells of the snail Biomphalaria glabrata are classified into hyalinocyte and granulocyte subtypes. Both subtypes are essential for the proper functioning of the snail immune response, which we understand best within the context of how it responds to challenge with the human parasite Schistosoma mansoni. Granulocytes are adherent phagocytic cells that possess conspicuous granules within the cell cytoplasm. Hyalinocytes, on the other hand, are predominantly non-adherent and are known to produce a handful of anti-S. mansoni immune effectors. While our understanding of these cells has progressed, an in-depth comparison of the functional capabilities of each type of immune cell has yet to be undertaken. Here, we present the results of a single-cell RNA-seq study in which single granulocytes and hyalinocytes from S. mansoni-susceptible M-line B. glabrata and S. mansoni-resistant BS-90 B. glabrata are compared without immune stimulation. This transcriptomic analysis supports a role for the hyalinocytes as producers of immune effectors such as biomphalysin and thioester-containing proteins. It suggests that granulocytes are primarily responsible for producing fibrinogen-related proteins and are armed with various pattern-recognition receptors such as toll-like receptors with a confirmed role in the anti-S. mansoni immune response. This analysis also confirms that the granulocytes and hyalinocytes of BS-90 snails are generally more immunologically prepared than their M-line counterparts. As the first single-cell analysis of the transcriptional profiles of B. glabrata immune cells, this study provides crucial context for understanding the B. glabrata immune response. It sets the stage for future investigations into how each immune cell subtype differs in its response to various immunological threats.

Molecular characterization and expression analysis of fibrinogen related protein (FREP) genes of Manila clam (Ruditapes philippinarum) after lipopolysaccharides challenge

Ruditapes philippinarum has high economic value and is distributed all over the world. Fibrinogen associated protein (FREP) is a type of pattern recognition receptor, participates in the innate immune response to eliminate pathogens after the invasion of pathogenic microorganisms. In this study, three FREP genes (FREP-1, FREP-2, and FREP-3) were identified and characterized from R. philippinarum. The protein sequence of FREPs were highly conserved with those homologous in vertebrates, and FBG domain possessed significantly high structural conservation in polypeptide binding site and Ca²⁺ binding site. The tissues expression analysis of FREPs in three shell color strains and two population of R. philippinarum were examined, with the highest expression level in gill and hepatopancreas. Besides, FREP genes were demonstrated to be induced by lipopolysaccharides injection, the significantly changes were observed after LPS injected. Our results suggest the involvement of FREPs in response to LPS injection, and it might exert a significant function on the innate immune defense of the Manila clam.

Outer membrane protein OmpU is related to iron balance in Vibrio alginolyticus

Outer membrane protein U (OmpU) is a major porin from Vibrio alginolyticus and has been considered a vaccine candidate against infection by V. alginolyticus. After pre-incubated with polyclonal antibody against rOmpU, V. alginolyticus showed a 78% decrease in extracellular iron level, suggesting that interruption of OmpU could increase intracellular iron level. The mRNA expression of ompU under iron-limited conditions was determined using real-time reverse transcriptase PCR. The mRNA level of ompU was downregulated to 0.27-, 0.036- and 0.019-fold after the addition of the iron chelator 2,2'-bipyridyl for 10, 30 and 60 min, respectively. In addition, the promoter of ompU contained a ferric uptake regulator (Fur) binding site, which revealed the potential regulation of ompU by Fur and iron. Fur from V. alginolyticus was purified and used for electrophoretic mobility shift assay. The result showed that in the absence of Fe²⁺, purified recombinant Fur could specifically bind to the promoter DNA of ompU, while in the presence of Fe²⁺, the binding of Fur and the promoter DNA was suppressed. Our study preliminarily explored the function of OmpU in iron balance in V. alginolyticus, and these findings were helpful in understanding iron metabolism in V. alginolyticus.