A positive feedback loop between two C-type lectins originated from gene duplication and relish promotes the expression of antimicrobial peptides in Procambarus clarkii

A positive loop between relish and cuticle proteins and their roles in regulating AMPs expression during bacterial infection in Eriocheir sinensis

Cuticle proteins (CPs) are the vital components of the cuticle and chitin lining covering the digestive tract of crustaceans. In this study, four new CP genes (designated as EsCP3, EsCP4, EsCP5, and EsCP8) were initially cloned and identified from the Chinese mitten crab Eriocheir sinensis. EsCP3/4/5/8 included 375, 411, 381, and 570 bp open reading frame encoding 124, 136, 126, and 189 amino acid proteins, respectively. Except for EsCP8, EsCP3/4/5 all contained a Chitin_bind_4 domain. EsCP3/4/5/8 were clustered into different groups in the phylogenetic tree. Quantitative real-time PCR results indicated that four EsCP genes have different patterns of tissue distribution. Changes in the expression levels of these four EsCP genes were observed in the intestine of crabs under Vibrio parahaemolyticus challenge. RNA interference assay showed that the knockdown of EsCPs in the intestine could inhibit the expression of antimicrobial peptides (AMPs), including crustins and anti-lipopolysaccharide factors. In addition, the knockdown of EsRelish in the intestine decreased the expression levels of these four EsCP genes. These results indicated that EsCPs were involved in regulating the expression of AMPs, and EsCPs were regulated by EsRelish.

PvMR1, a novel C-type lectin plays a crucial role in the antibacterial immune response of Pacific white shrimp, Penaeus vannamei

C-type lectins (CTLs) are important immune molecules in innate immune, which participate in non-self recognition and clearance of pathogens. Here, a new CTL with two distinct C-type lectin domains (CTLDs) from Pacific white shrimp Penaeus vannamei, designated as PvMR1 was identified. The obtained PvMR1 coding sequence (CDS) was 1044 bp long encoding a protein with 347 amino acids. PvMR1 had two CTLD, a conserved mannose-specific EPN motif and a galactose-specific QPD motif, clustering into the same branch as the crustacean CTLs. PvMR1 was widely distributed in shrimp tissues with the highest transcription level in the hepatopancreas, with significantly induced mRNA expression on the hepatopancreas and intestines after immune challenge with Vibrio anguillarum. In vitro assays with recombinant PvMR1 (rPvMR1) protein revealed that it exhibited a wide range of antimicrobial activity, bacterial binding ability, and bacterial agglutination activity in a Ca2+-independent manner. Moreover, PvMR1 promoted bacterial phagocytosis in hemocytes. Furthermore, rPvMR1 treatment could significantly enhance the bacterial clearance in hemolymph and greatly improved the survival of shrimp under V. anguillarum infection in vivo. These results collectively suggest that PvMR1 plays an important role in antibacterial immune response of P. vannamei.

Lectin diversity and their positive roles in WSSV replication through regulation of calreticulin expression and inhibiting ALFs expression

In biological evolution, gene duplication (GD) generates new genes to facilitate new functions. C-type lectins (CTLs) in crayfish have been extended by GD to expand their family members. In this study, four CTL genes generated by GD were identified from Procambarus clarkii (PcLec1-4). Among these four genes, PcLec1 can also generate new isoforms with different numbers of tandem repeats through DNA slip mispairing. PcLec1-4 was widely expressed in multiple tissues. The expression levels of PcLec1-4 were upregulated in the intestine of P. clarkii upon white spot syndrome virus (WSSV) challenge at multiple time points. Further analysis indicated that GATA transcription factor regulated PcLec1-4 expression. RNA interference and recombinant PcLec1-4 protein injection experiments suggested that PcLec1-4 promoted the expression of calreticulin (PcCRT) and negatively regulated the expression of antimicrobial peptides, thereby promoting WSSV replication. This study contributes to the understanding of the function of CTLs produced by GD during WSSV invasion in crustaceans.

A comprehensive review on the dynamic role of toll-like receptors (TLRs) in frontier aquaculture research and as a promising avenue for fish disease management

Toll-like receptors (TLRs) represent a conserved group of germline-encoded pattern recognition receptors (PRRs) that recognize pathogen-associated molecular patterns (PAMPs) and play a crucial role in inducing the broadly acting innate immune response against pathogens. In recent years, the detection of 21 different TLR types in various fish species has sparked interest in exploring the potential of TLRs as targets for boosting immunity and disease resistance in fish. This comprehensive review offers the latest insights into the diverse facets of fish TLRs, highlighting their history, classification, architectural insights through 3D modelling, ligands recognition, signalling pathways, crosstalk, and expression patterns at various developmental stages. It provides an exhaustive account of the distinct TLRs induced during the invasion of specific pathogens in various fish species and delves into the disparities between fish TLRs and their mammalian counterparts, highlighting the specific contribution of TLRs to the immune response in fish. Although various facets of TLRs in some fish, shellfish, and molluscs have been described, the role of TLRs in several other aquatic organisms still remained as potential gaps. Overall, this article outlines frontier aquaculture research in advancing the knowledge of fish immune systems for the proper management of piscine maladies.

Identification of two galectin-4 proteins (PcGal4-L and PcGal4-L-CRD) and their function in AMP expression in Procambarus clarkii

Galectins, a family of lectins that bind to β-galactoside, possess conserved carbohydrate recognition domains (CRDs) and play a crucial role in recognizing and eliminating pathogens in invertebrates. Two galectin-4 genes (PcGal4) isoforms, named PcGal4-L and PcGal4-L-CRD, were cloned from the cDNA library of Procambarus clarkia in our study. PcGal4-L contains an open reading frame (ORF, 1089 bp), which encodes a protein consisting of 362 amino acids including a single CRD and six low complexity regions. The full-length cDNA of PcGal4-L-CRD contains a 483 bp ORF that encodes a protein of 160 amino acids, with a single CRD and a low-complexity region. The difference between the two PcGal4 isoforms is that PcGal4-L has 202 additional amino acids after the CRD compared to the PcGal4-L-CRD. These two isoforms are grouped together with other galectins from crustaceans through phylogenetic analysis. Further study revealed that total PcGal4 (including PcGal4-L and PcGal4-L-CRD) was primarily expressed in the muscle, gills and intestine. The mRNA levels of total PcGal4 in gills and hemocytes were significantly induced after challenge with Aeromonas hydrophila. Both recombinant PcGal4-L and its spliced isoform, PcGal4-L-CRD, could directly bind to lipopolysaccharides, peptidoglycan and five tested microorganisms, inducing a wide spectrum of microbial agglutination. The spliced isoform PcGal4-L-CRD showed a stronger binding ability than PcGal4-L. In addition, when the PcGal4 was knockdown, transcriptions of seven antimicrobial peptides (AMPs) genes (ALF5, ALF6, ALF8, CRU1, CRU2, CRU3 and CRU4) in gills and seven AMPs genes (ALF5, ALF6, ALF8, ALF9, CRU1, CRU3 and CRU4) in hemocytes were significantly decreased. Meanwhile, the survival rate of P. clarkii decreased in the PcGal4-dsRNA group. In summary, these results indicate that PcGal4 can mediate the innate immunity in P. clarkii by bacterial recognition and agglutination, as well as regulating AMP expression, thus recognition and understanding of the functions of galectin in crustaceans in immune resistance.