Molecular characterization of a teleost-specific toll-like receptor 22 (tlr22) gene from yellow catfish (Pelteobagrus fulvidraco) and its transcriptional change in response to poly I:C and Aeromonas hydrophila stimuli

Structural and Functional Characteristics of TLR19 in Barbel Chub Compared to TLR19 in Grass Carp

The hybrid offspring of barbel chub Squaliobarbus curriculus and grass carp Ctenopharyngodon idella exhibit stronger resistance to the grass carp reovirus (GCRV) infection than grass carp. Toll-like receptors (TLRs) play indispensable roles in the antiviral immunity of fish. In this study, the structures and antiviral immune functions of barbel chub TLR19 (ScTLR19) and grass carp TLR19 (CiTLR19) were compared. The amino acid sequence of ScTLR19 shared high similarity (97.4%) and identity (94.0%) with that of CiTLR19, and a phylogenetic tree revealed the close evolutionary relationship between ScTLR19 and CiTLR19. Protein domain composition analyses showed that ScTLR19 possessed an additional leucine-rich repeat (designated as LRR9) located at amino acid positions 654-677 in the extracellular region, which was absent in CiTLR19. Multiple sequence alignment and three-dimensional structure comparison also indicated that the extracellular regions of ScTLR19 and CiTLR19 exhibited greater differences compared to their intracellular regions. Molecular docking revealed that the extracellular region of ScTLR19 (docking score = -512.31) showed a stronger tendency for binding with polyI:C, compared to the extracellular region of CiTLR19 (docking score = -474.90). Replacing LRR9 in ScTLR19 with the corresponding amino acid sequence from CiTLR19 reduced the binding activity of ScTLR19 to polyI:C, as confirmed by an ELISA. Moreover, overexpression experiments suggested that ScTLR19 could regulate both the IRF3-TRIF and IRF3-MyD88 signaling pathways during GCRV infection, while CiTLR19 only regulated the IRF3-MyD88 signaling pathway. Importantly, replacing LRR9 in ScTLR19 with the corresponding amino acid sequence from CiTLR19 altered the expression regulation on IRF3, MyD88, and TRIF during GCRV infection. These findings collectively reveal the structural and functional differences between ScTLR19 and CiTLR19, and they may provide data to support a deeper understanding of the molecular mechanisms underlying the differences in GCRV resistance between barbel chub and grass carp, as well as the genetic basis for the heterosis of GCRV resistance in their hybrid offspring.

Unravelling turbot (Scophthalmus maximus) resistance to Aeromonas salmonicida: transcriptomic insights from two full-sibling families with divergent susceptibility

Introduction

Furunculosis, caused by the gram-negative bacterium Aeromonas salmonicida subsp. salmonicida, remains a significant threat to turbot (Scophthalmus maximus) aquaculture. Identifying genetic backgrounds with enhanced disease resistance is critical for improving aquaculture health management, reducing antibiotic dependency, and mitigating economic losses.

Methods

In this study, five full-sibling turbot families were challenged with A. salmonicida, which revealed one family with significantly greater resistance. Transcriptomic analyses (RNA-Seq) were performed on resistant and susceptible families, examining both naïve and 24-h postinfection (hpi) samples from head kidney and liver tissues.

Results

In the absence of infection, differentially expressed genes (DEGs) were identified predominantly in the liver. Following infection, a marked increase in DEGs was observed in the head kidney, with many genes linked to immune functions. Interestingly, the resistant family displayed a more controlled inflammatory response and upregulation of genes related to antigen presentation and T-cell activity in the head kidney at early infection stages, which may have contributed to its increased survival rate. In the liver, transcriptomic differences between the families were associated mainly with cytoskeletal organization, cell cycle regulation, and metabolic processes, including insulin signalling and lipid metabolism, regardless of infection status. Additionally, many DEGs overlapped with previously identified quantitative trait loci (QTLs) associated with resistance to A. salmonicida, providing further insights into the genetic basis of disease resistance.

Discussion

This study represents the first RNA-Seq analysis comparing resistant and susceptible turbot families and contributes valuable knowledge for the development of selective breeding programs targeting disease resistance in turbot and other aquaculture species susceptible to A. salmonicida.

Molecular characterization, spatio-temporal expression patterns of crtc2 gene and its immune roles in yellow catfish (Pelteobagrus fulvidraco)

cAMP response element binding (CREB) protein 2 (CRTC2) is a transcriptional coactivator of CREB and plays an important role in the immune system. Thus far, the physiological roles of Crtc2 in teleost are still poorly understood. In this study, the crtc2 gene was identified and characterized from yellow catfish (Pelteobagrus fulvidraco; therefore, the gene is termed as pfcrtc2), and its evolutionary and molecular characteristics as well as potential immunity-related roles were investigated. Our results showed that the open reading frame of pfcrtc2 was 2346 bp in length, encoding a protein with 781 amino acids. Gene structure analysis revealed its existence of 14 exons and 13 introns. A phylogenetic analysis proved that the tree of crtc2 was clustered into five groups, exhibiting a similar evolutionary topology with species evolution. Multiple protein sequences alignment demonstrated high conservation of the crtc2 in various vertebrates with similar structure. Syntenic and gene structural comparisons further established that crtc2 was highly conserved, implying its similar roles in diverse vertebrates. Tissue distribution pattern detected by quantitative real-time PCR showed that the pfcrtc2 gene was almost expressed in all detected tissues except for eyes, with the highest expression levels in the gonad, indicating that Crtc2 may play important roles in various tissues. In addition, pfcrtc2 was transcribed at all developmental stages in yellow catfish, showing the highest expression levels at 12 h after fertilization. Finally, the transcriptional profiles of crtc2 were significantly increased in yellow catfishes injected with Aeromonas hydrophila or Poly I:C, which shared a consistent change pattern with four immune-related genes including IL-17A, IL-10, MAPKp38, and NF-κBp65, suggesting pfCrtc2 may play critical roles in preventing both exogenous bacteria and virus invasion. In summary, our findings lay a solid foundation for further studies on the functions of pfcrtc2, and provide novel genetic loci for developing new strategies to control disease outbreak in teleost.

Lactobacillus plantarum E2 regulates intestinal microbiota and alleviates Pseudomonas plecoglossicida induced inflammation and apoptosis in zebrafish (Danio rerio)

Pseudomonas plecoglossicida infection is a highly contagious epidemic in aquaculture, causing significant mortality among teleost. Our previous research has demonstrated that Lactobacillus plantarum E2 is beneficial for large yellow croaker in resisting infections caused by P. plecoglossicida. However, the relevant mechanisms remain largely unclear. In the present study, we used zebrafish (Danio rerio) to further explore the function of L. plantarum E2 and its mechanisms for resisting P. plecoglossicida infection. E2 supplementation diet significantly improved the growth rates and α-amylase and trypsin activities of the liver in zebrafish. After challenge with P. plecoglossicida strain PQLYC4, the survival rates of zebrafish were improved, and immune-related genes expression (IL-1β, TNF-α, IL-8, Ig-Z, TLR-22 and IL-12α) were down-regulated. Histological analysis showed that E2 group had a longer intestinal villus and thicker intestinal walls after 30 days of feeding and healthier intestinal structure after challenge with P. plecoglossicida strain PQLYC4. Furthermore, co-incubation of zebrafish embryo fibroblast (ZF-4 cells) with L. plantarum E2 reduced apoptosis of ZF-4 cells after exposed to P. plecoglossicida. Intestinal microbiota analysis showed that E2 strain significantly increased the relative abundance of Lactobacillus and Pseudomonas, and PCoA analysis revealed a noticeable divergence in the intestinal microbial communities after E2 supplement. Together, our results suggested that E2 strain may promote zebrafish survival against P. plecoglossicida infection by regulating the intestinal microbiota and alleviating inflammatory response and apoptosis, thus exhibiting the potential as a probiotic.

TLR pathway signaling molecules in burbot (Lota lota): molecular characterization, basal expression, and their response to Poly(I:C)

Burbot (Lota lota), a fish species of economic and ecological significance found across northern hemisphere freshwater ecosystems, was the focus of this study. We characterized 19 Toll-like receptor (TLR) genes in burbot, tracing their expression patterns following pathogen exposure. TLR genes, crucial to the innate immune system, including TLR13-1/2/3, TLR2/2-2/2-3/2-4/2-5, and TLR22a/22b/22c/22d, were discovered to be tandemly repeated, signifying an evolution in the fish's immune system. Notably, different TLR subfamilies displayed tissue-specific expressions, with TLR1 primarily in spleen and head kidney, TLR13 in head kidney, trunk kidney, and heart, TLR22 in trunk kidney and liver, and TLR3 and TLR9 predominantly in spleen and head kidney, but also in trunk kidney. Further, we investigated the response of TLR genes in burbot to pathogen exposure using qRT-PCR. This involved measuring mRNA expressions of identified TLR genes in spleen and liver tissues after injecting Poly(I:C) to simulate a double-stranded RNA viral infection. The results revealed a time and tissue-specific expression pattern. Specifically, LoTLR3 reached peak expression in the spleen 12 h post-injection, declining thereafter, while TLR2 subfamily members only began expressing after 24 h. In the liver, activation of the TLR3-IRF7 and TLR3-IRF3 signaling pathways was noted. Integrating these results with transcriptomic data illuminated the pivotal role of TLR genes in the burbot's immune response. Such findings are vital in shaping future disease prevention and treatment strategies.

Insect-pathogen crosstalk and the cellular-molecular mechanisms of insect immunity: uncovering the underlying signaling pathways and immune regulatory function of non-coding RNAs

Multicellular organisms are constantly subjected to pathogens that might be harmful. Although insects lack an adaptive immune system, they possess highly effective anti-infective mechanisms. Bacterial phagocytosis and parasite encapsulation are some forms of cellular responses. Insects often defend themselves against infections through a humoral response. This phenomenon includes the secretion of antimicrobial peptides into the hemolymph. Specific receptors for detecting infection are required for the recognition of foreign pathogens such as the proteins that recognize glucans and peptidoglycans, together referred to as PGRPs and βGRPs. Activation of these receptors leads to the stimulation of signaling pathways which further activates the genes encoding for antimicrobial peptides. Some instances of such pathways are the JAK-STAT, Imd, and Toll. The host immune response that frequently accompanies infections has, however, been circumvented by diseases, which may have assisted insects evolve their own complicated immune systems. The role of ncRNAs in insect immunology has been discussed in several notable studies and reviews. This paper examines the most recent research on the immune regulatory function of ncRNAs during insect-pathogen crosstalk, including insect- and pathogen-encoded miRNAs and lncRNAs, and provides an overview of the important insect signaling pathways and effector mechanisms activated by diverse pathogen invaders.

Identification of olive flounder (Paralichthys olivaceus) toll-like receptor genes: Involvement in immune response to temperature stress and Edwardsiella tarda infection

Toll-like receptor (TLR) genes are best known for their roles in the innate immune defense. However, studies focusing on the reaction mechanisms of TLR genes in olive flounder (Paralichthys olivaceus) immune responses are still limited. In this study, 11 TLR family members (PoTLRs) were identified and classified from P. olivaceus genome. Phylogenetic analysis showed that PoTLRs were highly conserved in olive flounder. The analysis of motif prediction and gene structure indicated that TLRs had high sequence similarity. The expression patterns in developmental stages and different tissues showed that TLR members were spatially and temporally specific. RNA-Seq analysis of temperature stress and Edwardsiella tarda infection suggested that TLR members were involved in inflammatory responses, PoTLR5b and PoTLR22 showed significant differences in response to both temperature stress and E. tarda stress, indicating their potential immune functions. The results of this study suggested that TLR genes played important roles in the innate immune response of olive flounder, and would provide a solid basis for further study of their functions.