Cloning, characterization, and function of MyD88 in silvery pomfret ( Pampus argenteus ) in response to bacterial challenge

Effects of high stocking density on growth performance and expression of MyD88, and its temporal expression under the challenge of Vibrio parahaemolyticus in the noble scallop Chlamys nobilis

High stocking density has been regarded as an adverse factor in bivalve aquaculture. However, its subsequent molecular response to pathogenic bacteria has been little studied. In order to study the question, a novel MyD88 was first cloned using adult noble scallops Chlamys nobilis (CnMyD88), and its tissue distribution was investigated. Then, 1860 juvenile scallops were divided into two groups with two initial densities of high density (200 individuals/layer, HD) and normal density (110 individuals/layer, ND) and in-situ cultured for three months, in which their growth, survival, and the differential expression of CnMyD88 were examined, respectively. Finally, scallops were injected with the Vibrio parahaemolyticus to assess the temporal expression of CnMyD88. As the results show, CnMyD88 cDNA has a full length of 2241 bp and contains an 1107 bp ORF that encodes a 368-derived protein. It was widely expressed in examined tissues with a significantly higher level in hemolymph, intestine, mantle, and gonad than others. Besides, the HD group showed lower growth (0.39 ± 0.05 mm/day) and survival (37.00 ± 8.49%) than the ND group (0.55 ± 0.02 mm/day and 76.82 ± 5.78%). More importantly, the HD group exhibited significantly lower expression levels of CnMyD88 in their examined tissues than the ND group. After V. parahaemolyticus challenging, CnMyD88 had significantly lower expression levels in the scallops from the HD group than that of the scallops from the ND group at 6th, 24th, and 36th. The present results indicated that high stocking density not only made adverse impacts on growth and survival but also may induce immunosuppression in the noble scallop. Therefore, appropriate low stocking density may be worth considering to adopt in scallop aquaculture.

The combined effect of a novel formula of herbal extracts on bacterial infection and immune response in Micropterus salmoides

Herbal extracts have been considered as ideal alternative to antibiotics in aquaculture and application of combinatory effective extracts always can exhibit the enhanced bioactivity with high efficiency. In our study, a novel herbal extract combination GF-7, which is composed of Galla Chinensis, Mangosteen Shell extracts as well as the effective parts of Pomegranate peel and Scutellaria baicalensis Georgi extracts, was prepared and applied for the therapy of bacterial infection in aquaculture. The HPLC analysis of GF-7 was also investigated for quality control and chemical identification. In the bioassay, GF-7 had excellent antibacterial activity against various aquatic pathogenic bacteria in vitro, and the related MIC values were between 0.045 and 0.36 mg/mL. After feeding Micropterus salmoide with GF-7 (0.1, 0.3, and 0.6%, respectively) for 28 days, the activities of ACP, AKP, LZM, SOD, and CAT of the liver in each treatment group were significantly increased and the content of MDA was significantly decreased. Meanwhile, the hepatic expression of the immune regulators including IL-1β, TNF-α, and Myd88 at different times was up-regulated in varying degrees. The challenge results exhibited a good dose-dependent protective effect on M. salmoides infected with A. hydrophila, which was further confirmed by liver histopathology. Our results imply that the novel combination GF-7 is a potential natural medicine for the prevention and treatment of numerous aquatic pathogenic infectious diseases in aquaculture.

Evolutionary and functional conservation of myeloid differentiation factor 88 (MyD88) in amphibian Xenopus tropicalis

As a universal adaptor used by most TLR members, the myeloid differentiation factor 88 (MyD88) plays essential roles in TLR-mediated inflammatory response of invertebrate and vertebrate animals, and functional features of MyD88 remain largely unknown in amphibians. In this study, a MyD88 gene named Xt-MyD88 was characterized in the Western clawed frog (Xenopus tropicalis). Xt-MyD88 and MyD88 in other species of vertebrates share similar structural characteristics, genomic structures, and flanking genes, suggesting that MyD88 is structurally conserved in different phyla of vertebrates ranging from fish to mammals. Moreover, Xt-MyD88 was widely expressed in different organs/tissues, and was induced by poly(I:C) in spleen, kidney, and liver. Importantly, overexpression of Xt-MyD88 triggered a marked activation of both NF-κB promoter and interferon-stimulated response elements (ISREs), implying that it may be play important roles in inflammatory responses of amphibians. The research represents the first characterization on the immune functions of amphibian MyD88, and reveals considerable functional conservation of MyD88 in early tetrapods.

Genome-Wide Identification and Characterization of Toll-like Receptors (TLRs) in Diaphorina citri and Their Expression Patterns Induced by the Endophyte Beauveria bassiana

Toll-like receptors (TLRs) are pathogen recognition receptors (PRRs), which play key roles in helping the host immune system fight pathogen invasions. Systematic information on TLRs at the genome-wide level and expression profiling in response to endophytic colonization is very important to understand their functions but is currently lacking in this field. Here, a total of two TLR genes were identified and characterized in Diaphorina citri. The TLR genes of D. citri were clustered into five families according to the phylogenetic analysis of different species' TLRs. The domain organization analyses suggested that the TLRs were constituted of three important parts: a leucine-rich repeat (LRR) domain, a transmembrane region (TR) and a Toll/interleukin-1 receptor (TIR) domain. The mRNA expression levels of the two TLR genes (DcTOLL and DcTLR7) were highly regulated in both nymphs and adults of D. citri. These results elucidated the potentiated TLR gene expression in response to endophytically colonized plants. Furthermore, the 3D structures of the TIR domain were highly conserved during evolution. Collectively, these findings elucidate the crucial roles of TLRs in the immune response of D. citri to entomopathogens systematically established as endophytes, and provide fundamental knowledge for further understanding of the innate immunity of D. citri.

The Role of Flagellin B in Vibrio anguillarum-Induced Intestinal Immunity and Functional Domain Identification

Vibrio anguillarum, an opportunistic pathogen of aquatic animals, moves using a filament comprised of polymerised flagellin proteins. Flagellins are essential virulence factors for V. anguillarum infection. Herein, we investigated the effects of flagellins (flaA, flaB, flaC, flaD and flaE) on cell apoptosis, TLR5 expression, and production of IL-8 and TNF-α. FlaB exhibited the strongest immunostimulation effects. To explore the functions of flaB in infection, we constructed a flaB deletion mutant using a two-step recombination method, and in vitro experiments showed a significant decrease in the expression of TLR5 and inflammatory cytokines compared with wild-type cells. However in the in vivo study, expression of inflammatory cytokines and intestinal mucosal structure showed no significant differences between groups. Additionally, flaB induced a significant increase in TLR5 expression based on microscopy analysis of fluorescently labelled TLR5, indicating interactions between the two proteins, which was confirmed by native PAGE and yeast two-hybrid assay. Molecular simulation of interactions between flaB and TLR5 was performed to identify the residues involved in binding, revealing two binding sites. Then, based on molecular dynamics simulations, we carried out thirteen site-directed mutations occurring at the amino acid sites of Q57, N83, N87, R91, D94, E122, D152, N312, R313, N320, L97, H316, I324 in binding regions of flaB protein by TLR5, respectively. Surface plasmon resonance (SPR) was employed to compare the affinities of flaB mutants for TLR5, and D152, D94, I324, N87, R313, N320 and H316 were found to mediate interactions between flaB and TLR5. Our comprehensive and systematic analysis of V. anguillarum flagellins establishes the groundwork for future design of flagellin-based vaccines.

Identification of Core Genes of Toll-like Receptor Pathway from Lymantria dispar and Induced Expression upon Immune Stimulant

The gypsy moth, Lymantria dispar, is a polyphagous forest pest worldwide. The baculovirus, Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV) is a natural pathogen of L. dispar. The Toll-like receptors (TLR) pathway plays a crucial role in both innate and adaptive immunity in animals. However, The TLR pathway and its underlying immune mechanism against baculovirus in L. dispar have not been explored. In this study, eleven TLRs and five downstream TLR pathway components were identified and characterized from L. dispar. Structural analysis indicated that intracellular Toll/interleukin-1 receptor (TIR) domains of LdTLRs and LdMyD88 contained three conserved motifs, and the 3D structures of TIR domains of LdTLRs possessed similar patterns in components arrangement and spatial conformation. The TLR proteins of L. dispar were placed into five monophyletic groups based on the phylogenetic analysis. LdTLR1, 2, 5, 6, 7, 8 and all identified downstream TLR pathway factors were highly induced upon LdMNPV infection, indicating that the TLR pathway of L. dispar was activated and might play a role in the immune response to LdMNPV infection. Collectively, these results help elucidate the crucial role of the TLR pathway in the immune response of L. dispar against LdMNPV, and offer a foundation for further understanding of innate immunity of the pest.

Survival and gene expression responses in immune challenged larval lake sturgeon

Larval lake sturgeon, Acipenser fulvescens, reared in hatcheries for stock enhancement of wild populations may be susceptible to early opportunistic bacterial infection. Thus, we examined survival and whole-body mRNA expression of both stress- and immune-related genes (MyD88, IL-1β, StAR, GR1, and HSP70) in 30 days post fertilization larval lake sturgeon following immune challenge with lipopolysaccharides (LPS). Larval sturgeon were exposed to 0, 25, 50, 100, 150, and 200 μg ml^-1 LPS and sampled after 30 min, 4 h, and 48 h. Mortality was zero in 0 and 25 μg ml^-1 LPS; 37.5% in 50 μg ml^-1 LPS and 100% in the higher concentrations. Expression of MyD88 and StAR mRNA were positively correlated and increased with time in the 50 μg ml^-1 LPS treatment. There was an influence of both treatment and time on IL-1β mRNA, with expression 10-fold higher than controls after 4 h. Expression of HSP70 mRNA was suppressed within 30 min of 50 μg ml^-1 LPS exposure and remained so throughout the time course. Correlated mRNA expression of GR1 with MyD88, StAR and IL-1β suggests a potential relationship between the innate immune and glucocorticoid responses of larval lake sturgeon during this early developmental stage. Data presented suggest that larval lake sturgeon largely responded with predicted changes in gene expression of immune related and stress response genes following LPS challenge. This study provides a foundation for future research examining the effects of hatchery and naturally occurring stressors on the immune responses of larval lake sturgeon.

Molecular identification and functional analysis of MyD88 in giant freshwater prawn (Macrobrachium rosenbergii) and expression changes in response to bacterial challenge

Myeloid differentiation factor 88 (MyD88) is a crucial adaptor protein for Toll-like receptor (TLR)-mediated signaling pathways and plays an important role in immune response. In this study, the full-length cDNA of MyD88 from Macrobrachium rosenbergii (MRMyD88) was cloned. The MRMyD88 cDNA is 1758 bp long and contains a 1398-bp open reading frame. Multiple sequence alignment and phylogenetic analysis revealed that the amino acid sequence of MRMyD88 shared high identity with the known MyD88 proteins. The MRMyD88 mRNA was widely expressed in all examined tissues, with highest level in intestine, followed by gonad and pleopod. Furthermore, the MRMyD88 promoter region, spanning 1622 bp, contains several transcription factor-binding sites, including nine GATA-1 box motifs. Electrophoretic mobility shift assay showed that Gfi-1, SRF, and Oct-1 bind to the upstream region of MRMyD88. Additionally, the results showed that the expression levels of TLR1, TLR2 and TLR3 were different in response to Vibrio anguillarum, Lactobacillus plantarum and Aeromonas hydrophila infections. However, these bacteria significantly increased the expression levels of MyD88 and prophenoloxidase. These data suggest that the TLR-mediated signaling pathway is MyD88-dependent in response to pathogenic and probiotic bacteria in M. rosenbergii.

Construction of a Vibrio anguillarum flagellin B mutant and analysis of its immuno-stimulation effects on Macrobrachium rosenbergii

Vibrio anguillarum is a globally distributed aquatic pathogen, and its flagellin B (FlaB) protein can evoke innate immune responses in hosts. In order to explore the role of FlaB in V. anguillarum infection, we constructed a FlaB-deficient mutant using overlapping PCR and two-step homologous recombination, and gene sequencing confirmed successful knockout of the FlaB gene. Scanning electron microscopy showed no significant differences in the morphological structure of the flagellum between wild-type and FlaB-deficient strains. The mutant was subsequently injected into the freshwater prawn (Macrobrachium rosenbergii) to explore its pathogenicity in the host, and expression of myeloid differentiation factor 88, prophenoloxidase, catalase, superoxide dismutase and glutathione peroxidase was investigated by real-time PCR. The results showed that deletion of FlaB had little effect on V. anguillarum-induced expression of these immune-related genes (p > 0.05). In general, the FlaB mutant displayed similar flagella morphology and immune characteristics to the wild-type strain, hence we speculated that knockout of FlaB might promote the expression and function of other flagellin proteins. Furthermore, this study provides a rapid and simple method for obtaining stable mutants of V. anguillarum free from foreign plasmid DNA.

Gill transcriptomes reveal expression changes of genes related with immune and ion transport under salinity stress in silvery pomfret (Pampus argenteus)

Salinity is a major ecological factor in the marine environment, and extremely important for the survival, development, and growth of fish. In this study, gill transcriptomes were examined by high-throughput sequencing at three different salinities (12 ppt as low salinity, 22 ppt as control salinity, and 32 ppt as high salinity) in an importantly economical fish silvery pomfret. A total of 187 genes were differentially expressed, including 111 up-regulated and 76 down-regulated transcripts in low-salinity treatment group and 107 genes differentially expressed, including 74 up-regulated and 33 down-regulated transcripts in high-salinity treatment group compared with the control group, respectively. Some pathways including NOD-like receptor signaling pathway, cytokine-cytokine receptor interaction, Toll-like receptor pathway, cardiac muscle contraction, and vascular smooth muscle contraction were significantly enriched. qPCR analysis further confirmed that mRNA expression levels of immune (HSP90A, IL-1β, TNFα, TLR2, IP-10, MIG, CCL19, and IL-11) and ion transport-related genes (WNK2, NPY2R, CFTR, and SLC4A2) significantly changed under salinity stress. Low salinity stress caused more intensive expression changes of immune-related genes than high salinity. These results imply that salinity stress may affect immune function in addition to regulating osmotic pressure in silvery pomfret.

Molecular cloning and expression analysis of myd88 from oriental weatherfish (Misgurnus anguillicaudatus) in response to bacterial challenge

Myeloid differentiation factor 88 (Myd88) plays an important role in both innate and adaptive immune response. In this study, the full-length complementary DNA (cDNA) of myd88 from Misgurnus anguillicaudatus was characterized. The myd88 cDNA is 1333 bp in length and contains an 855 bp open reading frame encoding a predicted protein of 284 amino acids. The predicted protein possesses typical Myd88 domain structural features including a death domain in the N-terminus, and box 1, 2, and 3 motifs of the Toll/IL-1 receptor domain in the C-terminus. Quantitative real-time PCR (qRT-PCR) revealed that myd88 messenger RNA (mRNA) was ubiquitously expressed in all examined tissues, especially highly in brain, kidney, blood, intestines and liver. qRT-PCR and western blotting were used to determine the mRNA and protein levels of Myd88 after Aeromonas veronii challenge, respectively. The Myd88 was remarkably upregulated in response to infection of A. veronii. These results suggested that Myd88 may play a vital role during the immune response of M. anguillicaudatus against bacterial infection.

Molecular cloning and expression analysis of MyD88 and TRAF6 in Qihe crucian carp Carassius auratus

Myeloid differentiation factor 88 (MyD88) and tumor necrosis factor receptor-associated factor 6 (TRAF6) are two critical signal transducers in toll-like receptor (TLR) pathway. In the present study, we identified and characterized the homologues of MyD88 and TRAF6 in Qihe crucian carp Carassius auratus, termed as CaMyD88 and CaTRAF6, respectively, and examined their roles during pathogenic infection. Full-length cDNA of CaMyD88 was 2463 bp, including a 191 bp 5'-untranslated region (UTR), a 1417 bp 3'-UTR, and an 855 bp open reading frame (ORF) encoding for a putative protein with 284 amino acids. Full-length cDNA of CaTRAF6 was identified to be 2555 bp, consisting of a 52 bp 5'-UTR, an 871 bp 3'-UTR, and a 1632 bp ORF encoding a protein of 543 amino acids. Deduced amino acid sequences of CaMyD88 and CaTRAF6 contained the typical domains (CaMyD88: death domain and TIR domain; CaTRAF6: one RING-type zinc finger domain, two TRAF-type zinc finger domains, one coiled-coil region, and one conserved C-terminal meprin and TRAF homology domain) as in other fish. Quantitative Real-Time PCR (qRT-PCR) analysis revealed that both CaMyD88 and CaTRAF6 were ubiquitously expressed throughout the development stages and appeared to be developmentally regulated. In addition, CaMyD88 and CaTRAF6 had a broadly distribution of expression in all examined eleven tissues of healthy fish, although the transcript levels varied among the different tissues. Moreover, it was found that mRNA expressions of CaMyD88 and CaTRAF6 were generally up-regulated after stimulation by polyI:C, flagellin, and Aeromonas hydrophila in spite of the down-regulation appeared at some time points or tissues. These results indicated that CaMyD88 and CaTRAF6 play the critical roles in the immune defense of Qihe crucian carp against pathogenic invasion. The present findings will provide the valuable information for understanding the innate immune responses of Qihe crucian carp and contribute to develop the preventive way against pathogens.

Characterization of TLR5 and TLR9 from silver pomfret (Pampus argenteus) and expression profiling in response to bacterial components

Toll like receptor (TLR) 5 and 9 are important members of the TLR family that play key roles in innate immunity in all vertebrates. In this study, paTLR5 and paTLR9 were identified in silver pomfret (Pampus argenteus), a marine teleost of great economic value. Open reading frames (ORFs) of paTLR5 and paTLR9 are 2646 and 3225 bp, encoding polypeptides of 881 and 1074 amino acids, respectively. Sequence analysis revealed several conserved characteristic features, including signal peptides, leucine-rich repeat (LRR) motifs, and a Toll/interleukin-I receptor (TIR) domain. Sequence, phylogenetic and synteny analysis revealed high sequence identity with counterparts in other teleosts, confirming their correct nomenclature and conservation during evolution. Quantitative real-time PCR revealed that the that both TLRs were ubiquitously expressed in all investigated tissues, most abundantly in liver, kidney, spleen, intestine and gill, but lower in muscle and skin. In vitro immunostimulation experiments revealed that Aeromonas hydrophila lipopolysaccharide (LPS) and Vibrio anguillarum flagellin induced higher levels of paTLR9 and paTLR5 mRNA expression in isolated fish intestinal epithelial cells (FIECs) than Lactobacillus plantarum lipoteichoic acid (LTA), but all increased the secretion of IL-6 and TNF-α and induced cell apoptosis and necrosis. Together, these results indicate that paTLR5 and paTLR9 may function in the response to bacterial pathogens. Our findings enhance our understanding of the function of TLRs in the innate immune system of silver pomfret and other teleosts.

A myeloid differentiation factor 88 gene from yellow catfish Pelteobagrus fulvidraco and its molecular characterization in response to polyriboinosinic polyribocytidylic acid and lipopolysaccharide challenge

Myeloid differentiation factor 88 (MyD88) is an adaptor protein of Toll-like receptor (TLR) signalling pathways that activates the innate immune system. Herein, MyD88 was identified in the economically important freshwater fish Pelteobagrus fulvidraco. The complete 2156 bp PfMyD88 cDNA includes a 147 bp 5'-untranslated region (UTR), a 1133 bp 3'-UTR, and an open reading frame (ORF) of 876 bp encoding a 291 residue protein containing Death and Toll/interleukin-1 receptor (TIR) domains. The deduced protein sequence shares 88.8%, 73.8% and 59.3% identity with orthologs in Ictalurus punctatus, Danio rerio and Homo sapiens, respectively. qRT-PCR revealed expression in all tested tissues, highest in trunk kidney, followed by spleen, and lowest in muscle. After challenge with lipopolysaccharide (LPS) or polyriboinosinic polyribocytidylic acid (Poly I:C), PfMyD88 expression was up-regulated in blood, liver, head kidney and spleen. Thus, PfMyD88 acts in innate immunity in P. fulvidraco.