Identification of the up-regulated expression genes in hemocytes of variously colored abalone (Haliotis diversicolor Reeve, 1846) challenged with bacteria

A novel C-type lectin, perlucin, from the small abalone, Haliotis diversicolor involved in the innate immune defense against Vibrio harveyi infection

C-type lectins (CTLs), a member of pattern recognition receptors, play an important role in the innate immunity by recognizing invading microorganisms. In this study, a novel perlucin gene (designated as HdPer 3), a typical CTLs was cloned and characterized from the small abalone Haliotis diversicolor. The open reading frame of HdPer 3 was 471 bp, encoding a protein of 156 amino acids that included a single carbohydrate-recognition domain. HdPer 3 was widely expressed in all tested tissues and developmental stage. HdPer 3 expression was significantly up-regulated after Vibrio harveyi infection, suggesting that HdPer 3 was activated in response to bacterial infection. The encapsulation ability of hemocytes could be significantly enhanced by the recombinant protein HdPer 3 (rHdPer 3). To understand the regulation mechanism of the HdPer 3, HdPer 3 was silenced in vivo by RNAi. Knocking down HdPer 3 decreased the hemocytes phagocytosis. Meanwhile, knocking down HdPer 3 can reduce the expression of 2 phagocytosis-related genes (Rab and Dynamin), TNF-α, and 2 MAPK pathway-related genes (MAPK-X1 and Ras) after V. harveyi infection. Moreover, HdPer 3 interference could increase the bacterial load in the hemolymph and the mortality of abalones after V. harveyi infection. All these results suggested that HdPer 3 played a crucial role in the defense against V. harveyi infection by recognizing bacterial pathogens and activating the expression of immune-related genes.

Morphologic, cytometric, quantitative transcriptomic and functional characterisation provide insights into the haemocyte immune responses of Pacific abalone (Haliotis discus hannai)

In recent years, the abalone aquaculture industry has been threatened by the bacterial pathogens. The immune responses mechanisms underlying the phagocytosis of haemocytes remain unclear in Haliotis discus hannai. It is necessary to investigate the immune mechanism in response to these bacterial pathogens challenges. In this study, the phagocytic activities of haemocytes in H. discus hannai were examined by flow cytometry combined with electron microscopy and transcriptomic analyses. The results of Vibrio parahaemolyticus, Vibrio alginolyticus and Staphylococcus aureu challenge using electron microscopy showed a process during phagosome formation in haemocytes. The phagocytic rate (PP) of S. aureus was higher than the other five foreign particles, which was about 63%. The PP of Vibrio harveyi was about 43%, the PP peak of V. alginolyticus in haemocyte was 63.7% at 1.5 h. After V. parahaemolyticus and V. alginolyticus challenge, acid phosphatase, alkaline phosphatase, total superoxide dismutase, lysozyme, total antioxidant capacity, catalase, nitric oxide synthase and glutathione peroxidase activities in haemocytes were measured at different times, differentially expressed genes (DEGs) were identified by quantitative transcriptomic analysis. The identified DEGs after V. parahaemolyticus challenge included haemagglutinin/amebocyte aggregation factor-like, supervillin-like isoform X4, calmodulin-like and kyphoscoliosis peptidase-like; the identified DEGs after V. alginolyticus challenge included interleukin-6 receptor subunit beta-like, protein turtle homolog B-like, rho GTPase-activating protein 6-like isoform X2, leukocyte surface antigen CD53-like, calponin-1-like, calmodulin-like, troponin C, troponin I-like isoform X4, troponin T-like isoform X18, tumor necrosis factor ligand superfamily member 10-like, rho-related protein racA-like and haemagglutinin/amebocyte aggregation factor-like. Some immune-related KEGG pathways were significantly up-regulated or down-regulated after challenge, including thyroid hormone synthesis, Th17 cell differentiation signalling pathway, focal adhesion, melanogenesis, leukocyte transendothelial migration, inflammatory mediator regulation of TRP channels, ras signalling pathway, rap1 signalling pathway. This study is the first step towards understanding the H. discus hannai immune system by adapting several tools to gastropods and providing a first detailed morpho-functional study of their haemocytes.

Thymosin beta-4 participate in antibacterial immunity and wound healing in black tiger shrimp, Penaeus monodon

Thymosin beta-4 (Tβ4) is a ubiquitous protein with multiple and diverse intracellular and extracellular functions in vertebrates, which play fundamental roles in innate immune against pathogens and wound healing. In this study, the full-length cDNA of Tβ4 was cloned from Penaeus monodon (designated as PmTβ4), using the technology of rapid amplification of cDNA ends (RACE). The cDNA of PmTβ4 was 1361 bp with an open reading frame (ORF) of 501 bp, which encoding a polypeptide of 166 amino acid. The Quantitative Real-time PCR (qRT-PCR) analysis results showed that PmTβ4 was ubiquitously expressed in all the tested shrimp tissues, with the highest expression level was detected in the hemolymph, while the lowest expression level in the muscle. The expression level of PmTβ4 was significantly up-regulated in hepatopancreas after challenged by Vibrio parahaemolyticus, Vibrio harveyi and Staphylococcus aureus. In vitro antimicrobial test showed that the recombinant protein of PmTβ4 (rPmTβ4) had broad-spectrum of antimicrobial activity, which could inhibit both the growth of gram-negative bacteria and gram-positive bacteria, including Vibrio vulnificus, V. parahaemolyticus, Streptococcus agalactiae, S. aureus and Aeromonas hydrophila. Moreover, rPmTβ4 had a certain binding ability to different bacteria, and this binding ability exhibits a strong dose-dependent effect. In vivo, PmTβ4 could facilitate external bacterial clearance in shrimp, and have beneficial to shrimp survival post V. parahaemolyticus infection. Furthermore, wound-healing assay was carried out to study the role of PmTβ4 in the process of wound healing. The results showed that the PmTβ4 expression was significantly up-regulated by injury treatment, and exerted positive effects to promote wound healing. In addition, PmTβ4 can significantly increase the expression level of superoxide dismutase (SOD) and Catalase (CAT) after injury treatment in shrimp, which would involve in scavenging reactive oxygen species (ROS) caused by the wound. In conclusion, these results indicated that PmTβ4 may play important roles in antibacterial immunity and wound healing in Penaeus monodon.

How Many Abalone Species Live in the Mediterranean Sea?

Morphological traits in Haliotidae may be highly variable and not consistently diagnostic for species identification, highlighting the need for an integrative approach to the taxonomy of the family, including genetic data. Four species of the genus Haliotis are currently reported for the Mediterranean Sea and the neighboring Atlantic Ocean: Haliotis tuberculata, the common European abalone with the widest Atlanto-Mediterranean range; Haliotis mykonosensis, from the Aegean, the Tyrrhenian, and the Adriatic; Haliotis stomatiaeformis, from Malta, Lampedusa, and southeastern Sicily; and the Lessepsian Haliotis pustulata, only known on the basis of few samples from the Levant. However, their taxonomic status still relies only on shell morphology. Here, sequences of two fragments of the mitochondrial molecular marker COI were obtained from 84 abalone specimens collected in the Mediterranean Sea and the neighboring Atlantic and analyzed in order to provide for the first time a genetic framework for species delimitation. This study’s results prove that H. mykonosensis is genetically identical to H. tuberculata, whereas H. stomatiaeformis is a distinct species, endemic to a restricted area of the southern Mediterranean Sea. Finally, Haliotis tuberculata coccinea from Macaronesia may deserve its status as a subspecies of H. tuberculata, with genetic signature of a limited gene flow found in specimens of the nominal subspecies (H. t. tuberculata) in both the Atlantic and the Mediterranean Sea.

Effect of low-frequency noise on the survival rate and immunity of infected Vibrio parahaemolyticus sea slug (Onchidium reevesii)

Anthropogenic noise in the marine environment has become a global environmental pollutant that affects the behavior, physiology and immunity of marine animals. However, the resistance of marine animals to pathogens while under the influence of noise is a topic that has received little attention. To assess the immune defense response of sea slugs against pathogens when exposed to low frequency noise, we performed 120 h exposure experiments on sea slugs after a Vibrio parahaemolyticus application in low frequency noise at 500 Hz and 1000 Hz. We found that after the infection with V. parahaemolyticus, the survival rate of the sea slugs decreased, the apoptosis rate and reactive oxygen species (ROS) production of hemocytes increased significantly (P < 0.05), the proliferation of hemocytes accelerated, the activities of enzymes such as superoxide dismutase (SOD), catalase (CAT), alkaline phosphatase (AKP), alanine transaminase (ALT) and lysozyme (LZM) in the hepatopancreas increased significantly, and the expression of TNF signaling pathway-related genes (TNF-α, FADD, Caspase 8, Caspase 3) and Hsp70 genes were generally upregulated. In addition, exposure of sea slug after infected with V. parahaemolyticus to low frequency noise resulted in a significant increase in both antioxidant and immune parameters, which were positively correlated with frequency. The results showed that noise frequency and exposure time had an interactive effect on the above indicators. In summary, low-frequency noise exposure increases the risk of pathogenic infections in sea slugs and exacerbates the negative effects on the antioxidant capacity and immune metabolism of the organism.

Transcriptome analysis reveals fluid shear stress (FSS) and atherosclerosis pathway as a candidate molecular mechanism of short-term low salinity stress tolerance in abalone

BACKGROUND

Transcriptome sequencing is an effective tool to reveal the essential genes and pathways underlying countless biotic and abiotic stress adaptation mechanisms. Although severely challenged by diverse environmental conditions, the Pacific abalone Haliotis discus hannai remains a high-value aquaculture mollusk and a Chinese predominantly cultured abalone species. Salinity is one of such environmental factors whose fluctuation could significantly affect the abalone's cellular and molecular immune responses and result in high mortality and reduced growth rate during prolonged exposure. Meanwhile, hybrids have shown superiority in tolerating diverse environmental stresses over their purebred counterparts and have gained admiration in the Chinese abalone aquaculture industry. The objective of this study was to investigate the molecular and cellular mechanisms of low salinity adaptation in abalone. Therefore, this study used transcriptome analysis of the gill tissues and flow cytometric analysis of hemolymph of H. discus hannai (DD) and interspecific hybrid H. discus hannai ♀ x H. fulgens ♂ (DF) during low salinity exposure. Also, the survival and growth rate of the species under various salinities were assessed.

RESULTS

The transcriptome data revealed that the differentially expressed genes (DEGs) were significantly enriched on the fluid shear stress and atherosclerosis (FSS) pathway. Meanwhile, the expression profiles of some essential genes involved in this pathway suggest that abalone significantly up-regulated calmodulin-4 (CaM-4) and heat-shock protein90 (HSP90), and significantly down-regulated tumor necrosis factor (TNF), bone morphogenetic protein-4 (BMP-4), and nuclear factor kappa B (NF-kB). Also, the hybrid DF showed significantly higher and sustained expression of CaM and HSP90, significantly higher phagocytosis, significantly lower hemocyte mortality, and significantly higher survival at low salinity, suggesting a more active molecular and hemocyte-mediated immune response and a more efficient capacity to tolerate low salinity than DD.

CONCLUSIONS

Our study argues that the abalone CaM gene might be necessary to maintain ion equilibrium while HSP90 can offset the adverse changes caused by low salinity, thereby preventing damage to gill epithelial cells (ECs). The data reveal a potential molecular mechanism by which abalone responds to low salinity and confirms that hybridization could be a method for breeding more stress-resilient aquatic species.

Long-read RNA sequencing of Pacific abalone Haliotis discus hannai reveals innate immune system responses to environmental stress

Haliotis discus hannai is a commercially important mollusk species, and the abalone aquaculture sector has been jeopardized by deteriorating environmental circumstances such as bacterial infection and thermal stress during the hot summers. However, due to a paucity of genetic information, such as transcriptome resources, our understanding of their stress adaptation is restricted. In this research, using single-molecule long-read (SMRT) sequencing technology, a library composed of ten tissues (i.e., haemocytes, gills, muscle, hepatopancreas, digestive tract, mantle, mucous gland, ovary, testis and head) was constructed and sequenced. In all, 41,855 high-quality unique transcripts, among which 24,778 were successfully annotated. Additionally, 13,463 SSRs, 1,169 transcription factors, and 18,124 lncRNAs were identified in H. discus hannai transcriptome. Furthermore, multiple immune-related transcripts were identified according to KEGG annotation, and a portion of these transcripts were mapped into several classical immune-related pathways, including the PI3K-AKT signaling pathway and Toll-like receptor signaling pathway. Additionally, 24 typical sequences related to the immunity pathway were detected by RT-PCR; the results showed that most of the immune-related genes showed significantly high expression at 72 h after bacterial challenges and thermal stress, especially the expression level of genes in gills was significantly higher than that in haemocytes under V. parahaemolyticus stress at 24 h. At the same time. The analysis of alternative splicing identified several innate immunity-related functions genes, including CD109 and caspase 2. These results suggest that the complex immune system, particularly the powerful innate immunity system, was crucial for H. discus hannai response to numerous environmental challenges.

Data scaling performance on various machine learning algorithms to identify abalone sex

This study aims to analyze the performance of machine learning algorithms with the data scaling process to show the method's effectiveness. It uses min-max (normalization) and zero-mean (standardization) data scaling techniques in the abalone dataset. The stages carried out in this study included data normalization on the data of abalone physical measurement features. The model evaluation was carried out using k-fold cross-validation with the number of k-fold 10. Abalone datasets were normalized in machine learning algorithms: Random Forest, Naïve Bayesian, Decision Tree, and SVM (RBF kernels and linear kernels). The eight features of the abalone dataset show that machine learning algorithms did not too influence data scaling. There is an increase in the performance of SVM, while Random Forest decreases when the abalone dataset is applied to data scaling. Random Forest has the highest average balanced accuracy (74.87%) without data scaling.

Construction of wound repair model and function of recombinant TIMP from Hyriopsis cumingii

Metalloproteinase tissue inhibitors (TIMPs) have the activity of inhibiting matrix metalloproteinases (MMPs), which can promote cell growth, bind to the matrix, inhibit angiogenesis, and play a key role in extracellular matrix (ECM) metabolism regulation. In this study, TIMP-1, 2 from Hyriopsis cumingii (designated as HcTIMP-1, 2) were cloned and identified. Full-length cDNA of HcTIMP-1, 2 was 1160 bp and 729 bp, encoding 235 and 150 amino acid residues, respectively. The predicted molecular weight of HcTIMP-1 and 2 protein was 27.26 and 16.58 kDa, with isoelectric points of 8.89 and 8.72, respectively. HcTIMP-2 contained only one netrin (NTR) domain at the N-terminal but lacked a C-terminal domain. The mRNA of HcTIMP-1, 2 was expressed in hepatopancreas, gills, muscles, hemocytes, and mantles, which had the highest expression in hemocytes and muscles. The expression of HcTIMP-1, 2 had increased remarkably in hemocytes after bacterial challenge. After trauma, HcTIMP-1, 2 genes had the highest expression level in the first day. This indicated that HcTIMP-1 and 2 were involved in the immune response of H. cumingii. The soluble recombinant proteins HcTIMP-1, 2 were expressed efficiently in Escherichia coli BL21 (DE3) by constructing pET32a-TIMP1, 2 recombinant plasmids. The concentration of the recombinant was 0.14 and 0.31 mg/mL, respectively. The recombinant HcTIMP-1, 2 proteins were shown to inhibit human MMP2 activity and promoted the growth of NBL-7 and HUVE cells.

A calmodulin targeted by miRNA scaffold659_26519 regulates IL-17 expression in the early immune response of oyster Crassostrea gigas

Calmodulin (CaM) is a highly conserved second messenger protein transducing calcium signals by binding and modulating intracellular calcium ions (Ca²⁺), and involves in the Ca²⁺-dependent physical processes including host defense in vertebrates. In the present study, a CaM homologue (designated as CgCaM) was identified from Pacific oyster Crassostrea gigas. The open reading frame of CgCaM cDNA was of 471 bp encoding a polypeptide of 156 amino acid residues. There were four EFh domains predicted in CgCaM, which shared high homologies with those in CaMs from oyster C. virginica and other invertebrates. The mRNA transcripts of CgCaM were constitutively expressed in all the tested tissues including labellum, mantle, gonad, gills, adductor muscle, haemocytes and hepatopancreas, with the highest expression level in haemocytes. The mRNA expression level of CgCaM in haemocytes decreased significantly (0.31-fold of that in blank, p < 0.05) at 3 h after LPS stimulation, while the intracellular Ca²⁺ (1.57-fold of that in blank, p < 0.05) and the mRNA expression of cytokine CgIL17-1 (4.87-fold of that in blank, p < 0.05) both increased in haemocytes. Meanwhile, an oyster miRNA scaffold659_26519 was identified, and it was proved to target the 3'-untranslated regions (3'-UTR) of CgCaM mRNA by luciferase reporter assay. The expression of scaffold659_26519 increased significantly at 3 h (43.523-fold of that of blank, p < 0.05) and 6 h (55.91-fold of that of blank, p < 0.05) after LPS stimulation. When the expression of scaffold659_26519 was inhibited by transfection with its inhibitor in vitro, the expression of CgIL17-1 declined significantly to 0.58-fold of that in LPS stimulation group. These findings indicated that the miRNA scaffold659_26519 targeted CaM was involved in the early inflammatory response of oyster immunity, and provided a new evidence for CaM-mediated immune mechanism in molluscs.

Regulatory effect of heat shock transcription factor-1 gene on heat shock proteins and its transcriptional regulation analysis in small abalone Haliotis diversicolor

Background

The effects of diverse stresses ultimately alter the structures and functions of proteins. As molecular chaperones, heat shock proteins (HSPs) are a group of highly conserved proteins that help in the refolding of misfolded proteins and the elimination of irreversibly damaged proteins. They are mediated by a family of transcription factors called heat shock factors (HSFs). The small abalone Haliotis diversicolor is a species naturally distributed along the southern coast of China. In this study, the expression of HdHSF1 was inhibited by RNAi in hemocytes in order to further elucidate the regulatory roles of HdHSF1 on heat shock responsive genes in abalone. Meanwhile, to understand the transcriptional regulation of the HdHSF1 gene, the 5′-upstream regulatory region of HdHSF1 was characterized, and the relative promoter activity was examined by dual-luciferase reporter gene assay system in HEK293T cell lines.

Results

After the inhibition of the H. diversicolor HSF1 gene (HdHSF1) by dsRNA (double-stranded RNA), the expression of most heat shock related-genes was down-regulated (p < 0.05). It indicated the importance of HdHSF1 in the heat shock response of H. diversicolor. Meanwhile, 5′-flanking region sequence (2633 bp) of the HdHSF1 gene was cloned; it contained a putative core promoter region, TATA box, CAAT box, CpG island, and many transcription elements. In HEK293T cells, the 5′-flanking region sequence can drive expression of the enhanced green fluorescent protein (EGFP), proving its promoter function. Exposure of cells to the high-temperature (39 °C and 42 °C) resulted in the activation of HdHSF1 promoter activity, which may explain why the expression of the HdHSF1 gene participates in heat shock response. Luciferase activity of different recombinant plasmids, which contained different truncated promoter fragments of the HdHSF1 gene in HEK293T cells, revealed the possible active regions of the promoter. To further identify the binding site of the critical transcription factor in the region, an expression vector with the site-directed mutation was constructed. After being mutated on the GATA-1 binding site, we found that the luciferase activity was significantly increased, which suggested that the GATA-1 binding site has a certain weakening effect on the activity of the HdHSF1 promoter.

Conclusions

These findings suggest that GATA-1 may be one of the transcription factors of HdHSF1, and a possible signaling pathway mediated by HdHSF1 may exist in H. diversicolor to counteract the adverse effects of heat shock stress.

Supplementary Information

Supplementary information accompanies this paper at 10.1186/s12860-020-00323-9.

Allograft Inflammatory Factor-1 in Metazoans: Focus on Invertebrates

Simple Summary

During their life, all living organisms defend themselves from pathogens using complex strategies. Vertebrates and invertebrates share mechanisms and molecules that guarantee their overall bodily integrity. Allograft inflammatory factor-1 (AIF-1) is a protein extensively studied in vertebrates, and especially in mammals. This factor, generally involved in inflammation events occurring upon pathogenic infection or tissue injury, is linked to several important human diseases. This review collects data on the presence and role of AIF-1 in invertebrates, which are still poorly investigated organisms. Multiple alignment and phylogenetic analysis reveal that AIF-1 is conserved in vertebrates and invertebrates, suggesting similarity of functions. In some invertebrate species, the expression of AIF-1 increases considerably after a bacterial challenge, indicating that it plays a key role during the immune responses. This review highlights the importance of studying this protein in invertebrates as a way to improve our knowledge of innate immunity mechanisms and to better understand inflammatory regulation events in mammals.

Abstract

Allograft inflammatory factor-1 (AIF-1) is a calcium-binding scaffold/adaptor protein often associated with inflammatory diseases. Originally cloned from active macrophages in humans and rats, this gene has also been identified in other vertebrates and in several invertebrate species. Among metazoans, AIF-1 protein sequences remain relatively highly conserved. Generally, the highest expression levels of AIF-1 are observed in immunocytes, suggesting that it plays a key role in immunity. In mammals, the expression of AIF-1 has been reported in different cell types such as activated macrophages, microglial cells, and dendritic cells. Its main immunomodulatory role during the inflammatory response has been highlighted. Among invertebrates, AIF-1 is involved in innate immunity, being in many cases upregulated in response to biotic and physical challenges. AIF-1 transcripts result ubiquitously expressed in all examined tissues from invertebrates, suggesting its participation in a variety of biological processes, but its role remains largely unknown. This review aims to present current knowledge on the role and modulation of AIF-1 and to highlight its function along the evolutionary scale.

Ancient but Not Forgotten: New Insights Into MPEG1, a Macrophage Perforin-Like Immune Effector

Macrophage-expressed gene 1 [MPEG1/Perforin-2 (PRF2)] is an ancient metazoan protein belonging to the Membrane Attack Complex/Perforin (MACPF) branch of the MACPF/Cholesterol Dependent Cytolysin (CDC) superfamily of pore-forming proteins (PFPs). MACPF/CDC proteins are a large and extremely diverse superfamily that forms large transmembrane aqueous channels in target membranes. In humans, MACPFs have known roles in immunity and development. Like perforin (PRF) and the membrane attack complex (MAC), MPEG1 is also postulated to perform a role in immunity. Indeed, bioinformatic studies suggest that gene duplications of MPEG1 likely gave rise to PRF and MAC components. Studies reveal partial or complete loss of MPEG1 causes an increased susceptibility to microbial infection in both cells and animals. To this end, MPEG1 expression is upregulated in response to proinflammatory signals such as tumor necrosis factor α (TNFα) and lipopolysaccharides (LPS). Furthermore, germline mutations in MPEG1 have been identified in connection with recurrent pulmonary mycobacterial infections in humans. Structural studies on MPEG1 revealed that it can form oligomeric pre-pores and pores. Strikingly, the unusual domain arrangement within the MPEG1 architecture suggests a novel mechanism of pore formation that may have evolved to guard against unwanted lysis of the host cell. Collectively, the available data suggest that MPEG1 likely functions as an intracellular pore-forming immune effector. Herein, we review the current understanding of MPEG1 evolution, regulation, and function. Furthermore, recent structural studies of MPEG1 are discussed, including the proposed mechanisms of action for MPEG1 bactericidal activity. Lastly limitations, outstanding questions, and implications of MPEG1 models are explored in the context of the broader literature and in light of newly available structural data.

Transcriptomics reveals specific molecular mechanisms underlying transgenerational immunity in Manduca sexta

The traditional view of innate immunity in insects is that every exposure to a pathogen triggers an identical and appropriate immune response and that prior exposures to pathogens do not confer any protective (i.e., adaptive) effect against subsequent exposure to the same pathogen. This view has been challenged by experiments demonstrating that encounters with sublethal doses of a pathogen can prime the insect's immune system and, thus, have protective effects against future lethal doses. Immune priming has been reported across several insect species, including the red flour beetle, the honeycomb moth, the bumblebee, and the European honeybee, among others. Immune priming can also be transgenerational where the parent's pathogenic history influences the immune response of its offspring. Phenotypic evidence of transgenerational immune priming (TGIP) exists in the tobacco moth Manduca sexta where first-instar progeny of mothers injected with the bacterium Serratia marcescens exhibited a significant increase of in vivo bacterial clearance. To identify the gene expression changes underlying TGIP in M. sexta, we performed transcriptome-wide, transgenerational differential gene expression analysis on mothers and their offspring after mothers were exposed to S. marcescens. We are the first to perform transcriptome-wide analysis of the gene expression changes associated with TGIP in this ecologically relevant model organism. We show that maternal exposure to both heat-killed and live S. marcescens has strong and significant transgenerational impacts on gene expression patterns in their offspring, including upregulation of peptidoglycan recognition protein, toll-like receptor 9, and the antimicrobial peptide cecropin.

The Complicated Evolutionary Diversification of the Mpeg-1/Perforin-2 Family in Cnidarians

The invertebrate innate immune system is surprisingly complex, yet our knowledge is limited to a few select model systems. One understudied group is the phylum Cnidaria (corals, sea anemones, etc.). Cnidarians are the sister group to Bilateria and by studying their innate immunity repertoire, a better understanding of the ancestral state can be gained. Corals in particular have evolved a highly diverse innate immune system that can uncover evolutionarily basal functions of conserved genes and proteins. One rudimentary function of the innate immune system is defense against harmful bacteria using pore forming proteins. Macrophage expressed gene 1/Perforin-2 protein (Mpeg-1/P2) is a particularly important pore forming molecule as demonstrated by previous studies in humans and mice, and limited studies in non-bilaterians. However, in cnidarians, little is known about Mpeg-1/P2. In this perspective article, we will summarize the current state of knowledge of Mpeg-1/P2 in invertebrates, analyze identified Mpeg-1/P2 homologs in cnidarians, and demonstrate the evolutionary diversity of this gene family using phylogenetic analysis. We will also show that Mpeg-1 is upregulated in one species of stony coral in response to lipopolysaccharides and downregulated in another species of stony coral in response to white band disease. This data presents evidence that Mpeg-1/P2 is conserved in cnidarians and we hypothesize that it plays an important role in cnidarian innate immunity. We propose that future research focus on the function of Mpeg-1/P2 family in cnidarians to identify its primary role in innate immunity and beyond.

iTRAQ-based quantitative proteomic profiling of the immune response of the South African abalone, Haliotis midae

The South African abalone Haliotis midae is a commercially important species farmed at high densities in land-based aquaculture systems. Disease outbreaks have had a severe financial impact on the abalone industry yet the molecular mechanisms underlying the immune response of H. midae remain obscure. In this study, a comparative shotgun proteomics approach using iTRAQ coupled with LC-MS/MS was employed to investigate H. midae proteome changes in response to Vibrio anguillarum challenge. A total of 118 non-redundant, unique haemocyte proteins were identified and quantified, with 16 proteins significantly regulated. Hierarchical clustering and pathway analysis uncovered a coordinated response dominated by calcium and cAMP signalling via activation of MAPK cascades. Early up-regulated biological processes involve phagocytosis, nitric oxide production and ATP-synthesis, whilst down-regulated responses were predominantly involved in the regulation of apoptosis. The late up-regulated response involved protein kinase activity and detoxification processes. Expression of selected proteins was validated by Western blot. A putative allograft inflammatory factor-1 protein was further selected to establish its functional molecular role in haemocytes. Confocal imaging revealed that allograft inflammatory factor-1 regulates phagocytosis via a functional interaction with filamentous actin. This is the first time a high-throughput proteomics approach has been used to investigate the immune response of H. midae.

Immunity-related genes and signaling pathways under hypoxic stresses in Haliotis diversicolor: a transcriptome analysis

Due to increased temperatures and aquaculture density, thermal and hypoxia stresses have become serious problems for the aquaculture of abalone Haliotis diversicolor. Stresses lead to immunosuppression, which can cause severe negative impacts on aquaculture farms. To study the mechanism of immunosuppression after hypoxia stress and bacterial challenge, transcriptomes of H. diversicolor hemocytes involved in immunity were profiled. A total of 307,395,572 clean reads were generated and assembled into 99,774 unigenes. KEGG analysis indicated that 225 unigenes with immunologic function were mapped into immune-related pathways. Expression of 41 unigenes measured by quantitative real-time PCR (qRT-PCR) showed consistent results with that of transcriptome analysis. When exposure challenge of Vibrio parahaemolyticus, it is indicated that the PI3K-AKT, MAPK, NF-κB and P53 signal pathways were involved in the hypoxia-induced immunosuppression of H. diversicolor. Furthermore, when the AKT gene (HdAKT) was inhibited by double-stranded RNA (dsRNA), expression levels of HdAKT was lower than the blank and control group in hemocytes at 4 h, 12 h and 24 h (p < 0.05).

Molecular characterization and functional analysis of Akirin from black tiger shrimp (Penaeus monodon)

Akirin, which are members of the NF-κB signaling pathway, play critical roles in regulating the expression of antimicrobial peptides. In the present study, the Akirin gene from Penaeus monodon was identified from a transcriptome database and designated as PmAkirin. The complete sequence of the PmAkirin cDNA was 1508 bp, encoding a protein of 213 amino acids, and it showed 99% amino acid identity to the Litopenaeus vannamei Akirin. Two predicted nuclear localization signals (NLSs) were found, and the amino acid sequence alignments showed that PmAkirin was highly conserved at the N-terminus and C-terminus. PmAkirin expression was found to be the highest in the hemolymph, followed by the heart, gill, stomach, hepatopancreas, intestine, and muscle. When challenged with Vibrio parahaemolyticus infection, the PmAkirin mRNA and three antimicrobial peptides (AMPs: PmALF2, PmALF3, and PmCrus4) were upregulated. However, another five AMPs (PmALF6, PmCrus1, PmPEN3a, PmPEN3b, and PmPEN5) were downregulated by V. parahaemolyticus infection. Silencing PmAkirin by dsRNA significantly decreased the expression of the eight AMPs, which lead to an increase in the blood concentration of V. parahaemolyticus and higher mortality in the shrimp. In contrast, the overexpression of PmAkirin significantly increased the expression of the eight AMPs, which led to a reduction in the blood concentration of V. parahaemolyticus and promoted the survival of the shrimp. Taken together, we concluded that PmAkirin plays an important role in regulating the expression of AMPs in black tiger shrimp to defend against V. parahaemolyticus infection.

The Penaeus stylirostris densovirus capsid protein interacts with the Litopenaeus vannamei BCCIP protein

Viral capsid proteins play an important role in the viral infection process. To identify the cellular proteins in shrimp that interact with the Penaeus stylirostris densovirus capsid protein (PstDNV-CP), we constructed a yeast two-hybrid (Y2H) cDNA library of the muscle tissue of Litopenaeus vannamei, and hybridized the bait vector pGBKT7-CP with this library. Cloning and sequencing showed that the shrimp protein interacting with PstDNV-CP was a homolog of BRCA2 and CDKN1A(p21)-interacting protein (BCCIP). We named this protein L. vannamei BCCIP (LvBCCIP). Further analysis showed that LvBCCIP interacted with L. vannamei calmodulin (LvCaM). We validated the interactions between PstDNV-CP and LvBCCIP, and between LvBCCIP and LvCaM, with GST pulldown assays. The gene expression of LvBCCIP increased significantly after PstDNV challenge. In addition, the PstDNV titer of PstDNV-challenged shrimp was significantly reduced after LvBCCIP expression was inhibited using double-stranded RNA (dsRNA) interference. These results indicated that LvBCCIP is critical to PstDNV pathogenesis in L. vannamei. Interestingly, the growth rate of L. vannamei was significantly reduced when LvBCCIP gene expression was silenced, indicating that LvBCCIP may also be associated with growth regulation in L. vannamei. Thus, the interaction between PstDNV-CP and LvBCCIP might explain why PstDNV infection leads to runt-deformity syndrome in shrimp.

Cloning and characteristic of MMP1 gene from Hyriopsis cumingii and collagen hydrolytic activity of its recombinant protein

Matrix metalloproteinases (MMPs) play an essential role in a variety of biological processes including wound healing, inflammation, cell invasion, angiogenesis and immune defense. In this study, a putative MMP1 cDNA was cloned and characterized from Hyriopsis cumingii (designated as HcMMP1). The cDNA was 1822 bp in length and encoded a putative protein of 510 amino acids, with a predicted molecular mass of 58.28 kDa and an isoelectric point (pI) of 9.27. HcMMP1 contained all prototype MMPs family signatures, such as signal peptide, prodomain, catalytic center, hinge region, and hemopexin like domain. Quantitative real time-PCR (qRT-PCR) revealed that in mussels HcMMP1 mRNA was expressed in all tissues tested, and the transcriptional expression levels were significantly up-regulated in hepatopancreas and hemocytes after Aeromonas hydrophila, peptidoglycan stimulations and in mantle after wounding. Moreover, the recombination HcMMP1 protein, successfully expressed in Escherichia coli, was purified by affinity chromatography with the concentration of final yield at 0.3 mg/mL. The recombinase had an essentially hydrolytic activity toward rat type I collagen, mouse II and IV collagen after renaturation.

Integrative transcriptome analysis and discovery of genes involving in immune response of hypoxia/thermal challenges in the small abalone Haliotis diversicolor

In recent years, the abalone aquaculture industry has been threatened by the deteriorating environmental conditions, such as hypoxia and thermal stress in the hot summers. It is necessary to investigate the molecular mechanism in response to these environmental challenges, and subsequently understand the immune defense system. In this study, the transcriptome profiles by RNA-seq of hemocytes from the small abalone Haliotis diversicolor after exposure to hypoxia, thermal stress, and hypoxia plus thermal stress were established. A total of 103,703,074 clean reads were obtained and 99,774 unigenes were assembled. Of the 99,774 unigenes, 47,154 and 20,455 had homologous sequences in the Nr and Swiss-Prot protein databases, while 16,944 and 10,840 unigenes could be classified by COG or KEGG databases, respectively. RNAseq analysis revealed that the differentially expressed genes (DEGs) after challenges of hypoxia, thermal stress, or hypoxia plus thermal stress were 24,189, 29,165 and 23,665, among which more than 3000 genes involved in at least 230 pathways, including several classical immune-related pathways. The genes and pathways that were involved in immune response to hypoxia/thermal challenges were identified by transcriptome analysis and further validated by quantitative real-time PCR and RNAi technology. The findings in this study can provide information on H. diversicolor innate immunity to improve the abalone aquaculture industry, and the analysis of the potential immune-related genes in innate immunity signaling pathways and the obtained transcriptome data can provide an invaluable genetic resource for the study of the genome and functional genes.

Nucleus-translocated matrix metalloprotease 1 regulates innate immune response in Pacific abalone (Haliotis discus hannai)

As an important economical shellfish in coastal area of China, abalone is susceptible to bacterial infection, especially Vibiro parahemolyticus (V. parahemolyticus). Matrix metalloproteinases (MMPs) have been extensively investigated in the immune response of mammals. However, little is known about the involvement of MMP in abalone innate immune system against pathogen infection. In this study, the role of MMP-1 in the immune response of Pacific abalone (Haliotis discus hannai) was explored. The results showed that V. parahemolyticus infection induced significantly elevated expression of MMP-1 as well as immune related genes including allograft inflammatory factor 1 (AIF-1), macrophage expressed gene 1 (MPEG-1) and TPA-inducible sequence 11 family protein (Tis11FP). Notably, silencing of MMP-1 reduced the expression of these genes, suggesting that MMP-1 was an upstream regulatory factor in V. parahemolyticus infection. Further analysis showed that MMP-1 was engaged in the regulation of cellular (phagocytosis, apoptosis) and humoral [superoxide dismutase (SOD), alkaline phosphatase (ALP), acid phosphatase (ACP)] immunity. Interestingly, the extracellularly distributed MMP-1 could be translocated to the nuclei of hemocytes, thereby functioning as a transcriptional regulator or by selectively activating or inactivating other components through proteolysis. Hence, our study established an important role of MMP-1 in abalone innate immunity against V. parahemolyticus infection and it represented the first report on the investigation of MMP in abalone.

Involvement of clip-domain serine protease in the anti-Vibrio immune response of abalone (Haliotis discus hannai)-Molecular cloning, characterization and functional analysis

Vibrio parahemolyticus (V. parahemolyticus) is a major pathogen for abalone, an important economical shellfish in coastal area of China. There is little known about the abalone innate immune system against pathogen infection. Clip-domain serine proteases (cSPs) are increasingly recognized to play important roles in host immune defense in invertebrates. In this study, we cloned a cSP (Hdh-cSP) from abalone (Haliotis discus hannai). We found out that Hdh-cSP was widely expressed in multiple tissues of abalone, with highest level in the immune-like organ, hepatopancreas. V. parahemolyticus infection induced significantly elevated expression of Hdh-cSP in addition to better-characterized innate immune component genes including Rel/NF-κB, allograft inflammatory factor (ALInFa), macrophage expressed protein (MEP) and caspase-8. Importantly, the silencing of Hdh-cSP reduced the expression of these genes, suggesting that Hdh-cSP was an upstream regulatory factor in V. parahemolyticus infection. Further analysis showed that apoptosis of hemocytes was inhibited when the transcription of Hdh-cSP was knocked down, suggesting that Hdh-cSP participated in cell apoptosis by regulation of caspase 8 expression in V. parahemolyticus infection. Therefore, our study established an important role of cSP in the innate immunity against V. parahemolyticus infection in abalone.

Molecular cloning, biochemical characterization, and expression analysis of two glutathione S-transferase paralogs from the big-belly seahorse (Hippocampus abdominalis)

Glutathione S-transferases (GSTs, EC 2.5.1.18) are important Phase II detoxifying enzymes that catalyze hydrophobic, electrophilic xenobiotic substance with the conjugation of reduced glutathione (GSH). In this study, GSTμ and GSTρ paralogs of GST in the big belly seahorse (Hippocampus abdominalis; HaGSTρ, HaGSTμ) were biochemically, molecularly, functionally characterized to determine their detoxification range and protective capacities upon different pathogenic stresses. HaGSTρ and HaGSTμ are composed of coding sequences of 681bp and 654bp, which encode proteins 225 and 217 amino acids, with predicted molecular masses of 26.06kDa and 25.74kDa respectively. Sequence analysis revealed that both HaGSTs comprise the characteristic GSH-binding site in the thioredoxin-like N-terminal domain and substrate binding site in the C-terminal domain. The recombinant HaGSTρ and HaGSTμ proteins catalyzed the model GST substrate 1-chloro-2, 4-dinitrobenzene (CDNB). Enzyme kinetic analysis revealed different K_m and V_max values for each rHaGST, suggesting that they have different conjugation rates. The optimum conditions (pH, temperature) and inhibitory assays of each protein demonstrated different optimal ranges. However, HaGSTμ was highly expressed in the ovary and gill, whereas HaGSTρ was highly expressed in the gill and pouch. mRNA expression of HaGSTρ and HaGSTμ was significantly elevated upon lipopolysaccharide, Poly (I:C), and Edwardsiella tarda challenges in liver and in blood cells as well as with Streptococcus iniae challenge in blood cells. From these collective experimental results, we propose that HaGSTρ and HaGSTμ are effective in detoxifying xenobiotic toxic agents, and importantly, their mRNA expression could be stimulated by immunological stress signals in the aquatic environment.

Evolutionary conserved mechanisms pervade structure and transcriptional modulation of allograft inflammatory factor-1 from sea anemone Anemonia viridis

Gene family encoding allograft inflammatory factor-1 (AIF-1) is well conserved among organisms; however, there is limited knowledge in lower organisms. In this study, the first AIF-1 homologue from cnidarians was identified and characterised in the sea anemone Anemonia viridis. The full-length cDNA of AvAIF-1 was of 913 bp with a 5' -untranslated region (UTR) of 148 bp, a 3'-UTR of 315 and an open reading frame (ORF) of 450 bp encoding a polypeptide with149 amino acid residues and predicted molecular weight of about 17 kDa. The predicted protein possesses evolutionary conserved EF hand Ca²⁺ binding motifs, post-transcriptional modification sites and a 3D structure which can be superimposed with human members of AIF-1 family. The AvAIF-1 transcript was constitutively expressed in all tested tissues of unchallenged sea anemone, suggesting that AvAIF-1 could serve as a general protective factor under normal physiological conditions. Moreover, we profiled the transcriptional activation of AvAIF-1 after challenges with different abiotic/biotic stresses showing induction by warming conditions, heavy metals exposure and immune stimulation. Thus, mechanisms associated to inflammation and immune challenges up-regulated AvAIF-1 mRNA levels. Our results suggest its involvement in the inflammatory processes and immune response of A. viridis.

Characterization and function of a novel calmodulin-like protein from crayfish Procambarus clarkii

Calmodulin plays an important role in calcium-dependent signal transduction pathways. In this experiment, a novel calmodulin-like gene (Pc-CaM-L) was identified in the crayfish Procambarus clarkii; it encodes a polypeptide of 145 amino acids. Quantitative real-time PCR analysis revealed that Pc-CaM-L was expressed in all examined tissues, including hepatopancreas, hemocytes, heart, gill, intestine and muscle; the highest Pc-CaM-L expression level was detected in the hepatopancreas. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and western blot analysis demonstrated that a recombinant Pc-CaM-L protein was successfully expressed in Escherichia coli. The calcium-binding activity of the purified Pc-CaM-L protein was confirmed by gel mobility shift assay. The expression of Pc-CaM-L was significantly upregulated in gut, gill and hemocytes after lipopolysaccharide or polyinosinic:polycytidylic acid induction. These results suggest that Pc-CaM-L plays a role in the immune response of P. clarkii.

Matrix metalloproteinases outside vertebrates

The matrix metalloproteinase (MMP) family belongs to the metzincin clan of zinc-dependent metallopeptidases. Due to their enormous implications in physiology and disease, MMPs have mainly been studied in vertebrates. They are engaged in extracellular protein processing and degradation, and present extensive paralogy, with 23 forms in humans. One characteristic of MMPs is a ~165-residue catalytic domain (CD), which has been structurally studied for 14 MMPs from human, mouse, rat, pig and the oral-microbiome bacterium Tannerella forsythia. These studies revealed close overall coincidence and characteristic structural features, which distinguish MMPs from other metzincins and give rise to a sequence pattern for their identification. Here, we reviewed the literature available on MMPs outside vertebrates and performed database searches for potential MMP CDs in invertebrates, plants, fungi, viruses, protists, archaea and bacteria. These and previous results revealed that MMPs are widely present in several copies in Eumetazoa and higher plants (Tracheophyta), but have just token presence in eukaryotic algae. A few dozen sequences were found in Ascomycota (within fungi) and in double-stranded DNA viruses infecting invertebrates (within viruses). In contrast, a few hundred sequences were found in archaea and >1000 in bacteria, with several copies for some species. Most of the archaeal and bacterial phyla containing potential MMPs are present in human oral and gut microbiomes. Overall, MMP-like sequences are present across all kingdoms of life, but their asymmetric distribution contradicts the vertical descent model from a eubacterial or archaeal ancestor. This article is part of a Special Issue entitled: Matrix Metalloproteinases edited by Rafael Fridman.

A molluscan extracellular signal-regulated kinase is involved in host response to immune challenges in vivo and in vitro

Extracellular signal-regulated kinases (ERKs) are a group of highly conserved serine/threonine-specific protein kinases that function as important signaling intermediates in mitogen-activated protein kinase (MAPK) pathways, which are involved in a wide variety of cellular activities, including proliferation, inflammation and cytokine production. However, little is known about the roles of this kinase in mollusk immunity. In this study, we identified a molluscan ERK homolog (ChERK) in the Hong Kong oyster (Crassostrea hongkongensis) and investigated its biological functions. The open reading frame (ORF) of ChERK encoded a polypeptide of 365 amino acids, with a predicted molecular weight of 41.96 kDa and pI of 6.43. The predicted ChERK protein contained typical characteristic motifs of the ERK family, including a dual threonine-glutamate-tyrosine (TEY) phosphorylation motif and an ATRW substrate binding site. Phylogenetic analysis revealed that ChERK belonged to the mollusk cluster and shared a close evolutionary relationship with ERK from Crassostrea gigas. In addition, quantitative real-time PCR analysis revealed that ChERK expression was detected in all of the examined tissues and stages of embryonic development; its transcript level was significantly induced upon challenge with bacterial pathogens (Vibrio alginolyticus and Staphylococcus haemolyticus) in vivo and PAMPs (lipopolysaccharide and peptidoglycan) in vitro. Moreover, ChERK was mainly located in the cytoplasm of HEK293T cells. Taken together, these findings may provide novel insights into the functions of molluscan ERKs, especially their roles in response to immune challenge in oyster.

c-Jun N-terminal kinase (JNK) is involved in immune defense against bacterial infection in Crassostrea hongkongensis

c-Jun N-terminal kinase (JNK) is a universal and essential subgroup of the mitogen-activated protein kinase (MAPK) superfamily, which is highly conserved from yeast to mammals and functions in a variety of physiological and pathological processes. In this study, we report the first oyster JNK gene homolog (ChJNK) and its biological functions in the Hong Kong oyster Crassostrea hongkongensis. The ChJNK protein consists of 383 amino acids and contains a conserved serine/threonine protein kinase (S_TKc) domain with a typical TPY motif. Phylogenetic analysis revealed that ChJNK shared a close evolutionary relationship with Crassostrea gigas JNK. Quantitative RT-PCR analyses revealed broad expression patterns of ChJNK mRNA in various adult tissues and different embryonic and larval stages of C. hongkongensis. When exposed to Vibrio alginolyticus or Staphylococcus haemolyticus, ChJNK mRNA expression levels were significantly up-regulated in the hemocytes and gills in a time-dependent manner. Additionally, subcellular localization studies that ChJNK is a cytoplasm-localized protein, and that its overexpression could significantly enhance the transcriptional activities of AP-1-Luc in HEK293T cells. In summary, this study provided the first experimental demonstration that oysters possess a functional JNK that participates in host defense against bacterial infection in C. hongkongensis.

PI3K-AKT signaling pathway is involved in hypoxia/thermal-induced immunosuppression of small abalone Haliotis diversicolor

The PI3K-AKT signal pathway has been found to be involved in many important physiological and pathological processes of the innate immune system of vertebrates and invertebrates. In this study, the AKT (HdAKT) and PI3K (HdPI3K) gene of small abalone Haliotis diversicolor were cloned and characterized for the important status of PI3K and AKT protein in PI3K-AKT signaling pathway. The full length cDNAs of HdAKT and HdPI3K are 2126 bp and 6052 bp respectively, encoding proteins of 479 amino acids and 1097 amino acids, respectively. The mRNA expression level of fourteen genes in the PI3K-AKT signaling pathway were detected by quantitative real-time PCR. The results showed that all these fourteen genes were ubiquitously expressed in seven selected tissues. Meanwhile, HdAKT was expressed in haemocytes with the highest expression level (p < 0.05) next in hepatopancreas (p < 0.05). On the other hand, the expression level of HdPI3K in haemocytes was higher than other tissues. Under normal condition, the gene expression level of HdAKT, HdPI3K, and other PI3K-AKT signaling pathway members were significantly up-regulated by Vibrio parahaemolyticus infection which demonstrated that HdAKT, HdPI3K, and other PI3K-AKT signaling pathway members play a role in the innate immune system of abalone. The mRNA expression of these genes in gills, haemocytes and hepatopancreas was significantly down-regulated after the Vibrio parahaemolyticus stimulation with environment stimulation (thermal, hypoxia and thermal & hypoxia). These results indicate that the dual/multiple stresses defeat the immune system and lead to immunosuppression in abalone. PI3K-AKT signaling pathway may be involved in hypoxia/thermal-induced immunosuppression of small abalone Haliotis diversicolor.

TANK-binding kinase-1 broadly affects oyster immune response to bacteria and viruses

As a benthic filter feeder of estuaries, the immune system of oysters provides one of the best models for studying the genetic and molecular basis of the innate immune pathway in marine invertebrates and examining the influence of environmental factors on the immune system. Here, the molecular function of molluscan TANK-binding kinase-1 (TBK1) (which we named CgTBK1) was studied in the Pacific oyster, Crassostrea gigas. Compared with known TBK1 proteins in other model organisms, CgTBK1 contains a conserved S-TKc domain and a coiled coil domain at the N- and C-terminals but lacks an important ubiquitin domain. Quantitative real-time PCR analysis revealed that the expression level of CgTBK1 was ubiquitous in all selected tissues, with highest expression in the gills. CgTBK1 expression was significantly upregulated in response to infections with Vibrio alginolyticus, ostreid herpesvirus 1 (OsHV-1 reference strain and μvar), and polyinosinic:polycytidylic acid sodium salt, suggesting its broad function in immune response. Subcellular localization showed the presence of CgTBK1 in the cytoplasm of HeLa cells, suggesting its potential function as the signal transducer between the receptor and transcription factor. We further demonstrated that CgTBK1 interacted with CgSTING in HEK293T cells, providing evidence that CgTBK1 could be activated by direct binding to CgSTING. In summary, we characterized the TBK1 gene in C. gigas and demonstrated its role in the innate immune response to pathogen infections.

Seafood-Associated Shellfish Allergy: A Comprehensive Review

Shellfish are diverse, serve as main constituents of seafood, and are extensively consumed globally because of their nutritional values. Consequently, increase in reports of IgE-mediated seafood allergy is particularly food associated to shellfish. Seafood-associated shellfish consists of crustaceans (decapods, stomatopods, barnacles, and euphausiids) and molluskans (gastropods, bivalves, and cephalopods) and its products can start from mild local symptoms and lead to severe systemic anaphylactic reactions through ingestion, inhalation, or contact like most other food allergens. Globally, the most commonly causative shellfish are shrimps, crabs, lobsters, clams, oysters, and mussels. The prevalence of shellfish allergy is estimated to be 0.5-2.5% of the general population but higher in coastal Asian countries where shellfish constitute a large proportion of the diet. Diversity in allergens such as tropomyosin, arginine kinase, myosin light chain, and sarcoplasmic binding protein are from crustaceans whereas tropomyosin, paramyosin, troponin, actine, amylase, and hemoyanin are reported from molluskans shellfish. Tropomyosin is the major allergen and is responsible for cross-reactivity between shellfish and other invertebrates, within crustaceans, within molluskans, between crustaceans vs. molluskans as well as between shellfish and fish. Allergenicity diagnosis requires clinical history, in vivo skin prick testing, in vitro quantification of IgE, immunoCAP, and confirmation by oral challenge testing unless the reactions borne by it are life-threatening. This comprehensive review provides the update and new findings in the area of shellfish allergy including demographic, diversity of allergens, allergenicity, their cross-reactivity, and innovative molecular genetics approaches in diagnosing and managing this life-threatening as well as life-long disease.

Ferritin has an important immune function in the ark shell Scapharca broughtonii

Ferritin, the principle cytosolic iron storage protein in the majority of living organisms, has important roles during immune process in invertebrates. Detailed information about ferritin in the ark shell Scapharca broughtonii, however, has been very limited. In this study, full-length ferritin (termed SbFer) was cloned by the rapid amplication of cDNA ends (RACE) method based upon the sequence from the transcriptome library. The cDNA contained a 182 bp 5'-untranslated region, a 519 bp open reading frame encoding a polypeptide of 172 amino acids, a 229 bp 3'-untranslated region, and three introns (902, 373 and 402 bp) embedded in four exons. There was an iron response element (IRE) in the 5'-untranslated region. The deduced amino acid sequence of SbFer possessed many characteristics of vertebrate H type ferritin, shared 63%-91% identity with mollusks and greater identity with vertebrate H type ferritin compared to the L type. The SbFer gene expression pattern examined by quantitative real-time PCR showed ferritin mRNA was expressed in all ark shell tissues examined. The highest levels of expression were found in hemocytes with decreasing levels of expression in foot, mantle, gill, adductor muscle and hepatopancreas. A challenge with Vibrio anguillarum resulted in time-dependent significant upregulation of SbFer mRNA, indicating SbFer participated actively in the bacterial defense process. Further analysis of the antibacterial activity indicated recombinant SbFer could function as an immune antibacterial agent to both Gram-positive and Gram-negative bacteria. Taken together, these results suggested strongly that ferritin of the ark shell is involved in immune defense against microbial infection and it is a constitutive and inducible acute-phase protein.

Transcriptome Analysis Revealed Changes of Multiple Genes Involved in Haliotis discus hannai Innate Immunity during Vibrio parahemolyticus Infection

Abalone (Haliotis discus hannai) is one of the most valuable marine aquatic species in Korea, Japan and China. Tremendous exposure to bacterial infection is common in aquaculture environment, especially by Vibrio sp. infections. It’s therefore necessary and urgent to understand the mechanism of H. discus hannai host defense against Vibrio parahemolyticus infection. However studies on its immune system are hindered by the lack of genomic resources. In the present study, we sequenced the transcriptome of control and bacterial challenged H. discus hannai tissues. Totally, 138 MB of reference transcriptome were obtained from de novo assembly of 34 GB clean bases from ten different libraries and annotated with the biological terms (GO and KEGG). A total of 10,575 transcripts exhibiting the differentially expression at least one pair of comparison and the functional annotations highlight genes related to immune response, cell adhesion, immune regulators, redox molecules and mitochondrial coding genes. Mostly, these groups of genes were dominated in hemocytes compared to other tissues. This work is a prerequisite for the identification of those physiological traits controlling H. discus hannai ability to survive against Vibrio infection.

A thymosin beta-4 is involved in production of hemocytes and immune defense of Hong Kong oyster, Crassostrea hongkongensis

Thymosin beta-4 (Tβ4) is a ubiquitous protein with multiple and diverse intracellular and extracellular functions in vertebrates. In this study, the full-length cDNA of Tβ4 was cloned and identified in Crassostrea hongkongensis, designated as ChTβ4. The full-length cDNA of ChTβ4 consists of 530 bp with an open reading frame of 126 bp encoding a 41 amino acid polypeptide. SMART analysis indicated that there is one thymosin domain and a highly conserved actin-binding motif (18LKKTET23) in ChTβ4. In vivo injection of recombinant ChTβ4 protein could significantly increase total hemocytes count in oysters, and knockdown of the expression of ChTβ4 resulted in a significant decrease in the circulating hemocytes. Tissue distribution analysis revealed a ubiquitous presence of ChTβ4, with the highest expression in hemocytes. The upregulated transcripts of ChTβ4 in response to bacterial challenge and tissue injury suggest that ChTβ4 is involved in both innate immunity against pathogen infection and wound healing. Moreover, bacteria-clearance experiment showed ChTβ4 could facilitate the clearance of injected bacteria in oysters. In vivo injection with ChTβ4 resulted in reduction of the intracellular ROS in hemocytes, which was associated with increased expression of antioxidant enzymes Cu/Zn superoxide dismutase (SOD), Catalase, and Glutathione Peroxidase (GPX) by pre-treatment with ChTβ4. These results suggest that ChTβ4 is a thymosin beta-4 homolog and plays a vital role in the immune defense of C. hongkongensis.

The complexity of apoptotic cell death in mollusks: An update

Apoptosis is a type of programmed cell death that produces changes in cell morphology and in biochemical intracellular processes without inflammatory reactions. The components of the apoptotic pathways are conserved throughout evolution. Caspases are key molecules involved in the transduction of the death signal and are responsible for many of the biochemical and morphological changes associated with apoptosis. Nowadays, It is known that caspases are activated through two major apoptotic pathways (the extrinsic or death receptor pathway and the intrinsic or mitochondrial pathway), but there are also evidences of at least other alternative pathway (the perforin/granzyme pathway). Apoptosis in mollusks seems to be similar in complexity to apoptosis in vertebrates but also has unique features maybe related to their recurrent exposure to environmental changes, pollutants, pathogens and also related to the sedentary nature of some stages in the life cycle of mollusks bivalves and gastropods. As in other animals, apoptotic process is involved in the maintenance of tissue homeostasis and also constitutes an important immune response that can be triggered by a variety of stimuli, including cytokines, hormones, toxic insults, viruses, and protozoan parasites. The main goal of this work is to present the current knowledge of the molecular mechanisms of apoptosis in mollusks and to highlight those steps that need further study.

Involvement of Antizyme Characterized from the Small Abalone Haliotis diversicolor in Gonadal Development

The small abalone Haliotis diversicolor is an economically important mollusk that is widely cultivated in Southern China. Gonad precocity may affect the aquaculture of small abalone. Polyamines, which are small cationic molecules essential for cellular proliferation, may affect gonadal development. Ornithine decarboxylase (ODC) and antizyme (AZ) are essential elements of a feedback circuit that regulates cellular polyamines. This paper presents the molecular cloning and characterization of AZ from small abalone. Sequence analysis showed that the cDNA sequence of H. diversicolor AZ (HdiODCAZ) consisted of two overlapping open reading frames (ORFs) and conformed to the +1 frameshift property of the frame. Thin Layer chromatography (TLC) analysis suggested that the expressed protein encoded by +1 ORF2 was the functional AZ that targets ODC to 26S proteasome degradation. The result demonstrated that the expression level of AZ was higher than that of ODC in the ovary of small abalone. In addition, the expression profiles of ODC and AZ at the different development stages of the ovary indicated that these two genes might be involved in the gonadal development of small abalone.

Perforin-2/Mpeg1 and other pore-forming proteins throughout evolution

Development of the ancient innate immune system required not only a mechanism to recognize foreign organisms from self but also to destroy them. Pore-forming proteins containing the membrane attack complex Perforin domain were one of the first triumphs of an innate immune system needing to eliminate microbes and virally infected cells. Membrane attack complex of complement and Perforin domain proteins is unique from other immune effector molecules in that the mechanism of attack is strictly physical and unspecific. The large water-filled holes created by membrane attack complex of complement and Perforin domain pore formation allow access for additional effectors to complete the destruction of the foreign organism via chemical or enzymatic attack. Perforin-2/macrophage-expressed protein 1 is one of the oldest membrane attack complexes of complement and Perforin domain protein involved in immune defense, and it is still functional today in vertebrates. Here, we trace the impact of Perforin-2/macrophage-expressed protein 1 from the earliest multicellular organisms to modern vertebrates, as well as review the development of other membrane attack complexes of complement and Perforin domain member proteins.

The early stages of the immune response of the European abalone Haliotis tuberculata to a Vibrio harveyi infection

Vibrio harveyi is a marine bacterial pathogen responsible for episodic abalone mortalities in France, Japan and Australia. In the European abalone, V. harveyi invades the circulatory system in a few hours after exposure and is lethal after 2 days of infection. In this study, we investigated the responses of European abalone immune cells over the first 24 h of infection. Results revealed an initial induction of immune gene expression including Rel/NF-kB, Mpeg and Clathrin. It is rapidly followed by a significant immuno-suppression characterized by reduced cellular hemocyte parameters, immune response gene expressions and enzymatic activities. Interestingly, Ferritin was overexpressed after 24 h of infection suggesting that abalone attempt to counter V. harveyi infection using soluble effectors. Immune function alteration was positively correlated with V. harveyi concentration. This study provides the evidence that V. harveyi has a hemolytic activity and an immuno-suppressive effect in the European abalone.

A novel molluscan Fos gene with immune defense function identified in the Hong Kong oyster, Crassostrea hongkongensis

The transcription factor Fos is a member of one of the best-studied AP-1 sub-families and has been implicated in a wide variety of biological processes, including the regulation of apoptosis, immune responses and cytokine production. In this report, a novel mollusk Fos (referred to as ChFos) gene was cloned and characterized from the Hong Kong oyster, Crassostrea hongkongensis. The deduced ChFos protein sequence comprised 333 amino acids and shared significant homology with invertebrate homologs. Phylogenetic analysis revealed that ChFos clusters with Fos from Crassostrea gigas and Crassostrea ariakensis. Quantitative real-time PCR analysis revealed that ChFos mRNA was broadly expressed in all tested tissues and during different stages of the oyster's embryonic and larval development. In addition, the expression of ChFos mRNA was significantly up-regulated under challenge with microorganisms (Vibrio alginolyticus, Staphylococcus haemolyticus and Saccharomyces cerevisiae) and pathogen-associated molecular patterns (PAMPs: LPS, PGN and polyI:C). Moreover, fluorescence microscopy showed that ChFos protein is localized in the nucleus in HEK293T cells. Reporter assays suggested that ChFos may act as an efficient transcription activator in the regulation of AP-1-responsive gene expression through interaction with ChJun. Overall, this study presents the first experimental evidence of the presence and functional characteristics of Fos in mollusks, which reveals its involvement in host protection against immune challenge in the oyster.

The identification of the first molluscan Akirin2 with immune defense function in the Hong Kong oyster Crassostrea hongkongensis

The Akirin protein is a nuclear factor in the innate immune system that is highly conserved from insects to mammals and plays key roles in diverse biological processes, including immunity, myogenesis, development and the cellular stress response. However, the function of Akirins in mollusk, the second most diverse group of animals, is still poorly understood. In this study, we report the discovery of an Akirin2 gene homolog (ChAkirin2) and its biological functions in the Hong Kong oyster Crassostrea hongkongensis. ChAkirin2 is 189 amino acids in length and shares significant homology with invertebrate homologs. Phylogenetic analysis results revealed that ChAkirin2 is clustered with invertebrate Akirin2s. A sequence analysis of the 5' flanking regions of ChAkirin2 indicated that it harbors several potential PAMP-activated transcription factor binding sites (TFB), including sites for NF-κB, C/EBPα, AP-1, SRF, Oct-1 and GATA-1. An RT-PCR analysis showed that ChAkirin2 mRNA was ubiquitously expressed in various tissues and at different embryonic and larval stages. Additionally, upon infection by pathogens (Vibrio alginolyticus, Staphylococcus haemolyticus and Saccharomyces cerevisiae) and pathogen-associated molecular patterns (PAMPs: LPS, PGN and polyI:C), the expression of ChAkirin2 was significantly up-regulated. Moreover, fluorescence microscopy observations show that ChAkirin2 is located in the nuclei of HeLa cells, and the overexpression of ChAkirin2 activated the transcriptional activities of the NF-κB reporter gene in HEK293T cells. Altogether, this report provided the first experimental demonstration that mollusks possess a functional Akirin2 that is involved in the innate defense and embryogenesis processes of the oyster.

Identification and expression analysis of immune-related genes linked to Rel/NF-κB signaling pathway under stresses and bacterial challenge from the small abalone Haliotis diversicolor

Inhibitor of NF-κB (IκB), nuclear factor-κB (NF-κB), and Akirin2 are all important members of Rel/NF-κB signaling pathway, which plays a pivotal role in regulating the innate immune response of vertebrates and invertebrates. In this study, the IκB (SaIκB) and Akirin2 (SaAkirin2) cDNAs of small abalone Haliotis diversicolor were cloned and characterized. The full length cDNA of SaIκB and SaAkirin2 were 1748 bp and 1452 bp respectively, encoding a protein of 401 aa and 187 aa respectively. A conserved degradation motif (DS56GIYS60) and six ankyrin repeats were identified in the SaIκB by SMART analysis. Meanwhile, a typical nuclear localization signal (NLS) was found at the N-terminal region of the SaAkirin2 protein. Also, the mRNA expression level of SaIκB, SaAkirin2, and AbNF-κB were detected by quantitative real-time PCR. The results revealed that all these three genes were ubiquitously expressed in 7 selected tissues. The expression level of SaIκB in gills was higher than that in other tissues (P < 0.05) while the expression level of AbNF-κB was significantly higher in hepatopancreas and haemocytes. The highest expression level of SaAkirin2 was detected in hepatopancreas, followed by mantle. The mRNA expression levels in either gills or haemocytes of SaIκB, SaAkirin2, and AbNF-κB were significantly up-regulated (P < 0.05) post thermal stress, hypoxia exposure, thermal plus hypoxia stress and the injection of Vibrio parahaemolyticus. These results indicated that these three NF-κB signaling pathway-related genes are involved in response to bacterial infection and play essential roles in response to thermal and hypoxia stress.

Calmodulin is a stress and immune response gene in Chinese mitten crab Eriocheir sinensis

Calmodulin (CaM) is a multifunctional calcium sensor protein that participates in various cellular processes under normal, stress and pathological conditions. In crabs, however, the involvement of CaM in response to environmental stress and immune challenges has not been revealed yet. In the present study, a CaM cDNA (EsCaM) was identified from Chinese mitten crab Eriocheir sinensis and its mRNA expression patterns in response to ambient (salinity and pH) stress and immune challenges was examined. EsCaM encodes a 149-amino-acid protein with a calculated molecular mass of 16.8 kDa and an isoelectric point of 4.09. In unstimulated healthy E. sinensis, EsCaM mRNA transcript was detected in all tested tissues with predominant expression in hepatopancreas and the lowest expression in haemocytes. Ambient salinity (15‰ and 30‰ salinities) and pH (pH 6 and 8.5) stress significantly altered EsCaM mRNA expression in gill, hepatopancreas, haemocytes, intestine and muscle in Chinese mitten crab. In addition, EsCaM gene expression was significantly and rapidly induced as early as 2 h after LPS and Poly(I:C) immune stimulations in haemocytes in vitro. Furthermore, EsCaM expression was significantly up-regulated in E. sinensis haemocytes, gill, hepatopancreas, intestine and muscle in response to Edwardsiella tarda and Vibrio anguillarum challenges. Collectively, our findings suggest that EsCaM is an important stress and immune response gene in Chinese mitten crab.

Tissue inhibitor of metalloproteinase gene from pearl oyster Pinctada martensii participates in nacre formation

Tissue inhibitors of metalloproteinases (TIMPs) are nature inhibitors of matrix metalloproteinases and play a vital role in the regulation of extracellular matrix turnover, tissue remodeling and bone formation. In this study, the molecular characterization of TIMP and its potential function in nacre formation was described in pearl oyster Pinctada martensii. The cDNA of TIMP gene in P. martensii (Pm-TIMP) was 901 bp long, containing a 5' untranslated region (UTR) of 51 bp, a 3' UTR of 169 bp, and an open reading fragment (ORF) of 681 bp encoding 226 amino acids with an estimated molecular mass of 23.37 kDa and a theoretical isoelectric point of 5.42; The predicted amino acid sequence had a signal peptide, 13 cysteine residues, a N-terminal domain and a C-terminal domain, similar to that from other species. Amino acid multiple alignment showed Pm-TIMP had the highest (41%) identity to that from Crassostrea gigas. Tissue expression analysis indicated Pm-TIMP was highly expressed in nacre formation related-tissues, including mantle and pearl sac. After decreasing Pm-TIMP gene expression by RNA interference (RNAi) technology in the mantle pallium, the inner nacreous layer of the shells showed a disordered growth. These results indicated that the obtained Pm-TIMP in this study participated in nacre formation.

Identification and functional characterization of a novel ferritin subunit from the tropical sea cucumber, Stichopus monotuberculatus

Ferritin is one of the major non-harm iron storage proteins that found in most cell types of animals, plants and microorganisms. In this study, a ferritin subunit named StmFer was identified from the sea cucumber (Stichopus monotuberculatus) and characterized functionally. The full-length cDNA of StmFer is 1184 bp in size with a 5'-untranslated region (UTR) of 131 bp, a 3'-UTR of 531 bp and an open reading frame of 522 bp that encoding a protein of 173 amino acids with a deduced molecular weight of 19.95 kDa. StmFer possesses both the ferroxidase center of vertebrate ferritin heavy subunit and iron nucleation sites of vertebrate ferritin light subunit. For the gene structure, StmFer contains only three exons separated by two introns. Higher levels of mRNA expression were noticed in intestine and coelomocyte of S. monotuberculatus by northern blot analysis. In in vitro experiments performed in coelomocytes, transcriptional expression of StmFer showed the strongest response to polyriboinosinic polyribocytidylic acid [Poly (I:C)] (9.08 fold up-regulation), followed by lipopolysaccharides (LPS), ferrous chloride (FeCl2) and inactivated bacteria (Vibrio alginolyticus) (7.84, 7.41 and 4.90 fold up-regulation, respectively) after 3 h post-challenge. In addition, the anti-oxidation activity and iron binding capacity of recombinant ferritin protein were demonstrated in this study. As a whole, our study suggested that the ferritin from sea cucumber may play critical roles not only in the cellular and organismic iron homeostasis, but also in the innate immune defense.

Molecular cloning, characterization and expression analysis of three heat shock responsive genes from Haliotis diversicolor

In this study, molecular characterization and expression of three heat shock responsive genes were analyzed as indicators to understand the mechanism of heat shock response of small abalone Haliotis diversicolor under stresses. The full length cDNA of heat shock transcriptional factor 1 (HdHSF1), heat shock factor binding protein 1(HSBP1), and heat shock protein 90 (HdHSP90) are 1548 bp, 809 bp, and 2592 bp respectively, encoding a protein of 515 aa, 75 aa, and 728 aa respectively. Real time quantitative PCR analysis revealed that these three genes are constitutively expressed in 7 selected tissues. The expression level of HdHSF1 in gills was higher than that in other tissues (p < 0.05). The highest expression level of HdHSBP1 was detected in hemocytes. The highest expression level of HdHSP90 was in the digestive tract and colleterial gland. The HdHSF1 expression level in the gills was up-regulated significantly (p < 0.05) after thermal stress and hypoxia exposure respectively. On the contrary, HdHSBP1 was down-regulated both in gills and hemocytes after thermal stress and the same as in gills after hypoxia stress. HdHSP90 expression level was also up-regulated in gills and hemocytes after both thermal and hypoxia stresses. These results indicated that these three heat shock responsive genes play important roles in response to thermal and hypoxia stress.

Activator protein-1 (AP-1) and response to pathogen infection in the Hong Kong oyster (Crassostrea hongkongensis)

Growing evidence suggests that the transcription factor activator protein-1 (AP-1), a downstream target of mitogen-activated protein kinase (MAPK) signaling, plays a major role in stimulating the synthesis of immune effector molecules during innate immune responses. We have characterized ChAP-1, an AP-1-like protein in Crassostrea hongkongensis that is a member of the AP-1 family of proteins. ChAP-1 is composed of 290 amino acid residues with a Jun and bZIP domain at the N- and C-termini, respectively, a structure similar to that of known Ap-1 proteins. ChAP-1 mRNA is expressed in several tissues analyzed, with highest expression in the mantle. Expression of ChAP-1 increases in response to Vibrio alginolyticus, Salmo haemolyticus or Salmo cerevisiae infection and, despite the location of GFP-tagged full-length ChAP-1 protein in the cytoplasm, ChAP-1 activates the transcription of an L8G5-luc reporter gene, and its over-expression can also activate the AP-1-Luc reporter gene in HEK293T cells.

The impacts of handling and air exposure on immune parameters, gene expression, and susceptibility to vibriosis of European abalone Haliotis tuberculata

Wild or farmed abalone are regularly exposed to stressors, such as air exposure and handling. Immune and transcriptional responses as well as susceptibility to vibriosis of sexually mature or immature European abalone acclimated at 16 or 19 °C were determined following handling or air exposure. Hemocyte density and H2O2 production increased while hemocyte viability and phagocytic index decreased following handling. Air exposure induces a decrease of hemocyte density and phagocytic index. Measurement of the expression of genes implicated in general metabolic, immunological and stress responses in gills, foot-muscle and hemocytes by real time q-PCR suggested that both stressors lead to a metabolic rate depression, characterized by a general inhibition of transcription. Finally, following handling a Vibrio harveyi challenge enhances almost 100% mortality of sexually immature animals at 19 °C while it has been previously demonstrated that only mature are susceptible to vibriosis.

A novel ortholog of serum response factor (SRF) with immune defense function identified in Crassostrea hongkongensis

Serum response factor (SRF) function is essential for transcriptional regulation of numerous growth-factor-inducible genes and triggers proliferation, differentiation and apoptosis of the cells. In this report, the first mollusk serum response factor like homolog gene (designated ChSRF) was identified and characterized from the Hong Kong oyster, Crassostrea hongkongensis. The full-length cDNA of ChSRF was 1716 bp in length and encodes a putative protein of 434 amino acids respectively, and shares the MADS domain at the N-terminal. ChSRF is ubiquitously expressed in various tissues, with the highest expression level observed in muscle. Temporal expression of ChSRF following microbe infection shows that the expression of ChSRF in hemocytes increases from 3 to 24 h post-challenge. As a target gene of SRF, β-actin demonstrates a similar gene expression mode in constitutive tissue and pathogen infection. Furthermore, some protein profiles of ChSRF was revealed, fluorescence microscopy results show that ChSRF located in the nuclei of HeLa cells and over-expression of ChSRF activated the transcriptional activities of MAPK signal pathway in HEK293T cells. These results indicate that ChSRF maybe play an important role in signal transduction in the immunity and development response of oysters. Furthermore, we found that ChSRF could regulate the expression of β-actin gene, which indicate that ChSRF is a muscle differentiation regulator in the oyster and it will help us to improve aquaculture production.

Distribution of MACPF/CDC proteins

Membrane Attack Complex/Perforin (MACPF) and Cholesterol-Dependent Cytolysins (CDC) form the MACPF/CDC superfamily of important effector proteins widespread in nature. MACPFs and CDCs were discovered separately with no sequence similarity at that stage being apparent between the two protein families such that they were not, until recently, considered evolutionary related. The breakthrough showing they are came with recent structural work that also shed light on the molecular mechanism of action of various MACPF proteins. Similarity in structural properties and conserved functional features indicate that both protein families have the same evolutionary origin. We will describe the distribution of MACPF/CDC proteins in nature and discuss briefly their similarity and functional role in different biological processes.