Proteomic identification of differentially expressed proteins in sea cucumber Apostichopus japonicus coelomocytes after Vibrio splendidus infection

Comparative proteomic analysis of the protein profile in the cuttlefish Sepia pharaonis associated with skin ulceration syndrome

Skin ulceration syndrome (SUS) is becoming a severe problem in the breeding and culturing process of the cuttlefish Sepia pharaonis. However, limited knowledge is available about the occurrence of this devastating disease. In this study, proteomic analysis was used to identify the differentially expressed proteins (DEPs) and the biological pathways enriched in SUS-diseased S. pharaonis. Both the healthy group and diseased group were analyzed in triplicate, with 4 cuttlefish in each replicate. The results showed that 85 DEPs were identified between the two groups, including 36 upregulated proteins and 49 downregulated proteins in the diseased group compared to the healthy group. GO enrichment analysis revealed that the DEPs were mainly enriched in cellular component organization or biogenesis, nucleus and ion binding processes. The results of the KEGG pathway analysis indicated that extracellular matrix (ECM)-receptor interaction was the most enriched upregulated pathway. Real-time reverse transcriptase PCR was used to identify the expression of two differentially expressed matrix metalloproteinases (MMPs), and the results showed that the mRNA expression of MMP14 and MMP19 was significantly upregulated in the skin tissue of the diseased group. Furthermore, the protease activity of the diseased group was higher than that of the healthy group. Our results offer basic knowledge on the changes in protein profiles during the occurrence of SUS in the cuttlefish S. pharaonis.

Proteomic map of the differentially expressed proteins in the skin of Ctenopharyngodon idella against Aeromonas hydrophila infection

The skin mucus of fish is an important part of the innate immune system, which is poorly understood at the proteomic level. The study established a complete map of the proteins in the skin mucus of Ctenopharangdon idella (C. idella) and discussed the Differentially Expressed Proteins (DEPs) after Aeromonas hydrophila (A. hydrophila) infection. Using Label Free Liquid Chromatography-Mass Spectrometry (LC-MS/MS) analysis, a total of 126 proteins were identified as differentially expressed, 89 proteins of which were upregulated, and 37 proteins were downregulated. Functional annotations of DEPs showed that the upregulated proteins in the skin mucus of the treated group were mostly associated with complement system and cytoskeleton proteins, whereas downregulated proteins were associated with metabolism. The key upregulated immune proteins were transferrin variant C, lysozyme g, annexin A11, 26S proteasome non-ATPase regulatory subunit 8, hypothetical protein ROHU_000884, 60S ribosomal L7a, calpain-2 catalytic subunit-like protein, calpain-9-like protein, complement component C9, complement C3, cathepsin S, cathepsin Z, 14 kDa apolipo, heat shock protein and intelectin, whereas, leukocyte elastase inhibitor, annexin A11, C-factor-like protein, biotinidase isoform X1 and epidermal growth factor receptor substrate 15-like were the downregulated proteins. Moreover, we for the first-time report proteins such as coactosin, lamin-B2 and kelch 12, which were never reported in fish. Our study directly pointing out the possible immunological biomarkers in the skin mucus of C. idella after A. hydrophila treatment. Each of the protein we report in this study could be used as base to establish their mechanism of action during bacterial infection that may contribute to the strategies against bacterial prevention and control in fishes.

Evolution of mitogen-activated protein kinase family and their immune function in Apostichopus japonicus

The mitogen-activated protein kinase family plays an important role in cell differentiation, growth, proliferation, and survival. However, the current research on the mitogen-activated protein kinase (MAPK) family in invertebrates is limited to the individual gene, and the analysis has not been conducted at the family level. In the present study, echinoderm MAPK family was identified by genomic screening, and five members, including three ERK subfamily members, one c-Jun N-terminal kinase (JNK) subfamily, and one p38-MAPK member were detected. Phylogenetic analysis showed that three MAPK subfamilies were separated into three separated clusters, and ERK subfamily appeared earlier than the other two subfamilies. Synteny analysis revealed that the p38 subfamily might be derived from the continuous gene duplication events of MAPK14 subfamily in invertebrates, which displayed genome expansion via gene duplication in vertebrates. The role of MAPK family in echinoderm immune defense was determined by investigating the expression profiles of MAPKs in Vibrio splendidus-challenged Apostichopus japonicus and LPS-exposed coelomocytes. The result showed that five MAPK members displayed induced expression profiles both in vitro and in vivo, and the peak expression was detected at different time points. Our study provides new insights into the evolutionary history of the MAPK family and show the similar immune function among MAPK members.

Comparative analysis for immune response of coelomic fluid from coelom and polian vesicle in Apostichopus japonicus to Vibrio splendidus infection

The polian vesicle and coelom of sea cucumber Apostichopus japonicus were full of coelomic fluid in which many types of coelomocytes with different functions were suspended. Our previous work has indicated the differences of coelomocytes between two sites mainly in subtype proportion, non-specific immune enzymes activities and several immune-related genes expression levels in healthy A. japonicus. However, the functional similarities and differences of coelomic fluid in two sites including the coelom and polian vesicle after pathogenic infection still remain unclear. Here, we investigated the changes of the total coelomocyte density (TCD) and differential coelomocyte density (DCD) after pathogen infection by Vibrio splendidus in coelom and polian vesicle. After infected by V. splendidus, the TCD in the coelom and polian vesicle rapidly declined at 12 h, and then the TCD in the coelom showed a stably ascending trend, while the TCD in the polian vesicle reached a peak at 24 h post infection (hpi), and then showed a continuously decline trend from 24 hpi to 72 hpi followed by a slow elevation until recovering the normal level from 72 hpi to 96 hpi. Then the activities of acidic phosphatase (ACP), alkaline phosphatase (AKP), catalase (CAT) and superoxide dismutase (SOD) were determined to evaluate the response of cell-free coelomic fluid to V. splendidus infection. The activities of ACP, AKP and CAT showed similar trends in the coelom and polian vesicle. The SOD activity significantly increased in the polian vesicle, whereas it exhibited a decreasing trend in the coelom. Finally, the expression profiles of nine immune-related genes including Aj-MyD88, Aj-IRAK4, Aj-i-Lys, Aj-Rel, Aj-p50, Aj-DMBT1, Aj-CDC, Aj-Rrp15 and Aj-Fibrinogen C were detected after V. splendidus challenge. The results suggested all the detected genes were significantly up-regulated both in the coelom and polian vesicle, and the expression levels of these genes in two sites shared similar trends except Aj-MyD88 and Aj-DMBT1. This research provides a new insight into the differentially immune roles of coelomic fluid and coelomocytes in polian vesicle and coelom response to bacterial infections and supplements comprehensive resources for better understanding the innate immune response of A. japonicus.

More than a simple epithelial layer: multifunctional role of echinoderm coelomic epithelium

In echinoderms, the coelomic epithelium (CE) is reportedly the source of new circulating cells (coelomocytes) as well as the provider of molecular factors such as immunity-related molecules. However, its overall functions have been scarcely studied in detail. In this work, we used an integrated approach based on both microscopy (light and electron) and proteomic analyses to investigate the arm CE in the starfish Marthasterias glacialis during different physiological conditions (i.e., non-regenerating and/or regenerating). Our results show that CE cells share both ultrastructural and proteomic features with circulating coelomocytes (echinoderm immune cells). Additionally, microscopy and proteomic analyses indicate that CE cells are actively involved in protein synthesis and processing, and membrane trafficking processes such as phagocytosis (particularly of myocytes) and massive secretion phenomena. The latter might provide molecules (e.g., immune factors) and fluids for proper arm growth/regrowth. No stem cell marker was identified and no pre-existing stem cell was observed within the CE. Rather, during regeneration, CE cells undergo dedifferentiation and epithelial-mesenchymal transition to deliver progenitor cells for tissue replacement. Overall, our work underlines that echinoderm CE is not a "simple epithelial lining" and that instead it plays multiple functions which span from immunity-related roles as well as being a source of regeneration-competent cells for arm growth/regrowth.

Proteomics reveals gender differences in physiological characteristics of the gonads and tube feet of the sea cucumber, Apostichopus japonicus

The sea cucumber Apostichopus japonicus is an important aquaculture species in China because of its high nutritional and medicinal values. Gender, as a factor affecting the physiology of organisms, is always considered when improving the breeding efficiency of economically important animals. In the present study, protein expression profiles of the gonads and tube feet of male and female A. japonicus were investigated using a comparative proteomics approach. A set of 7499 proteins were identified, which covered a broad range of functions based on function annotations. A significant difference in protein expression profiles was observed between the gonads and tube feet of A. japonicus; gonads showed more apparent gender differences than tube feet. Moreover, the findings revealed that male A. japonicus had more specific functions and most of these functions were associated with energy consumption. Further analyses suggested that the regulation of ERK activity and the capacity of tyrosine production and virus immunity might be more powerful in male and female A. japonicus, respectively. Some candidate proteins were also recognized as potential targets for gender identification of A. japonicus. Overall, our study provides new insights into the understanding of molecular mechanisms underlying gender-based physiological differences in A. japonicus. SIGNIFICANCE: The current study aimed to reveal gender differences in the physiological characteristics of gonads and tube feet of the sea cucumber A. japonicus. To the best of our knowledge, this is the first proteomics study to analyze the differences in the protein expression profiles of external organs between male and female A. japonicus. The analysis revealed gender differences in the protein expression profiles of both gonads and tube feet of A. japonicus, and the gender differences in gonads were quite apparent. Moreover, according to the recognition of differentially expressed proteins and the enrichment analyses based on Kyoto Encyclopedia of Genes and Genomes, a draft view of how the physiological functions of A. japonicus were affected by gender was obtained. Male A. japonicus could have more specific functions related to energy consumption than females. The regulation of ERK activity and virus immunity might be more robust in male and female A. japonicus, respectively. Some candidate proteins were also recognized as potential targets for gender identification of A. japonicus. The findings presented here will improve the understanding of researchers about the molecular mechanisms underlying gender-based differences in A. japonicus and contribute to the meticulous breeding of A. japonicus.

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

Fibrinogen-related proteins (FREPs) play important roles in innate immunity by recognizing pathogen associated molecular patterns on pathogenic bacteria surfaces via conserved fibrinogen-like domain (FBG). In this paper, the full-length cDNA of Apostichopus japonicus FREP (designated as AjFREP) was cloned combined with rapid amplification of cDNA ends (RACE) and transcriptome sequencing. The full-length cDNA of AjFREP was of 2110 bp with an open reading frame (ORF) of 1659 bp. SMART analysis revealed that the AjFREP contained a typical signal peptide of 19 amino acid residues, a FBG and two unusual epidermal growth factor-like domains (EGFs). Multiple sequence alignments suggested that FBG domain shared a remarkably high structural conservation in polypeptide binding site and Ca²⁺ binding site. Tissue distribution analysis revealed that AjFREP was constitutively expressed in all examined tissues with the largest magnitude in coelomocytes, indicating AjFREP might play an important role in immune defense. The mRNA level of AjFREP in coelomocytes was sharply up-regulated by Vibrio splendidus challenge, and reached its peak expression at 48 h. Knock-down AjFREP by specific siRNA could significantly repress the coelomocyte phagocytosis rate. Meantime, the survival number of V. splendidus in the coelomic fluid was promoted. All these current results indicated that AjFREP might be involved in pathogen clearance through mediating coelomocytes phagocytosis activity.

A novel p38 MAPK gene in the sea cucumber Apostichopus japonicus (Ajp38) is associated with the immune response to pathogenic challenge

The p38 mitogen-activated protein kinase (MAPK), an important component of the MAPK signal cascade, is activated by extracellular stimuli, such as environmental stress and pathogenic infection. To clarify the function of p38 MAPKs in echinoderms, we used transcriptome database mining and rapid amplification of cDNA ends (RACE) to identify a novel p38 MAPK gene in the sea cucumber Apostichopus japonicus (here designated Ajp38). The full-length cDNA of Ajp38 was 2231 bp, including an open reading frame encoding 356 amino acid residues. Our sequence analysis indicated that the predicted Ajp38 protein contained the dual phosphorylation site Thr-Gly-Tyr (TGY) and was similar to the p38 homolog in sea urchins. Quantitative real-time PCR analysis showed that Ajp38 was ubiquitously expressed in all examined tissues of healthy adult A. japonicus, with the highest level of expression identified in the coelomocytes. Ajp38 mRNA expression was significantly upregulated in the coelomocytes 4, 12, and 72 h post in vivo infection with Vibrio splendidus. Our results provide more information about the characteristics and immune functions of the p38 homolog in sea cucumbers.

Development of homologous enzyme-linked immunosorbent assays to quantify two forms of vitellogenin in guppy (Poecilia reticulata)

Guppy (Poecilia reticulata) is a promising model organism in toxicological studies, and vitellogenin (Vtg) is a commonly used biomarker for environmental estrogens. Although an ELISA for guppy Vtg has been developed previously, we found that guppy had two forms of Vtgs. In this study, two Vtgs were characterized and enzyme-linked immunosorbent assays (ELISAs) for each Vtg were developed. Two Vtgs purified from 17β-estradiol (E₂)-exposed guppy were characterized as phospholipoglycoproteins with molecular weights of ~ 520 and ~ 480 kDa, respectively. In SDS-PAGE, one purified Vtg appeared as three major bands of ~ 210, ~ 126, and ~ 102 kDa, and the other revealed a clear band of ~ 68 kDa. Matrix-assisted laser desorption/ionization-time of flight/time of flight mass spectrometry analysis showed that they were VtgAb and VtgC. Using purified Vtgs and their corresponding antibodies, two sandwich ELISAs with working ranges of 7.8~1000 and 15.6~500 ng/mL were developed. Precision tests showed that intra- and inter-assay coefficients of variations of both ELISAs were below 10%. Parallelism between Vtg standard curves and serial dilutions of whole body homogenate from E₂-exposed guppy confirmed that two ELISAs could quantify guppy Vtgs. Furthermore, two ELISAs were used to measure Vtg inductions in liver, caudal fin and whole body of male guppy exposed to 17a-ethinylestradiol to validate their use for detecting estrogenic effects of exogenous chemicals. These homologous Vtg ELISAs will promote the use of guppy as a model organism to study estrogenic chemicals.

RNA-seq based transcriptional analysis reveals dynamic genes expression profiles and immune-associated regulation under heat stress in Apostichopus japonicus

In this study, we explored the gene expression profiles in Apostichopus japonicus under continuous heat stress (6 h, 48 h and 192 h) by applying RNA-seq technique. A total of 676, 1010 and 1083 differentially expressed genes were detected at three heat stress groups respectively, which suggested complex regulation of various biological processes. Then we focused on the changing of immune system under HS in sea cucumbers. Key immune-associated genes were involved in heat stress response, which were classified into six groups: heat shock proteins, transferrin superfamily members, effector genes, proteases, complement system, and pattern recognition receptors and signaling. Moreover, the mRNA expression of the immune-associated genes were validated by the real time PCR. Our results showed that an immunological strategy in this species was developed to confront abrupt elevated temperatures in the environment.

Characterization and expression analysis of a thioredoxin-like protein gene in the sea cucumber Apostichopus japonicus

As the most important disulfide bond reducates of intracellular oxidordeuctase, thioredoxin (TRX) plays a crucial role in maintaining reducing state of intracellular proteins to normally perform their function. In this study, a cDNA of TRX-like protein gene from Apostichopus japonicus (denoted as AjTRX) was cloned and characterized. The full-length cDNA of AjTRXwas of 1870 bp, consisting of a 5'-UTR of 101 bp, a long 3'-UTR of 887 bp and a 882 bp open reading frame (ORF) encoding a 293 amino acids. The predicted molecular mass and the theoretical PI of the deduced amino acids of AjTRX were 32.3 kDa and 5.52, respectively. Phylogenetic trees showed that AjTRX had a closer evolution relationship with TRX from Strongylocentrotus purpuratus. AjTRX was found to be ubiquitously expressed in all examined tissues including longitudinal muscle, coelomocytes, tube feet, intestine, respiratory tree and body wall indicating a general role in physiological processes. Temporal expression pattern of AjTRX in coelomocytes showed that AjTRX reached two peak expression levels at 8 h and 48 h after Vibrio splendidus challenge with a 8.6 and 9.3-fold increase compared to their control groups, respectively. The recombinant AjTRX protein (rAjTRX) displayed obvious antioxidant activity in a dose-dependent manner, and the higher reducing activity was detected in 20 μM experimental group. All these results strongly suggested that AjTRX could play an important role as an antioxidant in a physiological context, and might be involved in the process of bacterial challenge.

Juvenile zebrafish in the vitellogenin blank period as an alternative test organism for evaluation of estrogenic activity of chemicals

The present study aimed to determine the suitable development period for zebrafish to evaluate estrogenic activities accurately. An enzyme-linked immunosorbent assay was developed and used to detect the vitellogenin (Vtg)-derived yolk proteins and newly produced Vtg, and 9 d to 56 d posthatching was determined as the Vtg-blank period. Juveniles in this period were found to have lower baseline Vtg levels than adult males and were considered an alternative test organism for detecting environmental estrogens. Environ Toxicol Chem 2016;35:1783-1787. © 2015 SETAC.

Expression analysis of microRNAs related to the skin ulceration syndrome of sea cucumber Apostichopus japonicus

MicroRNAs (miRNAs) are small non-coding RNAs that are involved in many biological processes. To investigate the miRNAs related to skin ulceration syndrome (SUS) of Apostichopus japonicus, small RNA libraries of body wall, intestine, respiratory tree and coelomocytes from healthy and diseased A. japonicus were sequenced on Illumina Hiseq 2000 platform. A total of 247 conserved and 10 novel miRNAs were identified across all libraries. After pair-wise comparisons, 215 miRNAs in body wall, 36 in intestine, 2 in respiratory tree and 38 in coelomocytes showed significant expression differences. Further analyses were conducted on some tissue-specific differentially expressed miRNAs: miR-8 and miR-486-5p in body wall, miR-200-3p, let-7-5p and miR-125 in intestine, miR-278a-3p and bantam in respiratory, miR-10a and miR-184 in coelomocytes. Notably, these miRNAs in some species were reported to function in various physiological or pathological processes associated with immune regulations. Using stem-loop quantitative real time PCR, six representative miRNAs in four tissues were selected to validate the sequencing results. The Pearson's correlation coefficient (R) of the six miRNAs ranged from 0.777 to 0.948, which confirmed the consistency and accuracy between these two approaches. This study provides comprehensive expression and regulation patterns of functional miRNAs in different tissues and gives insights into the tissue-specific immune response mechanisms in SUS-infected A. japonicus.

Cathepsin L of the sea cucumber Apostichopus japonicus-molecular characterization and transcriptional response to Vibrio splendidus infection

Cathepsin L, a lysosomal endopeptidase, has been noted for its involvement in the innate immune response in invertebrates. Here, the cathepsin L cDNA of the sea cucumber Apostichopus japonicus (AjCatL) is identified from an EST library and then cloned by the rapid amplification of the cDNA ends (RACE) PCR. The full-length cDNA is 1678 bp long containing an open reading frame (ORF) of 1002 bp, an 80 bp 5' UTR and a 599 bp 3' UTR. The cDNA encodes 333 amino acid residues with a predicted molecular mass of 37.07 kDa and a theoretical isoelectric point (pI) of 5.01. The full-length AjCatL contains three active sites of eukaryotic thiol (cysteine) protease at positions 133-144, 278-288 and 295-314. Analysis of the predicted tertiary structure of prepro-CatL (17-333 aa) and mature-CatL (116-333 aa) reveals that the propeptide region (17-115 aa) blocks access to the substrate-binding cleft. Phylogenetic analysis shows that the AjCatL is clustered together with two other CatLs from Strongylocentrotus purpuratus. The enzymatic activity of AjCatL was verified using a substrate hydrolyzing assay with recombinant mAjCatL. Further analysis of real time-PCR demonstrates that the expression of AjCatL mRNA is significantly up-regulated in the coelomocytes in cases of infection with the common bacterial pathogen, Vibrio splendidus. This suggests that the AjCatL is likely to be involved in the immune response.

Protective effects of chicken egg yolk antibody (IgY) against experimental Vibrio splendidus infection in the sea cucumber (Apostichopus japonicus)

Vibrio splendidus is one of the most harmful pathogens associated with skin ulceration syndrome in the sea cucumber (Apostichopus japonicus) due to its high virulence and frequency of appearance. The objective of this study was to determine the effectiveness of chicken egg yolk antibody (IgY) against V. splendidus infection in the sea cucumber. Whole V. splendidus cells were used as an immunogen to immunize 20 White Leghorn hens (25 weeks old). IgY was produced from egg yolks obtained from these immunized hens using water dilution, two-step salt precipitation and ultrafiltration. The purity of the IgY produced was approximately 83%. Enzyme-linked Immunosorbent Assay indicated a high specificity for IgY with a maximum antibody titer of 320,000. The growth of V. splendidus in liquid medium was significantly inhibited by IgY in a dose-dependent manner at concentrations ranging from 1 to 10 mg/mL. The protective effects of IgY were evaluated in sea cucumber by intraperitoneally injecting anti-V. splendidus IgY antibodies (10 mg/mL) or immersing the sea cucumber in aqueous IgY (1 g/L) after an intraperitoneal injection of V. splendidus. Intraperitoneal injection resulted in an 80% survival while immersion resulted in a 75% survival during the 11-day experimental period. The survival rates were significantly higher than the positive control and the non-specific IgY group (P < 0.05). As well, the bacterial burden in the respiratory tree, intestine and coelomic liquid was significantly (P < 0.05) lower in sea cucumber treated with specific IgY than those treated with non-specific IgY. The phagocytosis of coelomocytes for V. splendidus in the presence of specific IgY was significantly (P < 0.05) higher than that obtained with non-specific IgY or without IgY, suggesting that specific IgY enhanced phagocytic activity. The current work suggests that specific IgY has potential for protecting sea cucumbers against V. splendidus infection.

Cytoprotective Effects of Lysophospholipids from Sea Cucumber Holothuria atra

Lysophospholipids are important signaling molecules in animals and metazoan cells. They are widely distributed among marine invertebrates, where their physiological roles are unknown. Sea cucumbers produce unique lysophospholipids. In this study, two lysophospholipids were detected in Holothuria atra for the first time, lyso-platelet activating factor and lysophosphatidylcholine, with nuclear magnetic resonance and liquid chromatography-time-of-flight mass spectrometric analyses. The lipid fraction of H. atra contained lyso-platelet activating factor and lysophosphatidylcholine, and inhibited H2O2-induced apoptosis in the macrophage cell line J774A.1. The antioxidant activity of the lysophospholipid-containing lipid fraction of H. atra was confirmed with the oxygen radical absorbance capacity method. Our results suggest that the lysophospholipids from H. atra are potential therapeutic agents for the inflammation induced by oxidative stress.

Transcriptome Analysis and Discovery of Genes Involved in Immune Pathways from Coelomocytes of Sea Cucumber (Apostichopus japonicus) after Vibrio splendidus Challenge

Vibrio splendidus is identified as one of the major pathogenic factors for the skin ulceration syndrome in sea cucumber (Apostichopus japonicus), which has vastly limited the development of the sea cucumber culture industry. In order to screen the immune genes involving Vibrio splendidus challenge in sea cucumber and explore the molecular mechanism of this process, the related transcriptome and gene expression profiling of resistant and susceptible biotypes of sea cucumber with Vibrio splendidus challenge were collected for analysis. A total of 319,455,942 trimmed reads were obtained, which were assembled into 186,658 contigs. After that, 89,891 representative contigs (without isoform) were clustered. The analysis of the gene expression profiling identified 358 differentially expression genes (DEGs) in the bacterial-resistant group, and 102 DEGs in the bacterial-susceptible group, compared with that in control group. According to the reported references and annotation information from BLAST, GO and KEGG, 30 putative bacterial-resistant genes and 19 putative bacterial-susceptible genes were identified from DEGs. The qRT-PCR results were consistent with the RNA-Seq results. Furthermore, many DGEs were involved in immune signaling related pathways, such as Endocytosis, Lysosome, MAPK, Chemokine and the ERBB signaling pathway.

Molecular characterization of two novel molecular chaperones in bacterial-challenged Apostichopus japonicus

Molecular chaperones of 78 kDa glucose-regulated protein (GRP78) and protein disulfide isomerase (PDI) are involved in protein folding and assembly in the endoplasmic reticulum (ER). Increasing evidences also suggest that these two molecules play an important role in immune response. In the present study, we cloned and characterized GRP78 and PDI genes from Apostichopus japonicus by RNA-seq and RACE approaches (designated as AjGRP78 and AjPDI, respectively). The AjGRP78 cDNA was of 2355bp including an open reading frame (ORF) of 2013 bp encoding a protein of 670 amino acids with three heat shock protein 70 (HSP70) family signatures. AjGRP78 contained a 23-amino acid signal peptide at the N-terminus and a HDEL motif at the C-terminus, which supported the location of the protein in the ER. The full length cDNA of AjPDI was of 1893 bp with a 5' untranslated region (UTR) of 153 bp, a 3' UTR of 228 bp and an ORF of 1512 bp encoding a protein of 503 amino acids. A 17-amino acid signal peptide, two thioredoxin domains with two active sites of CGHC, and KDEL retention signal were totally conserved in the deduced amino acid of AjPDI. Phylogenic analysis and multiple alignments have shown that both genes shared remarkably higher degree of structural conservation and sequence identities with other counterparts from invertebrates and vertebrates, further supporting that the two proteins were novel members of molecular chaperone family. Spatial expression analysis revealed that AjGRP78 mRNA transcripts were dominantly expressed in the tentacle, while AjPDI mRNA levels were abundant in the muscle, intestine and respiratory trees. For Vibrio splendidus challenged sea cucumber, the peak expression of AjGRP78 and AjPDI mRNAs in coelomocytes were detected at 24h with 1.73-fold increase and at 6h with 1.83-fold increase compared with the control group, respectively. Similarly, a significant increase in the relative mRNA levels of AjGRP78 and AjPDI was also identified in 1 μg mL(-1) LPS exposed primary cultured coelomocytes. These results collectively suggested that AjGRP78 and AjPDI were ER chaperones of A. japonicus, of which expression is induced upon bacterial infection.

A review of the immune molecules in the sea cucumber

It is very important to identify and characterize the immune-related genes that respond to pathogens. Until recently, only some of the immune-related genes in sea cucumbers had been characterized. Their expression patterns after pathogen challenges have been analyzed via expressed sequence tag libraries, microarray studies and proteomic approaches. These genes include lectins, antimicrobial peptides, lysozyme, enzymes, clotting protein, pattern recognition proteins, Toll receptors, complement C3 and other humoral factors that might participate in the innate immune system of sea cucumbers. Although the participation of some of these immune molecules in the sea cucumber's innate immune defense against invading pathogens has been demonstrated, the functions of many of the molecules remain unclear. This review focuses on the discovery and functional characterization of the immune-related molecules from the sea cucumber for the first time and provides new insights into the immune mechanisms of the sea cucumber, which opens new possibilities for developing drugs for novel anti-bacterial and antiviral applications in fisheries.