Molecular cloning and characterization of a putative mitogen-activated protein kinase (Erk1/2) gene: Involvement in mantle immunity of Pinctada fucata

The impact of ascidian biofouling on the farmed Mediterranean mussel Mytilus galloprovincialis physiology and welfare, revealed by stress biomarkers

In biofouling communities, ascidians are among the most damaging species, presenting severe threats, such as depressed growth rates and decreased chances of lower survival, to shellfish aquaculture. However, little is known concerning the fouled shellfish physiology. In an effort to obtain information for the magnitude of stress caused by ascidians to farmed Mytilus galloprovincialis, five seasonal samplings took place in a mussel aquaculture farm suffering from ascidian biofoulants, in Vistonicos Bay, Greece. The dominant ascidian species were recorded and several stress biomarkers, including Hsp gene expression at both mRNA and protein levels, as well as MAPKs levels, and enzymatic activities of intermediate metabolism were examined. Almost all investigated biomarkers revealed elevated stress levels in fouled mussels compared to non-fouled. This enhanced physiological stress seems to be season-independent and can be attributed to the oxidative stress and/or feed deprivation caused by ascidian biofouling, thus illuminating the biological impact of this phenomenon.

Genome-wide identification and immune response analysis of serine protease inhibitor genes in the blood clam Tegillarca granosa

Serine protease inhibitors (SPIs) are the main regulators of serine protease activities. In this study, we present a genome-wide identification of SPI genes in T. granosa（TgSPI genes）and their expression characteristics in respond to Vibrio stress. A total of 102 TgSPI genes belonging to eight families, including Serpin, TIL (trypsin inhibitor like cysteine rich domain), Kunitz, Kazal, I84, Pacifastin, WAP (whey acidic protein) and A2M (Alpha-2-macroglobulin) were identified, while no genes belonging to Bowman-Birk, amfpi and Antistasin families were identified. The Kazal family has the most TgSPI genes with 38, and 11 TgSPI genes belong to the mollusc-specific I84 family. The TgSPI genes were found to be randomly distributed on 17 chromosomes with 12 tandem duplicate gene pairs. Expression profiles showed that most TgSPI genes were mainly expressed in immune-related tissues such as hepatopancreas, gill and mantle. In the hepatopancreas, most of TgSPI genes were sensitive to Vibrio stress, 28 and 29 TgSPI genes were up-regulated and down-regulated, respectively. Some up-regulated genes with signal peptides, such as the TgSPIs of I84 family, may act as a mechanism to directly prevent Vibrio from invasion. Six Kazal-type TgSPIs (TgSPI29, 45, 49, 50, 51 and 52) were intracellular proteins and their expression was down-regulated in hemocytes after Vibrio stress. This may have boosted protease activity in hemocytes to the point that more hemoglobin derived peptides were produced and secreted into the hemolymph to exert their anti-Vibrio effects. These findings may provide valuable information for further clarifying the roles of SPIs in the immune defense and will benefit future exploration of the immune function of SPIs in molluscs.

The role of a new insulin-like peptide in the pearl oyster Pinctada fucata martensii

Pinctada fucata martensii, is an economically important marine bivalve species cultured for seawater pearls. At present, we know little about the molecular mechanisms of the insulin signalling pathway in this oyster. Herein, we cloned and analysed an insulin-like peptide (PfILP) and its signalling pathway-related genes. We detected their expression levels in different tissues and developmental stages. Recombinant PfILP protein was produced and found to significantly increase primary mantle cell activity and induce the expression of the proliferating cell nuclear antigen (PCNA) gene. PfILP could also regulate the 293T cell cycle by stimulating the S phase and inhibiting the G1 and G2 phases. Recombinant PfILP protein induced the expression of its signalling pathway-related genes in mantle cells. In vitro co-immunoprecipitation analysis showed that PfILP interacts with PfIRR. PfILP activated expression of the pfIRR protein, and also activated the mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) pathways by stimulating phosphorylation of MAPK and AKT. Further analysis showed that PfILP up-regulated glycogen synthesis-related genes glycogen synthase kinase-3 beta (GSK-3β), protein phosphatase 1 (PP1) and glucokinase (GK) at the mRNA level, as well as the expression of the PP1 protein, and phosphorylation of GSK-3β. These results confirmed the presence of a conserved insulin-like signalling pathway in pearl oyster that is involved in cell activity, glycogen metabolism, and other physiological processes.

Grass carp (Ctenopharyngodon idella) RSK2 protects cells anti-apoptosis by up-regulating BCL-2

In mammals, toll-like receptor 3 (TLR3) is capable of recognizing double-stranded RNA and then initiates transcription of IFN-β. TLR3 can activate the innate immune system by phosphorylating extracellular signal-regulated kinase 1 (ERK1) in the mitogen-activated protein kinase (MAPK) pathway. As a downstream signaling protein of ERK1, ribosomal protein S6 kinase alpha 3 (RSK2) is activated through the "classical" MAPK pathway. So RSK2 plays a critical role in response to innate immune system induced by TRL3. However, the innate immune mechanism of RSK2 remains indistinct in fish. In this study, we cloned and characterized a full length cDNA sequence of RSK2 from Ctenopharyngodon idella (named CiRSK2, MH844551). The full length cDNA of CiRSK2 is 3930 bp with a coding sequence of 2202 bp encoding a polypeptide of 734 amino acids. The expression of CiRSK2 was ubiquitous and significantly up-regulated under the stimulation of poly (I:C) in eight different tissues of C. idella and C. idella kidney cells (CIK). In addition, poly (I:C) stimulation also up-regulated the expression of CiERK1 mRNA in CIK cells and the phosphorylation of CiERK1. We also demonstrated that the activated CiERK1 interacted with CiRSK2 by CO-IP assay and immunofluorescence assay. To further investigate the relationship between CiRSK2 and CiERK1, we performed subcellular localization of CiRSK2 at different periods of CiERK1 stimulation. The result showed that CiERK1 can make CiRSK2 enter the nucleus. Subsequently, we found that CiRSK2 increased the transcriptional level of CiBCL-2 and protein level of CiBCL-2 significantly. Then cell apoptosis was inhibited to a certain extent. Overall, our results suggested that CiRSK2 plays important roles in fish innate immunity and is able to inhibit cell apoptosis by up-regulating CiBCL-2.

Tissue distribution and functional characterization of mytimacin-4 in Mytilus galloprovincialis

Antimicrobial peptides (AMPs) play fundamental roles in the innate immunity of invertebrates. Mytimacin-4 is a kind of AMP gene previously sequenced from Mytilus galloprovincialis based on an identified EST sequence in our lab. In the present study, the tissue distribution and antimicrobial activities of mytimacin-4 were further investigated. A qRT-PCR analysis revealed that mytimacin-4 transcripts were constitutively expressed in all of the tested tissues of M. galloprovincialis, with the highest expression level in the posterior adductor muscle. After challenge by Vibrio anguillarum, the expression level of mytimacin-4 gene was significantly increased at 24 h (P < 0.05) in the mantle and increased at 48 h (P < 0.05) in the posterior adductor muscle. This finding suggested that mytimacin-4 transcripts were inducible upon pathogen infection. A minimal inhibitory concentration (MIC) assay indicated that recombinant mytimacin-4 protein had potent antimicrobial activities against gram-positive and gram-negative bacteria. Among the tested microorganisms, mytimacin-4 protein exhibited strong inhibition activities against Bacillus subtilis and Vibrio parahaemolyticus with MICs of 0.315 μM and 0.62 μM, respectively. This study provides for the first time direct evidence of antimicrobial action of mytimacin-4 in M. galloprovincialis.

Evolution and function analysis of interleukin-17 gene from Pinctada fucata martensii

Interleukin-17 (IL-17) is a proinflammatory cytokine that plays an important role in immune responses. In this study, we identified 57 IL-17 genes from the genomes of six marine invertebrates, including Pinctada fucata martensii, Crassostrea gigas, Lottia gigantea, Capitella teleta, Mizuhopecten yessoensis, and Mytilus galloprovincialis. Phylogenetic analysis showed that all invertebrate IL-17 genes were clustered into one group, implying that invertebrate IL-17 evolved from one common ancestral gene. From the extron-intron analysis, we found many intronless IL-17 genes in mollusks, which may be caused by retroposition. Tissue and development transcriptomic analysis showed that the expression of PmIL-17 was tissue and developmental stage-specific. Moreover, we cloned the full length of the IL-17-2 gene from P. f. martensii (PmIL-17-2) and explored its function in the immune response. The full-length cDNA of PmIL-17-2 is 719 bp, containing an open reading frame of 564 bp, a 5' -untranslated region (UTR) of 31 bp, and a 3' -UTR of 124 bp with a 30 bp poly (A) tail. PmIL-17-2 had a strong response to lipopolysaccharide (LPS), indicating that the PmIL-17-2 participates in innate immune responses. In situ hybridization of hemocytes showed that PmIL-17-2 was mainly produced by granulosa cells, and the number of the stained granulosa increased after LPS stimulation. These results lay the foundation for the research of IL-17 family in marine invertebrates.

c-Raf participates in adaptive immune response of Nile tilapia via regulating lymphocyte activation

RAF proto-oncogene serine/threonine-protein kinase (c-Raf) is a MAP kinase kinase kinase (MAPKKK) that participates in the Erk1/2 pathway and plays an important role in lymphocyte activation. However, the study on how c-Raf regulates adaptive immunity in non-mammal is still limited. In present study, based on analysis of sequence characteristics of c-Raf from Oreochromis niloticus (On-c-Raf), we investigated its regulation roles on teleost lymphocyte activation. The On-c-Raf was highly conserved during evolution, which was composed of a Raf-like Ras-binding domain (RBD), a protein kinase C conserved region 1 (C1) domain and a serine/threonine protein kinase catalytic (S_TKc) domain. Its mRNA showed a wide distribution in tissues of O. niloticus and with the highest expression in gill. After Aeromonas hydrophila infection, during the adaptive immune stage transcription level of On-c-Raf was significantly upregulated on day 8, but came back to original level on day 16 and 30, suggesting the potential involvement of On-c-Raf in primary response but not memory formation. Furthermore, On-c-Raf mRNA in leukocytes of Nile tilapias was obviously induced by in vitro stimulation of T cell mitogen PHA. More importantly, in vitro stimulation of lymphocytes agonist PMA augmented phosphorylation level of On-c-Raf in leukocytes detected by western-blot and immunofluorescent. Thus, c-Raf regulated lymphocyte activation of Nile tilapia on both mRNA and phosphorylation level. Together, our results revealed that the c-Raf from teleost Nile tilapia engaged in adaptive immune response by regulating lymphocytes activation. Since the regulatory mechanism of lymphocyte-mediated adaptive immunity is largely unknown in teleost, our study provided important evidences to understand teleost adaptive immunity, and also shed a novel perspective for the evolution of adaptive immune system.