Antiviral defense in shrimp: from innate immunity to viral infection

Identification of SNPs potentially related to immune responses and growth performance in Litopenaeus vannamei by RNA-seq analyses

Litopenaeus vannamei is one of the most important shrimp species for worldwide aquaculture. Despite this, little genomic information is available for this penaeid and other closely related taxonomic crustaceans. Consequently, genes, proteins and their respective polymorphisms are poorly known for these species. In this work, we used the RNA sequencing technology (RNA-seq) in L. vannamei shrimp evaluated for growth performance, and exposed to the White Spot Syndrome Virus (WSSV), in order to investigate the presence of Single Nucleotide Polymorphisms (SNPs) within genes related to innate immunity and growth, both features of great interest for aquaculture activity. We analyzed individuals with higher and lower growth rates; and infected (unhealthy) and non-infected (healthy), after exposure to WSSV. Approximately 7,000 SNPs were detected in the samples evaluated for growth, being 3,186 and 3,978 exclusive for individuals with higher and lower growth rates, respectively. In the animals exposed to WSSV we found about 16,300 unique SNPs, in which 9,338 were specific to non-infected shrimp, and 7,008 were exclusive to individuals infected with WSSV and symptomatic. In total, we describe 4,312 unigenes containing SNPs. About 60% of these unigenes returned GO blastX hits for Biological Process, Molecular Function and Cellular Component ontologies. We identified 512 KEGG unique KOs distributed among 275 pathways, elucidating the majority of metabolism roles related to high protein metabolism, growth and immunity. These polymorphisms are all located in coding regions, and certainly can be applied in further studies involving phenotype expression of complex traits, such as growth and immunity. Overall, the set of variants raised herein enriches the genomic databases available for shrimp, given that SNPs originated from nextgen are still rare for this relevant crustacean group, despite their huge potential of use in genomic selection approaches.

Molecular characterization of shrimp harbinger transposase derived 1 (HARBI1)-like and its role in white spot syndrome virus and Vibrio alginolyticus infection

The role of the nuclease, HARBI1-like protein (mjHARBI1-like) in the innate immunity of Marsupenaeus japonicus was explored in this study. The 1361 bp cDNA sequence of mjHARBI1-like was cloned from M. japonicus using RACE. RT-qPCR analysis results showed that the gills and hepatopancreas of M. japonicus were the main tissues where mjHARBI1-like is expressed. In addition, it was also found that white spot syndrome virus (WSSV) or Vibrio alginolyticus challenge could stimulate mjHARBI1-like expression. After mjHARBI1-likewas inhibited, expression of immune genes such as toll, p53, myosin, and proPO were significantly downregulated (P < 0.01). However, in shrimp hemocytes, hemocyanin and tumor necrosis factor-α (TNF-α) were up-regulated significantly (P < 0.01). This study demonstrated that mjHARBI1-like plays a key role in the progression of WSSV and V. alginolyticus infection. Specifically, the cumulative mortality of WSSV-infected and V. alginolyticus-infected shrimp was significantly advanced by double-strand RNA interference (dsRNAi) of mjHARBI1-like. Apoptosis studies indicated that mjHARBI1-dsRNA treatment caused a reduction in hemocyte apoptosis in bacterial and viral groups. In addition, phagocytosis experiments illustrated that mjHARBI1-dsRNA treatment led to a lower phagocytosis rate in hemocytes of V. alginolyticus-challenged shrimp. It was also found that knockdown of mjHARBI1-like inhibited shrimp phenoloxidase (PO) activity, superoxide dismutase (SOD) activity, and total hemocyte count (THC) after WSSV or V. alginolyticus infection. These data indicate a regulative role of mjHARBI1-likein the immunity of shrimp in response to pathogen infection. Resultantly, it was concluded that mjHARBI1-like might have a positive effect on the anti-WSSV immune response of shrimp by regulating apoptosis, THC, PO activity, and SOD activity. Additionally, mjHARBI1-like might promote anti-V. alginolyticus infection by participating in regulating phagocytosis, apoptosis, SOD activity, PO activity, and THC.

Functional elucidation of LvToll 3 receptor from P. vannamei through RNA interference and its potential role in the shrimp antiviral response

There is a continuing debate on whether an antiviral immunity similar to vertebrate interferon response exists in invertebrates. Recent advances in penaeid immunology identified several new members of the Toll receptor family and one of these is LvToll3 (Litopenaeus vannamei Toll3). It is hypothesized in this study that LvToll3 responds to pathogen associated molecular patterns (PAMPs) such as dsRNA, which then activates certain antiviral pathways in penaeids. RNA interference (RNAi) was used to determine differences in the expression levels of specific genes putatively involved in the antiviral response through qPCR. Results showed that LvToll3 upregulation could be elicited through the introduction of double stranded RNA (dsRNA) regardless of sequence relative to initial levels in the 3rd hour. Furthermore, statistically intriguing trend in the overall expression of Vago 4/5 and Interferon regulatory factor (IRF) suggests that both these genes are affected by the expression of LvToll3. Dicer showed no statistical difference between the experimentally treated (LvToll3-dsRNA), positive control (GFP-dsRNA), and control (PBS) samples corroborating the assertion that dicer is part of another antiviral mechanism that acts in concert with Toll system. These findings suggests that LvToll3 plays a critical role in penaeid antiviral immunity when molecular patterns associated with viruses are detected.

Identification and functional analysis of inhibitor of NF-κB kinase (IKK) from Scylla paramamosain: The first evidence of three IKKs in crab species and their expression profiles under biotic and abiotic stresses

IKK (inhibitor of NF-κB kinase) is the critical regulator for NF-κB (nuclear factor-κB) pathway against pathogenic invasion in vertebrates or invertebrates. However, the IKK from crab species has not yet been identified. In the present study, three full-length cDNA sequences of IKKs from mud crab Scylla paramamosain, designated as SpIKKβ, SpIKKε1 and SpIKKε2, were firstly cloned through RT-PCR and RACE methods. This is also the first report about the identification of two IKKε genes in mud crab and even in crustaceans. The SpIKKβ cDNA was 2824 bp in length with an open reading frame (ORF) of 2382 bp, which encoded a putative protein of 793 amino acids (aa). The ORF of two SpIKKε isoforms, SpIKKε1 and SpIKKε2, were 2400 bp and 2331 bp in length encoding 799 aa and 776 aa, respectively. The crucial conserved residues and functional domains, including the kinase domains (KDs) and leucine zipper (LZ), were identified in all SpIKKs. Phylogenetic analysis suggested that SpIKKβ was classified into the IKKs class while SpIKKεs could be grouped into the IKK-related kinases class. The qRT-PCR analysis showed that three SpIKKs were constitutively expressed in all tested tissues and the highest expression levels of SpIKKβ and SpIKKεs were all in hemocyte. The gene expression profiles of SpIKKs were distinct when crabs suffered biotic and abiotic stresses including the exposures of Vibrio alginolyticus, poly (I:C), cadmium and air exposure, suggesting that the SpIKKs might play different roles in response to pathogens infections, heavy metal and air exposure. Moreover, IKKs from mud crab can significantly activate mammalian NF-κB pathway, suggesting the function of IKKs might be evolutionally well-conserved. Results of the RNAi experiments suggested that SpIKKs might regulate the immune signaling pathway when hemocytes were challenged with V. parahemolyticus or virus-analog poly (I:C). All of these results indicated that the obtained SpIKKs might be involved in stress responses against biotic or abiotic stresses, and it also highlighted their functional conservation in the innate immune system from crustaceans to mammals.

Shrimp hemocyte homeostasis-associated protein (PmHHAP) interacts with WSSV134 to control apoptosis in white spot syndrome virus infection

Hemocyte homeostasis-associated protein (PmHHAP) was first identified as a viral-responsive gene, due to a high upregulation in transcription following white spot syndrome virus (WSSV) infection. Functional studies using RNA interference have suggested that PmHHAP is involved in hemocyte homeostasis by controlling apoptosis during WSSV infection. In this study, the role of PmHHAP in host-viral interactions was further investigated. Yeast two-hybrid assay and co-immunoprecipitation revealed that PmHHAP binds to an anti-apoptosis protein, WSSV134. The viral protein WSSV134 is a late protein of WSSV, expressed 24 h post infection (hpi). Gene silencing of WSSV134 in WSSV-infected shrimp resulted in a reduction of the expression level of the viral replication marker genes VP28, wsv477, and ie-1, which suggests that WSSV134 is likely involved in viral propagation. However, co-silencing of PmHHAP and WSSV134 counteracted the effects on WSSV infection, which implies the importance of the host-pathogen interaction between PmHHAP and WSSV134 in WSSV infection. In addition, caspase 3/7 activity was noticeably induced in the PmHHAP and WSSV134 co-silenced shrimp upon WSSV infection. Moreover, PmHHAP and WSSV134 inhibited caspase-induced activation of PmCasp in vitro in a non-competitive manner. Taken together, these results suggest that PmHHAP and WSSV134 play a role in the host-pathogen interaction and work concordantly to control apoptosis in WSSV infection.

Molecular characterization of diphthamide biosynthesis protein 7 in Marsupenaeus japonicus and its role in white spot syndrome virus infection

Diphthamide biosynthesis protein 7 (Dph7) is a vital protein for diphthamide biosynthesis in archaea and eukaryotes. The 1143 bp cDNA sequence of Dph7 was cloned from the gills of Marsupenaeus japonicus using RT-PCR and RACE. Data showed that Dph7 was highly expressed in the gills and digestive gland of M. japonicus. Furthermore, the expression of dph7 was induced by infection with white spot syndrome virus (WSSV). When Dph7 was knocked down, immune genes such as toll, prophenoloxidase (proPO), p53, tumor necrosis factor-α (TNF-α) and signal transducer and activator of transcription (STAT) were significantly down-regulated (P < 0.01) in hemocytes. First, we demonstrated that Dph7 is very important in the progression of WSSV infection and that the time of death for WSSV-infected shrimp was significantly advanced following RNAi targeting of Dph7. We also investigated the effect of Dph7 on apoptosis rate in M. japonicas and found that Dph7-dsRNA treatment caused lower levels of apoptosis in hemocytes, both in the disease-free group and the WSSV group. Knock-down of Dph7 affected the activity of both phenoloxidase (PO) and superoxide dismutase (SOD), and total hemocyte count (THC) after infection with WSSV, indicating that Dph7 plays a regulatory role in the immunological reaction of shrimp in response to WSSV infection. Thus, we conclude that Dph7 may promote the anti-WSSV immune response of shrimp by regulating apoptosis, SOD and PO activity, and can influence the progression of WSSV infection.

Wnt5b regulates apoptosis in Litopenaeus vannamei against white spot syndrome virus

The Wnt signaling mediated by Wnt proteins that orchestrate and influence a myriad of cellular processes, such as cell proliferation, differentiation, tumorigenesis, apoptosis, and participation in immune defense during microbe infection. Wnt5b is one of the Wnt signaling molecules that initiate the cascade. In this study, we cloned and characterized a Wnt5b homolog from Litopenaeus vannamei designed as LvWnt5b. The full length of LvWnt5b transcript was 1726 bp with an 1107 bp open reading frame that encoded a 368 aa protein, which contained 24 discontinuous and highly conserved cysteine. Real-time quantitative PCR showed that the transcriptional level of LvWnt5b was down-regulated when infected with white spot syndrome virus (WSSV). Knock-down of LvWnt5b resulted in inhibition of the transcriptional level of WSSV gene ie1, indicating that LvWnt5b mediated signaling pathway may play an important role in defense against WSSV infection. When LvWnt5b was silenced, caspase3/7 activity in hemocytes was increased significantly, and the transcription of viral gene was decreased as well. Moreover, overexpression of LvWnt5b in HEK293T cells led to inhibition of caspase3/7 activity, which further proved the role of LvWnt5b in restraining apoptosis. The study showed that the shrimp may decrease the expression of LvWnt5b initiatively to act as an immune defense mechanism against WSSV infection via promoting apoptosis. It will be helpful for understanding the function of Wnt signaling pathway in virus invasion and host defense.

Molecular cloning of Kuruma shrimp Marsupenaeus japonicus endonuclease-reverse transcriptase and its positive role in white spot syndrome virus and Vibrio alginolyticus infection

This study investigated the function of endonuclease-reverse transcriptase (mjERT) in Marsupenaeus japonicus. The 1129 bp cDNA sequence of mjERT was cloned from M. japonicus using rapid amplification of cDNA ends (RACE) PCR, and RT-qPCR analysis indicated that mjERT was highly expressed in the gills and hepatopancreas of M. japonicus. We also found that white spot syndrome virus (WSSV) or Vibrio alginolyticus challenge could enhance the expression of mjERT. When mjERT was inhibited, immune genes such as toll, p53, hemocyanin and tumor necrosis factor-α (TNF-α) were significantly down-regulated (P < .01) in the hemocytes of shrimp, while myosin was significantly up-regulated (P < .01). We demonstrated that mjERT is very important for the progression of WSSV infection and that the cumulative mortality of WSSV-infected and V. alginolyticus-infected shrimps was significantly increased following mjERT RNA interfere (RNAi). Apoptosis data provided information to suggest that mjERT-dsRNA challenge caused less apoptosis in hemocytes in both the disease-free and viral group. We also revealed that mjERT-dsRNA treatment resulted in a lower phagocytosis rate in the hemocytes of V. alginolyticus-challenged shrimp. Finally, we found that the absence of mjERT had an significantly negative impact upon shrimp phenoloxidase (PO) activity, superoxide dismutase (SOD) activity and total hemocyte count (THC) following WSSV or V. alginolyticus infection, indicating a regulative role for mjERT in the innate immunity of shrimp in response to pathogenic infection. In summary, we concluded that mjERT might promote the anti-WSSV immune response of shrimp by regulating apoptosis, PO activity, THC and SOD activity, and also exert a positive role in the immune response against V. alginolyticus by regulating phagocytosis, SOD activity, PO activity and THC.

Myeloid leukemia factor functions in anti-WSSV immune reaction of kuruma shrimp, Marsupenaeus japonicus

Myeloid leukemia factor (MLF) plays an important role in development, cell cycle, myeloid differentiation, and regulates the RUNX transcription factors. However, the function of MLF in immunity is still unclear. In this study, an MLF was identified and characterized in kuruma shrimp Marsupenaeus japonicus, and named as MjMLF. The full-length cDNA of MjMLF contained 1111 nucleotides, which had an opening reading frame of 816 bp encoding a protein of 272 amino acids with an MLF1-interacting protein domain. MjMLF could be ubiquitously detected in different tissues of shrimp at the transcriptional level. The expression pattern analysis showed that MjMLF could be upregulated in shrimp hemocytes and hepatopancreas after white spot syndrome virus challenge. The RNA interference and protein injection assay showed that MjMLF could inhibit WSSV replication in vivo. Flow cytometry assay showed that MjMLF could induce hemocytes apoptosis which functioned in the shrimp antiviral reaction. All the results suggested that MjMLF played an important role in the antiviral immune reaction of kuruma shrimp. The research indicated that MjMLF might function as a novel regulator to inhibit WSSV replication in shrimp.

Transcriptome analysis of Kuruma shrimp (Marsupenaeus japonicus) hepatopancreas in response to white spot syndrome virus (WSSV) under experimental infection

Kuruma shrimp (Marsupenaeus japonicus) is one of the most valuable crustacean species in capture fisheries and mariculture in the Indo-West Pacific. White spot syndrome virus (WSSV) is a highly virulent pathogen which has seriously threatened Kuruma shrimp aquaculture sector. However, little information is available in relation to underlying mechanisms of host-virus interaction in Kuruma shrimp. In this study, we performed a transcriptome analysis from the hepatopancreas of Kuruma shrimp challenged by WSSV, using Illumina-based RNA-Seq. A total of 39,084,942 pair end (PE) reads, including 19,566,190 reads from WSSV-infected group and 19,518,752 reads from non-infected (control) group, were obtained and assembled into 33,215 unigenes with an average length of 503.7 bp and N50 of 601 bp. Approximately 17,000 unigenes were predicted and classified based on homology search, gene ontology, clusters of orthologous groups of proteins, and biological pathway mapping. Differentially expressed genes (DEGs), including 2150 up-regulated and 1931 down-regulated, were found. Among those, 805 DEGs were identified and categorized into 14 groups based on their possible functions. Many genes associated with JAK-STAT signaling pathways, Integrin-mediated signal transduction, Ras signaling pathways, apoptosis and phagocytosis were positively modified after WSSV challenge. The proteolytic cascades including Complement-like activation and Hemolymph coagulations likely participated in antiviral immune response. The transcriptome data from hepatopancreas of Kuruma shrimp under WSSV challenge provided comprehensive information for identifying novel immune related genes in this valuable crustacean species despite the absence of the genome database of crustaceans.

Toll-receptor 9 gene in the black tiger shrimp (Penaeus monodon) induced the activation of the TLR-NF-κB signaling pathway

Toll receptors are important pathogen recognition receptors (PRRs) in shrimps, which play a vital role in defending against virus and bacterial challenge. In this paper, the characterization and functional analysis of a Toll9 receptor gene from Penaeus monodon was performed in HEK293T cells. Data showed that PmToll9 can activate the NF-κB promoter activities of TLR pathway, while ISRE and IFN-β promoter cannot be activated obviously in HEK293T cells using dual-luciferase reporter system. The downstream immune factors of IL-8, IκB-α, and TRAF6 were activated by PmToll9 and IL-8 showed the most significant up-regulation in expression levels, indicating the activities of NF-κB can be mediated by PmToll9. Six LRRs-deletion mutants were constructed and results showed these mutants had obvious declines in luciferase activities, among which the mutant pCMV-DeLRR4 showed the most significant decline. qPCR data indicated LRRs-deletion mutants efficiently impaired the activities of the downstream immune factors IL-8, IκB-α, and TRAF6. It demonstrates that LRRs-deletion mutants could result in the weaken abilities of PmToll9 in signaling transduction. Overexpression of PmToll9-GFP fusion protein in Hela cells revealed the primary cellular localization of PmToll9 is in the cytoplasm.

Fortilin: A Potential Target for the Prevention and Treatment of Human Diseases

Fortilin is a highly conserved 172-amino-acid polypeptide found in the cytosol, nucleus, mitochondria, extracellular space, and circulating blood. It is a multifunctional protein that protects cells against apoptosis, promotes cell growth and cell cycle progression, binds calcium (Ca²⁺) and has antipathogen activities. Its role in the pathogenesis of human and animal diseases is also diverse. Fortilin facilitates the development of atherosclerosis, contributes to both systemic and pulmonary arterial hypertension, participates in the development of cancers, and worsens diabetic nephropathy. It is important for the adaptive expansion of pancreatic β-cells in response to obesity and increased insulin requirement, for the regeneration of liver after hepatectomy, and for protection of the liver against alcohol- and ER stress-induced injury. Fortilin is a viable surrogate marker for in vivo apoptosis, and it plays a key role in embryo and organ development in vertebrates. In fish and shrimp, fortilin participates in host defense against bacterial and viral pathogens. Further translational research could prove fortilin to be a viable molecular target for treatment of various human diseases including and not limited to atherosclerosis, hypertension, certain tumors, diabetes mellitus, diabetic nephropathy, hepatic injury, and aberrant immunity and host defense.

Transcriptional profiling of immune-related genes in Pacific white shrimp (Litopenaeus vannamei) during ontogenesis

We have performed here a gene expression analysis to determine the developmental stage at the main genes involved in crustacean immune response begin to be expressed and their changes in mRNA abundance during shrimp development. By using a quantitative PCR-based approach, we have measured the mRNA abundance of 24 immune-related genes from different functional categories in twelve developmental stages ranging from fertilized eggs to larval and postlarval stages and also in juveniles. We showed for the first time that the main genes from the RNAi-based post-transcriptional pathway involved in shrimp antiviral immunity are transcribed in all developmental stages, but exhibit a diverse pattern of gene expression during shrimp ontogenesis. On the other hand, hemocyte-expressed genes mainly involved in antimicrobial defenses appeared to be transcribed in larval stages, indicating that hematopoiesis initiates early in development. Moreover, transcript levels of some genes were early detected in fertilized eggs at 0-4 h post-spawning, suggesting a maternal contribution of immune-related transcripts to shrimp progeny. Altogether, our results provide important clues regarding the ontogenesis of hemocytes as well the establishment of antiviral and antimicrobial defenses in shrimp.

The Role of Cytokine PF4 in the Antiviral Immune Response of Shrimp

During viral infection in vertebrates, cytokines play important roles in the host defense against the virus. However, the function of cytokines in invertebrates has not been well characterized. In this study, shrimp cytokines involved in viral infection were screened using a cytokine antibody microarray. The results showed that three cytokines, the Fas receptor (Fas), platelet factor 4 (PF4) and interleukin-22 (IL-22), were significantly upregulated in the white spot syndrome virus (WSSV)-challenged shrimp, suggesting that these cytokines played positive regulatory roles in the immune response of shrimp against the virus. Further experiments revealed that PF4 had positive effects on the antiviral immunity of shrimp by enhancing the shrimp phagocytic activity and inhibiting the apoptotic activity of virus-infected hemocytes. Therefore, our study presented a novel mechanism of cytokines in the innate immunity of invertebrates.

BAX, a novel cell pro-apoptotic protein, involved in hemocytes early antiviral immune response in fresh water crayfish, Procambarus clarkii

Apoptosis plays an important role in various biological processes and acts as a host defending mechanism by which infected cells are eliminated to restrict the virus propagation scale. Bax is a crucial pro-apoptotic protein, which mediates the release of cytochrome c from mitochondrion to cytosol in mammalian. However, its role in invertebrate is still obscure. Here, a novel pro-apoptotic protein gene was identified from hemocytes of red swamp crayfish. There was a Bcl-2 domain in the C-terminus of Pc-Bax, which possessed 497 amino acids residues. And an important transmembrane region existed in the C-terminus of Pc-Bax, which implied that Pc-Bax located in mitochondrial membrane. Besides, Pc-Bax was expressed at a relative high level in hemocytes, and a relative low expression levels in hepatopancreas, gills, and intestine. In hemocytes, Pc-Bax transcript was rapidly up-regulated from 12 h to 36 h after WSSV infection. And there was the same trend for Pc-Bax protein expression level in hemocytes after WSSV infection. Results of qRT-PCR testing for VP28 gene showed WSSV replication was obviously enhanced after Pc-Bax knockdown. Meantime, hemocytes apoptosis was suppressed in Pc-Bax knockdown crayfish after WSSV injection, compared with the dsGFP injection group and normal group. Taken together, these results revealed that crayfish hemocytes apoptosis scale was enhanced to suppress WSSV replication by up-regulating Bax protein expression level after WSSV infection.

Molecular cloning, characterization and expression analysis of Wnt4, Wnt5, Wnt6, Wnt7, Wnt10 and Wnt16 from Litopenaeus vannamei

The Wnt (Wg-type MMTV integration site) signaling represents as the negative regulator of virus-induced innate immune responses. Wnt genes act as ligands to activate the Wnt signaling. To know more about the information of Wnt genes in invertebrates, Litopenaeus vannamei Wnt genes (LvWnts) were identified and characterized. In this study, Six Wnt genes (LvWnt4, LvWnt5, LvWnt6, LvWnt7, LvWnt10 and LvWnt16) were obtained in L. vannamei. The complete cDNAs open reading frames (ORF) of LvWnt4, LvWnt5, LvWnt6, LvWnt7, LvWnt10 and LvWnt16 were 1077 bp, 1107 bp, 1350 bp, 1047 bp, 1509 bp and 1158 bp (GenBank accession no. KU169896, KU169897, KU169898, KU169899, KU169900 and KU169901), encoding 358, 368, 449, 348, 502 and 385 amino acid (aa) residues respectively. All the six members of LvWnts contain a Wnt1 domain, which is considered as an important feature of Wnt gene family. ClustalW analysis with amino acid sequences revealed that the proportion of identity with other species was more than 48% for all the LvWnts except LvWnt10 (36-41%). The phylogenetic relationship analysis illustrated that different subtype of Wnts formed their own separate branches and were placed in branch of invertebrates respectively with strong bootstrap support. The constitutive expressions of LvWnts were confirmed by RT-PCR in all the examined five developmental stages and eleven tissues of L. vannamei with different express patterns. LvWnt4, LvWnt5 and LvWnt10 were expressed highest in nerve while LvWnt6, LvWnt7 and LvWnt16 were expressed highest in intestine, stomach and gill, respectively. In addition, all the LvWnts were regulated by white spot syndrome virus (WSSV) challenges at different levels in hepatopancreas, gill and hemocytes, suggesting that Wnt genes may play a role in the defense against pathogenic virus infection in innate immune of L. vannamei.

Cloning, identification and functional analysis of a β-catenin homologue from Pacific white shrimp, Litopenaeus vannamei

Wnt signaling is known to control multiple of cellular processes such as cell differentiation, communication, apoptosis and proliferation, and is also reported to play a role during microbial infection. β-catenin is a key regulator of the Wnt signaling cascade. In the present study, we cloned and identified a β-catenin homologue from Litopenaeus vannamei termed Lvβ-catenin. The full-length of Lvβ-catenin transcript was 2797 bp in length within a 2451 bp open reading frame (ORF) that encoded a protein of 816 amino acids. Lvβ-catenin protein was comprised of several characteristic domains such as an N-terminal region of GSK-β consensus phosphorylation site and Coed coil section, a central region of 12 continuous Armadillo/β-Catenin-like repeat (ARM) domains and a C-terminal region. Real-time PCR showed Lvβ-catenin expression was responsive to Vibrio parahaemolyticus and white spot syndrome virus (WSSV) infection. Dual-reporter analysis showed that over-expression of Lvβ-catenin could induce activation of the promoter activities of several antimicrobial peptides (AMPs) such as shrimp PEN4, suggesting that Lvβ-catenin could play a role in regulating the production of AMPs. Knockdown of Lvβ-catenin enhanced the sensitivity of shrimps to V. parahaemolyticus and WSSV challenge, suggesting Lvβ-catenin could play a positive role against bacterial and viral pathogens. In summary, the results presented in this study provided some insights into the function of Wnt/β-catenin of shrimp in regulating AMPs and the host defense against invading pathogens.

Akirin interacts with Bap60 and 14-3-3 proteins to regulate the expression of antimicrobial peptides in the kuruma shrimp (Marsupenaeus japonicus)

Akirin is a recently discovered nuclear factor that plays important roles in innate immune responses. Akirin is a positive regulator of the NF-κB factor of the Drosophila immune deficiency (IMD) pathway, which shares extensive similarities with the mammalian tumor necrosis factor receptor (TNFR) signaling pathway. However, some studies found that the NF-κB transcriptional targets were also strongly repressed in akirin2 knockout mice following TLR, IL-1β and TNFα treatment. Therefore, the function of Akirin in the immune response requires further clarification. In this study, an Akirin homolog in the kuruma shrimp (Marsupenaeus japonicus) was identified. It was mainly expressed in hemocytes, heart and intestines. The expression of Akirin was upregulated by challenge with the Gram-negative bacterium Vibrio anguillarum, but was not significantly influenced by challenge with the Gram-positive bacterium Staphylococcus aureus. Knockdown of Akirin suppressed the expression of several IMD-Relish target effectors (antimicrobial peptides, AMPs). The limited regulating spectrum of Akirin might be associated with Bap60, a component of the Brahma (SWI/SNF) ATP-dependent chromatin-remodeling complex. In addition, Akirin also interacts with 14-3-3, which inhibited the expression of Akirin-target AMPs. The results suggested that Akirin is involved in the IMD-Relish pathway by interacting with Relish. The interaction of Akirin with Bap60 positively regulated the Akirin-Relish function, and its interaction with 14-3-3 negatively regulated the Akirin-Relish function.

Roles of small RNAs in the immune defense mechanisms of crustaceans

Small RNAs, 21-24 nucleotides in length, are non-coding RNAs found in most multicellular organisms, as well as in some viruses. There are three main types of small RNAs including microRNA (miRNA), small-interfering RNA (siRNA), and piwi-interacting RNA (piRNA). Small RNAs play key roles in the genetic regulation of eukaryotes; at least 50% of all eukaryote genes are the targets of small RNAs. In recent years, studies have shown that some unique small RNAs are involved in the immune response of crustaceans, leading to lower or higher immune responses to infections and diseases. SiRNAs could be used as therapy for virus infection. In this review, we provide an overview of the diverse roles of small RNAs in the immune defense mechanisms of crustaceans.

De novo assembly of the Carcinus maenas transcriptome and characterization of innate immune system pathways

Background

The European shore crab, Carcinus maenas, is used widely in biomonitoring, ecotoxicology and for studies into host-pathogen interactions. It is also an important invasive species in numerous global locations. However, the genomic resources for this organism are still sparse, limiting research progress in these fields. To address this resource shortfall we produced a C. maenas transcriptome, enabled by the progress in next-generation sequencing technologies, and applied this to assemble information on the innate immune system in this species.

Results

We isolated and pooled RNA for twelve different tissues and organs from C. maenas individuals and sequenced the RNA using next generation sequencing on an Illumina HiSeq 2500 platform. After de novo assembly a transcriptome was generated encompassing 212,427 transcripts (153,699 loci). The transcripts were filtered, annotated and characterised using a variety of tools (including BLAST, MEGAN and RSEM) and databases (including NCBI, Gene Ontology and KEGG). There were differential patterns of expression for between 1,223 and 2,741 transcripts across tissues and organs with over-represented Gene Ontology terms relating to their specific function. Based on sequence homology to immune system components in other organisms, we show both the presence of transcripts for a series of known pathogen recognition receptors and response proteins that form part of the innate immune system, and transcripts representing the RNAi, Toll-like receptor signalling, IMD and JAK/STAT pathways.

Conclusions

We have produced an assembled transcriptome for C. maenas that provides a significant molecular resource for wide ranging studies in this species. Analysis of the transcriptome has revealed the presence of a series of known targets and functional pathways that form part of their innate immune system and illustrate tissue specific differences in their expression patterns.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1667-1) contains supplementary material, which is available to authorized users.