Analysis of expression, cellular localization, and function of three inhibitors of apoptosis (IAPs) from Litopenaeus vannamei during WSSV infection and in regulation of antimicrobial peptide genes (AMPs)

A Novel TRIM9 Protein Promotes NF-κB Activation Through Interacting With LvIMD in Shrimp During WSSV Infection

The TRIpartite Motif (TRIM) proteins play key roles in cell differentiation, apoptosis, development, autophagy, and innate immunity in vertebrates. In the present study, a novel TRIM9 homolog (designated as LvTRIM9-1) specifically expressed in the lymphoid organ of shrimp was identified from the Pacific whiteleg shrimp Litopenaeus vannamei. Its deduced amino acid sequence possesses the typical features of TRIM proteins, including a RING domain, two B-boxes, a coiled-coil domain, a FN3 domain, and a SPRY domain. The transcripts of LvTRIM9-1 were mainly located in the lymphoid tubules of the lymphoid organ. Knockdown of LvTRIM9-1 could apparently inhibit the transcriptions of some genes from white spot syndrome virus (WSSV) and reduce the viral propagation in the lymphoid organ. Overexpression of LvTRIM9-1 in mammalian cells could activate the promoter activity of NF-κB, and an in vivo experiment in shrimp showed that knockdown of LvTRIM9-1 reduced the expression of LvRelish in the lymphoid organ. Yeast two-hybridization and co-immunoprecipitation (Co-IP) assays confirmed that LvTRIM9-1 could directly interact with LvIMD, a key component of the IMD pathway, through its SPRY domain. These data suggest that LvTRIM9-1 could activate the IMD pathway in shrimp via interaction with LvIMD. This is the first evidence to show the regulation of a TRIM9 protein on the IMD pathway through its direct interaction with IMD, which will enrich our knowledge on the role of TRIM proteins in innate immunity of invertebrates.

Inhibitor of apoptosis-1 gene as a potential target for pest control and its involvement in immune regulation during fungal infection

BACKGROUND

Environmentally friendly insect management technologies, including RNA interference (RNAi) and entomopathogenic fungi, have attracted increasing attention as options for pest control. Here, we sought to extend RNAi-directed targeting of the inhibitor of apoptosis protein 1 (IAP1) gene to the locust, and to examine its relationship to immune responses and susceptibility to Metarhizium acridum, a locust-specific fungal pathogen.

RESULTS

Expression of the locust LmIAP gene was induced in the hemolymph and fat body after M. acridum infection. RNAi-directed silencing of locust LmIAP1 resulted in increased caspase 3 activity, degeneration of the gut and dose-dependent mortality. Synergistic mortality was seen in RNAi-LmIAP/fungal co-infection experiments with median survival time (MST) values decreasing from ∼ 5 days for RNAi and M. acridum treatments alone, to 2.6 days for co-treatments. Reduced hemocyte numbers and antimicrobial peptide levels were seen in co-treated locusts, with changes in gut opportunistic pathogenic bacteria seen between treatments. Enhanced fungal sporulation on co-treated insect cadavers was also compared with fungal infection alone.

CONCLUSIONS

Silencing of the locust LmIAP1 gene results in direct mortality and increases insect susceptibility to insect fungal pathogens, in part by decreasing immunity and altering the gut microbiome. © 2019 Society of Chemical Industry.

An inhibitor of apoptosis protein (EsIAP1) from Chinese mitten crab Eriocheir sinensis regulates apoptosis through inhibiting the activity of EsCaspase-3/7-1

Inhibitor of apoptosis proteins (IAPs) maintain the balance between cell proliferation and cell death by inhibiting caspase activities and mediating immune responses. In the present study, a homolog of IAP (designated as EsIAP1) was identified from Chinese mitten crab Eriocheir sinensis. EsIAP1 consisted of 451 amino acids containing two baculoviral IAP repeat (BIR) domains with the conserved Cx2 Cx6 Wx3 Dx5 Hx6 C motifs. EsIAP1 mRNA was expressed in various tissues and its expression level in hemocytes increased significantly (p < 0.01) at 12–48 h after lipopolysaccharide stimulation. In the hemocytes, EsIAP1 protein was mainly distributed in the cytoplasm. The hydrolytic activity of recombinant EsCaspase-3/7-1 against the substrate Ac-DEVD-pNA decreased after incubation with rEsIAP1. Moreover, rEsIAP1 could directly combine with rEsCaspase-3/7-1 in vitro. After EsIAP1 was interfered by dsRNA, the mRNA expression and the hydrolytic activity of EsCaspase-3/7-1 increased significantly, which was 2.26-fold (p < 0.05) and 1.71-fold (p < 0.05) compared to that in the dsGFP group, respectively. These results collectively demonstrated that EsIAP1 might play an important role in apoptosis pathway by regulating the activity of EsCaspase-3/7-1 in E. sinensis.

Transcriptomic analysis of Macrobrachium rosenbergii (giant fresh water prawn) post-larvae in response to M. rosenbergii nodavirus (MrNV) infection: de novo assembly and functional annotation

Background

Macrobrachium rosenbergii, is one of a major freshwater prawn species cultured in Southeast Asia. White tail disease (WTD), caused by Macrobrachium rosenbergii nodavirus (MrNV), is a serious problem in farm cultivation and is responsible for up to 100% mortality in the post larvae stage. Molecular data on how M. rosenbergii post-larvae launches an immune response to an infection with MrNV is not currently available. We therefore compared the whole transcriptomic sequence of M. rosenbergii post-larvae before and after MrNV infection.

Results

Transcriptome for M. rosenbergii post-larvae demonstrated high completeness (BUSCO Complete: 83.4%, fragmentation: 13%, missing:3.3%, duplication:16.2%; highest ExN50 value: 94%). The assembled transcriptome consists of 96,362 unigenes with N₅₀ of 1308 bp. The assembled transcriptome was successfully annotated against the NCBI non-redundant arthropod database (33.75%), UniProt database (26.73%), Gene Ontology (GO) (18.98%), Evolutionary Genealogy of Genes: Non-supervised Orthologous Groups (EggNOG) (20.88%), and Kyoto Encyclopedia of Genes and Genome pathway (KEGG) (20.46%). GO annotations included immune system process, signaling, response to stimulus, and antioxidant activity. Differential abundance analysis using EdgeR showed 2413 significantly up-regulated genes and 3125 significantly down-regulated genes during the infection of MrNV.

Conclusions

This study reported a highly complete transcriptome from the post-larvae stage of giant river prawn, M. rosenbergii. Differential abundant transcripts during MrNV infection were identified and validated by qPCR, many of these differentially abundant transcripts as key players in antiviral immunity. These include known members of the innate immune response with the largest expression change occurring in the M. rosenbergii post-larvae after MrNV infection such as antiviral protein, C-type lectin, prophenol oxidase, caspase, ADP ribosylation factors, and dicer.

The Two NF-κB Pathways Regulating Bacterial and WSSV Infection of Shrimp

The outbreak of diseases ordinarily results from the disruption of the balance and harmony between hosts and pathogens. Devoid of adaptive immunity, shrimp rely largely on the innate immune system to protect themselves from pathogenic infection. Two nuclear factor-κB (NF-κB) pathways, the Toll and immune deficiency (IMD) pathways, are generally regarded as the major regulators of the immune response in shrimp, which have been extensively studied over the years. Bacterial infection can be recognized by Toll and IMD pathways, which activate two NF-κB transcription factors, Dorsal and Relish, respectively, to eventually lead to boosting the expression of various antimicrobial peptides (AMPs). In response to white-spot-syndrome-virus (WSSV) infection, these two pathways appear to be subverted and hijacked to favor viral survival. In this review, the recent progress in elucidating microbial recognition, signal transduction, and effector regulation within both shrimp Toll and IMD pathways will be discussed. We will also highlight and discuss the similarities and differences between shrimps and their Drosophila or mammalian counterparts. Understanding the interplay between pathogens and shrimp NF-κB pathways may provide new opportunities for disease-prevention strategies in the future.

A transcriptome study on Macrobrachium nipponense hepatopancreas experimentally challenged with white spot syndrome virus (WSSV)

White spot syndrome virus (WSSV) is one of the most devastating pathogens of cultured shrimp, responsible for massive loss of its commercial products worldwide. The oriental river prawn Macrobrachium nipponense is an economically important species that is widely farmed in China and adult prawns can be infected by WSSV. However, the molecular mechanisms of the host pathogen interaction remain unknown. There is an urgent need to learn the host pathogen interaction between M. nipponense and WSSV which will be able to offer a solution in controlling the spread of WSSV. Next Generation Sequencing (NGS) was used in this study to determin the transcriptome differences by the comparison of control and WSSV-challenged moribund samples, control and WSSV-challenged survived samples of hepatopancreas in M. nipponense. A total of 64,049 predicted unigenes were obtained and classified into 63 functional groups. Approximately, 4,311 differential expression genes were identified with 3,308 genes were up-regulated when comparing the survived samples with the control. In the comparison of moribund samples with control, 1,960 differential expression genes were identified with 764 genes were up-regulated. In the contrast of two comparison libraries, 300 mutual DEGs with 95 up-regulated genes and 205 down-regulated genes. All the DEGs were performed GO and KEGG analysis, overall a total of 85 immune-related genes were obtained and these gene were groups into 13 functions and 4 KEGG pathways, such as protease inhibitors, heat shock proteins, oxidative stress, pathogen recognition immune receptors, PI3K/AKT/mTOR pathway, MAPK signaling pathway and Ubiquitin Proteasome Pathway. Ten genes that valuable in immune responses against WSSV were selected from those DEGs to furture discuss the response of host to WSSV. Results from this study contribute to a better understanding of the immune response of M. nipponense to WSSV, provide information for identifying novel genes in the absence of genome of M. nipponense. Furthermore, large number of transcripts obtained from this study could provide a strong basis for future genomic research on M. nipponense.

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.

Establishment of lysozyme gene RNA interference systemand its involvement in salinity tolerance in sea cucumber (Apostichopus japonicus)

The lysozyme gene was silenced using RNA interference (RNAi) to analyze the function of lysozyme in sea cucumber under salt stress. The interfering efficiency of four lysozyme RNAi oligos ranged from 0.55 to 0.70. From the four oligos, p-miR-L245 was used for further interfering experiments because it had the best silencing efficiency. Peristomial film injection of p-miR-L245 (10 μg) was used for further interfering experiments. The lowest gene expression, determined by RT-PCR assay, in muscle, coelomic fluid, and parapodium occurred 48 h after p-miR-L245 injection, while that of body wall and tube foot was 96 h and 24 h, respectively. Lysozyme activity in muscle and body wall was significantly lower than the controls. The lowest lysozyme activity in muscle, body wall and parapodium, was found at 48, 72, and 48 h, respectively, which was consistent with the transcription expression of lysozyme. The lowest point of lysozyme activity was at 96 h in coelomic fluid and tube foot, which was laid behind lysozyme expression in transcription level. The expression profile of the lysozyme transcription level and lysozyme activity in the body wall and tube foot increased at 12 h after p-miR-L245 injection before the interference effect appeared. NKA gene expression was expressed at a high level in the positive control (PC) and negative control (NC) groups at 12, 24, and 48 h, while NKA was expressed at low levels in the lysozyme RNAi injection group at 12 and 24 h. The level of NKA gene expression recovered to the level of the PC and NC group at 48, 72, and 96 h after the lysozyme RNAi injection. NKCC1 gene expression was high in the PC and NC groups at 96 h, while the NKCC1 was expressed at a low level 96 h after lysozyme RNAi injection. The results suggest that lysozyme decay involves NKA and NKCC1 gene expression under salinity 18 psμ. The K⁺ and Cl^- concentration after lysozyme RNAi injection was lower than in the PC and NC group.

Analysis of digital gene expression profiling in hemocytes of white shrimp Litopenaeus vannamei under nitrite stress

Accumulation of nitrite in water is highly toxic to aquatic animals. To understand immune responses in shrimp under such environmental stress, a digital gene expression (DGE) technology was applied to detect the gene expression profile of the Litopenaeus vannamei hemocytes in response to nitrite for 48 h. A total of 1922 differently expressed unigenes were generated. Of these transcripts, 1269 and 653 genes were up- or down-regulated respectively. Functional categorization and pathways of the differentially expressed genes revealed that immune defense, xenobiotics biodegradation and metabolism, amino acid and nucleobase metabolic process, apoptosis were the differentially regulated processes occurring during nitrite stress. We selected 19 differential expression transcripts (DETs) to validate the sequencing results by real time quantitative PCR (qPCR). The Pearson's correlation coefficient (R) of the 19 DETs was 0.843, which confirmed the consistency and accuracy between these two approaches. Subsequently, we screened 10 genes to examine the changes in the time course of gene expression in more detail. The results indicated that expressions of ATP-binding cassette transporter (ABC transporter), caspase10, QM protein, C type lectin 4 (CTL4), protein disulfide isomerase (PDI), serine protease inhibitor 8 (SPI8), transglutaminase (TGase), chitinase1, inhibitors of apoptosis proteins (IAP) and cytochrome P450 enzyme (CYP450) were induced to participate in the anti-stress defense against nitrite. These results will provide a reference for follow-up study of molecular toxicology and valuable gene information for better understanding of immune response in L. vannamei under environmental stress.

Molecular and immune response characterizations of a novel AIF and cytochrome c in Litopenaeus vannamei defending against WSSV infection

Apoptosis inducing factor (AIF) and cytochrome c (CYC) are two mitochondrial apoptogenic factors. In the present study, the cDNA sequences of AIF (LvAIF) and CYC (LvCYC) were cloned from Pacific white shrimp, Litopenaeus vannamei. The LvAIF was 1664 bp, including a 5'-terminal untranslated region (UTR) of 154 bp, an open reading frame (ORF) of 1323 bp encoding a polypeptide of 440 amino acids (aa) and a 3' UTR of 187 bp. The LvCYC was 582 bp, including a 50 bp 5' UTR, a 315 bp ORF encoding for 104 aa, and a 217 bp 3' UTR. The deduced protein of LvAIF contained a conserved Pyr_redox and AIF_C domain at the N-terminal and the predicted LvCYC included a conservative cytochrome_C domain, respectively. Phylogenetic analysis revealed that LvAIF belonged to AIF1 subfamily and showed a close relationship with AIF1 from vertebrates and LvCYC showed the closest relationship with its counterparts from shrimp Marsupenaeus japonicus. Tissue expression profiles showed that both LvAIF and LvCYC existed in most tissues, with the most predominant expression of LvAIF in intestine, then followed muscle and the weakest expression in gill. The highest expression of LvCYC was detected in muscle, and the weakest expression was in hemocytes. Additionally, after white spot syndrome virus (WSSV) infection, the significant up-regulation of LvAIF, LvCYC and caspase 3 transcripts and the increase of pro-caspase 3 and active-caspase 3 protein were detected at most time points (P < 0.05). However, all of the three genes down-regulated in hemocytes in the early stage after WSSV infection. WSSV proliferation and shrimp mortality showed a time-dependent manner and the production of ROS in hemocytes were significantly increased at 6 and 24 h after infection. Our results showed that the apoptotic genes AIF, CYC and caspase 3 might play crucial roles in hepatopancreas, however, the production of ROS in hemocytes might be important in shrimp defense against WSSV infection.

The interaction between PmHtrA2 and PmIAP and its effect on the activity of Pm caspase

Apoptosis is an essential mechanism in multicellular organisms which results in the induction of cell death. Important apoptotic proteins, including high temperature requirement A2 (PmHtrA2; also known as serine protease), inhibitor of apoptosis protein (PmIAP) and Pm caspase, have been previously identified in black tiger shrimp, Penaeus monodon. However, the relevance among these proteins in apoptosis regulation has not been established yet in shrimp. Here, we showed that PmHtrA2 was able to interact with PmIAP and the binding of the two proteins was mediated by the BIR2 domain of PmIAP. In addition, the BIR2 of PmIAP was shown to be able to inhibit Pm caspase activity. The inhibitory effect of the BIR2 domain on Pm caspase was impaired under the presence of the IBM peptide of PmHtrA2, implying a role for PmHtrA2 in apoptosis activation. Our combined results suggested that P. monodon possesses a conserved mechanism by which the caspase-3 activity is modulated by HtrA2 and IAP, as previously seen in insects and mammals.

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.

A critical role for the Drosophila dopamine D1-like receptor Dop1R2 at the onset of metamorphosis

BACKGROUND

Insect metamorphosis relies on temporal and spatial cues that are precisely controlled. Previous studies in Drosophila have shown that untimely activation of genes that are essential to metamorphosis results in growth defects, developmental delay and death. Multiple factors exist that safeguard these genes against dysregulated expression. The list of identified negative regulators that play such a role in Drosophila development continues to expand.

RESULTS

By using RNAi transgene-induced gene silencing coupled to spatio/temporal assessment, we have unraveled an important role for the Drosophila dopamine 1-like receptor, Dop1R2, in development. We show that Dop1R2 knockdown leads to pre-adult lethality. In adults that escape death, abnormal wing expansion and/or melanization defects occur. Furthermore we show that salivary gland expression of this GPCR during the late larval/prepupal stage is essential for the flies to survive through adulthood. In addition to RNAi-induced effects, treatment of larvae with the high affinity D1-like receptor antagonist flupenthixol, also results in developmental arrest, and in morphological defects comparable to those seen in Dop1R2 RNAi flies. To examine the basis for pupal lethality in Dop1R2 RNAi flies, we carried out transcriptome analysis. These studies revealed up-regulation of genes that respond to ecdysone, regulate morphogenesis and/or modulate defense/immunity.

CONCLUSION

Taken together our findings suggest a role for Dop1R2 in the repression of genes that coordinate metamorphosis. Premature release of this inhibition is not tolerated by the developing fly.

A transcriptome study on Macrobrachium rosenbergii hepatopancreas experimentally challenged with white spot syndrome virus (WSSV)

The world production of shrimp such as the Malaysian giant freshwater prawn, Macrobrachium rosenbergii is seriously affected by the white spot syndrome virus (WSSV). There is an urgent need to understand the host pathogen interaction between M. rosenbergii and WSSV which will be able to provide a solution in controlling the spread of this infectious disease and lastly save the aquaculture industry. Now, using Next Generation Sequencing (NGS), we will be able to capture the response of the M. rosenbergii to the pathogen and have a better understanding of the host defence mechanism. Two cDNA libraries, one of WSSV-challenged M. rosenbergii and a normal control one, were sequenced using the Illumina HiSeq™ 2000 platform. After de novo assembly and clustering of the unigenes from both libraries, 63,584 standard unigenes were generated with a mean size of 698bp and an N50 of 1137bp. We successfully annotated 35.31% of all unigenes by using BLASTX program (E-value <10-5) against NCBI non-redundant (Nr), Swiss-Prot, Kyoto Encyclopedia of Genes and Genome pathway (KEGG) and Orthologous Groups of proteins (COG) databases. Gene Ontology (GO) assessment was conducted using BLAST2GO software. Differentially expressed genes (DEGs) by using the FPKM method showed 8443 host genes were significantly up-regulated whereas 5973 genes were significantly down-regulated. The differentially expressed immune related genes were grouped into 15 animal immune functions. The present study showed that WSSV infection has a significant impact on the transcriptome profile of M. rosenbergii's hepatopancreas, and further enhanced the knowledge of this host-virus interaction. Furthermore, the high number of transcripts generated in this study will provide a platform for future genomic research on freshwater prawns.

Knockdown of Litopenaeus vannamei HtrA2, an up-regulated gene in response to WSSV infection, leading to delayed shrimp mortality

HtrA2 is an apoptosis-activating gene that enhances the apoptotic process by preventing the formation of the IAP-caspase complex, thereby freeing caspase to trigger the apoptosis pathway. In this study, we presented the full-length cDNA sequence of HtrA2 from Litopenaeus vannamei (LvHtrA2). The full-length LvHtrA2 was 1335 bp, encoding 444 amino acids. This deduced amino acid sequence contained five conserved domains: a mitochondrial targeting signal (MTS), a transmembrane (TM) domain, an IAP-binding motif (IBM), a trimerization motif, a serine protease domain, and a PDZ domain normally found in the HtrA2 proteins of other organisms. A phylogenetic analysis revealed that LvHtrA2 clustered with the HtrA2 from other invertebrates and was closely related to Penaeus monodon HtrA2 (PmHtrA2). RT-PCR with RNA extracts from L. vannamei revealed that LvHtrA2 expression was found in several tissues, including the lymphoid organs, the haemocytes, the hepatopancreas, the gill, and the stomach, with different expression levels. When determining the role of LvHtrA2 in WSSV infection, it was found that LvHtrA2 transcription was early up-regulated in the WSSV-infected shrimp at 8h post-infection (p.i.) and expression still remained high at 48 h p.i.. It also demonstrated that dsRNA specific to LvHtrA2 reduced the cumulative mortality in the WSSV-infected shrimp compared with the control group. Additionally, depletion of the LvHtrA2 transcripts reduced expression levels for caspase-3 (Cap-3) gene in shrimp. This result could suggest that LvHtrA2 may involved in apoptosis mediated mortality rather than providing immune protection during WSSV infection.

Identification and functional characterization of the TAB2 gene from Litopenaeus vannamei

In Drosophila, TAB2, an important intermediate in the IMD signaling pathway, plays critical roles in the innate immune response in response to bacterial and viral infection. However, the role of TAB-related proteins in the immune response of shrimp has not yet been established. Here, we reported the identification of a TAB2-like gene in Litopenaeus vannamei designated as LvTAB2. The full-length cDNA of LvTAB2 was 2160 bp with an open reading frame of 1827 bp, which encoded a putative protein of 608 amino acids including a ubiquitin binding domain (CUE) at the N-terminal and a Zinc Finger domain (ZnF) at the C-terminus. Real-time RT-PCR analysis showed that LvTAB2 was expressed in all tested tissues and the expression levels of LvTAB2 in gills and hemocytes were positively induced in response to LPS, Vibrio parahemolyticus and White Spot Syndrome Virus (WSSV) challenges. Dual luciferase reporter assays demonstrated that LvTAB2 was able to induce the expression of antimicrobial peptide (AMP) genes, including Drosophila Attacin A and shrimp Penaeidins. Interestingly, over-expression of LvTAB2 could up-regulate the promoter activities of L. vannamei Vago1, Vago3 and Vago4 genes in S2 cells. To our knowledge, it was the first report that TAB2 participated in innate immune signaling to regulate the expression of Vago genes in invertebrates. Moreover, RNAi-mediated knockdown of LvTAB2 enhanced sensitivity of L. vannamei to Vibrio parahaemolyticus infection and caused elevated virus loads after WSSV infection. We suggested that the LvTAB2 may play important roles in the shrimp innate immunity.

Gene expression profiling in gill tissues of White spot syndrome virus infected black tiger shrimp Penaeus monodon by DNA microarray

White spot syndrome virus (WSSV) continues to be the most devastating viral pathogen infecting penaeid shrimp the world over. The genome of WSSV has been deciphered and characterized from three geographical isolates and significant progress has been made in developing various molecular diagnostic methods to detect the virus. However, the information on host immune gene response to WSSV pathogenesis is limited. Microarray analysis was carried out as an approach to analyse the gene expression in black tiger shrimp Penaeus monodon in response to WSSV infection. Gill tissues collected from the WSSV infected shrimp at 6, 24, 48 h and moribund stage were analysed for differential gene expression. Shrimp cDNAs of 40,059 unique sequences were considered for designing the microarray chip. The Cy3-labeled cRNA derived from healthy and WSSV-infected shrimp was subjected to hybridization with all the DNA spots in the microarray which revealed 8,633 and 11,147 as up- and down-regulated genes respectively at different time intervals post infection. The altered expression of these numerous genes represented diverse functions such as immune response, osmoregulation, apoptosis, nucleic acid binding, energy and metabolism, signal transduction, stress response and molting. The changes in gene expression profiles observed by microarray analysis provides molecular insights and framework of genes which are up- and down-regulated at different time intervals during WSSV infection in shrimp. The microarray data was validated by Real Time analysis of four differentially expressed genes involved in apoptosis (translationally controlled tumor protein, inhibitor of apoptosis protein, ubiquitin conjugated enzyme E2 and caspase) for gene expression levels. The role of apoptosis related genes in WSSV infected shrimp is discussed herein.

Nucleic acid-induced antiviral immunity in invertebrates: an evolutionary perspective

Nucleic acids derived from viral pathogens are typical pathogen associated molecular patterns (PAMPs). In mammals, the recognition of viral nucleic acids by pattern recognition receptors (PRRs), which include Toll-like receptors (TLRs) and retinoic acid-inducible gene (RIG)-I-like receptors (RLRs), induces the release of inflammatory cytokines and type I interferons (IFNs) through the activation of nuclear factor κB (NF-κB) and interferon regulatory factor (IRF) 3/7 pathways, triggering the host antiviral state. However, whether nucleic acids can induce similar antiviral immunity in invertebrates remains ambiguous. Several studies have reported that nucleic acid mimics, especially dsRNA mimic poly(I:C), can strongly induce non-specific antiviral immune responses in insects, shrimp, and oyster. This behavior shows multiple similarities to the hallmarks of mammalian IFN responses. In this review, we highlight the current understanding of nucleic acid-induced antiviral immunity in invertebrates. We also discuss the potential recognition and regulatory mechanisms that confer non-specific antiviral immunity on invertebrate hosts.

Antiviral defense in shrimp: from innate immunity to viral infection

The culture of penaeid shrimp is rapidly developing as a major business endeavor worldwide. However, viral diseases have caused huge economic loss in penaeid shrimp culture industries. Knowledge of shrimp innate immunity and antiviral responses has made important progress in recent years, allowing the design of better strategies for the prevention and control of shrimp diseases. In this study, we have updated information on shrimp antiviral immunity and interactions between shrimp hosts and viral pathogens. Current knowledge and recent progress in immune signaling pathways (e.g., Toll/IMD-NF-κB and JAK-STAT signaling pathways), RNAi, phagocytosis, and apoptosis in shrimp antiviral immunity are discussed. The mechanism of viral infection in shrimp hosts and the interactions between viruses and shrimp innate immune systems are also analyzed.

Pellino protein from pacific white shrimp Litopenaeus vannamei positively regulates NF-κB activation

Pellino, named after its property that binds Pelle (the Drosophila melanogaster homolog of IRAK1), is a highly conserved E3 class ubiquitin ligase in both vertebrates and invertebrates. Pellino interacts with phosphorylated IRAK1, causing polyubiquitination of IRAK1, and plays a critical upstream role in the toll-like receptor (TLR) pathway. In this study, we firstly cloned and identified a crustacean Pellino from pacific white shrimp Litopenaeus vannamei (LvPellino). LvPellino contains a putative N-terminal forkhead-associated (FHA) domain and a C-terminal ring finger (RING) domain with a potential E3 ubiquitin-protein ligase activity, and shows a high similarity with D. melanogaster Pellino. LvPellino could interact with L. vannamei Pelle (LvPelle) and over-expression of LvPellino could increase the activity of LvDorsal (a L. vannamei homolog of NF-κB) on promoters containing NF-κB binding motifs and enhance the expression of arthropod antimicrobial peptides (AMPs). The LvPellino protein was located in the cytoplasm and nucleus and LvPellino mRNA was detected in all the tissues examined and could be up-regulated after lipopolysaccharides, white spot syndrome virus (WSSV), Vibrio parahaemolyticus, and Staphylococcus aureus challenges, suggesting a stimulation response of LvPellino to bacterial and immune stimulant challenges. Knockdown of LvPellino in vivo could significantly decrease the expression of AMPs and increase the mortality of shrimps caused by V. parahaemolyticus challenge. However, suppression of the LvPellino expression could not change the mortality caused by WSSV infection, and dual-luciferase reporter assays demonstrated that over-expression of LvPellino could enhance the promoters of WSSV genes wsv069 (ie1), wsv303, and wsv371, indicating a complex role of LvPellino in WSSV pathogenesis and shrimp antiviral mechanisms.

Characterization of four novel caspases from Litopenaeus vannamei (Lvcaspase2-5) and their role in WSSV infection through dsRNA-mediated gene silencing

Apoptosis plays an important role in white spot syndrome virus (WSSV) pathogenesis, and caspases are central players in apoptosis. Here, we cloned four novel caspases (Lvcaspase2-5) from the Pacific white shrimp Litopenaeus vannamei, and investigated their potential roles in WSSV replication using dsRNA-mediated gene silencing. Lvcaspase2-5 have the typical domain structure of caspase family proteins, with the conserved consensus motifs p20 and p10. Lvcaspase2 and Lvcaspase5 were highly expressed in muscle, while Lvcaspase3 was highly expressed in hemocytes and Lvcaspase4 was mainly expressed in intestine. Lvcaspase2-5 could also be upregulated by WSSV infection, and they showed different patterns in various tissues. When overexpressed in Drosophila S2 cells, Lvcaspase2-5 showed different cellular localizations. Using dsRNA-medicated gene silencing, the expression of Lvcaspase2, Lvcaspase3, and Lvcaspase5 were effectively knocked down. In Lvcaspase2-, Lvcaspase3- or Lvcaspase5-silenced L. vannamei, expression of WSSV VP28 gene was significantly enhanced, suggesting protective roles for Lvcaspase2, Lvcaspase3 and Lvcaspase5 in the host defense against WSSV infection.