Identification and functional characterization of Dicer2 and five single VWC domain proteins of Litopenaeus vannamei

Single domain von Willebrand factor type C "cytokines" and the regulation of the stress/immune response in insects

The single domain von Willebrand factor type C (SVWC) appears in small secreted peptides that are arthropod-specific and are produced following environmental stress or pathogen exposure. Most research has focused on proteins with SVWC domain that are induced after virus infection and are hypothesized to function as "cytokines" to regulate the innate immune response. The expansion of SVWC genes in insect species indicates that many other functions remain to be discovered. Research in shrimp has elucidated the adaptability of Vago-like peptides in the innate immune response against bacteria, fungi and viruses after activation by Jak-STAT and/or Toll/Imd pathways in which they can act as pathogen-recognition receptors or cytokine-like signaling molecules. SVWC factors also appear in scorpion venoms and tick saliva, underlining their versatility to acquire new functions. This review discusses the discovery and function of SVWC peptides from insects to crustaceans and chelicerates and reveals the enormous gaps in knowledge that remain to be filled to understand this enigmatic group of secreted peptides.

RNAi-Based Therapy: Combating Shrimp Viral Diseases

Shrimp aquaculture has become a vital industry, meeting the growing global demand for seafood. Shrimp viral diseases have posed significant challenges to the aquaculture industry, causing major economic losses worldwide. Conventional treatment methods have proven to be ineffective in controlling these diseases. However, recent advances in RNA interference (RNAi) technology have opened new possibilities for combating shrimp viral diseases. This cutting-edge technology uses cellular machinery to silence specific viral genes, preventing viral replication and spread. Numerous studies have shown the effectiveness of RNAi-based therapies in various model organisms, paving the way for their use in shrimp health. By precisely targeting viral pathogens, RNAi has the potential to provide a sustainable and environmentally friendly solution to combat viral diseases in shrimp aquaculture. This review paper provides an overview of RNAi-based therapy and its potential as a game-changer for shrimp viral diseases. We discuss the principles of RNAi, its application in combating viral infections, and the current progress made in RNAi-based therapy for shrimp viral diseases. We also address the challenges and prospects of this innovative approach.

Cellular responses in crustaceans under white spot syndrome virus infection

Innate immunity plays the most important system responsible for protecting crustaceans against invading pathogens. White spot syndrome virus (WSSV) is considered a serious pathogen in crustaceans with high cumulative mortality and morbidity in infected animals. Understanding the mechanism of the response of hosts to WSSV infection is necessary, which is useful for effective prevention in controlling infection. In this review, we summarize the participation of signaling pathways (toll, immune deficiency, JAK/STAT, endocytosis, mitogen-activated protein kinase, PI3K/Akt/mTOR, cGAS-STING, Wingless/Integrated signal transduction, and prophenoloxidase (proPO) cascade) and the activity of cells (apoptosis, autophagy, as well as, reactive oxygen species and antioxidant enzymes) in the cellular-mediated immune response of crustaceans during WSSV infection. The information presented in this current review is important for a better understanding of the mechanism of the response of hosts to pathogens. Additionally, this provides a piece of basic knowledge for discovering approaches to strengthen the immune system and resistance of cultured animals against viral infections.

A simple sequence repeats marker of disease resistance in shrimp Litopenaeus vannamei and its application in selective breeding

The polymorphism of the simple sequence repeat (SSR) in the 5' untranslated coding region (5'-UTR) of the antiviral gene IRF (LvIRF) has been shown to be implicated in the resistance to viral pathogens in shrimp Litopenaeus vannamei (L. vannamei). In this study, we explored the potential of this (CT)n-SSR marker in disease resistance breeding and the hereditary property of disease resistance traits in offspring. From 2018 to 2021, eight populations were generated through crossbreeding by selecting individuals according to microsatellite genotyping. Our results demonstrated that shrimp with the shorter (CT)n repeat exhibited higher resistance to white spot syndrome virus (WSSV) or Decapod iridescent virus 1 (DIV1); meanwhile, these resistance traits could be inherited in offspring. Interestingly, we observed that the longer (CT)n repeats were associated with bacterial resistance traits. Accordingly, shrimp with longer (CT)n repeats exhibited higher tolerance to Vibrio parahaemolyticus infection. Taken together, these results indicate that the single (CT)n-SSR marker could be used to selective breeding for both resistance to virus and bacteria in shrimps.

A conserved RNAi molecule Ago2 involved in antiviral immunity of oyster Crassostrea gigas

Argonaute (Ago) is the core component of RNA-induced silencing complex to play a crucial role in the antiviral immunity, which always cooperates with Dicer in RNA interference (RNAi) to silence the target genes. In the present study, an Ago homologue (CgAgo2) was identified in the Pacific oyster Crassostrea gigas. There were four classical functional domains in the predicted CgAgo2 protein, including an N-terminal domain, a PAZ domain, a Mid domain, and a PIWI domain. The deduced amino acid sequence of CgAgo2 shared 63.52%-84.27% identity with other Agos. Transcriptome analysis showed that CgAgo2 was highly expressed in embryonic period and gradually decreased from blastula to gastrula. The transcripts of CgAgo2 were detectable in all the examined tissues of adult oysters, with the highest expression in haemocytes (36.61-fold of that in adductor muscle, p < 0.001). The expression level of CgAgo2 mRNA in haemocytes increased significantly at 12 h after poly (I:C) and dsRNA stimulation, which were 2.71-fold (p < 0.05) and 58.00-fold (p < 0.001) of that in the control group respectively. Immunocytochemistry assay revealed that CgAgo2 proteins were mainly distributed in the cytoplasm and nucleus of haemocytes. The interaction between the recombinant CgAgo2 protein (rCgAgo2) and cleavage protein rCgDicer was observed in vitro by BLI and pull-down assays. These results indicated that CgAgo2 participated in the antiviral immunity of oyster by functioning as a component of RNA-induced silencing complex in RNAi.

Analysis of Some Putative Novel Peptides from Iranian Scorpion Venom Glands, Hemiscorpius lepturus, Using cDNA Library Construction

Background: To date, more than 300,000 distinct peptides have been identified in scorpion venom. However, only a limited number of these peptides have been described. Objectives: We characterized some putative peptides from the venom gland cDNA library of the Iranian yellow scorpion Hemiscorpius lepturus”. Methods: Total RNA was extracted from yellow Iranian scorpion glands. Single-stranded cDNA (sscDNA) and double-stranded cDNA (dscDNA) were synthesized by polymerase chain reaction (PCR). A cDNA library was achieved by inserting dscDNA into a special vector and subsequently transformed to chemically competent Escherichia coli as a host. The library was screened by culturing the liquid library on Lysogeny broth (LB)-agar plates. Analysis of positive clones was performed by plasmid extraction and the sequencing of the inserts. Finally, all cDNA sequences were analyzed and characterized by bioinformatics software. Results: One hundred colonies were randomly analyzed. Eighty-nine cDNA sequences had acceptable quality for bioinformatics analysis. Five sequences were selected for further analysis. The peptides related to these sequences were divided into two groups, non-disulfide bridge peptides (NDBP) and disulfide bridge peptides (DBP), the application of which in health and medical issues has been suggested. Conclusions: The data obtained in this study may be an important resource for further in vivo and in vitro functional assays to identify valuable therapeutic peptides.

The interferon-like proteins, Vagos, in Fenneropenaeus merguiensis elicit antimicrobial responses against WSSV and VPAHPND infection

The Vago interferon-like protein participates in the interplay between interferon regulatory factors and the expression of immune-responsive genes. Vago was initially perceived to participate only in the antiviral activation through JAK/STAT pathway. However, certain isoforms of Vago can stimulate antimicrobial responses. Here we identify Vago isoforms in Fenneropenaeus merguiensis (FmVagos) and how they function in antiviral and antibacterial responses against highly invasive pathogens, including white spot syndrome virus (WSSV) and Vibrio parahaemolyticus (VP_AHPND). Three isoforms of FmVagos were identified: FmVago4, FmVago5a, and FmVago5b, and expressed throughout tissues of the shrimp. During infection, FmVago4, FmVago5a, and FmVago5b, were up-regulated after WSSV and VP_AHPND challenges at certain time points. Pre-injection of purified recombinant FmVago4 (rVago4), FmVago5a (rVago5a), and FmVago5b (rVago5b) proteins could significantly reduce the mortality of shrimp upon WSSV infection, while the increase of survival rate of VP_AHPND-infected shrimp was observed only in rVago4 treatment. The immunity routes that FmVagos might instigate in response to the pathogens were examined by qRT-PCR, revealing that the JAK/STAT pathway was activated after introducing rVago4, rVago5a, and rVago5b, while the Toll/IMD pathway and proPO system, combined with PO activity, were provoked only in the rVago4-treated shrimp. Our finding suggests cross-talk between Vago's antiviral and antimicrobial responses in shrimp immunity. These findings complement previous studies in which Vago and its specific isoform could promote viral and bacterial clearance in shrimp.

Single-cell RNA-seq uncovered hemocyte functional subtypes and their differentiational characteristics and connectivity with morphological subpopulations in Litopenaeus vannamei

Hemocytes play central roles in shrimp immune system, whereas whose subclasses have not yet been completely defined. At present, the morphological classification of hemocytes is inadequate to classify the complete hemocyte repertoire and elucidate the functions and differentiation and maturation processes. Based on single-cell RNA sequencing (scRNA-seq) of hemocytes in healthy Litopenaeus vannamei, combined with RNA-FISH and flow cytometric sorting, we identified three hemocyte clusters including TGase+ cells, CTL+ cells and Crustin+ cells, and further determined their functional properties, potential differentiation trajectory and correspondence with morphological subpopulations. The TGase+ cells were mainly responsible for the coagulation, exhibiting distinguishable characteristics of hyalinocyte, and appeared to be developmentally arrested at an early stage of hemocyte differentiation. The CTL+ cells and Crustin+ cells arrested at terminal stages of differentiation mainly participated in recognizing foreign pathogens and initiating immune defense responses, owning distinctive features of granule-containing hemocytes. Furthermore, we have revealed the functional sub-clusters of three hemocyte clusters and their potential differentiation pathways according to the expression of genes involved in cell cycle, cell differentiation and immune response, and the successive differentiation and maturation of hyalinocytes to granule-containing hemocytes have also mapped. The results revealed the diversity of shrimp hemocytes and provide new theoretical rationale for hemocyte classification, which also facilitate systematic research on crustacean immunity.

The Antioxidant Effect of Natural Antimicrobials in Shrimp Primary Intestinal Cells Infected with Nematopsis messor

Nematopsis messor infections severely impact on shrimp’s health with devastating economic consequences on shrimp farming. In a shrimp primary intestinal cells (SGP) model of infection, a sub-inhibitory concentration (0.5%) of natural antimicrobials (Aq) was able to reduce the ability of N. messor to infect (p < 0.0001). To prevent N. messor infection of SGP cells, Aq inhibits host actin polymerization and restores tight junction integrity (TEER) and the expression of Zo-1 and occluding. The oxidative burst, caused by N. messor infection, is attenuated by Aq through the inhibition of NADPH-produced H2O2. Simultaneous to the reduction in H2O2 released, the activity of catalase (CAT) and superoxide dismutase (SOD) were also significantly increase (p < 0.0001). The antimicrobial mixture inactivates the ERK signal transduction pathway by tyrosine dephosphorylation and reduces the expression of DCR2, ALF-A, and ALF-C antimicrobial peptides. The observed in vitro results were also translated in vivo, whereby the use of a shrimp challenge test, we show that in N. messor infected shrimp the mortality rate was 68% compared to the Aq-treated group where the mortality rate was maintained at 14%. The significant increase in CAT and SOD activity in treated and infected shrimp suggested an in vivo antioxidant role for Aq. In conclusion, our study shows that Aq can efficiently reduce N. messor colonization of shrimp’s intestinal cells in vitro and in vivo and the oxidative induced cellular damage, repairs epithelial integrity, and enhances gut immunity.

Transcriptomic Analysis of the Venom Gland and Enzymatic Characterization of the Venom of Phoneutria depilata (Ctenidae) from Colombia

The transcriptome of the venom glands of the Phoneutria depilata spider was analyzed using RNA-seq with an Illumina protocol, which yielded 86,424 assembled transcripts. A total of 682 transcripts were identified as potentially coding for venom components. Most of the transcripts found were neurotoxins (156) that commonly act on sodium and calcium channels. Nevertheless, transcripts coding for some enzymes (239), growth factors (48), clotting factors (6), and a diuretic hormone (1) were found, which have not been described in this spider genus. Furthermore, an enzymatic characterization of the venom of P. depilata was performed, and the proteomic analysis showed a correlation between active protein bands and protein sequences found in the transcriptome. The transcriptomic analysis of P. depilata venom glands show a deeper description of its protein components, allowing the identification of novel molecules that could lead to the treatment of human diseases, or could be models for developing bioinsecticides.

A Dicer2 from Scylla paramamosain activates JAK/STAT signaling pathway to restrain mud crab reovirus

A Dicer2 gene from Scylla paramamosain, named SpDicer2, was cloned and characterized. The full length of SpDicer2 mRNA contains a 121 bp 5'untranslated region (UTR), an open reading frame (ORF) of 4518 bp and a 3' UTR of 850 bp. The SpDicer2 protein contains seven characteristic Dicer domains and showed 34%-65% identity and 54%-79% similarity to other Dicer protein domains, respectively. The mRNA of SpDicer2 was high expressed in hemocytes, intestine and gill and low expressed in the eyestalk and muscle. Moreover, expression of SpDicer2 was significantly responsive to challenges by mud crab reovirus (MCRV), Poly(I:C), LPS, Staphylococcus aureus and Vibrio parahaemolyticus. SpDicer2 was dispersedly presented in the cytoplasm except for a small amount in the nucleus. SpDicer2 could activate SpSTAT to translocate from the cytoplasm to the nucleus, and significantly increase the transcription activity of the wsv069 promoter, suggesting that SpDicer2 activated the JAK/STAT pathway. Furthermore, silencing of SpDicer2 in vivo increased the mortality of MCRV infected mud crab and the viral load in tissues and down-regulated the expression of multiple components of Toll, IMD and JAK-STAT pathways and almost all the examined immune effector genes. These results suggested that SpDicer2 could play an important role in defense against MCRV via activating the JAK/STAT signaling pathways in mud crab.

Shrimp Vago5 activates an innate immune defense upon bacterial infection

Acute hepatopancreatic necrosis disease, AHPND, caused by a specific Vibrio parahaemolyticus (VP_AHPND) strain, results in a great loss of global shrimp production. This study performed suppression subtractive hybridization (SSH) to identify differentially expressed genes from white shrimp Penaeus vannamei hemocyte upon VP_AHPND infection. Among the immune-related genes identified, Vago5, kunitz, secretory leukocyte proteinase inhibitor, and profilin are the most abundant genes classified as the up-regulated genes in the SSH library. The qRT-PCR results show that only Vago5 was highly up-regulated at 3 and 6 h post-VP_AHPND challenge, whereas kunitz, secretory leukocyte proteinase inhibitor, and profilin were highly up-regulated at 48 h post-VP_AHPND challenge. As an early VP_AHPND infection-responsive gene, Vago5 was further functional characterized by RNA interference. Knockdown of Vago5 gene resulted in the significantly rapid increase of shrimp mortality and the number of bacteria in the stomach and hepatopancreas upon VP_AHPND infection. Moreover, downstream genes of Toll, IMD, and JAK/STAT pathways and phenoloxidase system were analyzed for the expression in the VP_AHPND-infected shrimp hemocyte after dsVago5 treatment. Vago5 gene knockdown resulted in a significant decrease in transcript levels of PEN4, TNF, and PO2 genes as well as PO activity in the hemolymph, suggesting that Vago5 might modulate antibacterial infection through activation of the genes in the NF-κB mediated pathways, JAK/STAT pathway, and phenoloxidase system.

Characterization of a single-domain von Willebrand factor type C protein (HaSVC) from the salivary gland of the tick Hyalomma asiaticum

As a widely distributed arthropod and vector for various pathogens, Hyalomma asiaticum presents great risk and potential losses in animal husbandry. Effective measures, including the use of vaccines, are necessary for controlling ticks and tick-borne diseases. A concise understanding of the tick-host interaction associated molecules and pathways is required for vaccine development. In the present study, a protein containing a single-domain von Willebrand factor type C (HaSVC) was isolated from H. asiaticum and was subjected to functional identification. As a result, the full-length sequence of the HaSVC (506 bp) gene was obtained, which putatively encodes 100 amino acids with a predicted molecular mass of 11 kDa, excluding the 23-amino acid signal peptide. HaSVC contains 8 cysteines to form 4 disulfide bonds. The native HaSVC protein was detected in multiple tick organs. HaSVC neither attenuated the anti-coagulation process nor directly affected the blood feeding of adult ticks. However, the purified recombinant protein HaSVC (rHaSVC/GST) significantly increased the proliferation of mice spleen cells. This might suggest a regulatory function for HaSVC on inflammation, thus providing new information that may explain the "crosstalk" between ticks and hosts.

Chromosome-Level Genome Assembly of Nephotettix cincticeps (Uhler, 1896) (Hemiptera: Cicadellidae: Deltocephalinae)

The green rice leafhopper, Nephotettix cincticeps (Uhler), is an important rice pest and a vector of the rice dwarf virus in Asia. Here, we produced a high-quality chromosome-level genome assembly of 753.23 Mb using PacBio (∼110×) and Hi-C data (∼94×). It contained 163 scaffolds and 950 contigs, whose scaffold/contig N50 lengths reached 85.36/2.57 Mb. And 731.19 Mb (97.07%) of the assembly was anchored into eight pseudochromosomes. Genome completeness was attained to 97.0% according to the insect reference Benchmarking Universal Single-Copy Orthologs (BUSCO) gene set (n = 1,367). We masked 347.10 Mb (46.08%) of the genome as repetitive elements. Nine hundred sixty-two noncoding RNAs were identified and 14,337 protein-coding genes were predicted. We also assigned GO term and KEGG pathway annotations for 10,049 and 9,251 genes, respectively. Significantly expanded gene families were primarily involved in immunity, cuticle, digestion, detoxification, and embryonic development. This study provided a crucial genomic resource for better understanding on the biology and evolution in family Cicadellidae.

Litopenaeus vannamei Sma and Mad related protein 5 gene is involved in stress response and white spot syndrome virus infection

Cell survival is based on the stability of intracellular state. It was well known that biochemical reactions in cells require specific intracellular environments, such as pH and calcium concentration. While the mechanism of stabilizing the intracellular environment is complex and far from clear. In this study, a Sma and Mad related protein 5 gene (LvSmad5) of Litopenaeus vannamei was cloned. LvSmad5 was located to both cytoplasm and nucleus. And subcellular localization of LvSmad5 was responsed to the changing of cells internal and external environment. Besides, it was found that subcellular localization of LvSmad5 was also regulated by unfolded protein response. Moreover, it was proved that nucleic localization of LvSmad5 could significantly increase the white spot syndrome virus (WSSV) infection in shrimp, and knockdown expression of LvSmad5 decreased the cumulative mortality of WSSV infection shrimp. Further investigation revealed that cytoplasm LvSmad5 could interplay with shrimp hexokinase 1, and contribute to glycolysis. These results indicated that LvSmad5 played a role in L. vannamei environmental stress response, and was used by WSSV for its replication.

Interferon functional analog activates antiviral Jak/Stat signaling through integrin in an arthropod

Drosophila Vago is a small antiviral peptide. Its ortholog in Culex mosquito was found to be an interferon-like cytokine that limits virus replication through activating Jak/Stat signaling. However, this activation is independent of Domeless, the sole homolog of vertebrate type I cytokine receptor. How Vago activates the Jak/Stat pathway remains unknown. Herein, we report this process is dependent on integrin in kuruma shrimp (Marsupenaeus japonicus). Shrimp Vago-like (MjVago-L) plays an antiviral role by activating the Jak/Stat pathway and inducing Stat-regulated Ficolin. Blocking integrin abrogates the role of MjVago-L. The interaction between MjVago-L and integrin β3 is confirmed. An Asp residue in MjVago-L is found critical for the interaction and MjVago-L's antiviral role. Moreover, Fak, a key adaptor of integrin signaling, mediates MjVago-L-induced Jak/Stat activation. Therefore, this study reveals that integrin, as the receptor of MjVago-L, mediates Jak/Stat activation. The establishment of the MjVago-L/integrin/Fak/Jak/Stat/Ficolin axis provides insights into antiviral cytokine signaling in invertebrates.

Phosphorylation of Shrimp Tcf by a Viral Protein Kinase WSV083 Suppresses Its Antiviral Effect

Nuclear DNA-binding TCF proteins, which act as the main downstream effectors of Wnt signaling, are essential for the regulation of cell fate and innate immunity. However, their role during viral infection in shrimp remains unknown. Herein, we demonstrated that Litopenaeus vannamei TCF (LvTcf) acts independently of Lvβ-catenin to promote interferon-like protein LvVago1 production, thus mounting the response to WSSV infection. Further, we observed that WSV083, a WSSV serine/threonine protein kinase, bound to LvTcf and phosphorylated it. Phosphorylated LvTcf was then recognized and degraded via the ubiquitin-proteasome pathway. Moreover, mass spectrometry analyses indicated that the T39 and T104 residues of LvTcf were target sites phosphorylated by WSV083. Point mutation analyses suggested that additional sites of LvTcf may undergo phosphorylation via WSV083. Taken together, the current work provides valuable insights into host immunity and viral pathogenesis. LvTcf is not only a modulator of shrimp innate immunity but is also an important target for WSSV immune evasion. Thus, the current findings will help improve disease control in shrimps.

A truncated intracellular Dicer-like molecule involves in antiviral immune recognition of oyster Crassostrea gigas

The enzyme Dicer is best known for its role as an endoribonuclease in the small RNA pathway, playing a crucial role in recognizing viral double-stranded RNA (dsRNA) and inducing down-stream cascades to mediate anti-virus immunity. In the present study, a truncated Dicer-like gene was identified from oyster Crassostrea gigas, and its open reading frame (ORF) encoded a polypeptide (designed as CgDCL) of 530 amino acids. The CgDCL contained one N-terminal DEAD domain and a C-terminal helicase domain, but lack the conserved PAZ domain, ribonuclease domain (RIBOc) and dsRNA binding domain. The mRNA transcripts of CgDCL were detected in all the examined tissues with high expression levels in lip, gills and haemocytes, which were 62.06-fold, 48.91-fold and 47.13-fold (p < 0.05) of that in mantle, respectively. In the primarily cultured oyster haemocytes, the mRNA transcripts of CgDCL were significantly induced at 12 h after poly(I:C) stimulation, which were 4.04-fold (p < 0.05) of that in control group. The expression level of CgDCL mRNA in haemocytes was up-regulated significantly after dsRNA and recombinant interferon-like protein (rCgIFNLP) injection, which was 12.87-fold (p < 0.01) and 3.22-fold (p < 0.05) of that in control group, respectively. CgDCL proteins were mainly distributed in the cytoplasm of haemocytes. The recombinant CgDCL protein displayed binding activity to dsRNA and poly(I:C), but no obvious dsRNA cleavage activity. These results collectively suggest that truncated CgDCL from C. gigas was able to be activated by poly(I:C), dsRNA and CgIFNLP, and functioned as an intracellular recognition molecule to bind nucleic acid of virus, indicating a potential mutual cooperation between RNAi and IFN-like system in anti-virus immunity of oysters.

RNAi-based antiviral immunity of shrimp

As a kind of important economic marine crustaceans in aquaculture, shrimp can be infected by more than 20 viruses. To fight against the virus invasion, shrimp have developed the innate immunity, including RNA interference (RNAi). RNAi, mediated by short interfering RNAs (siRNAs) or microRNAs (miRNAs), plays important roles in virus-host interactions. At present, RNAi is considered to be an efficient antiviral response of shrimp. The siRNA-based RNAi, first recognized as an antiviral response of animals to resist RNA viruses, has emerged in animals as an efficient antiviral strategy against the invasion of DNA viruses and RNA viruses. In shrimp, as well as in other animals, siRNA contains a seed region (2nd-7th nt) and a supplementary region (12th-17th nt). Based on the findings in shrimp and other animals, miRNAs are essential regulators of virus-host interactions, such as virus infection/latency, and host apoptosis, autophagy and phagocytosis. Except for the seed sequence (2nd-7th), the complementary bases (to the target mRNA sequence) of a miRNA 9th-18th non-seed sequence are essential for the miRNA targeting. So far, rapidly growing evidences have supported the existence of functional RNAi machinery in shrimp. In this review, we summarize the progress of RNAi in the antiviral immune response of shrimp. The potential applications of RNAi to control shrimp diseases were also summarized.

Assessment of the function of gonad-specific PmAgo4 in viral replication and spermatogenesis in Penaeus monodon

Argonaute family is phylogenetically subdivided into Ago and Piwi subfamilies that operate either transcriptional or post-transcriptional regulation in association with particular types of small RNAs. Among the four members of Ago subfamily (PmAgo1-4) found in black tiger shrimp Penaeus monodon, PmAgo4 exhibits gonad-restricted expression and takes part in transposon repression as the Piwi subfamily. While PmAgo1-3 participate in RNA interference (RNAi)-based mechanism, the role of PmAgo4 in RNAi is still mysterious, and was therefore investigated in this study. The results showed that knockdown of PmAgo4 in shrimp testis did not have a significant effect on the potency of PmRab7 silencing by dsPmRab7. In addition, replication of YHV as well as YHV-induced cumulative mortality in PmAgo4-knockdown shrimp are comparable to the control shrimp, suggesting the irrelevant association of PmAgo4 with RNAi-mediated gene silencing and antiviral immunity. Since PmAgo4 did not function in common with the Ago subfamily, its potential function in gametogenesis of male shrimp was further investigated. The reduction of PmAgo4 transcript levels in male shrimp revealed significant defect in testicular maturity as measured by Testicular Index (TI). Moreover, the numbers of mature sperm in spermatophore of PmAgo4-knockdown shrimp were significantly decreased comparing with the control shrimp. Our studies thus suggest a distinctive role of PmAgo4 that is not consistent with a dsRNA-mediate gene regulation and virus replication, but has a key function in controlling spermatogenesis in P. monodon.

A Litopenaeus vannamei TRIM32 gene is involved in oxidative stress response and innate immunity

Tripartite motif (TRIM) family proteins are named by the presence of tripartite motifs in their amino terminal domains. Apart from the amino terminal, their carboxyl terminal contain variable domains which mediate diverse functions of the TRIM proteins. It had been found that TRIM proteins played important roles in distinct biological processes, such as innate immunity, anti-tumor immunity, cell cycle regulation and so on. In the present study, we cloned a TRIM32 (LvTRIM32) gene from Litopenaeus vannamei. LvTRIM32 was highly expressed in hemocytes, gills and epidermis, and subcellular localization analysis indicated that it was widely distributed in S2 cells. In vitro ubiquitination assays indicated that LvTRIM32 had E3 ubiquitin ligase activity. Results of real-time RT-PCR assay showed that LvTRIM32 was induced in shrimp hemocytes upon oxidative stress. It was also proved that the promoter activity of LvTRIM32 was enhanced by NF-E2-related factor, and knocked-down expression of LvTRIM32 depressed the expression of malic enzyme and epoxide hydrolase. Downregulated LvTRIM32 suppressed the cumulative mortality of shrimp under oxidative stress. Moreover, it was found that LvTRIM32 could be induced in shrimp hemocytes upon immunostimulation, and downregulated LvTRIM32 increased the cumulative mortality of shrimp infected with white spot syndrome virus (WSSV) or Vibrio alginolyticus. Collecting results suggested that LvTRIM32 was a member of shrimp antioxidant stress system, and it was also involved in WSSV- or V. alginolyticus-infection resistance.

A novel Laccase gene from Litopenaeus vannamei is involved in the immune responses to pathogen infection and oxidative stress

Laccases (Lacs) are copper-containing oxidase enzymes that are found in various plants, fungi, and microorganisms. For invertebrates, particularly insects and crustaceans, Lacs have been shown to be involved in immune responses. In shrimp, a Lac gene has been cloned and functionally characterized, which revealed that it is involved in shrimp anti-pathogen infection. In the present study, a novel Lac gene (LvLac2) was cloned from Litopenaeus vannamei. Real-time RT-PCR analysis showed that LvLac2 is induced by white spot syndrome virus (WSSV)- or Vibrio alginolyticus infection. In addition, the downregulated expression of LvLac2 decreased the cumulative mortality of WSSV- or V. alginolyticus infected shrimps. Moreover, LvLac2 is also induced by oxidative stress. Knocking down the expression of LvLac2 decreased the severity of hepatopancreatic injury caused by oxidative stress, as well as reduced the cumulative shrimp mortality during oxidative stress. Furthermore, gene reporter assays showed that the expression of LvLac2 is regulated by NF-E2-related factor 2, which is the key transcription factor of the oxidative stress response signaling pathway. Our study revealed that LvLac2 not only participates in immune responses against infections in L. vannamei but is also involved in oxidative stress responses.

Key Mechanistic Principles and Considerations Concerning RNA Interference

Canonical RNAi, one of the so-called RNA-silencing mechanisms, is defined as sequence-specific RNA degradation induced by long double-stranded RNA (dsRNA). RNAi occurs in four basic steps: (i) processing of long dsRNA by RNase III Dicer into small interfering RNA (siRNA) duplexes, (ii) loading of one of the siRNA strands on an Argonaute protein possessing endonucleolytic activity, (iii) target recognition through siRNA basepairing, and (iv) cleavage of the target by the Argonaute's endonucleolytic activity. This basic pathway diversified and blended with other RNA silencing pathways employing small RNAs. In some organisms, RNAi is extended by an amplification loop employing an RNA-dependent RNA polymerase, which generates secondary siRNAs from targets of primary siRNAs. Given the high specificity of RNAi and its presence in invertebrates, it offers an opportunity for highly selective pest control. The aim of this text is to provide an introductory overview of key mechanistic aspects of RNA interference for understanding its potential and constraints for its use in pest control.

A Polymorphic (CT)n-SSR Influences the Activity of the Litopenaeus vannamei IRF Gene Implicated in Viral Resistance

Simple sequence repeats (SSRs) of short nucleotide motifs occur very frequently in the 5′ untranslated coding region (5′-UTR) of genes and have been implicated in the regulation of gene expression. In this study, we identified an SSR with a variable number of CT repeats in the 5′-UTR of the Litopenaeus vannamei IRF (LvIRF) gene that has been shown to mediate antiviral responses by inducing the expression of Vago, a functional homolog of mammalian IFN. We then explored the effects of varying the number of (CT)n repeats on the expression of LvIRF using both dual-luciferase reporter assays and Western blots. Our results demonstrate that the length of the (CT)n-SSR in this gene can influence the expressional level of LvIRF, in that a shorter (CT)n repeat had a stronger ability to induce the expression of LvIRF. Moreover, we found that the (CT)n repeat in LvIRF was associated with viral resistance in shrimp. Individual shrimps with shorter (CT)n repeats in the 5′-UTR of LvIRF exhibited high tolerance to white spot syndrome virus (WSSV), and this trait was inherited in offspring. Taken together, these results indicated that this (CT)n-SSR could be used as a molecular marker for shrimp breeding for WSSV resistance.

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.

Identification and functional characterization of a C-type lectin gene from Litopenaeus vannamei that is associated with ER-stress response

C-type lectins (CTLs), which bind carbohydrates in a Ca²⁺-dependent manner, are involved in many cellular activities, especially immunity. CTLs play important roles in both the antibacterial and the antiviral immune response and are also associated with autoimmunity. Several CTLs have been investigated in crustaceans, primarily with respect to their function in the immune response. In this study, we cloned a novel CTL gene (LvCTLU) from Litopenaeus vannamei. LvCTLU is involved in microbe agglutination and phagocytosis. Downregulating LvCTLU increased the cumulative mortality of L. vannamei after Vibrio parahemolyticus infection. Similar to other reported CTLs, LvCTLU also had antiviral properties. Downregulation of LvCTLU also increased the cumulative mortality of L. vannamei after infection with white spot syndrome virus. More importantly, LvCTLU expression was induced by the unfolded protein response (UPR), which is the key pathway in the endoplasmic reticulum (ER)-stress response of eukaryotic organism. Our results suggested that this protein might be involved in the shrimp ER-stress response. Reporter gene assay indicated that LvCTLU was regulated by X-box-binding protein 1, which is the key transcription factor in the UPR. Our study thus revealed that LvCTLU plays vital roles in both the anti-pathogen immune response and the ER-stress response.

Effects of environmental stress on shrimp innate immunity and white spot syndrome virus infection

The shrimp aquaculture industry is plagued by disease. Due to the lack of deep understanding of the relationship between innate immune mechanism and environmental adaptation mechanism, it is difficult to prevent and control the diseases of shrimp. The shrimp innate immune system has received much recent attention, and the functions of the humoral immune response and the cellular immune response have been preliminarily characterized. The role of environmental stress in shrimp disease has also been investigated recently, attempting to clarify the interactions among the innate immune response, the environmental stress response, and disease. Both the innate immune response and the environmental stress response have a complex relationship with shrimp diseases. Although these systems are important safeguards, allowing shrimp to adapt to adverse environments and resist infection, some pathogens, such as white spot syndrome virus, hijack these host systems. As shrimp lack an adaptive immune system, immunization therapy cannot be used to prevent and control shrimp disease. However, shrimp diseases can be controlled using ecological techniques. These techniques, which are based on the innate immune response and the environmental stress response, significantly reduce the impact of shrimp diseases. The object of this review is to summarize the recent research on shrimp environmental adaptation mechanisms, innate immune response mechanisms, and the relationship between these systems. We also suggest some directions for future research.

WSSV-host interaction: Host response and immune evasion

As invertebrates, shrimps rely on multiple innate defense reactions, including humoral immunity and cellular immunity to recognize and eliminate various invaders, such as viruses. White spot syndrome virus (WSSV) causes the most prevalent and devastating viral disease in penaeid shrimps, which are the most widely cultured species in the coastal waters worldwide. In the last couple of decades, studies about WSSV implicate a dual role of the immune system in protecting shrimps against the infection; these studies also explore on the pathogenesis of WSSV infection. Herein, we review our current knowledge of the innate immune responses of shrimps to WSSV, as well as the molecular mechanisms used by this virus to evade host immune responses or actively subvert them for its own benefit. Deciphering the interactions between WSSV and the shrimp host is paramount to understanding the mechanisms that regulate the balance between immune-mediated protection and pathogenesis during viral infection and to the development of a safe and effective WSSV defensive strategy.

Suppression of argonautes compromises viral infection in Penaeus monodon

Argonaute (Ago) proteins, the catalytic component of an RNA-induced silencing complex (RISC) in RNA interference pathway, function in diverse processes, especially in antiviral defense and transposon regulation. So far, cDNAs encoding four members of Argonaute were found in Penaeus monodon (PmAgo1-4). Two PmAgo proteins, PmAgo1 and PmAgo3 shared high percentage of amino acid identity to Ago1 and Ago2, respectively in other Penaeid shrimps. Therefore, the possible roles of PmAgo1 and PmAgo3 upon viral infection in shrimp were characterized in this study. The level of PmAgo1 mRNA expression in shrimp hemolymph was stimulated upon YHV challenge, but not with dsRNA administration. Interestingly, silencing of either PmAgo1 or PmAgo3 using sequence-specific dsRNAs impaired the efficiency of PmRab7-dsRNA to knockdown shrimp endogenous PmRab7 expression. Inhibition of yellow head virus (YHV) replication and delayed mortality rate were also observed in both PmAgo1-and PmAgo3-knockdown shrimp. In addition, silencing of PmAgo3 transcript, but not PmAgo1, revealed partial inhibition of white spot syndrome virus (WSSV) infection and delayed mortality rate. Therefore, our study provides insights into PmAgo1and PmAgo3 functions that are involved in a dsRNA-mediated gene silencing pathway and play roles in YHV and WSSV replication in the shrimp.

microRNAs in Macrobrachium olfersii embryos: Identification, their biogenesis components and potential targets

In embryonic development, microRNAs (miRNAs) regulate the complex gene expression associated with the complexity of embryogenesis. Today, few studies have been conducted on the identification of miRNAs and components of miRNA biogenesis on embryonic development in crustaceans, especially in prawns. In this context, the aim of this study was to identify in silico components of miRNA biogenesis, and miRNAs and potential target genes during embryonic development in the prawn Macrobrachium olfersii through small RNAs and transcriptome analyses. Using the miRDeep2 program, we identified 17 miRNA precursors in M. olfersii, which seven (miR-9, miR-10, miR-92, miR-125, miR-305, miR-1175, and miR-2788) were reported in the miRBase database, indicating high evolutionary conservation of these sequences among animals. The other 10 miRNAs of M. olfersii were novel miRNAs and only similar to Macrobrachium niponnense miRNAs, indicating genus-specific miRNAs. In addition, eight key components of miRNA biogenesis (DROSHA, PASHA/DGCR8, XPO5, RAN, DICER, TRBP2, AGO, and PIWI) were identified in M. olfersii embryos unigenes. In the annotation of miRNA targets, 516 genes were similar to known sequences in the GenBank database. Regarding the conserved miRNAs, we verified that they were differentially expressed during embryonic development in M. olfersii. In conclusion, this is the first study that identifies conserved and novel miRNAs in the prawn M. olfersii with some miRNA target genes involved in embryonic development. Our results will allow further studies on the function of these miRNAs and miRNA biogenesis components during embryonic development in M. olfersii and other prawns of commercial interest.

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.

Upregulation of Aedes aegypti Vago1 by Wolbachia and its effect on dengue virus replication

Dengue infection along with its related disease conditions poses a significant threat to human health. The pathogen responsible for this infection is dengue virus (DENV) which is primarily transmitted to humans through the bites of Aedes aegypti mosquitoes. Unavailability of a potent vaccine has recently sparked renewed research endeavours aimed at vector control. To date, Wolbachia as an endosymbiotic bacterium has shown promise as a novel biocontrol agent to restrict DENV replication in the vector, although the underlying antiviral mechanism remains elusive. Recent studies have demonstrated the potential role of Vago as a novel secretory protein involved in cross-talk between the innate immune pathways in Culex quinquefasciatus mosquitoes to restrict West Nile virus replication. In this study, we have identified two homologs of the Vago protein in Ae. aegypti and looked into their modulation in the case of Wolbachia wMelPop strain infection. Furthermore, we have investigated the role of AeVago1, that is highly induced by Wolbachia, in the context of Wolbachia-mosquito-DENV interactions. Knockdown studies of the AeVago1 gene in Wolbachia-infected cells led to significant increases in DENV replication, with no effect on Wolbachia density. Our results suggest that the Wolbachia-induced AeVago1 in Ae. aegypti may function as a host factor to suppress DENV replication in the mosquito.

The role of a single gene encoding the Single von Willebrand factor C-domain protein (SVC) in bumblebee immunity extends beyond antiviral defense

The Single von Willebrand factor C-domain proteins (SVCs) are a group of short proteins mainly found in arthropods. They are proposed to be responsive in relation to environmental challenges including the nutritional status, bacterial and viral infections. The SVC protein Vago acts as a cross-talk molecule between the small interfering RNA (siRNA) pathway and the Jak/STAT pathway upon viral infection in Drosophila melanogaster and Culex mosquito cells. Unlike flies and mosquitoes that possess diverse SVCs, most bee species only have one of which the function remains unclear. Here we investigated whether this single SVC within the genome of the bumblebee Bombus terrestris is also involved in the host antiviral immunity and whether links with other immune pathways can be found. We can show the presence of two key characteristics of Vago linked with the single SVC in B. terrestris (BtSVC). The antiviral character is proven by silencing BtSVC, which lead to increased Israeli acute paralysis virus (IAPV) levels in the fat body. Second, the silencing of BtDicer-2 resulted in a lower expression of BtSVC and increased IAPV levels, confirming the link between Dicer-2 and BtSVC. We were, however, unable to demonstrate a third known role of Vago in the activation of the Jak/STAT pathway. This is probably because we lack good markers for this pathway in bumblebees. Interestingly, we found that BtSVC contributes to the basal expression levels of four antimicrobial peptide (AMP)-coding genes in the fat body of the bumblebees. Therefore, the single SVC gene in bumblebees may be involved in both host antiviral immunity and basal AMPs expression.

Litopenaeus vannamei activating transcription factor 6 alpha gene involvement in ER-stress response and white spot symptom virus infection

A previous study found that inositol-requiring enzyme-1-X-box binding protein 1 (IRE1-XBP1) pathway and the protein kinase RNA (PKR)-like ER kinase-eIF2α (PERK-eIF2α) pathway of shrimp play roles in the unfolded protein response (UPR). And they also be proved that was involved in white spot symptom virus (WSSV) infection. Yet the functions of the third branch in shrimp UPR are still unclear. In this study, we showed that upon UPR activation, activating transcription factor 6 alpha (LvATF6α) of Litopenaeus vannamei was cleaved and transferred from the cytoplasm to the nucleus in 293T cells, indicating that the ATF6 pathway in shrimp is also a branch of UPR. Furthermore, LvATF6α could reduce the apoptosis rate of Drosophila Schneider 2 (S2) cells treated with actinomycin, and knock-down expression of LvATF6α increased the apoptosis rate of shrimp hemocytes. In vivo testing revealed that the short from LvATF6α (LvATF6α-s) was obviously increased after UPR activation or WSSV infection, indicating that the ATF6 pathway was activated in L. vannamei gills under such circumstances. Moreover, knock-down expression of LvATF6α could reduce the cumulative mortality and WSSV copy number in WSSV-infected shrimp. Further study revealed that WSSV may profit from shrimp ATF6 pathway activation in two aspects. First, LvATF6α-s significantly upregulated the expression of the WSSV genes (wsv023, wsv045, wsv083, wsv129, wsv222, wsv249, and wsv343). Second, LvATF6α-s inhibited apoptosis by negatively regulating the apoptosis signal-regulating kinase 1 - (c-Jun N-terminal kinase) pathway. All of these evidences suggested that the ATF6 pathway is a member of the L. vannamei UPR, and it is also engaged in WSSV infection.

Effect of immune gene silencing in WSSV infected tiger shrimp Penaeus monodon

White spot syndrome virus, continues to cause huge economic loss to aquaculture industry. In the absence of effective therapeutics to control WSSV, it is important to understand the host pathogen interaction at the molecular level. Suppression subtractive hybridization (SSH) cDNA library was constructed which led to identification of several differentially expressed genes in response to WSSV infection in Penaeus monodon. The genes expressed in SSH cDNA library of shrimp gill and gut tissues belonged to a wide range of biological functions. The three differentially expressed genes, Single von Willebrand factor type C domain protein (pmSVC), P53 protein gene (pmP53) and ADP ribosylation factor (pmArf) were up-regulated against WSSV infection and were further characterized by gene silencing to study the role of these shrimp immune genes on WSSV multiplication. The sequence-specific knock down of pmSVC, pmP53 and pmArf using the dsRNA revealed that in pmSVC-dsRNA inoculated shrimps WSSV replication was more with increased viral copy numbers when compared with pmP53-dsRNA and pmArf -dsRNA inoculated shrimps. The varied response of immune genes to WSSV infection, indicated that host genes may either inhibit virus replication to some extent or might act as a target to facilitate viral pathogenesis.

Heat shock 70 kDa protein cognate 5 involved in WSSV toleration of Litopenaeus vannamei

The expression levels of 97 unigenes encoding heat shock proteins of Litopenaeus vannamei was scanned, and ten of them were significantly induced by white spot syndrome virus (WSSV). Among these genes, heat shock 70 kDa protein cognate 5 (LvHSC70-5) was upregulated to the highest extent and subjected to further studies. Subcellular localization assay revealed that LvHSC70-5 was located in the mitochondria. Aside from WSSV infection, unfolded protein response activation and thermal stress could also upregulate LvHSC70-5. Results of reporter gene assay demonstrated that promoter of LvHSC70-5 was activated by L. vannamei heat shock factor protein 1, activating transcription factor 4 and thermal stress. A decrease in the expression of LvHSC70-5 could reduce the aggregation of proteins in hemocytes and the cumulative mortality of WSSV-infected L. vannamei. LvHSC70-5 in L. vannamei hemocytes was upregulated by mild thermal stress. In addition, mild thermal stress, decreased the copy number of WSSV in shrimp muscle and the cumulative mortality of WSSV-infected L. vannamei. Therefore, collecting results suggested that LvHSC70-5 should be involved in WSSV toleration of shrimp L. vannamei.

Characterization of an entomopathogenic fungi target integument protein, Bombyx mori single domain von Willebrand factor type C, in the silkworm, Bombyx mori

The insect cuticle works as the first line of defence to protect insects from pathogenic infections and water evaporation. However, the old cuticle must be shed in order to enter the next developmental stage. During each ecdysis, moulting fluids are produced and secreted into the area among the old and new cuticles. In a previous study, the protein Bombyx mori single domain von Willebrand factor type C (BmSVWC; BGIBMGA011399) was identified in the moulting fluids of Bo. mori and demonstrated to regulate ecdysis. In this study we show that in Bo. mori larvae, BmSVWC primarily locates to the integument (epidermal cells and cuticle), wing discs and head. During the moulting stage, BmSVWC is released into the moulting fluids, and is then produced again by epidermal cells after ecdysis. Fungal infection was shown to decrease the amount of BmSVWC in the cuticle, which indicates that BmSVWC is a target protein of entomopathogenic fungi. Thus, BmSVWC is mainly involved in maintaining the integrity of the integument structure, which serves to protect insects from physical damage and pathogenic infection.

White spot syndrome virus VP28 specific double-stranded RNA provides protection through a highly focused siRNA population

Several studies have demonstrated that injection of double-stranded RNAs (dsRNA) homologous to mRNA for the white spot syndrome virus (WSSV) viral protein 28 (VP28) can induce protection in shrimp against WSSV through RNA interference (RNAi). In comparison to shrimp injected with either PBS or a green fluorescent protein (GFP) nonspecific dsRNA, we obtained nearly complete protection against WSSV infection in shrimp injected with VP28 dsRNA. Upregulation of host genes associated with small RNA silencing was measured 48 hours post treatment in groups injected with dsRNA, and although the VP28-treated group remained moderately upregulated after challenge with WSSV, many-fold higher induction was observed in both control groups reflecting the ongoing viral infection. RNA sequencing of VP28-treated shrimp demonstrated a siRNA population dominated by high levels of 22 nt long molecules narrowly targeting the VP28 mRNA both before and after challenge with WSSV. Conversely, while no siRNAs targeting WSSV were detected before challenge, a broad response of 22 nt siRNAs mapping across the entire WSSV genome were found in both control groups after challenge. These results give detailed insight to how dsRNA targeting VP28 function to induce protection against WSSV, by generating a highly focused population of 22 nt long siRNA molecules.

Identification and functional characterization of a novel Spätzle gene in Litopenaeus vannamei

Shrimp innate immunity is the first line of resistance against pathogenic bacteria. The Toll-like receptor (TLR)-NF-κB pathway is vital in this immunity process. In this study, a novel Spätzle gene (LvSpz4) of Litopenaeus vannamei was cloned and functionally characterized. The open reading frame of LvSpz4 was 918 bp, which encoded a putative protein with 305 amino acids. LvSpz4 was most expressed in the gills of L. vannamei. This expression was induced by Vibrio alginolyticus or Staphylococcus aureus infection or lipopolysaccharide stimulation. The reporter gene assay showed that LvSpz4 could activate the promoters of Pen4, Drs, AttA, Mtk, and white spot syndrome virus immediate early gene1 in Drosophila Schneider 2 (S2) cells. Knockdown LvSpz4 increased the cumulative mortality of L. vannamei upon V. alginolyticus infection. The unfolded protein response (UPR) induced the expression of LvSpz4 in L. vannamei. Moreover, the promoter of LvSpz4 was activated by L. vannamei X-Box binding protein 1 and activating transcription factor 4 in S2 cells. These results suggested that LvSpz4 was involved in L. vannamei innate immunity and caused the crosstalk between the TLR-NF-κB pathway and UPR.

Two hemocyte sub-populations of kuruma shrimp Marsupenaeus japonicus

Hemocytes in the circulating hemolymph play important roles for immune responses in shrimp. Previous studies on immune responses by hemocytes in penaeid shrimp were based on gene expression analyses of the entire population of hemocytes and thus may have missed different immune responses of different hemocyte sub-populations. In this study, we separated hemocytes into two sub-populations by Percoll gradient centrifugation, morphological characteristics of each population were then analyzed by May-Giemsa staining, flow cytometry, and FACSCalibur. Results showed hemocytes were divided into an upper layer basophilic, and lower layer of eosinophilic hemocytes. Basophilic hemocytes were larger in size compared to eosinophilic hemocytes, which were more granulated than the basophilic hemocytes. Transcriptome analysis was then conducted through RNA-seq analysis by Miseq, which revealed 16 differentially-expressed transcripts between the two sub-populations. In the upper-layer, the highly expressed transcripts that were homologous to immune-related genes that suggest hemocytes from this layer may play as the regulator of immune system and control the action of other cells to eliminate pathogen. On the other hand, transcripts that were highly expressed in the lower-layer were homologous to the antimicrobial peptide (AMP) crustin, which supports that hemocytes on this layer have granules as crustins are normally secreted from hemocyte granules. The high expression of crustin in the lower-layer also provides insight on the mechanism of the anti-microbial function, where hemocytes produce and store AMPs in its granules. These differentially expressed genes are potential hemocyte molecular markers, and among them we identified one of the highly expressed genes in the hemocytes from the upper-layer (c11736_g1) to be a promising candidate molecular marker predicted to be a surface molecule, which is a common characteristic for molecular markers.

Insights from the Shell Proteome: Biomineralization to Adaptation

Bivalves have evolved a range of complex shell forming mechanisms that are reflected by their incredible diversity in shell mineralogy and microstructures. A suite of proteins exported to the shell matrix space plays a significant role in controlling these features, in addition to underpinning some of the physical properties of the shell itself. Although, there is a general consensus that a minimum basic protein tool kit is required for shell construction, to date, this remains undefined. In this study, the shell matrix proteins (SMPs) of four highly divergent bivalves (The Pacific oyster, Crassostrea gigas; the blue mussel, Mytilus edulis; the clam, Mya truncata, and the king scallop, Pecten maximus) were analyzed in an identical fashion using proteomics pipeline. This enabled us to identify the critical elements of a "basic tool kit" for calcification processes, which were conserved across the taxa irrespective of the shell morphology and arrangement of the crystal surfaces. In addition, protein domains controlling the crystal layers specific to aragonite and calcite were also identified. Intriguingly, a significant number of the identified SMPs contained domains related to immune functions. These were often are unique to each species implying their involvement not only in immunity, but also environmental adaptation. This suggests that the SMPs are selectively exported in a complex mix to endow the shell with both mechanical protection and biochemical 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.

Identification and functional characterization of a glucose regulated protein 94 gene in Litopenaeus vannamei and its responsiveness in WSSV infection

In the current study, a cDNA of glucose regulated protein 94 (LvGRP94) was cloned from Litopenaeus vannamei. Subcellular localization assay revealed that LvGRP94 expressed in endoplasmic reticulum (ER). And results of reported gene assays demonstrated that the promoter of LvGRP94 was activated by L. vannamei leucine zipper domain transcription factor X-box binding protein 1 (LvXBP1) or heat shock treatment. Furthermore, LvGRP94 was found to highly express in hemocytes as well as in epidermis by real-time RT-PCR. In addition, it was shown that LvGRP94 inhibited by LvXBP1 knocked-down in the hemocytes, was induced by white spot syndrome virus (WSSV) infection, or unfolded protein response (UPR) pathway activation. Importantly, decreasing LvGRP94 reduced the cumulative mortality of WSSV-infected shrimps and WSSV copies in shrimp muscle. These results suggested that LvGRP94 might involve in shrimp UPR pathway as well as WSSV infection.

Nidoviruses of Fish and Crustaceans

Viruses with diverse virion architectures demarcated into four families in the order Nidovirales have been discovered in vertebrate mammalian and fish species, as well as in invertebrate crustacean and mosquito species. The order is unified by nidoviruses sharing intermediate (12.7 kb) to very long (31.7 kb) (+) ssRNA genomes, each possessing a long 5′-terminal gene encoding overlapping ORF1a and ORF1b reading frames that contain a diversity of functionally related enzymes and that are translated in toto using a −1 ribosomal frameshift mechanism, as well as by semiconserved strategies for transcribing a nested set of 3′-coterminal subgenomic mRNAs that translate the viral proteins. The nidovirus that is most important to an aquaculture species is yellow head virus (YHV), which causes disease in shrimp farmed throughout the Eastern Hemisphere and is classified in the genus Okavirus, family Roniviridae. Fathead minnow nidovirus, genus Bafinivirus, subfamily Torovirinae, family Coronaviridae, also causes disease in minnows grown for the baitfish industry in the United States. Virions similar in morphology to okaviruses and bafiniviruses have also been detected in several crab species. Of these, however, only Eriocheir sinensis ronivirus, which causes disease in the Chinese mitten crab, an important freshwater aquaculture species in China, has been shown to possess a ~22 kb ssRNA genome that supports its being a nidovirus, but its taxonomic classification awaits genome sequence analysis. This chapter provides an overview of the structure, replication and biology of these viruses with a particular focus on YHV disease characteristics, diagnostic methods and disease prevention strategies.

Design and Construction of Shrimp Antiviral DNA Vaccines Expressing Long and Short Hairpins for Protection by RNA Interference

DNA vaccines present the aquaculture industry with an effective and economically viable method of controlling viral pathogens that drastically affect productivity. Since specific immune response is rudimentary in invertebrates, the presence of RNA interference (RNAi) pathway in shrimps provides a promising new approach to vaccination. Plasmid DNA vaccines that express short or long double stranded RNA in vivo have shown protection against viral diseases. The design, construction and considerations for preparing such vaccines are discussed.

Activation of Vago by interferon regulatory factor (IRF) suggests an interferon system-like antiviral mechanism in shrimp

There is a debate on whether invertebrates possess an antiviral immunity similar to the interferon (IFN) system of vertebrates. The Vago gene from arthropods encodes a viral-activated secreted peptide that restricts virus infection through activating the JAK-STAT pathway and is considered to be a cytokine functionally similar to IFN. In this study, the first crustacean IFN regulatory factor (IRF)-like gene was identified in Pacific white shrimp, Litopenaeus vannamei. The L. vannamei IRF showed similar protein nature to mammalian IRFs and could be activated during virus infection. As a transcriptional regulatory factor, L. vannamei IRF could activate the IFN-stimulated response element (ISRE)-containing promoter to regulate the expression of mammalian type I IFNs and initiate an antiviral state in mammalian cells. More importantly, IRF could bind the 5′-untranslated region of L. vannamei Vago4 gene and activate its transcription, suggesting that shrimp Vago may be induced in a similar manner to that of IFNs and supporting the opinion that Vago might function as an IFN-like molecule in invertebrates. These suggested that shrimp might possess an IRF-Vago-JAK/STAT regulatory axis, which is similar to the IRF-IFN-JAK/STAT axis of vertebrates, indicating that invertebrates might possess an IFN system-like antiviral mechanism.

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.

Instar-dependent systemic RNA interference response in Leptinotarsa decemlineata larvae

RNA interference (RNAi) is a promising approach to control Leptinotarsa decemlineata. In this study, RNAi efficiency by double-stranded RNA (dsRNA) targeting S-adenosyl-L-homocysteine hydrolase (LdSAHase) was compared among L. decemlineata first- to fourth-instar larvae. Ingesting dsLdSAHase successfully decreased the target gene expression, caused lethality, inhibited growth and impaired pupation in an instar- and concentration-dependent manner. To study the role of Dicer2 and Argonaute2 genes in RNAi efficiency, we identified LdDcr2a, LdDcr2b, LdAgo2a and LdAgo2b. Their expression levels were higher in young larvae than those in old ones. Exposure to dsegfp for 6 h significantly elevated LdDcr2a, LdDcr2b, LdAgo2a and LdAgo2b mRNA levels in the first-, second-, third- and fourth-instar larvae. When the exposure periods were extended, however, the expression levels were gradually reduced. Continuous exposure for 72 h significantly repressed the expression of LdAgo2a and LdAgo2b in the first, second and third larval instars, and the four genes in final instars. Moreover, we found that dsLdSAHase-caused LdSAHase suppressions and larval mortalities were influenced by previous dsegfp exposure: 12 h of previous exposure increased LdSAHase silencing and mortality of the final instar larvae, whereas 72 h of exposure reduced LdSAHase silencing and mortality. Thus, it seems the activities of core RNAi-machinery proteins affect RNAi efficiency in L. decemlineata.