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.

Toll receptor 2 (Toll2) positively regulates antibacterial immunity but promotes white spot syndrome virus (WSSV) infection in shrimp

The Toll family of receptors are a group of conserved pattern recognition receptors (PRRs) essentially controlling the initiation of innate immune responses. The white spot syndrome virus (WSSV) and Vibrio parahaemolyticus are major pathogens of aquaculture shrimp. Previous study has suggested that expression of the Toll2 receptor in Pacific white shrimp Penaeus vannamei was up-regulated by white spot syndrome virus (WSSV) infection but did not significantly changed upon infection with the bacterial pathogen Vibrio parahaemolyticus. The current study intends to investigate the role of P. vannamei Toll2 in antibacterial and antiviral immunity. We demonstrated that compared with the control, the Toll2-silenced shrimp was more susceptible to V. parahaemolyticus infection, suggesting that Toll2 may play a positive role in antibacterial immunity. However, silencing of Toll2 significantly enhanced survivorship of shrimp infected with WSSV and reduced the viral load in shrimp tissues. The expression of WSSV structural protein VP28 was also inhibited in Toll2-silenced shrimp. Histologic pathology analysis further showed that the WSSV infection was attenuated in stomach tissues from Toll2-silenced shrimp. These suggested that Toll2 could promote WSSV infection in shrimp. In Toll2-silenced shrimp, expression of antimicrobial peptides ALFs and PENs was significantly changed, which may contribute to the role of Toll2 in antibacterial immunity and WSSV infection.

Immune toxicity of phenanthrene and its combined effects of white spot syndrome virus on the survival of kuruma shrimp (Penaeus Japonicus)

Shrimp inhabiting coasts that are frequented by humans are exposed to various pollutants. Additionally, viral infections that cause serious damage to shrimp populations have been observed in these environments. The present study sought to evaluate the immunotoxic effects of phenanthrene (Phe), a pollutant detected in coastal environments, on kuruma shrimp (Penaeus japonicus). We further examined the survival of shrimp following combined exposure to Phe (30 or 300 μg/L) and white spot syndrome virus (WSSV). Results show that exposure to Phe for seven days decreased immune system-related parameters, including total hemocyte count and phenoloxidase activity in hemolymph (p < 0.05). However, these effects were not detected after three days of exposure. Moreover, a combined exposure assay revealed that shrimp mortality increased following exposure to 300 μg/L Phe and infection with WSSV. The number of WSSV gene copies was also observed to increase in these co-exposed shrimp. Taken together, these results indicate that long-term Phe exposure impairs the immune system of P. japonicus, resulting in fatal proliferation of WSSV. Hence, considering that combined exposure to Phe and WSSV leads to increased mortality of shrimp, it is imperative that the detrimental effects elicited by multiple stresses be considered, and controlled, in areas inhabited by kuruma shrimp.

LvCSN5 is involved in WSSV infection via interaction with wsv006

As an extremely virulent pathogen, white spot syndrome virus (WSSV) greatly threatens shrimp aquaculture worldwide. The interaction between virus and host is important for viral infection. In the present study, a yeast two-hybrid (Y2H) library was constructed to clarify the functions of wsv006, and the interaction between wsv006 and shrimp Litopenaeus vannamei (L. vannamei) was analyzed. Furthermore, we explored the role of the wsv006-interacting molecule L. vannamei COP9 constitutive photomorphogenic-like protein subunit 5 (LvCSN5) in WSSV infection. Y2H assay showed that wsv006 interacted with LvCSN5, and co-immunoprecipitation (Co-IP) assay confirmed such interaction. Multiple alignments of amino acid sequences with other species revealed that the LvCSN5 had high identity with Penaeusmonodon CSN5 (PmCSN5). LvCSN5 was mainly expressed in intestine, eye and hepatopancreas. In addition, the relative expression of LvCSN5 was significantly up-regulated both in intestine and hepatopancreas following the WSSV challenge. Besides, the relative expressions of IE1 and VP28, as well as the viral copy numbers were significantly increased in the LvCSN5-silenced shrimp. Our findings suggested that LvCSN5 was involved in WSSV infection by interacting with wsv006.

Identification and characterization of a Toll-like receptor gene from Macrobrachium nipponense

Outbreaks of infectious disease in shrimp pose a serious threat to shrimp agriculture worldwide. Shrimp lack adaptive immunity and depend only on innate immunity as a defense system against infectious disease. Toll-like receptors (TLR) are reported to play a critical role in the innate immune system. In this study, we identified a Toll-like receptor gene of a species of freshwater shrimp, Macrobrachium nipponense, designated MnToll, for the first time. The sequence of MnToll encoded 935 residues arranged as 10 leucine-rich repeat (LRR) domains, a leucine-rich repeat C-terminal (LRR CT) domain and a Toll/interleukin-1 receptor (TIR) domain and displayed 90% amino acid similarity to previously identified TLRs (Toll 1 and 2) of Macrobrachium rosenbergii. We additionally evaluated mRNA expression of MnToll in various tissues, including heart, gills, stomach, digestive gland, ventral nerve cord, antennal gland and muscle. Following infection with a viral pathogen, white spot syndrome virus (WSSV), MnToll expression was significantly upregulated between 12 and 72 h. Our data collectively suggest that the newly identified MnToll gene belongs to the TLR family in shrimp and is potentially involved in innate host defense, especially against WSSV.

The LARK protein is involved in antiviral and antibacterial responses in shrimp by regulating humoral immunity

The LARK proteins containing a C2HC-type zinc finger motif and two RNA recognition motifs are conserved across vertebrates and invertebrates. Previous studies have suggested that invertebrate LARKs and their mammalian counterparts, the RBM4 proteins, regulate gene expression by affecting RNA stability and post-transcriptional processing, participating in multiple life processes. In the current study, the LARK gene from Pacific white shrimp Litopenaeus vannamei was identified and functionally explored in the context of immunity. The LARK protein was mainly present in the nucleus of its expression vector-transfected S2 cells, and the LARK mRNA was detectable in all the tested shrimp tissues. Expression of LARK in gill was up-regulated by immune stimulation with various pathogens. In vivo experiments demonstrated that LARK played positive roles in both antiviral and antibacterial responses and silencing of LARK could make shrimp more susceptible to infection with Vibrio parahaemolyticus and white spot syndrome virus (WSSV). Although silencing of LARK did not affect the phagocytic activity of hemocytes, it regulated expression of many components of the NF-κB and JAK-STAT pathways and a series of immune function proteins. These suggested that LARK could be mainly involved in regulation of humoral immunity. The current study could help reveal the roles of LARK/RBM4 in immunity and further explore the regulatory mechanisms of shrimp immunity.

Heat shock protein 70 (HSP70) promotes air exposure tolerance of Litopenaeus vannamei by preventing hemocyte apoptosis

Brief pretreatment of cold shock at 13 °C for 3 min proved to be an inducer of heat shock protein 70 (HSP70) and improved stress tolerance as a molecular chaperone. With the improvement of air exposure tolerance, HSP70 in shrimp hemocytes was upregulated in mRNA and protein levels after cold shock. Both HSP70 RNA interference (RNAi) gene knockdown and recombinant HSP70 (rHSP70) injection were successfully established in order to investigate the role of HSP70 in response to air exposure stress. Shrimp receiving rHSP70 showed an improved survival rate (80%) with no significant difference (p > 0.05) compared to cold shock treated shrimp (control, 90%) under air exposure, but the survival rate of HSP70-knockdown shrimp was significantly lower (62%, p < 0.05). Reactive oxygen species (ROS) content, relative expression of cytochrome c, caspase-3 activity, and apoptosis rate in hemocytes of HSP70 enriched shrimp (i.e., cold shock and rHSP70 injection) were significantly lower (p < 0.05) than HSP70-knockdown shrimp. Results suggested that HSP70 could be induced by cold shock and contributed to improve the tolerance of shrimp suffering air exposure by blocking the apoptosis pathway through scavenging intracellular ROS, inhibiting cytochrome c expression, inhibiting release from mitochondria, and inactivating caspase-3. This work updates the understanding of cold shock mechanism in water-free transportation of aquatic animals.

F1 ATP synthase β subunit is a putative receptor involved in white spot syndrome virus infection in shrimp by binding with viral envelope proteins VP51B and VP150

White spot syndrome virus (WSSV) is highly virulent toward shrimp, and F1 ATP synthase β subunit (ATPsyn-β) has been suggested to be involved in WSSV infection. Therefore, in this study, interactions between Penaeus monodon ATPsyn-β (PmATPsyn-β) and WSSV structural proteins were characterized. Based on the results of yeast two-hybrid, co-immunoprecipitation, and protein pull-down assays, WSSV VP51B and VP150 were identified as being able to interact with PmATPsyn-β. Membrane topology assay results indicated that VP51B and VP150 are envelope proteins with large portions exposed outside the WSSV virion. Cellular localization assay results demonstrated that VP51B and VP150 co-localize with PmATPsyn-β on the membranes of transfected cells. Enzyme-linked immunosorbent assay (ELISA) and competitive ELISA results demonstrated that VP51B and VP150 bound to PmATPsyn-β in a dose-dependent manner, which could be competitively inhibited by the addition of WSSV virions. In vivo neutralization assay results further showed that both recombinant VP51B and VP150 could delay mortality in shrimp challenged with WSSV.

Novel Allergen Discovery through Comprehensive De Novo Transcriptomic Analyses of Five Shrimp Species

Shellfish allergy affects 2% of the world's population and persists for life in most patients. The diagnosis of shellfish allergy, in particular shrimp, is challenging due to the similarity of allergenic proteins from other invertebrates. Despite the clinical importance of immunological cross-reactivity among shellfish species and between allergenic invertebrates such as dust mites, the underlying molecular basis is not well understood. Here we mine the complete transcriptome of five frequently consumed shrimp species to identify and compare allergens with all known allergen sources. The transcriptomes were assembled de novo, using Trinity, from raw RNA-Seq data of the whiteleg shrimp (Litopenaeus vannamei), black tiger shrimp (Penaeus monodon), banana shrimp (Fenneropenaeus merguiensis), king shrimp (Melicertus latisulcatus), and endeavour shrimp (Metapenaeus endeavouri). BLAST searching using the two major allergen databases, WHO/IUIS Allergen Nomenclature and AllergenOnline, successfully identified all seven known crustacean allergens. The analyses revealed up to 39 unreported allergens in the different shrimp species, including heat shock protein (HSP), alpha-tubulin, chymotrypsin, cyclophilin, beta-enolase, aldolase A, and glyceraldehyde-3-phosphate dehydrogenase (G3PD). Multiple sequence alignment (Clustal Omega) demonstrated high homology with allergens from other invertebrates including mites and cockroaches. This first transcriptomic analyses of allergens in a major food source provides a valuable resource for investigating shellfish allergens, comparing invertebrate allergens and future development of improved diagnostics for food allergy.

In vitro and in vivo immunologic potentiation of herb extracts on shrimp (Litopenaeus vannamei)

In vitro and in vivo effects of Astragalus polysaccharide (APS), chlorogenic acid (CGA) and berberine (BBR) on shrimp (Litopenaeus vannamei) were studied. In vitro test showed that the combination of APS and BBR and the combination of APS and CGA have strong immune enhancement effects and no lysosomal membrane damage on hemocyte. Then, feeding experiment was proceeded to optimize the concentrations of compound herbal extracts. Four diets containing G1-G4(0.5 g kg ^-1 APS + 0.5 g kg ^-1 BBR, 1.0 g kg ^-1 APS +1.0 g kg ^-1 BBR, 0.5 g kg ^-1 APS +0.5 g kg ^-1 CGA, 1.0 g kg ^-1 APS + 1.0 g kg ^-1 CGA) associated with the control group (common diet) were compared and determined their biomolecule damage to hepatopancreas including DNA damage, lipid peroxidation and protein carbonyl. The results indicated that G3 (0.5 g kg ^-1 APS +0.5 g kg ^-1 CGA) showed higher total hemocyte counts, phagocytic activities, antibacterial activities and bacteriolytic activities during 6 days feeding, and without biomolecule damages after 6 days post-withdrawal. Therefore, the appropriate immunostimulants formula in this study was the combination of 0.5 g kg ^-1 APS and 0.5 g kg^-1 CGA, which was used for 6 days followed by 6 days post-withdrawal. Additionally, our study provides new support for screening composite immunostimulants formula by using primary shrimp hemocyte culture.

Effects of Phyllanthus amarus extract on nonspecific immune responses, growth, and resistance to Vibrio alginolyticus in white shrimp Litopenaeus vannamei

This study investigates the effects of Phyllanthus amarus extract (PAE) on immune responses, growth, and resistance to Vibrio alginolyticus in white shrimp (Litopenaeus vannamei). In vitro PAE treatment did not alter the cell viability of haemocytes and significantly enhanced immune parameters such as phenoloxidase (PO) activity, phagocytic activity, and superoxide anion (O₂^-) production. We conducted two feeding trials to examine the effects of PAE on the growth, disease resistance, and innate immune parameters of white shrimp. In the first in vivo trial, shrimps (4.01 ± 0.03 g) were fed a diet containing 0 g (control), 10 g (PAE10), 20 g (PAE20), or 40 g (PAE40) of PAE per kilogram of feed for 56 days. After the feeding period, the PAE20 group showed a significantly higher weight gain and specific growth rate than shrimp fed the control diet. Furthermore, after challenge with V. alginolyticus, shrimp fed a diet containing PAE showed significantly higher survival than those fed the control diet. The second in vivo trial (28 days) was performed to identify the mechanisms of enhanced immunity in PAE-fed shrimp. Shrimp fed the PAE20 diet generally had the highest total haemocyte count, PO activity, phagocytic activity, and O₂^- production, followed by the PAE40 and PAE10 groups. Thus, our results suggest that administration of 20 g of PAE per kilogram of feed can enhance immunity, growth, and resistance to V. alginolyticus in white shrimp.

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 double chitin catalytic domain-containing chitinase targeted by c-Jun is involved in immune responses in shrimp

Chitinases are a group of chitin-degrading enzymes widely distributed in organisms. Chitinases containing two chitin catalytic domains have been widely found in arthropods but their functions remain unclear. In this study, a member of these chitinases from Litopenaeus vannamei (dChi) was identified and functionally studied in the context of immunity. The promoter of dChi contained activator protein 1 (AP-1) binding sites and could be regulated by c-Jun. The recombinant dChi protein showed no bacteriostatic activity in vitro but knockdown of dChi in vivo increased the mortality of shrimp and the bacterial load in tissues after Vibrio parahaemolyticus infection, suggesting that dChi could play a positive role in antibacterial responses. However, silencing of dChi expression significantly decreased the mortality of WSSV-infected shrimp and down-regulated the viral load in tissues, indicating that dChi could facilitate WSSV infection. We further demonstrated that dChi was involved in regulation of the bacterial phagocytosis of hemocytes and expression of a series of immune related transcription factors and antimicrobial peptides. These indicated that the roles of dChi in antibacterial responses and anti-WSSV responses in vivo could result from its regulatory effects on the immune system. Taken together, the current study suggests that double chitin catalytic domain-containing chitinases could be important players in immune regulation in crustaceans.

Activating transcription factor 2 (ATF2) negatively regulates the expression of antimicrobial peptide genes through tumor necrosis factor (TNF) in Macrobrachium nipponense

Activating transcription factor 2 (ATF2), a member of the bZIP transcription factor family, is involved in multiple physiological and developmental processes, yet its role in the innate immunity remains unclear. In this study, two isoforms (named as MnATF2a and MnATF2b) of ATF2 gene were identified in Macrobrachium nipponense and were produced by exon skipping. The full length of MnATF2a is 2328 bp with an open reading frame of 2079 bp that encode 692 amino acids. MnATF2a has 237 bp nucleotides more than MnATF2b and the extra 237 bp is a complete exon. MnATF2a and MnATF2b proteins contain the same conserved and typical bZIP domain at the C-terminus. MnATF2a has 79 amino acids more than MnATF2b. MnATF2a and MnATF2b are widely distributed in a variety of immune tissues. After Vibrio parahaemolyticus and Staphylococcus aureus infection, the expression levels of MnATF2a and MnATF2b were significant up-regulated in the gills and stomach at 12 h. RNA interference analysis showed that knockdown of the total MnATF2 gene significantly inhibits the transcription of tumor necrosis factor (TNF) and promotes the expression of crustins (including Cru3, Cru4, and Cru7). Further study showed that knockdown of MnTNF evidently increase the expression of Cru3, Cru4, and Cru7. Our research indicates that ATF2 negatively regulate the expression of AMPs by regulating the transcription of TNF in M. nipponense. This study provides valuable information about the function of ATF2 family in the innate immunity in crustacean.

Pectin of cacao pod husk, an efficient immunostimulant for white shrimp, Litopenaeus vannamei

The disposal of cacao pod husk, a byproduct of cacao bean processing, can cause serious adverse environmental impacts, motivating scientist to explore and develop potential beneficial applications of this resource. Dried cacao pod husk was extracted with ethanol to obtain a 10.6% pectin of cacao pod husks (pCPH), and its effects on the immunocompetence of Litopenaeus vannamei were estimated. Measured variables included total haemocyte count, differential haemocyte count, phenoloxidase activity, respiratory bursts, as well as phagocytic activity and clearance efficiency against Vibrio alginolyticus after receiving pCPH at 0, 1.5, 3, and 6 μg shrimp^-1 for 0, 1, 3 and 7 days via injection, and their resistance to thermal stress and V. alginolyticus infection were further evaluated. No significant differences were observed in total haemocyte count, differential haemocyte count, and respiratory bursts in shrimp receiving pCPH at 1.5 μg shrimp^-1 for 1 day; however, these variables were significantly elevated after 3 days of injection, compared to the control group. The significantly increased phenoloxidase activity was assessed in shrimp receiving pCPH at 1.5, 3 and 6 μg shrimp^-1 within 3 days, and activity returned to the baseline after 7 days. Furthermore, the reduced phenoloxidase activity per granulocytes or respiratory bursts per haemocytes maintained homeostasis following the variation of haemogram. For gene expression assessments in haemocytes, the immune-related genes of the lipopolysaccharide and β-1,3-glucan binding protein, prophenoloxidase II and anti-lipopolysaccharide factor as well as innate immune signaling pathway-related genes of toll-like receptors 1 and 3 significantly increased after shrimp received pCPH for 1 day. The increases in phagocytic activity and clearance efficiency were only detected in shrimp receiving pCPH at 6 μg shrimp^-1 within 7 days, compared to the control. There was no significant difference in the mortality ratio of shrimp against hyperthermal stress when they received pCPH for 1 day, and the significant higher resistance to hypothermal stress and V. alginolyticus infection were found in shrimp received pCPH at 6 μg shrimp^-1 for 1 days than those in the other treatments. It is therefore found that pCPH triggers immune responses serving as an immunostimulant capable of enhancing resistance against V. alginolyticus and hypothermal stress.

The effect of dietary supplementation of Astragalus membranaceus and Bupleurum chinense on the growth performance, immune-related enzyme activities and genes expression in white shrimp, Litopenaeus vannamei

A 56-day feeding trial was conducted to investigate the effects of dietary supplementation of Astragalus membranaceus or/and Bupleurum chinense on the growth performance, immune enzymes, and related gene expression of Pacific white shrimp (Litopenaeus vanammei). Six experimental diets were formulated and supplemented with two levels (0.25% and 0.5%) of each herb and their combination. At the end of the trial, the specific growth rate and feed conversion ratio of shrimp were significantly (P < 0.05) improved by herbal diets. Besides, the activities of immune-related enzymes such as superoxide dismutase (SOD), alkaline phosphatase (AKP), and lysozyme in serum and hepatopancreas were significantly (P < 0.05) elevated in shrimp fed A. membranaceus or/and B. chinense. The high expression levels of immune deficiency (IMD), lysozyme, and Toll-like receptor mRNA directly or indirectly reflected the activation effect of innate immune in shrimp by dietary A. membranaceus or/and B. chinense. However, no significant difference (P > 0.05) among the herbal incorporated treatments was detected on the growth performance and immune response. In conclusion, the results suggest that A. membranaceus and B. chinense could be used as a beneficial feed additives and alternatives to antibiotics for white shrimp aquaculture.

Identification of two carcinin isoforms (MnCarc1 and MnCarc2) and their function in the antimicrobial immunity of Macrobrachium nipponense

Carcinin, a member of the crustin family, plays important roles in crustacean innate immunity. In this study, we identified two carcinin isoforms (MnCarc1 and MnCarc2) produced by alternative splicing from Macrobrachium nipponense. The full length of MnCarc1 and MnCarc2 cDNA are 1554 and 1495 bp with 687 and 609 bp open reading frame-encoding proteins that contain 228 and 202 amino acids, respectively. The genome of carcinin has nine exons and eight introns. MnCarc1 transcript contains all nine exons, whereas MnCarc2 only contains eight exons and lacks exon 4. MnCarc1 and MnCarc2 proteins contain a signal peptide, cysteine-rich regions, and a whey acidic protein domain. The phylogenetic tree shows that MnCarc1 and MnCarc2 are not grouped with other crustins and carcinins. MnCarc1 and MnCarc2 form a subgroup. MnCarc1 and MnCarc2 are widely distributed in various tissues. The expression of MnCarc1 and MnCarc2 were evidently upregulated at multiple time points in hemocytes and the intestine of M. nipponense after white spot syndrome virus, Vibrio parahaemolyticus, and Staphylococcus aureus challenges. Further studies showed that knockdown of MnDorsal or MnStat transcription factor could remarkably inhibit the upregulated expression of MnCarc1 and MnCarc2 caused by viral or bacterial challenges. In addition, recombinant MnCarc1 and MnCarc2 proteins could bind to various bacteria and polysaccharides and inhibit the growth of S. aureus and V. parahaemolyticus in vitro. This study indicated that carcinins from M. nipponense were involved in prawns innate immunity.

Molecular characterization of prohibitins and their differential responses to WSSV infection in hemocyte subpopulations of Fenneropenaeus chinensis

In our previous work, prohibitin1 (PHB1) was identified to be only expressed in granulocytes of Fenneropenaeus chinensis. In order to elucidate the potential immunological properties of prohibitins in hemocyte subpopulations, in this paper, the full-length cDNAs of PHB1 and PHB2 were firstly cloned from F. chinensis using rapid amplification of cDNA ends approach, and they were designated FcPHB1 and FcPHB2, respectively. Based on the sequence analysis and multiple sequence alignment, FcPHB1 and FcPHB2 were members of SPFH protein family. By quantitative real-time RT-PCR, the higher mRNA transcription levels of FcPHB1 and FcPHB2 were detected in intestine and hemocytes of F. chinensis, and these two genes in hemocytes were significantly up-regulated upon WSSV infection. The FcPHB1 and FcPHB2 were recombinantly expressed in Escherichia coli BL21 (DE3), and employed as immunogens to produce the polyclonal antibodies (PAbs) in rabbits. Indirect immunofluorescence assay (IFA) revealed that the FcPHB1 and FcPHB2 were located both in the cytoplasm and nuclei of hemocytes, which could also be specifically recognized by the PAbs against FcPHB1 or FcPHB2 in Western blot. Interestingly, it was found that FcPHB1 and FcPHB2 were only expressed in the granulocytes of heathy shrimp and highly expressed in the WSSV-infected granulocytes, however only weak expressions of FcPHB1 and FcPHB2 were observed in the hyalinocytes of WSSV-infected shrimp. Meanwhile, silencing of FcPHB1 and FcPHB2 genes were performed by small interfering RNA, and the results showed that the WSSV copies in hemocytes were increased by knockdown of either FcPHB1 or FcPHB2, and the cumulative mortalities of shrimp in the silenced groups were also markedly increased. These results demonstrated that FcPHB1 and FcPHB2 played important roles in anti-WSSV infection, and their differential expression characteristics in hemocyte subpopulations provided a further understanding of the immune functions of granulocytes and hyalinocytes.

Full-length transcriptome and long non-coding RNA profiling of whiteleg shrimp Penaeus vannamei hemocytes in response to Spiroplasma eriocheiris infection

Spiroplasma eriocheiris (S. eriocheiris) infection causes a significant economic loss in Penaeus vannamei (P. vannamei) culture industry. However, the response of P. vannamei hemocytes to S. eriocheiris infection has not been extensively studied. In this study, we conducted full-length transcriptome and long non-coding RNA (lncRNA) analyses of P. vannamei hemocytes by a challenge test with S. eriocheiris. Following assembly and annotation, there were 8077 high-quality unigenes. A total of 1168 differentially expressed genes (DEGs) were obtained, including 792 up-regulated and 376 down-regulated genes by differential expression analysis. Gene ontology (GO) enrichment analysis showed that the up-regulated DEGs were mainly clustered into immune system process, defense response, cell cycle and organelle organization. On the other hand, the down-regulated DEGs included that genes that were mainly clustered into metabolic processes related to organic compounds, metabolic process and cellular metabolic process. Protein-protein interaction (PPI) network analysis of DEGs indicated that the pivotal gene interactions were connected to stress response, immune system process and cell cycle. The lncRNA analysis identified multiple lncRNAs, which were highly co-expressed with the immune-related genes, such as lncRNA transcript-12631 and transcript-12631, suggesting that lncRNAs may be involved in the regulation of immune defense in shrimp hemocytes. Additionally, 20 hub unigenes and putative lncRNAs related to immune system were validated by quantitative real-time PCR (qRT-PCR), validating the reliability of RNA-Seq. This study revealed a close connection between the immune and metabolic systems of S. eriocheiris infected P. vannamei.

Immune response and oxidative stress of shrimp Litopenaeus vannamei at different moon phases

Moon phases influence the molting process of shrimp, which affect other physiological processes as immune response. This study analyzed some parameters of immune response: total hemocytes counts (THC), hemolymph clotting time and superoxide anion (O₂^-) production, total protein concentration, superoxide dismutase activity, and the presence of Vibrio spp. in Litopenaeus vannamei at different moon phases. The highest percentage of organisms in intermolt stage was observed in the first quarter moon phase (95%). The highest THC was observed at new moon phase, which was significantly different (p < 0.05) than that observed at the third quarter phase. Hemolymph clotting time and CFU values of Vibrio spp. showed no significant difference (p > 0.05) between different moon phases. The higher (p < 0.05) mean O₂^- production value (0.400 ± 0.168 nmol min^-1 mL^-1) was determined in hepatopancreas at new moon phase. No relationship was observed between O₂^- and SOD activity, indicating that this antioxidant response was enough to counteract the influence of oxidative stress in L. vannamei at different moon phases.

Penaeus stylirostris densovirus proteins CP and NS1 interact with peritrophin of Litopenaeus vannamei

The Penaeus stylirostris densovirus (PstDNV) is a major virus of shrimps that severely harms the shrimp farming industry. Peritrophin is a peritrophic membrane protein with chitin binding activity. To examine the roles of peritrophin in viral infection, we used yeast two-hybrid to analyze the interaction between the Pacific white shrimp (Litopenaeus vannamei) peritrophin and PstDNV proteins (CP, NS1 and NS2). The yeast two-hybrid results showed that NS1 and peritrophin had an interaction, CP and peritrophin had an interaction as well, and NS2 had no interaction with peritrophin. We validated the interactions with GST pull-down assays. We then conducted RNA interference and qRT-PCR. The results showed that when pre-injection of dsRNA-peritrophin, the quantity of PstDNV in the shrimps injected with viruses was significantly lower than in the control group (P < 0.01), indicating the viral infection was decreased when the peritrophin gene expression was inhibited. The results indicated that peritrophin of L. vannamei participated in the PstDNV infection.

Immunocompetence of Penaeus monodon under acute salinity stress and pathogenicity of Vibrio harveyi with respect to ambient salinity

Salinity is an important environmental factor which usually goes unnoticed in shrimp growout systems. In the present study an attempt was done to analyse the physiological and immunological responses of Penaeus monodon to Vibrio harveyi infection under acute salinity stress. Shrimps were challenged with V. harveyi under 5‰ salinity stress, 35‰ salinity stress and optimal salinity (15‰) conditions by intramuscular injection. A control was maintained without bacterial challenge. Haemolymph was collected from shrimps soon after salinity change before V. harveyi challenge (post salinity change day (PSD) 0), on post challenge day (PCD) 2, 7 and 10. Immune variables viz., total haemocyte count (THC), phenol oxidase activity (PO), Nitroblue tetrazolium salt (NBT) reduction, alkaline phosphatase activity (ALP), acid phosphatase activity (ACP) and metabolic variables viz., total protein (TP), total carbohydrates (TC), total free amino acids (TFAA), total lipids (TL), glucose (Gl) and cholesterol (Ch) were then determined. One way ANOVA followed by Duncan's multiple comparison of the means revealed significant differences between shrimps subjected to different salinity conditions and then challenged with V. harveyi (P < 0.05). Post challenge survival was significantly higher in shrimps maintained at 15‰ and acute salinity stress reduced the survival rate. However, pathogenicity of V. harveyi was slightly higher at 35‰ than at 5‰. At the onset of salinity stress, parameters viz., THC, NBT and ACP significantly reduced and TC increased at 5‰ and 35‰. Following V. harveyi challenge, an overall increase could be observed in metabolic variables on PCD2 and immune variables on PCD2 and 7 in P. monodon maintained at 15‰ compared to the control. Even though an increase in immune response and metabolic variables could be obtained on post challenge days in shrimps under salinity stress compared to the control, it was considerably low in comparison with shrimps maintained at 15‰. Regression analysis proved that NBT, ALP, TP and TL could be proposed as potential stress indicators to evaluate shrimp health status. In brief, it may be concluded from the study that acute salinity changes evoke physiological responses that affect the immunocompetence and metabolic performance of P. monodon against V. harveyi challenge, thereby increasing the susceptibility to infection. Moreover higher salinity enhanced the pathogenicity of V. harveyi.

Full-length transcriptome analysis provides new insights into the innate immune system of Marsupenaeus japonicus

As invertebrates, shrimp are generally thought to solely rely on their innate immune system to combat invading pathogens. Recently, an increasing number of studies have revealed that the innate immune response of invertebrates exhibits diversity and specificity based on their diverse immune molecules. Herein, a full-length transcriptome analysis of several immune-related tissues (hepatopancreas, gill, hemocytes, stomach and intestine) in the kuruma shrimp (Marsupenaeus japonicus) was conducted to identify immune-related molecules with a focus on transcript variations. In total, 11,222 nonredundant full-length transcripts with an N50 length of 5174 were obtained, and most of these transcripts (94.84%) were successfully annotated. In addition, a total of 147 long noncoding RNAs (lncRNAs) were also predicted. Importantly, transcript variants of several vital immune-related genes were observed, including twenty-five alpha-2-macroglobulins (α2-Ms), ten Toll-like receptors (TLRs), six C-type lectins (CTLs), five M-type lectins (MTLs) and three Down syndrome cell adhesion molecules (Dscams). Furthermore, 509 nonredundant full-length transcripts were predicted to be generated from alternative splicing (AS) events, which contribute to the diversity of immune molecules. Overall, our study provides valuable data on the full-length transcripts of M. japonicus, which will facilitate the exploration of immune molecules in this species. Moreover, numerous transcript variants of immune molecules detected in this study provide clues for further investigating the diversity and specificity of the innate immune response in shrimp.

Novel 2-Cys Peroxiredoxin gene confers biotic and abiotic stress resistance in Penaeus monodon

Peroxiredoxins (Prxs) are crucial antioxidant proteins that protect against biotic and abiotic stresses in many organisms, ranging from bacteria to mammals. In the present work, a novel 2-Cys Peroxiredoxin gene (PmPrxn), which contains a 153 bp 5'-terminal untranslated region (5'-UTR), a 636 bp open reading frame encoding a protein with 211 amino acids, and an 898 bp 3'-UTR, was successfully identified and characterized in the black tiger shrimp, Penaeus monodon. Tissue-specific expression analysis revealed that the PmPrxn mRNA was ubiquitously expressed and was comparatively highly expressed in the hepatopancreas. To explore the immunity-related and anti-stress roles of PmPrxn, the gills and hepatopancreas were chosen as target tissues in P. monodon and challenged with Vibrio harveyi, Streptococcus agalactiae, and toxic environmental stressors. The results indicate that PmPrxn might play a vital role in response to biotic and abiotic stresses. Furthermore, the antimicrobial and heavy metal toxicity stress-resistance properties of PmPrxn were evaluated and investigated in vitro using a prokaryotic expression system. These results provide useful information that will help further understand the functional mechanisms of PmPrxn in the defense against bacterial pathogens and environmental acute stresses in shrimp.

A SNP of the hemocyanin gene (LvHc) is a marker for high growth and ammonia-tolerance in Pacific white shrimp Litopenaeus vannamei

Expression levels of hemocyanin (LvHc), activating transcription factor 4 (LvAtf4), glutathione S-transferase (LvGst), caspase 2 (LvCasp2) and anti-lipopolysaccharide factor (LvAlf) were examined in the hepatopancreas of Pacific white shrimp Litopenaeus vannamei juveniles exposed to a lethal concentration of ammonia-N (32.15 mg/l). The expression levels of all transcripts except LvAlf were significantly greater (P < 0.05) in tolerant shrimp (Lv-AT; N = 30) that survived up to 72 h post treatment (hpt) than in susceptible shrimp (Lv-AS24 and Lv-AS72; N = 45 and 15), that died within 24 h or between 24 and 72 hpt, respectively. Subsequently, effects of non-lethal concentrations of ammonia-N (control, 10 and 20 mg/l) on the expression of LvHc in juvenile shrimp were examined. Compared to the control, expression levels of LvHc transcripts in hemocytes and the hepatopancreas of tested shrimp changed after exposure to ammonia-N. One SNP (C > T₅₄₅) was found in the LvHc₃₂₂ gene segment. Real-time PCR amplification of specific alleles (real-time PASA) was developed for detection of C > T₅₄₅ genotypes. Juveniles in the lethal exposure test that carried a C/T₅₄₅ genotype showed a greater average body weight and total length (8.46 ± 0.36 g and 10.05 ± 0.16 cm) than those with a C/C₅₄₅ genotype (7.48 ± 0.31 g and 9.60 ± 0.13 cm) (P < 0.05). Similar results were found in the second generation (G2) of a growth-improved stock (3 and 4 families of BIOTEC-G2-L1 and BIOTEC-G2-L2) and in commercially farmed shrimp (2 groups). Accordingly, expression levels and SNP of LvHc can serve as markers for selection high growth performance in ammonia-tolerant L. vannamei.