Effect of dietary poly-β-hydroxybutyrate (PHB) on growth performance, intestinal health status and body composition of Pacific white shrimp Litopenaeus vannamei (Boone, 1931)

In the present study, the effect of dietary supplementation of poly-β-hydroxybutyrate (PHB) on the growth performance, intestinal digestive and immune function, intestinal short-chain fatty acids (SCFA) content and body composition of Pacific white shrimp Litopenaeus vannamei (Boone, 1931) was evaluated. The shrimp was fed for 35 days with four different diets: 0%, 1%, 3% and 5% PHB supplemented feed. The results indicated that supplementation of PHB significantly increased the growth performance of the shrimp, and the feed conversion rate (FCR) in 3%PHB treatment group was significantly lower than the control (P < 0.05). The intestinal amylase, lipase and trypsin activity in the three PHB treatment groups were all significantly higher than that of the control (P < 0.05), but the pepsin activity were only significantly affected by 3%PHB treatment (P > 0.05). The activities of intestinal immune enzymes such as total antioxidant capacity (T-AOC) and inducible nitric oxide synthase (iNOS) was significantly induced by 3%PHB treatment (P < 0.05), while lysozyme (LSZ) activity was significantly affected by 5%PHB treatment and nitric oxide (NO) content was significantly induced in three PHB treatments. Meanwhile, PHB induced significantly the expression level of intestinal heat shock protein 70 (HSP70), Toll and immune deficiency (Imd) gene. HE staining showed that PHB induced the intestinal health status of L. vannamei. Intestinal SCFA content analysis revealed that the content of propionic and butyric acid of 3%PHB treatment were significantly higher than that of the control (P < 0.05). Body composition analysis showed that the crude protein in 3% and 5%PHB treatments, and the crude lipid in 1% and 5%PHB treatments were all significantly higher than the control (P < 0.05). These results revealed that PHB could improve the growth performance, modulated intestinal digestive and immune function, increased intestinal SCFA content and body composition in L. vannamei, and the optimum dietary PHB requirement by L. vannamei was estimated at 3% (w/w) diet.

Scavenger Receptor C Mediates Phagocytosis of White Spot Syndrome Virus and Restricts Virus Proliferation in Shrimp

Scavenger receptors are an important class of pattern recognition receptors that play several important roles in host defense against pathogens. The class C scavenger receptors (SRCs) have only been identified in a few invertebrates, and their role in the immune response against viruses is seldom studied. In this study, we firstly identified an SRC from kuruma shrimp, Marsupenaeus japonicus, designated MjSRC, which was significantly upregulated after white spot syndrome virus (WSSV) challenge at the mRNA and protein levels in hemocytes. The quantity of WSSV increased in shrimp after knockdown of MjSRC, compared with the controls. Furthermore, overexpression of MjSRC led to enhanced WSSV elimination via phagocytosis by hemocytes. Pull-down and co-immunoprecipitation assays demonstrated the interaction between MjSRC and the WSSV envelope protein. Electron microscopy observation indicated that the colloidal gold-labeled extracellular domain of MjSRC was located on the outer surface of WSSV. MjSRC formed a trimer and was internalized into the cytoplasm after WSSV challenge, and the internalization was strongly inhibited after knockdown of Mjβ-arrestin2. Further studies found that Mjβ-arrestin2 interacted with the intracellular domain of MjSRC and induced the internalization of WSSV in a clathrin-dependent manner. WSSV were co-localized with lysosomes in hemocytes and the WSSV quantity in shrimp increased after injection of lysosome inhibitor, chloroquine. Collectively, this study demonstrated that MjSRC recognized WSSV via its extracellular domain and invoked hemocyte phagocytosis to restrict WSSV systemic infection. This is the first study to report an SRC as a pattern recognition receptor promoting phagocytosis of a virus.

Shrimp aquaculture is a major industry in many coastal countries, where it contributes significantly to socio-economic development. However, during the rapid expansion of shrimp industry, a succession of previously unknown diseases, especially viral diseases, have emerged in farmed shrimp and spread rapidly across international boundaries, which have significant effects on shrimp production. Since 1994, it has been estimated that annual losses globally caused by viral diseases have been as high as $US3 billion. White spot syndrome, caused by white spot syndrome virus (WSSV), is the most serious disease in shrimp aquaculture. Here, we reveal that a scavenger receptor in kuruma shrimp, Marsupenaeus japonicus (MjSRC) functions as the pattern recognition receptor for WSSV. MjSRC binds to WSSV and initiates phagocytosis of the virus, ultimately leading to degradation of WSSV in the lysosomes of hemocytes. This is the first report of the MjSRC antiviral mechanism, which may be used as a control strategy to prevent WSSV infection in shrimp.

Dopamine beta-hydroxylase participate in the immunoendocrine responses of hypothermal stressed white shrimp, Litopenaeus vannamei

Dopamine beta-hydroxylase (DBH) plays a critical role in catecholamine (CA) synthesis of neuroendocrine regulatory network, and is suggested to be involved in the immunoendocrine responses of invertebrate against bacterial challenge. DBH has been identified in white shrimp, Litopenaeus vannamei, and further investigation on its potential function was conducted after hypothermal stress, pharmaceutical inhibition and gene silencing in the present study. Cloned DBH L. vannamei (LvDBH), belonging to the Copper type II, ascorbate-dependent monooxygenases, was characterized by a DOMON domain, a Cu2_monooxygen domain and three glycosylation sites, and its expression was abundant in thoracic ganglia and haemocytes determined by quantitative real-time PCR. The effects of hypothermal stress showed that LvDBH expression in thoracic ganglia, haemocytes and hepatopancreas as well as the DBH contents in haemocytes and dopamine (DA) and norepinephrine (NE) levels in haemolymph are obviously up-regulated. L. vannamei receiving disulfiram for 30-120 min revealed the inhibition of DBH and NE contents in haemocytes and haemolymph respectively, but high level of DA in haemolymph was noticed. Besides, a significant decrease of LvDBH expression in thoracic ganglia, haemocytes and hepatopancreas were also observed. Subsequently, LvDBH expression was successfully silenced in thoracic ganglia, haemocytes and hepatopancreas of shrimp that received LvDBH-dsRNA for 3 days, and meanwhile, a decrease of DBH contents in haemocytes accompanied by decreased levels of NE and DA in haemolymph were also observed. These results indicate that LvDBH possesses the functional domains responsible for CAs synthesis, and therefore, inhibiting DBH contents in haemocytes by disulfiram and by LvDBH-dsRNA resulted in the impaired synthesis of NE from DA in haemolymph. These also suggest that the increased release of DA and NE in haemolymph for potential modulation of physiological or immunological responses is the consequence of the upregulated LvDBH expression and DBH contents in L. vannamei exposed to hypothermal stress.

White shrimp Litopenaeus vannamei that have received fucoidan exhibit a defense against Vibrio alginolyticus and WSSV despite their recovery of immune parameters to background levels

White shrimp Litopenaeus vannamei receiving fucoidan at 2, 6, and 10 μg g^-1 after 0-144 h or 0-120 h were examined for immune parameters (haemograms, phenoloxidase activity, respiratory burst, and superoxide dismutase activity), proliferation of haemocyte in the haematopoietic tissue (HPT), gene expression, and phagocytic activity and clearance efficiency to Vibrio alginolyticus. Immune parameters and mitotic index of HPT increased after 3-24 h, reached their maxima after 48-72 h, and returned to background values after 144 h. Transcripts of lipopolysaccharide and β-1,3-glucan binding protein (LGBP), peroxinectin (PX), prophenoloxidase (proPO) I, proPO II, astakine, and haemocyte homeostasis-associated protein (HHAP) were up-regulated to a maximum after 48-72 h and returned to background values after 144 h. Phagocytic activity and clearance efficiency to V. alginolyticus increased after 12 h, reached its maximum after 48 h, and continued to remain higher after 120 h. In another experiment, shrimp receiving fucoidan after 48 h and 144 h were respectively challenged with V. alinolyticus at 6 × 10⁶ colony-forming units (cfu) shrimp^-1 or challenged with WSSV at 1.2 × 10⁵ copies shrimp^-1 and then placed in seawater. The survival rate of shrimp receiving fucoidan was significantly higher than in controls. In conclusion, shrimp receiving fucoidan showed a proliferation of HPT, increased immune parameters, and up-regulated transcripts of LGBP, PX, proPO I, proPO II, astakine, and HHAP after 48 h. Shrimp receiving fucoidan exhibited a defense against V. alginolyticus and WSSV, even after immune parameters recovered to background levels.

Differentially expressed transcripts in stomach of Penaeus monodon in response to AHPND infection

Acute Hepatopancreatic Necrosis Disease (AHPND) is an emerging disease in aquacultured shrimp caused by a pathogenic strain of Vibrio parahaemolyticus. As with several pathogenic bacteria, colonization of the stomach appeared to be the initial step of the infection for AHPND-causing Vibrio. To understand the immune responses in the stomach of black tiger shrimp (Penaeus monodon), differentially expressed transcripts (DETs) in the stomach during V. parahaemolyticus strain 3HP (VP3HP) infection was examined using Ion Torrent sequencing. From the total 42,998 contigs obtained, 1585 contigs representing 1513 unigenes were significantly differentially expressed with 1122 and 391 unigenes up- and down-regulated, respectively. Among the DETs, there were 141 immune-related unigenes in 10 functional categories: antimicrobial peptide, signal transduction pathway, proPO system, oxidative stress, proteinases/proteinase inhibitors, apoptotic tumor-related protein, pathogen recognition immune regulator, blood clotting system, adhesive protein and heat shock protein. Expression profiles of 20 of 22 genes inferred from RNA sequencing were confirmed with the results from qRT-PCR. Additionally, a novel isoform of anti-lipopolysaccharide factor, PmALF7 whose transcript was induced in the stomach after challenge with VP3HP was discovered. This study provided a fundamental information on the molecular response in the shrimp stomach during the AHPND infection that would be beneficial for future research.

Effect of mixed-Bacillus spp isolated from pustulose ark Anadara tuberculosa on growth, survival, viral prevalence and immune-related gene expression in shrimp Litopenaeus vannamei

The widespread overuse of antibiotics in aquaculture has led to the emergence of antibiotic-resistance shrimp pathogens, the negative impact on shrimp gut microbiota, and the presence of antimicrobial residues in aquaculture products, with negative consequences on human health. Alternatively, probiotics have positive effects on immunological responses and productive performance of aquatic animals. In this study, three probiotic bacteria, (Bacillus licheniformis MAt32, B. subtilis MAt43 and B. subtilis subsp. subtilis GAtB1), isolated from the Anadara tuberculosa were included in diets for juvenile shrimp, Litopenaeus vannamei, to evaluate their effects on growth, survival, disease prevalence, and immune-related gene expression. Shrimp naturally infected with WSSV and IHHNV were fed with the basal diet (control, T1) and diets supplemented with four levels of bacilli probiotic mix (1:1:1) at final concentration of (T2) 1 × 10⁶, (T3) 2 × 10⁶, (T4) 4 × 10⁶, and (T5) 6 × 10⁶ CFU g^-1 of feed. The specific growth rate of shrimp was significantly higher in T2 than in T1 (control) treatment, and the final growth as well as the survival were similar among treated groups. The prevalence of WSSV and IHHNV infected shrimp was reduced in T2 and T4 treatments, respectively, compared with control. The mRNA expression of proPO gene was higher in treatment T4 than control. The LvToll1 gene was significantly up-regulated in treatments T4 and T5 compared to control. The SOD gene was up-regulated in treatment T5 compared to control. In contrast, the mRNA expression of the Hsp70 gene was down-regulated in treatments T4 and T5 respect to control, and the TGase gene remained unaffected by the level of bacillus probiotic mix. As conclusion, the bacilli probiotic mix (Bacillus spp.) enhanced immune-related gene expression in WSSV and IHHNV naturally infected shrimp. This is the first report of probiotic potential of bacteria isolated from A. tuberculosa on the immune response and viral prevalence in shrimp Litopenaeus vannamei.

Shrimp STAT was hijacked by white spot syndrome virus immediate-early protein IE1 involved in modulation of viral genes

STATs are a family of transcription factors that regulate a cascade of cellular processes including cell growth, differentiation, apoptosis and immune responses. However, they are usually targeted by viruses to assist infection. In this study, we identified that white spot syndrome virus (WSSV) immediate-early protein IE1 interacted with Litopenaeus vannamei STAT (LvSTAT) and thereby led to its phosphorylation activation. In addition, we demonstrated that LvSTAT could bind to the promoters of the viral immediate-early genes wsv051 and ie1 through STAT-binding motifs in vitro and vivo, allowing the enhancement of their promoters' activities. Moreover, IE1 could promote the transcriptional activation activity of LvSTAT to augment the transcription of wsv051 and ie1. In conclusion, our findings revealed a novel linkage between WSSV IE1 and shrimp STAT, which was a clue to well understand how WSSV adopted the active strategies to modulate the shrimp signaling pathway.

Shrimp with knockdown of LvSOCS2, a negative feedback loop regulator of JAK/STAT pathway in Litopenaeus vannamei, exhibit enhanced resistance against WSSV

JAK/STAT pathway is one of cytokine signaling pathways and mediates diversity immune responses to protect host from viral infection. In this study, LvSOCS2, a member of suppressor of cytokine signaling (SOCS) families, has been cloned and identified from Litopenaeus vannamei. The full length of LvSOCS2 is 1601 bp, including an 1194 bp open reading frame (ORF) coding for a putative protein of 397 amino acids with a calculated molecular weight of ∼42.3 kDa. LvSOCS2 expression was most abundant in gills and could respond to the challenge of LPS, Vibrio parahaemolyticus, Staphhylococcus aureus, Poly (I: C) and white spot syndrome virus (WSSV). There are several STAT binding motifs presented in the proximal promoter region of LvSOCS2 and its expression was induced by LvJAK or LvSTAT protein in a dose dependent manner, suggesting LvSOCS2 could be the transcriptional target gene of JAK/STAT pathway. Moreover, the transcription of DmVir-1, a read out of the activation of JAK/STAT pathway in Drosophila, was promoted by LvJAK but inhibited by LvSOCS2, indicating that LvSOCS2 could be a negative regulator in this pathway and thus can form a negative feedback loop. Our previous study indicated that shrimp JAK/STAT pathway played a positive role against WSSV. In this study, RNAi-mediated knockdown of LvSOCS2 shrimps showed lower susceptibility to WSSV infection and caused lessened virus loads, which further demonstrated that the JAK/STAT pathway could function as an anti-viral immunity in shrimp.

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 of 10 transcripts of FREP in penaeid shrimp Litopenaeus vannamei

Fibrinogen-related proteins (FREPs) are widely distributed in vertebrates and invertebrates and known having Fibrinogen-related domains (FReDs) which function in multiple aspects, especially in innate immune response as pattern recognition receptors. However, there is no any report about FREP in penaeid shrimp Litopenaeus vannamei. Here, totally 10 transcripts of FREP were isolated and named LvFREP1.1, 1.2 until 1.10. All of the 10 transcripts have high identity in their 3' ends and encode conserved FReDs. Since the 10 transcripts are highly similar we could not design any primers that can amplify a single transcript. We chose a pair of primers corresponding to part of LvFREP1.1 and LvFREP1.5 to examine their expression. Tissue distribution indicated LvFREP1.1 and LvFREP1.5 mRNA locates in hemocytes, gills, intestine, hearts and slightly in nerve. The expression of LvFREP1.1 and LvFREP1.5 behaves differently post bacteria and virus infection. Besides, recombinant LvFReD could agglutinate bacteria Vibrio harveyi in the presence of Ca²⁺. These initial data presents the diversity of FREPs in penaeid shrimp and also push us to further explore their roles in shrimp immune response.

Differential expression of microRNAs of Litopenaeus vannamei in response to different virulence WSSV infection

WSSV is one of the most harmful pathogeny in the pacific white shrimp, and genetic variations caused the strains of different virulence. MicroRNAs (miRNAs) involved in the regulation of virus defense. To understand the different virulence of WSSV on miRNA expression in Litopeneaus vannamei, the deep sequencing was performed to compare two small RNA libraries prepared from hepatopancreas of Litopeneaus vannamei infected with normal-virulence or low-virulence WSSV. Approximately 29,398,623 raw reads from normal-virulence library and 35,291,803 raw reads from low-virulence library were obtained. There were about 37 miRNAs homologs identified. Sixteen miRNAs were significantly up-regulated and twenty-one miRNAs were significantly down-regulated in normal-virulence infection library compared with low-virulence infection library. Of these, Igi-miR-1175-3p was the most significant different miRNA, followed by bmo-miR-1175-3p and ipu-miR-26b, respectively. The putative target genes for differentially expressed miRNAs were concerned with biological processes, signal meditated, cell differentiation and apoptosis, immune recognition and other more functions. The results will help to understand the miRNAs response to different virulence WSSV infection.

Comparative microarray profile of the hepatopancreas in the response of "Huanghai No. 2" Fenneropenaeus chinensis to white spot syndrome virus

White spot syndrome virus (WSSV) infects all shrimp species and is the greatest detriment to shrimp culture. To better understand the mechanism of molecular responses to WSSV infection in "Huanghai No. 2" Fenneropenaeus chinensis, a microarray technique was used. Microarray gene expression profiling of 59,137 unigenes identified Differentially Expressed Genes (DEGs) both in live and moribund shrimp at early, peak and late phases. In live shrimp, 1307, 1479 and 1539 DEGs were obtained in the early, peak and late phase, respectively. Meanwhile, 1536, 2181 and 1591 DEGs were obtained in moribund shrimp. Twenty known annotation genes are uniquely expressed in the late phase of live shrimp, including adhesion regulating molecule 1, arginine kinase, BUD31 homolog, and QM. Compared to WSSV-susceptible shrimp, 75 known annotation genes are uniquely expressed in WSSV-resistant shrimp, including arginine kinase, BUD31 homolog, clottable protein 2, caspase 2, cathepsin C, calnexin, HMGBb, Histone 3, and selenoprotein M. The gene expression patterns of the infected shrimp were altered by WSSV infection. To further confirm the expression of differentially expressed genes, real-time RT-PCR was performed to test six randomly selected genes. The data will provide valuable information to understand the immune mechanism of shrimp's response to WSSV.

Characterization of a Kunitz-type protease inhibitor (MjKuPI) reveals the involvement of MjKuPI positive hemocytes in the immune responses of kuruma shrimp Marsupenaeus japonicus

Serine proteases and their inhibitors play vital roles in biological processes. Serine protease inhibitors, including Kunitz-type protease inhibitors play important roles not only in physiological process (i.e. blood clotting and fibrinolysis) but also in immune responses. In this study, we characterized a Kunitz-type protease inhibitor, designated MjKuPI, from kuruma shrimp Marsupenaeus japonicus. An expression profile showed that MjKuPI was mainly expressed in hemocytes. Immunostaining revealed that some hemocytes expressed MjKuPI (MjKuPI(+) hemocytes) and others did not (MjKuPI(-) hemocytes). Injection of shrimp with Vibrio penaeicida and white spot syndrome virus (WSSV) upregulated the mRNA level of MjKuPI, and a flow cytometry analysis revealed that the proportion of MjKuPI(+) hemocytes increased significantly 24 h after injection. Together, these results suggest that MjKuPI and MjKuPI(+) hemocytes have a role in the innate immune system of kuruma shrimp.

Beta 1,3/1,6-glucan and vitamin C immunostimulate the non-specific immune response of white shrimp (Litopenaeus vannamei)

This study mainly evaluated the effects of orally administered beta 1,3/1,6-glucan and vitamin C on the nonspecific immune responses of white shrimp (Litopenaeus vannamei). In this study, we found that the white shrimp oral administration with 1 g/kg of beta 1,3/1,6-glucan effectively enhanced O2(-) production and phenoloxidase and superoxide dismutase activity. Shrimp were oral administration with 0.2 g/kg of vitamin C presented beneficial nonspecific immune responses and enzyme activity and also observed in the beta 1,3/1,6-glucan treatment groups. Consequently, we compared the alterations in the immune activity between the beta 1,3/1,6-glucan and vitamin C groups and the evidence illustrated that combination of beta 1,3/1,6-glucan and vitamin C presented an additive effect on inducing the nonspecific immune responses of white shrimp.

Identification and function analysis of a novel vascular endothelial growth factor, LvVEGF3, in the Pacific whiteleg shrimp Litopenaeus vannamei

VEGF signaling pathway is first discovered in mammals and proved to play important roles in the biological processes of angiogenesis, tumor migration, cell differentiation, apoptosis, host-virus interaction etc. Three members in the VEGF signaling pathway, including LvVEGFR, LvVEGF1 and LvVEGF2 in shrimp have been proved to be related with WSSV infection in our previous studies. Currently, another member of VEGF family, LvVEGF3, was isolated and its function during the WSSV infection of shrimp was studied. The deduced amino acid sequence of LvVEGF3 contained a signal peptide, a typical PDGF/VEGF domain and a cysteine-knot motif (CXCXC). Tissue distribution analysis showed that LvVEGF3 was predominantly expressed in hemocytes. The transcriptional level of LvVEGF3 in hemocytes was apparently up-regulated during WSSV infection. Silencing of LvVEGF3 with double-stranded RNA caused a reduction of the cumulative mortality rate of shrimp during WSSV infection. The expression of LvVEGFR was apparently down-regulated after LvVEGF3 silencing and up-regulated after injection of recombinant LvVEGF3 protein, suggesting an interaction between LvVEGF3 and LvVEGFR. Furthermore, the interaction between LvVEGFR and LvVEGF3 was confirmed using the yeast two-hybrid system. The results provided new insights into understanding the role of VEGF signaling pathway during virus infection.

Identification and characterization of an 18.4kDa antimicrobial truncation from shrimp Litopenaeus vannamei hemocyanin upon Vibrio parahaemolyticus infection

Hemocyanin (HMC) is a multifunctional protein which plays many essential roles in invertebrate organism. Recently more and more immune-related functions have been discovered on this protein. Here the shrimp was infected with Vibrio parahaemolyticus and the shrimp sera were analyzed by two-dimensional gel electrophoresis. Totally 15 spots were identified as significantly up-regulated spots and further analyzed by MALDI-TOF/TOF mass spectrometry (MS). Four of them were identified as HMC derived truncations (HMCS1, HMCS3, HMCS4 and HMCS5). The HMCS4 primary sequence was further determined via Edman N terminal sequencing, MALDI-TOF MS and amino acid sequence alignment. The result indicated that the HMCS4 was a 165aa fragment from shrimp HMC small subunit C-terminal. The HMCS4 immunological activities were further analyzed by agglutination experiment and antibacterial assay in vitro. The results showed that the recombinant HMCS4 (rHMCS4) had strong agglutination and antibacterial activities against pathogenic bacteria at the optimum bacteriostasis concentration. In addition, the HMCS4 immunological activities were explored via mortality assay in vivo. The shrimp was challenged with V. parahaemolyticus and rHMCS4 V. parahaemolyticus mixture separately. The shrimp mortality rate was significantly decreased at 96 h post-infection with rHMCS4 injection. Our data showed that shrimp HMC truncation generation upon infection was an effective immune response against invaded pathogens. Moreover, these findings may have some potential applications in shrimp industry.

Cloning, characterization, and expression of the macrophage migration inhibitory factor gene from the black tiger shrimp (Penaeus monodon)

Macrophage migration inhibitory factor (MIF) is an ancient cytokine that engages in innate immune system of vertebrates and invertebrates. In this study, the MIF gene homologue (PmMIF) was cloned from the black tiger shrimp, Penaeus monodon. The full-length cDNA sequence of PmMIF was 838 bp and contained 78 bp 5' untranslated region (UTR) and 397 bp 3' UTR, and an open reading frame (ORF) of 363 bp which coded 120 amino acids (aa). Multiple alignment analysis showed that the deduced amino acid sequence shared 98% identities with MIF from closely related species of Litopenaeus vannamei. Quantitative real-time PCR (qRT-PCR) analysis indicated that PmMIF was highly expression observed in hepatotpancreas and gills. After Vibrio harveyi challenge, PmMIF mRNA level in hepatopancreas and gills were sharply up-regulated at 6 h post-injection, and reached the maximum at 12 h. PmMIF expression level in the hepatopancreas and gills were up-regulated markedly under low (2.3%) and high (4.3%) salinity exposure, respectively. PmMIF expression level in gills increased significantly at 12 h and reached peak values (2.5- fold, 6.4-fold and 1.8-fold compared with the control) at 12 h, 48 h and 12 h after zinc, cadmium and copper exposure, respectively. In the hepatopancreas, the expression of PmMIF reached maximum levels (8.5- fold, 6.2-fold and 2.1-fold compared with the control) at 24 h, 6 h and 48 h after zinc, cadmium and copper exposure, respectively. All the results indicate that PmMIF plays an important role in responding in the innate immune system of shrimps.

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

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

A hemocyte-expressed fibrinogen-related protein gene (LvFrep) from the shrimp Litopenaeus vannamei: Expression analysis after microbial infection and during larval development

Fibrinogen-related proteins (FREPs) comprise a large family of microbial recognition proteins involved in many biological functions in both vertebrate and invertebrate animals. By taking advantage of publicly accessible databases, we have identified a FREP-like homolog in the most cultivated penaeid shrimp, Litopenaeus vannamei (LvFrep). The obtained sequence showed a conserved fibrinogen-related domain (FReD) and displayed significant similarities to FREP-like proteins from other invertebrates and to ficolins from crustaceans. The expression of LvFrep appeared to be limited to circulating hemocytes. Interestingly, LvFrep gene expression was induced in shrimp hemocytes only in response to a Vibrio infection but not to the White spot syndrome virus (WSSV). Moreover, LvFrep transcript levels were detected early in fertilized eggs, suggesting the participation of this immune-related gene in the antimicrobial defenses during shrimp development.

Suppressor of cytokine signaling 2 (SOCS2) negatively regulates the expression of antimicrobial peptides by affecting the Stat transcriptional activity in shrimp Marsupenaeus japonicus

The suppressor of cytokine signaling (SOCS) family is a kind of negative regulators in the Janus kinase/signal transducer and activator of transcription (Jak/Stat) pathway in mammals and Drosophila. In kuruma shrimp, Marsupenaeus japonicus, SOCS2 is identified and its expression can be stimulated by peptidoglycan and polycytidylic acid. However, if SOCS2 participates in regulating Jak/Stat pathway in shrimp still needs further study. In this study, SOCS2 with Src homology 2 domain and SOCS box was identified in kuruma shrimp, M. japonicus. SOCS2 existed in hemocytes, heart, hepatopancreas, gills, stomach, and intestine, the expression of SOCS2 was upregulated significantly in the hemocytes and intestine of shrimp challenged with Vibrio anguillarum at 6 h. To analyze SOCS2 function in shrimp immunity, bacterial clearance and survival rate were analyzed after knockdown of SOCS2 in shrimp challenged with V. anguillarum. Results showed that bacterial clearance increased, and the survival rate improved significantly comparing with controls. The SOCS2 was expressed in Escherichia coli and the recombinant SOCS2 was injected into shrimp, and Stat phosphorylation and translocation were analyzed. The result showed that "overexpression" of SOCS2 declined Stat phosphorylation level and inhibited Stat translocation into the nucleus. After knockdown of SOCS2 in shrimp prior to V. anguillarum infection, the expression level of antimicrobial peptides, including anti-lipopolysaccharide factors C1, C2 and D1, and Crustin I was upregulated significantly, and the expression of the AMPs was declined after recombinant SOCS2 injection. The SOCS2 expression was also decreased in Stat-knockdown shrimp challenged by V. anguillarum at 6 and 12 h. Therefore, SOCS2 negatively regulates the AMP expression by inhibiting Stat phosphorylation and translocation into nucleus in shrimp, meanwhile, SOCS2 expression was also regulated by Jak/Stat pathway.

Immunity enhancement with administration of Gracilaria corticata and Saccharomyces cerevisiae compared to gamma irradiation in expose to WSSV in shrimp, in juvenile Litopenaeus vannamei: A comparative study

This paper investigates the efficacy of Gracilaria corticata, Saccharomyces cerevisiae and gamma irradiation WSSV as immunostimulants to white shrimp Litopenaeus vannamei. Seven hundred and twenty healthy shrimp SPF L. vannamei subadult with average weight of 10 ± 1.02 g were collected and divided into 8 groups. The first group (T1) was fed with commercial pellet, the second group (T2) fed with S. cerevisiae (2 g/kg), the third group (T3) fed with G. corticata powder mixed with shrimp feed (2 g/kg) and, finally, the fourth group (T4) was fed with commercial pellet and injected intramuscularly gamma irradiant WSSV (1 μl/gbw) for 10 days. The shrimps were then injected with WSSV and maintained for 25 days. The positive control group for each treatment was maintained in the same manner but without injection with WSSV. Moreover, survival rate and immune parameters such as total hemocyte count (THC), total protein plasma (TPP), superoxide dismutase (SOD) activity, peroxidase (POD) activity and phenoloxidase activity (PO) were determined. Results indicated that the survival rates for groups T4, T3 T2 and T1 were 57.05 ± 3.52%, 22.5 ± 0.5%, 15 ± 1.05% and 00.0 ± 0%, respectively. Ultimately, at the end of the study the shrimp group T4 showed higher hematological data: THC, TPP, SOD, POD and PO. The study concluded that gamma irradiant WSSV is effective immunostimulants in shrimp L. vannamei and the immunity has better performances than those of the G. corticata and S. cerevisiae.

Steroid hormone "cortisone" and "20-hydroxyecdysone" involved in the non-specific immune responses of white shrimp (Litopenaeus vannamei)

This study investigated the effect of two steroid hormones on phenoloxidase activity, O2(-) production in the haemocytes, total haemocyte count (THC), superoxide dismutase (SOD) activity, glutamate oxaloacetate transaminase (GOT) activity, glutamate pyruvate transaminase (GPT) activity, and plasma cholesterol concentrations in white shrimps (Litopenaeus vannamei). Phenoloxidase activity, THC and plasma cholesterol concentration in shrimps treated with cortisone and 20-hydroxyecdysone were found to be lower when compared with the control groups. In the observation of O2(-) production, treatment of cortisone and hydroxyecdysone were reducing the activity in the 1st day, but to be undiversified with the elapsed time. By contrast, SOD activity in the hepatopancreas, plasma GOT activity, and GPT activity were significantly increased when compared with the control groups.

Identification and pathogenicity of Vibrio parahaemolyticus isolates and immune responses of Penaeus (Litopenaeus) vannamei (Boone)

Five different Vibrio parahaemolyticus strains (SH8, SH108, SH58, AH5 and GD10) isolated from the hepatopancreas of moribund shrimp in farms of mainland China were identified and capable of inducing massive mortality of Penaeus (Litopenaeus) vannamei. The immersion challenge results with five isolates indicated variance of virulence, while only GD10 caused massive sloughing of tubule epithelial cells which was recognized as the most significant symptom of AHPND. Differences in immune responses were detected of P. vannamei during 48 h post-infection (p.i.) by injection or immersion challenge with V. parahaemolyticus (SH8, SH108 and GD10) isolates. When injected SH8 and SH108 isolates, the expression of lysozyme (LSZ) showing statistically significant upregulation at 16 and 48 h p.i. and that of Toll-like receptors (TLR) showed statistically significant upregulation at 48 h p.i. When immersion challenge with the GD10 isolate, TLR were upregulated after 8 h p.i. challenge with 10(4)  cfu mL(-1) ; however, LSZ was downregulated when challenged with 10(3)  cfu mL(-1) . The results suggested that LSZ and TLR serve as crucial molecular markers of innate immunity in shrimp against V. parahaemolyticus infection. LSZ is a vital marker for acute bacterial infection, while TLR serves as a crucial marker for chronic infection.

Cloning and characterization of tyrosine hydroxylase (TH) from the pacific white leg shrimp Litopenaeus vannamei, and its expression following pathogen challenge and hypothermal stress

Tyrosine hydroxylase (TH) belongs to the biopterin-dependent aromatic amino acid hydroxylase enzyme family, and it represents the first and rate-limiting step in the synthesis of catecholamines that are required for physiological and immune process in invertebrates and vertebrates. Cloned Litopenaeus vannamei TH (LvTH), containing a short alpha helix domain, a catalytic core, a regulatory domain, a phosphorylation site and two potential N-linked glycosylation sites as presented in vertebrate and insect THs without acidic region and signal peptide cleavage sites at the amino-terminal, exhibited a similarity of 60.0-61.2% and 45.0-47.0% to that of invertebrate and vertebrate THs, respectively. Further, LvTH expression was abundant in gill and haemocytes determined by quantitative real-time PCR. L. vannamei challenged with Vibrio alginolyticus at 10(5) cfu shrimp(-1) revealed significant increase of LvTH mRNA expression in haemocytes within 30-120 min and in brain within 15-30 min followed with recuperation. In addition, shrimps exposed to hypothermal stress at 18 °C significantly increased LvTH expression in haemocytes and brain within 30-60 and 15-60 min, respectively. The TH activity and haemolymph glucose level (haemocytes-free) significantly increased in pathogen challenged shrimp at 120 min and 60 min, and in hypothermal stressed shrimp at 30-60 and 30 min, respectively. These results affirm that stress response initiates in the brain while haemocytes display later response. Further, the significant elevation of TH activity in haemolymph is likely to confer by TH that released from haemocytes. In conclusion, the cloned LvTH in our current study is a neural TH enzyme appears to be involved in the physiological and immune responses of whiteleg shrimp, L. vannamei suffering stressful stimulation.

The Dorsal/miR-1959/Cactus feedback loop facilitates the infection of WSSV in Litopenaeus vannamei

miR-1959, a novel microRNA identified from Litopenaeus vannamei, mediates a positive feedback loop between Dorsal and Cactus that can continuously maintain the activation of the NF-κB pathway. It has been known that miR-1959 is involved in antibacterial immunity in shrimp, but its function in antiviral responses is still unknown. In this study, we focused on the role of miR-1959 in infection of white spot syndrome virus (WSSV), the major viral pathogen in shrimp worldwide. The expression of miR-1959 in shrimp hemocytes, gill, and hepatopancreas was significantly up-regulated upon WSSV infection. Dual-luciferase reporter assays demonstrated that miR-1959 could enhance the activity of the promoter of WSSV immediate early gene ie1. In vivo experiments also showed that inhibition of miR-1959 led to decrease of the mortality of WSSV-infected shrimp and the genome copies of WSSV in tissues, meanwhile the expression of WSSV ie1 and VP28 genes was down-regulated. In contrast, increase of the miR-1959 level in shrimp by injection of miR-1959 mimics produced opposite results. These suggested that the Dorsal/miR-1959/Cactus feedback loop could favor the infection of WSSV in shrimp. Thus, our study helps further reveal the interaction between WSSV and shrimp immune system.