Molecular characterization of a Ran isoform gene up-regulated in shrimp immunity

A ras-related nuclear protein Ran participates in the 20E signaling pathway and is essential for the growth and development of Locusta migratoria

The small GTPase Ran is a member of the Ras superfamily of small GTP-binding proteins, which plays a key role in the translocation of RNA and proteins through the nuclear pore complex. In this study, the full-length cDNA sequence of LmRan gene was obtained, which consists of 648-nucleotides open reading frame (ORF) and encodes 215 amino acids. RT-qPCR results revealed that LmRan was expressed in all developmental days and tissues investigated. Injection of dsLmRan into 4th and 5th instar nymphs, resulted in a significant down-regulation of LmRan transcripts, respectively. All dsLmRan-injected nymphs died before molting. Further hematoxylin and eosin staining of the integument showed that there was no apolysis occurred after silencing LmRan. In addition, the weight of dsLmRan-injected nymphs was significantly lower than that of the control group, and the gastric caecum and midgut was severely smaller. Especiallly, the mRNA level of LmCYP302a1, LmCYP315a1 and LmCYP314a1 responsible for 20E synthesis, LmE75 and LmE74 genes involved in the 20E signaling pathway, LmGfat, LmUAP1 and LmCHT10 genes involved in chitin metabolism pathway were dramatically decreased in the dsLmRan-injected nymphs. Together, the results indicated that LmRan participate in the 20E signaling pathway, which is essential for the growth and development of locusts.

Identification and function analysis of ras-related nuclear protein from Macrobrachium rosenbergii involved in Spiroplasma eriocheiris infection

A ras-related nuclear protein (Ran) protein was obtained from Macrobrachium rosenbergii, named MrRan. Phylogenetic analysis results showed that MrRan was clustered in one group together with other crustaceans. Tissue distribution analysis revealed that MrRan was expressed mainly in gill, intestine and stomach, and expressed weakly in muscle. The MrRan expression levels in gill and hemocyte of prawns were significantly up-regulated after challenged by Spiroplasma eriocheiris. The copy number of S. eriocheiris in MrRan dsRNA injection group was significantly less than control groups during infection. Meanwhile, silencing MrRan obviously increased the survival rate of prawns. The subcellular localization experiment suggested that recombinant MrRan was mainly located in the nucleus, and relatively weak in the cytoplasm. Finally, over-expression in Drosophila S2 cell indicated that MrRan could increase copies of S. eriocheiris and decrease of cell viability. The present study suggested that MrRan participated in regulating the phagocytosis of S. eriocheiris in M. rosenbergii.

Three members of Ras GTPase superfamily are response to white spot syndrome virus challenge in Marsupenaeus japonicus

Members of the Ras-like GTPase superfamily are key regulators of diverse cellular and developmental events, including differentiation, cell division, vesicle transport, nuclear assembly, and cytoskeleton control. In this study, three Ras family members (MjRap, MjRas, and MjRal) were cloned from Marsupenaeus japonicus. The full lengths of MjRap, MjRas, and MjRal are 788, 1330, and 2074 bp, which encode the proteins of 186, 202, and 198 amino acids respectively. Phylogenetic analysis showed that Rap, Ras, and Ral from different species gather together. The MjRap, MjRas, and MjRal genes were ubiquitously expressed in the hemocytes, hepatopancreas, gills, stomach, and muscle. Results from the quantitative real-time polymerase chain reaction (qRT-PCR) showed that MjRal in the gills was upregulated 48 and 72 h post-White spot syndrome virus (WSSV) challenge. No change in the MjRap or MjRas transcript was observed in the gills under the WSSV challenge. The RNAi of MjRal could enhance the WSSV replication. Injection of rMjRal protein could inhibit WSSV replication, but had no effect on VP28 expression. So, it could be concluded that MjRal was involved in shrimp anti-viral innate immune defense by inhibiting the WSSV replication.

Ran Involved in the Development and Reproduction Is a Potential Target for RNA-Interference-Based Pest Management in Nilaparvata lugens

Ran (RanGTPase) in insects participates in the 20-hydroxyecdysone signal transduction pathway in which downstream genes, FTZ-F1, Krüppel-homolog 1 (Kr-h1) and vitellogenin, are involved. A putative Ran gene (NlRan) was cloned from Nilaparvata lugens, a destructive phloem-feeding pest of rice. NlRan has the typical Ran primary structure features that are conserved in insects. NlRan showed higher mRNA abundance immediately after molting and peaked in newly emerged female adults. Among the examined tissues ovary had the highest transcript level, followed by fat body, midgut and integument, and legs. Three days after dsNlRan injection the NlRan mRNA abundance in the third-, fourth-, and fifth-instar nymphs was decreased by 94.3%, 98.4% and 97.0%, respectively. NlFTZ-F1 expression levels in treated third- and fourth-instar nymphs were reduced by 89.3% and 23.8%, respectively. In contrast, NlKr-h1 mRNA levels were up-regulated by 67.5 and 1.5 folds, respectively. NlRan knockdown significantly decreased the body weights, delayed development, and killed >85% of the nymphs at day seven. Two apparent phenotypic defects were observed: (1) Extended body form, and failed to molt; (2) The cuticle at the notum was split open but cannot completely shed off. The newly emerged female adults from dsNlRan injected fifth-instar nymphs showed lower levels of NlRan and vitellogenin, lower weight gain and honeydew excretion comparing with the blank control, and no offspring. Those results suggest that NlRan encodes a functional protein that was involved in development and reproduction. The study established proof of concept that NlRan could serve as a target for dsRNA-based pesticides for N. lugens control.

A Rac1 GTPase is a critical factor in the immune response of shrimp (Litopenaeus vannamei) to Vibrio alginolyticus infection

The small GTPase Rac1 acts as a molecular switch for signal transduction that regulates various cellular functions. However, its functions in crustaceans remain unclear. In this study, a cDNA encoding a RAS GTPase (LvRac1) in the Pacific white shrimp (L. vannamei) was identified and characterized. A recombinant variant of this GTPase, rLvRac1, was expressed in the model organism P. pastoris and its expression was confirmed by mass spectrometry. Biochemical assays indicated that the recombinant protein retained GTPase activity and was expressed in all of the organism's tested tissues. Injection of the bacterium V. alginolyticus into L. vannamei induced hepatopancreatic upregulation of LvRac1 expression. Moreover, knocking down LvRac1 in vivo significantly reduced the expression of the L. vannamei p53 and Cu/Zn superoxide dismutase genes (Lvp53 and LvCu/Zn SOD, respectively) while increasing that of the galectin gene (Lvgal). Hemolymph samples from control and LvRac1-silenced L. vannamei individuals were analyzed by flow cytometry, revealing that the latter exhibited significantly reduced respiratory burst activity and total hemocyte counts. Cumulative mortality in shrimp lacking LvRac1 was significantly greater than in control groups following V. alginolyticus challenge. The silencing of LvRac1 by double-stranded RNA injection thus increased the V. alginolyticus challenge sensitivity of L. vannamei and weakened its bacterial clearance ability in vivo. Suppressing LvRac1 also promoted the upregulation of Lvp53, LvCu/ZnSOD, and Lvgal following V. alginolyticus injection. Taken together, these results suggest that LvRac1 is important in the innate immune response of shrimp to V. alginolyticus infection.

Recent insights into host-pathogen interaction in white spot syndrome virus infected penaeid shrimp

Viral disease outbreaks are a major concern impeding the development of the shrimp aquaculture industry. The viral disease due to white spot syndrome virus (WSSV) observed in early 1990s still continues unabated affecting the shrimp farms and cause huge economic loss to the shrimp aquaculture industry. In the absence of effective therapeutics to control WSSV, it is important to understand viral pathogenesis and shrimp response to WSSV at the molecular level. Identification and molecular characterization of WSSV proteins and receptors may facilitate in designing and development of novel therapeutics and antiviral drugs that may inhibit viral replication. Investigations into host-pathogen interactions might give new insights to viral infectivity, tissue tropism and defence mechanism elicited in response to WSSV infection. However, due to the limited information on WSSV gene function and host immune response, the signalling pathways which are associated in shrimp pathogen interaction have also not been elucidated completely. In the present review, the focus is on those shrimp proteins and receptors that are potentially involved in virus infection or in the defence mechanism against WSSV. In addition, the major signalling pathways involved in the innate immune response and the role of apoptosis in host-pathogen interaction is discussed.

Comparison of immune response of Pacific white shrimp, Litopenaeus vannamei, after multiple and single infections with WSSV and Vibrio anguillarum

Our previous study demonstrated that Pacific white shrimp (Litopenaeus vannamei) infected by multiple pathogens showed higher mortality and death occurred more quickly than those infected by a single pathogen (Jang et al., 2014). For better understanding the defense mechanism against white spot syndrome virus (WSSV) and Vibrio anguillarum, immune responses of shrimp were evaluated in this study. The mRNA expression levels of five immune-related genes were analyzed by quantitative reverse real-time PCR, which included proPO-activating enzyme 1 (PPAE1), PPAE2, proPO activating factor (PPAF), masquerade-like serine proteinase (Mas) and ras-related nuclear gene (Ran). Results demonstrated that the transcription was suppressed more intensively in the multiple infection group than those in single infection groups. The transcriptional suppression was directly related to the higher mortality. The hypoimmunity could benefit pathogen invasion, replication and release of toxin in vivo. Results in this study will help to understand immune defense mechanism after shrimp were infected by multiple pathogens in aquaculture.

Transcriptome analysis on Chinese shrimp Fenneropenaeus chinensis during WSSV acute infection

Previous studies have discovered a lot of immune-related genes responding to white spot syndrome virus (WSSV) infection in crustacean. However, little information is available in relation to underlying mechanisms of host responses during the WSSV acute infection stage in naturally infected shrimp. In this study, we employed next-generation sequencing and bioinformatic techniques to observe the transcriptome differences of the shrimp between latent infection stage and acute infection stage. A total of 64,188,426 Illumina reads, including 31,685,758 reads from the latent infection group and 32,502,668 reads from the acute infection group, were generated and assembled into 46,676 unigenes (mean length: 676 bp; range: 200-15,094 bp). Approximately 24,000 peptides were predicted and classified based on homology searches, gene ontology, clusters of orthologous groups of proteins, and biological pathway mapping. Among which, 805 differentially expressed genes were identified and categorized into 11 groups based on their possible function. Genes in the Toll and IMD pathways, the Ras-activated endocytosis process, the RNA interference pathway, anti-lipopolysaccharide factors and many other genes, were found to be activated in shrimp from latent infection stage to acute infection stage. The anti-bacterially proPO-activating cascade was firstly uncovered to be probably participated in antiviral process. These genes contain not only members playing function in host defense against WSSV, but also genes utilized by WSSV for its rapid proliferation. In addition, the transcriptome data provides detail information for identifying novel genes in absence of the genome database of shrimp.

Immune gene discovery by expressed sequence tag (EST) analysis of hemocytes in the ridgetail white prawn Exopalaemon carinicauda

The ridgetail white prawn Exopalaemon carinicauda is one of the most important commercial species in eastern China. However, little information of immune genes in E. carinicauda has been reported. To identify distinctive genes associated with immunity, an expressed sequence tag (EST) library was constructed from hemocytes of E. carinicauda. A total of 3411 clones were sequenced, yielding 2853 ESTs and the average sequence length is 436 bp. The cluster and assembly analysis yielded 1053 unique sequences including 329 contigs and 724 singletons. Blast analysis identified 593 (56.3%) of the unique sequences as orthologs of genes from other organisms (E-value < 1e-5). Based on the COG and Gene Ontology (GO), 593 unique sequences were classified. Through comparison with previous studies, 153 genes assembled from 367 ESTs have been identified as possibly involved in defense or immune functions. These genes are categorized into seven categories according to their putative functions in shrimp immune system: antimicrobial peptides, prophenoloxidase activating system, antioxidant defense systems, chaperone proteins, clottable proteins, pattern recognition receptors and other immune-related genes. According to EST abundance, the major immune-related genes were thioredoxin (141, 4.94% of all ESTs) and calmodulin (14, 0.49% of all ESTs). The EST sequences of E. carinicauda hemocytes provide important information of the immune system and lay the groundwork for development of molecular markers related to disease resistance in prawn species.