An Ns1abp-like gene promotes white spot syndrome virus infection by interacting with the viral envelope protein VP28 in red claw crayfish Cherax quadricarinatus

Rab1A functioned as a binding protein involved in Macrobrachium rosenbergii Taihu virus infection

Macrobrachium rosenbergii Taihu virus (MrTV) is a virulent pathogen that mainly threatens M. rosenbergii larvae. Rab proteins, which are essential for controlling intracellular membrane trafficking, are hijacked by multiple viruses to complete their life cycle. In this paper, we studied the function of M. rosenbergii Rab1A (MrRab1A) in the MrTV infection. Upon MrTV infection, the transcription level of MrRab1A was significantly up-regulated, indicating MrRab1A was a MrTV responsive gene and might be important for MrTV infection. Co-IP and co-localization assays revealed that MrRab1A could directly bind with MrTV and its capsid protein VP3. Moreover, the in vivo neutralization assay demonstrated that pre-incubation of MrTV with recombinant MrRab1A could partially block MrTV infection. These findings indicated that MrRab1A functioned as a virus-binding protein involved in MrTV infection, which shed new light on the mechanism of MrTV infection and provided a potential target for developing anti-MrTV therapies.

Identification of an AnnexinB9 involve in white spot syndrome virus infection in red claw crayfish Cherax quadricarinatus

Annexin (Anx) family protein is a highly conserved protein family that plays important roles in immune defense of vertebrates and invertebrates against invading pathogens. In this study, a novel Anx was cloned and characterized from the red claw crayfish, Cherax quadricarinatus. The Open Reading Frame of CqAnxB9 consisted of 930 nucleotide bases pair and encoded 309 amino acids. The CqAnxB9 protein contained three repeat Anx domains and a typical KGLGT sequence. Tissue expression analysis showed that the expression levels of CqAnxB9 were mainly expressed in the intestine, hepatopancreas and hemocytes. After WSSV challenge, CqAnxB9 expression was up-regulated in the hematopoietic tissue (Hpt) cells. Moreover, knockdown of CqAnxB9 inhibited WSSV replication and VP28 expression, suggesting that CqAnxB9 plays a positive role in WSSV infection. Further studies revealed that recombinant CqAnxB9 protein was found to bind to the viral envelop protein VP28. All these findings indicate that new-found CqAnxB9 is likely to promote WSSV infection in crustaceans, which provides a better understanding of the pathogenesis of WSSV.

The effect of white spot syndrome virus (WSSV) envelope protein VP28 on innate immunity and resistance to white spot syndrome virus in Cherax quadricarinatus

VP28 is the most abundant membrane protein of WSSV, and the recombinant protein VP28 (VP26 or VP24) was constructed for the immune protection experiment in this study. Crayfish were immunized by intramuscular injection of recombinant protein V28 (VP26 or VP24) at a dose of 2 μg/g. The survival rate of crayfish immunized by VP28 showed a higher value than by VP26 or VP24 after WSSV challenge. Compared with the WSSV-positive control group, the VP28-immunized group could inhibit the replication of WSSV in crayfish, increasing the survival rate of crayfish to 66.67% after WSSV infection. The results of gene expression showed that VP28 treatment could enhance the expression of immune genes, mainly JAK and STAT genes. VP28 treatment also enhanced total hemocyte counts and enzyme activities including PO, SOD, and CAT in crayfish. VP28 treatment reduced the apoptosis of hemocytes in crayfish, as well as after WSSV infection. In conclusion, VP28 treatment can enhance the innate immunity of crayfish and has a significant effect on resistance to WSSV, and can be used as a preventive tool.

Dietary glycerol monolaurate protects Cherax quadricarinatus against white spot syndrome virus infection

Glycerol monolaurate (GML), one of the medium-chain fatty acid esters, is often used as an emulsifier or preservative. Its biological functions include antibacterial and antiviral activities. In this study, we examined the effects of dietary GML on the resistance of the red claw crayfish to WSSV infection. Crayfish fed with 4 g/kg GML showed higher survival rate and lower WSSV copy numbers than the control after WSSV infection. A RT-qPCR analysis showed that GML supplementation enhanced the expression of immune-related genes, especially JAK and caspase. Our data indicate that GML affects the immune parameters of crayfish, including the total hemocyte counts and phenoloxidase, acid phosphatase, superoxide dismutase, lysozyme, and peroxidase activities. After treatment with GML, the apoptosis of hemocytes increased significantly in both WSSV-infected and uninfected crayfish. In summary, GML reduced the mortality of WSSV-infected crayfish, perhaps by modulating the innate immunity of the crayfish. Our study shows that GML can be used to induce the innate immunity and enhance the immune protection of the red claw crayfish against WSSV infection, either therapeutically or as a preventive measure.

A new insight into the SNP genotyping using high-resolution melting method after the correlation analysis of the SNPs with WSSV-resistant traits

Procambarus clarkii is an important freshwater cultured crayfish in China. With the gradual development of its aquaculture industry, research on white spot disease, which is harmful to healthy culture of P. clarkii, increases gradually. The prophenoloxidase (proPO) system is an important part of crayfish's innate immunity and plays a role in virus resistance. In this study, based on the early discovery of three SNP sites in the intron of proPO gene, the linkage disequilibrium and haplotype were analyzed for the SNPs, and it was found that there was a strong linkage disequilibrium relationship among them. Through the analysis on association between the haplotypes and genotype of each SNP site with the WSSV-resistant traits, the detection of the SNP_7081 genotype was considered as the most convenient and efficient way for WSSV-resistant group selection. Furtherly, the high-resolution melting curve (HRM), which is a rapid and economic genotyping method, was chosen to establish for SNP_7081 site genotyping. The 68 bp target fragment with 27.94% GC content was amplified and melting curve analysis were performed. However, the appearance of false negatives which led to unable automatically grouped although the melting curves of genotypes CC, C>T and T>C were obviously different, and could be treated as standard to manually genotype the samples with an accuracy rate of 97.61%. The low GC content which correlated with the Tm value, was confirmed as the reason for the false negatives by the assay about the recombinant plasmid PMD18-T-SNP_7081 constructed with 45.24% GC content. Eventually, the adaptor primers were used to increase the GC content of the target fragment, and a modified HRM method for genotyping SNP_7081 site that could group automatically was established, which could provide a new insight for the HRM method to genotype SNPs.

LvCPG2 facilitated WSSV infection by interaction with VP26 and VP28

Chondroitin sulfate proteoglycans (CSP), widely distributed in extracellular matrices, have several important functions in vertebrates. In certain viruses, CSP acts as a receptor to promote infection. However, chondroitin proteoglycans lack sulfate are poorly understood in invertebrates. In this study, chondroitin proteoglycan 2 of Litopenaeus vannamei (LvCPG2) was cloned. The open reading frame of LvCPG2 cDNA is 2133 bp, which encodes a protein of 710 amino acids. LvCPG2 contained eight Chitin-binding domain type 2 (ChtBD2). LvCPG2 had the highest expression in lymphoid and significantly increased after WSSV challenge. The relative expression of IE1 and VP28, as well as the viral copy numbers were decreased significantly in LvCPG2-silenced shrimp. The far-western blotting result showed that LvCPG2 interacted with VP26 and VP28. Molecular docking complexes showed that N-terminal of LvCPG2 interacted with C-terminal VP26, while C-terminal of LvCPG2 combined with N-terminal of VP28. Flow cytometry analysis indicated that LvCPG2 could facilitate WSSV adhesion and penetration of shrimp hemocytes. Collectively, these findings suggested that LvCPG2 was involved in WSSV infection by interaction with VP26 and VP28.

14-3-3 is a VP3-binding protein involved in Macrobrachium rosenbergii Taihu virus infection in shrimp

Macrobrachium rosenbergii Taihu virus (MrTV) is a fierce pathogen that causes high mortality in M. rosenbergii larvae. Little is known about the pathogenesis of MrTV and host-virus interactions. In this study, a virus overlay protein binding assay (VOPBA), followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis, was carried out to search for novel host molecules that bind with VP3, one of the main capsid proteins of MrTV. Macrobrachium rosenbergii 14-3-3 protein (Mr14-3-3) was identified as the binding protein of VP3, which was further confirmed by co-immunoprecipitation (Co-IP) and co-localization assay. A preincubation assay was developed, which indicated that preincubation with recombinant Mr14-3-3 (rMr14-3-3) could significantly decrease the expression level of VP3 in MrTV-infected M. rosenbergii larvae, suggesting that preincubation with rMr14-3-3 could partially block MrTV infection. This study revealed that Mr14-3-3 acts as a binding protein for MrTV-VP3 and plays an important role in MrTV infection, offering a potential target for the development of anti-MrTV therapies.

A novel RING finger protein CqRNF152-like with self-ubiquitination activity inhibits white spot syndrome virus infection in a crustacean Cherax quadricarinatus

Really Interesting New Gene (RING) finger proteins are highly conserved molecules that participate in a variety of biological processes such as regulation of development, apoptosis and antiviral immunity in vertebrates. However, the functions of RING finger proteins are still poorly understood in crustaceans. Previously, we found that the transcript of a homolog of RING finger protein 152 (CqRNF152-like) was up-regulated in a differentially expressed transcriptome library of the haematopietic tissue (Hpt) cells from red claw crayfish Cherax quadricarinatus upon white spot syndrome virus (WSSV) infection, which is one of the most devastating viral diseases for crustaceans like shrimp and crayfish. The full-length cDNA sequence of CqRNF152-like was then identified with 975 bp, including an ORF of 685 bp that encoded a 195 amino acids protein, a 5'- UTR of 180 bp, and a 3'-UTR with a poly (A) tail of 207 bp. The conserved domain prediction showed that CqRNF152-like contained a conserved RING-finger domain. Gene expression analysis showed that CqRNF152-like was distributed in all tissues examined and the transcript is significantly up-regulated after WSSV challenge both in vivo in Hpt tissue and in vitro in cultured Hpt cells. Furthermore, the transcripts of both an immediate early gene ie1 and a late envelope protein gene vp28 of WSSV were clearly increased in the Hpt tissues, hemocytes and cultured Hpt cells after gene silencing of CqRNF152-like, which were further proved to be significantly decreased after overloading of recombinant CqRNF152-like protein in Hpt cell cultures. Meanwhile, CqRNF152-like was found to bind with WSSV envelope protein VP28 by proteins pull-down assay. Similar to most of RNF proteins, CqRNF152-like protein sequence contained a conserved RING-finger domain and showed self-ubiquitination activity in a RING finger domain dependent manner. Taken together, CqRNF152-like is likely to function as an antiviral molecular against WSSV infection through interaction with the envelope protein VP28 in a crustacean C. quadricarinatus. This is the first report that a RING finger protein with directly antiviral functions via interaction with viral protein and self-ubiquitination activity in crustacean, which sheds new light on the molecular mechanism of WSSV infection and the control of white spot disease.