Cloning, identification and function analysis of a Chibby homolog from Litopenaeus vannamei

Genome-wide identification and expression profiling of Wnt gene family in Neocaridina denticulata sinensis

Wnt proteins are a class of hydrophobic secreted glycoproteins involved in diverse important biological processes, such as tissue formation and regeneration, embryonic development and innate immunity. The Wnt gene family has an early origin and is present in all deuterostomes. In the process of evolution, the phenomenon of gene expansion, contraction and adaptive evolution occurs in the Wnt gene family. In the current study, eleven Wnt genes (NdWnt1-2, NdWnt4-7, NdWnt9-11, NdWnt16, and NdWntA) belonging to different subfamilies were obtained based on the genomic and transcriptomic data of Neocaridina denticulata sinensis. Then the expression patterns of all NdWnts were analyzed in various tissues, at different developmental stages and under different stresses. The expression profiles of NdWnts at different developmental stages showed that most NdWnt genes were initially expressed at gastrula stage, and the expression of NdWnt5 and NdWnt16 throughout all developmental stages. The spatial expression of NdWnt genes presented tissue specificity. They were mainly expressed in four tissues, namely gill, intestines, ovary and eyestalk. After Vibrio parahemolyticus infection and under copper exposure, the expression levels of five NdWnts (NdWnt1, NdWnt5, NdWnt10, NdWnt16 and NdWntA) were variable. Our findings enrich the research on the Wnt gene family of N. denticulata sinensis and provide valuable insights into relationship between structure and function of Wnt genes in crustaceans.

Comparative Transcriptome Analysis Reveals That WSSV IE1 Protein Plays a Crucial Role in DNA Replication Control

For DNA viruses, the immediate-early (IE) proteins are generally essential regulators that manipulate the host machinery to support viral replication. Recently, IE1, an IE protein encoded by white spot syndrome virus (WSSV), has been demonstrated to function as a transcription factor. However, the target genes of IE1 during viral infection remain poorly understood. Here, we explored the host target genes of IE1 using RNAi coupled with transcriptome sequencing analysis. A total of 429 differentially expressed genes (DEGs) were identified from penaeid shrimp, of which 284 genes were upregulated and 145 genes were downregulated after IE1 knockdown. GO and KEGG pathway enrichment analysis revealed the identified DEGs are significantly enriched in the minichromosome maintenance (MCM) complex and DNA replication, indicating that IE1 plays a critical role in DNA replication control. In addition, it was found that Penaeus vannamei MCM complex genes were remarkably upregulated after WSSV infection, while RNAi-mediated knockdown of PvMCM2 reduced the expression of viral genes and viral loads at the early infection stage. Finally, we demonstrated that overexpression of IE1 promoted the expression of MCM complex genes as well as cellular DNA synthesis in insect High-Five cells. Collectively, our current data suggest that the WSSV IE1 protein is a viral effector that modulates the host DNA replication machinery for viral replication.

Proteomics analysis reveals a critical role for the WSSV immediate-early protein IE1 in modulating the host prophenoloxidase system

White spot syndrome virus (WSSV) is a large enveloped double-stranded DNA virus that is a major impediment for shrimp aquaculture worldwide. So far, the mechanisms of WSSV-host interactions are ill-defined. Recent studies have revealed that IE1, an immediate-early protein encoded by WSSV, is a multifunctional modulator implicated in virus-host interactions. In this study, the biological functions of IE1 were further explored by identifying its interacting proteins using GST-pull down and mass spectrometry analysis. A total of 361 host proteins that potentially bind to IE1 were identified. Bioinformatics analysis revealed that the identified IE1-interacting proteins were key molecules involved in various signaling pathways such as prophenoloxidase (proPO) system, PI3K-AKT, MAPK, Focal adhesion, and cell cycle. Among these, the regulatory role of IE1 in the shrimp proPO system was further studied. The Co-immunoprecipitation (Co-IP) results confirmed that IE1 interacted with the Ig-like domain of Penaeus vannamei proPO or proPO-like proteins (proPO1/2 and hemocyanin). In addition, we found that in vivo RNAi mediated knockdown of IE1 reduced the viral genes expression and viral loads, as well as caused an increase in the PO activity of hemocytes during infection, whereas recombinant IE1 protein could inhibit the PO activity in a dose-dependent manner. Finally, our result demonstrated that WSSV could suppress the PO activity of hemocytes at the early infection stage. Collectively, our current data indicate that IE1 is a novel viral regulator that negatively modulates the shrimp proPO system, which provide additional insights into the biological functions of IE1 during WSSV infection.

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

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

Molecular characterization of a novel white spot syndrome virus response protein (dubbed LvWRP) from Litopenaeus vannamei

White spot syndrome, which is caused by white spot syndrome virus (WSSV), is a highly contagious disease of penaeid shrimp. However, there is currently incomplete understanding of the infection mechanism and pathogenesis of WSSV. In this study, a novel gene of a previously uncharacterized WSSV response protein (LvWRP) in Litopenaeus vannamei was identified and characterized. The LvWRP gene has an open reading frame (ORF) of 879 bp encoding a putative protein of 292 amino acids. Sequence analysis revealed that LvWRP shared 24.9% identity with an uncharacterized protein of Penaeus monodon nudivirus. Real-time qPCR analysis showed that LvWRP was ubiquitously expressed in shrimp tissues, with transcript levels induced in hemocytes upon immune challenge with Vibrio parahaemolyticus, Streptoccocus iniae, lipopolysaccharide (LPS), and WSSV. In addition, RNA interference-mediated knockdown of LvWRP followed by WSSV challenge revealed significant decrease in the transcript levels of WSSV IE1 and VP28 genes coupled with a reduction in WSSV copies in shrimp hemocytes. Moreover, depletion of LvWRP followed by WSSV challenge significantly increased the transcript levels of Vago4 and Vago5 as well as increased the phosphorylation of STAT, while hemocytes apoptosis in terms of caspase 3/7 activity was decreased. These results suggest that LvWRP is important for WSSV replication in shrimp, and therefore one of the vital host factors in WSSV infection.