Transfection of crayfish hematopoietic tissue cells

Transfection is a powerful tool useful for studying gene function. Establishing transfection methods that enable highly efficient DNA uptake has become increasingly important. The crayfish hematopoietic tissue (Hpt) cell cultures have been proven to be suitable for studies on immunity and cell differentiation in crustaceans including shrimps, but no efficient gene transfer and expression method is available for these cells. Here we report a novel and highly efficient DNA transfection system based on electroporation. This method depends on a recombinant plasmid with the promoter from white spot syndrome virus immediate-early gene wsv249. This plasmid could be introduced into primary cells and efficiently express foreign genes by electroporation. By optimizing different electroporation parameters, more than 30% transfection efficiency could be achieved with the relative viability of cells around 50%. This is the first report of gene introduction to crayfish Hpt cells and will be useful for the expanding our research on crustacean immunity.

Characterization of the promoter of white spot syndrome virus immediate-early gene wsv249

White spot syndrome virus immediate early (IE) gene wsv249 encodes an E3 ubiquitin ligase that can interact with a shrimp ubiquitin-conjugating enzyme to mediate ubiquitination. In this study, to understand the transcriptional regulation of wsv249, a serial of 5'-truncated mutations were made on its promoter and the activities of mutated promoters was analyzed. Four 25 bp regions potentially containing either positive or negative regulatory elements were identified. Notably, the deletion of -275/-250, which abolished a cAMP-response element (CRE), greatly reduced the promoter activity by 84.2%. CRE serves as the binding site for proteins belong to the cAMP responsive element-binding proteins (CREBs) family and the activator protein 1 (AP-1) family. Electrophoretic mobility shift assay (EMSA) showed that Lvc-Jun could directly bind to the CRE element in the promoter region of wsv249. In addition, the regulation of shrimp homolog of c-Jun and CREB on wsv249 promoter was further investigated. We found that Lvc-Jun greatly upregulated the activity of wsv249 promoter by ∼12.4 fold, and the CRE at -212/-205 but not the one at -256/-249 was essential for the regulation. In contrast, LvCREB-3 could not activate wsv249 promoter activity. These findings extend our knowledge of the transcriptional regulation of WSSV IE genes.

The promoter of the white spot syndrome virus immediate-early gene WSSV108 is activated by the cellular KLF transcription factor

A series of deletion and mutation assays of the white spot syndrome virus (WSSV) immediate-early gene WSSV108 promoter showed that a Krüppel-like factor (KLF) binding site located from -504 to -495 (relative to the transcription start site) is important for the overall level of WSSV108 promoter activity. Electrophoretic mobility shift assays further showed that overexpressed recombinant Penaeus monodon KLF (rPmKLF) formed a specific protein-DNA complex with the (32)P-labeled KLF binding site of the WSSV108 promoter, and that higher levels of Litopenaeus vannamei KLF (LvKLF) were expressed in WSSV-infected shrimp. A transactivation assay indicated that the WSSV108 promoter was strongly activated by rPmKLF in a dose-dependent manner. Lastly, we found that specific silencing of LvKLF expression in vivo by dsRNA injection dramatically reduced both WSSV108 expression and WSSV replication. We conclude that shrimp KLF is important for WSSV genome replication and gene expression, and that it binds to the WSSV108 promoter to enhance the expression of this immediate-early gene.