The MEF2 homolog of Penaeus vannamei is essential for maintaining the WSSV latent infection.

White spot syndrome virus (WSSV) is a lethal shrimp pathogen that has a latent infection cycle. The latent virus can easily turn into an acute infection when the culture environment changes, leading to widespread shrimp mortality. However, the mechanism of WSSV latent infection is poorly understood. Bioinformatic analysis revealed that the promoters of WSSV latency-related genes (i.e., wsv151, wsv366, wsv403, and wsv427) contained putative myocyte enhancer factor 2 (MEF2) binding sites. This suggested that the transcription factor MEF2 may be involved in WSSV latent infection. To further investigate this, a MEF2 homolog (PvMEF2) was cloned from Penaeus vannamei and its role in WSSV latent infection was explored. The results showed that knockdown of PvMEF2 led to an increase in the copy number of WSSV, indicating reactivation of WSSV from a latent infection. It was further demonstrated that suppression of PvMEF2 significantly decreased expression of the viral latency-related genes in WSSV-latent shrimp, while overexpression of PvMEF2 in Drosophila S2 cells activated the promoter activity of the viral latency-related gene. Additionally, we demonstrated that silencing of PvMEF2 was able to upregulate the expression of pro-apoptosis genes, thereby promoting cell apoptosis during latent infection. Collectively, the present data suggest that PvMEF2 could promote the expression of virus latency-related genes and enhance cell survival to maintain WSSV latent infection. This finding would contribute to a better understanding of the maintenance mechanism of WSSV latent infection.

The transcription factor CEBP homolog of Penaeus vannamei contributes to WSSV replication.

The cellular transcription factors are known to play important roles in virus infection. The present study cloned and characterized a transcription factor CCAAT/Enhancer-binding protein homolog from the shrimp Penaeus vannamei (designates as PvCEBP), and explored its potential functions in white spot syndrome virus (WSSV) infection. PvCEBP has an open reading frame (ORF) of 864 bp encoding a putative protein of 287 amino acids, which contained a highly C-terminal conserved bZIP domain. Phylogenetic tree analysis showed that PvCEBP was evolutionarily clustered with invertebrate CEBPs and closely related to the CEBP of Homarus americanus. Quantitative real-time PCR (qPCR) analysis revealed that PvCEBP was expressed in all examined shrimp tissues, with transcript levels increased in shrimp hemocytes and gill upon WSSV challenge. Furthermore, knockdown of PvCEBP mediated by RNA interference significantly decreased the expression of WSSV genes and viral loads, while enhanced the shrimp survival rate under WSSV challenge. In silico prediction and reporter gene assays demonstrated that PvCEBP could activate the promoter activity of the viral immediate-early gene ie1. Collectively, our findings suggest that PvCEBP is annexed by WSSV to promote its propagation by enhancing the expression of viral immediate-early genes.

Physicochemical properties and potential beneficial effects of porphyran from Porphyra haitanensis on intestinal epithelial cells.

This study examined the beneficial effects of porphyran from Porphyra haitanensis (PHP) on intestinal epithelial cells, in terms of cell proliferation and migration and elucidated the potential molecular mechanism of action of PHP. Purified PHP is a homogenous polysaccharide with a molecular weight of 2.01 × 105 Da, intrinsic viscosity [η] of 463.76 mL/g, and radius of gyration of 61.2 nm. When the intestinal epithelial wound healing activity of PHP was investigated in vitro using the IEC-6 cell line (intestinal epithelial cells-6), it was found that PHP could promote cell migration and proliferation. PHP enhanced the protein expression of cell division control protein 42, paxillin, and focal adhesion kinase, which suggest that PHP might modulate the expression of these proteins to improve intestinal epithelial healing. Thus, this study indicated that PHP could serve as a potential source of functional food constituents for intestinal epithelial protection and restoration.