cDNA cloning and expression analysis of glutaredoxin (Grx) 2 in the Pacific white shrimp Litopenaeus vannamei

Glutaredoxin 2 in the mud crab Scylla paramamosain: Identification and functional characterization under hypoxia and pathogen challenge

Glutaredoxin (Grx) is a glutathione-dependent oxidoreductase that plays a key role in antioxidant defense. In this study, a novel Grx2 gene (SpGrx2) was identified from the mud crab Scylla paramamosain, which consists of a 196 bp 5' untranslated region, a 357 bp open reading frame, and a 964 bp 3' untranslated region. The putative SpGrx2 protein has a typical single Grx domain with the active center sequence C-P-Y-C. The expression analysis revealed that the SpGrx2 mRNA was most abundant in the gill, followed by the stomach and hemocytes. Both mud crab dicistrovirus-1 and Vibrioparahaemolyticus infection as well as hypoxia could differentially induce the expression of SpGrx2. Furthermore, silencing SpGrx2 in vivo affected the expression of a series of antioxidant-related genes after hypoxia treatment. Additionally, SpGrx2 overexpression significantly increased the total antioxidant capacity of Drosophila Schneider 2 cells after hypoxia, resulting in a reduction of reactive oxygen species and malondialdehyde content. The subcellular localization results indicated that SpGrx2 was localized in both the cytoplasm and the nucleus of Drosophila Schneider 2 cells. These results indicate that SpGrx2 plays a crucial role as an antioxidant enzyme in the defense system of mud crabs against hypoxia and pathogen challenge.

Identification and functional characterization of glutaredoxin 5 from the mud crab (Scylla paramamosain) in response to cadmium and bacterial challenge

Glutaredoxin (Grx) is a class molecule oxidoreductase, which plays a key role in maintaining redox homeostasis and regulating cell survival pathways. However, the expression pattern and function of Grx remain unknown in the mud crab (Scylla paramamosain). In the present study, a novel full-length of Grx 5 from the mud crab (designated as Sp-Grx 5) was cloned and characterized. The open reading frame of Sp-Grx 5 was 441 bp, which encoded a putative protein of 146 amino acids. The amino acid sequence of Sp-Grx 5 contained a typical C-G-F-S redox active motif and several GSH binding sites. Sp-Grx 5 widely existed in all tested tissues with a high-level expression in hepatopancreas. Subcellular localization showed that Sp-Grx 5 was located in the cytoplasm and nucleus. The expression of Sp-Grx 5 was significantly up-regulated after Vibrio parahaemolyticus infection and cadmium exposure, suggesting that Sp-Grx 5 was involved in innate immunity and detoxification. Furthermore, overexpression of Sp-Grx 5 could improve cells viability after H₂O₂ exposure. All these results indicated that Sp-Grx 5 played important roles in the redox homeostasis and innate immune response in crustaceans.

Expression Analysis of a Novel Oxidoreductase Glutaredoxin 2 in Black Tiger Shrimp, Penaeus monodon

Glutaredoxin (Grx) is a glutathione-dependent oxidoreductase that is an important component of the redox system in organisms. However, there is a serious lack of sequence information and functional validation related to Grx in crustaceans. In this study, a novel Grx was identified in Penaeus monodon (PmGrx2). The full-length cDNA of PmGrx2 is 998 bp, with an open reading frame (ORF) of 441 bp, encoding 119 amino acids. Sequence alignment showed that PmGrx2 had the highest identity with Grx2 of Penaeus vannamei at 96.64% and clustered with Grx2 of other crustaceans. Quantitative real-time PCR (qRT-PCR) analysis showed that PmGrx2 was expressed in all examined tissues, with higher expression levels in the stomach and testis. PmGrx2 was continuously expressed during development and had the highest expression level in the zygote stage. Both ammonia-N stress and bacterial infection could differentially induce the expression of PmGrx2 in hepatopancreas and gills. When PmGrx2 was inhibited, the expression of antioxidant enzymes was suppressed, the degree of apoptosis increased, and the GSH content decreased with the prolongation of ammonia-N stress. Inhibition of PmGrx2 resulted in shrimp being exposed to a greater risk of oxidative damage. In addition, an SNP locus was screened on the exons of PmGrx2 that was significantly associated with an ammonia-N-stress-tolerance trait. This study suggests that PmGrx2 is involved in redox regulation and plays an important role in shrimps’ resistance to marine environmental stresses.

Vital Role of Glutamate Dehydrogenase Gene in Ammonia Detoxification and the Association Between its SNPs and Ammonia Tolerance in Sinonovacula constricta

Increasing evidence has revealed accumulated ammonia will cause adverse effects on the growth, reproduction, and survival of aquatic animals. As a marine benthic mollusk, the razor clam Sinonovacula constricta shows better growth and survival under high ammonia nitrogen environment. However, little is known about its adaptation mechanisms to high ammonia stress in an integrated mariculture system. In this study, we analyzed the association between the polymorphism of glutamate dehydrogenase gene (GDH), a key gene involved in ammonia nitrogen detoxification, and ammonia tolerance. The results showed that 26 and 22 single-nucleotide polymorphisms (SNPs) of GDH in S. constricta (denoted as Sc-GDH) were identified from two geographical populations, respectively. Among them, two SNPs (c.323T > C and c.620C > T) exhibited a significant and strong association with ammonia tolerance, suggesting that Sc-GDH gene could serve as a potential genetic marker for molecular marker–assisted selection to increase survival rate and production of S. constricta. To observe the histological morphology and explore the histocellular localization of Sc-GDH, by paraffin section and hematoxylin–eosin staining, the gills were divided into gill filament (contains columnar and flattened cells) and gill cilia, whereas hepatopancreas was made up of individual hepatocytes. The results of immunohistochemistry indicated that the columnar cells of gill filaments and the endothelial cells of hepatocytes were the major sites for Sc-GDH secretion. Under ammonia stress (180 mg/L), the expression levels of Sc-GDH were extremely significantly downregulated at 24, 48, 72, and 96 h (P < 0.01) after RNA interference. Thus, we can speculate that Sc-GDH gene may play an important role in the defense process against ammonia stress. Overall, these findings laid a foundation for further research on the adaptive mechanisms to ammonia–nitrogen tolerance for S. constricta.

Molecular characterization, redox regulation, and immune responses of monothiol and dithiol glutaredoxins from disk abalone (Haliotis discus discus)

Glutaredoxins (Grxs) are well-known oxidoreductases involved in a wide range of redox activities in organisms. In this study, two invertebrate Grxs (AbGrx1-like and AbGrx2) from disk abalone were identified and characterized in an effort to gain a deeper understanding into their immune and redox regulatory roles. Both AbGrxs share typical thioredoxin/Grx structures. AbGrx1-like and AbGrx2 were identified as monothiol and diothiol Grxs, respectively. AbGrxs were significantly expressed at the egg and 16-cell stage of early abalone development. Although the expression of both AbGrxs demonstrated similar patterns, the expression of AbGrx1-like was higher than AbGrx2 during development stages. In contrast, AbGrx2 expression was significantly higher than that of AbGrx1-like in adult tissues. Highest AbGrx1-like expression was observed in the hepatopancreas and digestive tract, while highest AbGrx2 expression was found in the gills, followed by the mantle, in healthy adult abalone tissues. The highest expression of AbGrx1-like was observed in the gills at 12 h and 6 h post injection (p.i) of Vibrio parahemolyticus and other stimulants, respectively. The highest expression of AbGrx2 in the gills were observed at 120 h, 6 h, 24 h, and 12 h post injection of V. parahaemolyticus, Listeria monocytogenes, Viral hemorrhagic septicemia virus, and Polyinosinic:polycytidylic acid, respectively. AbGrxs possessed significant 2-hydroxyethyl disulfide (HED) and dehydroascorbate (DHA) reduction activity, but AbGrx2 exhibited higher redox activity than AbGrx1-like. Altogether, our results suggest an important role of AbGrx1-like and AbGrx2 in redox homeostasis, as well as in the invertebrate immune defense system. Our findings will aid the development of new disease management strategies for this economically valuable species.

Glutaredoxin 2 from big belly seahorse (Hippocampus abdominalis) and its potential involvement in cellular redox homeostasis and host immune responses

Glutaredoxins are oxidoreductases present in almost all living organisms. They belong to the thioredoxin superfamily and share the thioredoxin structure and catalytic motif. Glutaredoxin 2 has been identified as a mitochondrial protein in vertebrates. In this study, the sequence of Glutaredoxin 2 from Hippocampus abdominalis (HaGrx2) was analyzed by molecular, transcriptional, and functional assays. In-silico analysis revealed that HaGrx2 shows the highest homology with Hippocampus comes, while distinctly cluster with fish Grx2 orthologs. Tissue distribution analysis showed that HaGrx2 is ubiquitously expressed in all tissues tested, and the highest expression was observed in the brain and skin. Significant HaGrx2 transcript modulation was identified in blood and liver upon injecting bacterial and Pathogen Associated Molecular Patterns. The redox activity of HaGrx2 was revealed by Dehydroascorbic reduction and insulin disulfide reduction activity assays. Further, the deglutathionylation activity of 1 nM HaGrx2 was found to be equivalent to that of 0.84 nM HaGrx1. HaGrx2 exhibited antiapoptotic activity against H₂O₂-induced oxidative stress in FHM cells. Altogether, the results of this study suggest that HaGrx2 plays a role in redox homeostasis and innate immune responses in fish.