Effects of acclimation salinity on the expression of selenoproteins in the tilapia, Oreochromis mossambicus

Characterization and tissue expression of twelve selenoproteins in yellow catfish Pelteobagrus fulvidraco fed diets varying in oxidized fish oil and selenium levels

BACKGROUND

Selenium (Se) functions through selenoproteins and is essential to growth and metabolism of vertebrates. The present study was conducted to identify twelve selenoproteins genes (selenoe, selenof, selenoh, selneoi, selenom, selenok, selneon, selenoo, selenot, selenos, selenou and msrb1) from yellow catfish. Their mRNA expression patterns, as well as their response to dietary oxidized fish oils and Se addition were explored.

METHODS

We use 3'and 5' RACE PCR to clone full-length cDNA sequence of twelve selenoprotein genes from yellow catfish. Their mRNA expression patterns were assessed via quantitative real-time PCR. Yellow catfish were fed diet adequate Se+ fresh fish oil, adequate Se+ oxidized fish oil, high Se+ fresh fish oil and high Se+ oxidized fish oil, respectively, for 10 weeks. Their kidney, heart, brain and testis were used to assess the mRNA expression of twelve selenoprotein.

RESULTS

Twelve selenoprotein genes had similar domains with mammals and the other fish. Their mRNAs were expressed widely in eleven tissues but varied with the tissues. Dietary oxidized fish oils and Se addition influenced their mRNA abundances of twelve selenoproteins in a tissue-dependent manner.

CONCLUSION

Our study demonstrated the characterization and expression of twelve selenoproteins, and elucidated their responses in yellow catfish fed diets varying in oxidized fish oils and Se addition, which increased our knowledge into the biological function and regulatory mechanism of Se and selenoproteins in fish.

Selenium Deficiency Leads to Changes in Renal Fibrosis Marker Proteins and Wnt/β-Catenin Signaling Pathway Components

Renal fibrosis is the final result of the progression of chronic kidney disease (CKD) to end-stage renal disease (ESRD). Earlier studies confirmed that selenium (Se) displays a close association with kidney diseases. However, the correlation between Se and fibrosis has rarely been explored. Thus, this article mainly aimed to investigate the effect of Se deficiency on renal fibrosis and the Wnt/β-catenin signaling pathway. Twenty BALB/c mice were fed a diet containing 0.02-mg/kg Se (Se-deficient diet) or 0.18-mg/kg Se (standard diet) for 20 weeks. A human glomerular mesangial cell (HMC) cell line was transfected with lentiviral TRNAU1AP-shRNA vector to establish a stable Se deficiency model in vitro. As indicated in this study, the glutathione (GSH) content in the Se-deficient group displayed an obvious decline compared with that in the control group, whereas the content of malondialdehyde (MDA) was obviously elevated. The results of Masson staining showed fibrosis around the renal tubules, and the results of immunohistochemistry showed that the area of positive fibronectin expression increased. In the Se-deficient group, the levels of collagen I, collagen III, matrix metalloproteinase 9 (MMP9), and other fibrosis-related proteins changed significantly in vivo and in vitro. Compared with the control group, the TRNAU1AP-shRNA group showed markedly reduced cell proliferation and migration abilities. Our data indicate that Se deficiency can cause kidney damage and renal fibrosis. Furthermore, the Wnt pathway is critical for the development of tissue and organ fibrosis. The data of this study demonstrated that the expression of Wnt5a, β-catenin, and dishevelled 1 (Dvl-1) was significantly upregulated in the Se-deficient group. Therefore, the Wnt/β-catenin pathway may play an important role in renal fibrosis caused by Se deficiency.

Molecular characterization and tissue distribution of nine selenoprotein genes in grass carp Ctenopharyngodon idella and their mRNA expressions in response to high-fat diet and high-fat diet supplemented with selenium

Our previous study has found that selenium (Se) can alleviate lipid accumulation caused by high-fat diet (HFD) in fish. This study aims to explore the selenoproteins (SePs) in grass carp Ctenopharyngodon idella by characterizing cDNAs of nine SeP genes (SELENOF, SELENOM, SELENOS, SELENOP1, SELENOP2, SELENOE, SELENOL, SELENOU1a and SELENOU1b) and measuring their transcriptional activity in response to HFD and HFD supplemented with 0.3 mg/Kg and 0.6 mg/Kg of Se (HSe 0.3 and HSe 0.6). Firstly, the nine SeP genes in grass carp encoded proteins with conserved functional protein regions in fish and other vertebrates. Secondly, the nine SeP genes except SELENOS showed high expression levels in the hepatopancreas, but in the adipose tissue, only SELENOS, SELENOE and SELENOU1b showed high expression levels. Further, HFD significantly up-regulated the expressions of SELENOF and SELENOS in the hepatopancreas and SELENOM in the adipose tissue of grass carp (P < 0.05), but significantly down-regulated the expressions of SELENOU1b in the hepatopancreas, SELENOP2, SELENOE, SELENOL and SELENOU1a in the adipose tissue and SELENOM in the muscle of grass carp (P < 0.05). In addition, for the hepatopancreas, the expressions of SELENOS in the HSe 0.3 group and SELENOF, SELENOM and SELENOP2 in the HSe 0.6 group significantly decreased compared with the HFD group (P < 0.05). For the adipose tissue, the expressions of SELENOF, SELENOP2, SELENOL, SELENOU1a and SELENOU1b in the HSe 0.3 group and SELENOP2, SELENOE, SELENOU1a and SELENOU1b in the HSe 0.6 group significantly increased compared with the HFD group (P < 0.05). In summary, the transcriptional activities of the nine SeP genes were regulated by the HFD and HFD supplemented with Se, indicating the potential role of these genes in the Se regulated lipid metabolism processes in grass carp, which is worthy of in-depth study.

Regulation of thyroid hormones and branchial iodothyronine deiodinases during freshwater acclimation in tilapia

Euryhaline fishes are capable of maintaining osmotic homeostasis in a wide range of environmental salinities. Several pleiotropic hormones, including prolactin, growth hormone, and thyroid hormones (THs) are mediators of salinity acclimation. It is unclear, however, the extent to which THs and the pituitary-thyroid axis promote the adaptive responses of key osmoregulatory organs to freshwater (FW) environments. In the current study, we characterized circulating thyroxine (T4) and 3-3'-5-triiodothyronine (T3) levels in parallel with the outer ring deiodination (ORD) activities of deiodinases (dios) and mRNA expression of dio1, dio2, and dio3 in gill during the acclimation of Mozambique tilapia (Oreochromis mossambicus) to FW. Tilapia transferred from seawater (SW) to FW exhibited reduced plasma T4 and T3 levels at 6 h. These reductions coincided with an increase in branchial dio2-like activity and decreased branchial dio1 gene expression. To assess whether dios respond to osmotic conditions and/or systemic signals, gill filaments were exposed to osmolalities ranging from 280 to 450 mOsm/kg in an in vitro incubation system. Gene expression of branchial dio1, dio2, and dio3 was not directly affected by extracellular osmotic conditions. Lastly, we observed that dio1 and dio2 expression was stimulated by thyroid-stimulating hormone in hypophysectomized tilapia, suggesting that branchial TH metabolism is regulated by systemic signals. Our collective findings suggest that THs are involved in the FW acclimation of Mozambique tilapia through their interactions with branchial deiodinases that modulate their activities in a key osmoregulatory organ.

Supplementation of nano-selenium in fish diet: Impact on selenium assimilation and immune-regulated selenoproteome expression in monosex Nile tilapia (Oreochromis niloticus)

Selenium (Se), a fundamental element of nutrigenomic science in fish nutrition, was used to investigate its impact on selenoproteome expression and Se regulation in tilapia. Different concentrations (T₁ - 0, T₂ - 0.5, T₃ - 1.0 and T₄ - 2.0 mg/kg of feed) of dietary nano-Se were incorporated in the diets of monosex Nile tilapia. A total of 180 tilapia fingerlings with initial weight (15.73 ± 0.05 g) were stocked in 150 L capacity FRP tanks categorized into four diet groups with triplicate each for a feeding trial of 90 days. At the end of first, second and third months of the feeding trial, gill, liver, kidney and muscle tissues were harvested to evaluate the effect on the kinetics of Se bioaccumulation and assimilation as well as immune-regulated selenoprotein transcripts (GPx2, SelJ, SelL, SelK, SelS, SelW and Sepp1a) and their synthesis factors (SPS1 and Scly). The findings depicted that significantly (p < 0.05) higher weight gain was found in the diet supplemented with 1.0 mg/kg of nano-Se. The theory of second-order polynomial regression supported the same. The liver showed significantly (p < 0.05) higher Se accumulation and concentration factor among the harvested tissues in a different timeline. All the selected immune-regulated selenoproteins and synthesis factors in different fish tissues showed significantly (p < 0.05) up-regulation in the diet supplemented with 1.0 mg/kg of nano-Se for the second month. Therefore, the present findings suggested that the supplementation of nano-Se could be more effective for improved growth, better selenium regulation and expression of immune-regulated selenoproteins in the fish model.

Characterization and expression analysis of seven selenoprotein genes in yellow catfish Pelteobagrus fulvidraco to dietary selenium levels

BACKGROUND

Selenium (Se) appears in the selenoproteins in the form of selenocysteine (Sec) and is important for the growth and development of vertebrates. The present study characterized seven selenoproteins, consisting of the GPX1, GPX3, GPX4, SELENOW, SELENOP, TXNRD2 and TXNRD3 cDNAs in various tissues of yellow catfish, explored their regulation to dietary Se addition.

METHODS

3' and 5' RACE PCR were used to clone full-length cDNA sequences of seven selenoprotein genes (GPX1, GPX3, GPX4, SELENOW, SELENOP, TXNRD2 and TXNRD3). Their molecular characterizations were analyzed, including conservative motifs and the SECIS elements. The phylogenetic trees were generated through neighbor-joining (NJ) method with MEGA 6.0 with 1000 bootstrap replications. Quantitative real-time PCR was used to explore their mRNA tissue distribution in the heart, anterior intestine, dorsal muscle, head kidney, gill, liver, brain, spleen and mesenteric fat. Yellow catfish (mixed sex) were fed diets with dietary Se contents at 0.03 (low Se), 0.25 (adequate Se) and 6.39 (high Se) mg Se/kg, respectively, for 12 weeks, and their spleen, kidney, testis and brain were used for the determination of the mRNA levels of the seven selenoproteins.

RESULTS

The seven selenoproteins had similar domains to their corresponding members of other vertebrates. They were widely expressed in nine tissues, including heart, liver, brain, spleen, head kidney, dorsal muscle, mesenteric fat, anterior intestine and gill, but showed tissue-dependent expression patterns. Dietary Se addition affected the expression of the seven genes in spleen, kidney, testis and brain tissues of yellow catfish.

CONCLUSION

Taken together, our study demonstrated the characterization, expression and regulation of seven selenoproteins, which increased our understanding of the biological functions of Se and selenoproteins in fish.

Transcriptome analysis of the brain provides insights into the regulatory mechanism for Coilia nasus migration

Background

Coilia nasus (C. nasus) is an important anadromous fish species that resides in the Yangtze River of China, and has high ecological and economical value. However, wild resources have suffered from a serious reduction in population, attributed to the over-construction of water conservancy projects, overfishing, and environmental pollution. The Ministry of Agriculture and Rural Affairs of the People’s Republic of China has issued a notice banning the commercial fishing of wild C. nasus in the Yangtze River. Wild C. nasus populations urgently need to recover. A better understanding of C. nasus migration patterns is necessary to maximize the efficiency of conservation efforts. Juvenile C. nasus experience a simultaneous effect of increasing salinity and cold stress during seaward migration, and the brain plays a comprehensive regulatory role during this process. Therefore, to explore the early seaward migration regulation mechanism of juvenile C. nasus, we performed a comparative transcriptome analysis on the brain of juvenile C. nasus under salinity and cold stress simultaneously.

Results

Relevant neurotransmitters, receptors, and regulatory proteins from three categories of regulatory pathway play synergistic regulatory roles during the migration process: neuronal signaling, the sensory system, and environmental adaptation. The significant differential expression of growth-related hormones, thyroid receptors, haptoglobin, and prolactin receptors was similar to the results of relevant research on salmonids and steelhead trout.

Conclusions

This study revealed a regulatory network that the brain of juvenile C. nasus constructs during migration, thereby providing basic knowledge on further studies could build on. This study also revealed key regulatory genes similar to salmonids and steelhead trout, thus, this study will lay a theoretical foundation for further study on migration regulation mechanism of anadromous fish species.

Selenocysteine β-Lyase: Biochemistry, Regulation and Physiological Role of the Selenocysteine Decomposition Enzyme

The enzyme selenocysteine β-lyase (SCLY) was first isolated in 1982 from pig livers, followed by its identification in bacteria. SCLY works as a homodimer, utilizing pyridoxal 5'-phosphate as a cofactor, and catalyzing the specific decomposition of the amino acid selenocysteine into alanine and selenide. The enzyme is thought to deliver its selenide as a substrate for selenophosphate synthetases, which will ultimately be reutilized in selenoprotein synthesis. SCLY subcellular localization is unresolved, as it has been observed both in the cytosol and in the nucleus depending on the technical approach used. The highest SCLY expression and activity in mammals is found in the liver and kidneys. Disruption of the Scly gene in mice led to obesity, hyperinsulinemia, glucose intolerance, and hepatic steatosis, with SCLY being suggested as a participant in the regulation of energy metabolism in a sex-dependent manner. With the physiological role of SCLY still not fully understood, this review attempts to discuss the available literature regarding SCLY in animals and provides avenues for possible future investigation.

Selenophosphate synthetase 1 and its role in redox homeostasis, defense and proliferation

Selenophosphate synthetase (SEPHS) synthesizes selenophosphate, the active selenium donor, using ATP and selenide as substrates. SEPHS was initially identified and isolated from bacteria and has been characterized in many eukaryotes and archaea. Two SEPHS paralogues, SEPHS1 and SEPHS2, occur in various eukaryotes, while prokaryotes and archaea have only one form of SEPHS. Between the two isoforms in eukaryotes, only SEPHS2 shows catalytic activity during selenophosphate synthesis. Although SEPHS1 does not contain any significant selenophosphate synthesis activity, it has been reported to play an essential role in regulating cellular physiology. Prokaryotic SEPHS contains a cysteine or selenocysteine (Sec) at the catalytic domain. However, in eukaryotes, SEPHS1 contains other amino acids such as Thr, Arg, Gly, or Leu at the catalytic domain, and SEPHS2 contains only a Sec. Sequence comparisons, crystal structure analyses, and ATP hydrolysis assays suggest that selenophosphate synthesis occurs in two steps. In the first step, ATP is hydrolyzed to produce ADP and gamma-phosphate. In the second step, ADP is further hydrolyzed and selenophosphate is produced using gamma-phosphate and selenide. Both SEPHS1 and SEPHS2 have ATP hydrolyzing activities, but Cys or Sec is required in the catalytic domain for the second step of reaction. The gene encoding SEPHS1 is divided by introns, and five different splice variants are produced by alternative splicing in humans. SEPHS1 mRNA is abundant in rapidly proliferating cells such as embryonic and cancer cells and its expression is induced by various stresses including oxidative stress and salinity stress. The disruption of the SEPHS1 gene in mice or Drosophila leads to the inhibition of cell proliferation, embryonic lethality, and morphological changes in the embryos. Targeted removal of SEPHS1 mRNA in insect, mouse, and human cells also leads to common phenotypic changes similar to those observed by in vivo gene knockout: the inhibition of cell growth/proliferation, the accumulation of hydrogen peroxide in mammals and an unidentified reactive oxygen species (ROS) in Drosophila, and the activation of a defense system. Hydrogen peroxide accumulation in SEPHS1-deficient cells is mainly caused by the down-regulation of genes involved in ROS scavenging, and leads to the inhibition of cell proliferation and survival. However, the mechanisms underlying SEPHS1 regulation of redox homeostasis are still not understood.