Cloning and expression of alpha class glutathione S-transferase gene from the small hermaphroditic fish Rivulus marmoratus (Cyprinodontiformes, Rivulidae)

The reference genome of the selfing fish Kryptolebias hermaphroditus: Identification of phases I and II detoxification genes

The selfing fish Kryptolebias hermaphroditus has unique reproductive system for self-fertilization, making genetically homozygous offsprings. Here, we report on high density genetic map-based genome assembly for the K. hermaphroditus Panama line (PanRS). The numbers of scaffolds were 5212 and the genome was 683,992,224 bp (N50 = 27.45 Mb). The length of anchored scaffold onto 24 linkage groups was 652,231,070 bp (95.3% of genome) with 0.01% of the gap and 39.33% of GC content and complete Benchmarking Universal Single-Copy Orthologs value was 96.6%. The numbers of annotated genes were 36,756 (average gene length 1368 bp) with the GC content of 54.1%. To examine the difference between the two sister species in the genus Kryptolebias, we compared the genomes of K. hermaphroditus PanRS and Kryptolebias marmoratus PAN line on the composition of transposable elements. To demonstrate applications of genome library, phase I and II detoxification related gene families have been analyzed, and compared the syntenies containing loci of CYP and GST genes on linkage groups. This K. hermaphroditus genome information will be helpful for a better understanding on genome-wide mechanistic view of detoxification and antioxidant-related genes over evolution in the view of fish environmental ecotoxicology.

Protective Role of Freshwater and Marine Rotifer Glutathione S-Transferase Sigma and Omega Isoforms Transformed into Heavy Metal-Exposed Escherichia coli

Glutathione S-transferases (GSTs) play an important role in phase II of detoxification to protect cells in response to oxidative stress generated by exogenous toxicants. Despite their important role in defense, studies on invertebrate GSTs have mainly focused on identification and characterization. Here, we isolated omega and sigma classes of GSTs from the freshwater rotifer Brachionus calyciflorus and the marine rotifer Brachionus koreanus and explored their antioxidant function in response to metal-induced oxidative stress. The recombinant Bc- and Bk-GSTs were successfully transformed and expressed in Escherichia coli. Their antioxidant potential was characterized by measuring kinetic properties and enzymatic activity in response to pH, temperature, and chemical inhibitor. In addition, a disk diffusion assay, reactive oxygen species assay, and morphological analysis revealed that GST transformed into E. coli significantly protected cells from oxidative stress induced by H₂O₂ and metals (Hg, Cd, Cu, and Zn). Stronger antioxidant activity was exhibited by GST-S compared to GST-O in both rotifers, suggesting that GST-S plays a prominent function as an antioxidant defense mechanism in Brachionus spp. Overall, our study clearly shows the antioxidant role of Bk- and Bc-GSTs in E. coli and provides a greater understanding of GST class-specific and interspecific detoxification in rotifer Brachionus spp.

Effects of sub-chronic exposure to lead (Pb) and ascorbic acid in juvenile rockfish: Antioxidant responses, MT gene expression, and neurotransmitters

Juvenile rockfish Sebastes schlegelii were exposed to varying levels of dietary lead (Pb²⁺) at 0, 120 and 240 mg/L, and ascorbic acid (AsA) at 100, 200 and 400 mg/L for four weeks. Antioxidant responses such as superoxide dismutase (SOD), glutathione S-transferase (GST), and glutathione (GSH) were analyzed to assess oxidative stress. SOD and GST activity in the liver and gills were considerably elevated by dietary Pb. In contrast, GSH levels in the liver and gills were significantly reduced following Pb exposure. High levels of AsA supplementation attenuated the increase in SOD and GST activity and reduction in GSH levels. The metallothionein gene (MT) in the liver was notably stimulated by Pb exposure, and AsA supplementation attenuated this increase. With respect to neurotoxicity, acetylcholinesterase (AChE) activity was substantially inhibited in the brain and muscle following Pb exposure. AsA supplementation also attenuated AChE inhibition following Pb exposure. The results of this study presented Pb exposure affected rockfish as toxicity, and AsA was effective to alleviate toxic effects of Pb.

Cloning of circadian rhythmic pathway genes and perturbation of oscillation patterns in endocrine disrupting chemicals (EDCs)-exposed mangrove killifish Kryptolebias marmoratus

To investigate the effect of endocrine disrupting chemicals (EDCs) on the circadian rhythm pathway, we cloned clock and circadian rhythmic pathway-associated genes (e.g. Per2, Cry1, Cry2, and BMAL1) in the self-fertilizing mangrove killifish Kryptolebias marmoratus. The promoter region of Km-clock had 1 aryl hydrocarbon receptor element (AhRE, GTGCGTGACA) and 8 estrogen receptor (ER) half-sites, indicating that the AhRE and ER half sites would likely be associated with regulation of clock protein activity during EDCs-induced cellular stress. The Km-clock protein domains (bHLH, PAS1, PAS2) were highly conserved in five additional fish species (zebrafish, Japanese medaka, Southern platyfish, Nile tilapia, and spotted green pufferfish), suggesting that the fish clock protein may play an important role in controlling endogenous circadian rhythms. The promoter regions of Km-BMAL1, -Cry1, -Cry2, and -Per2 were found to contain several xenobiotic response elements (XREs), indicating that EDCs may be able to alter the expression of these genes. To analyze the endogenous circadian rhythm in K. marmoratus, we measured expression of Km-clock and other circadian rhythmic genes (e.g. Per2, Cry1, Cry2, and BMAL1) in different tissues, and found ubiquitous expression, although there were different patterns of transcript amplification during different developmental stages. In an estrogen (E2)-exposed group, Km-clock expression was down-regulated, however, a hydroxytamoxifen (TMX, nonsteroid estrogen antagonist)-exposed group showed an upregulated pattern of Km-clock expression, suggesting that the expression of Km-clock is closely associated with exposure to EDCs. In response to the exposure of bisphenol A (BPA) and 4-tert-octyphenol (OP), Km-clock expression was down-regulated in the pituitary/brain, muscle, and skin in both gender types (hermaphrodite and secondary male). In juvenile K. marmoratus liver tissue, expression of Km-clock and other circadian rhythmic pathway-associated genes showed a regular oscillation pattern over a period of approximately 24h during a 12L:12D cycle. However, the circadian rhythm of BPA-exposed juvenile K. marmoratus liver tissue was perturbed over a 12L:12D period. This study will aid in our understanding of how EDCs perturb endogenous circadian rhythms, particularly in BPA-exposed fish liver tissue.

Cloning, expression and identification of two glutathione S-transferase isoenzymes from Perna viridis

Glutathione S-transferases (GSTs; EC 2.5.1.18) are phase II enzymes involved in major detoxification reactions of xenobiotic in many organisms. In the present study, two classes of GSTs (PvGST1 and PvGST2) were cloned from P. viridis by rapid amplification of cDNA ends method. Sequence alignments and phylogenetic analysis together supported that PvGST1 and PvGST2 belonged to the pi and omega classes, respectively. The PvGST1 cDNA was 1214 nucleotides (nt) in length and contained a 618 nt open reading frame (ORF) encoding 206 amino acid residues, and had 46 nt of 5'-untranslated region (UTR) and a 3' UTR of 550 nt including a tailing signal (AATAAA) and a poly (A) tail. The molecular mass of the predicted PvGST1 was 23.815kDa, with the calculated isoelectric point being 5.39. PvGST2 was 1093bp, consisting of a 5' UTR of 13bp, a 3' UTR of 246bp and an ORF of 834bp. The deduced protein was composed of 278 amino acids, with an estimated molecular mass of 32.476kDa and isoelectric point of 8.88. Tissue distribution analysis of the PvGST1 and PvGST2 mRNA revealed that the GST expression level was higher in digestive gland and gonad, while lower in gill and mantle in both genders. Molecular modeling analysis of two GSTs implicated their various functions account for their different enzymatic features.

Expression profiles of seven glutathione S-transferase (GST) genes from Venerupis philippinarum exposed to heavy metals and benzo[a]pyrene

Glutathione S-transferases (GSTs) are phase II enzymes that facilitate the detoxification of xenobiotics, and also play important roles in antioxidant defense. In this study, we reported the cloning and molecular characteristics of seven genes of the GST family (VpGSTS1, VpGSTS2, VpGSTS3, VpGSTO, VpGSTMi, VpGSTM and VpGSTR) from Venerupis philippinarum together with mRNA tissue distribution patterns and temporal expression profiles in response to cadmium, copper and benzo[a]pyrene (B[a]P) exposures. The deduced amino acid sequences of VpGSTs showed high similarities to counterparts of other species that clustered into the same clades in the phylogenetic analysis. At basal levels of tissue expression, most VpGSTs were highly expressed in hepatopancreas compared with other tissues. All VpGSTs showed differential response profiles depending on the concentrations of various toxicants and exposure times. More notably, the expressions of VpGSTS2 and VpGSTS3 transcripts were significantly up-regulated in hepatopancreas from Cu and B[a]P-exposed animals, indicating that these two sigma VpGSTs were highly sensitive to Cu and B[a]P exposure. However, the expressions of VpGSTM and VpGSTR were significantly induced by Cu or B[a]P exposure, respectively. These findings suggested the role of VpGSTS2, VpGSTS3, VpGSTM and VpGSTR in defense against oxidative stress and highlighted their potential as biomarkers to Cu or B[a]P exposure.

Gene expression analysis of ABC efflux transporters, CYP1A and GSTα in Nile tilapia after exposure to benzo(a)pyrene

The aim of this study was to evaluate the response of ABC transporters, CYP1A and class alpha (α) GST genes, upon water and dietary exposures to benzo(a)pyrene (BaP) in Oreochromis niloticus. Partial mRNA sequences of ABC transporters (ABCB1b, ABCB11, ABCC1, ABCC2 and ABCG2) were identified, and their tissue distribution patterns evaluated in liver, gill and intestine, showing similarities with other fish and mammals. After 14 days of water exposure to BaP, ABC transporters mRNA expression was up-regulated, namely ABCC2 in gill (up to 16-fold) and ABCG2 in liver (up to 2-fold) and proximal intestine (up to 7-fold). CYP1A mRNA expression was up-regulated in water exposed animals, with maximum fold inductions of 5, 35 and 155, respectively in liver, gill and proximal intestine. After dietary exposure, intestinal CYP1A mRNA showed a 13-fold increase in exposed animals. No significant changes were seen in ABCB1b, ABCC1 and GSTα mRNA expression after both routes of exposure to BaP. In conclusion, this study has shown that transcriptional expression of some ABC transporters and CYP1A respond to the presence of BaP, indicating a possible involvement and cooperation in the detoxification process in Nile tilapia.

Expression of catalase and glutathione S-transferase genes in Chironomus riparius on exposure to cadmium and nonylphenol

Antioxidant enzymes play important roles in the protection against oxidative damage caused by environmental pollutants by scavenging high levels of reactive oxygen species and have been quantified as oxidative stress markers. However, combining mRNA expressions of genes coding for detoxification enzymes along with enzyme activities will be more useful biomarkers of stress. Therefore, in this study the cDNA of the catalase gene from the aquatic midge, Chironomus riparius (CrCAT) was sequenced using 454 pyrosequencing. The 2139 bp CrCAT cDNA included an open reading frame of 1503 bp encoding a putative protein of 500 amino acids with a predicted molecular mass of 56.72 kDa. There was an 18 bp 5' and a long 618 bp 3' untranslated region with a polyadenylation signal site (AATAAA). The deduced amino acid sequence of CrCAT contained several highly conserved motifs including the proximal heme-ligand signature sequence RLFSYNDTX and the proximal active site signature FXRERIPERVVHAKGXGA. A comparative analysis showed the presence of conserved amino acid residues and all of the catalytic amino acids (His(70), Asn(143), and Tyr(353)) were conserved in all species. The CrCAT contained three potential glycosylation sites and a peroxisome targeting signal of 'AKM'. The mRNA was detected using RT-PCR at all developmental stages. The time-course expression of CrCAT was measured using quantitative real-time PCR after exposure to different concentration and durations of Paraquat (PQ), cadmium chloride (Cd) and nonylphenol (NP). The expression of CrCAT was significantly up regulated on exposure to 50 and 100mg/L PQ for 12 and 24h. Among the different concentrations and durations of Cd tested, significantly highest level of expression for CrCAT mRNA and catalase enzyme activity was observed on exposure to 10mg/L for 24h. In the case of NP, the highest level of CrCAT expression was observed after exposure to 100 μg/L for 24h. The expression profiles of three selected C. riparius glutathione S-transferase genes (CrGSTs) viz. CrGSTdelta3, CrGSTsigma4 and CrGSTepsilon1 was also studied on exposure to NP and were up or down regulated at different time points and concentrations. Significantly highest level of expression for CrGSTdelta3 was observed after 48 h and for CrGSTsigma4 and CrGSTepsilon1 after 24h exposure to 100 μg/L of NP. The results show that CrGSTs and CrCAT could be used as potential biomarkers in C. riparius for aquatic ecotoxicological studies.

Expression profiles of seven glutathione S-transferase (GST) genes in cadmium-exposed river pufferfish (Takifugu obscurus)

Glutathione S-transferase (GST; EC 2.5.1.18) plays a critical role in detoxification pathways. In this study, we report cloning and expression of seven genes of the GST family of the pufferfish Takifugu obscurus together with mRNA tissue distribution pattern and time-course of expression in response to exposure to cadmium. At basal levels of tissue expression, GST-Mu is highly expressed in liver compared with other tissues. When fish were exposed to cadmium (5 mg/L for 96 h), expression of GST-MAPEG, GST-Mu, GST-Omega, and GST-Zeta was greatly increased, whereas GST-Alpha and GST-Kappa genes showed no significant response. These findings suggest that gene expression of a number of GST isoforms in T. obscurus is modulated in response to exposure to cadmium. We propose GST-Mu, GST-Theta, and GST-Zeta as candidate biomarkers for heavy metal exposure in this fish.

Gene cloning of a sigma class glutathione S-transferase from abalone (Haliotis diversicolor) and expression analysis upon bacterial challenge

Glutathione S-transferases (GSTs) are a multigene family of xenobiotic metabolizing phase II detoxification enzymes which take part in many pathological and physiological processes, and which can potentially be used as indicators and biomarkers for cancer diagnoses and organic or inorganic pollutant exposure. In this study, a full-length cDNA of a sigma class GST (abGSTsigma) (GenBank accession number EF546619) from variously colored abalone (Haliotis diversicolor) was identified. It was 1328bp containing an open reading frame of 624bp, encoding 208 amino acid residues with a predicted protein molecular weight of 23.67kDa and an estimated pI of 5.67. Sequence analysis showed that the predicted protein sequence of abGSTsigma cDNA contained the conserved domain of the GST_N_Sigma_like (PSSM: cd03039) and GST_C_Sigma_like (PSSM: cd03192). Alignment analysis demonstrated that the abGSTsigma of H. diversicolor was in a branch position with other known class sigma GSTs from different organisms. The abGSTsigma mRNA was distributed in multiple tissues tested and was highly demonstrated in the gill and mantle of normal abalones. In bacteria-challenged abalone, the abGSTsigma gene was significantly expressed in the hemocytes, gill, mantle and digestive gland and the total GSTs enzyme and SOD were also induced in the four tissues. The increased activities of SOD and GSTs can result in the elimination of reactive oxygen species (ROS) indicating antioxidant activities involved. The preliminary work revealed that the sigma class glutathione S-transferase gene abGSTsigma, a phase II detoxification enzyme, had a positive response to bacterial challenge, and that will lead to an insightful study on elucidating the interactions between immune responses and biotransformation exerted by abGSTsigma.

Differential expression of metallothionein (MT) gene by trace metals and endocrine-disrupting chemicals in the hermaphroditic mangrove killifish, Kryptolebias marmoratus

Metallothionein (MT) gene expression was studied in different tissues, development stages and gender types of the mangrove killifish (Kryptolebias marmoratus). MT expression was also studied in a time-series experiment after exposure to trace metals and endocrine-disrupting chemicals (EDCs). The brain showed the highest level of MT transcripts. Although all the development stage showed some level of MT expression, the adult hermaphrodites showed the highest expression which was significantly higher than the secondary males. In the trace metal-exposed fish, cadmium caused the strongest induction of MT. However, other trace metals such as copper and zinc also caused MT gene induction. All the EDCs suppressed the expression of MT gene, and the effect of EDCs were not gender-specific. K. marmoratus has previously shown its suitability as a model species for toxicity studies and cancer research. This study demonstrated utility of MT as biomarker in K. marmoratus. However, confounding factors such as age, gender, and tissue types appear to influence the MT expression. Response of trace and organic pollutants such as EDCs also varied greatly. These observations suggest that MT would be a specific biomarker of trace metal exposure in K. marmoratus and expression would be influenced by intrinsic factors.

The effect of cyanobacterial crude extract on the transcription of GST mu, GST kappa and GST rho in different organs of goldfish (Carassius auratus)

The glutathione S-transferases play important roles in the detoxification of microcystin. Core-sequences of three classes of GST (mu, kappa and rho) were cloned from goldfish (Carassius auratus L.) i.p. injected with cyanobacterial crude extract at two doses (50 and 200 microg MC-LReq kg(-1)BW). The relative changes of the mRNA abundance in liver, kidney and intestine were analyzed by real-time PCR. The transcription of GST mu was inhibited in intestine at both doses and the transcription of GST kappa was inhibited from 12 to 48h in kidney at both doses. The decreased transcription of GST rho was detected in all three organs at the high dose. It is suggested that transcription inhibition of GST rho might be significant in MCs toxicity at higher toxin concentration in omnivorous freshwater fish. Alteration in transcription of GSTs stimulated by MCs implicates an increased health risk to fish.

Gonadotropin-releasing hormone receptor (GnRHR) gene expression is differently modulated in gender types of the hermaphroditic fish Kryptolebias marmoratus by endocrine disrupting chemicals

Gonadotropin-releasing hormone (GnRH) plays a pivotal role in the regulation of reproduction in vertebrates through interaction with a specific receptor. The GnRH-stimulated gonadotropin synthesis and release are regulated by the GnRH receptors (GnRHRs). In this study, we have identified a GnRH receptor (GnRHR) gene from the hermaphroditic fish Kryptolebias marmoratus. K. marmoratus GnRHR showed typical vertebrate GnRHR domains and motifs, and its cDNA contained 1634 bp including an open reading frame (ORF) of 1263 bp encoding a putative protein of 420 amino acids. To analyze expression patterns of GnRHR gene in various tissues and developmental stages of K. marmoratus, we carried out quantitative real-time reverse transcriptase polymerase chain reaction (RT-PCR). The K. marmoratus GnRHR gene expression was detected in all the tissues of adult fish with highest level in brain and gonad. The expression of K. marmoratus GnRHR mRNA increased from stage 1 (2 day post fertilization, dpf) to stage 4 (12 dpf) but steeply decreased at hatching stage (stage 5). Expression of K. marmoratus GnRHR after exposure to endocrine-disrupting chemicals such bisphenol A (BPA, 600 microg/L for 96 h) and 4-tert-octylphenol (OP, 300 microg/L for 96 h) in hermaphrodites as well as secondary males was highly up-regulated in almost all the tissues. Another EDC, 4-nonylphenol (NP, 300 microg/L for 96 h) showed no consistent response. 17beta-estrodiol (E2, 100 ng/L for 96 h), a known natural estrogen, suppressed expression of GnRHR in most of the tissues from hermaphrodites as well as secondary males. Tamoxifen (TMX, 10 microg/L), an estrogen antagonist, on the other hand, caused upregulation of GnRHR expression in the liver of hermaphrodites and the gonad and liver of secondary males. This is the first report of a GnRHR gene from K. marmoratus and modulation of its expression by EDCs. This study provides an insight into the molecular mechanism of endocrinological functions of this unique fish.

p53 gene expression is modulated by endocrine disrupting chemicals in the hermaphroditic fish, Kryptolebias marmoratus

The full-length of cDNA of tumour suppressor gene p53 from the self-fertilizing fish Kryptolebias marmoratus (Km-p53) was determined using molecular cloning and rapid amplification of cDNA ends (RACE). The Complete cDNA sequences of K. marmoratus (Km-p53) gene was 1.8 kb in length. K. marmoratus p53 amino acid sequence showed a high degree of homology with the sequences from fishes, amphibians, and mammals. Although basal level of expression of Km-p53 mRNA was low, all the studied tissues showed some level of expression. After exposure of K. marmoratus to endocrine disrupting chemicals (EDCs) such as bisphenol A, 4-nonylphenol, and 4-tert-octylphenol, Km-p53 expression was significantly increased within 3 h of exposure in juveniles. However, expression was down-regulated by exposure to most of the EDCs when measured at 96 h in adult fish. In adult fish, suppressive effect of EDCs was more pronounced in liver as compared to other tissues. These findings suggest that Km-p53 gene would be involved in cellular defense mechanism in early stage of exposure to EDCs and long-term exposure may suppress its expression. It may be possible that the suppression of p53 by EDCs may predispose the host to environmental chemical carcinogenesis.

Molecular cloning and characterization of omega class glutathione S-transferase (GST-O) from the polychaete Neanthes succinea: biochemical comparison with theta class glutathione S-transferase (GST-T)

We cloned and sequenced a full-length cDNA of an omega class glutathione S-transferase (GST-O) from the polychaete Neanthes succinea (ns-GST-O). The full-length cDNA of ns-GST-O was 1562 bp in length, containing an open reading frame (OR) of 732 bp that encoded a 244 amino acid protein. The deduced amino acid sequence of ns-GST-O showed a low similarity with the theta class N. suucinea GST (ns-GST-T). As GSTs play a significant role in antioxidant defense, we checked the expression pattern of ns-GST-O in N. succinea after exposure to copper (CuCl(2) 12 to 72 mug/L), which is an oxidative stress-inducing agent. After exposure to CuCl(2), ns-GST-O gene was dramatically up-regulated and when compared with ns-GST-T the expression pattern was more pronounced at all the concentrations of copper. Even the basal transcription levels of ns-GST-O were higher than those of ns-GST-T. To further characterize the catalytic properties of ns-GST-O, we constructed a recombinant ns-GST-O plasmid with a 6x His-Tag at the N-terminal of the full-length ns-GST-O cDNA. Recombinant ns-GST-O protein was highly expressed in transformed Escherichia coli. The effect of pH, temperature and chemical inhibitors on the enzyme activity of ns-GST-O was also studied and compared with the reported effect of these factors on recombinant ns-GST-T protein. These results suggest that, like other types of GSTs, ns-GST-O protein plays a conserved antioxidant role in the polychaete N. succinea.

Marine glutathione S-transferases

The aquatic environment is generally affected by the presence of environmental xenobiotic compounds. One of the major xenobiotic detoxifying enzymes is glutathione S-transferase (GST), which belongs to a family of multifunctional enzymes involved in catalyzing nucleophilic attack of the sulfur atom of glutathione (gamma-glutamyl-cysteinylglycine) to an electrophilic group on metabolic products or xenobiotic compounds. Because of the unique nature of the aquatic environment and the possible pollution therein, the biochemical evolution in terms of the nature of GSTs could by uniquely expressed. The full complement of GSTs has not been studied in marine organisms, as very few aquatic GSTs have been fully characterized. The focus of this article is to present an overview of the GST superfamily and their critical role in the survival of organisms in the marine environment, emphasizing the critical roles of GSTs in the detoxification of marine organisms and the unique characteristics of their GSTs compared to those from non-marine organisms.

Molecular cloning, expression, biochemical characteristics, and biomarker potential of theta class glutathione S-transferase (GST-T) from the polychaete Neanthes succinea

We cloned and sequenced the full-length cDNA of a theta class glutathione S-transferase (GST-T) from the polychaete Neanthes succinea. The open reading frame of N. succinea GST-T cDNA was 678bp and encoded 226 amino acid residues. We generated recombinant N. succinea GST-T by expression in transformed Escherichia coli and studied the kinetic properties as well as the effects of inhibitors, pH, and temperature on N. succinea GST-T. GST-T expression was studied using real-time RT-PCR in response to exposure to the model oxidative stress-inducing agent, CuCl(2). Copper induced a concentration-dependant increase in the expression of GST-T. Moreover, polychaetes collected from a heavily contaminated lake near an industrial complex showed significantly higher levels of GST-T expression. Interestingly, the site-collected polychaetes with the highest GST-T mRNA expression levels also showed the highest metallothioneins levels. These results suggest that GST-T in polychaetes may have an antioxidant role and that N. succinea GST-T expression may be a useful biomarker for exposure to environmental contaminants such as copper. Our findings provide a better understanding of the biochemical characteristics of N. succinea GST-T, and elucidate the potential role of GST-T in heavy metal-induced oxidative stress and as a biomarker for environmental contamination.

Molecular cloning and characterization of θ-class glutathione S-transferase (GST-T) from the hermaphroditic fish Rivulus marmoratus and biochemical comparisons with α-class glutathione S-transferase (GST-A)

We cloned and sequenced full-length cDNA of a theta-class-like glutathione S-transferase (GST-T) from liver tissue of the self-fertilizing fish Rivulus marmoratus. The full-length cDNA of rm-GST-T was 907 bp in length containing an open reading frame of 666 bp that encoded a 221-amino acid putative protein. Its derived amino acid sequence was clustered with other vertebrate theta-class GSTs in a phylogenetic tree. The deduced amino acid sequence of theta-like rm-GST (rm-GST-T) was compared with both classes (alpha and theta) of GST and alpha-class rm-GST (rm-GST-A). Tissue-specific expression of two rm-GST mRNAs was investigated using real-time RT-PCR. To further characterize the catalytic properties of this enzyme along with rm-GST-A, we constructed the recombinant theta-like rm-GST plasmid with a 6 x His-Tag at the N-terminal of rm-GST-T cDNA. Recombinant rm-GST-T was highly expressed in transformed Escherichia coli, and its soluble fraction was purified by His-Tag affinity column chromatography. The kinetic properties and effects of pH and temperature on rm-GST-T were further studied, along with enzyme activity and inhibition effects, and compared with recombinant rm-GST-A. These results suggest that recombinant rm-GSTs such as rm-GST-A and rm-GST-T play a conserved functional role in R. marmoratus.

Cloning and characterization of glutathione S-transferase gene in the intertidal copepod Tigriopus japonicus and its expression after exposure to endocrine-disrupting chemicals

To investigate the impacts of marine pollution on aquatic organisms, we tested the intertidal copepod Tigriopus japonicus as a model species. To analyze the copepods' responses to endocrine-disrupting chemicals (EDCs), we exposed them to two different chemicals: 4,4'-octylphenol (4,4'-OP, 12.5-100 microg/L for 2 h) and polychlorinated biphenyl (PCB, 6.25-25 microg/L for two days). 4,4'-OP was toxic, although exposure time was limited to 2h. After extracting total RNA from the exposed T. japonicus, we performed reverse transcriptase-polymerase chain reaction (RT-PCR) to determine gene expression patterns following chemical exposure. To analyze the gene expression of T. japonicus, we used glutathione S-transferase with GAPDH as an internal control. Of the genes tested using EDC-exposed samples, 4,4'-OP induced upregulation of the glutathione S-transferase (GST) gene, while PCB caused downregulation of the GST gene. These results suggest that the two EDCs act in different manners in T. japonicus.

Nonylphenol modulates expression of androgen receptor and estrogen receptor genes differently in gender types of the hermaphroditic fish Rivulus marmoratus

To uncover the effect of estrogenic chemicals [4-nonylphenol (NP) and bisphenol A (BisA)] on the expression of androgen receptor (AR) and estrogen receptors (ERalpha and ERbeta) in the hermaphroditic fish Rivulus marmoratus, we cloned the full length of the cDNAs encoding AR, ERalpha, and ERbeta from gonadal tissue of R. marmoratus and analyzed the modulation of expression of these genes following exposure to estrogenic chemicals using real-time RT-PCR. R. marmoratus AR, ERalpha, and ERbeta genes showed a high similarity to the relevant fish species on amino acid residues, respectively. Rm-ERalpha and Rm-ERbeta cDNAs included a serine-rich region when compared to other teleost fish ER genes. Tissue-specific expression of Rm-AR and Rm-ERbeta mRNAs in adult hermaphrodite R. marmoratus was high in the gonad, while Rm-ERalpha mRNA was high in the liver based on real-time RT-PCR. In addition, Rm-AR and Rm-ERalpha mRNAs increased along with developmental stage from stage 3 (5 dpf) to hatching, while Rm-ERbeta mRNA increased from stage 2 (2 dpf). To uncover the effect of estrogenic chemicals on R. marmoratus, we exposed the fish to NP (300 microg/l) and BisA (600 microg/l) for 96 h. Significant down-regulation of Rm-AR, Rm-ERalpha, and Rm-ERbeta mRNA was observed in gonadal tissue after exposure to NP but not BisA. In the liver, there were gender differences in gene expression after EDC exposure. These results demonstrate that expression patterns of the Rm-AR, Rm-ERalpha, and Rm-ERbeta genes in the hermaphroditic fish, R. marmoratus, vary according to tissue and developmental stage as well as the specificity of environmental estrogenic chemicals. These genes can be useful as molecular biomarkers in assessing the potential impact of estrogenic compounds using this species as a model system.

Endocrine disrupting chemicals (bisphenol A, 4-nonylphenol, 4-tert-octylphenol) modulate expression of two distinct cytochrome P450 aromatase genes differently in gender types of the hermaphroditic fish Rivulus marmoratus

To understand the effect of endocrine-disrupting chemicals (EDCs) on cytochrome P450 aromatase (rm-cyp19) gene expression between gender types in the hermaphroditic fish Rivulus marmoratus, we cloned two distinct rm-cyp19 genes using RT-PCR with degenerative primers, obtained full-length cDNAs using 5'- and 3'-RACE-PCR methods, and completely sequenced them. The brain aromatase (rm-cyp19b) cDNA consisted of 2,124 bp including the open reading frame (ORF), which encoded a putative protein of 505 amino acids. The ovarian aromatase (rm-cyp19a) cDNA consisted of 2,075 bp, including the ORF encoding a putative protein of 516 amino acids. Expression patterns of rm-cyp19b and rm-cyp19a mRNAs were investigated in embryos of different developmental stages and in seven different tissues of adult fish. The rm-cyp19b gene in hermaphrodite and secondary male R. marmoratus was predominantly expressed in the brain, while the rm-cyp19a gene was expressed gender-specifically in the gonad. The expression of rm-cyp19b mRNA increased from stage 1 (2 d post fertilization) to stage 4 (12 d post fertilization) in a developmental stage-dependent manner but steeply decreased in the hatching stage. Compared to the rm-cyp19b gene, the abundance of ovarian aromatase rm-cyp19a transcripts was very low, and its expression was first detected at stage 3 and then decreased gradually to the hatching stage. Alteration of rm-cyp19b and rm-cyp19a gene expression was further analyzed in the brain and gonad by real-time RT-PCR 96 h after EDC exposure in hermaphrodites and secondary males. The brain aromatase rm-cyp19b gene was up-regulated in the brain after 4-nonylphenol (4-NP)-exposure, while the ovarian aromatase rm-cyp19a gene was significantly down-regulated in the gonad. In 300 microg/L 4-tert octylphenol (4-tert-OP), or 600 microg/L bisphenol A-exposed brain and gonad, both rm-cyp19b and rm-cyp19a genes were up-regulated. In the case of secondary males, the rm-cyp19b gene was highly expressed in the 4-NP-exposed brain, while expression of the rm-cyp19a gene was not detected in the gonad. These results indicate that the expression of rm-cyp19a and rm-cyp19b genes is differently modulated according to estrogenic compounds and gender type of R. marmoratus.

cDNA cloning and expression of a cytochrome P450 1A (CYP1A) gene from the hermaphroditic fish Rivulus marmoratus

We previously described the genomic structure of the cytochrome P450 1A (CYP1A) gene from the hermaphroditic fish Rivulus marmoratus [Kim, I.-C., Kim, Y.J., Yoon, Y.-D, Kawamura, S., Lee, Y.-S., Lee, J.-S., 2004a. Cloning of cytochrome P450 1A (CYP1A) genes from the hermaphroditic fish Rivulus marmoratus and the Japanese medaka Oryzias latipes. Mar. Environ. Res. 58, 125-129]. To further characterize R. marmoratus CYP1A, we cloned the cDNA sequence of a CYP1A gene from this species and also expressed its recombinant protein in an E. coli system. We exposed R. marmoratus to 4-nonylphenol, and found a small induction of CYP1A mRNA in the treated animals. In this paper, we discuss the characteristics of R. marmoratus CYP1A gene as well as its potential use in a biomonitoring assay.