Cloning of cytochrome P450 1A (CYP1A) genes from the hermaphrodite fish Rivulus marmoratus and the Japanese medaka Oryzias latipes

Cytochrome P450 1A mRNA in the Gambusia affinis and Response to Several PAHs

Cytochrome P4501A (CYP1A) has been used as a specific biomarker for monitoring water contamination such as PAHs, PCBs and dioxins. In the present study, the cyp1a gene of Gambusia affinis was cloned and sequenced and their expressions under PAHs exposure were characterized. The newly identified cyp1a encodes a protein with 521 amino acids that shared 96-80% identity with other Cyprinodontiformes fishes. RT-PCR analysis revealed that the basal mRNA level of cyp1a was highly expressed in liver and intestine. The expression level of cyp1a was significantly induced by exposure to 100 μg/L 3, 4-Benzopyrene (BaP) for 5 days in the muscle, testis, brain, liver and intestine of adult male fish. Except in the testis, the induced mRNA level of cyp1a ultimately decreased after prolonging the exposure time to 25 days. As for testis, the induced mRNA level of cyp1a was maintained at a high level during the entire exposure time under 100 μg/L BaP exposure. Furthermore, the expression of cyp1a increased with exposure time under a relatively low exposure concentrations 1 μg/L. Regarding the effects of other PAHs, D(a,h)A, BbF, and BaA showed a statistically significant effect of induction on mRNA level of cyp1a in the muscle, testis, brain, liver and intestine.

Gene structure and comparative and phylogenetic analyses of Catla catla CYP1A full-length cDNA and its responsiveness to benzo(a)pyrene and copper sulphate at early developmental stages

In the present study, full-length CYP1A cDNA from Catla catla (Catla) has been identified, and its real-time quantitative reverse transcription PCR (qRT-PCR) expression has been evaluated in different tissues, developmental stages (0, 3, 6, 12 and 24 h and 5, 7 and 9 days post-fertilization) and copper sulphate and benzo(a)pyrene (BaP)-treated 5-day post-fertilization (dpf) larvae (6 to 6.5 mm). Various structural, comparative and phylogenetic analyses of the deduced amino acid sequence revealed that the identified gene of Catla belongs to the CYP1A1 subfamily. Among different tissues of Catla, the highest CYP1A expression was observed in the kidney followed by the liver, muscle, gill, intestine and brain. CYP1A mRNA expression was detected during all the larval developmental stages, including the unfertilized egg with the highest expression on 9 dpf. BaP (3.5 ppb) and copper sulphate (sublethal dose 0.516 ppm) challenge test for 96 h to Catla larvae revealed the highest CYP1A1 expression at 48 h post-challenge. CYP1A1 transcript also showed a concentration-dependent increase in expression following exposure at 1.75 and 3.5 ppb of BaP for 48 h. Its expression profiling indicates that it is functional at early developmental stages. It can also be used to develop a specific biomarker tool for monitoring environmental pollution.

Identification of 74 cytochrome P450 genes and co-localized cytochrome P450 genes of the CYP2K, CYP5A, and CYP46A subfamilies in the mangrove killifish Kryptolebias marmoratus

BACKGROUND

The mangrove killifish Kryptolebias marmoratus is the only vertebrate that reproduces by self-fertilizing and is an important model species in genetics and marine ecotoxicology. Using whole-genome and transcriptome sequences, we identified all members of the cytochrome P450 (CYP) family in this model teleost and compared them with those of other teleosts.

RESULTS

A total of 74 cytochrome P450 genes and one pseudogene were identified in K. marmoratus. Phylogenetic analysis indicated that the CYP genes in clan 2 were most expanded, while synteny analysis with other species showed orthologous relationships of CYP subfamilies among teleosts. In addition to the CYP2K expansions, five tandem duplicated gene copies of CYP5A were observed. These features were unique to K. marmoratus.

CONCLUSIONS

These results shed a light on CYP gene evolution, particularly the co-localized CYP2K, CYP5A, and CYP46A subfamilies in fish. Future studies of CYP expression could identify specific endogenous and exogenous environmental factors that triggered the evolution of tandem CYP duplication in K. marmoratus.

The cytochrome P450 genes of channel catfish: their involvement in disease defense responses as revealed by meta-analysis of RNA-Seq data sets

BACKGROUND

Cytochrome P450s (CYPs) encode one of the most diverse enzyme superfamily in nature. They catalyze oxidative reactions of endogenous molecules and exogenous chemicals.

METHODS

We identified CYPs genes through in silico analysis using EST, RNA-Seq and genome databases of channel catfish. Phylogenetic analyses and conserved syntenic analyses were conducted to determine their identities and orthologies. Meta-analysis of RNA-Seq databases was conducted to analyze expression profile of CYP genes following bacterial infection.

RESULTS

A full set of 61 CYP genes was identified and characterized in channel catfish. Phylogenetic tree and conserved synteny provided strong evidence of their identities and orthorlogy. Lineage-specific gene duplication was evident in a number of clans in channel catfish. CYP46A1 is missing in the catfish genome as observed with syntenic analysis and RT-PCR analysis. Thirty CYPs were found up- or down-regulated in liver, while seven and eight CYPs were observed regulated in intestine and gill following bacterial infection.

CONCLUSION

We systematically identified and characterized a full set of 61 CYP genes in channel catfish and studied their expression profiles after bacterial infection. While bacterial challenge altered the expression of large numbers of CYP genes, the mechanisms and significance of these changes are not known.

GENERAL SIGNIFICANCE

This work provides an example to systematically study CYP genes in non-model species. Moreover, it provides a basis for further toxicological and physiological studies in channel catfish.

Sublethal effects of CuO nanoparticles on Mozambique tilapia (Oreochromis mossambicus) are modulated by environmental salinity

The increasing use of manufactured nanoparticles (NP) in different applications has triggered the need to understand their putative ecotoxicological effects in the environment. Copper oxide nanoparticles (CuO NP) are toxic, and induce oxidative stress and other pathophysiological conditions. The unique properties of NP can change depending on the characteristics of the media they are suspended in, altering the impact on their toxicity to aquatic organisms in different environments. Here, Mozambique tilapia (O. mossambicus) were exposed to flame synthesized CuO NP (0.5 and 5 mg·L⁻¹) in two environmental contexts: (a) constant freshwater (FW) and (b) stepwise increase in environmental salinity (SW). Sublethal effects of CuO NP were monitored and used to dermine exposure endpoints. Fish exposed to 5 mg·L⁻¹ CuO in SW showed an opercular ventilation rate increase, whereas fish exposed to 5 mg·L⁻¹ in FW showed a milder response. Different effects of CuO NP on antioxidant enzyme activities, accumulation of transcripts for metal-responsive genes, GSH∶GSSG ratio, and Cu content in fish gill and liver also demonstrate that additive osmotic stress modulates CuO NP toxicity. We conclude that the toxicity of CuO NP depends on the particular environmental context and that salinity is an important factor for modulating NP toxicity in fish.

Evaluation of biomarker potential of cytochrome P450 1A (CYP1A) gene in the marine medaka, Oryzias melastigma exposed to water-accommodated fractions (WAFs) of Iranian crude oil

CYP1A is involved in the metabolism of diverse chemicals, including polycyclic aromatic hydrocarbons and alkylated-PAHs, as a first line of detoxification mechanism. First, we identified and characterized the CYP1A gene from the marine medaka, Oryzias melastigma. O. melastigma CYP1A (Om-CYP1A) showed a high similarity of motifs/domains compared to those of vertebrates in their amino acid sequences. To check whether the Om-CYP1A would be inducible, we tested two strong CYP1A inducers, β-naphthoflavone (β-NF) and benzo[α]pyrene (B[α]P), and observed concentration-dependent transient expression on transcripts of Om-CYP1A for 96 h over a wide range of concentrations. Om-CYP1A mRNA level was significantly increased in exposure to different concentrations of β-NF and B[α]P, and its expression was highly transcribed within 12 h upon the exposure to low concentrations of both chemicals. Inducible transcript profiles revealed that Om-CYP1A would be associated with the toxicant metabolism via AhREs/DREs/XREs in its promoter region. To uncover the effects of the water-accommodated fraction (WAF) of crude oil on transcripts of Om-CYP1A, we measured mRNA expression of Om-CYP1A towards different concentrations of WAF for 24h. As a result, WAF exposure significantly increased Om-CYP1A transcripts at all concentrations as well as during time-course experiments for 96 h. In this paper, we demonstrated that WAF would trigger up-regulation of the CYP1A gene that would be associated with the initiation of the cellular defense systems. This finding provides a better understanding of the molecular mechanism of cellular protection particularly that involved in the WAF-mediated cellular response in O. melastigma.

Cytochrome P450 (CYP) in fish

Cytochrome P450 (CYP) enzymes are members of the hemoprotein superfamily, and are involved in the mono-oxygenation reactions of a wide range of endogenous and exogenous compounds in mammals and plants. Characterization of CYP genes in fish has been carried out intensively over the last 20 years. In Japanese pufferfish (Takifugu rubripes), 54 genes encoding P450s have been identified. Across all species of fish, 137 genes encoding P450s have been identified. These genes are classified into 18 CYP families: namely, CYP1, CYP2, CYP3, CYP4, CYP5, CYP7, CYP8, CYP11, CYP17, CYP19, CYP20, CYP21, CYP24, CYP26, CYP27, CYP39, CYP46 and CYP51.We pinpointed eight CYP families: namely, CYP1, CYP2, CYP3, CYP4, CYP11, CYP17, CYP19 and CYP26 in this review because these CYP families are studied in detail. Studies of fish P450s have provided insights into the regulation of P450 genes by environmental stresses including water pollution. In this review, we present an overview of the CYP families in fish.

Evaluation of the toxic impact of silver nanoparticles on Japanese medaka (Oryzias latipes)

The increased use of nano-sized metallic materials is likely to result in the release of these particles into the environment. It is, however, unclear if these materials are harmful to aquatic animals. Furthermore, because the dissolution of such nanomaterials will occur, it is probable that some of the adverse effects resulting will result from the dissolved metal species. In this study, therefore, we investigated the health and environmental impact of silver nanoparticles (Ag-NPs) on Japanese Medaka by studying changes in the expression of stress-related genes using real time RT-PCR analysis and compared these results with those of Medaka exposed to soluble silver ions. The stress-related genes selected here were metallothionein, HSP 70, GST, p53, CYP 1A and the transferrin gene. The expression levels of each gene were determined using two different Ag-NPs dosages and were quantified by measuring the mRNA concentrations in liver extracts with the Taqman-based Real-Time PCR method. The results suggest that these two silver forms have distinguishable toxic fingerprints between them. While the Ag-NPs led to cellular and DNA damage, as well as carcinogenic and oxidative stresses, genes related with metal detoxification/metabolism regulation and radical scavenging action were also induced. In contrast, the ionic silver led to an induction of inflammatory response and metallic detoxification processes in the liver of the exposed fish, but resulted in a lower overall stress response when compared with the Ag-NPs.

Chronic Mycobacterium marinum infection acts as a tumor promoter in Japanese Medaka (Oryzias latipes)

An accumulating body of research indicates there is an increased cancer risk associated with chronic infections. The genus Mycobacterium contains a number of species, including M. tuberculosis, which mount chronic infections and have been implicated in higher cancer risk. Several non-tuberculosis mycobacterial species, including M. marinum, are known to cause chronic infections in fish and like human tuberculosis, often go undetected. The elevated carcinogenic potential for fish colonies infected with Mycobacterium spp. could have far reaching implications because fish models are widely used to study human diseases. Japanese medaka (Oryzias latipes) is an established laboratory fish model for toxicology, mutagenesis, and carcinogenesis; and produces a chronic tuberculosis-like disease when infected by M. marinum. We examined the role that chronic mycobacterial infections play in cancer risk for medaka. Experimental M. marinum infections of medaka alone did not increase the mutational loads or proliferative lesion incidence in all tissues examined. However, we showed that chronic M. marinum infections increased hepatocellular proliferative lesions in fish also exposed to low doses of the mutagen benzo[a]pyrene. These results indicate that chronic mycobacterial infections of medaka are acting as tumor promoters and thereby suggest increased human risks for cancer promotion in human populations burdened with chronic tuberculosis infections.

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.

cDNA cloning and expression of a xenobiotic metabolizing cytochrome P4501A (CYP1A) from the yellow catfish, Pelteobagrus fulvidraco (Siluriformes)

We cloned the full-length cDNA sequence of xenobiotic metabolizing cytochrome P4501A (CYP1A) gene from the yellow catfish (Pelteobagrus fulvidraco, Siluriformes, Bagridae). P. fulvidraco is a commercially important fish generally distributed in Southeast Asian countries and Korea. This is the first report of any xenobiotic metabolizing gene from this fish species. Tissue distribution of CYP1A was studied by real-time PCR. Induction pattern of CYP1A was studied by exposing fish to beta-naphthoflavone (BNF). Liver showed the highest level of expression in control as well as BNF-treated fish. However, high levels of expression were also recorded in brain, intestine, and kidney and the least in the muscles. Information on CYP genes in fish from order Siluriformes is limited as compared with other fish orders. This study provides an insight into the xenobiotic metabolizing system of P. fulvidraco and offers baseline information for further research related to biomarker use of CYP1A and detoxification strategies of this commercially important fish species.

Molecular cloning and beta-naphthoflavone-induced expression of a cytochrome P450 1A (CYP1A) gene from an anadromous river pufferfish, Takifugu obscurus

In recent years, there has been a decline in the wild populations of river pufferfish, Takifugu obscurus. Besides overexploitation for commercial purposes, environmental pollution is believed to have contributed to its decline. However, almost no information exists about genes involved in metabolism of xenobiotics by this species. Nevertheless, there is interest in fugu fishes, since they possess the smallest genome among vertebrates. We cloned and characterized the full-length cDNA sequence of a cytochrome P450 1A (CYP1A) gene from T. obscurus. Phylogenic relationship of T. obscurus CYP1A was also compared to other fish species. The tissue distribution and time-dependant induction of CYP1A mRNA were studied by real-time PCR in T. obscurus exposed to an aryl hydrocarbon receptor (Ahr) agonist, beta-naphthoflavone (BNF). The greatest basal expression in livers of control as well as BNF-treated individuals. However, brain, gill, gonad, intestine, and kidney also expressed CYP1A. Muscles expressed the least CYP1A. The results of the time-course study revealed induction in brain and gills after 6h and at 12h in most tissues. Except for gills, all other organs retained induced expression of CYP1A mRNA up to 96h.

Age-dependent in situ hepatic and gill CYP1A activity in the see-through medaka (Oryzias latipes)

We used a recently introduced strain of medaka, the see-through medaka, whose internal organs can be seen through the skin, to develop an in situ toxicity assay of ethoxyresorufin-O-deethylase (EROD) activity that detected fluorescence from resorufin, a metabolite of ethoxyresorufin and thus an indicator of CYP1A activity. EROD activity in the liver and gills of 2-week post-hatch see-through medaka exposed simultaneously to various concentrations of 3-methylcholanthrene and 200 microg/L ethoxyresorufin for 24 h was proportional to the 3-methylcholanthrene dose. Activities in the liver and gills peaked at 40 microg/L of 3-methylcholanthrene and then decreased at higher doses, possibly because of 3-methylcholanthrene toxicity. At 1-week post-hatch stage, however, constant high EROD activity was observed in controls and at all 3-methylcholanthrene doses. Four-week post-hatch see-through medaka exhibited less EROD activity than 2-week post-hatch see-through medaka, and activity in the liver peaked at 100 microg/L of 3-methylcholanthrene. Adult see-through medaka were not suitable for fluorescence detection owing to their thick skin, muscle and/or tissue. In tests of oxidative activity response to ethoxyresorufin, 1-day and 1-week post-hatch see-through medaka exhibited high intrinsic EROD activity in the liver, gills, and other organs in the absence of 3-methylcholanthrene. This intrinsic activity declined with growth and explained the high constant EROD activity at 1-week post-hatch stage.

Functional Analysis of a Metal Response Element in the Regulatory Region of Flounder Cytochrome P450 1A and Implications for Environmental Monitoring of Pollutants

Cytochrome P450 1A (CYP 1A) is a member of a multigene family of xenobiotic metabolizing enzymes. CYP 1A is highly inducible by numerous environmental contaminants including polycyclic aromatic hydrocarbons (PAHs) and is widely used in biomonitoring studies. Therefore, understanding the regulation of this gene is important for accurate interpretation of biomarker data. We describe here the functional role of a metal response element (MRE) in the European flounder CYP 1A promoter region. To help elucidate the potential role of this MRE, reporter gene constructs, with or without site-directed mutagenesis, were used in conjunction with a dual-luciferase assay. The electrophoretic mobility shift assay (EMSA) was also used to investigate potential protein binding at this MRE site. Treatment with the prototypical PAH 3-methylcholanthrene (3MC) (1.0 microM) produced a dose-dependent response at the CYP 1A promoter, whereas treatment with cadmium (0-1.0 microM) produced little transcriptional activity at either the wild-type or mutated promoter. Cotreatment with cadmium (1.0 microM) and 3MC (1.0 microM) reduced induction at this promoter to 1.83-fold compared to 3MC treatment alone (4.0-fold induction). Mutation of the MRE site resulted in abolishment of this cadmium-related loss of 3MC-dependent activity. Furthermore, a retarded band was observed in the EMSA when the MRE was used as a probe and incubated with liver nuclear protein from flounder treated with cadmium. The results not only add to knowledge of the diversity in vertebrate CYP 1A regulation but also raise the complexity of interpretation of CYP 1A induction in monitoring studies that involve mixtures of PAHs and metals.

Dynamic gene expression changes precede dioxin-induced liver pathogenesis in medaka fish

A major challenge for environmental genomics is linking gene expression to cellular toxicity and morphological alteration. Herein, we address complexities related to hepatic gene expression responses after a single injection of the aryl hydrocarbon receptor (AHR) agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin) and illustrate an initial stress response followed by cytologic and adaptive changes in the teleost fish medaka. Using a custom 175-gene array, we find that overall hepatic gene expression and histological changes are strongly dependent on dose and time. The most pronounced dioxin-induced gene expression changes occurred early and preceded morphologic alteration in the liver. Following a systematic search for putative Ah response elements (AHREs) (5'-CACGCA-3') within 2000 bp upstream of the predicted transcriptional start site, the majority (87%) of genes screened in this study did not contain an AHRE, suggesting that gene expression was not solely dependent on AHRE-mediated transcription. Moreover, in the highest dosage, we observed gene expression changes associated with adaptation that persisted for almost two weeks, including induction of a gene putatively identified as ependymin that may function in hepatic injury repair. These data suggest that the cellular response to dioxin involves both AHRE- and non-AHRE-mediated transcription, and that coupling gene expression profiling with analysis of morphologic pathogenesis is essential for establishing temporal relationships between transcriptional changes, toxicity, and adaptation to hepatic injury.

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.