BDE-47 causes developmental retardation with down-regulated expression profiles of ecdysteroid signaling pathway-involved nuclear receptor (NR) genes in the copepod Tigriopus japonicus

Persistent organic pollutants (POPs) in marine crustaceans: Bioaccumulation, physiological and cellular responses

Persistent organic pollutants (POPs) are ubiquitous in marine ecosystems. These compounds can be accumulated in water, sediments and organisms, persist in time, and have toxic effects in human and wildlife. POPs can be uptaken and bioaccumulated by crustaceans, affecting different physiological processes, including energy metabolism, immunity, osmoregulation, excretion, growth, and reproduction. Nonetheless, animals have evolved sub-cellular mechanisms for detoxification and protection from chemical stress. POPs induce the activity of enzymes involved in xenobiotic metabolism and antioxidant systems, that in vertebrates are importantly regulated at gene expression (transcriptional) level. However, the activation and control of these enzyme systems upon the exposure to POPs have been scarcely studied in invertebrate species, including crustaceans. Herein, we summarize various aspects of the bioaccumulation of POPs in marine crustaceans and their physiological effects. We specially focus on the regulation of xenobiotics metabolism and antioxidant enzymes as key sub-cellular mechanisms for detoxification and protection from chemical stress.

Herbicide prometryn adversely affects the development and reproduction of Tigriopus japonicus by disturbing the ecdysone signal pathway and chitin metabolic pathway

Prometryn, a widely used triazine herbicide in agriculture and aquaculture, has been commonly detected in marine environments, but its effects on the marine copepod are unknown. In this study, marine copepod Tigriopus japonicus was chronically exposed to environmentally relevant concentrations of prometryn to investigate its impacts and potential mechanism of action. The results showed that 0.5, 5, and 50 μg/L prometryn delayed the first spawning time and hatching time, reduced the fecundity, and inhibited the population growth rate. Moreover, exposure to 0.5, 5 and 50 μg/L prometryn decreased food ingestion, the content of C and N elements, nutrient accumulation and body size, but increased the content of 20-hydroxyecdysone (20E). Transcriptome analysis showed that 50 μg/L prometryn down-regulated 1431 genes, which were mainly enriched in lysosome pathway and chitin binding and cuticle construction process. The results of qRT-PCR showed that the expression of key genes involved in juvenile hormone synthesis and chitin metabolic pathways were also inhibited after prometryn exposure. Molecular docking revealed that prometryn could bind to ecdysone receptor (EcR) and UDP-N-acetylglucosamine pyrophosphorylase (UAP), components of the ecdysteroid nuclear receptor complex. Therefore, environmental relevant prometryn delayed the molting and development of T. japonicus by disrupting the ecdysone signal pathway and chitin metabolic pathway through binding to EcR and UAP. This study provides new insights into toxic effects and molecular mechanisms of prometryn on marine copepods.

Exposure to perfluorooctane sulfonate reduced cell viability and insulin release capacity of β cells

Per- and polyfluoroalkyl substances (PFAS) are found to have multiple adverse outcomes on human health. Recently, epidemiological and toxicological studies showed that exposure to PFAS had adverse impacts on pancreas and showed association with insulin abnormalities. To explore how PFAS may contribute to diabetes, we studied impacts of perfluorooctane sulfonate (PFOS) on cell viability and insulin release capacity of pancreatic β cells by using in vivo and in vitro methods. We found that 28-day administration with PFOS (10 mg/(kg body weight•day)) caused reductions of pancreas weight and islet size in male mice. PFOS administration also led to lower serum insulin level both in fasting state and after glucose infusion among male mice. For cell-based in vitro bioassay, we used mouse β-TC-6 cancer cells and found 48-hr exposure to PFOS decreased the cell viability at 50 μmol/L. By measuring insulin content in supernatant, 48-hr pretreatment of PFOS (100 μmol/L) decreased the insulin release capacity of β-TC-6 cells after glucose stimulation. Although these concentrations were higher than the environmental concentration of PFOS, it might be reasonable for high concentration of PFOS to exert observable toxic effects in mice considering mice had a faster removal efficiency of PFOS than human. PFOS exposure (50 μmol/L) to β-TC-6 cells induced intracellular accumulation of reactive oxidative specie (ROS). Excessive ROS induced the reactive toxicity of cells, which eventually invoke apoptosis and necrosis. Results in this study provide evidence for the possible causal link of exposure to PFOS and diabetes risk.

Validation of reference genes for quantitative real-time PCR in chemical exposed and at different age's brackish water flea Diaphanosoma celebensis

Real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR), a primary approach for evaluating gene expression, requires an appropriate normalization strategy to confirm relative gene expression levels by comparison, and rule out variations that might occur in analytical procedures. The best option is to use a reference gene whose expression level is stable across various experimental conditions to compare the mRNA levels of a target gene. However, there is limited information on how the reference gene is differentially expressed at different ages (growth) in small invertebrates with notable changes such as molting. In this study, expression profiles of nine candidate reference genes from the brackish water flea, Diaphanosoma celebensis, were evaluated under diverse exposure to toxicants and according to growth. As a result, four different algorithms showed similar stabilities of genes for chemical exposures in the case of limited conditions using the same developmental stage (H2A was stable, whereas Act was fairly unstable in adults), while the results according to age showed a significantly different pattern in suite of candidate reference genes. This affected the results of genes EcRA and GST, which are involved in development and detoxification mechanisms, respectively. Our finding is the first step towards establishing a standardized real-time qRT-PCR analysis of this environmentally important invertebrate that has potential for aquatic ecotoxicology, particularly in estuarine environments.

Post-diapause transcriptomic restarts: insight from a high-latitude copepod

Background

Diapause is a seasonal dormancy that allows organisms to survive unfavorable conditions and optimizes the timing of reproduction and growth. Emergence from diapause reverses the state of arrested development and metabolic suppression returning the organism to an active state. The physiological mechanisms that regulate the transition from diapause to post-diapause are still unknown. In this study, this transition has been characterized for the sub-arctic calanoid copepod Neocalanus flemingeri, a key crustacean zooplankter that supports the highly productive North Pacific fisheries. Transcriptional profiling of females, determined over a two-week time series starting with diapausing females collected from > 400 m depth, characterized the molecular mechanisms that regulate the post-diapause trajectory.

Results

A complex set of transitions in relative gene expression defined the transcriptomic changes from diapause to post-diapause. Despite low temperatures (5–6 °C), the switch from a “diapause” to a “post-diapause” transcriptional profile occurred within 12 h of the termination stimulus. Transcriptional changes signaling the end of diapause were activated within one-hour post collection and included the up-regulation of genes involved in the 20E cascade pathway, the TCA cycle and RNA metabolism in combination with the down-regulation of genes associated with chromatin silencing. By 12 h, females exhibited a post-diapause phenotype characterized by the up-regulation of genes involved in cell division, cell differentiation and multiple developmental processes. By seven days post collection, the reproductive program was fully activated as indicated by up-regulation of genes involved in oogenesis and energy metabolism, processes that were enriched among the differentially expressed genes.

Conclusions

The analysis revealed a finely structured, precisely orchestrated sequence of transcriptional changes that led to rapid changes in the activation of biological processes paving the way to the successful completion of the reproductive program. Our findings lead to new hypotheses related to potentially universal mechanisms that terminate diapause before an organism can resume its developmental program.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07557-7.

Using meiobenthic taxa, nematofauna biological traits, and bacterial abundance to assess the effects of the polybrominated diphenyl ethers compound: Case study of tetrabromo diphenyl ether BDE-47

Trophic web structuring in aquatic sediments is dependent on the biological interactions between metazoans and microbial communities. The presence of pollutants in these biotas can therefore impact the meiofauna structure via the modification of the microbial communities. The current study examined in a laboratory bioassay the response of meiobenthic communities, particularly marine nematode taxa from the Bizerte Lagoon to the effect of the most detected polybrominated diphenyl ether in this aquatic environment, BDE-47. Four doses [D1 (2.5 ppb Dry weight (DW)), D2 (25 ppb DW), D3 (50 ppb DW), and D4 (100 ppb DW)] were gradually applied and sediment microcosms were incubated for 30 days in the presence or absence of meiofauna. Our results show that BDE-47-enriched sediments decreased the meiofaunal taxa and bacterial abundance. A lower taxonomic diversity of the nematodes' general structure was observed with all doses used. The numerical analysis of the two dimensional (2D) non-metric multidimensional scaling (nMDS) plots and the evolution of the relative abundances of each functional group of nematode genus assemblages revealed that the abundance of all biological traits was modified. Nevertheless, only three of the functional traits, adult length, feeding group, and amphid shape, showed a clear difference between the control and the treated microcosms. The similarity percentage analysis (SIMPER) revealed that the average dissimilarity between nematode genera communities and biological traits increased with BDE-47-enriched sediments. The nMDS second-stage ordination of inter-matrix rank correlations for matrices including genera and biological traits showed that the amphid shape was the functional trait closest to the generic distribution. Finally, the Principal Component Analysis (PCA) for the nematode biological traits and bacteria indicated a positive correlation of these microbes with the functional groups [1A, Cr, and ef], and a negative correlation only with the "cla"-type tail shape.

Ecotoxicity of polybrominated diphenyl ether (BDE-47) on a meiobenthic community with special emphasis on nematodes: Taxonomic and trophic diversity assessment

The response taxonomic and trophic of meiobenthic organisms, especially marine nematodes to polybrominated diphenyl ether (BDE-47) was studied using a community from Bizerte lagoon (Nord-East Tunisia). Four concentrations of BDE-47 [D1 (2.5 μg/kg dw), D2 (25 μg/kg dw), D3 (50 μg/kg dw), and D4 (100 μg/kg dw)] were applied, and responses were determined 30 days after exposure. Species abundance and all univariate indices were significantly affected in all treated microcosms compared to the control. The non-parametric cluster based on species abundance separated the nematode population into two groups: control + all treated microcosms. After grouping nematode species according to their trophic diversity, their abundance showed differential responses. The non-metric multi-dimensional scaling analysis and cumulative k-dominance based on the abundance of trophic groups abundances reflected significant separation between the control microcosm and each treatment condition. The correspondence analysis 2D plot generated from nematode species and trophic groups abundance showed the control microcosm was dominated by microvores, represented by two species of Terschellingia. However, when treated with the highest concentration of BDE-47, the community was occupied by the resistant trophic groups of facultative predators and epigrowth feeders represented by Metoncholaimus pristiurus and Paracomesoma dubium, respectively.

The genome of the European estuarine calanoid copepod Eurytemora affinis: Potential use in molecular ecotoxicology

In this study, we sequenced and assembled the genome of a European estuarine calanoid copepod using Oxford Nanopore PromethION and Illumina HiSeq 2500 platforms. The length of the assembled genome was 776.1 Mb with N50 = 474.9 kb (BUSCO 85.9%), and the genome consisted of 2473 contigs. A total of 18,014 genes were annotated and orthologous gene clusters were analyzed in comparison to other copepods. In addition, genome-wide identification of cytochrome P450s, glutathione S-transferases, and ATP-binding cassette transporters in E. affinis was performed to determine gene repertoire of these detoxification-related gene families. Results revealed the presence of species-specific gene inventories, indicating that these gene families have evolved through species-specific gene loss/expansion processes, possibly due to adaptation to different environmental stressors. Our study provides a new inventory of the European estuarine calanoid copepod E. affinis genome with emphasis on phase I, II, and III detoxification systems.

The genome of the marine water flea Diaphanosoma celebensis: Identification of phase I, II, and III detoxification genes and potential applications in marine molecular ecotoxicology

To assemble the genome of the marine water flea Diaphanosoma celebensis, a sentinel model for marine environmental monitoring, we constructed a high-quality genome using PromethION and HiSeq 2500 platforms. The total length of the assembled genome was 100.08 Mb, with N50 = 2.56 Mb (benchmarking universal single-copy orthologs, 96.9%) and consisted of 179 scaffolds. A total of 15,427 genes were annotated, and orthologous gene clusters in D. celebensis were analyzed and compared with those of the cladocerans Daphnia magna and Daphnia pulex. In addition, phase I, II, and III detoxification gene families of cytochrome P450s, glutathione S-transferases, and ATP-binding cassette were fully identified and revealed lineage-specific gene loss and/or expansion, suggesting that the evolution of detoxification gene families likely modulates fitness and susceptibility in response to environmental stressors. The study improves our understanding of the detoxification-related gene system and should contribute to future studies of molecular ecotoxicology in cladoceran species and their responses to emerging pollutants.

Adverse effects in Daphnia magna exposed to e-waste leachate: Assessment based on life trait changes and responses of detoxification-related genes

The sharp increase in e-waste derived from great consumption of electronic products has become a potential global environmental challenge. Limited information is available about the potential detrimental impact of e-waste on aquatic organisms. The present study investigated the expression of detoxification-related genes and life-history parameter changes in Daphnia magna exposed to e-waste leachate, simultaneously integrating with the chemical analysis of typical pollutants from e-waste leachate. The study aims at assessing impacts of e-waste to aquatic invertebrates and providing insights into its toxic mechanisms. The results showed high concentration of heavy metals like Cu (1657.14 ± 259.3 μg g^-1, DW) and persistent organic compounds like polybrominated diphenyl ethers (7831.32 ± 1273.86 ng g^-1, DW) in stream sediments near e-waste dismantling areas. Chronic exposure to these pollutants can affect the growth and reproduction of D. magna, resulting in significant development retardation, decreased total egg production per female, and even smaller body size. Expression of some detoxification and reproduction-related genes including DappuHR96, CYP360a, P-gp, EcR, CYP314 and Vtg exhibited different response patterns depending on the e-waste leachate concentration. E-waste leachate may affect the expression of detoxification-related and growth and reproduction-related genes and disrupt the growth and reproduction processes of D. magna.

Invisible endocrine disruption and its mechanisms: A current review

The research on impacts of environmental chemicals on crustacean molting dates back to the 1970s when ground-breaking studies investigated the disruption of molting in Crustacea by organochlorines. With the emergence of a new scientific inquiry, termed environmental endocrine disruption, in the early 1990s, increasing attention has been attracted to the possibility that environmental chemicals capable of wreaking havoc on sex steroid-regulated processes in vertebrates can also adversely affect ecdysteroid-mediated processes, e.g. molting, in crustaceans. Given the fact that many molting-disrupting chemicals accumulate in crustacean tissues and that the effect on molting is not readily visible in the field, the disruption of molting by environmental chemicals has been dubbed the invisible endocrine disruption. In recent years, much advancement has been made in both the documentation of the phenomenon of molting disruption and the search for mechanisms, by which molting disruption occurs. This review provides an overview of the current status of the field of invisible endocrine disruption, and perspectives on future directions are also presented.

Paracetamol affects the expression of detoxification- and reproduction-related genes and alters the life traits of Daphnia magna

Paracetamol (APAP) is a widely used non-steroidal anti-inflammatory drug and has been frequently detected in aquatic environment. However, limited information is provided about the toxic effects and detoxification mechanism of APAP in aquatic invertebrates. In the present study, the change of life traits of Daphnia magna (e.g., body length, growth rate and reproduction) was investigated under the chronic APAP exposure (0-5000 μg/L) for 21 day, and the effects of APAP on the expression of the detoxification- and reproduction-related genes including HR96, CYP360A8, CYP314, MRP4, P-gp, EcR and Vtg in the acute exposure (up to 96 h) were also determined. Results showed that the molting frequency, days to the first brood and days to the first egg production of D. magna were affected under the 50 μg/L concentration of APAP in the chronic exposure test. In the acute test, the transcriptional expression of HR96 was up-regulated under APAP exposure for 24 and 48 h. Similar performances were also observed in the expression of CYP360A8, CYP314, MRP4 and P-gp. However, with exposure time extended to 96 h, the induction of HR96 decreased or even reversed in some cases. It may indicate that the defense system in Daphnia is activated for a short time of exposure or becomes adaptive after longer term of exposure. APAP exposure also affected reproduction-related genes expression, which was related to the exposure time and concentration of APAP. In summary, APAP significantly affected the expression of genes associated with detoxification metabolism and altered some physiological parameters in D. magna.

Impact of juvenile hormone analogue insecticides on the water flea Moina macrocopa: Growth, reproduction and transgenerational effect

The increasing quantities of insecticides that leach into water bodies severely affect the health of the aquatic environment. Juvenile hormone analogue (JHA) insecticides are endocrine disrupters that interfere with hormonal activity in insects by mimicking juvenile hormones (JHs). Because the structure and functions of methyl farnesoate in crustaceans are similar to the insect JHs, exogenous JHA insecticides may cause adverse effects on the growth and reproduction in crustaceans similar to those observed in insects. This study examined the toxic effects of two JHA insecticides, methoprene and fenoxycarb, on the water flea Moina macrocopa. The 24-h and 48-h LC₅₀ values for fenoxycarb and methoprene were 0.53 and 0.32 mg/L and 0.70 and 0.54 mg/L, respectively. Chronic exposure to the two JHAs caused a series of toxic effects in M. macrocopa, including shortening of life expectancy, repression of body growth, reduction in fecundity, and disturbed the expression of genes involved in the JH signaling pathway, in cuticle development, and in the carbohydrate, amino acid, and ATP metabolic processes. Moreover, JHA exposure impaired the growth and reproduction of the offspring of M. macrocopa exposed to JHAs, even when the neonates were not exposed to the chemicals. In addition, changes in the expression of genes related to histone methylation indicate that epigenetic changes may promote transgenerational impairment in M. macrocopa. These results demonstrate the toxic effects of fenoxycarb and methoprene on non-target aquatic organisms. The damages done by these JHA insecticides to the aquatic environment is worthy of our attention and further studies.

Effects of two juvenile hormone analogue insecticides, fenoxycarb and methoprene, on Neocaridina davidi

Juvenile hormone analogue (JHA) insecticides are endocrine disrupters that interfere with hormonal action in insects by mimicking their juvenile hormones (JH). As the structure and functions of methyl farnesoate in crustaceans are similar to those of JH in insects, exogenous JHA insecticides could have adverse effects on the development and reproduction of crustaceans. This study examined the toxic effects of two JHA insecticides, fenoxycarb and methoprene, on a freshwater shrimp model of cherry shrimp, Neocaridina davidi. Both insecticides had detrimental effects on cherry shrimp, but fenoxycarb was more toxic than methoprene. Chronic exposure to these insecticides reduced the shrimp's body length and molting frequency. Based on transcriptome annotations for N. davidi, we identified important gene homologues that were active in both insect JH biosynthetic and degradative pathways as well as JH and ecdysteroid signaling pathways. Chronic treatments with JHAs had significant effects on these genes in N. davidi. Our transcriptomic analysis showed that genes involved in the pathways related to cuticle development, serine protease activity, and carbohydrate, peptide and lipid metabolic processes were differentially expressed in shrimp exposed to JHAs. These results demonstrate the toxicity of fenoxycarb and methoprene to freshwater crustaceans and indicate the need to monitor the use of JHA insecticides.

Effects of atrazine on life parameters, oxidative stress, and ecdysteroid biosynthetic pathway in the marine copepod Tigriopus japonicus

Atrazine is a widely used pesticide which acts as an endocrine disruptor in various organisms. The aim of this study was to investigate adverse effects of atrazine on life parameters, oxidative stress, and ecdysteroid biosynthetic pathway in the marine copepod Tigriopus japonicus. In T. japonicus, no mortality was shown in response to atrazine up to 20 mg/L in acute toxicity assessment. In nauplii, retardation in the growth and prolonged molting and metamorphosis resulted under chronic exposure of atrazine at 20 mg/L. In addition, body sizes of T. japonicus nauplii were significantly decreased (P < 0.01 in length and P < 0.001 in width) in response to 20 mg/L of atrazine. Furthermore, atrazine induced oxidative stress by the generation of reactive oxygen species at all concentrations compared to the control in the nauplii. Also, significant increase in glutathione-S transferase activity was observed in adult T. japonicus at low concentration of atrazine. To understand effects of atrazine on ecdysteroid biosynthetic pathway-involved genes (e.g., neverland, CYP307E1, CYP306A1, CYP302A1, CYP3022A1 [CYP315A1], CYP314A1, and CYP18D1) were examined with mRNA expressions of ecdysone receptor (EcR) and ultraspiracle (USP) in response to 20 mg/L atrazine in nauplii and adults. In the nauplii, these genes were significantly downregulated (P < 0.05) in response to atrazine, compared to the control but not in the adult T. japonicus. These results suggest that atrazine can interfere in vivo life parameters by oxidative stress-induced retrogression and ecdysteroid biosynthetic pathway in this species.

Effects of methylparaben, ethylparaben, and propylparaben on life parameters and sex ratio in the marine copepod Tigriopus japonicus

Parabens are used as a preservative substance in a wide range of man-made products causing deleterious effects on aquatic organisms and therefore, the concern of their effects to aquatic organisms has been increased. In this study, acute toxicity of methylparaben (MeP), ethylparaben (EtP), and propylparaben (PrP) was assessed in the marine copepod Tigriopus japonicus. The acute toxicity assessment resulted in the median lethal concentration (LC50) values of MeP, EtP, and PrP were 29,754, 11,659, and 113 μg/L, respectively, for male and 38,183, 15,371, and 357 μg/L, respectively, for female, indicating the strongest toxicity of PrP, compared to MeP and EtP and the higher sensitivity of males compared to females. Developmental retardation and reproduction rate were also measured under chronic exposure. Furthermore, significant alteration in sex ratio was shown in PrP-exposed group, indicating PrP would have feminization effect in T. japonicus. Here we report different toxicity of three types of parabens and also shows potential estrogenic effects of PrP in T. japonicus.

Toxic effects of pentachlorophenol and 2,2',4,4'-tetrabromodiphenyl ether on two generations of Folsomia candida

The standard Folsomia candida test (ISO 11267), in which only the survival and reproduction of the parental generation (F0) were determined, is insufficient to assess the toxicity of chemicals, like endocrine disrupting chemicals (EDCs), since the effects of EDCs could last for several generations and sometimes can be transgenerational. It's necessary to assess the effects on subsequent generations to address the long-term consequences of these chemicals exposure. In this study, the effects of pentachlorophenol (PCP) and 2,2',4,4'-tetrabromodiphenyl (BDE47) were assessed on F0 and the first filial generation (F1) of F. candida after 28-day or 10-day exposure of F0. In the 28-day exposure method, F0 was exposed to PCP or BD47 for 28 days and F1 was exposed for about 21 days. In the 10-day exposure method, F0 was exposed for 10 days and F1 was not exposed. The F. candida reproduction of F0 and F1 can be assessed in both methods, while transgenerational effects can further be evaluated in the 10-day exposure method. The numbers of F1 and F2 (second filial generation) juveniles in the 28-day exposure method and F1 juveniles in the 10-day exposure method decreased significantly for the PCP treatment. For BDE47, only the number of F1 juveniles in the 28-day exposure method significantly decreased. The EC50 values of F0 reproduction (the number of F1 juveniles) in the 28-day exposure method were 89 and 306 mg/kg dry soil for PCP and BDE47, respectively. Results suggested that PCP could affect F. candida egg hatching or juvenile survival and adult reproductive capacity, while BDE47 was more likely to affect egg hatchability or juvenile survival rather than adult reproductive capacity. It also indicated that F. candida exposed to PCP or BDE47 could recover in clean soil. Transgenerational effects were not observed for neither PCP nor BDE47 in this study.

RNA-Seq-based transcriptome profiling and expression of 16 cytochrome P450 genes in the benzo[α]pyrene-exposed estuarine copepod Eurytemora affinis

The calanoid copepod Eurytemora affinis is one of the most abundant estuarine species and is considered to be an ideal candidate species for ecotoxicological research. An RNA-Seq-based transcriptome was developed from whole bodies of this species. Among 142,442 contigs of the de novo assembly by Trinity, 48,480 open reading frame (ORF) contigs were found using TransDecoder. A total of 17,762 genes were identified by BLAST analysis, which covers about 75% of the annotated genes in the E. affinis genome. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that most annotated sequences were related to metabolism pathways, including xenobiotic biodegradation. Using transcriptome data, we identified putative transcripts related to xenobiotic processing genes including phase I enzymes, phase II enzymes, transporters, and transcription factors. To understand the CYP-mediated detoxification metabolism of xenobiotics, we measured the transcriptional levels of 16 CYPs (within full sequences) of E. affinis in response to benzo[α]pyrene (B[α]P). Most Ea-CYP genes were significantly down- and/or up-regulated (P < 0.05) in response to B[α]P, suggesting that Ea-CYP genes are likely involved in detoxification (mainly in biotransformation of xenobiotics) with particular genes, demonstrating significant upregulation or downregulation compared to others, as shown in other copepod model species (e.g. Tigriopus japonicus and Paracyclopina nana). This study will provide insight into the potential role of E. affinis in response to various toxic or xenobiotic chemicals in the marine environment.

Single and mixture toxicities of BDE-47, 6-OH-BDE-47 and 6-MeO-BDE-47 on the feeding activity of Daphnia magna: From behavior assessment to neurotoxicity

Although 2,2',4,4'-tetrabrominated diphenyl ether (BDE-47), 6-hydroxy-2,2',4,4'-tetrabromodiphenyl ether (6-OH-BDE-47) and 6-methoxy-2,2',4,4'-tetrabromodiphenyl ether (6-MeO-BDE-47) clearly disrupt the endocrine system, current knowledge of their single and/or mixture toxicities on other behaviors of aquatic organisms remains limited. In the present study, Daphnia magna was used to investigate the single and mixture toxicities of BDE-47, 6-OH-BDE-47 and 6-MeO-BDE-47 as measured by inhibition of feeding during exposure and post-exposure periods. Additionally, the biochemical performance, i.e., the activities of super oxidase dismutase (SOD), glutathione peroxidase (GPx) and acetylcholinesterase (AChE) of the test organism was studied to investigate the potential mechanisms of the toxicity of the target compounds. The three target compounds produced an obvious depressive effect on feeding behavior during the exposure period, and the effect increased with increasing concentrations. D. magna was most sensitive to 6-OH-BDE-47. The toxicity of the ternary mixture showed an obvious concentration-dependent effect, whereas the binary mixture toxicity showed the characteristics of hormesis. During the post-exposure period, overcompensation occurred, indicating a short-term effect of the target compounds on D. magna. Additionally, significant changes occurred in neurological responses, indicating that these compounds might have neurobehavioral toxicity in D. magna. The decrease in oxidative stress enzymes (SOD and GPx) indicated that the antioxidant response of D. magna was destroyed.

ATP-binding cassette (ABC) proteins in aquatic invertebrates: Evolutionary significance and application in marine ecotoxicology

The ATP-binding cassette (ABC) protein superfamily is known to play a fundamental role in biological processes and is highly conserved across animal taxa. The ABC proteins function as active transporters for multiple substrates across the cellular membrane by ATP hydrolysis. As this superfamily is derived from a common ancestor, ABC genes have evolved via lineage-specific duplications through the process of adaptation. In this review, we summarized information about the ABC gene families in aquatic invertebrates, considering their evolution and putative functions in defense mechanisms. Phylogenetic analysis was conducted to examine the evolutionary significance of ABC gene families in aquatic invertebrates. Particularly, a massive expansion of multixenobiotic resistance (MXR)-mediated efflux transporters was identified in the absence of the ABCG2 (BCRP) gene in Ecdysozoa and Platyzoa, suggesting that a loss of Abcg2 gene occurred sporadically in these species during divergence of Protostome to Lophotrochozoa. Furthermore, in aquatic invertebrates, the ecotoxicological significance of MXR is discussed while considering the role of MXR-mediated efflux transporters in response to various environmental pollutants.

WAFs lead molting retardation of naupliar stages with down-regulated expression profiles of chitin metabolic pathway and related genes in the copepod Tigriopus japonicus

Oil pollution is considered being disastrous to marine organisms and ecosystems. As molting is critical in the developmental process of arthropods in general and copepods, in particular, the impact will be adverse if the target of spilled oil is on molting. Thus, we investigated the harmful effects of water accommodated fractions (WAFs) of crude oil with an emphasis on inhibition of chitin metabolic pathways related genes and developmental retardation in the copepod Tigriopus japonicus. Also, we analysed the ontology and domain of chitin metabolic pathway genes and mRNA expression patterns of developmental stage-specific genes. Further, the developmental retardation followed by transcriptional modulations in nuclear receptor genes (NR) and chitin metabolic pathway-related genes were observed in the WAFs-exposed T. japonicus. As a result, the developmental time was found significantly (P<0.05) delayed in response to 40% WAFs in comparison with that of control. Moreover, the NR gene, HR3 and chitinases (CHT9 and CHT10) were up-regulated in N4-5 stages, while chitin synthase genes (CHS-1, CHS-2-1, and CHS-2-2) down-regulated in response to WAFs. In brief, a high concentration of WAFs repressed nuclear receptor genes but elicited activation of some of the transcription factors at low concentration of WAFs, resulting in suppression of chitin synthesis. Thus, we suggest that WAF can lead molting retardation of naupliar stages in T. japonicus through down-regulations of chitin metabolism. These findings will provide a better understanding of the mode of action of chitin biosynthesis associated with molting mechanism in WAF-exposed T. japonicus.

Ecdysone receptor (EcR) and ultraspiracle (USP) genes from the cyclopoid copepod Paracyclopina nana: Identification and expression in response to water accommodated fractions (WAFs)

Ecdysteroid hormones are pivotal in the development, growth, and molting of arthropods, and the hormone pathway is triggered by binding ecdysteroid to a heterodimer of the two nuclear receptors; ecdysone receptors (EcR) and ultraspiracle (USP). We have characterized EcR and USP genes, and their 5'-untranslated region (5'-UTR) from the copepod Paracyclopina nana, and studied mRNA transcription levels in post-embryonic stages and in response to water accommodated fractions (WAFs) of crude oil. The open reading frames (ORF) of EcR and USP were 1470 and 1287bp that encoded 490 and 429 amino acids with molecular weight of 121.18 and 105.03kDa, respectively. Also, a well conserved DNA-binding domain (DBD) and ligand-binding domain (LBD) were identified which confirmed by phylogenetic analysis. Messenger RNA transcriptional levels of EcR and USP were developmental stage-specific in early post-embryonic stages (N3-4). However, an evoked expression of USP was observed throughout copepodid stage and in adult females. WAFs (40 and 80%) were acted as an ecdysone agonist in P. nana, and elicited the mRNA transcription levels in adults. Developmental stage-specific transcriptional activation of EcR and USP in response to WAFs was observed. USP gene was down-regulated in the nauplius in response to WAF, whereas up-regulation of USP was observed in the adults. This study represents the first data of molecular elucidation of EcR and USP genes and their regulatory elements from P. nana and the developmental stage specific expression in response to WAFs, which can be used as potential biomarkers for environmental stressors with ecotoxicological evaluations in copepods.

Toxic effects of diclofenac on life history parameters and the expression of detoxification-related genes in Daphnia magna

Diclofenac (DCF), as a widely used drug, has been detected in various environmental media such as municipal wastewater effluent. However, there is little information on the effects of DCF on freshwater invertebrates potentially exposing to its residues in surface water. In the present study, we investigated the toxic effects of DCF on the physiological parameters (e.g., survival, growth rate, and reproduction) of a crustacean, Daphnia magna, via a 21-d chronic toxicity test, and we also evaluated the effects of DCF on the expression of the genes related to the detoxification metabolism, growth, development and reproduction (e.g., HR96, P-gp, CYP360A8, CYP314, GST, EcR and Vtg) in acute exposure (up to 96h) with RT-PCR. Significant toxic effects of DCF to D. magna were observed at 50μgL^-1, the expression of these selected genes was inhibited with 24h of exposure, and induced after 48h to some extents. The expression of Vtg was induced at high concentrations of DCF (500μgL^-1 and 5000μgL^-1) after 24h and 48h of exposure, but also significantly induced at low concentration (50μgL^-1) after 96h of exposure. Dose- and time-dependent relationships were observed for gene expression of the seven selected genes. In the 21-d chronic toxicity test, the days to the first brood and the days to the first egg production were both significantly delayed at 50μgL^-1. However, there were no significant differences observed among the molting frequency, number of eggs produced in the first brood, total number of eggs per individual, total number of broods per individual, body length and intrinsic growth rate. Our results suggested that the reproduction parameters are more sensitive endpoints than the survival and growth for evaluating the toxicity of DCF to aquatic invertebrates.

BDE-47 induces oxidative stress, activates MAPK signaling pathway, and elevates de novo lipogenesis in the copepod Paracyclopina nana

Brominated flame retardant, 2, 2', 4, 4'-tetrabromodiphenyl ether (BDE-47), has received grave concerns as a persistent organic pollutant, which is toxic to marine organisms, and a suspected link to endocrine abnormalities. Despite the wide distribution in the marine ecosystem, very little is known about the toxic impairments on marine organisms, particularly on invertebrates. Thus, we examined the adverse effects of BDE-47 on life history trait (development), oxidative markers, fatty acid composition, and lipid accumulation in response to BDE-47-induced stress in the marine copepod Paracyclopina nana. Also, activation level of mitogen-activated protein kinase (MAPK) signaling pathways along with the gene expression profile of de novo lipogenesis (DNL) pathways were addressed. As a result, BDE-47 induced oxidative stress (e.g. reactive oxygen species, ROS) mediated activation of extracellular signal-regulated kinase (ERK) and c-Jun-N-terminal kinase (JNK) signaling cascades in MAPK pathways. Activated MAPK pathways, in turn, induced signal molecules that bind to the transcription factors (TFs) responsible for lipogenesis to EcR, SREBP, ChREBP promoters. Also, the stress stimulated the conversion of saturated fatty acids (SFAs) to polyunsaturated fatty acids (PUFAs), a preparedness of the organism to adapt the observed stress, which could be correlated with the elongase and desaturase gene (e.g. ELO3, Δ5-DES, Δ9-DES) expressions, and then extended to the delayed early post-embryonic development and increased accumulation of lipid droplets in P. nana. This study will provide a better understanding of how BDE-47 effects on marine invertebrates particularly on the copepods, an important link in the marine food chain.