Gene expression profiling of copper-induced responses in the intertidal copepod Tigriopus japonicus using a 6K oligochip microarray

Multigenerational effects of glyphosate-based herbicide and emamectin benzoate insecticide on the reproduction and gene expression of the copepod Pseudodiaptomus annandalei (Sewell, 1919)

This study investigates the effects of glyphosate-based herbicide (GLY) and pure emamectin benzoate (EB) insecticide on the brackish copepod Pseudodiaptomus annandalei. The 96h median lethal concentration (96 h LC50) was higher in the GLY exposure (male: 3420.96 ± 394.67 μg/L; female: 3093.46 ± 240.67 μg/L) than in the EB (male: 79.10 ± 7.30 μg/L; female: 6.38 ± 0.72 μg/L). Based on the result of 96h LC50, we further examined the effects of GLY and EB exposures at sub-lethal concentrations on the naupliar production of P. annandalei. Subsequently, a multigenerational experiment was conducted to assess the long-term impact of GLY and EB at concentrations 375 μg/L, and 0.025 μg/L respectively determined by sub-lethal exposure testing. During four consecutive generations, population growth, clutch size, prosome length and width, and sex ratio were measured. The copepods exposed to GLY and EB showed lower population growth but higher clutch size than the control group in most generations. Gene expression analysis indicated that GLY and EB exposures resulted in the downregulation of reproduction-related (vitellogenin) and growth-related (myosin heavy chain) genes, whereas a stress-related gene (heat shock protein 70) was upregulated after multigenerational exposure. The results of the toxicity test after post-multigenerational exposure indicated that the long-term GLY-exposed P. annandalei displayed greater vulnerability towards GLY toxicity compared to newly-exposed individuals. Whereas, the tolerance of EB was significantly higher in the long-term exposed copepod than in newly-exposed individuals. This suggests that P. annandalei might have greater adaptability towards EB toxicity than towards GLY toxicity. This study reports for the first time the impacts of common pesticides on the copepod P. annandalei, which have implications for environmental risk assessment and contributes to a better understanding of copepod physiological responses towards pesticide contaminations.

Decoupled responses of the copepod Eurytemora affinis transcriptome and its microbiota to dissolved copper exposure

Chemical contamination is a common threat to biota thriving in estuarine and coastal ecosystems. Of particular importance is that trace metals tend to accumulate and exert deleterious effects on small invertebrates such as zooplankton, which are essential trophic links between phytoplankton and higher-level consumers in aquatic food webs. Beyond the direct effects of the contamination, we hypothesized that metal exposure could also affect the zooplankton microbiota, which in turn might further impair host fitness. To assess this assumption, copepods (Eurytemora affinis) were sampled in the oligo-mesohaline zone of the Seine estuary and exposed to dissolved copper (25 µg.L^-1) over a 72-hour time period. The copepod response to copper treatment was assessed by determining transcriptomic changes in E. affinis and the alteration of its microbiota. Unexpectedly, very few genes were differentially expressed in the copper-treated copepods compared to the controls for both male and female samples, while a clear dichotomy between sex was highlighted with 80% of the genes showing sex-biased expression. In contrast, copper increased the taxonomic diversity of the microbiota and resulted in substantial compositional changes at both the phyla and genus levels. Phylogenetic reconstruction of the microbiota further suggested that copper mitigated the phylogenetic relatedness of taxa at the basal tree structure of the phylogeny, whereas it strengthened it at the terminal branches. Increased terminal phylogenetic clustering in the copper-treated copepods coincided with higher proportions of bacterial genera previously identified as copper resistant (e.g., Pseudomonas, Acinetobacter, Alkanindiges, Colwellia) and a higher relative abundance of the copA_ox gene encoding a periplasmic inducible multi-copper oxidase. The enrichment in micro-organisms likely to perform copper sequestration and/or enzymatic transformation processes, underlines the need to consider the microbial component during evaluation of the vulnerability of zooplankton to metallic stress.

Nanoplastics pose a greater effect than microplastics in enhancing mercury toxicity to marine copepods

Due to human activities, high abundances of nano/microplastics (N/MPs) concurrent with metal pollution have become a serious problem in the global marine environment. Because of displaying a high surface-area-to-volume ratio, N/MPs can serve as the carriers of metals and thus increase their accumulation/toxicity in marine biota. As one of the most toxic metals, mercury (Hg) causes adverse effects on marine organisms but whether environmentally relevant N/MPs can play a vector role of this metal in marine biota, as well as their interaction, is poorly known. To evaluate the vector role of N/MPs in Hg toxicity, we first performed the adsorption kinetics and isotherms of N/MPs and Hg in seawater, as well as ingestion/egestion of N/MPs by marine copepod Tigriopus japonicus, and second, the copepod T. japonicus was exposed to polystyrene (PS) N/MPs (500-nm, 6-μm) and Hg in isolation, combined, and incubated forms at environmentally relevant concentrations for 48 h. Also, the physiological and defense performance including antioxidant response, detoxification/stress, energy metabolism, and development-related genes were assessed after exposure. The results indicated N/MPs significantly increased Hg accumulation and thus its toxicity effects in T. japonicus as exemplified by decreased transcription of genes related to development and energy metabolism and increased transcriptional levels of genes functioning in antioxidant and detoxification/stress defense. More importantly, NPs were superimposed onto MPs and produced the most vector effect in Hg toxicity to T. japonicus, especially in the incubated forms. Overall, this study highlighted the role of N/MPs as a potential risk factor for increasing the adverse effects of Hg pollution, and emphasized the adsorption forms of contaminants by N/MPs should doubly be considered in the continuing researches.

Effects of environmental concentrations of the fragrance amyl salicylate on the mediterranean mussel Mytilus galloprovincialis

Amyl salicylate (AS) is a fragrance massively used as a personal care product and following the discharged in wastewaters may end up in the aquatic environment representing a potential threat for the ecosystem and living organisms. AS was recently detected in water of the Venice Lagoon, a vulnerable area continuously subjected to the income of anthropogenic chemicals. The lagoon is a relevant area for mollusc farming, including the Mediterranean mussels (Mytilus galloprovincialis) having an important economic and ecological role. Despite high levels of AS occurred in water of the Lagoon of Venice, no studies investigated the possible consequences of AS exposures on species inhabiting this ecosystem to date. For the first time, we applied a multidisciplinary approach to investigate the potential effects of the fragrance AS on Mediterranean mussels. To reach such a goal, bioaccumulation, cellular, biochemical, and molecular analyses (RNA-seq and microbiota characterization) were measured in mussels treated for 7 and 14 days with different AS Venice lagoon environmental levels (0.1 and 0.5 μg L^-1). Despite chemical investigations suggested low AS bioaccumulation capability, cellular and molecular analyses highlighted the disruption of several key cellular processes after the prolonged exposures to the high AS concentration. Among them, potential immunotoxicity and changes in transcriptional regulation of pathways involved in energy metabolism, stress response, apoptosis and cell death regulations have been observed. Conversely, exposure to the low AS concentration demonstrated weak transcriptional changes and transient increased representation of opportunistic pathogens, as Arcobacter genus and Vibrio aestuarianus. Summarizing, this study provides the first overview on the effects of AS on one of the most widely farmed mollusk species.

Effects of particulate matter (PM2.5) on life history traits, oxidative stress, and defensome system in the marine copepod Tigriopus japonicus

Particulate matter (PM_2.5) generated in large cities creates new problems in marine ecosystems and may adversely affect its inhabitants. However, the mechanisms underlying the same remain unclear; hence, we investigated the effects of PM_2.5 on life history traits (e.g., mortality, development, and fecundity), cellular reactive oxygen species (ROS) levels, antioxidant enzyme (e.g., glutathione peroxidase [GPx], superoxide dismutase [SOD], and catalase [CAT]) activities, and the transcript levels of detoxification-related genes (cytochrome P450s [CYPs]) and antioxidant (glutathione S-transferases [GSTs]) in the copepod Tigriopus japonicus. Among the life history traits, developmental time was the only trait to significantly deviate (P < 0.05) in response to PM_2.5 (compared to that in the controls). Significant changes in ROS levels and antioxidant enzymatic activities (P < 0.05) in response to PM_2.5, suggested that PM_2.5 can induce oxidative stress, leading to adverse effects on the T. japonicus life history. In addition, PM_2.5 induced a differential regulation of various CYP and GST genes, particularly CYP307E1, GST-kappa, and GST-sigma were significantly upregulated (P < 0.05), suggesting that these genes likely play crucial roles in detoxification mechanisms and could be useful as reliable biomarkers for PM_2.5 toxicity. Overall, the results of this study provide new insights into the potential toxicity of PM_2.5.

Heavy Metal Contamination of Natural Foods Is a Serious Health Issue: A Review

Heavy metals play an important role in the homeostasis of living cells. However, these elements induce several adverse environmental effects and toxicities, and therefore seriously affect living cells and organisms. In recent years, some heavy metal pollutants have been reported to cause harmful effects on crop quality, and thus affect both food security and human health. For example, chromium, cadmium, copper, lead, and mercury were detected in natural foods. Evidence suggests that these elements are environmental contaminants in natural foods. Consequently, this review highlights the risks of heavy metal contamination of the soil and food crops, and their impact on human health. The data were retrieved from different databases such as Science Direct, PubMed, Google scholar, and the Directory of Open Access Journals. Results show that vegetable and fruit crops grown in polluted soil accumulate higher levels of heavy metals than crops grown in unpolluted soil. Moreover, heavy metals in water, air, and soil can reduce the benefits of eating fruits and vegetables. A healthy diet requires a rational consumption of foods. Physical, chemical, and biological processes have been developed to reduce heavy metal concentration and bioavailability to reduce heavy metal aggregation in the ecosystem. However, mechanisms by which these heavy metals exhibit their action on human health are not well elucidated. In addition, the positive and negative effects of heavy metals are not very well established, suggesting the need for further investigation.

Parental exposures increase the vulnerability of copepod offspring to copper and a simulated marine heatwave

Extreme temperatures from marine heatwaves (MHWs) and pollution are dominant stressors in tropical marine ecosystems. However, we know little about the role of transgenerational effects of metals and MHWs in shaping the offspring's vulnerability to these stressors. We addressed this fundamental knowledge gap by exposing the planktonic copepod Pseudodiaptomus incisus to copper (Cu: control, 15 and 60 μg L^-1) under 2 temperatures (30 and a simulated marine heatwave at 34 °C) in the first generation (F1) and 16 treatments in F2: offspring from each of 4 F1 conditions (control or 15 μg Cu L^-1 × 30 or 34 °C) was reared in 4 F2 conditions (control or 15 μg Cu L^-1 × 30 or 34 °C). We assessed changes in copepod performance, particularly survival, adult size, grazing, and reproduction. In F1, Cu or marine heatwave (MHW) exposures reduced all fitness traits of F1; the effects were particularly strong when both stressors were present. Transgenerational effects of Cu or MHW also strongly reduced F2 performance. Direct Cu and MHW effects on the offspring were further strengthened by transgenerational effects, resulting in more substantial reductions in F2 performance when both generations were exposed to these stressors. As copepods are major food resources for corals, shrimps, or fish larvae and juveniles, strong transgenerational and direct effects of Cu and MHW can have a cascading effect on entire coastal food webs. These results highlight the importance of considering the interaction of transgenerational and direct effects of multiple stressors, particularly relevant for short-lived organisms in tropical marine ecosystems.

Differential gene expression profile of male and female copepods in response to cadmium exposure

In this study, the whole transcriptome and sex-specific differential gene expression of the copepod Pseudodiaptomus annandalei exposed to cadmium (Cd) were investigated. P. annandalei were exposed to 40 μg/L Cd from the naupliar stage to male and female adults. High-throughput transcriptome sequencing (RNA-seq) was performed with copepod samples using an Illumina Hiseq™ 2000 platform. TransDecoder analysis found 32,625 putative open reading frame contigs. At p-values of <0.001, a total of 4756 differentially expressed genes (DEGs) (2216 up-regulated and 2540 down-regulated genes) were found in male copepods. Whereas a total of 2879 DEGs (2007 up-regulated and 872 down-regulated genes) were found in female copepods. A few selected cellular stress response genes, involved in xenobiotic metabolism, energy metabolism, growth, and development as a result of Cd exposure in the copepods were discussed. The study showed that most of these processes were changed in a sex-specific manner, accounting for the different sensitivities of male and female copepods. Results suggest and reinforce that sex is an important factor to be considered in ecotoxicogenomics.

Contrasting Effects of Predation Risk and Copper on Copepod Respiration Rates

Natural biotic and anthropogenic stressors can interact to alter contaminant toxicity. Energetic restrictions are potential mechanisms causing this pattern. To identify processes underlying observed effects of predation risk and copper (Cu) on delayed copepod age at maturity, we examined how these 2 stressors affect respiration rates. We tested 2 very different copepod species: the large, pelagic calanoid Calanus finmarchicus and the small, semibenthic harpacticoid Tigriopus brevicornis. Adult individuals were exposed for 12 h to the treatments: predation risk, Cu (23 µg L^-1 ), combined predation risk and Cu (23 µg L^-1 ), or control. Oxygen concentrations were monitored continuously. The 2 species differed in their responses. We found no clear effects of either stressor in C. finmarchicus. In T. brevicornis, predation risk increased respiration rates, whereas Cu alone had little impact. In contrast, combined exposure to predation risk and Cu interacted to reduce respiration rates to less than expected. We further observed an effect of sex because female-biased T. brevicornis replicates were more sensitive to both predation risk (increased respiration rates) and Cu exposure (reduced respiration rates). The present study provides further evidence that predation risk can interact with copepod responses toward Cu exposure. Interactive effects of biotic stressors ought to be considered to improve future marine environmental monitoring. Environ Toxicol Chem 2020;39:1765-1773. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Development of metal adaptation in a tropical marine zooplankton

Tropical marine ecosystems are highly vulnerable to pollution and climate change. It is relatively unknown how tropical species may develop an increased tolerance to these stressors and the cost of adaptations. We addressed these issues by exposing a keystone tropical marine copepod, Pseudodiaptomus annandalei, to copper (Cu) for 7 generations (F1–F7) during three treatments: control, Cu and pCu (the recovery treatment). In F7, we tested the “contaminant-induced climate change sensitivity” hypothesis (TICS) by exposing copepods to Cu and extreme temperature. We tracked fitness and productivity of all generations. In F1, Cu did not affect survival and grazing but decreased nauplii production. In F2-F4, male survival, grazing, and nauplii production were lower in Cu, but recovered in pCu, indicating transgenerational plasticity. Strikingly, in F5-F6 nauplii production of Cu-exposed females increased, and did not recover in pCu. The earlier result suggests an increased Cu tolerance while the latter result revealed its cost. In F7, extreme temperature resulted in more pronounced reductions in grazing, and nauplii production of Cu or pCu than in control, supporting TICS. The results suggest that widespread pollution in tropical regions may result in high vulnerability of species in these regions to climate change.

Genotoxic Response and Mortality in 3 Marine Copepods Exposed to Waterborne Copper

Copper (Cu) is an essential trace metal, but may also be toxic to aquatic organisms. Although many studies have investigated the cytotoxicity of Cu, little is known about the in vivo genotoxic potential of Cu in marine invertebrates. We investigated the genotoxicity of Cu in 2 pelagic calanoid copepods, Acartia tonsa and Temora longicornis, and the intertidal harpacticoid copepod Tigriopus brevicornis by exposing them for 6 and 72 h to waterborne Cu (0, 6, and 60 µg Cu/L). A subsequent 24-h period in filtered seawater was used to investigate delayed effects or recovery. Genotoxicity was evaluated as DNA strand breaks in individual copepods using the comet assay. Copper did not increase DNA strand breaks in any of the species at any concentration or time point. The treatment did, however, cause 100% mortality in A. tonsa following exposure to 60 µg Cu/L. Acartia tonsa and T. longicornis were more susceptible to Cu-induced mortality than the benthic harpacticoid T. brevicornis, which appeared to be unaffected by the treatments. The results show major differences in Cu susceptibility among the 3 copepods and also that acute toxicity of Cu to A. tonsa is not directly associated with genotoxicity. We also show that the comet assay can be used to quantify genotoxicity in individual copepods. Environ Toxicol Chem 2019;38:2224-2232. © 2019 SETAC.

Insights into the morphology and molecular characterisation of glacial relict Eurytemoralacustris (Poppe, 1887) (Crustacea, Copepoda, Calanoida, Temoridae)

Eurytemoralacustris (Poppe, 1887) is a stenothermic glacial relict whose narrow environmental requirements make it an indicator species for good ecological conditions. The primary threats to this species are eutrophication and global warming. Many authors have described E.lacustris in taxonomic keys; however, its morphological description is unsatisfactory. Therefore, in this study, we aimed to review morphological characteristics of E.lacustris that were previously undescribed in the literature and to provide the molecular characteristics based on the two conservative mitochondrial genes: cytochrome c oxidase I (COI) and cytochrome b (cytb). The new record of E.lacustris indicates that it is a more widespread species than previously hypothesized. Width-to-length ratio of the last female endopod segment of legs indicates variation among the widely distributed species of the genus in Europe (i.e., E.lacustris, E.velox (Lilljeborg, 1853), and E.affinis (Poppe, 1880)). We also found variability of number of setae on the second segment of male endopod. Furthermore, our analysis confirms the occurrence of species in different than exclusively freshwater habitats.

Selection of biochemical and physiological parameters in the croaker Micropogonias furnieri as biomarkers of chemical contamination in estuaries using a generalized additive model (GAM)

Biochemical and physiological parameters in the croaker Micropogonias furnieri were evaluated as biomarkers of chemical contaminants in estuaries. Juvenile croakers (10-20 cm total body length) were collected in summer and winter (2011 and 2012), in two sites at the Lagoa dos Patos estuary (southern Brazil). Fish were also collected in summer (2011 and 2012) in one site at the Barra do Chui estuary (southern Brazil). Tissue (gills, muscle or liver) samples were dissected and analyzed for contaminants [metals, polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs)] and selected biochemical and physiological parameters [metallothionein-like proteins (MTLP), acetylcholinesterase (AChE) activity, ethoxyresorufin-O-deethylase (EROD) activity, and lipid peroxidation (LPO)]. Additionally, water samples were collected for water chemical analyses (salinity, pH, temperature, dissolved oxygen, total alkalinity, and sulfate concentration). Data obtained were integrated and analyzed, using Principal Component Analysis (PCA) and Generalized Additive Model (GAM) approaches. Results showed that changes in concentrations of chemical contaminants and responses of biochemical and physiological parameters did not show any pattern according to the site, season and year of fish collection. However, they were influenced by fish body length and water temperature and salinity. Liver LPO and EROD activity were not responsive to PAHs. However, liver LPO was responsive to HCB, p,p-DDD, p,p-DDT and endosulfan sulfate. In turn, gill MTLP concentration, muscle AChE activity and liver EROD activity were responsive to non-essential metals (Pb, Cd and Ag). Considering that the ecotoxicological modeling approach adopted (GAM) accounted for biological, spatial and temporal variability of data associated with fish body size and site, season and year of fish collection, gill MTLP concentration, muscle AChE activity, as well as liver LPO and EROD activity can be considered as reliable biomarkers of fish exposure to chemical contaminants in estuaries.

Predation Risk Potentiates Toxicity of a Common Metal Contaminant in a Coastal Copepod

To examine whether natural stressors like predation risk affect responses to anthropogenic contaminants, we exposed nauplii of the copepod Tigriopus brevicornis to chemical cues from fish (kairomones) and copper (Cu). We tested effects of these treatments, singly and combined, on copepod age and size at maturity, and development stage sensitivity, while controlling for effects of genetic heterogeneity (clutch identity). Predation risk, Cu and clutch identity interacted in their effect on development time. Predation risk alone had minor effects, but potentiated Cu toxicity in the combined treatment by doubling the delay in age at maturity, as compared to Cu exposure alone. This potentiating effect on developmental delay appeared already at the first copepodite stage. The specific strength of response varied among nauplii from different females' clutches. There were no differences in copepod size at maturity among treatments. We did, however, find an interaction between the effect of Cu and clutch identity on copepod growth. Our results demonstrate the importance of ecological interactions for potentiating the toxicity of environmental contaminants. We also demonstrate the need to consider genetic heterogeneity in ecotoxicology. Natural variation in stressor responses has implications for the interpretation of results from toxicological studies using single-clone or inbred culture populations.

Impacts of the combined exposure to seawater acidification and arsenic on the proteome of Crassostrea angulata and Crassostrea gigas

Proteomic analysis was performed to compare the effects of Arsenic (As), seawater acidification (Low pH) and the combination of both stressors (Low pH + As) on Crassostrea angulata and Crassostrea gigas juveniles in the context of global environmental change. This study aimed to elucidate if two closely related Crassostrea species respond similarly to these environmental stressors, considering both single and combined exposures, to infer if the simultaneous exposure to both stressors induced a differentiated response. Identification of the most important differentially expressed proteins between conditions revealed marked differences in the response of each species towards single and combined exposures, evidencing species-related differences towards each experimental condition. Moreover, protein alterations observed in the combined exposure (Low pH + As) were substantially different from those observed in single exposures. Identified proteins and their putative biological functions revealed an array of modes of action in each condition. Among the most important, those involved in cellular structure (Actin, Atlastin, Severin, Gelsolin, Coronin) and extracellular matrix modulation (Ependymin, Tight junction ZO-1, Neprilysin) were strongly regulated, although in different exposure conditions and species. Data also revealed differences regarding metabolic modulation capacity (ATP β, Enolase, Aconitate hydratase) and oxidative stress response (Aldehyde dehydrogenase, Lactoylglutathione, Retinal dehydrogenase) of each species, which also depended on single or combined exposures, illustrating a different response capacity of both oyster species to the presence of multiple stressors. Interestingly, alterations of piRNA abundance in C. angulata suggested genome reconfiguration in response to multiple stressors, likely an important mode of action related to adaptive evolution mechanisms previously unknown to oyster species, which requires further investigation. The present findings provide a deeper insight into the complexity of C. angulata and C. gigas responses to environmental stress at the proteome level, evidencing different capacities to endure abiotic changes, with relevance regarding the ecophysiological fitness of each species and competitive advantages in a changing environment.

Effects of short- and long-term exposures to copper on lethal and reproductive endpoints of the harpacticoid copepod Tigriopus fulvus

The long-term exposure provides a realistic measurement of the effects of toxicants on aquatic organisms. The harpacticoid copepod Tigriopus fulvus has a wide geographical distribution and is considered as an ideal model organism for ecotoxicological studies for its good sensitivity to different toxicants. In this study, acute, sub-chronic and chronic toxicity tests based on lethal and reproductive responses of Tigriopus fulvus to copper were performed. The number of moults during larval development was chosen as an endpoint for sub-chronic test. Sex ratio, inhibitory effect on larval development, hatching time, fecundity, brood number, nauplii/brood, total newborn production, etc, were calculated in the chronic test (28d). Lethal effect of copper to nauplii showed the LC50-48h of 310 ± 72µgCu/L (mean ± sd). It was observed a significant inhibition of larval development at sublethal copper concentrations, after 4 and 7 d. After 4d, the EC50 value obtained for the endpoint in "moult naupliar reduction" was of 55.8 ± 2.5µgCu/L (mean ± sd). The EC50 for the inhibition of naupliar development into copepodite stage, was of 21.7 ± 4.4µgCu/L (mean ± sd), after 7 days. Among the different traits tested, copper did not affect sex ratio and growth, while fecundity and total nauplii production were the most sensitive endpoints. The reproductive endpoints offer the advantage of being detectable at very low pollutant concentrations.

Do microplastic particles affect Daphnia magna at the morphological, life history and molecular level?

Microplastic particles are ubiquitous not only in marine but also in freshwater ecosystems. However, the impacts of microplastics, consisting of a large variety of synthetic polymers, on freshwater organisms remains poorly understood. We examined the effects of two polymer mixtures on the morphology, life history and on the molecular level of the waterflea Daphnia magna (three different clones). Microplastic particles of ~40 μm were supplied at a low concentration (1% of the food particles) leading to an average of ~30 particles in the digestive tract which reflects a high microplastic contamination but still resembles a natural situation. Neither increased mortality nor changes on the morphological (body length, width and tail spine length) or reproductive parameters were observed for adult Daphnia. The analyses of juvenile Daphnia revealed a variety of small and rather subtle responses of morphological traits (body length, width and tail spine length). For adult Daphnia, alterations in expression of genes related to stress responses (i.e. HSP60, HSP70 & GST) as well as of other genes involved in body function and body composition (i.e. SERCA) were observed already 48h after exposure. We anticipate that the adverse effects of microplastic might be influenced by many additional factors like size, shape, type and even age of the particles and that the rather weak effects, as detected in a laboratory, may lead to reduced fitness in a natural multi-stressor environment.

Effects of triclosan (TCS) on fecundity, the antioxidant system, and oxidative stress-mediated gene expression in the copepod Tigriopus japonicus

Triclosan (TCS) is an antimicrobial agent that has been widely dispersed and detected in the marine environment. However, the effects of TCS in marine invertebrates are poorly understood. In this study, the effects of TCS on life cycle history (e.g. mortality and fecundity) along with cellular reactive oxygen species (ROS) levels, GSH content, antioxidant enzymatic activities, and mRNA expression levels of oxidative stress-mediated genes were measured in the copepod Tigriopus japonicus. The no observed effect concentration (NOEC) and median lethal concentration (LC50) of TCS in the adult stage were determined to be 300μg/L and 437.476μg/L, respectively, while in the nauplius stages the corresponding values were 20μg/L, and 51.76μg/L, respectively. Fecundity was significantly reduced (P<0.05) in response to TCS at 100μg/L. Concentration- and time-dependent analysis of ROS, GSH content (%), and antioxidant enzymatic activities (e.g. GST, GPx, and SOD) were significantly increased (P<0.05) in response to TCS exposure. Additionally, mRNA expression of detoxification (e.g., CYPs) and antioxidant (e.g., glutathione S-transferase-sigma isoforms, Cu/Zn superoxide dismutase, catalase) genes was modulated in response to TCS exposure at different concentrations over a 24h period. Our results revealed that TCS can induce reduced fecundity and oxidative stress with transcriptional regulation of oxidative stress-mediated genes with activation of the antioxidant system in the copepod T. japonicus.

Ultraviolet B radiation induces impaired lifecycle traits and modulates expression of cytochrome P450 (CYP) genes in the copepod Tigriopus japonicus

To evaluate the effects of ultraviolet B (UV-B) radiation at the developmental, reproductive, and molecular levels in aquatic invertebrates, we measured UV-B-induced acute toxicity, impairments in developmental and reproductive traits, and UV-B interaction with the entire family of cytochrome P450 (CYP) genes in the intertidal benthic copepod Tigriopus japonicus. We found a significant, dose-dependent reduction (P<0.05) in the survival of T. japonicus that began as a developmental delay and decreased fecundity. The 48h LD10 and LD50 were 1.35 and 1.84kJ/m², and the CYP inhibitor (PBO) elevated mortality, confirming the involvement of CYP genes in UV-B induced toxicity. Low-dose UV-B (1.5kJ/m²) induced developmental delays, and higher doses (6-18kJ/m²) caused reproductive impairments in ovigerous females. The significant up-regulation of CYP genes belonging to clans 2/3/MT/4/20 in T. japonicus exposed to UV-B (12kJ/m²) confirmed molecular interaction between UV-B and CYP genes. Moreover, orphan CYPs, such as CYP20A1, provide good insight on the deorphanization of invertebrate CYPs. Overall, these results demonstrate the involvement of UV-B radiation in the expression of all the CYP genes in T. japonicus and their susceptibility to UV-B radiation. This will provide a better understanding of the mechanistic effects of UV-B in copepods through the predicted AhR-mediated up-regulation of CYP genes.

Comparative quantitative proteomics unveils putative mechanisms involved into mercury toxicity and tolerance in Tigriopus japonicus under multigenerational exposure scenario

In our earlier work, Tigriopus japonicus were subjected to different mercuric chloride treatments (0-50 μg/L in the seawater) for five generations (F0-F4), and they were subsequently resumed under clean environments for one generation, i.e., F5. Accumulative effects were hypothesized to participate in mercury (Hg) multigenerational toxicity, however phenotypic plasticity could be responsible for metal resistance in this copepod against the long term exposure. Here, we specifically investigated the proteome profiles in the F0, F2, and F5 copepods of the control and 50 μg/L metal treatment, respectively, so as to elucidate the action mechanisms for Hg toxicity/tolerance in T. japonicus under the long term exposure. Functional enrichment analysis showed that a quite different proteomic response was observed in F5 compared with F0 and F2. Namely, the vast majority of enrichments were correlated with the down-regulated proteins in F0 and F2, whereas the enrichments for F5 were mostly attributable to the up-regulated proteins, suggesting that different mechanisms are responsible for Hg toxicity and tolerance (i.e., phenotypic plasticity). Hg toxicity prohibited many proteins in F0 and F2 which are related to several critical processes/pathways, e.g., protein translation, macromolecule metabolic process, DNA replication, cell cycle, cuticle organization, vitellogenesis, etc. In F5, many up-regulated proteins were enriched into compensatory systems, such as carbohydrate metabolism, myosin reorganizations, and stress-related defense pathway. Notably, glycolysis (an oxygen-independent pathway) was enhanced for energy allocation into metal detoxification and tolerance. Taken together, proteomics provides novel mechanistic insights into phenotypic plasticity used by T. japonicus when challenged with cumulative effects due to Hg multigenerational toxicity.

Transcriptional profiling induced by pesticides employed in organic agriculture in a wild population of Chironomus riparius under laboratory conditions

Copper (Cu) and azadirachtin (AZA-A+B) are pesticides allowed in organic agriculture whose environmental risk and toxicity for aquatic wildlife is only partially known. Reverse Transcription Polymerase Chain Reaction was used to assess the molecular effect of acute and short-term exposure (3, 24h) of Cu (0.01, 0.05, 1, 10, 25mgl(-1)) and AZA-A+B (0.2, 0.3, 0.4, 0.5, 1mgl(-1)) on the expression of five candidate genes (hsp70, hsc70, hsp40, hsp10 and cyP450) in a non-target species, Chironomus riparius. Fourth-instar larvae were collected from a mountain stream polluted by agricultural land run-off. All genes were responsive to both pesticides but each gene had a specific response to the different experimental concentrations and exposure times. A few similarities in transcriptional profiling were observed, such as a linear concentration-dependent response of hsp70 after 24h of exposure (at ≥1mgl(-1) of Cu and ≥0.2mgl(-1) of AZA-A+B) and an up-regulation regardless of the concentration of hsc70 after 24h of exposure (at ≥0mgl(-1) of Cu and ≥0.2mgl(-1) of AZA-A+B and the up-regulation of hsp70 after 3h of exposure at ~LC50 (Cu-LC50=26.1±2.5mgl(-1), AZA-A+B-LC50=1.1±0.2mgl(-1)). According to the results, hsp40, hsp10 and cyP450 may be defined as pesticide-dependent (i.e., hsp40 and hsp10 seemed to responded mainly to AZA-A+B and cyP450 to Cu), while hsc70 as time-dependent regardless of the pesticide (i.e., hsc70 responded only after 24h of treatment with Cu and AZA-A+B). This study gives new insights on the potential role of the C. riparius's hsps and cyP450 genes as sensitive biomarkers for freshwater monitoring.

β-Naphthoflavone induces oxidative stress in the intertidal copepod, Tigriopus japonicus

β-Naphtoflavone (β-NF) is a flavonoid and enhances oxidative stress in vertebrates with little information from aquatic invertebrates as yet. In this study, we investigated the effects of β-NF on the antioxidant defense systems of the intertidal copepod Tigriopus japonicus. To measure the β-NF-triggered changes in oxidative stress markers, such as intracellular reactive oxygen species (ROS), glutathione (GSH) concentration, residual glutathione S-transferase (GST), glutathione peroxidase (GPx), glutathione reductase (GR), and superoxide dismutase (SOD) activity, T. japonicus were exposed to β-NF (0.5 and 1 mg/L) for 72 h. Significant (P < 0.05) induction of the intracellular ROS content (%) was observed in 1 mg/L of β-NF exposed T. japonicus, compared to the negative control and H2O2-exposed group. The GSH levels were significantly increased in the 0.5 mg/L of β-NF-exposed group for 12 h and 1 mg/L of β-NF-exposed groups for 12-24 h. GPx, GST, and GR activities showed a significant increase in the 1 mg/L β-NF-exposed group, indicating that β-NF induces oxidative stress in T. japonicus. To understand the effects of β-NF at the level of transcript expression, a 6K microarray analysis was employed. Transcript profiles of selected antioxidant-related genes were modulated after 72 h exposure to 1 mg/L of β-NF. From microarray data, 10 GST isoforms, GR, GPx, PH-GPx, and Se-GPx were chosen for a time-course test by real-time RT-PCR. T. japonicus GST-S, GST-O, GST-M, and GST-D1 were significantly increased in a 1 mg/L β-NF-exposed group. T. japonicus GPx, GR, and Se-GPx mRNA levels were also significantly increased at both concentrations. Our results revealed that oxidative stress was induced by β-NF exposure in T. japonicus.

Acclimation and adaptation to common marine pollutants in the copepod Tigriopus californicus

Establishing water quality criteria using bioassays is complicated by variation in chemical tolerance between populations. Two major contributors to this variation are acclimation and adaptation, which are both linked to exposure history, but differ in how long their effects are maintained. Our study examines how tolerance changes over multiple generations of exposure to two common marine pollutants, copper (Cu) and tributyltin oxide (TBTO), in a sexually reproducing marine copepod, Tigriopus californicus. Lines of T. californicus were chronically exposed to sub-lethal levels of Cu and TBTO for 12 generations followed by a recovery period of 3 generations in seawater control conditions. At each generation, the average number of offspring produced and survived to 28 d was determined and used as the metric of tolerance. Lines exposed to Cu and TBTO showed an overall increase in tolerance over time. Increased Cu tolerance arose by generation 3 in the chronically exposed lines and was lost after 3 generations in seawater control conditions. Increased TBTO tolerance was detected at generation 7 and was maintained even after 3 generations in seawater control conditions. It was concluded from this study that tolerance to Cu is consistent with acclimation, a quick gain and loss of tolerance. In contrast, TBTO tolerance is consistent with adaptation, in which onset of tolerance was delayed relative to an acclimation response and maintained in the absence of exposure. These findings illustrate that consideration of exposure history is necessary when using bioassays to measure chemical tolerance.

Ecotoxicity of triphenyltin on the marine copepod Tigriopus japonicus at various biological organisations: from molecular to population-level effects

Triphenyltin compounds (TPTs), as effective biocides for different industrial and agricultural purposes, have been detected in coastal marine environments worldwide, in particular in Asian countries. However, little is known about their toxicity to marine organisms. This study comprehensively investigated the molecular, individual and population responses of the marine copepod, Tigriopus japonicus upon waterborne exposure to TPT chloride (TPTCl). Our results indicated that TPTCl was highly toxic to adult T. japonicus, with a 96-h LC50 concentration at 6.3 μg/L. As shown in a chronic full life-cycle test, T. japonicus exposed to 1.0 μg/L TPTCl exhibited a delay in development and a significant reduction of population growth, in terms of the intrinsic rate of increase (r m ). Based on the negative relationship between the r m and exposure concentration, a critical effect concentration was estimated at 1.6 μg/L TPTCl; at or above which population extinction could occur. At 0.1 μg/L TPTCl or above, the sex ratio of the second generation of the copepod was significantly altered and changed to a male-biased population. At molecular level, the inhibition of the transcriptional expression of glutathione S-transferase related genes might lead to dysfunction of detoxification, and the inhibition of retinoid X receptor mRNA expression implied an interruption of the growth and moulting process in T. japonicus. As the only gene that observed up-regulated in this study, the expression of heat shock protein 70 (hsp70) increased in a concentration-dependent manner, indicating its function in protecting the copepod from TPT-mediated oxidative stress. The study advances our understanding on the ecotoxicity of TPT, and provides some initial data on its toxic mechanisms in small crustaceans like copepods.

Crude oil exposure results in oxidative stress-mediated dysfunctional development and reproduction in the copepod Tigriopus japonicus and modulates expression of cytochrome P450 (CYP) genes

In this study, we investigated the effects of the water-accommodated fraction (WAF) of crude oil on the development and reproduction of the intertidal copepod Tigriopus japonicus through life-cycle experiments. Furthermore, we investigated the mechanisms underlying the toxic effects of WAF on this benthic organism by studying expression patterns of cytochrome P450 (CYP) genes. Development of T. japonicus was delayed and molting was interrupted in response to WAF exposure. Hatching rate was also significantly reduced in response to WAF exposure. Activities of antioxidant enzymes such as glutathione S-transferase (GST), glutathione reductase (GR), and catalase (CAT) were increased by WAF exposure in a concentration-dependent manner. These results indicated that WAF exposure resulted in oxidative stress, which in turn was associated with dysfunctional development and reproduction. To evaluate the involvement of cytochrome P450 (CYP) genes, we cloned the entire repertoire of CYP genes in T. japonicus (n=52) and found that the CYP genes belonged to five different clans (i.e., Clans 2, 3, 4, mitochondrial, and 20). We then examined expression patterns of these 52 CYP genes in response to WAF exposure. Three TJ-CYP genes (CYP3024A2, CYP3024A3, and CYP3027C2) belonging to CYP clan 3 were significantly induced by WAF exposure in a time- and concentration-dependent manner. We identified aryl hydrocarbon responsive elements (AhRE), xenobiotic responsive elements (XREs), and metal response elements (MRE) in the promoter regions of these three CYP genes, suggesting that these genes are involved in detoxification of toxicants. Overall, our results indicate that WAF can trigger oxidative stress and thus induce dysfunctional development and reproduction in the copepod T. japonicus. Furthermore, we identified three TJ-CYP genes that represent potential biomarkers of oil pollution.

Development of enzyme-linked immunosorbent assay (ELISA) for glutathione S-transferase (GST-S) protein in the intertidal copepod Tigriopus japonicus and its application for environmental monitoring

To utilize the GST-S protein as a useful biomarker for environmental contamination, we developed a polyclonal antibody-based enzyme-linked immunosorbent assay (ELISA) in the intertidal copepod Tigriopus japonicus. Two polyclonal antibodies, TJ-GST-S1 and TJ-GST-S2, were raised against two TJ-GST-S synthetic peptides. Also a recombinant TJ-GST-S protein was purified as a standard for ELISA development. Each polyclonal antibody was tested by Western blot analysis and indirect ELISA. Of two polyclonal antibodies, TJ-GST-S2 ELISA was further employed due to its wide range of detection and the limit of specificity compared to those of TJ-GST-S1 ELISA system. After exposure to 4 metals (Ag, As, Cd, and Cu) to T. japonicus, the amount of TJ-GST-S protein was significantly elevated in a concentration-dependent manner. Also, TJ-GST-S protein was upregulated at relative high concentrations of B[α]P, PCB, and TBT. In this paper, we suggest that T. japonicas ELISA for TJ-GST-S2 is useful as a potential indicator system for marine contaminants.

Expression profile analysis of antioxidative stress and developmental pathway genes in the manganese-exposed intertidal copepod Tigriopus japonicus with 6K oligochip

Manganese (Mn) provides one of aquatic pollutants in marine ecosystem. Here we used a 6K oligomicroarray to identify the effect of Mn on transcriptomes in the copepod Tigriopus japonicus. A total of 5594 spots were significantly modulated on a 6K oligomicroarray with hierarchical clustering after exposure to Mn over 24h. Of them, 186 and 489 genes were significantly upregulated and downregulated, respectively. Particularly, several genes involved in stress, detoxification, and developmental functions were significantly modulated in T. japonicus exposed for 24h. In detail, Mn exposure specifically up-regulated genes that were related to intracellular stress, antioxidant, and detoxification pathways such as cytochrome P450s (CYPs), glutathione S-transferases (GSTs), and heat shock proteins (hsps), while a majority of downregulated genes was associated with developmental pathways such as cuticle protein, ecdysone receptor, and vitellogenin. These results demonstrated that Mn exposure modulated gene expression in relation to intracellular stress, leading to developmental retardation in the intertidal copepod, T. japonicus, and provide a better understanding of mechanistic molecular studies of Mn-induced cellular damage.

Copper induces apoptotic cell death through reactive oxygen species-triggered oxidative stress in the intertidal copepod Tigriopus japonicus

The copepod, Tigriopus japonicus is an important model for toxicity testing. However, no attempt has been made in analyzing the effect of toxicants at the level of the ROS-mediated signal transduction pathway. To understand copper-induced cytotoxicity at the molecular level, we employed several cellular and biochemical assays after exposure to copper, and found a significant induction of enzyme activities of antioxidant proteins with increased intracellular reactive oxygen species (ROS) as well as an increase of TUNEL-positive cells, but a decrease of BrdU-positive cells. In addition, several important genes such as p38 MAPK, antioxidant-related genes, Hsps, and apoptosis-related genes were significantly modulated by copper exposure. Taken together, we suggest that copper-induced cytotoxicity is mediated by the formation of intracellular ROS and oxidative stress in T. japonicus. Whole body biochemical assays such as TUNEL- and BrdU-assay will provide a better understanding of cellular responses such as apoptosis and cell death upon cytotoxic exposure of copper in T. japonicus.

Acute and chronic toxicities of Irgarol alone and in combination with copper to the marine copepod Tigriopus japonicus

Irgarol 1051 has been widely used as a booster biocide in combination with copper (Cu) in antifouling paints. The combined toxicity of Irgarol with Cu on marine organisms, however, has not been fully investigated. This study investigated the acute and chronic toxicities of binary mixtures of Irgarol and CuSO(4) to the marine copepod Tigriopus japonicus. The acute combined toxicity of Irgarol and Cu was simple additive as revealed by two response surface models and their contours. However, based on chronic full life-cycle tests, when Irgarol was combined with Cu at an environmentally realistic concentration (10 μg L(-1)), a slightly synergistic effect was observed at a high Irgarol concentration (940 μg L(-1)), as shown by a significant increase in larval mortality. As Cu contamination is widespread in coastal environments, our results entail the importance of considering the combined toxic effect of the booster biocide and Cu for setting ecologically realistic water quality criteria.

A plea for the use of copepods in freshwater ecotoxicology

Standard species used in ecological risk assessment are chosen based on their sensitivity to various toxicants and the ease of rearing them for laboratory experiments. However, this mostly overlooks the fact that species in the field that may employ variable life-history strategies, which may have consequences concerning the vulnerability of such species to exposure with contaminants. We aimed to highlight the importance of copepods in ecology and to underline the need to include freshwater copepods in ecotoxicology. We carried out a literature search on copepods and Daphnia in ecology and ecotoxicology to compare the recognition given to these two taxa in these respective fields. We also conducted a detailed analysis of the literature on copepods and their current role in ecotoxicology to characterize the scale and depth of the studies and the ecotoxicological information therein. The literature on the ecology of copepods outweighed that in ecotoxicology when compared with daphnids. Copepods, like other zooplankton, were found to be sensitive to toxicants and important organisms in aquatic ecosystems. The few studies that were conducted on the ecotoxicology of copepods mainly focused on marine copepods. However, very little is known about the ecotoxicology of freshwater copepods. To enable a more realistic risk higher tier environmental risk assessment, we recommend considering freshwater copepods as part of the hazard assessment process. This could include the establishment of laboratory experiments to analyse the effects of toxicants on copepods and the development of individual-based models to extrapolate effects across species and scenarios.

Transcriptomics of coping strategies in free-swimming Lepeophtheirus salmonis (Copepoda) larvae responding to abiotic stress

The salmon louse Lepeophtheirus salmonis is a marine ectoparasite of wild and farmed salmon in the Northern Hemisphere. Infections of farmed salmon are of economic and ecological concern. Nauplius and copepodid salmon lice larvae are free-swimming and disperse in the water column until they encounter a host. In this study, we characterized the sublethal stress responses of L. salmonis copepodid larvae by applying a 38K oligonucleotide microarray to profile transcriptomes following 24 h exposures to suboptimal salinity (30–10 parts per thousand (‰)) or temperature (16–4 °C) environments. Hyposalinity exposure resulted in large-scale gene expression changes relative to those elicited by a thermal gradient. Subsequently, transcriptome responses to a more finely resolved salinity gradient between 30 ‰ and 25 ‰ were profiled. Minimal changes occurred at 29 ‰ or 28 ‰, a threshold of response was identified at 27 ‰, and the largest response was at 25 ‰. Differentially expressed genes were clustered by pattern of expression, and clusters were characterized by functional enrichment analysis. Results indicate larval copepods adopt two distinct coping strategies in response to short-term hyposaline stress: a primary response using molecular chaperones and catabolic processes at 27 ‰; and a secondary response up-regulating ion pumps, transporters, a different suite of chaperones and apoptosis-related transcripts at 26 ‰ and 25 ‰. The results further our understanding of the tolerances of L. salmonis copepodids to salinity and temperature gradients and may assist in the development of salmon louse management strategies.

Transcriptional responses of heat shock protein 70 (Hsp70) to thermal, bisphenol A, and copper stresses in the dinoflagellate Prorocentrum minimum

The heat shock protein 70 (Hsp70) family is an important part of the cell's machinery for protein folding, and helps to protect cells from environmental stress. Although Hsp70 functions have been discovered in various organisms, studies on dinoflagellate Hsps are limited, except for a few phylogenetic attempts. In this study, we sequenced the complete open reading frame of the dinoflagellate Prorocentrum minimum Hsp70 (PmHsp70), and characterized its molecular functions. The putative PmHsp70 protein contained 3 signature patterns of the Hsp70 family. Phylogenetic analysis revealed that PmHsp70 belonged to the dinoflagellate clade. Real-time (RT)-PCR analyses revealed that PmHsp70 was upregulated by thermal stress. Further, we examined the transcriptional response of PmHsp70 to copper (Cu) and bisphenol A (BPA) exposures. In toxicity assays, Cu and BPA exhibited EC(50)-72 h values of 1.07 ± 0.138 mg L(-1) and 1.51 ± 0.110 mg L(-1), respectively, in P. minimum. Expression of PmHsp70 was significantly upregulated in response to Cu and BPA exposures (one-way ANOVA, P<0.05). PmHsp70 displayed different expression patterns in response to different concentrations of Cu and BPA. This study evaluated typical characteristics and, for the first time, toxicant-related functions of PmHsp70. The results suggest that Hsp70 genes may play a vital role in the environmental stress responses of dinoflagellates.

Gene expression patterns and stress response in marine copepods

Aquatic organisms are constantly exposed to both physical (e.g. temperature and salinity variations) and chemical (e.g. endocrine disruptor chemicals, heavy metals, hydrocarbons, diatom toxins, and other toxicants) stressors which they react to by activating a series of defense mechanisms. This paper reviews the literature on the defense systems, including detoxification enzymes and proteins (e.g. glutathione S-transferases, heat shock proteins, superoxide dismutase and catalase), studied in copepods at the molecular level. The data indicate high inter- and intra-species variability in copepod response, depending on the type of stressor tested, the concentration and exposure time, and the enzyme isoform studied. Ongoing -omics approaches will allow the identification of new genes which will give a more comprehensive overview of how copepods respond to specific stressors in laboratory and/or field conditions and the effects of these responses on higher trophic levels.

8-Oxoguanine DNA glycosylase 1 (OGG1) from the copepod Tigriopus japonicus: molecular characterization and its expression in response to UV-B and heavy metals

8-Oxoguanine DNA glycosylase 1 (EC 3.2.2.23) is encoded by OGG1 gene and plays a key role in removing 8-oxo-7,8-dihydroguanine (8-oxoG) base in DNA lesion by reactive oxygen species (ROS). To identify and characterize OGG1 gene (TJ-OGG1) in the copepod Tigriopus japonicus, the full-length cDNA sequence, genomic structure, and promoter region was analyzed. In addition, to investigate transcriptional change of TJ-OGG1 mRNA under oxidative stress conditions, T. japonicus were exposed to environmental oxidative inducers, H(2)O(2), UV-B, and heavy metals (Cd, Cu, and Zn), respectively. The full-length cDNA of TJ-OGG1 gene was 1708 bp in length, encoding 343 amino acid residues. The deduced amino acid sequences of TJ-OGG1 showed a 56% similarity with human. Two conserved motifs (HhH and PVD loop) and two conserved residues (lysine and aspartic acid) in active sites were also observed. TJ-OGG1 genome structure contained six exons and five introns and putative transcription factor binding sites such as Nrf-2, p53, ERE-half sites, and XRE were detected on the promoter region. TJ-OGG1 mRNA level was increased at approximately three-fold (P<0.05) at 1mM and approximately 4-fold (P<0.01) at 10mM of H(2)O(2), respectively. UV-B enhanced the expression of TJ-OGG1 mRNA at 15kJ/m(2) (P<0.05) and more (P<0.001). In a time-course experiment, TJ-OGG1 gene was highly transcribed within 12h after exposure of 10 kJ/m(2) (P<0.01) and 20 kJ/m(2) (P<0.001). The expression of TJ-OGG1 mRNA after exposure to Cu and Cd for 96 h was significantly up-regulated at 0.1 μg/L and then remarkably reduced in a dose-dependent manner. Their transcript levels did not change at low dose (0.1 and 1 μg/L) but were dose-dependently down-regulated at high dose (10 and 100 μg/L). These findings suggest that H(2)O(2), UV-B, and heavy metals induce oxidative stress and generate oxidatively damaged DNA. Consequently, the enhanced TJ-OGG1 gene expression would be associated with active involvement of TJ-OGG1 gene in DNA repair process as a cellular protection mechanism. This is the first report on the cloning and characterization of OGG1 gene in aquatic animals. This study is helpful for a better understanding of the molecular mechanisms of cellular protection against various environmental oxidative stress inducers such as UV-B and heavy metals in aquatic invertebrates.

Expression pattern analysis of DNA repair-related and DNA damage response genes revealed by 55K oligomicroarray upon UV-B irradiation in the intertidal copepod, Tigriopus japonicus

Ultraviolet-B (UV-B) radiation affects the genome stability of aquatic organisms by absorption of certain wavelength at the molecular level. Recently, extensive gene information has been identified from the intertidal copepod, Tigriopus japonicus. Here, we developed a 55K (54,254 genes) oligomicroarray and tested its usefulness to identify the effect of single dose of UV-B irradiation (12 kJ/m(2)) on transcriptomes of the copepod T. japonicus. A total of 35,361 spots were identified to be significantly modulated on the 55K oligomicroarray by hierarchical clustering after exposure to UV-B irradiation over 48 h (6, 12, 24, and 48 h). Of them, 1300 and 588 genes were observed to be up-regulated and down-regulated at all time points, respectively. Particularly, it was observed that several genes involved in DNA repair mechanism were significantly modulated in the UV-B-exposed T. japonicus by microarray and quantitative real-time RT-PCR analysis. In detail, UV-B irradiation specifically up-regulated some genes in non-homologous end-joining (NHEJ), homologous recombination (HR), base excision repair (BER), and mismatch repair (MMR) pathways. On the other hand, a majority of down-regulated genes were representatives for the nucleotide excision repair (NER) mechanism. These results demonstrated that DNA damage would be induced by UV-B irradiation in this species, resulting in reliable induction or repression of various DNA repair mechanism on UV-B-induced DNA damage. In this report, we suggest that a high density microarray-based approach for risk assessment of UV-B irradiation would be useful to elucidate the mechanistic analysis in a non-model organism. This study could also provide a better understanding of molecular mechanisms of cellular protection against UV-B-induced stress.

Observing copepods through a genomic lens

Background

Copepods outnumber every other multicellular animal group. They are critical components of the world's freshwater and marine ecosystems, sensitive indicators of local and global climate change, key ecosystem service providers, parasites and predators of economically important aquatic animals and potential vectors of waterborne disease. Copepods sustain the world fisheries that nourish and support human populations. Although genomic tools have transformed many areas of biological and biomedical research, their power to elucidate aspects of the biology, behavior and ecology of copepods has only recently begun to be exploited.

Discussion

The extraordinary biological and ecological diversity of the subclass Copepoda provides both unique advantages for addressing key problems in aquatic systems and formidable challenges for developing a focused genomics strategy. This article provides an overview of genomic studies of copepods and discusses strategies for using genomics tools to address key questions at levels extending from individuals to ecosystems. Genomics can, for instance, help to decipher patterns of genome evolution such as those that occur during transitions from free living to symbiotic and parasitic lifestyles and can assist in the identification of genetic mechanisms and accompanying physiological changes associated with adaptation to new or physiologically challenging environments. The adaptive significance of the diversity in genome size and unique mechanisms of genome reorganization during development could similarly be explored. Genome-wide and EST studies of parasitic copepods of salmon and large EST studies of selected free-living copepods have demonstrated the potential utility of modern genomics approaches for the study of copepods and have generated resources such as EST libraries, shotgun genome sequences, BAC libraries, genome maps and inbred lines that will be invaluable in assisting further efforts to provide genomics tools for copepods.

Summary

Genomics research on copepods is needed to extend our exploration and characterization of their fundamental biological traits, so that we can better understand how copepods function and interact in diverse environments. Availability of large scale genomics resources will also open doors to a wide range of systems biology type studies that view the organism as the fundamental system in which to address key questions in ecology and evolution.

Selenium in water enhances antioxidant defenses and protects against copper-induced DNA damage in the blue mussel Mytilus edulis

Selenium and copper are naturally occurring elements in the environment that have important roles in cellular function. Selenium is known for its role in antioxidant defense, whereas copper is a redox-active metal capable of acting as a pro-oxidant. We investigated the effects of short term selenium (Na(2)SeO(3)) supplementation (4 μg/L for 3 days) on antioxidant parameters of the blue mussel, Mytilus edulis, and its possible protective effects against a subsequent copper (CuSO(4)) exposure (56 μg/L for 3 days). Selenium supplementation caused a 4-fold increase in glutathione levels in gills. The activity of selenium-dependent glutathione peroxidase was modulated by selenium in gills (2-fold increase) and also in cell-free haemolymph (40% increase). Copper exposure produced decreases in protein thiol levels (35%) and in thioredoxin reductase activity (60%) in gills and induced an increase in DNA damage in haemocytes (70% increase in % tail DNA observed using the comet assay). The decrease in thioredoxin reductase activity may constitute a mechanism of copper toxicity in bivalves, warranting further investigation. Pre-treatment with selenium largely prevented these deleterious effects of copper on protein thiols, thioredoxin reductase activity and DNA damage. The results suggest that induction of key antioxidant defenses such as glutathione and selenium-dependent glutathione peroxidase, as a result of selenium supplementation, may play an important role in protection of aquatic organisms against oxidative stress.

Using comparative genomic hybridization to survey genomic sequence divergence across species: a proof-of-concept from Drosophila

Background

Genome-wide analysis of sequence divergence among species offers profound insights into the evolutionary processes that shape lineages. When full-genome sequencing is not feasible for a broad comparative study, we propose the use of array-based comparative genomic hybridization (aCGH) in order to identify orthologous genes with high sequence divergence. Here we discuss experimental design, statistical power, success rate, sources of variation and potential confounding factors. We used a spotted PCR product microarray platform from Drosophila melanogaster to assess sequence divergence on a gene-by-gene basis in three fully sequenced heterologous species (D. sechellia, D. simulans, and D. yakuba). Because complete genome assemblies are available for these species this study presents a powerful test for the use of aCGH as a tool to measure sequence divergence.

Results

We found a consistent and linear relationship between hybridization ratio and sequence divergence of the sample to the platform species. At higher levels of sequence divergence (< 92% sequence identity to D. melanogaster) ~84% of features had significantly less hybridization to the array in the heterologous species than the platform species, and thus could be identified as "diverged". At lower levels of divergence (≥ 97% identity), only 13% of genes were identified as diverged. While ~40% of the variation in hybridization ratio can be accounted for by variation in sequence identity of the heterologous sample relative to D. melanogaster, other individual characteristics of the DNA sequences, such as GC content, also contribute to variation in hybridization ratio, as does technical variation.

Conclusions

Here we demonstrate that aCGH can accurately be used as a proxy to estimate genome-wide divergence, thus providing an efficient way to evaluate how evolutionary processes and genomic architecture can shape species diversity in non-model systems. Given the increased number of species for which microarray platforms are available, comparative studies can be conducted for many interesting lineages in order to identify highly diverged genes that may be the target of natural selection.

The copepod Tigriopus japonicus genomic DNA information (574Mb) and molecular anatomy

The intertidal copepod, Tigriopus japonicus, has been recognized as a promising model species for marine environmental genomics. To obtain extensive genomic DNA sequences from this species, we sequenced genomic DNA from adult copepods using genomic sequencers GS-FLX and GS-FLX-Titanium and attained 1,914,995 reads (average read length 299.8 bp) including 574.2 Mb of genomic DNA information. After subjecting them to assembly, we acquired 193,642 contigs (total contigs length 129.7 Mb), and finally were able to obtain 10,894 unigenes (E-value>0.1; length>200 bp) containing 33,081,455 bp after a nonredundant (NR) blast search. In this paper, we summarize the genomic DNA sequences of T. japonicus and discuss its potential use in environmental genomics and ecotoxicological studies for uncovering mechanisms of environmental stresses and chemical toxicities to marine crustaceans.