Identification of Methylmercury Tolerance Gene Candidates in Drosophila

Methylmercury (MeHg) is a ubiquitous environmental contaminant that preferentially targets the developing nervous system. Variable outcomes of prenatal MeHg exposure within a population point to a genetic component that regulates MeHg toxicity. We therefore sought to identify fundamental MeHg tolerance genes using the Drosophila model for genetic and molecular dissection of a MeHg tolerance trait. We observe autosomal dominance in a MeHg tolerance trait (development on MeHg food) in both wild-derived and laboratory-selected MeHg-tolerant strains of flies. We performed whole-genome transcript profiling of larval brains of tolerant (laboratory selected) and nontolerant (control) strains in the presence and absence of MeHg stress. Pairwise transcriptome comparisons of four conditions (+/−selection and +/−MeHg) identified a “down-down-up” expression signature, whereby MeHg alone and selection alone resulted in a greater number of downregulated transcripts, and the combination of selection + MeHg resulted in a greater number of upregulated transcripts. Functional annotation cluster analyses showed enrichment for monooxygenases/oxidoreductases, which include cytochrome P450 (CYP) family members. Among the 10 CYPs upregulated with selection + MeHg in tolerant strains, CYP6g1, previously identified as the dichlorodiphenyl trichloroethane resistance allele in flies, was the most highly expressed and responsive to MeHg. Among all the genes, Turandot A (TotA), an immune pathway–regulated humoral response gene, showed the greatest upregulation with selection + MeHg. Neural-specific transgenic overexpression of TotA enhanced MeHg tolerance during pupal development. Identification of TotA and CYP genes as MeHg tolerance genes is an inroad to investigating the conserved function of immune signaling and phase I metabolism pathways in MeHg toxicity and tolerance in higher organisms

Fluctuating Water Temperatures Affect Development, Physiological Responses and Cause Sex Reversal in Fathead Minnows

Natural and human activities can result in both high temporal and spatial variability in water temperature. Rapid temperature changes have the potential to dramatically affect physiological processes in aquatic organisms and, due to their limited mobility, fish early life stages are particularly vulnerable to ambient temperature fluctuations. In this study, we examined how the magnitude and frequency of temperature fluctuations affect survival, growth, development, expression of thermoresponsive genes, and gonadal differentiation in fathead minnows, <i>Pimephales promelas</i>. We exposed individuals (0 to 4 days post fertilization) of known genotypic sex to fluctuations of Δ4 °C over 12-h, Δ8 °C over 12- and 24-h, and three stable temperatures (21, 25, and 29 °C) for up to 45 d. Expression of <i>hsp70</i> in fish exposed to the highest-magnitude, highest-frequency fluctuating treatment cycled in concert with temperature and was upregulated initially during exposure, and may have contributed to temperature fluctuations having little effect on time to and size at hatching (whole-organism responses). This treatment also caused fish to undergo nondirectional sex reversal. These results indicate that <i>hsp70</i> may be involved in mediating thermal stress from subdaily temperature fluctuations and that sex determination in fathead minnows can be influenced by cycling temperatures

Vascular toxicity of silver nanoparticles to developing zebrafish (<i>Danio rerio</i>)

<p>Nanoparticles (NPs, 1–100 nm) can enter the environment and result in exposure to humans and other organisms leading to potential adverse health effects. The aim of the present study is to evaluate the effects of early life exposure to polyvinylpyrrolidone-coated silver nanoparticles (PVP-AgNPs, 50 nm), particularly with respect to vascular toxicity on zebrafish embryos and larvae (<i>Danio rerio</i>). Previously published data has suggested that PVP-AgNP exposure can inhibit the expression of genes within the vascular endothelial growth factor (VEGF) signaling pathway, leading to delayed and abnormal vascular development. Here, we show that early acute exposure (0–12 h post-fertilization, hpf) of embryos to PVP-AgNPs at 1 mg/L or higher results in a transient, dose-dependent induction in VEGF-related gene expression that returns to baseline levels at hatching (72 hpf). Hatching results in normoxia, negating the effects of AgNPs on vascular development. Interestingly, increased gene transcription was not followed by the production of associated proteins within the VEGF pathway, which we attribute to NP-induced stress in the endoplasmic reticulum (ER). The impaired translation may be responsible for the observed delays in vascular development at later stages, and for smaller larvae size at hatching. Silver ion (Ag⁺) concentrations were < 0.001 mg/L at all times, with no significant effects on the VEGF pathway. We propose that PVP-AgNPs temporarily delay embryonic vascular development by interfering with oxygen diffusion into the egg, leading to hypoxic conditions and ER stress.</p

Mitochondrial Dysfunction, Disruption of F‑Actin Polymerization, and Transcriptomic Alterations in Zebrafish Larvae Exposed to Trichloroethylene

Trichloroethylene (TCE) is primarily used as an industrial degreasing agent and has been in use since the 1940s. TCE is released into the soil, surface, and groundwater. From an environmental and regulatory standpoint, more than half of Superfund hazardous waste sites on the National Priority List are contaminated with TCE. Occupational exposure to TCE occurs primarily via inhalation, while environmental TCE exposure also occurs through ingestion of contaminated drinking water. Current literature links TCE exposure to various adverse health effects including cardiovascular toxicity. Current studies aiming to address developmental cardiovascular toxicity utilized rodent and avian models, with the majority of studies using relatively higher parts per million (mg/L) doses. In this study, to further investigate developmental cardiotoxicity of TCE, zebrafish embryos were treated with 0, 10, 100, or 500 parts per billion (ppb; μg/L) TCE during embryogenesis and/or through early larval stages. After the appropriate exposure period, angiogenesis, F-actin, and mitochondrial function were assessed. A significant dose–response decrease in angiogenesis, F-actin, and mitochondrial function was observed. To further complement this data, a transcriptomic profile of zebrafish larvae was completed to identify gene alterations associated with the 10 ppb TCE exposure. Results from the transcriptomic data revealed that embryonic TCE exposure caused significant changes in genes associated with cardiovascular disease, cancer, and organismal injury and abnormalities with a number of targets in the FAK signaling pathway. Overall, results from our study support TCE as a developmental cardiovascular toxicant, provide molecular targets and pathways for investigation in future studies, and indicate a need for continued priority for environmental regulation

Combined Effects of \u3ci\u3eDeepwater Horizon\u3c/i\u3e Crude Oil and Environmental Stressors On \u3ci\u3eFundulus grandis\u3c/i\u3e Embryos

In the present study, we examined how sensitivity to oil changes in combination with environmental stressors in Fundulus grandis embryos. We exposed embryos (fertilization) to a range of high‐energy water accommodated fraction (HEWAF) concentrations (0–50 parts per billion [ppb] total polycyclic aromatic hydrocarbons [PAHs]) made from Macondo crude oil in conjunction with various environmental conditions (temperature: 20 and 30 °C; salinity: 3, 7, and 30 practical salinity units [PSU]; and dissolved oxygen: 2 and 6 mg/L). Endpoints included mortality, hatching rates, and expression of cytochrome p450 1a and 1c (cyp1a, cyp1c) in hatched larvae. There was 100% mortality for all fish under the 2 parts per million (ppm) dissolved oxygen regimes. For the 6 mg/L dissolved oxygen treatments, mortality and median lethal time (LT50) were generally higher in the 30 °C treatments versus the 20 °C treatments. Oil increased mortality in fish exposed to the highest concentration in the 20‐3‐6 (°C‐PSU‐mg/L), 25‐7‐6, and 30‐30‐6 conditions. Hatching was driven by environmental conditions, with oil exposure having a significant impact on hatching in only the 25‐7‐6 and 30‐30‐6 groups at the greatest HEWAF exposure. Expression of cyp1a was up‐regulated in most treatment groups versus the controls, with cyp1c expression exhibiting a similar pattern. These data suggest interactive effects among temperature, salinity, and PAHs, highlighting a need to further assess the effects of oil exposure under various environmental conditions. Environ Toxicol Chem 2018;37:1916–1925. © 2018 SETA

Mitochondrial Dysfunction, Disruption of F‑Actin Polymerization, and Transcriptomic Alterations in Zebrafish Larvae Exposed to Trichloroethylene

Trichloroethylene (TCE) is primarily used as an industrial degreasing agent and has been in use since the 1940s. TCE is released into the soil, surface, and groundwater. From an environmental and regulatory standpoint, more than half of Superfund hazardous waste sites on the National Priority List are contaminated with TCE. Occupational exposure to TCE occurs primarily via inhalation, while environmental TCE exposure also occurs through ingestion of contaminated drinking water. Current literature links TCE exposure to various adverse health effects including cardiovascular toxicity. Current studies aiming to address developmental cardiovascular toxicity utilized rodent and avian models, with the majority of studies using relatively higher parts per million (mg/L) doses. In this study, to further investigate developmental cardiotoxicity of TCE, zebrafish embryos were treated with 0, 10, 100, or 500 parts per billion (ppb; μg/L) TCE during embryogenesis and/or through early larval stages. After the appropriate exposure period, angiogenesis, F-actin, and mitochondrial function were assessed. A significant dose–response decrease in angiogenesis, F-actin, and mitochondrial function was observed. To further complement this data, a transcriptomic profile of zebrafish larvae was completed to identify gene alterations associated with the 10 ppb TCE exposure. Results from the transcriptomic data revealed that embryonic TCE exposure caused significant changes in genes associated with cardiovascular disease, cancer, and organismal injury and abnormalities with a number of targets in the FAK signaling pathway. Overall, results from our study support TCE as a developmental cardiovascular toxicant, provide molecular targets and pathways for investigation in future studies, and indicate a need for continued priority for environmental regulation