The study, published online today (Wednesday, Dec. 20) in the journal Environmental Science & Technology, focused on the water flea Daphnia magna, considered the lab rat of ecotoxicology because of its sensitivity to contaminants in its environment. The organism is commonly used by regulators to monitor freshwater toxicity, but the tests used typically look at levels of toxicity that will kill the water flea within 24 hours of exposure.
Those tests employ "a 'kill 'em and count 'em' technique that doesn't provide a great deal of insight into the mechanism of action," said Dr. Chris Vulpe, associate professor of nutritional sciences and toxicology at UC Berkeley's College of Natural Resources and principal investigator of the study.
There also is a chronic toxicity test that assesses the impact of lower levels of exposure on reproduction, but again, exactly how the toxicant is affecting the organism is unclear, the researchers said.
But with toxicogenomics, scientists are hoping to understand toxicants based upon characteristic changes in an organism's gene expression. "By looking at the pattern of genes turned on and off in response to toxicants, we can get an idea of what is causing the toxicity," said Vulpe, who is also a member of the Berkeley Institute for the Environment on campus, which brings together diverse programs and units focused on environmental research. Vulpe worked with Helen Poynton, UC Berkeley graduate student in nutritional sciences and toxicology and lead author of the study.
In an effort to test the viability of gene expression assays in environmental toxicity screening, the researchers exposed the water flea to copper, cadmium and zinc, three metal contaminants that are commonly found in the environment, particularly in parts of California because of the state's history of mining. The metals are also used in industrial parts ranging from brake pads to batteries, and can be found in urban runoff.
For the study, the researchers chose sublethal exposure levels that are comparable to what is found in the environment.
For each metal, the researchers found a decrease in the expression of alpha amylase genes, which are needed to break down starch and as a result interferes with digestion. They also found that exposure to copper decreased the activity of genes that encode glucan binding proteins and lectins, which are possibly involved in the water flea's ability to recognize an infection.
"It's possible that the decrease in expression of these genes is responsible for the immune system suppression seen in other copper-exposed organisms," said Poynton.
Signs of oxidative stress were discovered when the water flea was exposed to cadmium. The researchers saw an increase in activity of genes related to glutathione-S-transferase and peroxiredoxins, both of which protect cells from oxidative damage.
Exposure to zinc led to a significant decrease in chitinase gene activity, the researchers found. They noted that chitinase is needed to break up the exoskeleton of crustaceans during molting, an activity necessary for growth and reproduction. The researchers followed up with a chronic toxicity test and found that exposure to high levels of zinc decreases reproduction rates for the water flea.
"Our study is one of the first proof-of-concepts that aquatic toxicogenomics is possible," said Poynton. "The extra information we get from looking at gene expression could help us make more informed decisions about how harmful a toxicant is, and it could give regulators a new direction that we should be pursuing in monitoring water quality. For instance, we could find that it's necessary to regulate toxicant levels at lower levels, so we can act before toxicants get to the level of actually killing a population. There are sublethal effects of these metal contaminants suggested by our data."
Toxicogenomics could also be used for chemical screening, the researchers said. "For those in industry, chemicals could be screened for potentially ecological consequences while they are still in development," said Poynton. "In pursuing 10 different chemicals for one application, it may be discovered that one is particularly toxic, so it can be ditched right away. At the same time, if screening reveals that there is little or no impact on gene expression from a particular chemical, why not pursue that one for commercial development?"
However, the researchers are also careful to acknowledge the limitations of relying upon gene expression as the sole indicator of ecotoxicity. "It remains to be seen whether a particular gene expression actually leads to adverse outcomes for the organism," said Vulpe. "Does the gene expression lead to actual changes biologically? Also, some changes may be adaptive, helping an organism survive. Just because a gene is changing isn't bad."
Nevertheless, the results of this study suggest that genomics can play a significant role in assessing the toxicity of potential environmental contaminants, the researchers said.
"A 24-hour acute assay won't tell you that you're messing up the feeding mechanisms of the water flea, and chronic tests only look at reproduction," said Vulpe. "What you really want to know is whether there is something that will impact an organism's ability to survive well, including its ability to eat, escape predators or fight infection. That is what genomics could do."
Other co-authors of the study include researchers from the Children's Hospital Oakland Research Institute, the University of New Hampshire, Eon/Terragenomics, and the U.S. Army Corps of Engineers.
The U.S. Environmental Protection Agency, National Science Foundation, National Institutes of Health and the U.S. Army Engineer Research and Development Center provided support for this research.
Sarah Yang | EurekAlert!
Study relating to materials testing Detecting damages in non-magnetic steel through magnetism
23.07.2018 | Technische Universität Kaiserslautern
Innovative genetic tests for children with developmental disorders and epilepsy
11.07.2018 | Christian-Albrechts-Universität zu Kiel
Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.
When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...
Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.
Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....
Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.
Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...
Scientists have discovered that the electrical resistance of a copper-oxide compound depends on the magnetic field in a very unusual way -- a finding that could help direct the search for materials that can perfectly conduct electricity at room temperatur
What happens when really powerful magnets--capable of producing magnetic fields nearly two million times stronger than Earth's--are applied to materials that...
The quality of materials often depends on the manufacturing process. In casting and welding, for example, the rate at which melts solidify and the resulting microstructure of the alloy is important. With metallic foams as well, it depends on exactly how the foaming process takes place. To understand these processes fully requires fast sensing capability. The fastest 3D tomographic images to date have now been achieved at the BESSY II X-ray source operated by the Helmholtz-Zentrum Berlin.
Dr. Francisco Garcia-Moreno and his team have designed a turntable that rotates ultra-stably about its axis at a constant rotational speed. This really depends...
08.08.2018 | Event News
27.07.2018 | Event News
25.07.2018 | Event News
14.08.2018 | Information Technology
14.08.2018 | Life Sciences
14.08.2018 | Life Sciences