EcoArray is bringing gene microarrays, a robust technology widely used in human disease research, to water testing. We use fish as sentinel species to detect waterborne compounds, much the way miners once used canaries in mines to test for low oxygen conditions. The study of human disease has made microarrays a $1 billion market. Because disease is a function of both inherited genes and the environment, we think that microarrays will have a similar impact on the environmental market. The EPA does, too, and has worked exclusively with EcoArray to develop the 2,000-gene fathead minnow microarray that was introduced in November 2005.
Our microarrays will be used by industry to screen new compounds for toxic effect, by environmental analysts to evaluate water quality, and by research scientists to look at the connection between the environment and human health. The process to use a microarray is simple: as figure 2 shows, fish are taken from water to be tested. Their genetic material is tagged with a fluorescent dye, and then applied to a microarray in a step called hybridization. A specialized scanner then reads the microarray. The resulting data is compared to a database of information on the gene expression patterns observed for different chemicals to determine what chemicals are affecting the test fish.
Gene microarrays offer better answers on water quality than existing testing methods. Looking at the impact of an environment on the functioning of genes in fish gives a richly detailed picture of the cause and effect relationship of chemicals in the environment. Rather than looking at symptoms of disease (one current method of testing), the gene data looks at causes. Rather than looking at the amount of a chemical in the water, the gene microarray looks at actual effects on a fish. Looking at the genetic level creates a more direct link between the environment and human disease as well, since many genes in fish are similar to those in humans. Finally, genes are altered in fish exposed to toxins in a few hours, whereas current methods may require observation and statistical sampling over several weeks to many months. The practical result is that gene microarrays give answers that are specific, detailed and inexpensive.
Here’s an example of how EcoArray uses microarrays to detect the presence of estrogenic compounds in water. (This example uses a nylon membrane-based array for simplicity). Many chemicals present in the environment disrupt endocrine function. These endocrine disrupting compounds (EDCs) can harm the hormonal system of an organism in a number of ways, which can cause a variety of physiological problems including feminization of males, abnormal sexual behavior, birth defects, altered sex ratios, decreased sperm density and size of testes, cancer, reproductive failure, and thyroid dysfunction. A change in the normal physiology of an animal due to exposure to these types of contaminants is ultimately a result of changes at the molecular and cellular levels. Since EDC's have both profound environmental impact and direct and derivative human health consequences, the US Government has mandated through two legislative acts (Food Quality Protection Act and Safe Drinking water Act) that the EPA develop tests for identifying EDCs
Vitellogenin, the egg york precursor protein, is normally expressed in livers of female fathead minnows but this gene is not normally expressed in liver of male fathead minnows. Exposure of male fathead minnows to estradiol, or compounds present in the environment that mimic estradiol, results in the induction of the vitellogenin gene, as well as other genes, in male fish.