Hormones, such as estrogen found in water supplies have been seen to cause feminization of aquatic animals, reducing fertility. Other studies have suggested that long term exposure to low levels of estrogens in drinking water may adversely affect human health.
Zebrafish that have been genetically modified to contain Green Florescent Proteins sensitive to estrogen can detect the effects of low concentrations of estrogenic endocrine disrupting chemicals (EDCs) present in our waterways. Until now, it has been known that environmental estrogens alter hormone signalling in the body that can induce reproductive abnormalities in humans and wildlife. In 2002, a team at Mahavir Hospital and Research Centre, Hyderabad, India, showed how estrogen in the environment causes male infertility. They evaluated semen parameters such as ejaculate volume and sperm count of 21 infertile men and 32 control men, finding that environmental estrogens were present in the semen of infertile men.
But does estrogen affect other areas besides the reproductive system?
In January 2007, Song Houyan and Zhong Tao, two professors at Fudan’s molecular medicine lab, Beijing, cloned estrogen-sensitive genes and injected them into the fertile eggs of zebrafish. The genetically modified fish becomes a biosensor by glowing green when placed in water that is polluted by estrogen. This small tropical fish has become one of the favoured animal model systems for studying gene function, as they have transparent embryos, making it easier to see morphological changes during development. This transparency also means researchers can make use of a naturally fluorescing protein called GFP (Green Fluorescent Protein) – which can be used to label individual cells, organs or even organelles.
In a report by scientists at the University of Exeter this year ‘’Biosensor Zebrafish Provide New Insights into Potential Health Effects of Environmental Estrogens’’, Environmental Health Perspectives, the team used cloned estrogen-sensitive genes in zebrafish to detect the affect of environmental estrogens on signalling mechanisms in a whole body system rather than just the reproductive system. This study was led by Okhyun Lee at the College of Life and Environment Sciences, University of Exeter. The team found that exposure of the zebrafish larvae to endocrine disrupting chemicals induced specific Green Florescent Protein expressions in a wide variety of tissues including the liver, hearth and skeletal muscle. These tissues had not been established previously as targets for estrogen in fish. It was also observed that tissues reacted differently to different chemicals suggesting different potential health defects.
Through this study, the team at Exeter have developed a powerful new model for the understanding of toxicological effects, mechanisms and health impacts of environmental estrogens in vertebrates.