Fluorescent fish shed light on the impact of contaminants

What’s black and white but green all over? A genetically engineered zebrafish that’s helping scientists figure out how endocrine-disrupting pollutants damage the body.

This zebrafish glows greenest in the parts of its body where the chemicals are most active. The pollutants in question are “oestrogenic compounds”, which chemically mimic the female hormone oestrogen. Previous studies have shown that these and other endocrine disruptors can wreak havoc on the reproductive system, whether they promote breast and testicular cancer in humans or cause male fish and frogs to switch genders.

Described in the journal Environmental Health Perspectives, the green zebrafish were created by scientists at the University of Exeter and University College London. The results reveal that more organs and body parts react to environmental oestrogens than previously thought.

“This is an exciting development in the international effort to understand the impact of oestrogenic chemicals on the environment and human health,” co-author Charles Tyler says. “This zebrafish gives us a more comprehensive view of the potential effects of these hormone-disrupting chemicals on the body.”

The glowing fish are transgenic, meaning they have DNA from another organism artificially added to their genome. Such fluorescent zebrafish are not new – the company GloFish has sold them as pets for years, and scientists already use them to study health issues such as cell disease and gene therapy. But the Exeter/UCL fish add a twist by glowing only in response to specific endocrine disruptors, which lets us see where the chemicals affect their bodies. The idea is that this will shed light on health effects in humans exposed to similar substances.

The researchers tested their transgenic fish’s sensitivity to several chemicals that mimic oestrogen, including ethinyloestradiol (used in birth control and hormone replacement therapy), nonylphenol (used in paints and industrial detergents) and bisphenol-A, or BPA (used in many types of plastic). This eventually yielded a fish that was sensitive enough to give fluorescent green signals in the affected body parts. The fish were exposed to chemicals at levels found in local rivers, allowing researchers to watch in real time as specific organs and sections of tissue glowed green.

These experiments unveiled both established and novel reactions to environmental oestrogens. Some affected the liver, for example, and BPA specifically showed signs of activity in the fish’s hearts. Other responses that weren’t previously known showed up in skeletal muscles, the eyes and even parts of the brain.

“By being able to localise precisely where different environmental oestrogens act in the body, we will be able to more effectively target health effects analyses for these chemicals of concern,” Tyler says. “While it is still early days, we are confident that our zebrafish model can help us better understand the way the human body responds to these pollutants.”

McClatchy-Tribune