Genetically altered zebrafish glow green when exposed to hormone-disrupting chemicals, including BPA, birth control, paints and detergents. (Photo: Exeter University)

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.

Actually, this zebrafish isn't quite green all over — it glows greenest in parts of its body where the chemicals are most active. The pollutants in question are "estrogenic compounds," or substances that chemically mimic the female hormone estrogen. Previous studies have shown that these, along with other endocrine disruptors, can wreak havoc with the reproductive system, whether they promote breast and testicular cancer in humans or cause male fish and frogs to switch genders.

Described in a new study in the journal Environmental Health Perspectives, the green zebrafish were created by scientists at the University of Exeter and University College London. According to the study's authors, they reveal that more organs and body parts react to environmental estrogens than previously thought.

"This is a very exciting development in the international effort to understand the impact of estrogenic chemicals on the environment and human health," co-author Charles Tyler says in a press release. "This zebrafish gives us a more comprehensive view than ever before of the potential effects of these hormone-disrupting chemicals on the body."

The glowing fish are transgenic, meaning they've had 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 like cell disease and gene therapy. But the Exeter/UCL fish add a new twist by glowing only in response to specific endocrine disruptors, which lets scientists see where the chemicals affect their bodies. The idea is that this will shed light on health effects in humans exposed to the same substances.

The researchers tested their transgenic fish's sensitivity to several chemicals that mimic estrogen, 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. They then exposed the fish to chemicals at levels found in local rivers, allowing them to watch in real time as specific organs and sections of tissue glowed green.

These experiments unveiled both established and novel reactions to environmental estrogens. 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 localize precisely where different environmental estrogens 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."

Also on MNN: