This year’s TIME 100 is, as always, full of personalities whose influence is at once lasting and admirable, and who have done big, powerful things to shake the world. But many big, powerful things have their roots in small, humble things – things like the inch-and-a-half-long zebrafish created by a University of Exeter team that may help us understand which parts of our body are most affected by pollutants, for instance. When exposed to certain chemicals in the environment, these genetically engineered zebrafish glow bright green in those organs and tissues that are reacting most strongly to the chemical exposure.
The chemicals in question are “environmental estrogens,” which can change hormone signaling in our bodies. In humans, this can mean lower sperm quality or count and other health problems such as breast and testicular cancer; meanwhile, fish deal with impaired reproductive development, the feminization of males, and altered sexual behavior. The scientists looked at substances like estradiol, an ingredient in the contraceptive pill and hormone replacement therapy; bisphenol A, often used as a plasticizer; and 4-nonylphenol, found in industrial surfactants. These chemicals lurk in sewage, agricultural and industrial waste, and food, and many end up in rivers where they find their way to aquatic flora and fauna – and, eventually, us.
But while major international programs have tried hard to screen for these environmental estrogens before they mess up our health, existing testing systems mostly focus on specific, isolated mechanisms rather than on organisms as a whole. So when the University of Exeter team conducted their study, which is published in an April issue of Environmental Health Perspectives, they used a sensitive transgenic zebrafish model to examine systems that hadn’t been on the radar before.
“We found there are so many unknown tissues in the body that may be highly affected by such toxic materials,” study co-author and University of Exeter developmental biology lecturer Tetsuhiro Kudoh said. Kudoh and the team observed green fluorescent signals – from the expression of green fluorescent protein, or GFP – in the liver, heart, skeletal muscle, otic vesicle, and forebrain, among others. They also noticed that the real-time green glow didn’t just appear in different tissues in response to different chemicals, but also affected the tissues in different degrees. This likely means that individual chemicals produce their own distinct health outcomes.
Making a chemical-tester fish probably isn’t something you could do at home – the research team inserted a genetic sequence into fish embryos that would amplify their reaction to environmental estrogens, and raised the ones with a positive response to adulthood. They chose to use zebrafish because the species is the most popular model for biological, medical, and ecological research, according to Kudoh.
“We’re pretty confident that this model could identify a potential effect on human health,” study co-author and University of Exeter environmental biology professor Charles Tyler explained. “For every chemical that’s been shown to be an estrogen in fish…in the same tests in mammals, they have done essentially the same things.”
It’s the early days yet, and we still have many gaps to fill in our knowledge of how environmental estrogens work their way through our bodies. But the team’s zebrafish is one of the most comprehensive and intelligent sensor systems to date for tracking the physiological and pathological impacts of the chemicals on precise areas of the body, which means a lot for future health assessments and our understanding of just what pollution can do to us and other animals. That’s a pretty big achievement for a glow-in-the-dark fish the size of my pinky finger.