Transparent Zebrafish Used for Research - Transparency Week

By Tanya Silverman

Photo courtesy of Bernat Arlandis.

Last year, a laboratory at the U.K.’s University of Exeter published a study after successfully genetically modifying a zebrafish to glow green for the purpose of detecting endocrine disruptors.

Here’s a basic biology refresher: the endocrine system is responsible for regulating body function through the secretion of different hormones into the bloodstream. An endocrine disruptor is a chemical that could interfere with this system and cause adverse effects. A zebrafish is a small tropical freshwater fish, often used to study subjects like vertebrate development and disease.

Getting back to the study, the research team at the University of Exeter, led by Charles Tyler, wanted to examine how several known endocrine disruptor chemicals affect the body. The designated class of chemicals included ethinylostradial (from contraceptive pills), nonylphenol (wetting agents common in industrial detergents) and bisphenol A (part of many plastics).

Considered pollutants, all of these endocrine disruptors had previously been known to affect estrogen and imitate the processes of sexual hormones. They are considered harmful because they cause detrimental effects on the reproductive system, such as lowering sperm count and causing breast cancer. Additionally, previous research had determined that these chemicals caused fish to change gender.

Given this information, in order to further test how these chemicals affect the internal components and processes of an organism, the scientists genetically modified young zebrafish to have their bodies emit a green glow produced in reaction to the presence of the endocrine disruptors.

Upon release of these chemicals to these transgenic fish, the scientists observed that the zebrafish emitted a green glow throughout several areas of the body, including the eyes and skeletal muscles, parts that had been previously unknown. The zebrafish heart would also glow when exposed to bisphenol A, confirming previous scientific studies that this endocrine disruptor has significant effects on this vital organ.

So why did these researchers choose to work with a zebrafish? Lead researcher of the study, Charles Tyler, explains to BTR that “the genome is sequenced, so we have all this genetic information about the species.” Such knowledge was helpful for the team of researchers in effectively manipulating and “creating these transgenic fish.”

Size also matters: the zebrafish are very small, thereby easy to maintain within a laboratory setting. Storing a volume of zebrafish also facilitates scientists’ ability to study multiple generations at a time, and see whether the offspring are more susceptible to hormones or chemicals than their parents.

Well, even if zebrafish are scientifically utilitarian, and green-glowing organs and tissue in this fish are very intriguing, how is this all relevant to us, as warm-blooded, non-scaled species?

“If we look to see what we get in our zebrafish, we start to compare to what’s known in mammals and in humans,” says Charles Tyler. He explains this connection by indicating that many key life processes are conserved across the vertebrate classes, which is very true when it comes to the way that animals respond to hormones. The elements that control or mediate a response to estrogen, whether it’s within a fish or a mammal’s body, have more similarities than one may initially presume.

“It’s beginning to become much clearer that estrogens have a whole variety of functions in our bodies, everything ranging from immune function right through to repairs of neurons right through to growth.”

Consequently, while estrogen-affecting endocrine disruptors had initially been thought to react mainly with organs like the liver, ovaries, and testes, this study reveals that many other organs and body tissues, including parts of the brain, are also affected by these EDCs, indicated by the green glow.

When asked whether humans in industrialized countries have frequent contact with chemicals like bisphenol A and nonyphenol, Tyler responds, “There is no question that humans have a lot of contact with these compounds.”

He continues to explain that bisphenols are “are plasticizers which are used very widely” and are found in things like “food packaging and wrapping.” In fact, bisphenols are prevalent enough in our environment that it’s possible to measure the presence of these chemicals in human blood.

This study’s results were released over a year ago, but more scientific research is underway. Amongst other studies, scientists at the University of Exeter have been collecting the hearts of the exposed zebrafish and examining how the genetic messages are responding, in order to get a better understanding of how bisphenol A further affects the body when it is broken down.

The initial study had been conducted on young zebrafish, as their lack of skin pigmentation makes it easy for scientists to monitor the green glowing response to the endocrine disruptors. Since then, the team has begun using Casper zebrafish, a mutant strain with transparent skin, to implement the same transgenic model. This way, the researchers are able to see how the experiments work on any stage of the zebrafish’s life, from embryonic stage, through development into adulthood.

Although it is possible that you’ve heard of this study among a list of other glowing animal experiments, Tyler confirms that this zebrafish study “certainly hasn’t been influenced” by any of them. Another disclaimer: these transparent, transgenic zebrafish are in no way connected to the colorful aquarium features of GloFish, no matter how intriguingly one may marvel at the bright aesthetics of this neon aquatic novelty.

“Our work has been more focused on creating an organism that helps us identify how chemicals interact with the body and what sort of potential health implications might be,” Charles Tyler distinguishes this independent scientific project.

For less on colorful animals and more on the dangers of endocrine disruptors pose to humans check out this article from Danger Week.