Anyone who reads the news has seen it: every year, a headline appears proclaiming the creation of a new glow-in-the-dark animal. In 2006, we had glow-in-the-dark pigs from a university in Taiwan. In 2007, South Korean scientists reported glow-in-the-dark cats. Since then, sheep, dogs, pigs, rabbits, monkeys, and fish have all been modified in the same way. The body of these articles is strangely formulaic: a joke about how pigs still can’t fly, a simplified overview of the methodology explaining that jellyfish DNA was inserted into these organisms, and usually a single vague sentence explaining the purpose of the experiment.

Reading these articles gives one the strong impression that scientists are just doing this for the hell of it – that the long-term goal is simply to have as many glow-in-the-dark creatures running around as possible. The “mad scientist” stereotype is often evoked. The resulting confusion is obvious when you read the comment sections these articles, where hundreds of people decry the use of cute animals to create something so useless and silly. Granted, the type of person to leave vitriolic comments on anonymous forums is hardly a representative sample of the population, but it’s not hard to see the source of their misunderstanding. I hope this post will clarify the motives and utility of producing genetically-modified glow-in-the-dark organisms.

Glow-in-the-dark animals don’t really glow in the dark

I realize it’s like hearing that Santa doesn’t exist, but let’s just get this out of the way: very few of these organisms actually glow in the dark, at least not in the normal sense of the term. Genuine glowing organisms exhibit what we call bioluminescence. This means using a chemical reaction inside the organism to emit photons. Fireflies are the classic example of bioluminescence, but it can also be seen in certain fish, squid, jellyfish, and plankton. I highly recommend this TED talk if you want to learn more about bioluminescence.

While researchers have begun to insert bioluminescence genes into organisms (see bioluminescence imaging, for example), the amount of light emitted is not typically visible by the naked eye, and the emission of light still requires the injection of other chemicals.

What we really see in these animals is fluorescence. When a compound is fluorescent, it means it takes in light at one wavelength (or colour), and uses that energy to re-emit light at a different wavelength. In the case of Green Fluorescent Protein (GFP), the jellyfish-derived gene that most of these articles are talking about, the colour of light that triggers fluorescence is ultraviolet - out of the range of light that the human eye can detect. If you’ve ever been around a blacklight, you’ve seen the effect – the room may be dark, but some objects have a bright glow. These objects are re-emitting the light in the visible spectrum. My hope in clarifying this is that, instead of focusing on the glow-in-the-dark aspect as a gimmick, people will realize that it’s just a tool that will help a much more massive research project.

Why make glow-in-the-dark fluorescent animals?

In response to the gaggle of bitter internet commenters, there are two predominant reasons we insert GFP into animals. The first is simply as a proof-of-concept for future gene insertion. Inserting and deleting specific genes in animals is crucial in determining a gene’s function. Imagine you see a car for the first time, and wish to figure out what each part does. Removing the steering wheel and suddenly losing the ability to steer would be a fast indication of its original function. The method seems crude, but when you consider that we’re looking at molecules that even most microscopes can’t see, we can get a surprising amount of information out of it. More controversially, there is potential utility in inserting genes into animals for commercial purposes. A recent example is the Enviropig™, a line of pigs that aims to reduce phosphorus pollution through the insertion of a single gene. GFP is used initially to test whether we actually can insert genes into an organism. If the organism glows under ultraviolet light, then we know it worked.

The second common use of GFP is to look at specific genes in great detail. Genes are often thought of as a “blueprint” for life, giving all the instructions on how to make a human. While that’s partially true, the analogy is far from complete. Genes aren’t just about development; your genes are constantly at work keeping you alive. The gene for insulin, for example, is activated to help lower your blood glucose. Everything you do turns some genes on and others off, so to fully understand any gene, we need to know when and where it’s active. While we generally can’t see genes, we can see GFP. By sticking GFP together with a gene we want to study, we can now see when and where in the organism our gene is activated. This results in some absolutely beautiful pictures, by the way.

A message for journalists

It’s fine to put “glow-in-the-dark” in your headline, and it’s fine to spend time talking about how cool the technology is – it is cool, and it’s great that people find it cool. But the end goal of all of this research is not to make animals glow in the dark. GFP is just a tool we use, like microscopes, pipettes, and test tubes, to help accomplish a bigger goal. While I’m focussing on GFP, it is really just one example of this specific brand of poor journalism. I’ve read so many science news articles that completely miss the point of the experiment and instead focus on a trivial but catchy detail. It is really unfortunate witness this extraordinary ability to discuss such fascinating research without actually discussing the research.