Like penicillin, it all started with an accident.

In 1997 a Japanese researcher named Masaru Okabe was looking for a way to track sperm development. His thought was to cram a jellyfish gene encoding a glowing protein — green fluorescent protein, or GFP — into a mouse’s sperm. Then the sperm cells would literally light up when exposed to a certain wavelength of light, allowing him to track them as they developed. But instead, he wound up with the inverse: nearly everything but the sperm glowed. He had a full-on fluorescent green mouse.

The mistake was fortuitous. Glowing mice aren’t just seriously cool; they’re also medically relevant. For instance, other researchers have similarly tagged human cancer cells with a glowing red protein and injected them into glowing green mice (engineered to be fur-less as well, so that the glow is visible). Then they can track the cancer as it grows and spreads, differentiating it from healthy cells by color alone.

Glowing cancer cells in glowing mouseRed tumor in green mouse

(Left: Fluorescent red cancer cells lined with the fluorescent green blood vessels of a fluorescent green mouse. Right: Fluorescent red tumor in a fluorescent green mouse. Both images from here.)

Below the fold: glowing fishies, bunnies, and kitties…

Next, in 1999, came the fish. Researchers in Singapore also filched the GFP gene from jellyfish, this time stuffing it into the genome of a zebrafish. The result was a zebrafish that glowed green. This was followed shortly thereafter by a red-glowing zebrafish (thanks to a coral protein) and a yellow-glowing zebrafish (thanks to a modified jellyfish protein). Just like the glowing mice, these bizarre creatures had their existence justified by an Important Practical ApplicationTM: they would be used to detect water pollution.

How would that work? By tacking something called an inducible promoter onto the gene, the scientists want to create fish that only glow in the presence of a certain trigger. For example, they could add an estrogen-responsive promoter that would switch on the gene — and thus the glowing — when estrogen was present. And poof, suddenly you have a fish that will light up in water contaminated with estrogen.

Next came the glowing bunny. This time, the critter was engineered not in the name of an Important Practical ApplicationTM, but in the name of ArtTM. Artist requested that a French laboratory insert the GFP gene into a rabbit, creating for him a work of “bio art.” He named the rabbit, which gives off a freaky green color under blue light, Alba.


(Alba the glowing rabbit, from Although frankly this picture makes me skeptical, because she appears to have green fur. It’s her skin that should glow, partially or totally obscured by her fur coat.)

Alba was a one-off. But it wasn’t long before glowing animals entered the mainstream en masse. Now, anyone in the U.S. (excepting Californians) can purchase their own GloFish — a commercialized version of the glowing zebrafish used in research. Just trick out your aquarium with black lights and you’ll have your very own glow-in-the-dark fish.


(GloFish in various colors. From

Now, for the latest glowing animal incarnation: the glowing cat. Korean scientists have just come out with a trio of kittens that fluoresce red. Supposedly, like those glowing mice, these cats are meant for biomedical research. But given the success of GloFish, and the overwhelming interest received by a (failed) cat cloning service and a (possibly fraudulent) hypoallergenic kitty company, it’s hard not to wonder whether these cats are destined to be marketed as novelty pets.

Glow cats

(Glowing kittens under normal light (left) and UV light (right). Image from MSNBC.)

Hat-tip to Discovering Biology in a Digital World for calling my attention to the cats.