CBS/Screenshot
CBS/Screenshot

7 Genetically Modified Animals That Glow in the Dark

CBS/Screenshot
CBS/Screenshot

By Lauren Hansen

This is no party trick. These radiant sheep, dogs, and cats help further research of human diseases.

1. Sheep

Good news, nighttime shepherds: Sheep can now glow in the dark. Well, technically, only nine of the wooly animals can. And they're in Uruguay.

When these sheep were born in October 2012, scientists at the Animal Reproductive Institute of Uruguay immediately injected them with a green protein found in the Aequorea Victoria jellyfish. As the sheep grew, they looked and acted like any other four-legged balls of fluff, except that they gave off a greenish glow after being exposed to certain ultraviolet light. Check 'em out:

Typically, these green fluorescent proteins are used to monitor the activity of altered genes. They have proved to be of great help in the study of diseases. In fact, the method's scientific pioneers were awarded the Nobel Prize for chemistry in 2008. In the case of these sheep, scientists hope that one day they'll be able to use this sort of procedure to create animals with super health-boosting milk. Here, a look back at the radiant animals at the center of these genetic studies throughout the last decade.

2. A rabbit

Ekac.org/Chrystelle Fontaine

This endeavor was actually an artistic one. Eduard Kac is an artist known to use genetic engineering techniques to create unique living works of art. In May 2000, Kac introduced the world to his "GFP bunny," an albino rabbit named Alba that glowed fluorescent when exposed to blue light. Alba was actually just one component of the project, which was also supposed to include a public debate about the practice of manipulating genes in animals for research. Kac wanted to conclude the project by taking Alba home to live with his family. A research institute in France actually created the rabbit for Kac — the florescent jellyfish protein was injected into a fertilized rabbit egg — and later hesitated over releasing the animal due to protests from animal rights groups over Alba's very creation. The scientists also claimed that they never agreed for Kac to take the bunny home. Two years after Alba was born, and long before Alba could make her trip to the states, the unique rabbit died — an abrupt end to the battle between science and art.

3. Pigs

In 2008, scientists in Taiwan claimed to have a world first: Pigs that glowed from the inside out. While other researchers had bred partially fluorescent pigs, these genetically modified pigs had not only glowing skin and eyes, but also organs, including the heart. Scientists added DNA from fluorescent jellyfish to more than 260 pig embryos, which were then implanted into eight different sows, four of which became pregnant. The result was three male piglets whose eyes, teeth, and snouts had a slightly greenish tint during the day, but would glow entirely green in the dark after being introduced to a blue light.

4. Monkeys

E. Sasaki et al 2009

In this 2009 study, the same jellyfish DNA injection was used, but for different purposes. Scientists in Japan wanted to see if the jellyfish gene was inherited by the second generation of a genetically modified monkey. The team at the Central Institute for Experimental Animals in Kawasaki, Japan, added a fluorescent gene to the marmoset embryos, which were then transferred into surrogate females who produced five live births. All of the modified marmosets carried the genes in their body. When they produced offspring, two passed the fluorescent gene onto their young. This was the first time a genetically modified animal passed such genes down a generation. Researchers said it could be a major step in understanding Parkinson's and motor neuron disease.

5. Dogs

A 2009 experiment by a team at Seoul National University reportedly produced the first transgenic dog. Five beagles were created by cloning fibroblast cells that express a red florescent gene produced by sea anemones. Under natural light you can see the faint essence of the red protein under the pale skin. In the dark and under an ultraviolet light, the dogs glow a reddish orange. The five healthy dogs eventually grew to spawn their own florescent offspring. The experiment was meant to prove the principle of transgenic animals, particularly dogs, who, due to their lifespan and reproductive cycle, are good stand-ins for human disease research. Two years later, a team at the same university bred a beagle name Tegon whose fluorescent gene could be controlled. When the dog eats food containing a doxycycline antibiotic and then is exposed to ultraviolet light, it glows green. When the drug is no longer added to the food, the glow eventually fades. Scientists say the study opens opportunities for better understanding genes that trigger fatal diseases, like Alzheimer's and Parkinson's, in humans.

6. Cats

A glowing kitten stands next to a normal cat. Photo courtesy of the Mayo Clinic.

Cats are susceptible to a close relative of HIV called feline immunodeficiency virus. The viral disease infects mostly feral cats, of which there are reportedly a half a billion in the world. In a 2011 study, a team of scientists from the U.S. and Japan inserted a gene into cats that helps them resist this feline form of AIDS. Then, to be able to easily mark the cells, scientists also inserted the green fluorescent protein. Both genes were transferred into feline eggs. They were then able to more readily monitor how the resistant gene developed in the cats' bodies when looking at them under a microscope. Like the other animals, the cats appeared normal during the day, but could glow at night if prompted.

7. Fish

University of Exeter

One of the biggest downsides to helpful industrial products like, say, plastic, or female contraceptives, is that they contain bad chemicals called endocrine disrupters. These substances become pollutants that harm animal and human bodies. They have reportedly been associated with lower sperm counts and breast and testicular cancers. So you can see why scientists may want to study them. The problem has been that it is difficult to track the endocrine disrupters once they enter the body. And so a team of scientists used green fluorescent proteins and genetically engineered zebrafish to glow in places where an endocrine-disrupting chemical is present. As we've previously illustrated, the fluorescent protein doesn't interfere with the body, but, when studied under a microscope, can be easily found. The glowing green areas within the fish then become a roadmap for scientists homing in on the pollutants' potential health impacts.

Sources: ABC NewsBBCDiscovery, The GuardianNational GeographicNBC NewsNew Scientist (2), The RegisterTaipai Times

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How Does Catnip Work?
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If you have a cat, you probably keep a supply of catnip at home. Many cats are irresistibly drawn to the herb, and respond excitedly to its scent, rubbing against it, rolling around on the floor, and otherwise going nuts. There are few things that can get felines quite as riled up as a whiff of catnip—not even the most delicious treats. But why does catnip, as opposed to any other plant, have such a profound effect on our feline friends?

Catnip, or Nepeta cataria, is a member of the mint family. It contains a compound called nepetalactone, which is what causes the characteristic catnip reaction. Contrary to what you might expect, the reaction isn’t pheromone related—even though pheromones are the smelly chemicals we usually associate with a change in behavior. While pheromones bind to a set of specialized receptors in what’s known as a vomeronasal organ, located in the roof of a cat's mouth (which is why they sometimes open their mouths to detect pheromones), nepetalactone binds to olfactory receptors at the olfactory epithelium, or the tissue that lines the mucus membranes inside a cat’s nose and is linked to smell.

Scientists know the basics of the chemical structure of nepetalactone, but how it causes excitement in cats is less clear. “We don’t know the full mechanisms of how the binding of these compounds to the receptors in the nose ultimately changes their behavior,” as Bruce Kornreich, associate director of the Cornell Feline Health Center, tells Mental Floss. Sadly, sticking a bunch of cats in an MRI machine with catnip and analyzing their brain activity isn’t really feasible, either from a practical or a financial standpoint, so it’s hard to determine which parts of a cat’s brain are reacting to the chemical as they frolic and play.

Though it may look like they’re getting high, catnip doesn’t appear to be harmful or addictive to cats. The euphoric period only lasts for a short time before cats become temporarily immune to its charms, meaning that it’s hard for them to overdo it.

“Cats do seem to limit themselves," Michael Topper, president of the American Veterinary Medical Association, tells Mental Floss. "Their stimulation lasts for about 10 minutes, then it sort of goes away.” While you may not want to turn your house into a greenhouse for catnip and let your feline friend run loose, it’s a useful way to keep indoor cats—whose environment isn’t always the most thrilling—stimulated and happy. (If you need proof of just how much cats love this herb, we suggest checking out Cats on Catnip, a new book of photography from professional cat photographer Andrew Martilla featuring dozens of images of cats playing around with catnip.)

That said, not all cats respond to catnip. According to Topper, an estimated 70 percent of cats react to catnip, and it appears to have a genetic basis. Topper compares it to the genetic variation that causes some individuals to smell asparagus pee while others don’t. Even if a cat will eventually love the smell of catnip, it doesn’t come out of the womb yearning for a sniff. Young kittens don’t show any behavioral response to it, and may not develop one until several months after birth [PDF].

But some researchers contend that more cats may respond to catnip than we actually realize. In one 2017 study, a group of researchers in Mexico examined how cats might subtly respond to catnip in ways that aren’t always as obvious as rolling around on the floor with their tongue hanging out. It found that 80 percent of cats responded to catnip in a passive way, showing decreased motor activity and sitting the “sphinx” position, an indicator of a relaxed state.

There are also other plants that have similar effects on cats, some of which may appeal to a wider variety of felines than regular old catnip. In a 2017 study in the journal BMC Veterinary Research, researchers tested feline responses to not just catnip, but several other plants containing compounds similar in structure to nepetalactone, like valerian root, Tatarian honeysuckle, and silver vine. They found that 94 percent of cats responded to at least one of the plants, if not more than one. The majority of the cats that didn’t respond to catnip itself did respond to silver vine, suggesting that plant might be a potential alternative for cats that seem immune to catnip’s charms.

Despite the name, domestic cats aren’t the only species that love catnip. Many other feline species enjoy it, too, including lions and jaguars, though tigers are largely indifferent to it. The scent of the plant also attracts butterflies. (However, no matter what you’ve heard, humans can’t get high off it. When made into a tea, though, it reportedly has mild sedative effects.)

The reason Nepeta cataria releases nepetalactone doesn’t necessarily have to do with giving your cat a buzz. The fact that it gives cats that little charge of euphoria may be purely coincidental. The chemical is an insect repellant that the plant emits as a defense mechanism against pests like aphids. According to the American Chemical Society, nepetalactone attracts wasps and other insect predators that eat aphids, calling in protective reinforcements when the plant is in aphid-related distress. That it brings all the cats to the yard is just a side effect.

Because of this, catnip may have even more uses in the future beyond sending cats into a delighted frenzy. Rutgers University has spent more than a decade breeding a more potent version of catnip, called CR9, which produces more nepetalactone. It’s not just a matter of selling better cat toys; since catnip releases the compound to ward off insects, it’s also a great mosquito repellant, one that scientists hope can one day be adapted for human use. In that case, you might be as excited about catnip as your cat is.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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12 Furry Facts About Red Pandas
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iStock

Red pandas have always lived in the shadow of the other, more famous panda. But now it's time to give the little guy its due.

1. THEY HAVE TWO EXTINCT RELATIVES.

Red panda in a tree.
iStock

Currently, red pandas live in the Eastern Himalayas. But the first red panda fossil was found a little bit further afield than that—in the United Kingdom. In 1888, a fossil molar and lower jaw of a cougar-sized animal called the Giant Panda (unrelated to the modern giant panda) were discovered. More fossils have been found in Spain, Eastern Europe, and even the United States. Around 5 million years ago, Tennessee was home to a giant red panda that probably went extinct with the arrival of raccoons.

2. THEY'RE VEGETARIAN CARNIVORES.

Red panda eating bamboo.
iStock

It might seem like an oxymoron, but carnivore in this case doesn't mean meat eater. Carnivore is a biological order that includes groups like bears, dogs, and cats, and while these animals are generally carnivores, some are omnivores, and some are vegetarians. Red pandas are classified as carnivores because they're descended from the same ancestors as the other carnivores, but they rarely eat anything other than bamboo and a few insects. And while giant pandas eat all of a bamboo plant, red pandas eat only the young leaves. Because this is such a nutritionally poor food source, they need to spend 13 hours a day eating and looking for food and can lose upwards of 15 percent of their body weight in winter.

3. THEY'RE SLIGHTLY BIGGER THAN A DOMESTIC CAT.

Red panda sleeping on a branch.
iStock

But their tails add as much as 18 inches to their length. Red pandas live solitary lives in trees, high up in the mountains, so they wrap those big, bushy tails around themselves to keep warm. (They also use them for balance.)

4. THEY HAVE A FALSE THUMB.

Red panda perched on a log.
iStock

This is another feature (along with diet) that red pandas and giant pandas share. Because both pandas have false thumbs—which is actually an extended wrist bone—it was thought that it must be an adaption to eating bamboo. But the red panda's more carnivorous ancestors had this feature as well. According to a 2006 study, what happened was "one of the most dramatic cases of convergence among vertebrates." Convergent evolution is when two unrelated animals faced with similar circumstances evolve to look similar. In this case, the red panda's false thumb evolved to help it climb trees, and only later became adapted for the bamboo diet, while giant pandas evolved this virtually identical feature because of their bamboo diet.

5. THEY'RE ESCAPE ARTISTS.

Red panda climbing across a tree.
iStock

Rusty the red panda had been at the Smithsonian National Zoo for just three weeks when he made a break for it in June 2013. His method of escape? A tree branch that was pushed down over his enclosure's electric fence by heavy rains. The ensuing panda hunt (and endless bad jokes about panda-monium) captivated Twitter (tweeters used the hashtag #findrusty) until he was found in a nearby neighborhood. Soon after his daring escape, Rusty became a father, forcing him to put his wild youth behind him and settle down. But it could have been worse. After a similar escape in Dresden, Germany, the authorities got another red panda down from a tree by using a fire hose to spray it with water. The panda fell 30 feet to the ground, giving it a concussion. (Ultimately, the animal was OK.)

Red pandas have also escaped from zoos in London, Birmingham, and Rotterdam. The Association of Zoos and Aquariums even warn in their official care manual "beware: red pandas are escape artists" [PDF].

6. ONE ESCAPE LED TO SOMETHING CALLED THE RED PANDA EFFECT.

Red panda peeking out from behind some tree branches.
iStock

Sadly, the red panda involved in the 1978 Rotterdam escape was found dead not long after the search for it began. But the event led to a very peculiar psychological observation. Even after the body of the panda was found, more than 100 people reported seeing it, very much alive. These sightings were clearly mistaken; there's no reason to think that multiple red pandas were loose in Rotterdam, and red pandas are distinctive enough that mistaking them for a dog or cat was unlikely. It's believed that people expected to see a red panda, so they saw one, even though there wasn't one there; researchers called it the Red Panda Effect.

7. THERE'S AN INTERNET BROWSER NAMED AFTER THEM.

The Mozilla Firefox logo.
LEON NEAL, AFP/Getty Images

Mozilla's flagship browser, Firefox, means red panda. Originally, Mozilla wanted to name the browser Firebird, but found that another open source project was using that name. Not wanting to upset anyone, they decided to go with Firefox, another name for the red panda. And in a true example of adorableness, in 2010 Mozilla adopted two baby red pandas that had been born at Tennessee's Knoxville Zoo.

8. THERE IS ONLY ONE TRUE PANDA—AND YOU CAN PROBABLY GUESS WHICH ONE IT IS.

Engraving of a parti-colored bear.
Engraving of a parti-colored bear, from The New Natural History Volume II by Richard Lydekker, 1901.

After the red panda was discovered in the 1820s, it was just called the panda (the origin of the name is controversial, but it probably comes from the Nepali word ponya, meaning "bamboo or plant eating animal"). Forty years later, Europeans found a new animal in China and called it the Parti-Colored bear—because unlike polar bears, black bears, or brown bears it was multi-colored.

9. THERE HAS BEEN A 140-YEAR TAXONOMIC MIX-UP.

A red panda walking toward the camera.
iStock

Prepare to be confused: In the late 19th century, scientists noticed that the parti-colored bear and the (red) panda were very similar. Their jaws were more like each other than they were like any other animal, they lived near each other, they both had false thumbs, and their diets were similar. The decision was made to officially consider the (red) panda as a type of bear.

By the early 20th century, that decision was reversed: Parti-colored bears were declared bears, and (red) pandas were classified as cousins of the raccoon.

Then, in the 1910s, it was decided that parti-colored bears weren't actually bears at all, but were actually large pandas, and also distant relatives of the raccoon. But because parti-colored bears weren't classed as bears anymore, they had to have a name change. They became giant pandas, while the one true panda was renamed the red or lesser panda (to quote a 1920 issue of Popular Science: "Zoologists reverently refer to this rare beast as the "giant panda." Its more popular cognomen is the 'bear-raccoon'").

10. BUT RED PANDAS ARE THEIR OWN THING.

Two red pandas touch noses.
iStock

By the 1980s, genetic evidence indicated that giant pandas actually were a type of bear, and red pandas belonged in their own family, the Ailuridae. They might seem similar, but they're not related.

All of this means that if you're the type of person who rolls their eyes when someone calls a bison a buffalo, or a koala a bear, you need to stop calling the bear a panda and instead refer to it as a "parti-colored bear," the original English name (but if you wanted to call it the bear-raccoon, no one would stop you). Giant pandas are not pandas. There is only one true panda.

11. BUT THIS DOESN'T AFFECT KUNG FU PANDA 3.

Red panda with teeth bared.
iStock

There's still a kung fu panda in the series: Shifu, a red panda.

12. THEY'RE ENDANGERED.

Red panda laying down and sticking his tongue out.
iStock

According to the World Wildlife Fund, there are fewer than 10,000 red pandas left in the wild. Habitat destruction increases the species' chances of extinction.

This story originally ran in 2015.

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