Sign up for CNN’s Wonder Theory Science Newsletter. Explore the universe with news about fascinating discoveries, scientific advances and more.
CNN
–
New research may have revealed exactly what makes the Orange Cats so special, but that may not be the reason you think.
Ginger kittens are known to be particularly friendly and energetic among cat owners. But for geneticists, the uniqueness of cats in these houses comes from the extraordinary way they get their colour. Now, scientists say they have unraveled the long-standing mystery by identifying the specific DNA mutations that cause the golden shade. And the mutant has not been found in other animals.
Genetic variants are first described in a paper published in the Journal Current Biology on May 15th.
“This is a truly rare type of mutation,” says Christopher Kaelin, a senior genetics scientist at Stanford University in California.
The majority of completely orange cats are male, and scientists deduced decades ago that the orange genetic code was carried to the X chromosome. Like other mammals, female cats have two X chromosomes, while males have one X and one Y. Male cats carrying orange traits to one X chromosome become completely orange. Women are less likely because they need to completely orange the traits of both X chromosomes (one from each of their parents). Instead, most female cats with orange fur have a patch-like pattern (calico or torteshell) that may contain black and white.
However, when mutations are present in the X chromosome, and how they cause the orange colour, has been a mystery up until now. Mutations that lead to yellow or orange fur in animals (and red hair in humans) occur within color-controlling genes. And these genes are not transported to the X chromosome. Greg Bersch, professor emeritus in genetics and pediatrics at Stanford, said:
The findings not only unravel the unique origins of charismatic colours in some cats, but also reveal new insights into familiar genes.
Step 1 was to identify genetic mutations endemic to orange cats. For 10 years, Kaelin frequently visited cat shows and asked ginger-colored cat owners if they could take samples of animal DNA with swabs on their cheeks. (He is also interested in patterns similar to those found in wild cats, such as leopards and ocelots, which are common in popular breeds such as Bengali cats and toys.)
Compared to the cat genome that sequenced his DNA collection over the past five to ten years, he and his research team discovered 51 genetic variations on the X chromosome shared by orange men. However, 48 have also been found in orange cats, leaving three candidates behind, with the elusive mutation potential.
One was the small 5,076 base pair deletion, which removed approximately 0.005% of the X chromosome in a region that appears to not encode a particular protein. Deletion was not usually found within the gene where mutations were found. However, the mutation lies between two sites associated with a nearby gene called Arhgap36, which regulates the important hormonal signaling pathway used by almost all mammalian cells and tissues. There was no known connection to pigmentation. The genes are not even turned on in chromogenic cells.
To investigate how genes affect color, Kaelin studied its effects in living tissues collected in castration clinics that would otherwise have been discarded. In the experiment, we showed that somehow, the deletion activates Arhgap36 in pigment cells, where it blocks the production of black pigments, producing orange instead.
This variant has not been found in other animals, including wild cats that produced domestic cats.
“This is a genetic exception I noticed over 100 years ago,” Kaelin said in a Stanford University news release. “It was actually relatively genetic puzzles that motivated my interest in Sex Link Orange.”
That specificity suggests that the mutation occurred once during domestication, and was subsequently reserved selectively, Kaelin said. “All orange cats have a single mutation that occurs because they see the same mutations they see in a wide geographical area,” he said. “And we know that mutations are very old because Chinese art dating back to the 12th century has a portrayal of calico cats,” he added that prehistoric DNA experts may be able to use new discoveries to determine when and where they occurred.
“They’re also known as Hanes Rohi, a professor of veterinary biological sciences and genetics at the University of Helsinki, Finland,” said: Lohi was not involved in this study.
In the meantime, Kaelin and his collaborators want to understand how small deletions within a gene that are not itself can alter the activity of nearby genes.
“It’s true, we learn about mutations,” Barsh said. He pointed out that although it is considered genetic, there are many conditions in humans whose genetic mutations are not identified. Maybe he assumes, the problem is that we have not only found mutations, but we also do not understand all the ways that can cause disease properties in the first place.
And can the unusual genetics of the Orange Cats explain their particular personality? So far, Kaelin says he and his colleagues have no reason to think so, but other researchers say findings from new research can be used to look for a link between behavior and coat color. “I think the orange cats really convinced their owners that they’re different, but they haven’t yet convinced us,” he said.
Amanda Schpack is a New York City science and health journalist.