The scientific community has long been at a loss to explain the genetic mutation responsible for the colour of orange or ginger cats, fondly known in Malaysia as “Oyen“. Now, two independent research teams believe they might have solved the mystery.
In most mammals, including humans, ginger hair results from mutations in a protein called Mc1r. This protein instructs melanocytes to produce either dark or light pigment with red-yellow highlights. When it is less active, these skin pigment cells are limited to producing a light pigment with a red-yellow hue, giving rise to red hair.
In cats, however, the gene coding for the Mc1r protein does not appear to be the cause of ginger hair, as the majority of ginger cats do not have Mc1r mutations. “It’s been a genetic mystery, a conundrum,” said Greg Barsh, a geneticist at Stanford University, speaking to Science magazine.
Barsh and colleagues sought to understand the genetic mechanisms that produce orange hair in cats by taking skin samples from eight cat foetuses – four ginger and four non-ginger – from neuter clinics. By analysing the RNA produced by melanocytes, the researchers identified the genes activated in these cells.
They found that the melanocytes of the cats produced 13 times more RNA from a specific gene, Arhgap36, located on the X chromosome. This discovery could explain the origin of the orange colour, the researchers suggested in a paper published on the bioRxiv pre-publication platform.
However, on closer examination of the Arhgap36 gene, the scientists found it had no mutations that could account for the orange colour of some cats. They did, however, discover that the orange cats were missing a nearby stretch of DNA located just upstream of this gene.
This deletion didn’t affect the protein’s amino-acid components but was likely to influence skin or, pertinently, hair pigmentation.
These results were corroborated by professor Hiroyuki Sasaki at Kyushu University, who also demonstrated the role of the Arhgap36 gene in the orange colouration of certain cats’ coats. He and his colleagues revealed the same genetic deletion in 24 feral and pet cats from Japan, as well as among 258 cat genomes collected from around the world.
Although this is a major discovery, more research is required to further our knowledge of these fascinating felines. Nevertheless, experts are thrilled by the two studies.
“It’s a long-awaited finding,” said Leslie Lyons, a feline geneticist at the University of Missouri, who has long been curious as to where and when the mutation first appeared: there is some evidence, she noted, that certain mummified Egyptian cats were orange.
Research into cat colour has revealed all kinds of phenomena, she added, including how the environment influences gene expression. “Everything you need to know about genetics, you can learn from your cat.”