New research has identified the specific gene that determines the fur color of orange cats, like the famous Garfield.
Garfield, star of the comic strip of the same name created by Jim Davis in 1978, is, like many of the cats that roam our homes, orange color.
The iconic cat is orange — in the same way that some people are redheaded or some horses are brown — but there’s an important difference.
For all other animals, including redheaded humans, we know what causes this characteristic color, but surprisingly, We didn’t know what caused it. in cats – and felines in general – until now.
Two articles have just been published on bioRxiv – one of the most popular repositories of unreviewed articles before publication – that explain genetics behind the orange cats. comes from the laboratory of Greg Barsh at Stanford University in California. The is from Hiroyuki Sasaki’s laboratory at Kyushu University, Japan.
Eumelanin and pheomelanin: the two mammalian pigments
Mammals have only two pigments, which are two colors of melanin: eumelanina (dark brown, black) and black voice (yellowish, reddish or orange). Redheads only produce pheomelanin, while dark-skinned people accumulate mainly eumelanin. All other skin and hair colors fall somewhere in between, thanks to 700 genes that regulate pigmentation in animals.
In primates, horses, rodents, dogs, cows and many other animals, the production of melanin and the decision to produce eumelanin or pheomelanin is in the hands of a membrane protein called MC1R. This controls skin cells known as melanocytes that release melanin.
If a melanocyte-stimulating hormone (alpha-MSH) is released, the melanocytes begin to produce eumelanin. If an antagonist such as agouti signaling protein or beta-defensin in dogs comes into play, dark eumelanin production stops and melanocytes produce orange pheomelanin.
However, cats are a completely different matter. Anyone who has a cat at home knows that they are very peculiar animals, very special in every way, and this extends to their pigmentation.
In cats, the production of eumelanin or pheomelanin is not controlled by the MC1R receptor. Instead, is in the hands of a locus (whose gene was, until now, unknown) called “orange”. A locus is a physical location in the genome whose effects are known (e.g., black or orange fur), but not the details of the exact DNA sequence it contains, nor the gene to which it belongs.
For this reason, we typically identify the locus first and then, over time, discover and describe the associated gene in detail. The orange locus in cats can come in two versions: an ‘O’ variant that supports the production of pheomelanin (orange), and an ‘o’ variant that is responsible for the production of eumelanin (black).
One detail to keep in mind is that the orange locus is found on the X chromosome. Female cats are XX and cats are XY, like all other mammals. And as in all female mammals, all cells throughout development will randomly inactivate one of the two copies of the X chromosome. Oo cats – carrying the O variant on one X chromosome and the O variant on the other – will generate areas of their bodies that they are orange (in the areas where they inactivated the ‘o’ allele) and others that are black (when they inactivate the ‘O’ allele).
This means that when we see a bicolor (black/orange) or tricolor (black/orange/white) cat, or one of their more diluted versions, we know that must be a femaleand your pigmentation pattern will be completely unique.
Male cats are orange or black (they have only one X chromosome), but cannot be bicolor or tricolorunless they carry a chromosomal alteration equivalent to Klinefelter syndrome in humans (in which males are born with an extra X chromosome).
Calico Cats
Females may therefore have the unique mosaic patterns so prized by cat lovers. When it coincides with another mutation that affects the proliferation and differentiation of melanocytes (producing white spots, without pigmentation), it generates a tricolor cat, commonly known as calico.
Each cheetah is unique, as inactivation of one of the X chromosomes in each pigment cell occurs randomly during development. The earlier this inactivation occurs during development, the larger the resulting stain will be. The later it occurs, the smaller the spots will be.
The feline orange fur gene
Until now, we didn’t know what gene was hidden behind the orange locus in felines. Recent work by Barsh and Sasaki has identified that it is not the feline homologue of MC1R, but a different one: o gene Arhgap36. Male cats with orange coats, as well as orange markings of calico cats, carry a mutation in this gene that blocks eumelanin production and allows pheomelanin production.
These two studies are a great example of good, basic, solid research that simply aims to satisfy scientific curiosity without knowing its immediate applications, and understanding, in this case, why the naughty cat Garfield is orange.
