Why are almost all red cats male?
A red coat colour like Garfield's is usually only seen in males, whereas red and black or tricoloured cats are almost always female. The reason for this has now been found.
For more than 60 years, experts have been searching for the gene that causes the red coat colour of cats. Unlike in humans, the colouring of pets is related to their sex: While red house tigers are almost exclusively male cats, red-black or tricoloured fur is almost exclusively found in females. Now tworesearch teams have independently identified the gene mutation that produces the red coat colour - and have come across an unexpected protein. The work, which has not yet been peer-reviewed, was published on "BioRxi" at the end of November 2024.
When a red and a black cat have offspring, either black and red (or tricoloured) kittens can be produced or unicoloured kittens. The former are usually female, while males are almost always unicoloured. This indicates that the gene variants for black and red fur are part of the X chromosome. As female cats receive two X chromosomes, their cells can decide which of the chromosomes is activated - different areas of the coat can therefore have different colours. A male cat from this litter, on the other hand, is usually a single colour, as he only receives one X chromosome from one of the two parents.
In most mammals, including humans, a mutation in the MC1R protein (a melanocortin receptor) causes the red colour in fur or hair. However, this appears to be different in cats. The gene that contains this protein is not located on the X chromosome in cats. In addition, most red cats do not have a mutation of MC1R. "It was a genetic puzzle," said geneticist Greg Barsh from Stanford University to Science, who was involved in one of the new papers.
An unsuspected protein
He and his team collected skin samples from four red and non-red cat embryos in neutering clinics. They analysed how much RNA the respective melanocyte pigment cells produce and which gene they belong to. The red cats produced around 13 times more RNA of a gene called ARHGAP36, which is located on the X chromosome - a clear indication that this causes the red coat colouring.
A research group led by developmental biologist Hiroyuki Sasaki from Japan's Kyushu University found similar evidence when they analysed the genomes of more than 280 cats collected worldwide. Apparently, the ARHGAP36 gene produces an excess of RNA - but not through a mutation. The DNA that ARHGAP36 produces looks the same in all cats. Instead, red cats seem to lack a neighbouring DNA segment that controls RNA production. This is why they produce much more of it than non-red conspecifics.
Cats seem to have something special about them
Until now, no one had suspected a connection between ARHGAP36 and the colouring of skin or hair cells. It is also unusual that a gene deletion (the missing regulatory DNA sections) makes certain genes more active instead of weakening them, said geneticist Carolyn Brown from the University of British Columbia to "Science", who was not involved in the studies.
Spectrum of Science
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Original article on Spektrum.de
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