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Of the nearly 60 million domestic cats in the United States, one of the most common is the classic tabby cat – a coat pattern with stripes, dots, and swirls and an M.
As popular as tabbies are (think Garfield the cat), scientists know little about how to get that distinctive look.
In a study published this week in Nature Communications, scientists report that the genes that make up the tabby pattern are activated in the skin cells of an embryo before the cat’s fur develops. The early skin cells even mimic tabby strips under the microscope, a discovery never seen before in embryonic cells.
This unique genetic process could be the same mechanism that creates stripes and spots in wild cats, the authors theorize. The word “tabby” is derived from al-‘Attābiyya, a neighborhood in Baghdad that produced a fine, striped silk taffeta in the 16th century. But the stripes themselves likely come from the domestic cat’s direct ancestor, the striped wildcat of the Middle East.
“There [is] the satisfaction of understanding a little more about the world, ”said director Greg Barsh, a researcher at the Hudson Alpha Institute for Biotechnology, a research facility in Huntsville, Alabama. But the discovery is amazing in other ways too, he says: “Biology uses the same tools over and over again, so it’s very rare to find something that doesn’t apply to many other situations. This should also be the case in this situation. “
The genetics behind the colors and patterns of domestic cats have long fascinated scientists. Charles Darwin, for example, suggested that most deaf cats were white with blue eyes. During development, he said, styles sometimes have insignificant changes, like hair color, because they are associated with other, more useful changes. (Read How Domesticated Cats Domesticated Themselves.)
Some, he added, we can’t even see. He didn’t have modern genetics, but it turned out he was right: it’s an inherited genetic abnormality.
Cat cells from another stripe
As part of an ethical research protocol, Barsh and colleagues collected nearly a thousand embryos that would otherwise have been discarded from veterinary clinics that castrate feral cats, many of which are pregnant at admission.
When Kelly McGowan, a senior scientist on the team, examined the skin cells of embryos aged 25 to 28 days under a microscope, she found that thicker areas of skin were interspersed with thinner areas, creating a temporary color pattern that resembled the tabby coloration an adult cat.
She was particularly surprised to find such a pattern so early in the development of an embryo, long before there were hair follicles and pigments, which are key to coloring in animals. (Read about little-known little wildcats.)
To take a closer look, the team analyzed the individual skin cells of the embryos and found two different types, each of which expressed different sets of genes. Among these genes, the most different gene was the elaborately named Dickkopf WNT Signaling Pathway Inhibitor 4, or DKK4.
When they looked at how cells expressed DKK4 in embryos around 20 days old, they found that the cells involved were the ones that formed the thick skin pattern a few days later.
Barsh explains that DKK4 is also a messenger protein called a “secreted molecule” that signals signals to other cells around it, essentially saying, “You are special. You are the area in which dark hair has to grow. “
Tabby stripes come from the direct ancestor of the house cat, the wild cat from the Middle East.
Photo by TODD GIPSTEIN, Nat Geo Image Collection
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If everything goes as planned, cells with DKK4 will eventually become the dark markings that turn tabby cats into tabbies. But mutations often occur that lead to other coat colors and patterns, such as white spots or thinner stripes. Changes can also occur in the pigmentation: A completely black coating occurs, for example, when pigment cells that should have formed colors only produce dark pigment. (Learn surprising things you never knew about your cat.)
A spontaneous pattern develops
To find out how these cells actually form a striped pattern on a cat’s body, the team turned to Alan Turing, computer scientist and founder of mathematical biology. In 1952, Turing described a way to mathematically explain how patterns can arise spontaneously in nature.
His theory, known as reaction diffusion, predicted that during development, in the presence of molecules (or those produced by genes in the case of cats) – activators and inhibitors – that move or diffuse from cell to cell, organize yourself. at different prices. If one inhibitor that diffuses further or faster than the other were an activator, then the system would mathematically sort itself out. In tabby cats, the inhibitor is the DKK4 gene, but the activator is unknown.
Turing didn’t know what the activator or inhibitor would be. He didn’t even know if they existed. But 70 years later, the tabby discovery is one of a number of others who have agreed that Turing was right.
“We tend to think of cells that move during development, but we think of them so early in this kind of three-dimensional way, where they actually get those stripes as thickness … that’s really advanced,” says Elaine Ostrander, studying the genetics of domestic dogs at the National Human Genome Research Institute of the National Institute of Health in Bethesda, Maryland.
Ostrander, who was not involved in the study, adds that analyzing the individual cells “allowed them to grasp some of these different processes, all of which are important to ultimately arrive at the patterns that our children’s storybooks contain are included “.
Barsh’s team now sees the creation of cat color swatches as a two-step process. First, skin cells determine whether the tabby patterns are dark or light. Then hair follicles grow and form pigments.
By studying how these processes work in other animals – why some animals get stripes and others don’t – the team hopes to decipher how color patterns evolve over time. You might even stumble upon discoveries, Barsh says, that don’t seem to have anything to do with fur patterns – like the invisible differences Darwin once imagined.