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Monday, September 20, 2021

How the cat gets its stripes: It’s genetics, not a folk tale

A team of geneticists reported Tuesday in the journal Nature Communications that it had identified a gene in domestic cats that plays a key role in creating the traditional tabby stripe pattern, and that the pattern is evident in embryonic tissue even before hair follicles start to grow.

By: New York Times |
September 8, 2021 10:25:45 am
The research depended on a collaboration with programs that trap feral cats, spay or castrate them, and release them in order to reduce overpopulation and improve the health of feral cats. (Representational)

Written by James Gorman

Folklore is full of stories about the coat patterns of cats: How the tiger got its stripes. How the leopard got its spots. And scientists ask the same questions, although not necessarily about large predators. The research may focus instead on something like the mackerel tabby pattern in domestic shorthairs.

The question of how cat stripes and splotches are made touches on some of the deepest theoretical puzzles of biology. How does a blob of cells organize itself into a fruit fly, or a panda? What tells the bones in a limb to become a hand, or paw, or the ribbing of a leathery wing? What tells some skin cells to grow dark hair and others lighter hair?

A team of geneticists reported Tuesday in the journal Nature Communications that it had identified a gene in domestic cats that plays a key role in creating the traditional tabby stripe pattern, and that the pattern is evident in embryonic tissue even before hair follicles start to grow.

The inheritance of cat coats — how to breed for this or that pattern — is well known. But how patterns emerge in a growing embryo “really has been an unsolved mystery,” said Gregory S. Barsh, an author of the new report.

“We think this is really the first glimpse into what the molecules might be” that are involved in the process, he added.

The research team included Barsh, Christopher B. Kaelin and Kelly A. McGowan, all affiliated with the HudsonAlpha Institute for Biotechnology in Alabama and the Stanford University School of Medicine.

“It’s a very beautiful study,” said Hopi E. Hoekstra, an evolutionary biologist at Harvard University, who has collaborated with Barsh but was not part of this research.

“It advances our understanding of one of the most fundamental questions in developmental biology: How do patterns form?” Hoekstra said.

Barsh said the theoretical basis of the team’s work dated back to a groundbreaking paper by Alan Turing, famous for his work in computer science and code breaking. Turing’s genius was not limited to computers, however. He wrote a paper called “The Chemical Basis of Morphogenesis” in 1952 that “really laid the groundwork for the entire field of mathematical biology,” Barsh said.

The paper describes what is called a reaction diffusion process in which two chemicals, one that stimulates gene activity and one that inhibits it, can result in regular, alternating patterns. Researchers who study the development of coat patterns have thought this process could produce stripes in cat coats; Barsh said the team’s research had confirmed this hypothesis.

Further, he said, the study shows for the first time that the gene Dkk4 and the protein it produces are central to the process. Dkk4 is the inhibitor in the process.

The research depended on a collaboration with programs that trap feral cats, spay or castrate them, and release them in order to reduce overpopulation and improve the health of feral cats. Many female cats that are spayed in these programs are pregnant. The embryos, at too early a growth stage to be viable, are usually discarded. For this study, the researchers collected the embryonic tissue and brought it to the lab.

From more than 200 prenatal litters, McGowan looked for patterns in the tissue at the different stages of growth in the embryos. She found a pattern of what she described as thick and thin areas of tissue in the top layer of the embryonic skin, never before reported. The regions, she said, “mimic what’s going on in the adult cat pigmentation patterns.” The same patterns that will appear in an adult cat’s coat as stripes or blotches appear first in the embryo before there is any hair or even hair follicles.

The team then looked for genes that might be active at that period in early embryonic growth.

When Kaelin looked at the tissue that showed the thick and thin tissue pattern that was the precursor of stripes, he said, “the one molecule that stood out from the rest was this Dkk4.” The full name of the protein and the gene is Dickkopf 4: The name is German for “thick head,” a characteristic the gene produced in frogs.

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