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Have you ever wondered how your favorite furry feline got their stripes? A new study in domestic cats has revealed which genes give felines their distinctive fur patterns and suggests that the same genetics can grant to feral cats, such as tigers and cheetahs, their characteristic coats.
How cats get their stripes is a decades-old mystery in the life sciences, senior author Dr. Gregory Barsh, a geneticist at the HudsonAlpha Institute for Biotechnology in Huntsville, Alabama, told Live Science. About 70 years ago, scientists began to develop theories as to why and how organisms come to wear periodic patterns, like the stripes on a zebra or the soft segments of a caterpillar’s body.
In some animals, such as zebrafish, these patterns emerge due to the arrangement of different types of cells. “But in mammals, the skin and the hair cells are exactly the same all over the body, and the color pattern is due to the differences in genetic activity between, say, cells underlying a dark band and cells underlying a light band, ”Barsh said. So the question of how cats get their stripes boils down to how and when various genes activate in their cells and how these genes influence animals’ development. In short, it’s complicated.
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But now, in a new study, published Tuesday (September 7) in the journal Nature CommunicationBarsh and his colleagues have identified several genes that work together to give cats their coat patterns.
A gene, called Transmembrane aminopeptidase Q (Taqpep), which they had previously identified, in a study published in 2012 in the journal Science. Cats that carry a version of the Taqpep gene are found adorned with narrow, dark stripes, while those with a mutant version of the gene carry “large whorls” of dark fur; the “tourniquet” version of the uncomfortable is more common in feral cats.
To study what additional genes might shape the various markings on cats’ coats, the team began collecting discarded tissue from clinics that sterilize feral cats; some of the resected cat uteri contained non-viable embryos, which the researchers examined in the lab.
They noticed that around the age of 28 to 30 days, cat embryos develop areas of “thick” and “thin” skin; in later stages of development, the thick, thin skin gives rise to hair follicles which produce different types of melanin – eumelanin for dark fur and pheomelanin for light fur.
Remarkably, “the developmental mechanism responsible for the color pattern takes place early in development, before hair follicle formation, and in cells that do not produce any pigment but instead contribute to the structure of hair follicles,” Barsh said. Spotting this pattern, the team looked at which genes were active leading to the development of thick skin, to see if specific genes directed the formation of the patterns.
The team found that, in 20-day-old embryos, several genes involved in cell growth and development suddenly activate in the skin, destined to thicken and give rise to follicles that produce dark fur. These genes are known to be involved in a “Wnt signaling pathway”, a molecular chain reaction that causes cells to grow and develop into specific cell types, and one gene in particular, called Dkk4, has emerged. marked out as particularly active.
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Dkk4 encodes a protein that refuses Wnt signaling, and when it comes to cat fur, the tussle between Dkk4 and Wnt seems to dictate whether a patch of fur turns dark or light, the authors found. In dark areas Dkk4 and Wnt balance out, but in light areas Dkk4 beats Wnt.
This discovery supports a theory that the computer pioneer Alain turing developed in the 1950s, The science magazine reported. Turing proposed that animal periodic patterns, such as stripes, arise when an “activator” molecule stimulates the production of an “inhibitor” molecule and these two molecules mix in the same tissue; in this case, Wnt would be the activator and Dkk4 the inhibitor. Following Turing’s hypothesis, Barsh’s team believe that Dkk4 spreads through tissue faster than Wnt signaling, and that this uneven distribution generates periodic spots of light and dark in cats.
Additionally, a cat’s Taqpep genotype – that is, whether it carries the “band” or “whorl” version of the gene – also dictates where the Dkk4 gene can be turned on, Barsh said. “But we don’t know exactly how it’s going,” he added. Taqpep encodes a protease, an enzyme that breaks down other proteins, but as of yet, the team is uncertain whether this enzyme directly or indirectly affects Dkk4 activity.
Following the embryo scans, the team looked at the cat’s genome sequences from a database called the 99 Lives Collection. They found that the Abyssinian and Singapura races, which do not bear any stripes or spots and instead have a uniform appearance, carry mutant versions of Dkk4 that turn off the gene. In future work, the team wants to see if similar mutations occur in feral cats.
Previous studies have suggested that for cheetahs (Acinonyx jubatus), at least a cat’s Taqpep genotype affects the appearance of its spots, and so could Dkk4, the authors noted. Then there is the serval (Cats), an African wildcat who typically sports bold black spots, but occasionally grows a layer of tightly packed tiny spots instead. Could a Dkk4 mutation explain this variation?
“Our observations to date are only for domestic cats,” Barsh said. “The molecules and mechanisms studied in domestic cats are highly likely to apply to all more than 30 species of feral cats, but we will need to conduct further studies in the feral cat. DNA to find out for sure. ”
Beyond feral cats, the team wants to study whether the same mechanisms are also at play in distant mammals, such as zebras and giraffes.
Originally posted on Live Science.
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