What’s behind the variations? Researchers have gained new insights into the genetic basis of coat colors and patterns in dogs. In doing so, they also came across a mysterious lead: a gene variant that ensures light fur apparently entered the family tree of wolves and dogs about two million years ago through the crossing of an extinct representative of the canids.
In addition to the different sizes and shapes, the variety of dog breeds is also known to be characterized by color variations. They range from very light to yellowish and reddish tones to dark brown and black. There are also patterns and shades on different parts of the body that characterize many races. It is already known that a number of genetic factors underlie this diversity in coat characteristics. It is believed that the differences in color patterns were caused by mutations and breeding during and after the domestication of wolves. But there is still some uncertainty about how the coat characteristics developed and are genetically controlled.
Basically, the coat color in wolves and dogs is based on two types of pigments – the black eumelanin and the light pheomelanin, which can provide whitish to yellowish and reddish tones. The different characteristics of the coat are created by controlling the production of these two pigments at the right time and in the right parts of the body. The international research team has now devoted itself to the investigation of a genetic make-up, which was already known to have a role in this system: it is a gene that is responsible for the production of the so-called agouti signal protein.
Gene regulation leads to diversity
This protein acts as a signal for the production of the yellow pheomelanin: As soon as the agouti signal protein is present, the pigment-forming cells of the skin produce the yellowish pheomelanin. If, on the other hand, there is no agouti signal protein, the black eumelanin is formed. “It was clear to us that the causal gene variants for the different colors had to be so-called regulatory variants that ensure that more or less agouti signal protein is formed,” explains senior author Tosso Leeb from the University of Bern. This means that the researchers’ focus was on the “switch areas” of the agouti gene – the so-called promoters.
As the researchers explain, the gene has two starting areas for reading the genetic information to which certain trigger molecules bind: On the one hand, dogs have a so-called ventral promoter, which ensures that the agouti signal protein is formed in the animal’s stomach area. In addition, they also have a hair cycle-specific switch area, which ensures that the signal protein is only formed in certain phases of hair growth. This can lead to banded hair, for example, which produces certain color characteristics. As part of their study, the researchers have now for the first time precisely characterized these two genetic switch areas in dogs.
In this way they were able to show that there are two different ventral promoters. One variant ensures that the agouti signal protein is produced in normal quantities. The other variant is overactive and causes increased production and thus for lighter shades. In the hair cycle-specific promoter, the researchers even found three different variants with different activities. Based on these gene variants on the two individual promoters, the researchers were able to identify five combinations that are associated with different color characteristics in dogs.
Trace of a “Neanderthal Wolf”
They then expanded their research to include the genetics of wolves. It was shown that the ancestors of the dogs also had the two variants for overactive ventral and hair cycle-specific promoters. Presumably, these genetic traits enabled wolves to have light coat colors as an adaptation to snowy environments during the past cold ages, the statement said. Even today these light fur colors can be found in wolves in the polar regions and in the Himalayan mountains. “We discovered that white wolves and brightly colored dogs have an almost identical configuration of the regulatory regions of the agouti gene,” says co-author Christopher Kaelin of Stanford University.
The scientists also came across a mysterious lead: comparisons of the gene sequences with those in other species from the canine family suggest special roots of the overactive variant of the hair cycle-specific promoter: “It is becoming apparent that this variant was at least two million years ago originated in a now extinct relative of wolves, ”says Leeb. Thus, the gene segment for the light coat color apparently entered the family tree of today’s wolves and dogs through a cross. A small piece of the DNA of this extinct species can be found in the brightly colored dogs and white wolves to this day. “This is reminiscent of the sensational news that modern humans carry a small proportion of the DNA of the now extinct Neanderthals in their genetic make-up,” says Leeb.
Source: University of Bern, University of California in Davis, specialist article: Nature Ecology and Evolution, doi: 10.1038 / s41559-021-01524-x