Techniques for comparing widespread changes in the genetic code of different mammals could enable scientists to investigate issues that have profound implications for human health. That is, what genes were developed to protect naked mole rats from cancer, whether human genes can be manipulated to treat or prevent cancer, and so on. disease? What genetic changes allowed bowhead whales to live much longer than humans, up to 200 years?
“I think it’s a very powerful application,” said Peter Sudmant, an assistant professor in the Department of Integrative Biology at the University of California, Berkeley, who was not involved in the research. The research method used emerged when sequencing technology rapidly advanced, allowing scientists to read long sequences of his DNA faster and more accurately.
“I think we are at the dawn of a very important era in medical genetics and comparative evolutionary genomics,” said Sudmant.
Nathan Clarke of the University of Utah, who conducted research with Amanda Kowalczyk of Carnegie Mellon University in Pittsburgh and Maria Chikina of the University of Pittsburgh, found that hundreds of genes may be responsible for most of our body hair loss. Using computational tools they helped develop, the authors found that genes for full body hair coverage remained in the genetic code, but were weakened. .
“The initial loss of hair in many species was probably very adaptive,” Clark said. need to streamline. They don’t have to cover that hair anymore.”
One theory is that in humans, the loss of body hair proved to be an advantage for hunting in warmer climates.coupled with less hair The development of a system to cool the body through perspiration may have been a key change that allowed humans to become better hunters and chase prey to exhaustion.
The fossil record is inadequate to pinpoint exactly when ancient humans lost all their hair, but Clark said: It probably became so important to us that the ability to sweat probably came about at the same time. ”
“That’s my guess,” Clark said, clarifying that “this paper doesn’t prove it.”
New research shows the insights gained by looking at evolution through the lens of multiple species. Trying to identify a specific gene to turn off in one of his hairless animals is, as Clark puts it, “a needle in a haystack.”
But finding genetic changes common to many animals that have lost their hair is much more manageable. can focus on areas that remain constant. This approach takes advantage of an underappreciated fact of evolution. Humans share much of their DNA with other mammals, despite their vastly different appearance and behavior. That is 99% in chimpanzees, 85% in mice and 80% in cows.
Clarke and his colleagues compared over 19,000 genes and approximately 350,000 regulatory regions to focus on those associated with hair maintenance or loss. Many of the genes associated with hair growth contain instructions for making the protein keratin, which forms the outer layer of hair, nails and skin.
Scientists have looked at animals that have lost all their hair and those that have retained full fur coats, including bison, guinea pigs, aardvarks and bears. They designed the study to discount gene regions encoding his two confounding variables, life in water and large body size. The numbers of light-haired mammals are disproportionately large, and land-dwelling mammals in hot climates will face the challenge of dissipating heat.
Some animals that have lost their hair may have recently undergone an evolutionary change.
“If you look at African elephants and Indian elephants, they are relatively hairless, but they had very close relatives who lived hundreds of thousands of years and were completely shaggy,” Clark said. “You have this dichotomy [woolly mammoths] go north, leave all their thick hair, [elephants] Down south they lost everything. They have very sparse hair coverings. ”
According to the paper, the process of hair loss was very slow, occurring at least nine times in mammals. If so, selective pressure favored animals with whole-body hair genes dialed down or turned off.
For example, a temperate climate that reduced tundra vegetation is thought to be responsible for the extinction of the woolly mammoth about 10,000 years ago.
“If a hairy animal that doesn’t sweat enough dies because it’s overheating trying to chase some food source, it’s going to be a big disadvantage,” Clark said.
If there were any obvious benefits, the loss of body hair would have occurred over hundreds of generations and could have taken thousands of years, Clark said. But body hair no longer matters, and it probably took thousands of generations or more.
The techniques used in this paper also shed light on less understood areas of our genetic blueprint. About 20,000 genes have instructions for making proteins, They only make up about 2% of the genome. Other areas act like dimmer switches for lights, influencing the degree to which genes or gene groups are louder or lower. Activating a gene almost always makes more of a particular protein.
Mark Springer, emeritus professor of evolution, ecology, and biobiology at the University of California, Riverside, said, “Not much research has been done on these regions. It points the way.There is so much more to learn.”
In 2017, Clarke and some of his colleagues used a similar technique to compare the genome evolution of ground-dwelling animals and blind subterranean mammals. They found many vision- and skin-related genes that changed at a faster rate in underground animals. They also identified genes and regulatory regions that could be used as potential targets for the treatment of congenital eye diseases.
“I have to say this kind of stuff is incredibly cool,” Sudmant said. “We are looking at 75 million years of evolution.