Horses, orangutans and rats are covered in it, but humans are not. Why we have significantly less body hair than other mammals has long been a mystery.
But the first-ever comparison of the genetic codes of 62 animals, including horses, is revealing how humans and other mammals lost their hair.
Humans appear to have the genes for full body hair coverage, but evolution has disabled them, scientists from the Utah Health College and the University of Pittsburgh report in their journal. e-life.
This finding points to a set of genes and genomic regulatory regions that appear to be essential for hair formation.
This study answers fundamental questions about the mechanisms that shape this defining human trait. Scientists believe it could eventually lead to new ways to restore hair after hair loss, chemotherapy, or in people with disorders that cause hair loss.
This study shows that nature has deployed the same strategy at least nine times in mammals sitting on different branches of the evolutionary tree. The ancestors of rhinos, naked mole rats, dolphins, and other hairless mammals trampled, crouched, and swam the same trails to inactivate their common gene sets and shed their hair and fur.
“We’ve taken a creative approach to using biodiversity to learn our own genetics,” said Amanda Kowalczyk and Malia, who did much of the research at the University of Pittsburgh. says Nathan Clarke, a human geneticist at Utah Health University. Chikina.
“This helps us identify regions of the genome that contribute to something important to us.”
Benefits of being hairless
We see different amounts of fur in the animal kingdom, such as the coarse fur of monkeys, the soft fur of cats, and the dense fur of horses. The same goes for hairless. Humans have characteristic hair tufts on their heads, but body hair is inconspicuous, so they are classified as “hairless.” Joining us are other mammals with hints of hair, such as sparsely covered elephants, thin-haired pigs and mustachioed walruses.
A receding hairline has its advantages. Without dense hair, elephants cool off more easily in hot climates, and walruses glide effortlessly through the water. They found that mammals with no phenotype accumulated mutations in many of the same genes. These include the gene that encodes keratin and additional elements that build the hair shaft and promote growth.
This study also showed that regulatory regions of the genome appear to be important as well. These regions don’t code for the structure that makes hair, but they indirectly affect the process. They guide when and where specific genes are turned on and how much is made.
Furthermore, the screen revealed genes whose roles in hair growth have not yet been defined. These findings, combined with additional evidence such as signs of activity in the skin, highlight a new set of genes that may be involved in hair growth.
“There are a lot of genes that we don’t know much about,” says Kowalczyk. “We believe they may play a role in hair growth and maintenance.”
detangle loose hair
To solve the mystery of mammalian hair loss, Clark, Kowalczyk, and Chikina looked for genes in hairless animals that evolved at a faster rate than those with hair.
“As animals are under evolutionary pressure to lose hair, the genes that encode hair become less important,” says Clark. “That’s why it speeds up the rate of genetic change allowed by natural selection. Some genetic changes may be responsible for hair loss. Others are concomitant after hair stops growing.” damage.
To perform the search, they developed a computational method that compares hundreds of genomic regions simultaneously. They investigated 19,149 genes and 343,598 regulatory regions conserved across dozens of mammalian species analyzed. They took steps to downplay genetic regions involved in the evolution of other species-specific traits, such as adaptation to aquatic life.
The fact that the unbiased screen identified known hair genes showed that the approach worked, explains Clarke. It also suggests that less well-defined genes identified in the screen may be just as important for the presence or absence of hair.
Clark and colleagues are now using the same approach to define gene regions involved in cancer prevention, life extension, and understanding other health conditions.
“This is how we determine the global genetic mechanisms underlying different traits,” says Clark.
This research was supported by the US National Institutes of Health.
Amanda KowalczykMaria ChikinaNathan Clark (2022) Complementary evolution of coding and noncoding sequences underlies hairlessness in mammals eLife 11:e76911.
https://doi.org/10.7554/eLife.76911
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