Body hair is a defining characteristic of mammals, but several mammals, such as whales, naked mole rats, and humans, have noticeably less hair. Why we have significantly less body hair than most other mammals has long remained a mystery.
To find the genetic basis of decreased hair, scientists at the University of Utah Health and the University of Pittsburgh identified the coding and noncoding sequences that develop at significantly different rates in hairless mammals compared to hairy mammals.
They found that humans seem to have the genes for a full coat of body hair. The research identifies several genes and genomic regions that are critical to hair development. The study shows that nature has used the same tactics on mammals from different evolutionary tree branches at least nine times. To turn off a shared set of genes needed to lose their hair and fur, the ancestors of rhinoceros, naked mole rats, dolphins and other hairless mammals stomped, descended and swam down the same route.
Nathan Clark, Ph.D., a human geneticist at U of U Health who conducted much of the research, said: “We took the creative approach of using biological diversity to learn more about our genetics. This helps us pinpoint regions of our genome that contribute to something important to us.”
Scientists used the evolution-based method, RERconverge, to perform a genome-wide scan across 62 mammalian species using 19,149 genes and 343,598 conserved non-coding regions. They took steps to exclude genetic regions responsible for developing other species-specific traits, such as adaptation to aquatic life.
The analysis revealed that many hairless mammals had mutations in many of the same genes. These include genes that code for keratin and additional elements that shape the hair shaft and promote growth.
The study also revealed that regulatory regions of the genome appear to be equally important. These regions indirectly influence the process rather than encoding the structures that produce it. They determine how much is made and where and when specific genes are activated.
Kowalczyk said: “There are a lot of genes that we don’t know much about. We think they may play a role in hair growth and maintenance.
clark says, “As animals are under evolutionary pressure to lose hair, the genes that code for hair become less important. Therefore, they accelerate the rate of genetic changes allowed by natural selection. Some genetic changes may be responsible for hair loss. Others can be collateral damage after hair stops growing.
“The fact that the unbiased screen identified known hair genes showed that the approach worked. It also suggests that the genes identified in the screen that are less well defined may be just as important for having hair – or not having it.”
“This is a way to determine global genetic mechanisms underlying different traits.”
- Amanda Kowalczyk, Maria Chikina, Nathan Clark, et al. Complementary evolution of coding and noncoding sequence underlies hairlessness in mammals. eLife. DOI: 10.7554/eLife.76911