Why do some parts of the body have hair and others don’t?

Researchers at the Perelman School of Medicine at the University of Pennsylvania may have solved the mystery of why we have hair on some parts of our body but not on others. The experts have discovered the presence of a naturally-occurring inhibitor in hairless skin that blocks signaling to the WNT pathway, which controls hair growth.

“We know that WNT signaling is critical for the development of hair follicles; blocking it causes hairless skin, and switching it on causes formation of more hair,” said study co-senior author Dr. Sarah E. Millar. “In this study, we’ve shown the skin in hairless regions naturally produces an inhibitor that stops WNT from doing its job.”

This natural inhibitor is known as Dickkopf 2 (DKK2), a protein that is found in certain embryonic and adult tissues and plays a variety of different roles.

In the plantar skin of mice, which is comparable to the skin on the underside of the human wrist, the researchers found that DKK2 was highly expressed. When DKK2 was genetically removed, hair began to grow in this hairless area of the skin.

“This is significant because it tells us WNT is still present in hairless regions, it’s just being blocked,” said Dr. Millar.

Unlike mice, mammals such as rabbits develop hair in their plantar skin. The research team discovered that DKK2 is not highly expressed in rabbit plantar skin, which explains why hair develops there.

The study findings suggest that the production of DKK2 has evolved to allow for hairy or hairless skin according to the needs of each animal.

The production of hair follicles stops after birth, and these follicles cannot regenerate after severe burns or deep skin wounds. The team is currently investigating whether WNT inhibitors suppress hair follicle regrowth in these cases.

“We hope that these lines of investigation will reveal new ways to improve wound healing and hair growth, and we plan to continue to pursue these goals moving forward,” said Dr Millar.

The study is published in the journal Cell Reports.

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By Chrissy Sexton, Earth.com Staff Writer