How the Whale lost its Hair

Scientists identify the genes responsible for the evolution of hairless skin in whales, which evolved from land (and hairy) mammals eons ago.

Hair is important, specially if you're a land mammal as it keeps you warm. But for a whale, hair just gets in the way. What matters most in a marine environment is streamlining, improving your ability to catch a prey. Now, a research group from  Nanjing,  Normal University in China, has pinpointed the genes responsible for whale's hairless lifestyle.

The research, led by Dr. Guang Yang, found that natural selection acting on two genes responsible for hair creation and loss, called Hr and FGF5, allowed whales and other cetaceans to evolve hairless skin. Dr. Yang's research appears in the February 9 issue of BMC Evolutionary Biology.

Hair is produced continuously in hair follicles, which create hair in cycles throughout the life of the animal. These follicles are regulated by several genes, including the "hairless" or Hr gene, and fibroblast growth factor 5, or FGF5. The Hr gene helps boost the growth of hair through the first part of the cycle involving active growth (called anagen). When the Hr gene is absent, complete baldness results. FGF5, meanwhile, controls the regression part of the hair cycle (called catagen) of creating and replacing hair.

Cetaceans (whales, dolphins, orcas and others) are unusual because they are the only mammals that returned to the sea after evolving from land-based creatures. Part of this evolutionary process involved losing the hair and fur that were essential to survival on land. As the authors explain, such event is "remarkable and evolutionarily significant, although few studies have investigated the molecular basis of this process".

Dr. Yang's team studied the hair-related genes from seven cetacean species, and found that changes to the Hr gene resulted in its complete loss of function in whales, thus halting the early development of hair. Meanwhile, the FGF5 was expressed (and possibly over-expressed) in cetaceans, accelerating the entry into the "catagen" or regressive stage, which induces hair loss.

While comparisons of the Hr and FGF5 whale genes to those of terrestrial mammals found no major mutations that would alter gene function, they did discover small deletions and individual swaps of amino acids in the whale Hr gene. These changes would have eventually shut its activity down, although younger and fetal whales do show some hair and whisker growth, which suggest a degree of functioning for this gene. Meanwhile, further analysis of the FGF5 gene showed that evolutionary changes selected for a fully functioning gene, which aided in cessation of hair growth.

"The evolutionary changes in these two genes may provide new insights into the molecular basis of significant hair loss in cetaceans during their transition from land to water," the authors wrote. But they also suggested that other genes are involved with hair growth and merit further research.

Article: http://www.biomedcentral.com/1471-2148/13/34/abstract