June 2, 2014
One Slight Genetic Change Responsible For Blond Hair In Humans
redOrbit Staff & Wire Reports - Your Universe Online
A subtle alternation in DNA involving one single-letter change in the genetic code is enough to generate blond hair in men and women, researchers from Howard Hughes Medical Institute and the Stanford University Medical Center report in Sunday’s edition of the journal Nature Genetics.
According to developmental biology professor Dr. David Kingsley and his colleagues, a molecule essential to stem cell function plays a vital role in determining a person’s hair color. Their analysis for the first time explains the molecular basis for one of our most noticeable physical characteristics.
This genetic mutation “is the biological mechanism that helps create that [blond] color naturally,” Kingsley, who is also an investigator with Howard Hughes Medical Institute, told Karen Weintraub of National Geographic News. “This is a great biological example of how traits can be controlled, and what a superficial difference blond hair color really is.”
He added that the study also provides new insight into how the human genome works, since this particular mutation does not impact the protein production of any of its 20,000 genes. Rather, it causes regularly darker hair to become blonde through a process Dr. Kingsley likens to a 20 percent turn of the metaphorical “thermostat dial” regulating a signaling gene located in the skin’s hair follicles, Weintraub added.
“We've been trying to track down the genetic and molecular basis of naturally occurring traits – such as hair and skin pigmentation – in fish and humans to get insight into the general principles by which traits evolve,” Dr. Kingley said in a statement. “Now we find that one of the most crucial signaling molecules in mammalian development also affects hair color.”
The signaling gene in question regulates the expression of a gene that encodes KITLG, a protein that is also known as a stem cell factor. It is also involved in the formation of blood, egg, sperm and stem cells, so completely switching it on or off could have disastrous consequences. However, the mutation impacts the amount of KITLG that is expressed in the hair follicles without altering the way it’s expressed elsewhere in the body.
In order to discover the blond-hair DNA mutation, the study authors examined a part of the genome that had previously been associated with blondness in people from Iceland and the Netherlands, Weintraub explained. They identified the single-letter change responsible for the trait, and then tested what that alternation did by growing human skin cells in a petri dish. The cells demonstrated a reduction in activity in the switch controlling the signaling gene.
Upon introducing the change into normally brown-haired laboratory mice, the researchers observed that the coats of the rodents became significantly lighter. Furthermore, their study demonstrated that noticeable morphological effects can be observed following slight, tissue-specific changes in the expression of genes, as well as emphasizing how difficult it is to clearly link particular DNA changes with specific clinical or phenotypic outcomes.
“This is a good example of how fine-tuned regulatory differences may be to produce different traits,” Dr. Kingley, who served as senior author, said of the research. “The genetic mechanism that controls blond hair doesn't alter the biology of any other part of the body. It's a good example of a trait that's skin deep – and only skin deep.”
“Despite the challenges, we now clearly have the methods to link traits to particular DNA alterations. I think you will see a lot more of this type of study in the future, leading to a much better understanding of both the molecular basis of human diversity and of the susceptibility or resistance to many common diseases,” he added.