It's all over the news today: Blonds aren't stupid.
Well, that's what most of the media would have you believe is the take-home message of the latest research by developmental biologist David Kingsley, PhD. And although I'm happy to see such great coverage, I'm hoping that readers realize that Kingley's study on human hair color, which was published yesterday in Nature Genetics (subscription required), describes something much more subtle, and less superficial. From our release:
The study describes for the first time the molecular basis for one of our most noticeable traits. It also outlines how tiny DNA changes can reverberate through our genome in ways that may affect evolution, migration and even human history.
Kingsley, who is known for his study of a tiny fish called the threespine stickleback, is interested in learning how organism adapt to new environments by developing new traits. He's found that this type of adaptation is most-often accomplished by changes in DNA regulatory regions that affect when, where and how a gene is expressed, rather than through (possibly disruptive) changes in the genes themselves.
In this case, he and his colleagues turned his attention to the blond hair common to many northern European and Icelanders. A previous study had shown that a single nucleotide change on human chromosome 12 was a major driver in hair color. As explained in the release:
The researchers found that the blond hair commonly seen in Northern Europeans is caused by a single change in the DNA that regulates the expression of a gene that encodes a protein called KITLG, also known as stem cell factor. This change affects how much KITLG is expressed in the hair follicles without changing how it’s expressed in the rest of the body. Introducing the change into normally brown-haired laboratory mice yields an animal with a decidedly lighter coat — not quite Norma Jeane to Marilyn Monroe, but significant nonetheless.
The involvement of KITLG, with its critical role in stem cell biology, is certainly interesting. But there's also a more global lesson about the specificity of gene expression their effect on phenotype:
The study shows that even small, tissue-specific changes in the expression of genes can have noticeable morphological effects. It also emphasizes how difficult it can be to clearly connect specific DNA changes with particular clinical or phenotypic outcomes. In this case, the change is subtle: A single nucleotide called an adenine is replaced by another called a guanine on human chromosome 12. The change occurs over 350,000 nucleotides away from the KITLG gene and only alters the amount of gene expression about 20 percent — a relatively tiny blip on a biological scale more often assessed in terms of gene expression being 100 percent “on” or “off.”
“What we’re seeing is that this regulatory region exercises exquisite control over where, and how much, KITLG expression occurs,” said Kingsley. “In this case, it controls hair color. In another situation — perhaps under the influence of a different regulatory region — it probably controls stem cell division. Dialing up and down the expression of an essential growth factor in this manner could be a common mechanism that underlies many different traits.”
And now, the hook that excited most of the news media:
[Kingsley] added: “It’s clear that this hair color change is occurring through a regulatory mechanism that operates only in the hair. This isn’t something that also affects other traits, like intelligence or personality. The change that causes blond hair is, literally, only skin deep.”
Previously: Something fishy: Threespine stickleback genome published by Stanford researchers, Hey guys, sometimes less really is more , Tickled by stickle(backs) and Blond hair evolved more than once, and why it matters
Photo by Traci Lawson