There’s an expression about having junk in your trunk, but the real junk — that is, junk DNA — is actually in each of our faces. According to findings of Axel Visel and his fellow researchers at California’s Lawrence Berkeley National Laboratory, even the faces which most of us consider to be the most attractive or handsome are created with junk DNA.
Their discovery might lead scientists to discovering why some humans are born with congenital conditions like cleft palates despite the fact that the genes which are responsible for shaping our faces seem to be working as they should.
While the overall shape of our faces is constrained, to a large degree, by genetics, just a relatively minute number of these genes have been identified. They only account for a small percentage of facial variations.
Short sequences of DNA, called distant-acting enhancers, account for much of the variation in the faces of humans, according to Vixel and his colleagues. These DNA sequences are located in non-coding genome regions,but are important in influencing the activity of genes associated with our faces.
Visel states that these distant-acting enhancers (also known as “transcriptional enhancers”)”are part of the 98 percent of the human genome” that has been considered for a long time to be “junk” DNA, though it’s becoming more and more apparent that this junk DNA really contains many important functions in determining things such as variations in the faces of humans.
Using a technique to test out their theories, called optical projection tomography, Visel and his fellow researchers have studied three-dimensional models of the developing embryo of mice. The technique enables Visel to see gene variations in each region of a mouse’s face. Visel and his team of researchers have identified 120 enhancers that played a role in the overall development of the mouse’s face. The researchers chose three of these 120 enhancers and bioengineered three groups of mice, each group lacking one of these enhancers, in order to see what differences it would make in their faces.
At the age of eight weeks, the researchers then compared the faces and skulls of the three groups of mice with a control group which had not had any enhancers removed. One of the enhancers that had been removed from one of the three groups of mice made the mice in that group have broader and shorter skulls but longer faces than the mice of the control group.
The study, published Thursday in the journal Science, is important, according to University of Bristol geneticist Lavinia Paternoster, because key areas of the genome responsible for the shapes of the faces of the mice were identified.
She disagrees, though, with Visel in the importance of junk DNA in accounting for facial variations. Paternoster, in the studies she’s done, has not discovered much evidence about the effect of non-coding regions of the DNA on facial variations. She admits “that some enhancers do harbor some variants” that have an influence on facial shape, but she does not think that these enhancers are “the Holy Grail of missing heritability.”
According to Visel, while none of the enhancers he’s studied would be enough to account for a facial variation like a cleft palate,”it is possible or even likely that in some of these cases mutations in enhancers play a role.”
Visel suggests that, rather than focusing on finding mutations in our genes to explain cleft palates and other facial variations, perhaps we should be looking for mutations in the enhancers that, in turn, have an influence on the genes.
One of the goals of his research, according to Visel, is to “understand the underlying causes of these defects better.” By understanding the causes, possibly the knowledge will one day help diagnose, prevent, and treat “such conditions,” as cleft palates.
By controlling the enhancers in the genes responsible for the configuration of faces, might lead to scientists learning how to manipulate the sequences of these enhancers. Then, scientists could have some degree of control over which genes express themselves.
According to Visel, there is a direct correlation between his findings involving the mice and enhancers that influence the shapes of human faces. He says that the faces of mice are similar, in many respects, with human faces.
There are more than 4000 of these enhancer series in both mice and human faces. Each one of them has an impact on facial variations. Through the research of Visel and his colleagues, as well as others, the day might not be far off when scientists and doctors can detect which groups of enhancers in our genes are responsible for birth defects such as cleft palates so that they can make them a thing of the past. When it comes to human DNA, there’s no such thing as junk.
Written by: Douglas Cobb