From the size of the nose to the shape of the eyes, every human face is unique, just like our fingerprints. Genetics, like blueprints, certainly play a major part in craniofacial development, but little is known about exactly how our genes control the way our faces look. Now scientists say something called “junk” DNA may hold clues to how coding for facial features works.
Junk DNA – referring to the part of the genome that does not encode for proteins – were originally thought to lack function, New Scientist reported. The “transcriptional enhancers” could be what switch genes on or off in different parts of the face, which might explain how one person gets a chiseled chin, and another dimples.
"Enhancers are part of the 98 per cent of the human genome that is non-coding DNA – long thought of as junk DNA," study co-author Axel Visel, a geneticist with Berkeley Lab's genomics division, told New Scientist. "It's increasingly clear that important functions are embedded in this 'junk'."
Researchers from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory studied how this seemingly inoperative DNA actually “fine-tuned” the faces and skulls of mice. Their results, published Thursday in Science, suggest that the same might apply to humans.
“Our results suggest it is likely there are thousands of enhancers in the human genome that are somehow involved in craniofacial development,” Visel told the University Herald. “We don’t know yet what all of these enhancers do, but we do know that they are out there and they are important for craniofacial development.”
Visel and his team were able to identify 4,000 genetic enhancer sequences, which we inherit from our parents, that determine how our features develop. “The majority of these sequences are at least partially conserved between humans and mice, and many are located in chromosomal regions associated with normal facial morphology or craniofacial birth defects,” researchers noted in the study. “Characterization of more than 200 candidate enhancer sequences in transgenic mice revealed a remarkable spatial complexity of in vivo expression patterns.”
"If you think about face development, a gene that is important for both development of the nose and the mouth might have two different enhancers and one of them activates the gene in the nose and the other just in the mouth," said Visel, according to The Guardian.
The researchers suggest that their study of junk DNA’s role in facial configuration could actually lead to scientists changing the sequence of these enhancers. This could be used to control which genes express themselves and which don’t, “without having to mess with the gene itself.”
To test this, the researchers genetically engineered mice by switching off three of the enhancers they had identified. Using computed tomography, they then scanned the skulls of the mice after eight weeks and compared the 3D images to those of normal mice at the same age.
According to The Guardian, the skulls of the modified mice had changes, although microscopic, in the length and width of their faces. “Targeted deletions of three craniofacial enhancers near genes with known roles in craniofacial development resulted in changes of expression of those genes as well as quantitatively subtle but definable alterations of craniofacial shape,” the researchers noted.
"When you look at the anatomy and development of the mouse versus the human, we find that the faces are actually very similar,” Visel said. “The same genes that are important for mouse face development are important in humans."