Two faced

two-faced-portrait Winter 2016

Chimpanzees are our nearest relatives, genetically speaking. Yet their ears and brows are more prominent, their noses, chins and cheeks less defined and their faces more covered with hair than even the swarthiest human.

Variations in gene expression, rather than dissimilarities among the genes themselves, help explain the differences, according to School of Medicine researchers. Chimps and humans express different levels of proteins known to control facial development, including some involved in jaw and nose length and skin pigmentation.

“We are interested in craniofacial structures, which have undergone a number of adaptations in head shape, eye placement and facial structure that allow us to house larger brains, walk upright and even use our larynx for complex speech,” says Joanna Wysocka, PhD, professor of developmental biology and of chemical and systems biology, who shares senior authorship of the study with senior research scientist Tomasz Swigut, PhD. Graduate student Sara Prescott is the lead author of the study, which was published in September in Cell.

The researchers compared areas of DNA known as enhancer regions, which contain chemical tags and proteins bound to the DNA that control the expression of nearby genes, in human and chimpanzee cranial neural crest cells. About 1,000 were more active in one species than the other. Many of those, Wysocka says, “have been previously shown to be important in craniofacial development or associated with normal intrahuman facial variation.”