Prescott and her colleagues coaxed human and chimpanzee iPS cells to become cranial neural crest cells by growing them in the laboratory under a specific set of conditions. Although iPS cells from humans have been well-studied, they’ve only recently been made from chimpanzees in the laboratory of Fred Gage, PhD, a professor of genetics at the Salk Institute for Biological Studies and a co-author of the study. IPS cells, which are made from easy-to-obtain skin or blood samples, can be coaxed to become other tissues. To obtain this elusive cell type, the researchers used induced pluripotent stem cells, or iPS cells, made from chimpanzees. But accessing early cell types like neural crest cells can be quite difficult, especially when studying primates.” If we were to look later in development or in adult tissues, we would see differences between the species but they will tell us little about how those differences were created during embryogenesis. “If we want to understand what makes human and chimp faces different, we have to look to the source - to the cell types responsible for making these early patterning decisions. Although they first appear along what eventually becomes the spinal cord, the neural crest cells then migrate over time to affect facial morphology and differentiate into bone, cartilage and connective tissue of the head, and face. The cells, called cranial neural crest cells, originate in humans within about five to six weeks after conception. To conduct the study, however, Prescott and her colleagues had to obtain a specialized type of cell present only in very early primate development. “Many recent studies have shown that changes in the DNA sequences of enhancers may mediate morphological differences among species.” “We wanted to look at how the activity of these enhancer regions may have changed during recent evolution,” said Wysocka. ![]() Prescott and her colleagues wondered whether differences in the way proteins bind to these enhancer regions during development could explain morphological differences between humans and chimpanzees. These regions contain chemical tags and proteins bound to the DNA that control when, where and how nearby genes are expressed. The role of enhancer regionsįor their comparison, the researchers focused on areas of DNA known as enhancer regions in human and chimpanzee genomes. Wysocka and senior research scientist Tomasz Swigut, PhD, share senior authorship of the study. Graduate student Sara Prescott is the lead author. The researchers coined the term “cellular anthropology” to explain how some steps of early primate development can be mimicked in a dish, and thus used to study gene-expression changes that can shed light on our recent evolutionary past.Ī study describing the research was published online Sept. “In particular, 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.” ![]() “We are trying to understand the regulatory changes in our DNA that occurred during recent evolution and make us different from the great apes,” said Joanna Wysocka, PhD, associate professor of developmental biology and of chemical and systems biology. In particular, the researchers found that chimps and humans express different levels of proteins known to control facial development, including some involved in jaw and nose length and skin pigmentation. The key lies in how genes involved in facial development and human facial diversity are regulated - how much, when and where the genes are expressed- rather than dissimilarities among the genes themselves. Now researchers at the Stanford University School of Medicine have begun to pinpoint how those structural differences could arise in two species with nearly identical genetic backgrounds. The face of a chimpanzee is decidedly different from that of a human, despite the fact that the apes are our nearest relative in the primate tree.
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