Changes in gene expression behind differences between man and ape: study

Changes in gene expression behind differences between man and ape: study

In spite of having 99 per cent of genes and 98 per cent of DNA in common, humans and apes look and behave differently. This phenomenon has continued to baffle scientists for years altogether. Now, a new study by researchers from Yale University, University of Chicago, and the Hall Institute in Australia, has found that it is changes in gene expression and not gene coding changes that are responsible for the differences between the two.

“We think gene expression is a major part of what separates chimps and humans,” said Kevin White, a Yale University professor and lead author of the study. Using a new method of determining gene expression, the researchers studied the liver cells of humans, chimpanzees, orangutans and macaques and compared over 1056 genes in each of the four primates. They analyzed how the genes were different as far as their expression went and found that around 60 per cent of them were identical.

However, 19 of the genes were significantly different in their expression in apes and humans. In humans, most of these 19 genes had active 'transcription factors' that regulate how other genes behave. “When we looked at gene expression, we found fairly small changes in 65 million years of the macaque, orangutan, and chimpanzee evolution, followed by rapid change, along the 5 million years of the human lineage, that was concentrated on these specific groups of genes. This rapid evolution in transcription factors occurred only in humans,” added Yoav Gilad, an author of the study from the University of Chicago.

Genes for transcription factors had four times greater chances of altering their expression than the genes without them. Such alterations drove the evolution of humans, which was fuelled by dietary changes like cooked food. “If you change when and where genes are active, you are going a long way toward explaining the differences between humans and other apes. Perhaps something in the cooking process altered the biochemical requirements for maximal access to nutrients as well as the need to process the natural toxins found in plant and animal foods,” Gilad said.

The basic finding of the study brings no surprises. It merely corroborate a theory floated by Mary-Claire King and Allan Wilson of the University of California, Berkeley, in 1975, which said that gene regulation and not gene alterations led to the differences between humans and chimpanzees.
Gilad felt that not only does the study tie together loose ends in the evolution theory, but also opens avenues for exploring the genetics of certain diseases like cancers. “These findings suggest that focusing on genes with conserved expression levels among primates may be helpful in identifying promising candidates for disease-association studies,” the researchers wrote in a report published in Nature.

“When we looked at the list of misregulated genes that are known to be associated with liver cancer, they were more likely to be on our evolutionarily conserved list. The implications of that are pretty broad for disease and particularly for cancer,” White added.

According to National Human Genome Research Institute's Francis Collins, the study is one step ahead in the explanation of human evolution. “I don't think anybody would have predicted that we would begin to see this kind of really interesting evidence of evolutionary imprints on Homo sapiens this soon. It will both change our sense of where we've come from and offer us some pretty interesting ideas of why we fall ill to various problems,” he said.