March 8, 2006

Gene regulation separates humans from chimps -study

By Patricia Reaney

LONDON (Reuters) - How can humans and chimpanzees, who
share about 99 percent of the same genes be so different?

Scientists in the United States and Australia say changes
in the gene expression, not just genes, is a big part of what
separates humans from their nearest relatives.

Gene expression is the process by which genes are turned on
or off. Not all of the estimated 30,000 genes in humans are
activated at the same time in every cell.

"We think gene expression is a major part of what separates
chimps and humans," said Kevin White, an associate professor of
genetics, ecology and evolution at Yale University in the
United States.

White and researchers from the University of Chicago in
Illinois and the Hall Institute in Parkville, Victoria in
Australia looked at gene expression in humans, chimpanzees,
orangutans and rhesus monkeys.

They used new gene-array technology to compare the level of
expression of 1,056 genes in the four species.

"When we looked at gene expression, we found fairly small
changes in 65 million years of macaque, orangutan and
chimpanzee evolution," said Dr Yoav Gilad of the University of
Chicago, lead author of the study.

But he said it was followed by quick changes in specific
groups of genes known as transcription factors, which control
the expression of other genes, since humans diverged from their
ape ancestors during the last 5 million years.

"This rapid evolution in transcription factors occurred
only in humans," Gilad added in a statement.

The research, which is published in the journal Nature,
supports a 30-year-old hypothesis by scientists Mary-Claire
King and Allan Wilson who suggested that key differences
between humans and chimpanzees might be found in the way they
express their genes.

Until the mapping of the human genome and the development
of gene array technology that allows for large-scale analysis
of gene expression, it has not been possible to test the

Gilad, White and their colleagues used samples of liver
tissue from five adult males from each of the four species in
their study.

They found about 60 percent of the genes had consistent
levels of expression in humans and the primates.

But genes for transcription factors were more likely to
have changed their expression patterns than the genes they

"Specifically in the human lineage the transcription
factors are changing or evolving in their expression at a
faster pace than in the other lineages, particularly as
compared with chimps," White said.

The researchers do not know what caused the shift in gene
expression in humans but they suspect it could be due to
changes in the environment, the acquisition of fire and a
preference for cooked food.

They plan to use other types of tissue to look at large
arrays of genes in future studies.