RESEARCHERS DISCOVER GENES THAT DISTINGUISH HUMAN BRAIN FROM NONHUMAN
Findings Shed Light on the Evolution of Human Cognition, the Capacity
for Long Lifespan and the Potential for Neurodegenerative Disease
ATLANTA ≠ A research team from the Salk Institute, the Yerkes National
Primate Research Center of Emory University and the University of California
≠ Los Angeles (UCLA), has identified genes in the cerebral cortex that
differ in levels of activity between humans and nonhuman primates, including
chimpanzees and rhesus monkeys. These findings, which appear in the
online journal of the Proceedings of the National Academy of Sciences,
may provide essential clues to the unusual cognitive abilities of humans.
They also may help researchers understand why humans have a longer lifespan
than other primate species and yet are so vulnerable to age-related,
Because the DNA sequences of humans are so similar to those of chimpanzees,
scientists have long speculated that differences in the activity levels
of particular genes, otherwise known as gene expression, and, as a result,
the amounts of particular proteins cells produce, are what distinguish
humans from chimpanzees. The recent sequencing of the human genome has
led to the development of "gene chips" that enable researches to examine
the expression levels of thousands of genes at a time as well as compare
expression levels in different species.
Using gene chips to compare samples of the cerebral cortex of humans,
chimpanzees and rhesus monkeys, the research team at the Salk, the Yerkes
Center and UCLA identified 91 genes that are expressed in different
amounts in humans compared to the other primate species. Upon further
study, the team observed 83 of these genes showed higher levels of activity
in humans, and as a result, regulated neural activity.
"When we looked at other tissues, such as heart and liver, we found
nearly equal numbers of genes showing higher or lower levels of expression
in humans as compared to chimpanzees and rhesus," said Todd Preuss,
PhD, associate research professor of neuroscience at the Yerkes Research
Center. "The changes in gene activity in the cortex suggest increases
in the rate of brain activity, providing a basis for the evolution of
the enhanced cognitive abilities in humans."
In addition to finding changes in activity-related genes, the researchers
found the human brain shows increased expression of genes that protect
against activity-related damage. This finding may help explain why humans
have the potential to live decades longer than other primates, but also
why humans are especially vulnerable to age-related, neurodegenerative
diseases, such as Alzheimerís disease.
"It is probable that the combination of long lifespan and high neural
activity makes humans particularly vulnerable to neurodegenerative disease,"
said Mario Caceres, PhD, a postdoctoral fellow now at Emory University
and lead investigator on the study. "Activity-related damage accumulates
with age and has the potential to cause catastrophic breakdown late
in life. By understanding how humans protect their brains from activity-related
damage, we hope to better understand why those mechanisms fail."
The Yerkes National Primate Research Center of Emory University is one
of eight National Primate Research Centers funded by the National Institutes
of Health. The Yerkes Research Center is a multidisciplinary research
institute recognized as a leader in biomedical and behavioral studies
with nonhuman primates. Yerkes scientists are on the forefront of developing
vaccines for AIDS and malaria, and treatments for cocaine addiction
and Parkinsonís disease. Other research programs include cognitive development
and decline, childhood visual defects, organ transplantation, the behavioral
effects of hormone replacement therapy and social behaviors of primates.
Leading researchers located worldwide seek to collaborate with Yerkes