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Social status changes affect primates' genes expression: study

04-10-2012 10:28 BJT

WASHINGTON, April 9 (Xinhua) -- The ranking of a monkey within its social environment and the stress accompanying that status dramatically alters the expression of nearly 1,000 genes, said a study published online Monday in the Proceedings of the National Academy of Sciences.

In a comparison of high-ranking rhesus macaque females with their low-ranking companions, researchers discovered significant differences in the expression of genes involved in the immune response and other functions.

When a female's rank improved, her gene expression also changed within a few weeks, suggesting that social forces can rapidly influence genetic regulation.

The research was conducted with rhesus macaques housed in groups of five at the Yerkes National Primate Research Center in Atlanta.

As in the wild, each group self-organizes into a dominance hierarchy, defined by which individual finishes first during competition over food, water and grooming partners.

In captivity, dominance is determined by the order of introduction into the group, giving researchers an opportunity to study how changes in rank lead to biological effect.

Previous research on rhesus macaques discovered that social rank influenced components of the stress response, brain, and immune system. With gene chip technology for measuring the expression of over 6,000 different genes, researchers from Duke University, Emory University and Johns Hopkins University looked for the first time in primates at the effects of social rank on genetic function.

Comparing 49 different female monkeys of different rank revealed significant changes in the expression of 987 genes, including 112 genes associated with immune system function.

The result fits with data in monkeys where low rank and chronic stress lead to compromised immune function, and, more loosely, with human studies linking low socioeconomic status and high social stress to elevated disease risk.

The overall genetic "signature" of expression changes was robust enough that researchers could predict an individual monkey's social rank with high accuracy from their gene expression profile alone.

That predictive power also enabled an unanticipated second test of whether gene expression would reflect unplanned changes in dominance rank.

When a couple of animals were removed from cages for various reasons and new ones were introduced to the groups, it turned out to improve the rank of a few monkeys. The researchers could take advantage of this switch and see if their classifier still works.

By analyzing blood samples from these monkeys before and after their move, the researchers were able to use gene expression signatures to correctly predict the change in rank for six of seven monkeys.

The result demonstrates that socially-induced gene expression changes are not stable, but can change rapidly in response to changes in social environment.

The researchers also investigated the mechanisms by which social status could influence gene expression. Dominance rank affected signaling of the glucocorticoid "stress hormone" system and the cell composition of blood samples, both of which contributed to changes in gene expression.

Experiments also demonstrated for the first time that social rank influenced the DNA methylation status of many genes, an epigenetic mechanism of transiently turning genes on and off.

Genes that changed expression with rank status were more likely to be methylated than unaffected genes, suggesting that this mechanism also plays a role in the social influence on genetic regulation.

The authors caution that the experiments used monkeys in captivity, and stressed that the relationship between stress and gene regulation in the wild might not look the same.

The influence of social factors on human genetics also remains to be tested, and measuring status while controlling for confounding factors in people would be a difficult endeavor, the researchers say.

Editor:Wang Lingfei |Source: Xinhua

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