Rebalancing the genome

Cells trying to keep pace with a constantly changing environment must strike a fine balance between maintaining their genomic integrity and allowing enough genetic flexibility to adapt to new conditions.

When the going gets tough, yeast cells can loosen the reins on their genome, discovered Stowers Investigator Rong Li, PhD, and her team. Readily acquiring or losing whole chromosomes to enable rapid adaptation.

Most often associated with cancer and developmental defects, chromosome instability, or aneuploidy, is generally detrimental to the integrity of a multicellular organism. Yet, from a single cell's perspective, an abnormal number of chromosomes is not necessarily a bad thing. Many wild yeast strains and their commercial cousins, used to make bread or brew beer, have adapted to their living environs by rejiggering the number of chromosomes they carry.

"Cells with a regular set of chromosomes are optimized to thrive under ‘normal’ conditions," says Li. "In stressful environments, additional or missing chromosomes can confer a distinct advantage on cells when it comes to finding creative solutions to road blocks they encounter in the environment.”

Known as adaptive genetic change, the concept of stress-induced genetic variation first emerged in bacteria and departs from a long-held basic tenet of evolutionary theory, which holds that genetic diversity—evolution’s raw material from which natural selection picks the best choice under any given circumstance—arises independently of hostile environmental conditions.

The observation of stress-induced aneuploidy in yeast cells casts the molecular mechanisms driving cellular evolution into a new perspective and may help explain how cancer cells elude the body's natural defense mechanisms or the toxic effects of chemotherapy drugs.

This study was published in the January 29, 2012 online issue of Nature.