Researchers at the University of Chicago have discovered the first molecular mechanism for promoting evolutionary change in response to the environment. The mechanism works by allowing multiple small genetic variations to accumulate and then expose themselves when that organism is under environmental stress.
"For the first time we have a molecular mechanism that explains how organisms that have stuck to the same morphology for eons can evolve new traits that help them adapt to changing conditions," says Susan Lindquist, Ph.D., professor of molecular genetics & cell biology at the University of Chicago, Howard Hughes Investigator and lead author of the paper in the November 26 issue of Nature.
The expression of these variations depends on a protein called heat shock protein 90 (Hsp 90) which normally keeps certain inherent genetic variations in a population silent, but can reveal them during times of stress, such as climate change.
All organisms make heat shock proteins, also known as chaperones, in response to high temperatures. It is the chaperone's job to prevent other proteins from getting into trouble--misfolding or loosing their unique shapes. Once this happens, the misshaped protein can no longer function, and regular cellular metabolism cannot proceed.
Hsp 90's charges are special. They are proteins called signal transducers, which regulate development and cell differentiation. Hsp 90 keeps them poised and ready for action. "Signal transducers control morphological development. They make sure the right part grows at the right spot at the right time. That's why you have two hands and two feet instead of four hands," says Lindquist.
During times of stress, however, all sorts of proteins start to unfold, and Hsp 90 is recruited away from its normal duties to help out. The signal transduction pathways are then 'sensitized' to small genetic variations that otherwise go unnoticed, and development takes a twist.