"Scientists might assume that natural selection would prune any sloppiness at the level of gene expression, but recent studies by our group at UCSD and others have shown that is definitely not the case," said Jeff Hasty, a bioengineering professor at UCSD's Jacobs School of Engineering. "Many individual genes produce less than 10 copies of regulatory messenger molecules, which is such a small number that it makes clockwork-like regularity of downstream cellular circuits statistically impossible. Our group and others have detected and classified significant downstream fluctuations that result from this source of 'intrinsic noise' in gene expression."
Hasty leads a team of researchers at UCSD that will report in the Dec. 21 issue of Nature a mathematical description of "extrinsic noise," an even larger component of variation in gene expression. This second type of noise results because no two genetically identical cells can keep the same time. The measurement of extrinsic noise was based on experiments involving baker's yeast, Saccharomyces cerevisiae, but the phenomenon and the way it is described mathematically would apply to other types of cells and other species.
"Individual yeast cells exist at various stages of their growth cycle, and this extrinsic variability explains a large component of the noise that must be accounted for in creating a mathematical model of the cell," said Dmitri Volfson, project scientist and a co-author of the study. "In this case, one yeast cell may be preparing to divide, another may be the result of a
Source:University of California - San Diego