Gene expression is noisy
Randomness could explain monozygotic twin phenotype differences
By Cathy Holding

The random fluctuations-also known as noise-of gene expression could account
for phenotypic variations ranging from the minor-such as different
fingerprints in identical twins-to the major, including normal embryonic
development, according to a study in the May 27 Science.

The authors, Erin K. O'Shea and Jonathan M. Raser at the Howard Hughes
Medical Institute, University of California at San Francisco, say their
measurements of noise in single budding yeast cells suggest that noise also
provides a means, albeit temporary, of cellular adaptation to the
environment.

O'Shea and Raser cloned two-cyan and yellow-fluorescent protein reporter
genes under the control of identical budding yeast PHO5 gene promoters to
look at cell-to-cell differences in a population of yeast cells. When all
cells express similar quantities of the fluorescent proteins at similar
times, then little variability-meaning little randomness-in gene expression
is occurring, Raser said.

"If we see substantial differences between two independent but identical
genes-if the yellow fluorescent protein appears 30 minutes before the cyan
appears [in one cell but not in another]-then we can say that's due to
randomness, because the cell can't tell the two proteins apart at all,"
Raser, co-author of the paper, told The Scientist.

Raser said that noise contributes to variability at the population level.
"Noisy genes will have highly variable expression at the population level,
and genes that are much less noisy will be very consistent at the population
level," he said.

The team also identified mutations that could convert a gene from a less to
a more noisy state, and vice versa, Raser said, "so it's clearly very
possible that this is something that a cellular population can take
advantage of: to evolve to better adapt to an environment."

Read the rest at TheScientist
http://www.biomedcentral.com/news/20040528/01

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