Article: On Noise in Gene Expression

ON NOISE IN GENE EXPRESSION

The following points are made by J.M. Raser and E.K. O'Shea (Science 2005
309:2010):

1) Any individual in a population of living organisms or cells is unique.
Much of population variability is due to genetic differences, but
environment and history also contribute to variability in cellular
phenotype. Indeed, identical twin humans or cloned cats differ in appearance
and behavior. However, even cells or organisms with the same genes, in the
same environment, with the same history, display variations in form and
behavior that can be subtle or dramatic. Investigations have focused on the
possibility that such variability is inevitable in biological systems
because of the random nature of chemical reactions within a cell . When
large numbers of molecules are present, chemical reactions may proceed in a
predictable manner. However, when only a few molecules of a specific type
exist in a cell, stochastic effects can become prominent.

2) Gene expression, as defined by the set of reactions that control the
abundance of gene products, influences most aspects of cellular behavior,
and its variation is often invoked to explain phenotypic differences in a
population of cells. Because DNA, RNA, and proteins can be present and
active at a few copies per cell, the abundance of gene products is
theoretically sensitive to stochastic fluctuations. Four potential sources
of variation in gene expression must be considered: (i) as described above,
the inherent stochasticity of biochemical processes that are dependent on
infrequent molecular events involving small numbers of molecules; (ii)
variation in gene expression owing to differences in the internal states of
a population of cells, either from predictable processes such as cell cycle
progression or from a random process such as partitioning of mitochondria
during cell division; (iii) subtle environmental differences, such as
morphogen gradients in multicellular development; and (iv) ongoing genetic
mutation, either random or directed. The authors use the term "noise" in
gene expression to refer to the measured level of variation in gene
expression among cells, regardless of source, within a supposedly identical
population.

Full Text at ScienceWeek
http://scienceweek.com/2005/sw051125-1.htm

Posted by
Robert Karl Stonjek


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