In a study of changes in gene expression covering taxa from bacteria to human published in the PNAS Online Early Edition issue of the Proceedings of the National Academy of Sciences, Hiroki R. Ueda of the RIKEN Center for Developmental Biology (Kobe, Japan) and colleagues report their discovery of a fundamental governing principle to the dynamics capable of producing the heterogeneous distribution of gene expression.
Ueda, who heads the CDB Laboratory for Systems Biology, found that changes in gene expression scaled closely with initial expression levels in every organism studied; highly expressed genes tend to change in a highly dynamic way, while genes with lower expression levels are less likely to show such variability. Such proportionality governs many forms of expression changes, such as temporal oscillations, responses to environmental stimuli and developmentally determined or tissue-specific gene regulation, and underlies the heterogeneous distribution of gene expression. The distribution of gene expression can be described using what is known as a gpower lawh distribution. In such a system, it can be shown that the number of genes having expression level X is 100 times larger than that of the population having a tenfold greater expression level (10X).
The basic dynamics that underlie and produce this power-law distribution have yet to be worked out, but Ueda and colleagues now propose that the proportional dynamic operating in gene expression changes might be described as a "rich-travel-more" mechanism, a counter concept to the "rich-get-richer" metaphor that has been used to explain other power law-based distributions, such as the growth of network connections in the World Wide Web.
Doug Sipp | EurekAlert!
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