Tutorial: Complex Systems Biology: In search of Universal Statistical Dynamics in Reproduction, Adaptation, and Phenotypic Evolution

Kunihiko Kaneko (University of Tokyo, Komaba and ERATO Complex Systems Biology, JST)

Abstract

Biological system generally consists of a hierarchy of different levels, each of which is under stochastic dynamics. We discuss three topics – reproduction, adaptation, and evolution – in relationship with such fluctuations. First, as a result of consistency between molecule replication and cell reproduction, universal statistical laws on chemical abundances over cells are derived as are also confirmed experimentally. They include power-law distribution (Zipf’s law) of gene expressions and embedding of the power law into the network connectivity. Fluctuations of chemical abundances over (isogeinc) cells are shown to obey log-normal distribution, which are generally rather large in magnitude.

Second, a novel adaptation mechanism in a cell is proposed, that does not rely on specific signal transduction network but takes advantage of the stochasticity in gene expression, to show that the mechanism works as a universal property of a growing cell. An experimental demonstration of this mechanism is discussed by using bacteria with embedded gene network.

Third, general relationship between phenotypic fluctuation and genetic variance is derived from evolutionary stability hypothesis. Proportionality between evolution speed and isogenic phenotypic fluctuation is derived as an extension of fluctuation-dissipation relationship in physics. The obtained relationships are confirmed in models of catalytic reaction network and gene expression dynamics, as well as in laboratory experiments in bacterial evolution. Link between robustness to mutation and to noise is discussed.

Reference

Life: An Introduction to Complex Systems Biology, Springer (2006);

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