Lundi 15 Décembre

Kunihiko KANEKO (Tokyo, Japon)

Exploring Universality in Life Systems through Constructive and Dynamical Systems Approach:

We intend to understand life as a `complex system', by unveiling universal features underlying all biological systems. For this purpose, we take a constructive approach, by setting up a simple system both experimentally and theoretically, and answer general questions on a biological system. After surveying this standpoint, I discuss some of recent studies along this line, both in theory and experiment.

First, as a first step in an investigation of the origin of genetic information, I discuss how some molecule species play the role for the carrier of heredity. Taking a simple model we discuss molecules that are slow in synthesis speed and minority in number start to play the role, in the sense that they control the behavior of a cell relatively strongly and are preserved well. We also discuss discreteness-induced transition in reaction dynamics, as well as relevance of this minority controlled state to evolvability.

Second, I discuss universal statistical laws of chemical abundances in a cell that sustains recursive production. From theoretical study of simple protocell models, we discover a power law law in average gene expression and log-normal distribution of the abundances of each chemical. Experimental verification, as well as its relevance to evolution, is discussed, while fluctuation-response relationship in evolution is proposed.

Next, differentiation of phenotypes of cells, triggered by fluctuations but robust against them, is discussed. Finally, if time is allowed, I will also touch upon a problem of evolution (in particular speciation) as a consolidation process to genes of this interaction-induced phenotypic differentiation.

Thierry Dauxois