Kunihiko Kaneko (The University of Tokyo)
Abstract. Life systems generally consist of different levels with hierarchy, from molecules, cells, tissues, organisms, to ecosystem. States at each level change dynamically in time, while consistency between different levels is generally formed for a stable biosystem. Such consistency is shown to lead to general laws in reproduction, adaptation, development, and evolution, to be satisfied in any biological systems. After surveying this general principle, I discuss three specific topics.
First, by considering a toy cell model that can reproduce itself through a network of catalytic reactions and active transport of resources, it is shown that the system shows adaptation to an optimal growth state, where a critical state with power-law in abundances is self-organized. Agreement with statistical laws observed in cell-biology experiments is discussed.
Second, differentiation from stem cells is discussed. By carrying out extensive simulations of a model of interacting cells with intracellular gene-expression dynamics and cell divisions, core network structures are identified that show stemness i.e., both proliferation and cell-differentiation. We found that model stem cells always exhibited oscillatory expression dynamics, which leads to autonomous regulation of number distribution of distinct cell types. These findings may explain the recently observed heterogeneity and dynamic equilibrium in cellular states of stem cells, as well as procedures to regain pluripotency (iPS or STAP cells).
Third, consistency between developmental and evolutionary scales is discussed. Through bacterial evolution experiments and numerical simulations, we found proportionality between evolution speed and (isogenic) phenotypic fluctuation, akin to fluctuation-response relationship in statistical physics. This relationship is derived from evolutionary stability hypothesis, where robustness to noise in development leads also robustness to genetic change through evolution.
Reference:
Kaneko K., Life: An Introduction to Complex Systems Biology, Springer (2006)
Furusawa C. and Kaneko K., Phys. Rev. Lett. 108 (2012) 208103
Furusawa C. and Kaneko K., "A Dynamical-Systems View of Stem Cell Biology," Science 338 (2012) 215-217
Kaneko K., in Evolutionary Systems Biology, Springer (2012) (ed. O. Soyer)