Volume 4, Number 2, p. 50-63
Microtubule self-organization as an example of the development of order in living systems
J. Tabony 1, N. Glade 1,2, C. Papaseit1, and J. Demongeot2
1
Commissariat l’Energie Atomique, Dèpartement Rèponse et Dynamique Cellulaires, Laboratoire d’Immunochimie, INSERM U548, D.S.V, C.E.A. Grenoble, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France.
2
Institut d’Informatique et Mathèmatiques AppliquÈes de Grenoble, Laboratoire des Techniques de l’Imagerie, de la Modèlisation et de la Cognition, Facultè de Mèdecine, Domaine de la Merci, 38706 La Tronche Cedex, France.
We address the physico-chemical processes underlying biological self-organization by which a solution of reacting chemicals spontaneously self-organizes. Theoreticians have predicted that macroscopic self-organization can arise from a non-linear coupling of reactive processes with molecular diffusion. In some cases, the presence of an external symmetry-breaking factor such as gravity can determine the morphology that subsequently develops. The formation in vitro of microtubules, a major element of the cellular skeleton, shows this type of behaviour. Preparations self-organize by reaction and diffusion, and the morphology that develops depends upon the presence of a weak external factor, such as gravity or a magnetic field, at a critical bifurcation time early in the process. Numerical simulations of the reaction-diffusion process based on the chemical dynamics of a population of microtubules successfully predict the main features of the experimental behaviour. These simulations provide insight as to how self-organization occurs at a microscopic level and how it is triggered by weak external factors. Individual microtubules communicate with each other by reactive processes involving the formation of chemical trails of free tubulin and which show analogies with the way that ants self-organize. Evidence is presented that processes of this type occur in vivo both during embryogenesis and in the course of the cell cycle.
Keywords: bifurcations, biological self-organization, dissipative structures, numerical simulations, reaction-diffusion, cytoskeleton