Abstract

Self-organisation processes lead to the generation of dynamic patterns that often acquire new properties impossible to predict in a linear way from the individual characteristics of the parts. Moreover such processes occur at various scales, from the atomic/ molecular level to societies and even stellar systems. I have been trying to understand how the mitotic spindle of animal cells, which is involved in the segregation of chromosomes during mitosis, becomes organised in a perfect bipolar structure. In one given cell type, the spindle has an amasingly reproducible shape and size. Yet its components turn-over in a few minutes at the expense of a large amount of chemical energy dissipation. So, the structure is a steady-state dissipative structure. The challenge was to identify the nature of the principles underlying specifically the self-organisation of the tubes that constitute the spindle, the microtubules, into an antiparallel, bipolar array, centered on the chromosomes. We have shown that this happens through the formation of a gradient of regulatory molecules around the chromosomes, that provides spatial cues for the collective behavior of microtubules and molecular motors that eventually self-organize into a steady-state bipolar anti-parallel array.