Colloquium on April 7th, 2008

Albrecht Ott
Universität des Saarlandes

Criticality and spontaneous symmetry breaking are part of Hydra's developmental program for axis definition

Hydra is an about cm sized polyp of roughly 105 cells with surprising robustness. It can regenerate even from a random cell aggregate made from its own cells. During such a reorganization, Hydra first forms a hollow cell sphere. We show that even a weak temperature gradient directs the axis of the regenerating animal - but only if it is applied during the symmetry-breaking moment. We observe that the spatial distribution of the early expressed, head-specific gene ks1 has become scale-free and fractal at that point. We suggest the self-organized critical state to reflect long range signaling, which is required for axis definition and arises from cell next-neighbor communication. We further present a little overview on recent results from ongoing research on microarray technology and DNA hybridization.