FBS Colloquia No.208Laboratory of Single Molecule Biology

Self-organization of anterior-posterior polarity in eukaryotic motile cells

Cells migrate in random directions under spatially homogeneous environments. An anterior-posterior polarity establishes within the cell spontaneously even without extracellular spatial cues. We can observe the spontaneous symmetry break in a social amoeba, Dictyostelium discoideum, that shows traveling waves of PIP3 (phosphatidylinositol 3,4,5-trisphosphate), an anterior signaling molecule, on the cell membrane. How does the collective movement of molecules emerge from individually stochastic molecules? We have investigated the self-organization mechanism by single-molecule imaging of these signaling molecules in living cells, statistical analysis of their reaction and diffusion, and mathematical modeling using the experimentally quantified parameters. I will introduce our recent study showing how the symmetry is broken through an excitability of a small G protein, Ras, and the phosphoinositide signaling system.