Patterns make patterns: how hierarchical self-organization couples cell geometry to biochemical dynamics - Experiment

Many cellular and developmental processes rely crucially on self-organization of protein patterns in space and time. When these protein patterns are coupled to force generation pathways, they can precisely pattern mechanical stress during processes such as cell division or tissue folding. Importantly, these mechanical processes generate shape deformations and cytoplasmic flows, which can modulate intracellular reaction-diffusion dynamics. This suggests a close coupling between cell mechanics and biochemical dynamics. But how do these protein patterns respond to a mechanically changing environment? Here, we use the Rho GTPase driven surface contractions waves in starfish oocytes as a model system to study these effects. By constraining oocytes in microfabricated shape chambers, we found that the behavior of the Rho waves can be qualitatively modulated. Further experiments show that the upstream regulator Cdk1 forms a cytosolic gradient which is modulated by cell geometry, forming a template for downstream pattern formation. We demonstrate that the surface contraction wave is a result of a cascade of coupled protein patterns, which we call ‘hierarchical self-organization’.