Abstract
Spontaneous formation of spatiotemporal patterns is ubiquitous throughout living organisms, from the spots and stripes on animal skin to traveling waves of proteins on cell membranes. The formation of these patterns – called Turing patterns - has been associated with reaction-diffusion equations. Pattern-forming proteins can also be found in cells whose cytoplasm gets spontaneously mixed by flows resulting from molecular motors pushing and pulling the cell cytoskeleton. However, little is understood about how such cytoplasmic flows affect protein self-organization. The reconstitution of these reaction-diffusion patterns in an active fluid – a liquid composed of spontaneously moving molecules - can provide insights into how patterns are robustly maintained despite cytoplasmic flows observed in living cells. To address this question, we developed a novel in vitro assay combining reconstituted proteins that self-organize into a variety of dynamic Turing patterns on a lipid membrane combined with cytoskeletal proteins that spontaneously churn the solution. Our assay combines the self-organizing Min proteins, which regulate cell division in Escherichia coli, with a continuously moving network of kinesin and microtubule bundles to generate chaotic flows. The Min proteins self-assemble into spirals and waves irrespectively of the presence of microtubule-driven flows. While the overall type of pattern remains constant, some characteristics of the traveling waves appear altered when in the presence of advective mixing from the microtubules. We observed that 1. the microtubule flows seem to facilitate the formation of more breaks in the wavefronts, and 2. the flows appear to delay the establishment of the pattern on the membrane. Overall, our results suggest that cellular components can remain robustly organized even in a chaotic, but minimal, reconstituted system.