Rapid diffusion-state switching underlies stable cytoplasmic gradients in the Caenorhabditis elegans zygote

Significance Intracellular concentration gradients regulate essential processes including the organization of the mitotic spindle, cytokinesis, and cell polarity. Unlike tissue-scale gradients, little is known about how intracellular gradients form. We used single-particle tracking to characterize the behaviors of individual molecules that sculpt gradients in the cytoplasm of theCaenorhabditis elegans zygote. Our findings suggest that MEX-5 and PIE-1 rapidly switch between fast- and slow-diffusing states with kinetics that vary along the axis of the cell. As a consequence, slow-diffusing MEX-5 and PIE-1 particles are highly polarized, giving rise to their respective gradients. Using mathematical modeling, we show that rapid diffusion-state switching can quickly pattern gradients across a range of temporal and spatial scales.