Size regulation of multiple intracellular structures self-assembled from a shared resource pool*

How cells regulate the size of filamentous structures, networks and organelles, despite continuous turnover in their component parts, is a longstanding question. Recent experiments suggest that size control of many intracellular structures and organelles is achieved through depletion of a limiting subunit pool in the cytoplasm. While the limiting pool mechanism ensures organelle size scaling with cell size, it does not provide a mechanism for sensing and regulating individual organelle size.

Here we present a physical theory for non-equilibrium self-assembly and size regulation of sub-cellular structures, based on negative feedback between structure size and growth rate. This model provides a mechanism for robust size regulation of multiple structures in the presence of stochasticity and competition for resources. Using this model we predict size regulation of multiple organelles, filaments, and networks, in quantitative agreement with available experimental data. We also demonstrate how competition for subunit resources between multiple networks can lead to spontaneous cell polarisation.