Active flows in endoplasmic reticulum networks

The endoplasmic reticulum (ER) is a network of fluid-filled tubules and sheets which performs essential cellular functions such as protein and lipid synthesis and processing. Single particle tracking in peripheral ER networks has revealed slow diffusive motion inside nodes (i.e. the junctions between tubules) and much faster transport across tubules. The uncoordinated stochastic pinching of tubules was proposed as a possible mechanism behind ER solute transport (Holcman et al. 2018 Nature Cell Biol. vol. 20). We study theoretically the fluid dynamics of such active networks using a viscous hydraulic model of realistic ER geometries forced stochastically by finite-size pinching. We find that our model predicts tubule traversal speeds an order of magnitude lower than those measured experimentally, suggesting that pinching tubules may not be able to account for ER solute transport. We next explore alternative mechanisms for flow generation within the network.