A few can sometimes move a lot

In the realm of embryology and developmental dynamics, there are many circumstances at cellular and sub-cellular levels in which a viscous cytoplasmic flow is stirred or moved by the action of the cytoskeletal assembly. Such activity driven transport can mitigate the ineffectiveness of diffusion-based transport in the crowded cell environment, and in the case of larger cells, yield large-scale net bulk flow. The viscous drag caused by translocating motors and payloads enhances the circulation of the cytoplasm as has been previously observed in the cytoplasmic streaming inside the Drosophila oocyte. In this talk, we study a different streaming mechanism facilitated by the microtubule-dynein assembly within cytoplasmic bridges that connect nurse cells to the oocyte during Drosophila oogenesis. We propose a simple but illuminating model that focuses on how the presence of only a few microtubules in a confined space can rapidly induce and pump a large amount of bulk cytoplasmic flow. We mathematically study the model’s pumping performance and pose the arrangement of microtubules as an optimization problem. We find arrangements that maximize the pumping performance under no constraint on the energy consumption, as well as for a fixed rate of energy dissipation and power consumption of molecular motors.