Microtubule-based unidirectional pumping in confinement

We use two and three-dimensional discrete and coarse-grained biophysical models to study unidirectional streaming through tube-like connectors between cells, such as ring canals in Drosophila egg chambers. There, streaming is facilitated by molecular motors moving on static tracks of a unipolar microtubule array oriented along the passage. We demonstrate how the presence of only a few microtubules, in a model connector of much larger diameter, can pump a large amount of bulk cytoplasmic flow. Our calculations, based on a sampling distribution of microtubules positions, show that most arrangements in the population give a fair fraction of the maximum flux. We also explore the structure of flux maximizing arrangements, which are not entirely intuitive, and may prove useful in the design of artificial microfluidic devices.