Reconstructing large-scale intracellular flows

Cytoplasmic streaming is essential to intracellular transport and mixing in large plant and animal cells. Drosophila oogenesis is an extensively studied biological process where streaming can be studied quantitatively by focusing on the cytoplasmic flows in the growing oocyte. Due to limitations in imaging and analytical approaches, the three-dimensional structure of these flows has remained unknown. We present the first quantitative view of its structure, using particle image velocimetry, biophysical modelling, and computational analysis. Our results reveal a single vortex that spans the entire oocyte, has the maximal fluid speed of ~100 nm/s, and can be quantitatively explained with a model whereby a passive fluid is entrained by a self-organized cytoskeletal activity underneath the plasma membrane. The emerging picture sheds light on related biological contexts and highlights the wealth of open questions in the applied mathematics and computational physics of intracellular flows.