A cellular funicular: A hydrodynamic coupling between the anterior- and posterior-directed cytoplasmic flows.

Organelles inside cells move to position themselves at the right place at the right time. A mechanism for generating active force exists for each of such directed organelle movements. In our recent study on cytoplasmic streaming in the Caenorhabditis elegans one-cell embryo, we demonstrated that an anterior-directed force generated by myosin could drive not only anterior-directed cortical flow but also posterior-directed cytoplasmic flow. This coupling of flows in opposing directions is mediated by the hydrodynamic properties of the cytoplasm. This work provided a good example of an active force generation mechanism that drives organelle movements in two opposite directions inside the cell, just as a funicular moves up and down a slope. Interestingly, the funicular-like coupling of intracellular movements is also seen in our recent studies on centrosome positioning in the C. elegans embryo and on interkinetic nuclear movement during mouse neurogenesis. Thus, funicular-like coupling may be a general strate...