What controls travel lengths in vivo?
S.P. Gross, M.A. Welte, S.M. Block, E.F. Wieschaus (2000). "Dynein-mediated
cargo transport in vivo. A switch controls travel distance" J. Cell Biol.
Abstract Full Text
In this paper, we investigate the regulation of cytoplasmic dynein, a microtubule-based motor with diverse cellular roles. We combine mutational analysis and bi ophysical measurements to demonstrate that this motor is responsible for the minus-end motion of bidirectionally moving lipid droplets in early Drosophila embryos: dynein localizes to lipid droplets, and mutations in the heavy chain of cytoplasmic dynein alter the transport of individual lipid droplets as well as their global distribution (top half of figure). This analysis provides an estimate of the force that a single cytoplasmic dynein exerts in vivo (1.1 pN).
To investigate how the cell controls travel distances of dynein-driven cargoes, we quantitate how far droplets travel in single runs (i.e. segments of uninterrupted motion). Travel distances are much shorter than expected based on in vitro estimates of cytoplasmic dynein processivity. We therefore propose the existence of a process that terminates runs before motor processivity becomes limiting. We call this process a "switch" (see cartoon). A process with similar properties governs plus-end motion. These switches are apparently subject to developmental control, resulting in regulation of net transport direction. Given dynein's diverse roles in many cellular processes, similar switches will likely be crucial for determining net transport of other organelles wherever bidirectional transport is observed.