Figure 1.

Membrane organelles require multiple motors and cytoskeletal filaments for their distribution. (A) In a steady-state eukaryotic cell, the molecular motors kinesin and dynein transport cargo over long distances along radially arranged microtubules (purple). Actin filaments (dark yellow) are denser near the cell periphery and primarily support short-range transport events by myosin motors. (B) The architecture of the cytoskeletal transport machinery in a neuron is somewhat analogous, with bundles of microtubules (purple tracks) extending from the cell body into the axon and dendrites (not highlighted in this figure), and with actin concentrated in the growth cone at the axon terminal. (C) Organelles are often moved by multiple motors, including motors of opposite polarity and on different cytoskeletal tracks. (D) Microtubules and actin also provide scaffolding where organelle interactions can take place, as attachment to a filament restricts three-dimensional diffusion of organelles to movement in one dimension. The activity of these motors, and the way in which individual cargoes are transported, is likely regulated by molecular factors specific to individual organelles to allow for rapid changes in distribution and motility. (Modified from Barlan et al. 2013b.) Note that the various motors, cargoes, and cellular constituents are not illustrated here to scale.