Abstract
The cytoplasm is a highly complex and heterogeneous medium that is structured by the cytoskeleton. How local transport depends on the heterogeneous organization and dynamics of F-actin and microtubules is poorly understood. Here we use a novel delivery and functionalization strategy to utilize quantum dots (QDs) as probes for active and passive intracellular transport. Rapid imaging of non-functionalized QDs reveals two populations with a 100-fold difference in diffusion constant, with the faster fraction increasing upon actin depolymerization. When nanobody-functionalized QDs are targeted to different kinesin motor proteins, their trajectories do not display strong actin-induced transverse displacements, as suggested previously. Only kinesin-1 displays subtle directional fluctuations, because the subset of microtubules used by this motor undergoes prominent undulations. Using actin-targeting agents reveals that F-actin suppresses most microtubule shape remodelling, rather than promoting it. These results demonstrate how the spatial heterogeneity of the cytoskeleton imposes large variations in non-equilibrium intracellular dynamics.
Highlights
The cytoplasm is a highly complex and heterogeneous medium that is structured by the cytoskeleton
Based on the very slow diffusion of beads and single-walled carbon nanotubes (SWNT) observed in earlier works[2,3], the cytoplasm has recently been proposed to be a dense elastic network in which most particles are trapped in the actin meshwork
By fast tracking of nonfunctionalized quantum dots (QDs), we instead revealed two populations of diffusive QDs that differed in diffusion constant by almost two orders of magnitude and the faster fraction could be increased by F-actin depolymerization
Summary
The cytoplasm is a highly complex and heterogeneous medium that is structured by the cytoskeleton. Using actin-targeting agents reveals that F-actin suppresses most microtubule shape remodelling, rather than promoting it These results demonstrate how the spatial heterogeneity of the cytoskeleton imposes large variations in non-equilibrium intracellular dynamics. Kinesin-1 bound QDs, display directional fluctuations, because the subset of modified microtubules used by this motor undergoes more prominent undulations This shape remodelling is not caused by active contractility of actomyosin network, but instead suppressed by it. These results demonstrate how the heterogeneity of the mammalian cytoskeleton imposes a large spatial variation in non-equilibrium cellular dynamics, which precludes straightforward application of physical approaches that model the cytoplasm as a viscoelastic homogeneous and isotropic medium
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