Anomalous transport across scales in crosslinked actin-microtubule composites*

The diffusion of microscopic particles through the cell is largely controlled by the cytoskeletal network, comprised of semiflexible actin filaments, rigid microtubules, and crosslinking proteins. Yet, how the interactions between actin and microtubules and the various types of filament crosslinking affect particle transport remain unresolved. In our experiments, we couple single-particle tracking (SPT) with differential dynamic microscopy (DDM) to characterize the transport of micron-sized particles diffusing through crosslinked composite networks of actin filaments and microtubules. Specifically, we investigate the impact of permanently crosslinking actin to actin, microtubules to microtubules, and actin to microtubules. By combining SPT and DDM, we are able to couple single-particle dynamics to ensemble transport phenomena, and link particle diffusion to the viscoelastic characteristics of the networks. We find that subtle changes to the crosslinking interactions between cytoskeleton filaments play surprisingly important roles in the anomalous subdiffusion that particles exhibit within a composite cytoskeletal system.