Local Motion Analysis Reveals Impact of the Dynamic Cytoskeleton on Intracellular Subdiffusion

Abstract

Intracellular transport is a complex interplay of ballistic transport along filaments and of diffusive motion, reliably delivering material and allowing for cell differentiation, migration, and proliferation. The diffusive regime, including subdiffusive, Brownian, and superdiffusive motion, is of particular interest for inferring information about the dynamics of the cytoskeleton morphology during intracellular transport. The influence of dynamic cytoskeletal states on intracellular transport are investigated in Dictyostelium discoideum cells by single particle tracking of fluorescent nanoparticles, to relate quantitative motion parameters and intracellular processes before and after cytoskeletal disruption. A local mean-square displacement (MSD) analysis separates ballistic motion phases, which we exclude here, from diffusive nanoparticle motion. In this study, we focus on intracellular subdiffusion and elucidate lag-time dependence, with particular focus on the impact of cytoskeleton compartments like microtubules and actin filaments. This method proves useful for binary motion state distributions. Experimental results are compared to simulations of a data-driven Langevin model with finite velocity correlations that captures essential statistical features of the local MSD algorithm. Specifically, the values of the mean MSD exponent and effective diffusion coefficients can be traced back to negative correlations of the motion's increments. We clearly identify both microtubules and actin filaments as the cause for intracellular subdiffusion and show that actin-microtubule cross talk exerts viscosifying effects at timescales larger than 0.2 s. Our findings might give insights into material transport and information exchange in living cells, which might facilitate gaining control over cell functions.

The effect of nanoparticle uptake on cellular behavior: disrupting or enabling functions?

“…44 While the active forces that drive non-thermal fluctuations in cells act primarily through the cytoskeleton, these fluctuations can have important consequences for the transport and stirring of small particles not associated with the cytoskeleton, such as organelles and perhaps even individual proteins or protein complexes, due to mechanical resistance of the surrounding medium. This is because of the fundamental hydrodynamic coupling of cytoskeletal filaments to the surrounding cytoplasm: the motion of the cytoskeleton does not occur in a stationary cytoplasmic fluid, but drags this fluid along.…”

“…76 The resulting reduction of mitochondrial activity induces a decrease in ATP production that is necessary for many cellular functions, including cell motility and intracellular trafficking. This point is of particular interest, since the different components of cytoskeleton interact to control multiple functions, including migration, cell morphology and structural integrity, 77 division, deformation, intracellular transport, 44 and tissue organization. 73 Any modification in cytoskeleton architecture can also lead to alteration in the expression of cytoskeleton-associated proteins.…”

Active Phase and Amplitude Fluctuations of Flagellar Beating

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“…cellular deformity) can be attributed to cytoskeletal compartments, such as actin filaments, intermediate filaments, and microtubules (Otten et al, 2012; Windoffer et al, 2011). Polymerization of filament monomers gives the resulting polymers viscoelasticity, which is assumed to provide cellular stiffness in epithelial cells (Beil et al, 2003; Yamada et al, 2003).…”