Anomalous Diffusion in Microtubule-based Transport in Living Cells

Avi Caspi, Rony Granek, Michael Elbaum

Research output: Contribution to journalArticlepeer-review

Abstract

Motor proteins associate with filaments of the cellular cytoskeleton to generate directed forces. These interactions have been studied extensively in vitro. Here we present measurements on beads engulfed into living cells, where near the cell center the bead performs a direction-less wandering motion due to collective activity of microtubule-associated motors. This driven diffusion shows anomalous scaling in the mean square displacement, where ~ t^3/2 on short time scales accessible by video-based measurement techniques, and ~ t^1/2 on longer time scales. These exponents can be explained in terms of a time-dependent friction, or a generalized Einstein relation, that links them as well to the t^3/4 monomer diffusion scaling observed in semi-flexible polymer networks. As the passive movement is sub-diffusive, the driven movement is sub-ballistic in the non-Newtonian environment. In order to access shorter time scales, we developed and apply an optical force correlation spectroscopy based on two-photon fluorescence excitation of the probe bead.

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