Representing DNA Tranport Phenomena in Cytoskeletal Networks

In the cytoskeleton, motor proteins consume energy from their surroundings to exert forces upon the network’s polymers. This activity complicates transport dynamics across the network, often leading to anomalous diffusion distinct from normal Brownian motion. Many studies have characterized such transport with ensemble-averaged mean-squared displacement (MSD), relating MSD to lag time by MSD ~ Δt^α, where α < 1 and α > 1 indicate subdiffusion and superdiffusion, respectively. Here, we use single-particle tracking to examine the transport of fluorescent microspheres, circular DNA, and linear DNA across cytoskeletal networks of microtubules and kinesin. However, while traditional ensemble MSDs give us a rudimentary understanding of particle movement, we notice unprecedented multi-phasic behavior that compels us to seek an alternative method of data representation. Disaggregating the MSDs reveals distinct populations of particles that ensemble MSDs average together. By examining videos with split spatial heterogeneity, we color-code the particle MSDs to conclude that the differences between these populations are related to diffusion dynamics. To better present these dynamics, we plot density distributions of the anomalous scaling exponents (α) for each particle MSD at a given lag time. Such distributions present intriguing transport dynamics that the traditional ensemble MSDs do not suffice to encapsulate, and our results have implications for many biological and industrial processes.