Local Analysis of Heterogeneous Intracellular Transport: Slow and Fast Moving Endosomes.

Nickolay Korabel,Sergei Fedotov,Gianni Pagnini,Thomas Andrew Waigh,Daniel Han,Viki Allan,Alessandro Taloni

doi:10.3390/e23080958

Abstract

Trajectories of endosomes inside living eukaryotic cells are highly heterogeneous in space and time and diffuse anomalously due to a combination of viscoelasticity, caging, aggregation and active transport. Some of the trajectories display switching between persistent and anti-persistent motion, while others jiggle around in one position for the whole measurement time. By splitting the ensemble of endosome trajectories into slow moving subdiffusive and fast moving superdiffusive endosomes, we analyzed them separately. The mean squared displacements and velocity auto-correlation functions confirm the effectiveness of the splitting methods. Applying the local analysis, we show that both ensembles are characterized by a spectrum of local anomalous exponents and local generalized diffusion coefficients. Slow and fast endosomes have exponential distributions of local anomalous exponents and power law distributions of generalized diffusion coefficients. This suggests that heterogeneous fractional Brownian motion is an appropriate model for both fast and slow moving endosomes. This article is part of a Special Issue entitled: “Recent Advances In Single-Particle Tracking: Experiment and Analysis” edited by Janusz Szwabiński and Aleksander Weron.

Highlights

Intracellular transport of organelles, such as endosomes, has been described by anomalous diffusion caused by different mechanisms [1,2]
We found that both ensemble-averaged mean squared displacements (EMSD) and E-time-averaged MSD (TMSD) of slow endosomes are decreasing functions of time, which to our knowledge has never been observed before
The anomalous exponent extracted from EMSD or ensemble-time-averaged MSD (E-TMSD) of fast endosomes is α ' 1, smaller than the anomalous exponent obtained by considering all trajectories without distinction into fast or slow, i.e., α ' 1.26

Summary

Introduction

Intracellular transport of organelles, such as endosomes, has been described by anomalous diffusion caused by different mechanisms [1,2]. Various models have been proposed to describe it, such as fractional Brownian motion (FBM), continuous time random walks and fractional Langevin equations [3]. Which of these models is the best is a current topic of much debate. The traditional statistical analysis of trajectories includes quantification of ensemble evolution in time and space using the ensemble-averaged mean squared displacements (EMSD), time-averaged MSD (TMSD), probability density functions of displacements and correlation functions. New methods of trajectory analysis were developed, such as local time-averaged MSD [5], first passage probability analysis [6,7,8] and time-averaged diffusion coefficients [9]

Methods

Results

Conclusion