title: Identifying directional persistence in intracellular particle motion using Hidden Markov Models.
abstract: Particle tracking is a widely used and promising technique for elucidating complex dynamics of the living cell. The cytoplasm is an active material, in which the kinetics of intracellular structures are highly heterogeneous. Tracer particles typically undergo a combination of random motion and various types of directed motion caused by the activity of molecular motors and other non-equilibrium processes. Random switching between more and less directional persistence of motion generally occurs. We present a method for identifying states of motion with different directional persistence in individual particle trajectories. Our analysis is based on a multi-scale turning angle model to characterize motion locally, together with a Hidden Markov Model with two states representing different directional persistence. We define one of the states by the motion of particles in a reference data set where some active processes have been inhibited. We illustrate the usefulness of the method by studying transport of vesicles along microtubules and transport of nanospheres activated by myosin. We study the results using mean square displacements, durations, and particle speeds within each state. We conclude that the method provides accurate identification of states of motion with different directional persistence, with very good agreement in terms of mean-squared displacement between the reference data set and one of the states in the two-state model.
authors.affiliation: Department of Mathematical Statistics, Chalmers University of Technology and Gothenburg University, Gothenburg, Sweden. Electronic address: roding@chalmers.se.
authors.forename: Magnus
authors.initials: M
authors.lastname: Röding
authors.affiliation: School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA.
authors.forename: Ming
authors.initials: M
authors.lastname: Guo
authors.affiliation: School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Weitz
authors.affiliation: Department of Mathematical Statistics, Chalmers University of Technology and Gothenburg University, Gothenburg, Sweden.
authors.forename: Mats
authors.initials: M
authors.lastname: Rudemo
authors.affiliation: Department of Mathematical Statistics, Chalmers University of Technology and Gothenburg University, Gothenburg, Sweden.
authors.forename: Aila
authors.initials: A
authors.lastname: Särkkä
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D055592:Biophysical Phenomena; D002460:Cell Line; D003593:Cytoplasm / Q000502:physiology*; D008390:Markov Chains; D055641:Mathematical Concepts; D008870:Microtubules / Q000502:physiology; D008954:Models, Biological; D020409:Molecular Motor Proteins / Q000502:physiology; D009038:Motion; D009218:Myosins / Q000502:physiology; D054118:Nanospheres; D011137:Polystyrenes; D051381:Rats
chemical_list: D020409:Molecular Motor Proteins; D011137:Polystyrenes; D009218:Myosins
keywords: Hidden Markov Models; Intracellular transport; Particle tracking; Transport processes