Bidirectional transport and pulsing states in a multi-lane ASEP model

TL;DR

This paper introduces a multi-lane ASEP model simulating bidirectional organelle transport along microtubules, revealing how lane changes influence efficiency and lead to pulsing states with phase transitions.

Contribution

The paper develops a novel multi-lane ASEP model incorporating lane changes and bidirectional motion, inspired by in vivo organelle transport experiments.

Findings

Lane changes improve transport efficiency.

Optimal particle direction change rate matches experimental data.

Identification of pulsing states with phase transitions.

Abstract

In this paper, we introduce an ASEP-like transport model for bidirectional motion of particles on a multi-lane lattice. The model is motivated by {\em in vivo} experiments on organelle motility along a microtubule (MT), consisting of thirteen protofilaments, where particles are propelled by molecular motors (dynein and kinesin). In the model, organelles (particles) can switch directions of motion due to "tug-of-war" events between counteracting motors. Collisions of particles on the same lane can be cleared by switching to adjacent protofilaments (lane changes). We analyze transport properties of the model with no-flux boundary conditions at one end of a MT ("plus-end" or tip). We show that the ability of lane changes can affect the transport efficiency and the particle-direction change rate obtained from experiments is close to optimal in order to achieve efficient motor and organelle transport in a living cell. In particular, we find a nonlinear scaling of the mean {\em tip size} (the number of particles accumulated at the tip) with injection rate and an associated phase transition leading to {\em pulsing states} characterized by periodic filling and emptying of the system.