3D motion of vesicles along microtubules helps them to circumvent obstacles in cells

Abstract

Vesicle transport is regulated at multiple levels, including regulation by scaffolding proteins and the cytoskeleton. This tight regulation is essential, since slowing or stoppage of transport can cause accumulation of obstacles and has been linked to diseases. Understanding the mechanisms by which transport is regulated as well as how motor proteins overcome obstacles can give important clues as to how these mechanisms break down in disease states. Here, we describe that the cytoskeleton architecture impacts transport in a vesicle-size-dependent manner, leading to pausing of vesicles larger than the separation of the microtubules. We further develop methods capable of following 3D transport processes in living cells. Using these methods, we show that vesicles move using two different modes along the microtubule. Off-axis motion, which leads to repositioning of the vesicle in 3D along the microtubule, correlates with the presence of steric obstacles and may help in circumventing them.

Kinesin-1 and dynein use distinct mechanisms to bypass obstacles

“…We also showed that fluidity of the cargo is not essential for this process. 29 These results show that multiplicity of motors not only increases the collective force generation and the length of processive runs on an MT, but also enables motors to maneuver around obstacles in their path. Future studies are required to address how the motor copy number affects the ability of a cargo to bypass dynamic obstacles, such as MAPs.…”

“…30 In addition, correlative live-cell and super-resolution microscopy showed that rotational movement could be used by cargos to avoid steric obstacles. 29 These studies proposed that rotational movement and off-axis stepping might result from having a mix of motors, such as kinesin-2 or dynein, on the cargo along with kinesin-1. While transient back-and-forth movement of a cargo may allow it to change the protofilament track, our results clearly show that tug-of-war between opposite polarity motors is not required to bypass large obstacles.…”

“…Avoiding obstacles larger than a QD, such as a stationary organelle or intersecting cytoskeletal filament, may require a cargo to rotate to the other side of the MT before continuing forward movement. 29 In vivo studies have observed both anterograde and retrograde cargos to bypass stationary organelles 8 . It has been proposed that rotation of a cargo around the MT requires the presence of both kinesin and dynein motors on the cargo or the distortion of the lipid cargo.…”

“…It has been proposed that rotation of a cargo around the MT requires the presence of both kinesin and dynein motors on the cargo or the distortion of the lipid cargo. 26,29,30 To test whether a single type of motor can rotate a rigid cargo around the MT, we tracked beads driven by multiple kinesins or dyneins on MT bridges. If the beads were positioned below the MT when they reached the end of the bridge, they were challenged to bypass the PDMS wall ( Fig.…”

3D rotational motion of an endocytic vesicle on a complex microtubule network in a living cell

“…Additionally, the three-dimensional obstacle-circumventing motion of a vesicle along microtubules was recently reported (18), although the rotations were not found. In the latter study, the circumventing motion of a vesicle was detected when the vesicle encountered an obstacle, such as an intersection of microtubules.…”