Non-invasive force measurement reveals the number of active kinesins on a synaptic vesicle precursor in axonal transport regulated by ARL-8

TL;DR

This study introduces a non-invasive force measurement method to quantify active kinesin-3 motors on synaptic vesicle precursors in C. elegans, revealing ARL-8's role in motor activation during axonal transport.

Contribution

It provides a novel non-invasive technique to measure forces on vesicles and demonstrates ARL-8's regulatory effect on motor activation in vivo.

Findings

Fewer force-producing units in arl-8 mutants

Active motor number correlates with ARL-8 presence

Force distribution indicates multiple FPUs per vesicle

Abstract

Kinesin superfamily protein UNC-104, a member of the kinesin-3 family, transports synaptic vesicle precursors (SVPs). In this study, the number of active UNC-104 molecules hauling a single SVP in axons in the worm Caenorhabditis elegans was counted by applying a newly developed non-invasive force measurement technique. The distribution of the force acting on a SVP transported by UNC-104 was spread out over several clusters, implying the presence of several force-producing units (FPUs). We then compared the number of FPUs in the wild-type worms with that in arl-8 gene-deletion mutant worms. ARL-8 is a SVP-bound arf-like small guanosine triphosphatase, and is known to promote unlocking of the autoinhibition of the motor, which is critical for avoiding unnecessary consumption of adenosine triphosphate when the motor does not bind to a SVP. There were fewer FPUs in the arl-8 mutant worms. This finding indicates that a lack of ARL-8 decreased the number of active UNC-104 motors, which then led to a decrease in the number of motors responsible for SVP transport.