  In this review, we focus on the kinesin-3 family molecular motor protein
UNC-104 and its regulatory protein ARL-8. UNC-104, originally identified in
Caenorhabditis elegans (C. elegans), has a primary role transporting synaptic
vesicle precursors (SVPs). Although in vitro single-molecule experiments have
been performed to primarily investigate the kinesin motor domain, these have
not addressed the in vivo reality of the existence of regulatory proteins, such
as ARL-8, that control kinesin attachment to/detachment from cargo vesicles,
which is essential to the overall transport efficiency of cargo vesicles. To
quantitatively understand the role of the regulatory protein, we review the in
vivo physical parameters of UNC-104-mediated SVP transport, including force,
velocity, run length and run time, derived from wild-type and arl-8-deletion
mutant C. elegans. Our future aim is to facilitate the construction of a
consensus physical model to connect SVP transport with pathologies related to
deficient synapse construction caused by the deficient UNC-104 regulation. We
hope that the physical parameters of SVP transport summarized in this review
become a useful guide for the development of such model.
