Abstract
Neurons are highly polarized cells that consist of a cell body (soma), dendrites and a long and thin axon. In axons, cytoskeletal filaments (microtubules or microfilaments) serve as “tracks” for transport directed and processive transport of cargo (as synaptic vesicles and precursors). Microtubules are polarized filaments with their plus-ends directed to the synapse and their minus-ends directed towards the cell body of the neuron. Molecular motors carry different cargos along microtubules. There are two classes of molecular motors responsible for cargo transport along microtubules, the kinesin super family motors and cytoplasmic dynein. Kinesin-3 (KIF1A in mammals and UNC-104 in C. elegans) is the major transporter of synaptic vesicles with net movemetns towards plus-ends while dynein is able to transport cargo back towards the minus-ends. Kinesin collaborates with dynein for axonal bi-directional transports. UNC-104 is a monomeric motor that needs to dimerize to become processive while dynein needs an additional adaptor dynactin that facilitates processivity transport. Though kinesin and dynein-based bi-directional movement of vesicles has been well described in the literature, we still lack knowledge about molecular signals that trigger and regulate the specific type of axonal transport. In this study, we use several dynein and dynactin mutant/knockdown strains to study the motility and cluster pattern of UNC-104 in C. elegans. Dynactin mutants and RNAi knockdown affect both anterograde and retrograde transport indicated that dynactin plays a role in both directions of axonal transport. Dynein heavy chain mutant also shows effects in both directions, while the effect on anterograde transport indicates that dynein directly interact with UNC-104 to regulate its motility. Knockdown of dlc-1, dli-1, dyrb-1, and dylt-1 mRNA shows as well defects in both anterograde and retrograde transport. By further analyzing the data, we conclude that dynein affects the bi-directional transport on longer run length, and the effect is more serious for retrograde movements. Dryb-1 and dylt-1 are important for motor persistency no matter in short or long ranges. Most of all, dynein is essential for both retrograde and anterograde axonal bi-directional movement. In this study, mutating as well as knockdown of specific subunits of the dynein/dynactin complex in vivo provides important information how motors and scaffold proteins may cooperatively work and function in axonal bi-directional transport. Our study indicates that dynein and dynactin both play an important role in axonal bi-directional transport.