Abstract
Neurons are specialized cells with an axon for signal conduction and transmission and dendrites for signal reception. Newly synthesized proteins in the cell body are packed into vesicular structures and are then transported by individual transporters to their destinations. Molecular motors as kinesins and dyneins are responsible for the long-range cargo (precursors, synaptic vesicles, mitochondria, RNA granules etc.) transport in neurons. Motor-cargo recognition and regulation of transport, however, remains broadly elusive. Kinesin-3 motor KIF1A/UNC-104 is responsible for synaptic vesicle precursor transport. Recent studies reveal that the pre-synaptic protein Liprin-α/SYD-2 regulates KIF1A/UNC-104 clustering along axons and motor transport efficiency. KIF1A/UNC-104 is known to attach to synaptic vesicles through a motor-lipid interaction. The C-terminal PH-domain of KIF1A/UNC-104 can specifically and directly bind to acidic phospholipids (PIP2), which are located in the vesicle membrane, and thereby connect the motor to the cargo. However, in this study we propose that the sole lipid-PH-domain interaction may not be sufficient for motor-cargo binding and recognition. Interestingly, RIM/UNC-10 reveals a binding site for Liprin-α/SYD-2 at the C-terminus while its N-terminus binds to Rab3/RAB-3. Therefore, we propose an additional linker RAB-3/UNC-10/SYD-2 for the UNC-104/vesicle interaction. Thus, we set out to investigate colocalization between UNC-104ΔPH::GFP and SNB-1::mRFP as well as UNC-104ΔPH::GFP and mCherry::RAB-3 to understand whether or not the additional linkage exists between UNC-104 and synaptic vesicle, and results revealed that there is no difference between RAB-3- or SNB-1-carrying vesicles. To understand the role of UNC-10 and SYD-2 on SNB-1 and RAB-3 vesicle transport, we monitored axonal trafficking using confocal spinning disk microscopy in C. elegans carrying unc-10 and syd-2 null mutations, and results revealed that both RAB-3 and SNB-1 trafficking were affected in syd-2 background, while in unc-10 mutants only RAB-3 trafficking was affected, and this may suggest that the proposed additional linkage RAB-3—UNC-10—SYD-2 may exist and help motor associate with its cargo.