Sub-cellular distribution of UNC-104(KIF1A) upon binding to adaptors as UNC-16(JIP3), DNC-1(DCTN1/Glued) and SYD-2(Liprin-α) in C. elegans neurons.

The accumulation of cargo (tau, amyloid precursor protein, neurofilaments etc.) in neurons is a hallmark of various neurodegenerative diseases while we have only little knowledge how axonal transport is regulated. Kinesin-3 UNC-104(KIF1A) is the major transporter of synaptic vesicles and recent reports suggest that a cargo itself can affect the motor's activity. Inspecting an interactome map, we identify three putative UNC-104 interactors, namely UNC-16(JIP3), DNC-1(DCTN1/Glued) and SYD-2(Liprin-α), known to be adaptors in essential neuronal protein complexes. We then employed the novel method bimolecular fluorescence complementation (BiFC) assay to visualize motor-adaptor complexes in the nervous system of living C. elegans. Interestingly, the binding of UNC-104 to each adaptor protein results in different sub-cellular distributions and has distinctive effects on the motor's motility. Specifically, if UNC-104 bound to UNC-16, the motor is primarily localized in the soma of neurons while bound to DNC-1, the motor is basically found in axonal termini. On the other hand, if UNC-104 is bound to SYD-2 we identify motor populations mostly along axons. Therefore, these three adaptors inherit different functions in steering the motor to specific sub-cellular locations in the neuron.

Mechanisms of mitochondria-neurofilament interactions.

Mitochondria are localized to regions of the cell where ATP consumption is high and are dispersed according to changes in local energy needs. In addition to motion directed by molecular motors, mitochondrial distribution in neuronal cells appears to depend on the docking of mitochondria to microtubules and neurofilaments. We examined interactions between mitochondria and neurofilaments using fluorescence microscopy, dynamic light scattering, atomic force microscopy, and sedimentation assays. Mitochondria-neurofilament interactions depend on mitochondrial membrane potential, as revealed by staining with a membrane potential sensitive dye (JC-1) in the presence of substrates/ADP or uncouplers (valinomycin/carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone) and are affected by the phosphorylation status of neurofilaments and neurofilament sidearms. Antibodies against the neurofilament heavy subunit disrupt binding between mitochondria and neurofilaments, and isolated neurofilament sidearms alone interact with mitochondria, suggesting that they mediate the interactions between the two structures. These data suggest that specific and regulated mitochondrial-neurofilament interactions occur in situ and may contribute to the dynamic distribution of these organelles within the cytoplasm of neurons.