The ability of neurons to generate multiple arbor terminals from a single axon is crucial for establishing proper neuronal wiring. Although growth and retraction of arbor terminals are differentially regulated within the axon, the mechanisms by which neurons locally control their structure remain largely unknown. In the present study, we found that the kinesin-1 (Kif5 proteins) head domain (K5H) preferentially marks a subset of arbor terminals. Time-lapse imaging clarified that these arbor terminals were more stable than others, because of a low retraction rate. Local inhibition of kinesin-1 in the arbor terminal by chromophore-assisted light inactivation (CALI) enhanced the retraction rate. The microtubule turnover was locally regulated depending on the length from the branching point to the terminal end, but did not directly correlate with the presence of K5H. By contrast, F-actin signal values in arbor terminals correlated spatiotemporally with K5H, and inhibition of actin turnover prevented retraction. Results from the present study reveal a new system mediated by kinesin-1 sorting in axons that differentially controls stability of arbor terminals.

No abstract

Neurons can extend branches from a single axon to send signals to multiple target cells. Axonal arbor morphology must be changed to establish and alternate neuronal wiring properly. For this purpose, the elongation and retraction rate of each terminal in a single axonal arbor are differentially regulated. In addition, competitive growth regulation between 2 neighboring branch processes has been observed. The intracellular systems involved in how neurons differentially regulate growth and stability of axonal branches within the same arbor remain largely unknown. Microtubules play critical roles in the formation and maintenance of axonal morphology, and their functions can be differentially regulated in a region-dependent manner within a single cell. Based on our findings, we propose a microtubule-dependent model that contributes to the differential branch growth in axonal arbors.