Figure 4. Various transporting behaviors among freely
orientated axons. (A) Forward or backward transport model. Red arrow:
forward moving, green arrow: backward moving. (B) Stop-and-go model.
Red arrow: moving particle, blue
arrow: static particle. (C) Repeated back-and-forth transport model. Red
arrow: moving particle. (D) Cross-branch transport model. Red arrow:
moving particle. Outer scale bar: 20 μm. Inner scale bar: 5 μm.
Another two models are related to axon branches, one is repeated
back-and-forth transport model (Figure 4C and Video S3), a particle
moved back-and-forth across the axon branching point several times, and
the other one is the one-way cross-branch transport model (Figure 4D and
Video S4), a particle came across the axon branching point without
direction change. Unlike linear-orientated axons, collateral branching
derives from a reorganization of microtubule
arrays[32] thereupon making multifurcated axons
more intractable to understand in axonal transport. We suggested that
the original reorganized microtubules at the branch point were not as
orderly as that in the linear axons,[23,33] and
the proteins that are responsible for shunt migration interfered with
each other, which may affect the direction or velocity of moving
particles. These results suggested the axonal transport route in freely
orientated axons is more complicated than that in the linear-orientated
axons, since there are a lot of bends and branch transportation routes
in freely orientated axons.