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.