3.4. Axonal transport imaging in freely orientated axons
In addition to the above work for fluorescence imaging, we further
undertook axonal transport imaging in freely orientated axons.
Unlike the microchannel-culturing
method,[10,27] coverslip-culturing method provided
a freely orientated growth pattern for natural morphogenesis owing to no
space limitation in the culture environment, thus obtaining
multifurcated axons with mCherry located at lysosomes. Hence, four
axonal transport models were observed. The first one is the forward or
backward transport model (Figure 4A and Video S1) in a ring-like axon,
most of the particles moved forward while others moved backwards. One
classic interpretation comes from the tug-of-war
model[28] that mainly contained two kinds of motor
proteins, dyneins and kinesins, which determine the direction by
integrating the force from a mole ratio between these two proteins,
retrograde or anterograde.[29] The second model is
the stop-and-go model in which particles previously moved then suddenly
came to rest together at a certain moment (Video S2). In Figure 4B,
particles were moving before 215 s, and keeping still for the rest of
the time. On the one hand, we attributed this static state to the
discontinuity of ATP supply because axonal transport is dependent on the
supply of ATP to drive the motor proteins.[30] On
the other hand, axonal transport-related regulatory proteins in axons
may also contribute to stop or start the transport of particles in the
axons.[31]