Spatial organization of axonal microtubules

Area of Science:

• Neuroscience
• Cell Biology
• Cytoskeleton Dynamics

Background:

• Axonal microtubules exhibit a highly uniform polarity orientation, with the plus (+) end consistently distal to the neuronal cell body.
• The mechanisms underlying this precise spatial organization within axons remain incompletely understood.

Purpose of the Study:

• To investigate whether intra-axonal structures or mechanisms are responsible for the uniform polarity of axonal microtubules.
• To explore the role of cold-stable microtubule fragments in microtubule organization and reassembly within axons.

Main Methods:

• Depolymerization of microtubules in isolated cat sympathetic nerve fibers using cold treatment.
• Assessment of cold-stable microtubule fragments and their distribution.
• Induction of microtubule repolymerization and determination of the polarity orientation of reassembled microtubules.

Main Results:

• Cold treatment significantly depolymerized axonal microtubules, leaving fewer than 10% intact.
• A majority of repolymerized microtubules in cold-treated fibers reacquired the original polarity orientation, though less uniformly.
• The degree of original polarity restoration correlated with the number of remaining cold-stable microtubules.
• Rapid microtubule reassembly, followed by a transient decline in number, was observed in most fibers.

Conclusions:

• Stable microtubule fragments likely serve as nucleation sites, playing a crucial role in the spatial organization and polarity of neuronal microtubules.
• The findings support a model of microtubule elongation from existing nucleation centers within the axon.
• The transient peak in microtubule number during reassembly warrants further investigation.