Developmental Regulation of Sensory Axon Regeneration in the Absence of Growth Cones

J Neurobiol, 2006 · DOI: 10.1002/neu.20309 · Published: December 1, 2006

Regenerative Medicine Neurology Genetics

Simple Explanation

This study investigates how nerve cells (neurons) regenerate their long extensions (axons) during development. The researchers looked at early (E7) and late (E14) embryonic chicken sensory neurons. They found that early neurons need a structure made of actin (F-actin) to regenerate, while later neurons can regenerate even without it. This difference is linked to changes in the way another structure, microtubules, works in the neurons. The study suggests that targeting microtubules might be a way to help mature neurons regenerate after injury.

Study Duration

Not specified

Participants

Chicken embryonic dorsal root ganglia neurons at embryonic day (E) 7 and 14

Evidence Level

In vitro experimental study

Key Findings

1
Early embryonic (E7) sensory axons strictly require F-actin for axon maintenance and regeneration, whereas later embryonic (E14) axons can extend even in the absence of F-actin.
2
The ability of E14 axons to extend without F-actin is dependent on microtubule tip polymerization, indicating a developmental switch in the cytoskeletal mechanisms of axon regeneration.
3
E14 axons exhibit decreased net microtubule dynamics relative to E7 axons, but their extension is more sensitive to inhibition of microtubule dynamic instability.

Research Summary

This study demonstrates that the mechanism of axon regeneration undergoes a developmental switch between E7 and E14 from strict dependence on F-actin to a greater dependence on microtubule polymerization. The growth cones of E7 axons contained more F-actin and were more elaborate than those of E14 axons. The study indicates that microtubule polymerization may be a therapeutic target for promoting regeneration of mature neurons.

Practical Implications

Therapeutic Target

Microtubule polymerization may be a therapeutic target for promoting regeneration of mature neurons.

Developmental Stage Consideration

The developmental age of the neuron must be taken into consideration when comparing and designing experiments on the mechanisms of axon extension.

Extrapolation Caution

Care must be taken in the extrapolation of information obtained from studies of the cytoskeletal basis of axon extension in early embryonic neurons to the mechanism of axon extension underlying the regeneration of more mature axons.

Study Limitations

1
In vitro model system may not fully replicate in vivo conditions.
2
Axons regenerating in vitro may experience different extracellular signals compared to in vivo.
3
Growth cones and axons may be responding in a developmentally regulated manner to some aspect of the culturing environment.

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