Severed Nerves, Reunited

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Science  22 Apr 2011:
Vol. 332, Issue 6028, pp. 399
DOI: 10.1126/science.332.6028.399-c
CREDIT: NEUMANN ET AL., DEV. DYN. 240, 10.1002/DVDY.22606 (2011)

Peripheral nerves show some ability to regenerate after damage, but it is not an easy process. When an axon is severed, the neuronal cell body must convert the remaining axon stump into a developing axon with a growth cone. Then the axon must find its way past the damaged region and on to its original target, along the way contending with disrupted tissues, inhibitory signals, and an absence of the developmental signals that built the connection in the first place. In crayfish, earthworm, and leech, the tip of a severed axon can actually fuse with the distal remainder of the axon, leapfrogging over regeneration hurdles. Now, Neumann et al. show that axons severed by lasers in the nematode Caenorhabditis elegans can fuse and reestablish function. As the axon stumps regenerated, they often came into contact with the distal remainder, which could then be reincorporated into neuronal function. The membranes fused and cytoplasmic movements connected pre- and post-injury portions of the axon. Without such contact, the distal remainder degenerated and disappeared. When more than one axon was severed, the axons usually found the correct partners. The molecular cues that help a growth cone identify its fusion partner remain to be elucidated.

Dev. Dyn. 240, 10.1002/dvdy.22606 (2011).

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