Fruit Fly Neuron Can Reprogram Itself After Injury

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Fruit Fly Neuron Can Reprogram Itself After Injury

http://www.medicalnewstoday.com/articles/173168.php

Studies with fruit flies have shown that the specialized nerve cells called

neurons can rebuild themselves after injury.

These results, potentially relevant to research efforts to improve the treatment

of patients with traumatic nerve damage or neurodegenerative disease, were

presented at the American Society for Cell Biology (ASCB) 49th Annual Meeting,

Dec. 5-9, 2009 in San Diego.

An injured neuron's remarkable ability to reprogram itself was reported by

Stone, Rolls, Ph.D., and colleagues at Penn State University

(PSU).

The scientists said that the reprogramming was particularly surprising because

once formed, neurons normally are relatively staid and stable, and because the

injured part of the neuron was " replaced " by a very structurally and

functionally different component of the same cell.

It's in the nature of the neuron's job to maintain and keep the parts that were

present when it was created.

The PSU scientists experimentally induced the injury to the neuron in the

Drosophila melanogaster's brain by using a laser to cut off the entire axon, the

long, slender part that sends the neuron's signals to the brain's other cells.

In response to the injury, the dendrites, the parts of the neuron that receives

signals from other cells in the brain, reshuffled their internal support

structures, or cytoskeletons. Eventually one of the dendrites switched its

polarity and grew into a permanent replacement for the damaged axon.

Polarity refers to the varying degrees of structural and functional asymmetry

that characterize the neuron's parts.

The polarity of the microtubules in axons and dendrites differ, reflecting the

different roles of these cellular structures.

Microtubules, the basic units of the cytoskeleton, are polymerized proteins that

stack up into a strong, stable and highly polarized cellular backbone that also

acts as an internal trackway for long-range intracellular transport.

When the researchers used a laser to cut off the entire axon of the Drosophila

neuron, the supposedly stable dendritic microtubules burst into action,

essentially deconstructing and rebuilding the entire dendritic microtubule

cytoskeleton.

Growing microtubules dramatically increased in number, and their polarity became

fluid. This dynamic microtubule response, the researchers said, was specific to

axon, not dendrite, injury.

Only two to three days after the injury, the one dendrite finally took on its

new axonal microtubule polarity and began forming an axon.

Microtubule dynamics settled down in the remaining dendrites, assuming the

normal overall layout that characterized the neuron before the injury. The

repaired neuron had one axon and several dendrites with opposite microtubule

orientation.

Stone and colleagues said that they believe that exploring microtubule control

is critical to understanding how axons regenerate from dendrites.

By manipulating levels of intracellular proteins, the researchers discovered

that they could speed up the dendrite-to-axon transformation by slowing down

microtubule dynamics.

This antagonism could be important to allow the neuron to correctly repolarize

its microtubules before growing the new axon, they said. Finding the exact

mechanisms that control dendrite regeneration is the work ahead.

The paper, " Reversal of neuronal polarity after axon removal: converting a

dendrite into a regenerating axon by rebuilding the microtubule cytoskeleton, "

was presented Sunday, Dec. 6, 10:15-10:35 a.m. Minisymposium #3 Cell Polarity,

Program #19, Room 28A-E.