Opening the Way for Nerve Regeneration Studies in Worms

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Opening the Way for Nerve Regeneration Studies in Worms December 16, 2004

http://www.hhmi.org//news/jin.html (photos at website)

Using a precisely targeted laser, researchers have snipped apart a single neuron

in the roundworm C. elegans — an achievement that opens a new avenue for

studying nerve regeneration in this genetically manipulable animal. Indeed,

their initial studies have demonstrated that the severed nerves of worms are

capable of regenerating and regaining full function.

According to the researchers, studying nerve regeneration in the worm could

provide answers to questions that are not accessible currently by doing

experiments in more complex animals, including mice and zebrafish.

“Until now there has been little study of nerve regeneration using genetic

methodology, because most studies have been done on higher vertebrate

organisms.” Yishi Jin

A research team that included Yishi Jin, a Medical Institute

investigator at the University of California, Santa Cruz (UCSC),

Chisholm, also of UCSC, and Adela Ben-Yakar, who was at Stanford University and

is now at the University of Texas at Austin, reported its achievement in the

December 16, 2004, issue of the journal Nature. Other co-authors are from

Stanford University and UCSC.

The researchers used a laser that produces energy pulses of 200-quadrillionths

of a second in a beam focused to less than one-hundredth the diameter of a human

hair. The laser can vaporize tissue precisely without causing extensive heat or

damage that would compromise the viability of the targeted cell or surrounding

tissue, said the researchers.

“This new capability of cutting individual nerves offers the opportunity to use

the well-characterized genetics of C. elegans to study the basic mechanisms of

nerve regeneration,” said Jin. “Until now there has been little study of nerve

regeneration using genetic methodology, because most studies have been done on

higher vertebrate organisms, where following the consequences of genetic

manipulation is not yet readily accessible.” Such studies, said Jin, would

involve making mutations in genes believed to be involved in nerve regeneration

and studying the effects on regeneration following laser severing of the nerves.

In the experiments reported in Nature, the researchers first introduced a gene

that produced a green fluorescent protein in the target nerve, in this case, one

that controls a particular muscle movement in the worm. When they directed the

laser at the cable-like axon that snaked away from the nerve-cell body, they

found they could precisely sever the axon. They observed that both ends of the

severed nerve axon immediately retracted, but that in about half the cases, the

nerve regrew in about a day. By doing dye-uptake experiments, the researchers

could see that the laser had actually cut the axons, and had not simply bleached

the region hit by the beam.

The researchers also noticed an intriguing and potentially important result: The

worms that had been operated on showed evidence that the nerves had regrown and

also regained the ability to move the muscle served by the neuron. This

observation indicated that the regrowth of the nerve caused functional changes.

Among the immediate questions raised by the new experiments is how the nerves

regrow after cutting, said Jin. “We see that the proximal end, nearest the cell

body, appears to begin regrowth, and the distal end seems to hang around for a

while. Depending on how fast the proximal end regrows, it might attach to the

distal end. Otherwise, the distal end seems to deteriorate, and the nerve

regeneration will proceed from the proximal end. However, we will need to do

more detailed studies to determine whether regeneration is of the two cut axons,

or due to a complete regrowth,” she said.

According to Jin, the laser they used had a custom-built apparatus to permit the

precise focus of laser on biological samples, but the laser itself is available

commercially. Thus, the technique can be readily adopted by other laboratories,

she said. And with its proven ability to cut individual nerves, Jin said she

could envision the laser being used for other applications, such as selective

ablation of subcellular structures, to explore their role in nerve regeneration.