Scientists discover the molecular switch for nerve cells' insulating jelly rolls

[Guest guest]

Scientists discover the molecular switch for nerve cells' insulating

jelly rolls

http://www.medicalnewstoday.com/medicalnews.php?newsid=29943

01 Sep 2005

(I realize this refers more to MS, but in CMT 1A for example, myelin is

affected, so this could help CMT too ~ Gretchen)

Scientists at New York University School of Medicine report in a new

study that they have identified the molecular switch that turns on

the production of myelin, the fatty insulation around nerve cells

that ensures swift and efficient communication in the nervous system.

The study, published in the September 1, 2005, issue of the journal

Neuron, may provide a new avenue for treating nervous system diseases

such as multiple sclerosis, which are associated with damage to

myelin.

A team led by L. Salzer, M.D., Ph.D., Professor of Cell Biology

and Neurology at NYU School of Medicine, identified the long-sought

factor that determines whether or not nerve cells will be wrapped in

thick layers of myelin, producing the biological equivalent of a

jelly roll.

Using a sophisticated system for growing nerve cells in laboratory

dishes, the team identified a gene called neuregulin as the myelin

signal. This signal directs Schwann cells, the nervous system's

cellular architects, to build elaborate sheaths of myelin around the

axons of nerve cells. Axons are the long cable-like arms of nerve

cells that send messages to other cells. The construction of myelin

sheath has been called one of the most beautiful examples of cell

specialization in nature.

Myelin forms the so-called white matter in the nervous system and

constitutes 50 percent of the weight of the brain. It is also an

important component of the spinal cord, and of nerves in other parts

of the body. It has been known for almost 170 years that there are

two kinds of axons --one is wrapped in myelin and appears white and

the other is not and appears gray. Myelinated axons transmit messages

in the nervous system up to 100 times faster than their unmyelinated

cousins and are critical for proper neurological function. However,

it wasn't known what actually initiated myelin production.

The neuregulin gene encodes a growth protein made by neurons. Last

year a group of German scientists discovered that it was implicated

in determining the thickness of the myelin sheath around axons;

however, until now it wasn't clear whether the gene also switched on

production of the sheath.

In a series of experiments, Dr. Carla Taveggia, the first author of

the study and an NYU research scientist, together with collaborators

at NYU, Columbia University College of Physicians and Surgeons, and

other institutions, showed that unmyelinated neurons do not possess

an active neuregulin gene and that myelinated neurons do. In the

first set of experiments, they transplanted unmyelinated axons from

the peripheral nervous system (outside of the brain and spinal cord)

of embryonic mice into laboratory dishes. They then added Schwann

cells to the dishes. They observed that the Schwann cells sat on the

axons and did not produce any myelin.

In the next set of experiments, they inserted the neuregulin gene

into the unmyelinated axons. Instead of just sitting on the axons,

the Schwann cells now produced thick myelin sheaths around them. So

it appears that the gene instructs the Schwann cells to build the

myelin wrap.

Dr. Salzer's group is investigating whether neuregulin has the same

effect on myelination in the central nervous system--the brain and

spinal cord. If so, it may one day be possible to enhance or fix

damaged spinal cords and brain tracts that have lost their myelin due

to injury or disease by transplanting into, or turning on, a

functioning neuregulin gene in nerve cells. " Is it possible that this

same switch can reprogram a nerve cell that has lost myelin due to

injury or disease to repair itself? That is a key question that our

laboratory and others are now actively trying to answer, " he says.

Dr. Salzer's study was supported by grants from the National

Institutes of Health and the National Multiple Sclerosis Society,

among other groups.

New York University Medical Center and School of Medicine

http://www.med.nyu.edu