(mentions CMT) Researchers disprove 15-year-old theory about the nervous system

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Researchers disprove 15-year-old theory about the nervous system

http://www.bio-medicine.org/biology-news-1/Researchers-disprove-15-

year-old-theory-about-the-nervous-system-6934-2/

A delay in traffic may cause a headache, but a delay in the nervous

system can cause much more. University of Missouri researchers have

uncovered clues identifying which proteins are involved in the

development of the nervous system and found that the proteins

previously thought to play a significant role, in fact, do not.

Understanding how the nervous system develops will give researchers a

better understanding of neurological diseases, such as multiple

sclerosis and Charcot-Marie-Tooth disorders.

" Speed is the key to the nervous system, " said ,

investigator in the S. Bond Life Sciences Center and

assistant professor of biological sciences in the MU College of Arts

and Science. " The peripheral nervous system 'talks' to muscles

through nerve impulses in response to external stimuli. When babies

are born, they do not have fully developed nervous systems, and their

systems run slower. Eventually, the nervous system matures. Our study

tried to understand that maturation process. "

The process of nerve cells maturation is called myelination. During

myelination, a layer of myelin (electrically insulating material)

wraps or forms around the axons (part of the nerve cell that conducts

electrical impulses). Nerve impulses travel faster in myelinated

nerve cells.

" Myelination is important for signal transmission because it

increases nerve conduction velocity, " said. " The relationship

between axons and myelinating cells is a reciprocal one, with each

cell type sending and receiving signals from the other cell. One

signal originates from myelinating cells and results in a large

increase in axonal diameter. "

When nerve cells are unmyelinated, the axon has a smaller diameter

and contains neurofilaments that are less modified and are more

compact. Neurofilaments are a group of proteins that are essential

for diameter growth. The protein group includes neurofilament

subunits that are classified as light, medium and heavy. Loss of all

neurofilaments in the axon results in myelinated axons with slowed

conduction velocities.

For the last 15 years, the proposed underlying mechanism for an

axon's diameter growth has focused on myelin-dependent modification

of regions of neurofilaments that are located within the heavy and

medium subunits. In a previous study, genetically removing the region

of the medium subunit that is modified impaired growth and slowed

nerve conduction. However, this did not directly test if the proposed

modification was required as a much larger region was genetically

removed. In the current study, researchers genetically altered the

neurofilament medium subunit such that it could no longer be modified

in response to myelination. Surprisingly, found that

prevention of what was thought to be an extremely important

modification did not affect axonal diameter.

" It is now clear that the basic mechanism for how neurofilaments

affect axonal diameters remains unanswered, " said. " This

discovery introduces a lot of new questions. "