Claudin 11 Stops The Leaks In Neuronal Myelin Sheaths

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Claudin 11 Stops The Leaks In Neuronal Myelin Sheaths

http://www.medicalnewstoday.com/articles/131339.php

Devaux and Gow demonstrate how a tight junction protein called

claudin 11 makes the neuronal myelin sheath a snug fit. The study

will be published in the December 1, 2008 issue of the Journal of

Cell Biology (http://www.jcb.org).

Like the rubber coating on a copper wire, the myelin sheath - a

membrane extension of glial cells that spirals around the axons of

neurons - creates an insulation layer that prevents current leakage

from axons and aids electrical conduction along the length of the

axon.

Claudin 11 forms tight junctions between successive spiral layers of

the myelin sheath, but it was unknown whether it was required for

myelin to act as a good insulator. To examine this question, Devaux

and Gow compared electrical recordings from the optic nerve of wild-

type and claudin 11 knockout mice. They found that although claudin

11 deficiency caused no gross defects in the appearance of the myelin

sheath, it slowed electrical signals - at least in neurons with small-

diameter axons.

Using a computer model that incorporates the resistive and capacitive

properties of axons (and their myelin sheaths), the authors showed

that claudin 11 adds to the electrical resistance of myelin by

preventing leakage of charged ions (and electrical current) through

the spiral space between myelin layers. The reduced resistance in the

absence of claudin 11 affects small-diameter axons most severely

because such axons have thinner myelin sheaths and thus less

insulation to begin with. Because neurons with small-diameter axons

are mostly found in the CNS, the authors speculate that defects in

claudin 11 could be associated with deficits in cognition and

perception, like those found in schizophrenia or neurodegenerative

diseases.