schwann cells

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Abstract from Nature 431, 191 - 195 (09 September 2004);

doi:10.1038/nature02841

Restricted growth of Schwann cells lacking Cajal bands slows conduction

in myelinated nerves

FELIPE A. COURT, DIANE L. SHERMAN, THOMAS PRATT, EMER M. GARRY, RICHARD

R. RIBCHESTER, DAVID F. COTTRELL, SUSAN M. FLEETWOOD-WALKER & PETER J.

BROPHY

Centre for Neuroscience Research, University of Edinburgh, Edinburgh EH9

1QH, UK

Nerve impulses are propagated at nodes of Ranvier in the myelinated

nerves of vertebrates. Internodal distances have been proposed to affect

the velocity of nerve impulse conduction; however, direct evidence is

lacking, and the cellular mechanisms that might regulate the length of

the myelinated segments are unknown. Ramón y Cajal described

longitudinal and transverse bands of cytoplasm or trabeculae in

internodal Schwann cells and suggested that they had a nutritive

function. Here we show that internodal growth in wild-type nerves is

precisely matched to nerve extension, but disruption of the cytoplasmic

bands in Periaxin-null mice impairs Schwann cell elongation during nerve

growth. By contrast, myelination proceeds normally. The capacity of

wild-type and mutant Schwann cells to elongate is cell-autonomous,

indicating that passive stretching can account for the lengthening of

the internode during limb growth. As predicted on theoretical grounds,

decreased internodal distances strikingly decrease conduction velocities

and so affect motor function. We propose that microtubule-based

transport in the longitudinal bands of Cajal permits internodal Schwann

cells to lengthen in response to axonal growth, thus ensuring rapid

nerve impulse transmission.