Syndecan-3 and syndecan-4 are enriched in Schwann cell perinodal processes.
BACKGROUND
Nodes of Ranvier correspond to specialized axonal domains where voltage-gated sodium channels are highly concentrated. In the peripheral nervous system, they are covered by Schwann cells microvilli, where three homologous cytoskeletal-associated proteins, ezrin, radixin and moesin (ERM proteins) have been found, to be enriched. These glial processes are thought to play a crucial role in organizing axonal nodal domains during development. However, little is known about the molecules present in Schwann cell processes that could mediate axoglial interactions. The aim of this study is to identify by immunocytochemistry transmembrane proteins enriched in Schwann cells processes that could interact, directly or indirectly, with axonal proteins.


RESULTS
We show that syndecan-3 (S3) and syndecan-4 (S4), two proteoglycans expressed in Schwann cells, are enriched in perinodal processes in rat sciatic nerves. S3 labeling was localized in close vicinity of sodium channels as early as post-natal day 2, and highly concentrated at nodes of Ranvier in the adult. S4 immunoreactivity accumulated at nodes later, and was also prominent in internodal regions of myelinated fibers. Both S3 and S4 were co-localized with ezrin in perinodal processes.


CONCLUSIONS
Our data identify S3 and S4 as transmembrane proteins specifically enriched in Schwann cell perinodal processes, and suggest that S3 may be involved in early axoglial interactions during development.
Goutebroze
Laurence
L
INSERM U536, UPMC, Institut du Fer à Moulin, 17 rue du Fer à Moulin, 75005 Paris, France. goutebro@fer-a-moulin.inserm.fr
Carnaud
Michèle
M
Denisenko
Natalia
N
Boutterin
Marie-Claude
MC
Girault
Jean-Antoine
JA
D000818:Animals; D000918:Antibody Specificity; D019556:COS Cells; D002522:Chlorocebus aethiops; D003598:Cytoskeletal Proteins; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D009413:Nerve Fibers, Myelinated / Q000378:metabolism / Q000648:ultrastructure; D010750:Phosphoproteins / Q000096:biosynthesis; D011509:Proteoglycans / Q000235:genetics / Q000378:metabolism*; D011901:Ranvier's Nodes / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats; D012583:Schwann Cells / Q000378:metabolism* / Q000648:ultrastructure; D012584:Sciatic Nerve / Q000378:metabolism / Q000648:ultrastructure; D015222:Sodium Channels / Q000378:metabolism; D053670:Syndecan-3; D053671:Syndecan-4; D014162:Transfection; D000099149:Ezrin
D003598:Cytoskeletal Proteins; D008562:Membrane Glycoproteins; D010750:Phosphoproteins; D011509:Proteoglycans; D015222:Sodium Channels; D053670:Syndecan-3; D053671:Syndecan-4; D000099149:Ezrin; C508303:Sdc3 protein, rat; C508307:Sdc4 protein, rat