title: Role of radial fibers in controlling the onset of myelination.
abstract: Recent in vitro study showed that astrocytes induce oligodendrocyte processes to adhere to axons. However, the role of astrocytes in myelination in vivo remains unknown. We have, therefore, conducted a study to clarify the possible involvement of astrocytes during the initial myelination process. In newborn mice, the expression of glial fibrillary acidic protein (GFAP), a marker for astrocytes, was restricted to a few fibrous architectures in the subventricular zone (SVZ), but we did not observe any GFAP-positive astrocytes. Prior to the onset of myelination, GFAP became transiently expressed in the cells with radial fibers elongating from the SVZ to the pia of cerebral cortex, and myelin-associated glycoprotein (MAG)-positive premyelinating oligodendrocytes appeared as neighbors to them, with the processes attaching to radial fibers, but not to axons. These GFAP-positive "radial" cells lost their fibrous architecture and became typical GFAP-positive astrocytes at about 10 days postnatally, when myelination set in, indicating that the disappearance of radial fibers coordinates with the initiation of myelination. From these results, we propose that premyelinating oligodendrocytes are in contact with radial fibers rather than axons and that the cytoarchitectural transformation of radial fibers into astrocytes is involved substantially in controlling the onset of initial myelination. Our proposal was further confirmed by GFAP-deficient mice, in which the disappearance of these radial fibers and the initiation of myelination were delayed in parallel. Our findings together suggest that myelination in vivo is in concert with astrocytic differentiation, involving radial fibers therein, rather than being a mere axon-oligodendrocyte interaction.
authors.affiliation: Department of Anatomy, Keio University School of Medicine, Shinanomachi, Shinjuku, Tokyo, Japan.
authors.forename: Jin
authors.initials: J
authors.lastname: Nakahara
authors.forename: Masaaki
authors.initials: M
authors.lastname: Takemura
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Gomi
authors.forename: Ken-Ichiro
authors.initials: K
authors.lastname: Tsunematsu
authors.forename: Shigeyoshi
authors.initials: S
authors.lastname: Itohara
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Asou
authors.forename: Masaharu
authors.initials: M
authors.lastname: Ogawa
authors.forename: Sadakazu
authors.initials: S
authors.lastname: Aiso
authors.forename: Kyoko
authors.initials: K
authors.lastname: Tan-Takeuchi
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000166:cytology / Q000502:physiology*; D015153:Blotting, Western; D002454:Cell Differentiation / Q000502:physiology; D002540:Cerebral Cortex / Q000166:cytology* / Q000254:growth & development* / Q000378:metabolism; D005260:Female; D005904:Glial Fibrillary Acidic Protein / Q000172:deficiency / Q000235:genetics; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D018613:Microscopy, Confocal; D018992:Myelin-Associated Glycoprotein / Q000378:metabolism; D009413:Nerve Fibers, Myelinated / Q000502:physiology*; D009836:Oligodendroglia / Q000166:cytology / Q000502:physiology*; D013234:Stem Cells / Q000502:physiology
chemical_list: D005904:Glial Fibrillary Acidic Protein; D018992:Myelin-Associated Glycoprotein