Glutamate transporter GLT-1 is transiently localized on growing axons of the mouse spinal cord before establishing astrocytic expression.
The glutamate transporter GLT-1 is expressed in astrocytes of the mature brain and spinal cord. In the present study, we examined its expression in the developing mouse spinal cord. By in situ hybridization, 35S-labeled antisense oligonucleotide probes for GLT-1 mRNA consistently labeled the mantle zone/gray matter from embryonic day 11 through the adult stage. However, immunohistochemistry with a specific antibody visualized distinct regional and cellular localizations during the time between the fetal and postnatal stages. At fetal stages, GLT-1 immunoreactivity predominated in the marginal zone/white matter, observed as tiny puncta in cross-sections and as thin fibers in longitudinal sections. The GLT-1-immunopositive structures were also labeled for neuron-specific enolase, a glycolytic enzyme specific to postmitotic neurons and endocrine cells. By electron microscopy, GLT-1 immunoreactivity was detected in axons forming frequent enlargements and was focally localized on a small portion of the axolemma, particularly that facing adjacent axons. At early postnatal stages, GLT-1 disappeared from axons in white matter tracts and, instead, appeared in astrocytic processes surrounding various neuronal elements in the gray matter. Therefore, before switching to astrocytic expression, GLT-1 is transiently expressed in neurons and localized in differentiating axons. Together with our previous finding on the localization of glutamate transporter GLAST in radial glial fibers, GLT-1 and GLAST are thus localized during development on distinct directional cellular elements along which young neurons elongate their axons or move their cell bodies, respectively.
Department of Anatomy, Hokkaido University School of Medicine, Sapporo 060-8638, Japan.
K
K
Yamada
M
M
Watanabe
T
T
Shibata
M
M
Nagashima
K
K
Tanaka
Y
Y
Inoue
D018528:ATP-Binding Cassette Transporters / Q000032:analysis*; D000595:Amino Acid Sequence; D027322:Amino Acid Transport System X-AG; D000818:Animals; D000917:Antibody Formation; D001253:Astrocytes / Q000737:chemistry*; D001369:Axons / Q000737:chemistry*; D001692:Biological Transport / Q000502:physiology; D005314:Embryonic and Fetal Development / Q000502:physiology; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000032:analysis*; D009474:Neurons / Q000737:chemistry* / Q000648:ultrastructure; D013116:Spinal Cord / Q000737:chemistry* / Q000196:embryology / Q000254:growth & development; D013997:Time Factors
D018528:ATP-Binding Cassette Transporters; D027322:Amino Acid Transport System X-AG; D009419:Nerve Tissue Proteins