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.
Yamada
K
K
Department of Anatomy, Hokkaido University School of Medicine, Sapporo 060-8638, Japan.
Watanabe
M
M
Shibata
T
T
Nagashima
M
M
Tanaka
K
K
Inoue
Y
Y
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