Variations in Promoter Activity Reveal a Differential Expression and Physiology of Glutamate Transporters by Glia in the Developing and Mature CNS

Abstract

Glutamate transporters regulate excitatory neurotransmission and prevent glutamate-mediated excitotoxicity in the CNS. To better study the cellular and temporal dynamics of the expression of these transporters, we generated bacterial artificial chromosome promoter Discosoma red [glutamate-aspartate transporter (GLAST)] and green fluorescent protein [glutamate transporter-1 (GLT-1)] reporter transgenic mice. Analysis of these mice revealed a differential activation of the transporter promoters not previously appreciated. GLT-1 promoter activity in the adult CNS is almost completely restricted to astrocytes, often and unexpectedly in a nonoverlapping pattern with GLAST. Spinal cord GLT-1 promoter reporter, protein density, and physiology were 10-fold lower than in brain, suggesting a possible mechanism for regional sensitivity seen in disease. The GLAST promoter is active in both radial glia and many astrocytes in the developing CNS but is downregulated in most astrocytes as the mice mature. In the adult CNS, the highest GLAST promoter activity was observed in radial glia, such as those located in the subgranular layer of the dentate gyrus. The continued expression of GLAST by these neural progenitors raises the possibility that GLAST may have an unanticipated role in regulating their behavior. In addition, GLAST promoter activation was observed in oligodendrocytes in white matter throughout many (e.g., spinal cord and corpus callosum), but not all (e.g., cerebellum), CNS fiber tracts. Overall, these studies of GLT-1 and GLAST promoter activity, protein expression, and glutamate uptake revealed a close correlation between transgenic reporter signals and uptake capacity, indicating that these mice provide the means to monitor the expression and regulation of glutamate transporters in situ.

Critical role of aquaporin-4 (AQP4) in astrocytic Ca 2+ signaling events elicited by cerebral edema

“…Astrocytes were readily detected by two-photon imaging after the slice had been incubated with the fluorescent dye Texas red hydrazide, an approach similar to that described for sulphorhodamine 101 (11,12). Dye loading of slices obtained from transgenic mice that express EGFP under control of the Glt-1 promoter (Glt-1-EGFP BAC transgenic mice) (13) confirmed that Texas red hydrazide was selectively taken up by GFP-expressing astrocytes (Fig. 1D).…”

Plasticity of astroglial networks in olfactory glomeruli

“…1073/pnas.1107386108/-/DCSupplemental. the glutamate transporter-1 (GLT-1)/EGFP BAC reporter mice (15), in which most astrocytes are GFP + . Indeed, in the GL, GFAP and S100 immunoreactivity was detected in most of the GFP + cells, whereas GFP never colocalized with NeuN or NG2 immunoreactivity (SI Appendix, Fig.…”

Loss of Glial Glutamate and Aspartate Transporter (Excitatory Amino Acid Transporter 1) Causes Locomotor Hyperactivity and Exaggerated Responses to Psychotomimetics: Rescue by Haloperidol and Metabotropic Glutamate 2/3 Agonist

“…Second, although acute loss of glutamate clearance provides a plausible mechanism for the 'schizophrenia-related' abnormalities in GLAST KO, this does not exclude the potential for constitutive loss of GLAST to cause more permanent neural changes resulting from excitotoxicity (18,20) or developmental abnormalities. The neurodevelopment issue is particularly intriguing given that high transient GLAST gene promoter activity is present during early postnatal mouse development in both the cortex and hippocampus (23) and the posited neurodevelopmental ontogeny of schizophrenia. Third, possible GLAST KO abnormalities on behaviors pertinent to the negative and cognitive symptoms of schizophrenia await further study.…”