GFAP promoter-controlled EGFP-expressing transgenic mice: A tool to visualize astrocytes and astrogliosis in living brain tissue

We have generated transgenic mice in which astrocytes are labeled by the en hanced green fluorescent protein (EGFP) under the control of the human glia l fibrillary acidic protein (GFAP) promoter. In all regions of the CNS, suc h as cortex, cerebellum, striatum, corpus callosum, hippocampus, retina, an d spinal cord, EGFP-positive cells with morphological properties of astrocy tes could be readily visualized by direct fluorescence microscopy in living brain slices or whole mounts. Also in the PNS, nonmyelinating Schwann cell s from the sciatic nerve could be identified by their bright green fluoresc ence. Highest EGFP expression was found in the cerebellum. Already in acute ly prepared whole brain, the cerebellum appeared green-yellowish under norm al daylight. Colabeling with GFAP antibodies revealed an overlap with EGFP in the majority of cells. Some brain areas, however, such as retina or hypo thalamus, showed only low levels of EGFP expression, although the astrocyte s were rich in GFAP. In contrast, some areas that were poor in immunoreacti ve GFAP were conspicuous for their EGFP expression. Applying the patch clam p technique in brain slices, EGFP-positive cells exhibited two types of mem brane properties, a passive membrane conductance as described for astrocyte s and voltage-gated channels as described for glial precursor cells. Electr on microscopical investigation of ultrastructural properties revealed EGFP- positive cells enwrapping synapses by their fine membrane processes. EGFP-p ositive cells were negative for oligodendrocyte (MAG) and neuronal markers (NeuN). As response to injury, i.e., by cortical stab wounds, enhanced leve ls of EGFP expression delineated the lesion site and could thus be used as a live marker for pathology. GLIA 33:72-86, 2001. (C) 2001 Wiley-Liss, Inc.