Mice carrying this transgene express beta galactosidase in the nuclei of astrocytes. Transgenic mice exhibit upregulation of GFAP gene activity similar to that which follows injury to the brain. The transgene inserted on the X Chromosome and appears to undergo the usual random inactivation that achieves gene dosage compensation in females. The brains of hemizygous females stain uniformly rather than displaying mosaic patches, suggesting that astrocytes intermingle following their formation.