Human Glial Fibrillary Acidic Protein delta (GFAP-delta) is a GFAP protein isoform that is encoded by an alternative splice variant of the GFAP-gene. As a result, GFAP-delta protein differs from the predominant splice form, GFAP-alpha, by its C-terminal protein sequence. GFAP-delta protein is not expressed by all GFAP expressing astrocytes but specifically by a subpopulation located in the subpial zone of the cerebral cortex, the subgranular zone of the hippocampus and, most intensely, by a ribbon of astrocytes following the ependymal layer of the cerebral ventricles. Therefore, at least in the sub ventricular zone (SVZ), GFAP-delta specifically marks the population of astrocytes that contain the neural stem cells in the adult human brain. Interestingly, the SVZ astrocytes actively splice GFAP-delta transcripts, in contrast to astrocytes adjacent to this layer. Data shows that GFAP-delta protein, unlike GFAP-alpha, is not upregulated in astrogliosis. Data indicates a different functional role for GFAP-delta in astrocyte physiology. Transfection studies showed that GFAP-delta protein expression has a negative effect on GFAP filament formation, and therefore could be important for modulating intermediate filament cytoskeletal properties, possibly facilitating astrocyte motility. Further studies on GFAP-delta and the cells that express it are important for gaining insights into its function during differentiation, migration and during health and disease (Roelofs, RF, et al., Glia (2005) 52:289-300.).