GFAPδ Expression in Glia of the Developmental and Adolescent Mouse Brain

Glial fibrillary acidic protein (GFAP) is the major intermediate filament (IF) protein in astrocytes. In the human brain, GFAP isoforms have unique expression patterns, which indicate that they play distinct functional roles. One isoform, GFAP delta, is expressed by proliferative radial glia in the developing human brain. In the adult human, GFAP delta is a marker for neural stem cells. However, it is unknown whether GFAP delta marks the same population of radial glia and astrocytes in the developing mouse brain as it does in the developing human brain. This study characterizes the expression pattern of GFAP delta throughout mouse embryogenesis and into adolescence. GFAP delta transcripts are expressed from E12, but immunohistochemistry shows GFAP delta staining only from E18. This finding suggests a translational uncoupling. GFAP delta expression increases from E18 to P5 and then decreases until its expression plateaus around P25. During development, GFAP delta is expressed by radial glia, as denoted by the co-expression of markers like vimentin and nestin. GFAP delta is also expressed in other astrocytic populations during development. A similar pattern is observed in the adolescent mouse, where GFAP delta marks both neural stem cells and mature astrocytes. Interestingly, the GFAP delta/Gfap alpha transcript ratio remains stable throughout development as well as in primary astrocyte and neurosphere cultures. These data suggest that all astroglia cells in the developing and adolescent mouse brain express GFAP delta, regardless of their neurogenic capabilities. GFAP delta may be an integral component of all mouse astrocytes, but it is not a specific neural stem cell marker in mice as it is in humans.