Non-neuronal GFP+ cells displayed characteristics of protoplasmic astrocytes. A–C, Non-neuronal GFP+ cells in developmental columns in adult mice exhibited characteristic protoplasmic astrocyte morphologies (arrows). D–F, A total of 97.5 ± 1.5% (603 cells examined in n = 3 mice) of non-neuronal GFP+ cells expressed S100B, an astrocytic marker. A total of 8.2 ± 3.7% of non-neuronal GFP+ cells (611 cells examined in n = 3 mice) expressed GFAP, a protein expressed in reactive and fibrous astrocytes in cortex. G–I, Labeled cells with neuronal morphologies expressed neither S100B nor GFAP (arrowheads). Conversely, GFP+ cells with astrocytic morphologies did not express NeuN, a mature neuronal marker. The processes of GFP+ astrocytes often encompassed GFP+ neurons. Scale bars: A–F, 10 μm; G–I, 25 μm.