Fig. 3. Postnatal cortical progenitor cells are restricted to a glial cell fate. Mouse P5 GFP cortical cells were isolated from the subventricular zone, dissociated, cultured over rat E18 or P15 cortical slices for 5 days in vitro, and then processed for double immunofluorescence using anti-GFP (green channel) and anti-MAP-2 (A,B) or anti-BrdU antibodies (C,D; red channel). (A,B) Examples of GFP+/MAP-2- glia growing on top of an E18 slice (A) and a P15 slice (B). (C,D) Examples of GFP+/BrdU+ glia growing on top of an E18 slice (C) and a P15 slice (D). (E,F) Quantification of GFP cells that differentiated into neurons (filled bars) or glia (open bars) when cultured over E18 or P15 slices. Bar heights represent mean ± s.e.m. Note that although P5 GFP cells differentiate into glia in the presence of E18 or P15 slices, the cells acquire different morphologies in the two cases, suggesting that developmentally regulated signals may also play a role in specifying glial morphology. The glia that differentiate on top of E18 slices are always multipolar, while those that differentiate on top of P15 slices have a flattened morphology typical of type 2 astrocytes.