Fig. 4

GFP expression in a dose-dependent and cell-type specific manner. GFP expression in transfected primary glial cells is both inducible and cell-specific. Astrocytes (A–F) and oligodendrocytes (G–L) were transfected via electroporation with pTetra-MBP-GFP (A–D and G–L) or pEGFP-N2 (E–F), incubated for 24 hr with various concentrations of DOX, and photographed by phase (A, C, E, G, I, K) or fluorescent (B, D, E, H, J, L) microscopy. In the absence of DOX, astrocytes expressed little or no GFP (B), whereas oligodendrocytes expressed low basal levels (H). The presence of 5 µg/ml DOX significantly increased the percentage of GFP⁺ oligodendrocytes (J) but not GFP⁺ astrocytes (D). The percentage of positive cells and the intensity of GFP expression by oligodendrocytes (L) were further increased by 10 µg/ml DOX. The relatively high percentage and intensity of GFP expression by astrocytes transfected with the CMV-GFP construct (F) demonstrated that these cells are readily transferable. Bar = 20 µm. (M) Enlargement of an oligodendrocyte depicted in L expressing GFP.