Fig. 1. Transient Olig2 expression in developing cortical astrocytes. (A-E) Sagittal cortical sections from wild-type mice at P5 were immunostained with antibodies against GFAP, Olig2 or glutamine synthetase (GS). (A) GFAP⁺ cells (red) at this stage expressed a high level of Olig2 (green) as judged by staining intensity. Orthogonal reconstructions of confocal images at z-axis level are shown in side panels (along the right-hand edge and beneath). Arrowheads indicate GFAP⁺ Olig2⁺ double-positive cells. A GFAP⁺ Olig2⁺ cell, marked by cross-lines, is shown at a higher magnification in B-B''. (C-E) Co-expression (E) of GFAP (C, red) and GS (D, green) was observed in the astrocytes of the neonatal cortex. (F-K) Sagittal cortical sections of wild-type mice at P5 (F,G), P14 (H,I) and P21 (J,K) were immunostained with antibodies against Olig2 and GS. Confocal images at z-axis level are shown in side panels of G and I. (F,G) GS⁺ astrocytes (red) express a high level of Olig2 (green) at P5. Arrowheads indicate GS⁺ Olig2⁺ double-positive cells. (H,I) At P14, Olig2 expression in GS⁺ astrocytes (arrowheads) is reduced to a low level as compared with the intense Olig2 expression in GS^- cells (blue arrows). (J,K) At P21, Olig2 expression (green) is undetectable in GS⁺ astrocytes (red) in the cortex. (L-O) The corpus callosum region of wild-type mice at P5 was immunostained with antibodies against GFAP and Olig2. Arrowheads indicate GFAP⁺ Olig2⁺ double-positive cells in this developing white matter. The boxed area in L is shown at a higher magnification in M-O. Orthogonal reconstructions of confocal images at z-axis level are shown for a GFAP⁺ Olig2⁺ cell marked by crosslines in O. Scale bars: 50 µm in A,F-L.