(A–A′) Expression of Tenascin C, a glycoprotein secreted by astrocyte precursor cells, is strongly reduced in the E18.5 Mek1,2\Nes cortex. (B–B′) BLBP immunostaining revealed a dramatic reduction in astrocyte precursor number in mutant cortex. Scale bar=100 μm. (C–C′) High magnification images of BLBP+ cells from delineated areas in B and B′. BLBP+ cell somas, which represent astrocytes precursors, were nearly absent in the mutant cortex at P0. Scale bars=50μm. (n=3). (D–E′) The numbers of Olig2+ and PDGFRα+ oligodendrocyte progenitor cells are profoundly reduced in the E19.5 mutant dorsal cortex. (n=3). Scale bar=100μm. (F) Western blotting confirms reduced Aldh1l1 and Acsbg1 expression in Mek1,2\Nes dorsal cortex compared to WT. 1 and 2 indicate duplicate protein samples. (mean ± s.e.m; ** = p-value < 0.01, paired t-test). (G) Microarray analysis shows dramatic reductions of mRNAs expressed specifically in glial progenitors in Mek1,2\Nes dorsal cortex, while expression of the neuronal genes shown was not altered. See also Figure S2.