Fig. 6. Ascl1 facilitates restriction of progenitor cells to the neuronal lineage during neurogenesis. Ascl1-CreER^TM;R26R-YFP transgenic spinal cords, either Ascl1 wild-type (A-F) or Ascl1 null (A'-F'), were examined at E17.5 after tamoxifen induction of Cre at E10.5. Double-label immunofluorescence for YFP (green) and for markers of neurons (NeuN; A,A'), oligodendrocytes (Sox10; B,B'), astrocytes (GFAP; C,C'), neural progenitors or astrocytes (Glast; D,D'), oligodendrocyte progenitors (Olig2; E,E') or proliferation (BrdU incorporation; F,F'). The fate of E10.5 Ascl1-expressing cells shifts from almost exclusively neurons (A, arrowheads) to cells with astrocytic or immature markers such as GFAP, Glast, Olig2 and BrdU in the Ascl1 null (C'-F', arrowheads). Quantification of these experiments is shown in the graph as the percentage of the total YFP-expressing cells that coexpress each marker. At least nine sections from three different embryos of each genotype were used. This resulted in over 350 total YFP+ cells counted in experiments for each marker.