Fig. 4. Ascl1 defines lineage-restricted precursors of neurons and oligodendrocytes. (A) Time line depicting major periods of neurogenesis and gliogenesis during mouse embryonic spinal cord development. Arrowheads indicate individual time points for tamoxifen induction. (B-N) P30 spinal cords from Ascl1-CreER^TM;R26R-lacZ (B,C,E-H,K-N) or Nestin-CreER^T2;R26R-lacZ (D,I,J) stained for ß-gal activity (B-D,K-N) or double-label immunofluorescence for ß-gal (green) and NeuN (red) (E,G,I) or APC (red) (F,H,J). In Ascl1-CreER^TM;R26R-lacZ mice, activation of Cre by tamoxifen at E10.5 results in X-gal labeled cells largely restricted to the dorsal horn gray matter (B) in cells that co-label with the neuronal marker NeuN (E, arrows). Activation of Cre at E15.5 results in X-gal labeled cells largely restricted to white matter regions (C) in cells that co-label with the oligodendrocyte marker APC (H, arrows). By contrast, in Nestin-CreER^T2;R26R-lacZ, activation of Cre at E10.5 results in X-gal labeled cells in both gray and white matter throughout the dorsoventral axis (D) and cells co-label with both NeuN and APC (I,J, arrows).