Fig. 6. Build-up of unspecified postmitotic precursor cells in the IZ of the Ngn2 mutants. (A-C,I-K) Lack of Ngn2 function caused an increase in the number of GFP/GLAST-positive neural progenitors with maintained contact to the ventricular surface compared with wild type (arrows). (D,E) BrdU labeling, however, did not show an increase in the number of proliferating cells or an expansion of the VZ in the Ngn2 mutants. (L,M,O,P) Staining for the neuronal determination factor Neurod1 (double staining with GFP) showed that these IZ cells, in addition to being Nurr1-negative, were Neurod1-negative, with the exception of a few laterally positioned precursors. (G,H) Nuclear DAPI stain of the Neurod1/GFP double-stained sections shows the distribution of cells in the IZ. (F,N) At E15.5, the accumulation of cells, as detected by DAPI, in the VZ/IZ has diminished and more cells are present in the MZ compared with at E13.5 (Fig. 3E,J).