Our results indicated that hippocampal NPCs were able to generate neurons with phenotypic markers and functional properties that were characteristic of mature DG granule neurons. Next, we determined whether these neurons were able to integrate into the DG in vivo. The hippocampal DG is unique in that it continues to mature during the first 2 weeks of postnatal development in rodents (Hollrigel and Soltesz, 1997). Therefore, we grafted hippocampal NPCs labeled with chicken β-actin (CAG) enhanced green fluorescent protein (EGFP) lentiviral vector into the hippocampus of postnatal day 12 NOD-SCID mice. At 6 weeks posttransplantation, we observed extensive integration of GFP+ cells into the granular cell layer (GCL) of the DG (Figure 5A). We verified the origin of these GFP+ cells using human nuclei (HuNu) staining in the DG of the host tissue (Figure 5C). Quantification of GFP+ cells in the GCL showed that majority of these grafted cells (>80%) stained positive for the neuronal marker, TUJ1, and ∼40% were also positive for the DG granule neuron marker, PROX1 (Figure 5B). These grafted neurons had cell bodies within the GCL
