Neurogenesis occurs in a specialized local “niche” that not only houses neural stem cells, but also regulates their development through extrinsic factors (Ma et al., 2005; Ming and Song, 2005). A number of growth factors have been implicated in regulating different steps of the adult neurogenesis process, especially in response to activation of the existing neuronal circuitry, including brain-derived neurotrophic factor (BDNF), fibroblast growth factors (FGFs), vascular endothelial growth factor (VEGF) and neuregulins (NRGs) (Ghashghaei et al., 2006; Jin et al., 2002; Li et al., 2008; Ma et al., 2009; Schmidt and Duman, 2007). AKT signaling is a major pathway in response to these growth factors and recent studies have implicated its role in morphogenesis and dendritic development of post-mitotic dentate granule cells in the adult hippocampus (Kwon et al., 2006; Zhou et al., 2009). In the adult dentate gyrus, the basal levels of pAKT and pS6 are very low in both DCX+ immature neurons and DCX- mature neurons (Figure 1), indicating the existence of an active mechanism to keep AKT signaling in check. Our in vitro biochemical study and
