The neurogenic niche is thought to be a specialized microenvironment within the adult brain, which has the capacity to sustain self-renewal of multipotent NSC and promote their migration, as well as their differentiation into neurons and glia (Ninkovic and Gotz, 2007). Adult progenitor cells derived from nonneurogenic areas exhibit self renewal and multipotentiality once transplanted in a neurogenic brain area, and can differentiate in a region-specific context, suggesting that the microenvironment has a crucial role in providing and regulating fate-determining cues of in the adult brain (Shihabuddin et al., 2000). What makes the SVZ and SGL special in supporting the proliferation and differentiation of multipotent neural progenitors is an area of intensive investigation. It is postulated that endothelial cells and some special astrocytes provide a unique neurogenic niche and have the capability to promote proliferation and neuronal fate determination (Lie et al., 2004; Doetsch, 2003a; Doetsch, 2003b; Lim and Alvarez-Buylla, 1999; Song et al., 2002a). In contrast, astrocytes from nonneurogenic regions, e.g., the adult spinal cord, do not promote either proliferation or neuronal differentiation (Song et al., 2002a). In vivo
