The neurogenic niche is comprised of soluble, membrane-tethered and extracellular matrix signaling molecules expressed by endothelial cells, astrocytes and progenitor cells, as well as ependymal cells in the SVZ niche (Lim et al., 2007). Progenitor cells actively interact with their microenvironment and have the capability to regulate it (Song et al., 2002a; Wurmser et al., 2004; Shen et al., 2004). Numerous signaling pathways, some of which are developmental signals, are implicated in regulation of adult neurogenesis, such as GABA receptors, E2F, Ephrins and Eph receptors, the sonic hedgehog signaling pathway, WNT signaling pathway, Notch 1, neural cell adhesion molecule (NCAM), bone morphogenetic protein (BMP), neurogenesin1 (NG1), noggin, reelin signaling pathway, and paired box 6 (PAX6) (Yoshikawa, 2000; Cooper-Kuhn et al., 2002; Conover et al., 2000; Machold et al., 2003; Machold et al., 2007; Lai et al., 2003; Lie et al., 2005; Amoureux et al., 2000; Grandbarbe et al., 2003; Kohwi et al., 2005; Heinrich et al., 2006; Won et al., 2006; Zhao et al., 2007).
