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 hot spots of cell proliferation in the SGL are found to be in close proximity to capillaries and astrocytes (Palmer et al., 2000; Seri et al., 2001). It is thought that astrocytes in the neurogenic niche have a broad diversity of functions; some exhibit stem cell characteristics (Seri et al., 2001; Doetsch et al., 1999), some provide neurogenic signals (Lim and Alvarez-Buylla, 1999; Song et al., 2002a), and some provide synaptogenic factors (Song et al., 2002b). The neurogenic niche is believed to play a regulatory role in all steps of NSC maturation (Seidenfaden et al., 2006).
