Patterning of Neurogenesis

sion of members of the Zic gene family (Brewster et al., 1998).cells (Guillemot, 2007). This generation of differentiated cells over a prolonged period necessitates that sufficient neural progenitor cells are maintained throughout development. The regulation of neurogenesis and patterning along the anterior-posterior or dorsoventral axis. These factors can act in a cooper-ative or antagonistic manner; for example, the promotion ofdifferentiation of the correct number of neurons and mainte-nance of progenitors are regulated by extrinsic and intrinsic factors that promote or inhibit neurogenesis, and that regulate neurogenesis by RA being opposed by FGF signaling in the caudal spinal cord (Diez del Corral et al., 2003; Diez del Corral and Storey, 2004). However, for many of these signals, theirDuring development of the vertebrate central nervous system, progenitor cells that comprise the neural epithelium differentiate to form a wide variety of neuronal and glial cell types at appro-priate locations and in correct numbers. The specific cell types formed are regulated spatially by signals that underlie subdivi-sion of the neural epithelium into domains with distinct identity, or that specify distinct subtypes within these regions. Different neuronal and glial cell types are born at different times, with switches in the differentiation of a progenitor population to generate, for example, initially neurons, and subsequently glial An important question is the identity of extrinsic signaling factors that regulate the promotion or inhibition of neurogenesis. A number of signals have been implicated in the control of neurogenesis, including retinoic acid (RA), Wnt, BMP, Shh, and fibroblast growth factor (FGF) family members (Dono, 2003