Neurogenesis in the Vertebrate Embryo

The goal of this chapter is to provide a brief overview of how neural progenitors first arise during embryonic development, and how the fate of these progenitors are determined so that they give rise to the diverse types and number of neurons that comprise different regions of the vertebrate central nervous system (CNS). General principles are illustrated by focusing on the spinal cord and the formation of neural precursors that give rise to a specific neuronal subtype, the motor neuron (MN).The development of the central nervous system (CNS) can be represented as a series of fate choices that are progressively made by embryonic cells in response to both intrinsic and extrinsic cues. One of the first fate decisions is made in the ectoderm, where cells form the neuroepithelial cells (NECs) of the neural plate rather than differentiating into nonneural tissues. A key process during neural induction is neural patterning, during which a complex network of gene expression is established along the neuraxis, thereby specifying the position and subsequent fate of NECs. These complex genetic networks dictate patterns of neurogenesis by controlling when and where NECs undergo neuronal differentiation. The patterning genes appear to regulate neurogenesis by converging on the activity of the proneural bHLH proteins. Thus, the neural precursors for the CNS initially choose their fate by default, but neural patterning is instrumental in instructing their subsequent neuronal fate by establishing a complex code of gene expression that drives the bHLH cascade at the proper time and place. © 2009