13 Proneuronal Genes Drive Neurogenesis on the Road from Development to Adulthood

The ongoing production of neurons in selected areas of the adult mammalian brain is tantalizing and has become an active area of research for many investigators. It is exciting to consider the functional importance of adding new neurons to mature circuits, as well as the intricate biological processes regulating their production (Meltzer et al. 2005; Ming and Song 2005; Lledo et al. 2006). Many investigators are also fascinated by the potential of repairing the injured nervous system with adult-generated neurons, those either produced in specialized adult neurogenic niches or induced in regions where little (if any) neurogenesis normally persists, such as the spinal cord or neocortex. Whether the inspiration is systems neuroscience, basic biology, or biomedical applications, the advancement of the field of neurogenesis depends on understanding the underlying molecular mechanisms regulating this process. When considering this central issue, most investigators have posited that molecular pathways important for development must have similar roles in the adult (Deisseroth et al. 2004; Meltzer et al. 2005; Ming and Song 2005). It is important to realize, however, that the number of studies demonstrating a required and specific role for any developmental regulators in adult neurogenesis is quite small. Adult neurogenesis is contingent on the functioning of the neurogenic niche, which must be produced during development, maintained during postnatal life, and regulated during adulthood. This presents a significant barrier for interpreting most genetic manipulations, as it is virtually impossible to distinguish adult requirements from developmental insults in most studies examining these pathways. To establish...