Temporal fate specification and neural progenitor competence during development

The vast neural diversity in the CNS is generated from a small pool of progenitors that produce distinct cell types in a specific order. The generation of a particular cell type depends on the spatial position of the progenitor (spatial patterning) as well as changing intrinsic and extrinsic signals (temporal patterning).Neural progenitors sequentially express a series of transcription factors, which specify the fate of the progeny on the basis of birth timing (temporal identity). Distinct neural lineages can use the same temporal-identity factor to specify different progeny fates.Distinct temporal-patterning cues in the neural progenitor and the progeny can act combinatorially to increase neural diversity.Studies of neurogenesis in multiple organisms show that the molecular players involved in temporal fate specification are highly conserved.In addition to the sequential specification of distinct cell fates, neural stem cells undergo dynamic changes in competence states, such that a given cell type can be specified during only a limited window of development. Thus, the specification of a particular cell fate requires the progenitor to be in the correct competence state to respond appropriately to the cell-fate-determining factors.Emerging evidence indicates that global changes in chromatin architecture play an important part in the regulation of competence states.