Strategies for the generation of neuronal diversity in the developing central nervous system

During development, the neural tube produces a large diversity of neuronal phenotypes from a morphologically homogeneous pool of precursor cells. In recent years, the cellular and molecular mechanisms by which specific types of neurons are generated have been explored, in the hope of discovering features common to development throughout the nervous system. This article focuses on three strategies employed by the CNS to generate distinct classes of neuronal phenotypes during development: dorsal-ventral polarization in the spinal cord, segmentation in the hindbrain, and a lamination in the cerebral cortex. The mechanisms for neurogenesis exemplified by these three strategies range from a relatively rigid, cell lineage-dependent specification with a high degree of subservance to early patterns of gene expression, to inductions and cell-cell interactions that determine cell fates more flexibly.