STRATEGIES FOR THE GENERATION OF NEURONAL DIVERSITY IN THE DEVELOPINGCENTRAL-NERVOUS-SYSTEM

During development, the neural tube produces a large diversity of neur onal phenotypes from a morphologically homogeneous pool of precursor c ells, In recent years, the cellular and molecular mechanisms by which specific types of neurons are generated have been explored, in the hop e 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 relat ively rigid, cell lineage-dependent specification with a high degree o f subservance to early patterns of gene expression, to inductions and cell-cell interactions that determine cell fates more flexibly.