DIVERSITY AND PATTERN IN THE DEVELOPING SPINAL-CORD

The generation of distinct neuronal cell types in appropriate numbers and at precise positions underlies the assembly of neural circuits tha t encode animal behavior. Despite the complexity of the vertebrate cen tral nervous system, advances have been made in defining the principle s that control the diversification and patterning of its component cel ls. A combination of molecular genetic, biochemical, and embryological assays has begun to reveal the identity and mechanism of action of mo lecules that induce and pattern neural tissue and the role of transcri ption factors in establishing generic and specific neuronal fates. Som e of these advances are discussed here, focusing on the spinal cord as a model system for analyzing the molecular control of central nervous system development in vertebrates.