Development - Editorial overview

Abstract

The purpose of neural development is to assemble functional circuits that control behavior, a process that requires both the proper specification of neuronal identities and the establishment of appropriate patterns of connectivity between distinct neuronal subtypes. Given the vast number of neurons in the brain, the even larger number of specific connections, and the relatively small number of genes, the problem of how to accomplish this appears daunting. Nevertheless, considerable progress has been made over the past several years in deciphering a number of the general cellular and molecular mechanisms that are used to assemble the nervous system. This issue of Current Opinion in Neurobiology focuses primarily on the problems of neuronal identity specification and circuit formation, as they relate both to early development and to the emergence of complex behaviors. We have endeavored to strike a balance between providing updates on fast-moving fields of central importance and including areas that received relatively less coverage in the review literature but that are emerging as exciting new frontiers. The result is a somewhat idiosyncratic and certainly noncomprehensive collection of reviews that reflects our own biased perceptions of what is interesting. Consequently, there are major areas and approaches not represented, with our chief sin of omission being the absence of reviews explicitly focused on invertebrate genetic systems; however, several of the reviews draw on insights provided by such systems, and many of the advances in vertebrate neural development derive from concepts originally revealed in Drosophila. For the purposes of this overview, we have divided the reviews into four groups. The first group deals with neurogenesis, the diversification of neurons and muscles, and some aspects of patterning. The second group concerns the mechanisms that guide the selection of targets by growing axons. The third group surveys the relative contributions of electrical activity and neurotrophins to circuit formation. Finally, the fourth group deals with the role of social interactions between animals and its influence on the development of learned behaviors.