The contribution of gene manipulation techniques to understanding dorsoventral patterning in the vertebrate nervous system

Our understanding of patterning along the dorsoventral (DV) axis has been advanced by embryological studies which have allowed the identification of dorsal and ventral organizing centers, and of molecular signals that can actin vitroto specify cell fate. However, in order to establish anin-vivorole for a signal it is necessary to show that the molecule is present in the right place and time, that exogenous addition or ectopic expression of the signal mimics its proposed effect and that deletion of its activity results in an absence of the presumed biological response. Such evidence can be provided by gene deletion (knock-out) or ectopic expression (transgenic) studies. In this review, experimental embryological studies that have increased our understanding of DV patterning will be discussed, and studies in which gene manipulation has provided evidence about the in-vivo role of a molecule will be highlighted.