How the Dorsal gradient works: insights from postgenome technologies.

Gradients of extracellular signaling molecules and transcription factors are used in a variety of developmental processes, including the patterning of the Drosophila embryo, the establishment of diverse neuronal cell types in the vertebrate neural tube, and the anterior-posterior patterning of vertebrate limbs. Here, we discuss how a gradient of the maternal transcription factor Dorsal produces complex patterns of gene expression across the dorsal-ventral (DV) axis of the early Drosophila embryo. The identification of 60-70 Dorsal target genes, along with the characterization of approximately 35 associated regulatory DNAs, suggests that there are at least six different regulatory codes driving diverse DV expression profiles.