Dorsoventral patterning in the Drosophila embryo is controlled by the transcription factor Dorsal. A Dorsal gradient in the early embryo initiates the differentiation of several embryonic tissues by regulating target gene expression in a concentration-dependent manner. On , Markstein and colleagues have computationally identified enhancer sequences in Dorsal target genes that are activated by intermediate levels of Dorsal, and reveal a regulatory code for neurogenic gene expression in Drosophila. Co-regulated enhancers in the rhomboid, ventral nervous system defective and brinker genes contain binding sites for Dorsal,and for the transcription factors Twist and Suppressor of Hairless, plus an additional shared motif. A search of the Drosophila genome for other enhancers with these motifs revealed two more (in vein and single-minded) that direct gene expression to the ventral neurogenic ectoderm. The same regulatory code also acts as a neurogenic enhancer in Anopheles.
