... be activated in cells containing intermediate levels of Dpp. We show that C15 expression requires both dpp and zen , thus forming a genetic feed-forward loop. The C15 regulatory element contains clusters of Smad- and Zen-binding sites in close proximity. Mutational analysis shows that the number of intact Smad...

... levels of Smads in the presumptive amnioserosa set the expression domain of zen , and then Smads act in combination with Zen to directly activate Race . This situation resembles a feed-forward mechanism of transcriptional regulation. In addition, we demonstrate that ectopically expressed Zen can activate...