In the leg disc, the 30A-GAL4 insertion is expressed dorsally in cells of the presumptive femur, in the distal tip of the leg, and in a central ring corresponding to the fifth tarsal segment. Both of these elements are responsive to Ci. Given the antagonism between Dpp and Wg in the leg, it was necessary to analyze clones mutant for a component of each pathway. Mad is a downstream effector in the Dpp signaling pathway that has been shown to bind DNA and transcriptionally regulate some Dpp target genes directly. It can reasonably be concluded that loss of D- h results from the loss of Mad, since there is no duplicated Wg in these clones.
Several questions remain open regarding the placement of leg sensory organs.
There is much to be learned about the regulation of the eight Ac leg stripes. In the absence of H function, ac is expressed in four broad stripes, which may represent four zones that are competent to express ac . The precellular Drosophila embryo contains approximately 10 well characterized transcriptional repressors. The two long-range repressors can function over distances of 1 kilobase or more to silence transcription. Previous studies have shown that three of the five short-range repressors interact with a common corepressor protein, dCtBP .