GENETIC-ANALYSIS OF HEDGEHOG SIGNALING IN THE DROSOPHILA EMBRYO

The segment polarity genes play a fundamental role in the patterning o f cells within individual body segments of the Drosophila embryo. Two of these genes wingless (wg) and hedgehog (hh) encode proteins that en ter the secretory pathway and both are thought to act by instructing t he fates of cells neighbouring those in which they are expressed. Gene tic analysis has identified the transcriptional activation of wg as on e of the targets of hh activity: here me present evidence that transdu ction of the hh-encoded signal is mediated by the activity of four oth er segment polarity genes, patched, fused, costal-2 and cubitus interr uptus. The results of our genetic epistatsis analysis together with th e molecular structures of the products of these genes where known, sug gest a pathway of interactions leading from reception of the hh-encode d signal at the cell membrane to transcriptional activation in the cel l nucleus. We have also found that transcription of patched is regulat ed by the same pathway and describe the identification of cis-acting u pstream elements of the ptc transcription unit that mediate this regul ation.