Hedgehog (Hh), a secreted morphogen, acts in a paracrine fashion to regulate tissue patterning during embryogenesis. Its tissue-specific effects are mediated by the transcription factor Cubitus interruptus (Ci), but how it exerts such effects is unclear. On , Thomas Kornberg and colleagues address this question by identifying novel Drosophila Hh targets. Using chromatin-binding experiments to identify genes that are bound by Ci during Drosophila organogenesis, and by using expression data from wild-type embryos and Hh pathway mutants, they identified a set of Hh-responsive genes, many of which represent novel targets. Their validation of these targets in developing tissues, such as the dorsal ectoderm, showed that they are expressed in a tissue-specific manner, but, unexpectedly, that some targets are induced in an autocrine fashion. The authors also show that, in the tracheal primordium, some Hh target expression is subject to combinatorial control by Ci and an Hh-independent transcription factor. These unexpected features of Hh signalling provide new insights into our understanding of this pathway.
