Figure 1.

The Hh signalling pathway, based on what is known in flies. In the absence of Hh, Ptc inhibits signalling from Smo. Full-length Ci is cleaved after forming a microtubule complex with several segment polarity genes (fused, costal-2 and suppressor of fused) and the 75 kDa Ci product act as a transcriptional repressor protein. On the binding of Hh to Ptc, the inhibitory effect on Smo is released, leading to the dissociation of the microtubule complex. Ci cleavage is prevented and Ci activates the transcription of target genes.