The morphogen Sonic Hedgehog (Shh) plays a critical role in the development of different tissues, both in invertebrates and vertebrates. Shh mediates its action via a receptor com-plex associating two transmembrane proteins: Patched1 (Ptch1) and Smoothened (Smo). The repression exerted by Ptch1 on Smo is relieved when Shh, the ligand, binds to Ptch1, which leads to a complex signaling cascade involving the transcription factors of the Gli family and finally, to the activation of targeted genes including Ptch1 and Gli them-selves.