Figure 2.

In the absence of Hh signal, Patched1 (Ptch1) inhibits the Hh pathway through the modulation of the Smoothened (Smo). Since Smo is inactivated, the Glioma-associated oncogene- Suppressor of Fused (Gli-Sufu) complex is retained in the cytosol, where it is exposed to phosphorylation by protein kinase A (PKA), thereby inhibiting signal transduction by Gli. When Hh signal is present (here represented by Shh), its binding to Ptch1 relives pathway inhibition, induces its translocation away from the cilium, allowing activated Smo and Gli-Sufu complex transport to the tip of the cilium, where Gli becomes dissociated from Sufu. Subsequent retrograde transport of Gli then brings it to the nucleus, where it regulates expression of target genes. Image adapted from Reference [76,77].