Fig. 4. The Hh signaling network.

In vertebrates, Hh binding to Ptc modulates one or more of the following signaling modules: non-canonical type I Hh signaling exclusively through Ptc; canonical Hh signaling through Ptc, Smo, and Glis (mediated in some instances by G_i proteins); and a noncanonical type II signaling through Smo and G_i proteins. The cellular responses to each signaling module are illustrated at the bottom. The red crosses indicate inhibition of the pathway in the presence of Hh proteins.