Shh

Shh is an extracellular signalling protein which modulates expression of a number of genes. The Hh protein binds to a transmembrane protein called Patched (Ptch). This binding stops Ptch from inhibiting another transmembrane protein called Smoothen (Smo). When Smo is active, it is able to induce the Gli transcription factors to being transcribing genes. While many of the genes regulated by Hh/Gli are known, further experiments continue to identify new genes.