Figure 1.

Hh signaling is initiated when a Hh ligand binds to the cell surface receptor PTCH1, which results in repression and accumulation of the cell surface protein SMO in the primary cilium. SMO then triggers downstream signal transduction through proteins such as Sufu and Gli1/2/3. Other cellular factors, such as proteinase kinase A (PKA), casein kinase 1 (CK1), glycogen synthase kinase β3 (GSK3β), β-Arrestin, the kinesin family member 3a (Kif3a), beta-transducin repeats-containing proteins (β-TrCP), and the potassium channel tetramerisation doman containing 11 (KCTD11), engage in the regulation of downstream Hh transcription.