Figure 1.

SHH protein binds to the PTCH receptor (1). In the absence of the ligand, PTCH inhibits SMO, a downstream protein in the pathway (2). The binding of SHH relieves SMO inhibition, leading to activation of the GLI transcription factors: the activators GLI1 and GLI2 and the repressor GLI3 (3). Activated GLI accumulates in the nucleus (4) and controls the transcription of Hh target genes (5).