Fig. 2

Cilia-related signaling pathways. a Several Shh proteins are located in cilia. In repression state, Gpr161 and Ptch are present in cilia, but SMO is excluded from cilia. Gli proteins are cleaved as the repressive form to inhibit Shh target gene transcription. With the binding of Shh ligand, GPR161 and Ptch move out from cilia, but SMO is transported into cilia. The stabilized Gli proteins are activated to trigger the transcription of Shh target genes. b Primary cilium provides an additional brake for canonical Wnt signaling by promoting the degradation of β-catenin. c Cilia are involved in the regulation of PCP signaling, disruption of which leads to abnormal cell orientation. Abnormal cell polarity is a major symptom of diseases with defective cilia