Figure 3

Various signaling pathways modulated by the primary cilium. (a) Platelet-derived growth factor (PDGF) signaling through PDGF receptor αα requires ciliary localization of the receptor to activate downstream targets mediated by the MAP kinase kinase (MEK)-extracellular signal-regulated kinase (ERK) pathway. (b) Canonical Wnt signaling through LRP5/6 and Frizzled (Fzd) is probably inhibited by the primary cilium, whereas the planar cell polarity (PCP) non-canonical pathway requires factors essential for ciliogenesis for activity, probably by mediating cellular polarity and polarized basal body localization, and is then activated by Dishevelled (Dvl) interacting with either Fzd or other PCP components. (c) Binding of Shh to patched 1 (Ptc1) activates Shh signaling by releasing inhibition of smoothened (Smo)-Gli-mediated downstream target gene transcription.