FIGURE 1.

Distinct mechanism of ciliary protein transport. Structure of primary cilium to highlight distinct ciliary membrane composition in inset. Ciliary trafficking of receptors such as GPCRs involves vesicle budding from the Golgi that docks at the base of the cilium with intraflagellar (IFT)- mediated transportation via anterograde kinesin motors. IFT-A-mediated entry requires TUB like protein 3 (TULP3), a member of the Tubby family of proteins that interacts with the IFT-A core as an effector. The BBSome localizes to the basal body and transition zone and represents a docking point for proteins destined to enter the cilium. The BBSome has also been implicated in the exit of ciliary GPCRs out of the cilium as disruption of its functions leads to accumulation of GPCRs within the cilium. In addition to the BBSome, removal of proteins is mediated by retrograde transport with IFT complexes coupled to dynein motors. The question mark represents the uncertainty regarding how GPCR- associated cAMP and calcium oscillations are transmitted from the cilium to the rest of the neuron.