Figure 1.

A common vesicular trafficking module in the assembly of the immune synapse and the primary cilium. Left. Following encounter with specific antigen (Ag) associated to the major histocompatibility complex (MHC) on an antigen presenting cell (APC), engaged TCRs initiate a signaling cascade that promotes polarized recycling of the non-engaged TCRs from an intracellular endosome-associated pool to the immune synapse. IFT20 promotes transit of TCR⁺ vesicles to Rab11⁺ recycling endosomes that are transported to the centrosome. Rab8 regulates the last step of vesicle transport and fusion with the contact area by interacting with the v-SNARE VAMP3. Right. The delivery of the ciliary receptor Smoothened (Smo) to the ciliary membrane requires IFT20, which is associated with vesicles destined for the primary cilium asnd subsequently directed to a Rab8⁺ vesicle compartment at the base of the cilium. Rab8 and its GEF Rabin8 are transported to this location in Rab11⁺ vesicles. Vesicles subsequently dock at and fuse with the periciliary membrane as a result of the interaction of Rab8 with the v-SNARE VAMP3.