Fig. 3.

The multiple phases and regulation of cilium assembly. The process of cilium assembly involves several successive stages. Cilium assembly is initiated upon cell cycle exit or after receiving developmental signals (1). PCVs are transported via microtubule-actin networks to the distal end of the MC and fuse into a larger CV (2). The process is accompanied by reorganization of the cytoskeleton, which drives the migration of centrioles from the cytoplasm to the cell membrane. CP110 is removed. Next, IFT complexes are continuously recruited to the ciliary base to allow axoneme elongation, while Rab8a is recruited to the MC to facilitate ciliary membrane extension (3). The transition zone is then assembled, and this is followed by axoneme elongation and membrane fusion. Inhibition of the ciliary disassembly pathway also allows outgrowth of the cilium (4). Key proteins that play a regulatory role at each stage of the assembly process are shown. PI(4)P, PtdIns(4)P.