Ciliogenesis: building the cell's antenna

Cilia are complex sensory and motile organelles found on almost all cells of the body. The complexity of the cilium raises the question of how it is built in an orderly fashion.Ciliary assembly proceeds in a stepwise manner: centrioles form basal bodies, dock on the cortex and induce outgrowth of the cilium. Assembly also involves protein-trafficking from the cytoplasm to the base of the cilium and selective import of ciliary proteins through a channel that may be analogous to the nuclear pore complex.Sustained growth of cilia requires active transport, which is provided by the intraflagellar transport (IFT) system.Assembly of cilia is a function of cell cycle stage and is tightly regulated to control the length of the final structure.Ciliary length seems to result from a continuous steady-state balance of assembly and disassembly, with the inherent length-dependence of IFT-mediated transport leading to a length-dependent assembly rate.