Cilia

Non-motile cilia

Cilia are assembled during the G₁ phase and are disassembled before mitosis occurs. Disassembly of cilia requires the action of aurora kinase A. The current scientific understanding of primary cilia views them as "sensory cellular antennae that coordinate many cellular signaling pathways, sometimes coupling the signaling to ciliary motility or alternatively to cell division and differentiation." The cilium is composed of subdomains and enclosed by a plasma membrane continuous with the plasma membrane of the cell. For many cilia, the basal body, where the cilium originates, is located within a membrane invagination called the ciliary pocket. The cilium membrane and the basal body microtubules are connected by distal appendages (also called transition fibers). Vesicles carrying molecules for the cilia dock at the distal appendages. Distal to the transition fibers form a transition zone where entry and exit of molecules is regulated to and from the cilia. Some of the signaling with these cilia occur through ligand binding such as Hedgehog signaling. Other forms of signaling include G protein-coupled receptors including the somatostatin receptor 3 in neurons.