Fig. 6. A model shows the formation of cilia during the development of epithelial tubes. During epithelium differentiation, the cilium forms. The formation of the cilia requires hi459/scorpion and IFT components. The cilium protrudes into the lumen from the apical surface of epithelial cells and serves as an antenna of the cell. Mechanosensory channels (polycystins, etc.) on the cilium could be activated by liquid flow, interaction with neighboring cells or chemicals/ligands in the lumen. A resultant Ca²⁺ influx triggers a signaling cascade that regulates cell proliferation and/or size. Defects in cilia formation or function lead to uncontrolled proliferation of epithelial cells and eventually cyst formation in local areas.