Circulation. 2008;117:1124-1126. Adapted for this thesis.

The single non-motile primary cilium, protruding several microns from the apical surface, contains cytoskeletal elements in a specific fashion. It consists of 9 circularly arranged microtubule doublets, as revealed by transmission electron microscopy1, but lacks the central ones characteristic for motile cilia and flagellae. The primary cilium is anchored to the basal body and is thereby connected to the cytoskeletal apparatus. Sorokin1 concluded that primary cilia were probably vestigial remnants of motile cilia. We now know that ciliary functions are abundant. Examples include processes involving Hedgehog and Wnt signaling2 and determining left-right asymmetry3. Cilia functioning as sensory antennas in insect ears and the human retina are well established4. Because of the widespread presence of primary cilia, it does not come as a surprise that many diseases, often syndromic, are caused by ciliary dysfunction. Several diseases are related to disruption of intraflagellar transport in the case of mutation in, for example, Polaris, Kif3a or various Bbs proteins that can lead to such conditions as obesity and Bardet Biedl Syndrome5. Other cilium-related proteins involve cell membrane-bound Ca2+ channels such as the complex formed by polycystin-1 and-2, encoded from Pkd1 and Pkd2, respectively. Mutations cause polycysti