PIP 2 determines length and stability of primary cilia by balancing membrane turnovers.
Simon StillingTheodoros KalliakoudasHannah Benninghoven-FreyTakanari InoueBjörn H FalkenburgerPublished in: Communications biology (2022)
Primary cilia are sensory organelles on many postmitotic cells. The ciliary membrane is continuous with the plasma membrane but differs in its phospholipid composition with phosphatidylinositol 4,5-bisposphate (PIP 2 ) being much reduced toward the ciliary tip. In order to determine the functional significance of this difference, we used chemically induced protein dimerization to rapidly synthesize or degrade PIP 2 selectively in the ciliary membrane. We observed ciliary fission when PIP 2 was synthesized and a growing ciliary length when PIP 2 was degraded. Ciliary fission required local actin polymerisation in the cilium, the Rho kinase Rac, aurora kinase A (AurkA) and histone deacetylase 6 (HDAC6). This pathway was previously described for ciliary disassembly before cell cycle re-entry. Activating ciliary receptors in the presence of dominant negative dynamin also increased ciliary PIP 2 , and the associated vesicle budding required ciliary PIP 2 . Finally, ciliary shortening resulting from constitutively increased ciliary PIP 2 was mediated by the same actin - AurkA - HDAC6 pathway. Taken together, changes in ciliary PIP 2 are a unifying point for ciliary membrane stability and turnover. Different stimuli increase ciliary PIP 2 to secrete vesicles and reduce ciliary length by a common pathway. The paucity of PIP 2 in the distal cilium therefore ensures ciliary stability.