Excessive F-Actin and Microtubule Formation Mediates Primary Cilia Shortening and Loss in Response to Increased Extracellular Osmotic Pressure

The primary cilium is a small organelle protruding from the cell surface and is recognized as an antenna for signals from the extracellular milieu. Maintenance of primary cilia structure is crucial for proper behaviors of cells, tissues, and organs. While a dozen of studies have reported that several genetic factors impair the structure of primary cilia, evidence for environmental stimuli affecting primary cilia structures is limited. Here, we investigated an extracellular stress that affected primary cilia morphology and its underlying mechanisms. Hyperosmotic shock with increased extracellular sodium chloride concentration induced shortenings and disassembly of primary cilia in murine intramedullary collecting ducts cells. The shortening of primary cilia caused by hyperosmotic shock followed a loss of axonemal microtubules and delocalization of pericentriolar materials (PCMs). The primary cilia shortening/disassembly and PCMs delocalization were reversible. In parallel with these hyperosmotic shock-induced changes of primary cilia and PCMs, excessive microtubule and F-actin formation occurred in the cytoplasm. A microtubule-disrupting agent, Nocodazole, prevented the hyperosmotic shock-induced primary cilia disassembly partially, while preventing the delocalization of PCMs almost 100%. An actin polymerization inhibitor, Latrunculin A, also prevented partially the hyperosmotic shock-induced primary cilia shortening and disassembly, while preventing the delocalization of PCMs almost 100%. Taken together, we demonstrate that hyperosmotic shock induces reversible morphological changes in primary cilia and PCMs in a manner dependent on excessive formation of microtubule and F-actin.