Pathways to Ciliopathies: Visualizing and Manipulating Cell Signaling in Primary Cilia

Primary cilia are short hair-like processes which are found on almost all eukaryotic cells. They are tiny entities - roughly 0.5 microns wide and  several microns in length - which only constitute approximately one ten thousandth of a cell’s total volume. The existence of primary cilia has been appreciated for more than 100 years, but it was only recently that scientists begin to explore its function. Unlike normal cilia that move to generate forces, primary cilia are immotile and thought to function as an “antenna” for sensing various environmental factors such as mechanical, chemical, or photothermal stimuli. For example, in the case of renal epithelial cells, primary cilia extend into the apical lumen, putatively functioning as a sensor for liquid flow in tubules. It is increasingly appreciated that abnormal ciliary structure and function results in many disorders such as loss of smell and sight, and kidney failure. These disorders are collectively termed “ciliopathies”. Despite its significant involvement in physiology and pathophysiology, studies of primary cilia have been hampered primarily due to its small size. It is extremely challenging to distinguish signaling events inside primary cilia from those of elsewhere in the same cell. There is virtually no technique to “see” or “touch” dynamic signaling events inside primary cilia. We have previously developed a novel technique that allows for rapid, inducible perturbation of various signaling molecules at specific locations in living cells. We will use intracellular calcium signaling and polycystic kidney disease as a model to elucidate signaling pathways regulating structures and functions of primary cilia. By uniquely combining our perturbation technique with real-time, live-cell fluorescence imaging, we will visualize and manipulate dynamic calcium signaling events specifically in primary cilia. This research will not only provide a powerful technology for probing signaling complexity in primary cilia, but also offer far-reaching implications for the cure of ciliopathies.
Visualization of calcium signals in primary cilia. (Su and Phua et al. Nat Methods, 2013)