Dysfunction of many ciliary proteins has been linked to a list of diseases, from cystic kidney to obesity and from hypertension to mental retardation. We previously proposed that primary cilia are unique communication organelles that function as microsensory compartments that house mechanosensory molecules. Here we report that primary cilia exhibit membrane swellings, which based on their unique ultrastructure and motility, could be mechanically regulated by fluid-shear stress. Together with the ultrastructure analysis of the bulb, which contains monosialodihexosylganglioside (GM3), our results show that ciliary membrane swelling has a distinctive set of functional proteins, including GM3 synthase (GM3S), bicaudal-c1 (Bicc1) and polycystin-2 (PC2). In fact, results from our cilia isolation demonstrated for the first time that GM3S and Bicc1 are members of the primary cilia proteins. Although these proteins are not required for ciliary membrane swelling formation under static condition, fluid-shear stress induced swelling formation is partially modulated by GM3S. We therefore propose that the ciliary membrane swelling exhibits a sensory function within the mechano-ciliary structure. Overall, our studies provided an important step toward understanding the ciliary membrane swelling function and structure.
Mohieldin, Ashraf M., Hanan S. Haymour, Shao T. Lo, Wissam A. AbouAlaiwi , Kimberly F. Atkinson, Christopher J. Ward, Min Gao, Oliver Wessely and Surya M. Nauli. "Protein Composition and Movements of Membrane Swellings Associated with Primary Cilia." Cellular and Molecular Life Sciences (2015). doi: 10.1007/s00018-015-1838-x