ABSTRACT
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 or ciliary bulbs, which based on their unique ultrastructure and motility, could be mechanically regulated by fluid-shear stress. Together with the ultrastructure analysis of the swelling, which contains monosialodihexosylganglioside (GM3), our results show that ciliary bulb 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 bulb exhibits a sensory function within the mechano-ciliary structure. Overall, our studies provided an important step towards understanding the ciliary bulb function and structure.
Subject(s)
Cell Membrane/physiology , Cilia/physiology , Epithelial Cells/metabolism , Kidney/metabolism , Mechanotransduction, Cellular/physiology , RNA-Binding Proteins/metabolism , Sialyltransferases/metabolism , TRPP Cation Channels/metabolism , Animals , Epithelial Cells/cytology , Image Processing, Computer-Assisted , Immunoblotting , Kidney/cytology , RNA, Small Interfering/genetics , RNA-Binding Proteins/antagonists & inhibitors , RNA-Binding Proteins/genetics , Sialyltransferases/antagonists & inhibitors , Sialyltransferases/genetics , Swine , TRPP Cation Channels/antagonists & inhibitors , TRPP Cation Channels/geneticsABSTRACT
Primary cilia, thin hair-like structures protruding from the apical surface of most mammalian cells, have gained the attention of many researchers over the past decade. Primary cilia are microtubule-filled sensory organelles that are enclosed within the ciliary membrane. They originate at the cell surface from the mother centriole that becomes the mature basal body. In this review, we will discuss recent literatures on the roles of cilia as sophisticated sensory organelles. With particular emphasis on vascular endothelia and renal epithelia, the mechanosensory role of cilia in sensing fluid shear stress will be discussed. Also highlighted is the ciliary involvement in cell cycle regulation, development, cell signaling and cancer. Finally, primary cilia-related disorders will be briefly described.
