Structure and function of the primary cilium

Abstract

Primary cilia are microtubule-based organelles that extend from the apical surface of most mammalian cells. They have evolved to function as cellular antennas that receive and transmit signals from the extracellular environment such as mechanical stimuli, light, proteins and chemicals. The sensory functions of the primary cilia are highlighted by their link to the human genetic diseases termed ciliopathies, which are characterized by a multitude of symptoms including cystic kidney disease, neurodevelopmental abnormalities, obesity, retinal degeneration among other developmental ones. Over the past decade, the earlier ultrastructural description of the cilia has been dissected at the molecular level. Importantly the underlying mechanisms of the assembly and disassembly of cilia, maintenance of the ciliary composition and the disease mechanisms of ciliopathies have started to emerge with unexpected complexity. In this chapter, we will present an integrative viewpoint on the structural features of the cilium that contribute to its function, discuss the components and interactions that assemble and maintain a functional cilium and conclude with its signaling functions and disease links. For each section, we summarize the mechanisms and describe the current status of our understanding by focusing on the recent discoveries and the emerging technologies in the field.