Taking Down the Primary Cilium: Pathways for Disassembly in Differentiating Cells.

Primary cilia are customized subcellular signaling compartments leveraged to detect signals in diverse physiological contexts. Although prevalent throughout mammalian tissues, primary cilia are not universal. Many non-ciliated cells derive from developmental lineages that include ciliated progenitors; however, little is known about how primary cilia are lost as cells differentiate. Here, we examine how ciliated and non-ciliated states emerge during development and are actively maintained. We highlight several pathways for primary cilia loss, including cilia resorption in pre-mitotic cells, cilia deconstruction in post-mitotic cells, cilia shortening via remodeling, and cilia disassembly preceding multiciliogenesis. Lack of ciliogenesis is known to decrease primary cilia frequency and cause ciliopathies. Failure to maintain cilia can also cause primary cilia to be absent. Conversely, defects in primary cilia suppression or disassembly can lead to the presence of primary cilia in non-ciliated cells. We examine how changes in ciliation states could contribute to tumorigenesis and neurodegeneration.