Specification of Ciliated Cells

It is believed that the last common eukaryotic ancestor was a ciliated organism that used cilia for locomotion and sensation. Many extant ciliated protozoans exemplify this archetypal condition. However, in metazoans, particularly vertebrates, there appears to be a demarcation of cilia types. Thus, immotile primary cilia function in sensory neurons for the perception of environmental stimuli and in many other cells for the transduction of morphogenetic and physiological signals. By contrast, motile cilia are more restricted in their distribution, and their rhythmic beating drives fluid flow over epithelia or cellular locomotion. Here, we review the mechanisms that regulate ciliated cell specification, focusing principally on ciliogenic transcriptional networks and inductive signals that activate them in different cell lineages. We also highlight human disorders that arise from misspecification of ciliated cells and conclude with a discussion on how ciliated cell specification pathways could be utilized for the amelioration of disease phenotypes in ciliopathies.