Temporal Relationship between Primary and Motile Ciliogenesis in Airway Epithelial Cells

Abstract

Cilia are traditionally classified as motile or primary. Motile cilia are restricted to specific populations of well-differentiated epithelial cells, including those in the airway, brain ventricles, and oviducts. Primary cilia are nonmotile, solitary structures that are present in many cell types, and often have sensory functions such as in the retina and renal tubules. Primary cilia were also implicated in the regulation of fundamental processes in development. Rare depictions of primary cilia in embryonic airways led us to hypothesize that primary cilia in airway cells are temporally related to motile ciliogenesis. We identified primary cilia in undifferentiated, cultured airway epithelial cells from mice and humans and in developing lungs. The solitary cilia in the airways express proteins considered unique to primary cilia, including polycystin-1 and polycystin-2. A temporal analysis of airway epithelial cell differentiation showed that cells with primary cilia acquire markers of motile ciliogenesis, suggesting that motile ciliated cells originate from primary ciliated cells. Whereas motile ciliogenesis requires Foxj1, primary ciliogenesis does not, and the expression of Foxj1 was associated with a loss of primary cilia, just before the appearance of motile cilia. Primary cilia were not found in well-differentiated airway epithelial cells. However, after injury, they appear in the luminal layer of epithelium and in basal cells. The transient nature of primary cilia, together with the temporal and spatial patterns of expression in the development and repair of airway epithelium, suggests a critical role of primary cilia in determining outcomes during airway epithelial cell differentiation.

Generation of multiciliated cells in functional airway epithelia from human induced pluripotent stem cells

“…It has been shown that primary cilia are found transiently in the airways but not in well-differentiated airway epithelium. In addition, primary cilia have been observed in the luminal layers of epithelium and basal cells after lung injury (44). Inhibition of notch signaling is known to be involved in the switch from a primary ciliated cell to an MCC (24,27,28,45).…”

Lung Epithelial Healing: A Modified Seed and Soil Concept

“…We and others have shown that air-liquid-interface (ALI) cultures of primary mouse tracheal epithelial cells can be used to evaluate the cellular and molecular mechanisms regulating FBP function (20,29,38,39,(48)(49)(50). We showed that FBP initiate ALI cultures and that K5/K15/K14 triple-positive basal cells comprise 98% of the ALI culture on Culture Day 2 (38).…”

Induction of multiciliated cells from induced pluripotent stem cells

“…There are two types of cilia: motile and primary cilia (9,10). Airway epithelial cells that are destined to develop motile cilia first generate primary cilia, and therefore the presence of primary cilia represents an early stage of multiciliated cells.…”

“…Airway epithelial cells that are destined to develop motile cilia first generate primary cilia, and therefore the presence of primary cilia represents an early stage of multiciliated cells. Foxj1 expression is not required for primary cilia formation, but is turned on as motile cilia develop (9). The iPSC-derived epithelium described by Firth et al (3) demonstrates acetylated α-tubulin expression on the apical surface of the cells, and is suggestive of primary cilia.…”