Single-cell RNA-sequencing of wildtype murine tracheal epithelial cells cultured at air-liquid interace for one, three, nine, and thirty-six days.

The canonical mitotic cell cycle coordinates cell growth, DNA replication, centriole duplication and cytokinesis to generate two cells from one. In certain contexts, such as in mammalian trophoblast giant cells or hepatocytes, cells employ cell cycle variants like the endocycle or endomitosis to increase DNA content without undergoing cytokinesis. Multiciliated cells, found in the mammalian airway, brain ventricles and reproductive tracts, generate hundreds of centrioles during differentiation, each of which extend a motile cilium. We found that multiciliated cells utilize a variant of the cell cycle, which we refer to as the multiciliation cycle. The multiciliation cycle redeploys much of the mitotic cell cycle regulatory framework, including cell division kinases (CDKs) and cyclins, to generate hundreds of centrioles without undergoing DNA synthesis or cytokinesis. Unlike the mitotic cycle, a transcriptional repressor, E2F7, is upregulated during the multiciliation cycle. E2F7 directly represses genes encoding DNA synthesis machinery during the multiciliation cycle. Loss of E2F7 results in aberrant DNA synthesis and disruption of centriole biogenesis in differentiating multiciliated cells. Thus, multiciliation is coordinated by a variant cell cycle that uses E2F7 to uncouple centriole synthesis from DNA replication.