The highly conserved FOXJ1 target CFAP161 is dispensable for motile ciliary function in mouse and Xenopus.

Cilia are protrusions of the cell surface and composed of hundreds of proteins many of which are evolutionary and functionally well conserved. In cells assembling motile cilia the expression of numerous ciliary components is under the control of the transcription factor FOXJ1. Here, we analyse the evolutionary conserved FOXJ1 target CFAP161 in Xenopus and mouse. In both species Cfap161 expression correlates with the presence of motile cilia and depends on FOXJ1. Tagged CFAP161 localises to the basal bodies of multiciliated cells of the Xenopus larval epidermis, and in mice CFAP161 protein localises to the axoneme. Surprisingly, disruption of the Cfap161 gene in both species did not lead to motile cilia-related phenotypes, which contrasts with the conserved expression in cells carrying motile cilia and high sequence conservation. In mice mutation of Cfap161 stabilised the mutant mRNA making genetic compensation triggered by mRNA decay unlikely. However, genes related to microtubules and cilia, microtubule motor activity and inner dyneins were dysregulated, which might buffer the Cfap161 mutation.

Notch signaling induces either apoptosis or cell fate change in multiciliated cells during mucociliary tissue remodeling.

Multiciliated cells (MCCs) are extremely highly differentiated, presenting >100 cilia and basal bodies. Therefore, MCC fate is thought to be terminal and irreversible. We analyzed how MCCs are removed from the airway-like mucociliary Xenopus epidermis during developmental tissue remodeling. We found that a subset of MCCs undergoes lateral line-induced apoptosis, but that the majority coordinately trans-differentiate into goblet secretory cells. Both processes are dependent on Notch signaling, while the cellular response to Notch is modulated by Jak/STAT, thyroid hormone, and mTOR signaling. At the cellular level, trans-differentiation is executed through the loss of ciliary gene expression, including foxj1 and pcm1, altered proteostasis, cilia retraction, basal body elimination, as well as the initiation of mucus production and secretion. Our work describes two modes for MCC loss during vertebrate development, the signaling regulation of these processes, and demonstrates that even cells with extreme differentiation features can undergo direct fate conversion.