Investigation of the role of Fritz and its associated factors, septin and CCT in ciliogenesis of Xenopus laevis epidermis

Cilia are evolutionarily conserved microtubule-based organelles projecting from nearly all vertebrate cells, and ciliary defects result in a variety of human disorders known as ciliopathies. Recent studies have shown that several planar cell polarity (PCP) proteins are essential for cilia functions. Here, we focused on Fritz, known as a novel PCP effector protein in Drosophila, in multi-ciliated cells in the epidermis of Xenopus laevis embryos. To investigate the role of Fritz, using confocal and scanning electron microscopy, we discovered that Fritz localizes along the ciliary axonemes and that knockdown of Fritz causes severe reductions in both axoneme length and number. Then, using pull-downs and mass-spectrometry, we identified Chaperonin Containing T-complex polypeptide 1 (CCT) and septin as interacting partners of Fritz. CCT is the key chaperonin interacting with septins, and both have been implicated in ciliogenesis. Using tagged CCT subunit constructs, we found that the tagged CCTα and CCTε co-localize with Fritz along the ciliary axonemes of multi-ciliated cells. Knockdown of Fritz resulted in the accumulation of CCT at the apical cytoplasm of multi-ciliated cells; however, it was confirmed that Fritz does not affect the CCT holoenzyme assembly. Septins, another interacting partner of Fritz, are novel cytoskeletal elements. Using septin antibodies, we found that endogenous septins also localize along the ciliary axonemes and accumulate in the apical cytoplasm of multi-ciliated cells in Fritz morphants. Similar ciliary defects were observed in septin morphants. Our results reveal that Fritz is essential for ciliogenesis, and that CCT and septin interact with Fritz to control ciliogenesis in Xenopus multi-ciliated cells. Additionally, tubulin acetylation is markedly reduced by Fritz knockdown, suggesting that Fritz affects tubulin acetylation.