The cilia protein IFT88 is required for spindle orientation in mitosis

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Abstract
Intraflagellar transport proteins (IFTs) are mostly known for their role in cilia assembly and maintenance. The cilial protein IFT88 is now found to transport microtubule clusters containing microtubule-nucleating proteins to spindle poles to promote astral microtubule formation and correct spindle orientation. Cilia dysfunction has long been associated with cyst formation and ciliopathies1. More recently, misoriented cell division has been observed in cystic kidneys2, but the molecular mechanism leading to this abnormality remains unclear. Proteins of the intraflagellar transport (IFT) machinery are linked to cystogenesis and are required for cilia formation in non-cycling cells3,4. Several IFT proteins also localize to spindle poles in mitosis5,6,7,8, indicating uncharacterized functions for these proteins in dividing cells. Here, we show that IFT88 depletion induces mitotic defects in human cultured cells, in kidney cells from the IFT88 mouse mutant Tg737o r p k and in zebrafish embryos. In mitosis, IFT88 is part of a dynein1-driven complex that transports peripheral microtubule clusters containing microtubule-nucleating proteins to spindle poles to ensure proper formation of astral microtubule arrays and thus proper spindle orientation. This work identifies a mitotic mechanism for a cilia protein in the orientation of cell division and has important implications for the etiology of ciliopathies.

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