RanGTP regulates cilium formation and ciliary trafficking of a kinesin-II subunit independent of its nuclear functions

Abstract

9Kinesin is part of the microtubule (MT)-binding motor protein superfamily, which exerts crucial 10 functions in cell division and intracellular transport in different organelles. The heterotrimeric 11 kinesin-2, consisting of the kinesin like protein KIF3A/3B heterodimer and kinesin-associated 12 protein KAP3, is highly conserved across species from the green alga Chlamydomonas to 13 humans. It plays diverse roles in cargo transport including anterograde (base to tip) trafficking in 14 cilium. However, the molecular determinants mediating trafficking of heterotrimeric kinesin-2 15 itself is poorly understood. Using the unicellular eukaryote Chlamydomonas and mammalian 16 cells, we show that RanGTP regulates ciliary trafficking of KAP3. We found the armadillo repeat 17 region 6-9 (ARM6-9) of KAP3, required for its nuclear translocation, is sufficient for its targeting 18 to the ciliary base. Given that KAP3 is essential for cilia formation and the emerging roles of 19 RanGTP/importin β in ciliary protein targeting, we further investigate the effect of RanGTP in 20 cilium length regulation in these two different systems. We demonstrate that precise control of 21 RanGTP levels, revealed by different Ran mutants, is crucial for cilium formation and 22 maintenance. Most importantly, we were able to segregate RanGTP regulation of ciliary protein 23 incorporation from of its nuclear roles. Our work provides important support for the model that 24 nuclear import mechanisms have been coopted for independent roles in ciliary import. 25 26

Centrosome and ciliary abnormalities in fetal akinesia deformation sequence human fibroblasts

“…Briefly, cargoes are carried from the nucleus to the cytoplasm by nuclear export receptors regulated by the small GTPase Ran. There is emerging evidence that the nuclear export receptor CRM1 regulates non-centrosomal (nc) MT nucleation in a RanGTP-dependent mechanism, and that depletion of CRM1 in yeasts results in increased ncMT nucleation after cold-treatment (Bao et al, 2018;Huang and Avasthi, 2019). Furthermore, Gle1, which has a crucial role in mRNA export and is closely associated with the nuclear pore complex, has been shown to locate to centrosomes and the basal body, and to regulate MT organization (Jao et al, 2017).…”