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A size-exclusion permeability barrier and nucleoporins characterize a ciliary pore complex that regulates transport into cilia

2012; Nature Portfolio; Volume: 14; Issue: 4 Linguagem: Inglês

10.1038/ncb2450

1476-4679

Hooi Lynn Kee, John F. Dishinger, T. Lynne Blasius, Chia‐Jen Liu, Ben Margolis, Kristen J. Verhey,

Microtubule and mitosis dynamics

Entry into the cilium is restricted by a network of proteins at its base. Verhey and colleagues now show that nucleoporins, which localize to the nuclear envelope and regulate nuclear–cytoplasmic traffic, are also present at the cilium base, where they form a size-dependent exclusion barrier. The cilium is a microtubule-based organelle that contains a unique complement of proteins for cell motility and signalling functions. Entry into the ciliary compartment is proposed to be regulated at the base of the cilium1. Recent work demonstrated that components of the nuclear import machinery, including the Ran GTPase and importins, regulate ciliary entry2,3,4. We hypothesized that the ciliary base contains a ciliary pore complex whose molecular nature and selective mechanism are similar to those of the nuclear pore complex. By microinjecting fluorescently labelled dextrans and recombinant proteins of various sizes, we characterize a size-dependent diffusion barrier for the entry of cytoplasmic molecules into primary cilia in mammalian cells. We demonstrate that nucleoporins localize to the base of primary and motile cilia and that microinjection of nucleoporin-function-blocking reagents blocks the ciliary entry of kinesin-2 KIF17 motors. Together, this work demonstrates that the physical and molecular nature of the ciliary pore complex is similar to that of the nuclear pore complex, and further extends functional parallels between nuclear and ciliary import.