Cell Biology

Knocking on Cilia's Door

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Science  30 Mar 2012:
Vol. 335, Issue 6076, pp. 1546
DOI: 10.1126/science.335.6076.1546-d

Primary cilia are hairlike projections found at the surface of differentiated cells that play a role in development and signalling. Defects in ciliary protein localization and function are linked to human diseases, including retinal degeneration, polycystic kidney diseases, skeletal defects, and obesity. Microtubules provide cilia with their fundamental structural integrity, but cilia contain a multitude of specific proteins and are ensheathed by a specialized membrane. The entry of proteins from the cytosol into the cilium appears to be restricted at its base, and there is evidence that components of the nuclear import machinery may play a role. Kee et al. exploited the potential similarities between nuclear import and ciliary protein import to try to dissect the molecular mechanisms involved. Like the nuclear pore, the base of the cilium in mammalian tissue culture cells excluded microinjected proteins larger than ∼40 kD, whereas smaller proteins freely diffused into the cilium. This diffusion barrier appeared to be related to the presence of nucleoporins, some of which could be localized at the base of the cilium. Indeed, microinjection of nucleoporin function–blocking agents restricted the entry of a ciliary motor protein. Thus, the base of the cilium appears to play a role similar to that of the nuclear pore in restricting access. How ciliary proteins are then specifically allowed to enter, however, remains unclear.

CREDIT: NAT. CELL BIOL. 14, 10.1038/NCB2450 (2012)

Nat. Cell Biol. 14, 10.1038/ncb2450 (2012).

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