Cell Biology

The Scenic Route

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Science  27 Nov 2009:
Vol. 326, Issue 5957, pp. 1164-1165
DOI: 10.1126/science.326.5957.1164-d

The plasma membrane contains a large number of proteins and lipids, many of which are organized spatially into regions that mediate processes such as motility, adhesion, and signal transduction. Cilia are hairlike extensions that protrude from the plasma membrane and are found on the surface of most cells. They mediate mechanical and sensory interactions between the cell and its environment, as well as act as signaling centers for the Hedgehog and Wingless developmental pathways. In order to support these functions, proteins must be targeted to the ciliary membrane. For the transmembrane receptor protein Smoothened, which is part of the Hedgehog pathway and localizes to the cilium upon activation, current models have focused on its delivery by membrane vesicles moving from the Golgi apparatus to the cell surface. Milenkovic et al. have identified an alternative route: lateral transport within the plasma membrane. They found that Smoothened could move to the ciliary membrane from the bulk plasma membrane when the Hedgehog pathway was activated. Increasing the levels of the second-messenger molecule cAMP, which is involved in lateral transport in algae, could also induce lateral transport of Smoothened, suggesting a conserved mechanism of regulation. Perhaps to improve efficiency and accuracy, Smoothened is transported to the ciliary membrane along two different routes.

J. Cell Biol. 187, 365 (2009).

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