Single molecule imaging reveals a major role for diffusion in the exploration of ciliary space by signaling receptors.
The dynamic organization of signaling cascades inside primary cilia is key to signal propagation. Yet little is known about the dynamics of ciliary membrane proteins besides a possible role for motor-driven Intraflagellar Transport (IFT). To characterize these dynamics, we imaged single molecules of Somatostatin Receptor 3 (SSTR3, a GPCR) and Smoothened (Smo, a Hedgehog signal transducer) in the ciliary membrane. While IFT trains moved processively from one end of the cilium to the other, single SSTR3 and Smo underwent mostly diffusive behavior interspersed with short periods of directional movements. Statistical subtraction of instant velocities revealed that SSTR3 and Smo spent less than a third of their time undergoing active transport. Finally, SSTR3 and IFT movements could be uncoupled by perturbing either membrane protein diffusion or active transport. Thus ciliary membrane proteins move predominantly by diffusion, and attachment to IFT trains is transient and stochastic rather than processive or spatially determined. DOI:http://dx.doi.org/10.7554/eLife.00654.001.
Department of Molecular and Cellular Physiology , Stanford University School of Medicine , Stanford , United States ; Department of Biology , Stanford University , Stanford , United States.
Fan
F
Ye
David K
DK
Breslow
Elena F
EF
Koslover
Andrew J
AJ
Spakowitz
W James
WJ
Nelson
Maxence V
MV
Nachury
D002923:Cilia / Q000378:metabolism*; D004058:Diffusion; D008565:Membrane Proteins / Q000378:metabolism; D021381:Protein Transport; D011956:Receptors, Cell Surface / Q000378:metabolism*; D015398:Signal Transduction
D008565:Membrane Proteins; D011956:Receptors, Cell Surface
Human; IFT; Mouse; cilia; diffusion; motors; signaling