TY - JOUR
T1 - Regulated membrane protein entry into flagella is facilitated by cytoplasmic microtubules and does not require IFT
AU - Belzile, Olivier
AU - Hernandez-Lara, Carmen I.
AU - Wang, Qian
AU - Snell, William J.
N1 - Funding Information:
We thank Neal Jetton for assistance in generating SAG1-HA/sag1-5 cells. We are indebted to Khrishen Cunnusamy (UT Southwestern) for his generosity in teaching us electroporation methods for transformation and to Amita Sahu (UT Southwestern) for assistance in several portions of this work. We thank Dennis Diener and Joel Rosenbaum (Yale University) for antibodies. This work was supported by National Institutes of Health grant GM-25661 to W.J.S.
PY - 2013/8/5
Y1 - 2013/8/5
N2 - The membrane protein composition of the primary cilium, a key sensory organelle, is dynamically regulated during cilium-generated signaling [1, 2]. During ciliogenesis, ciliary membrane proteins, along with structural and signaling proteins, are carried through the multicomponent, intensely studied ciliary diffusion barrier at the base of the organelle [3-8] by intraflagellar transport (IFT) [9-18]. A favored model is that signaling-triggered accumulation of previously excluded membrane proteins in fully formed cilia [19-21] also requires IFT, but direct evidence is lacking. Here, in studies of regulated entry of a membrane protein into the flagellum of Chlamydomonas, we show that cells use an IFT-independent mechanism to breach the diffusion barrier at the flagellar base. In resting cells, a flagellar signaling component [22], the integral membrane polypeptide SAG1-C65, is uniformly distributed over the plasma membrane and excluded from the flagellar membrane. Flagellar adhesion-induced signaling triggers rapid, striking redistribution of the protein to the apical ends of the cells concomitantly with entry into the flagella. Protein polarization and flagellar enrichment are facilitated by cytoplasmic microtubules. Using a conditional anterograde IFT mutant, we demonstrate that the IFT machinery is not required for regulated SAG1-C65 entry into flagella. Thus, integral membrane proteins can negotiate passage through the ciliary diffusion barrier without the need for a motor.
AB - The membrane protein composition of the primary cilium, a key sensory organelle, is dynamically regulated during cilium-generated signaling [1, 2]. During ciliogenesis, ciliary membrane proteins, along with structural and signaling proteins, are carried through the multicomponent, intensely studied ciliary diffusion barrier at the base of the organelle [3-8] by intraflagellar transport (IFT) [9-18]. A favored model is that signaling-triggered accumulation of previously excluded membrane proteins in fully formed cilia [19-21] also requires IFT, but direct evidence is lacking. Here, in studies of regulated entry of a membrane protein into the flagellum of Chlamydomonas, we show that cells use an IFT-independent mechanism to breach the diffusion barrier at the flagellar base. In resting cells, a flagellar signaling component [22], the integral membrane polypeptide SAG1-C65, is uniformly distributed over the plasma membrane and excluded from the flagellar membrane. Flagellar adhesion-induced signaling triggers rapid, striking redistribution of the protein to the apical ends of the cells concomitantly with entry into the flagella. Protein polarization and flagellar enrichment are facilitated by cytoplasmic microtubules. Using a conditional anterograde IFT mutant, we demonstrate that the IFT machinery is not required for regulated SAG1-C65 entry into flagella. Thus, integral membrane proteins can negotiate passage through the ciliary diffusion barrier without the need for a motor.
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U2 - 10.1016/j.cub.2013.06.025
DO - 10.1016/j.cub.2013.06.025
M3 - Article
C2 - 23891117
AN - SCOPUS:84881313610
SN - 0960-9822
VL - 23
SP - 1460
EP - 1465
JO - Current Biology
JF - Current Biology
IS - 15
ER -