Functional coordination of intraflagellar transport motors

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Abstract

Cilia have diverse roles in motility and sensory reception, and defects in cilia function contribute to ciliary diseases such as Bardet–Biedl syndrome (BBS). Intraflagellar transport (IFT) motors assemble and maintain cilia by transporting ciliary precursors, bound to protein complexes called IFT particles, from the base of the cilium to their site of incorporation at the distal tip1,2,3. In Caenorhabditis elegans, this is accomplished by two IFT motors, kinesin-II and osmotic avoidance defective (OSM)-3 kinesin, which cooperate to form two sequential anterograde IFT pathways that build distinct parts of cilia4,5,6,7. By observing the movement of fluorescent IFT motors and IFT particles along the cilia of numerous ciliary mutants, we identified three genes whose protein products mediate the functional coordination of these motors. The BBS proteins BBS-7 and BBS-8 are required to stabilize complexes of IFT particles containing both of the IFT motors, because IFT particles in bbs-7 and bbs-8 mutants break down into two subcomplexes, IFT-A and IFT-B, which are moved separately by kinesin-II and OSM-3 kinesin, respectively. A conserved ciliary protein, DYF-1, is specifically required for OSM-3 kinesin to dock onto and move IFT particles, because OSM-3 kinesin is inactive and intact IFT particles are moved by kinesin-II alone in dyf-1 mutants. These findings implicate BBS ciliary disease proteins and an OSM-3 kinesin activator in the formation of two IFT pathways that build functional cilia.

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Figure 1: Genetic screen of ciliary mutants and characterization of dyf-1.
Figure 2: Model for the functional coordination of the two IFT motors by BBS proteins and DYF-1.

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Acknowledgements

We thank W. M. Saxton, G. Rogers, D. Sharp, S. Gross, L. S. Rose and many other colleagues for comments. We thank E. Schwarz and M. Barr for help with DYF-1 protein domain analysis and T. Stiernagle, A. Fire, Y. Kohara and A. Coulson for reagents. This work was supported by grants from the Michael Smith Foundation (O.E.B. and M.R.L.), Canadian Institutes of Health Research and Heart and Stroke Foundation of B.C. & Yukon (M.R.L.) and the National Institutes of Health (J.M.S.).

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Correspondence to Jonathan M. Scholey.

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Supplementary information

Supplementary Figure S1

DYF-1 homologs are present in various ciliated organisms but not in non-ciliated ones. (PDF 117 kb)

Supplementary Figure S2

Dissociation of IFT-motors and IFT subcomplex A and B components in bbs-7 and bbs-8 mutants. (PDF 797 kb)

Supplementary Video S1

Transport of DYF-1 and BBS proteins (DYF-1::GFP) along sensory cilia of wild-type. The display rate is 10 frames per second with total elapsed time of 60s. (MOV 3350 kb)

Supplementary Video S2

Transport of DYF-1 and BBS proteins (BBS-7::GFP) along sensory cilia of wild-type. The display rate is 10 frames per second with total elapsed time of 60s. (MOV 3167 kb)

Supplementary Video S3

Transport of DYF-1 and BBS proteins (BBS-8::GFP) along sensory cilia of wild-type. The display rate is 10 frames per second with total elapsed time of 60s. (MOV 4217 kb)

Supplementary Videos S4

Motility of IFT motors Kinesin-II (KAP-1::GFP) along sensory cilia in bbs-7(n1606) mutant. The display rate is 10 frames per second with total elapsed time of 60s. (MOV 2784 kb)

Supplementary Videos S5

Motility of IFT motors OSM-3-kinesin (OSM-3::GFP) along sensory cilia in bbs-7(n1606) mutant. The display rate is 10 frames per second with total elapsed time of 60s. (MOV 2214 kb)

Supplementary Video S6

Transport of IFT-particle A subcomplex (CHE-11::GFP) along sensory cilia of WT. The display rate is 10 frames per second with total elapsed time of 60s. (MOV 4303 kb)

Supplementary Video S7

Transport of IFT-particle A subcomplex (CHE-11::GFP) along sensory cilia of bbs-7(n1606) mutant. The display rate is 10 frames per second with total elapsed time of 60s. (MOV 3037 kb)

Supplementary Video S8

Transport of IFT-particle B subcomplex (CHE-2::GFP) along sensory cilia of WT. The display rate is 10 frames per second with total elapsed time of 60s. (MOV 4021 kb)

Supplementary Video S9

Transport of IFT-particle B subcomplex (CHE-2::GFP) along sensory cilia of bbs-7(n1606) mutant. The display rate is 10 frames per second with total elapsed time of 60s. (MOV 3451 kb)

Supplementary Video S10

Motility of IFT-particle (OSM-6::GFP) along sensory cilia in dyf-1(mn335) mutant. The display rate is 10 frames per second with total elapsed time of 60s. (MOV 3694 kb)

Supplementary Video S11

Motility of IFT motors Kinesin-II (KAP-1::GFP) along sensory cilia in dyf-1(mn335) mutant. The display rate is 10 frames per second with total elapsed time of 60s. (MOV 3237 kb)

Supplementary Video S12

Motility of OSM-3-kinesin (OSM-3::GFP) along sensory cilia in dyf-1(mn335) mutant. The display rate is 10 frames per second with total elapsed time of 60s. (MOV 2857 kb)

Supplementary Video S13

Transport of DYF-1::GFP along sensory cilia of osm-3(p802) mutant. The display rate is 10 frames per second with total elapsed time of 60s. (MOV 3289 kb)

Supplementary Video S14

Transport of DYF-1::GFP along sensory cilia of klp-11(tm324) mutant. The display rate is 10 frames per second with total elapsed time of 60s. (MOV 4013 kb)

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Ou, G., E. Blacque, O., Snow, J. et al. Functional coordination of intraflagellar transport motors. Nature 436, 583–587 (2005) doi:10.1038/nature03818

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