Abstract
The construction of cilia and flagella depends on intraflagellar transport (IFT), the bidirectional movement of two protein complexes (IFT-A and IFT-B) driven by specific kinesin and dynein motors. IFT-B and kinesin are associated to anterograde transport whereas IFT-A and dynein participate to retrograde transport. Surprisingly, the small GTPase IFT27, a member of the IFT-B complex, turns out to be essential for retrograde cargo transport in Trypanosoma brucei. We reveal that this is due to failure to import both the IFT-A complex and the IFT dynein into the flagellar compartment. To get further molecular insight about the role of IFT27, GDP- or GTP-locked versions were expressed in presence or absence of endogenous IFT27. The GDP-locked version is unable to enter the flagellum and to interact with other IFT-B proteins and its sole expression prevents flagellum formation. These findings demonstrate that a GTPase-competent IFT27 is required for association to the IFT complex and that IFT27 plays a role in the cargo loading of the retrograde transport machinery.DOI: http://dx.doi.org/10.7554/eLife.02419.001.
Highlights
Cilia and flagella are microtubule-based organelles surrounded by a specialized plasma membrane
BLAST analyses show that IFT27 shares significant homology (E value = 2e−27) with the Rab-like 4 (RABL4) GTPase found in Homo sapiens and vertebrates
Several small GTPases have been associated with the flagellum: ARL-13b is involved in the stabilization of ciliary assembly in C. elegans and its mutations are associated with a ciliopathy named Joubert syndrome (Cantagrel et al, 2008; Cevik et al, 2010; Li et al, 2010)
Summary
Cilia and flagella (interchangeable terms) are microtubule-based organelles surrounded by a specialized plasma membrane. These organelles are found protruding at the surface of a wide range of eukaryotic cells where they exert several roles including cellular motility, sensory reception and developmental signaling (Fliegauf et al, 2007; Drummond, 2012). During IFT, large protein complexes called IFT trains are moved from the base to the tip of the flagellum by kinesin-2 (anterograde IFT) (Kozminski et al, 1995) and back towards the base by cytoplasmic dynein-1b/2 (retrograde IFT) (Pazour et al, 1998). Inactivation of IFT-B proteins or of the kinesin motor results in the failure to construct the flagellum whereas IFT-A proteins and the IFT dynein contribute to retrograde transport. Little is known about how the two processes are interconnected, as the interaction between the IFT complexes and their molecular motors is still poorly understood
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