Transport within cilia is mediated by the multiprotein complexes IFT-A and IFT-B, which carry proteins towards the ciliary tip and back to the cell body in a motor-protein-dependent manner. Recent research has suggested that IFT-A and IFT-B have distinct roles in cilial transport, although these roles have been unclear. On page 428, Che-Chia Tsao and Martin Gorovsky investigate the function of IFT-A by knocking out IFT122A, a conserved component of the complex, in the ciliate protozoan Tetrahymena. The authors show that cilia are still able to form in Tetrahymena that lack IFT122A, although these cells swim more slowly than wild-type cells. By contrast, other research has shown that knocking out an IFT-B component leads to the formation of short cilia, or none at all. Notably, cells without IFT122A accumulate other IFT proteins (Ift88p and Ift172p) at the tips of cilia. The authors propose, therefore, that IFT-A plays a role in transport towards the cell body (retrograde transport). These results shed light on the mechanics of protein transport in cilia and flagella.
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