Intraflagellar transport is required for the maintenance of the trypanosome flagellum composition but not its length

Intraflagellar transport (IFT) is required for construction of most cilia and flagella. Here, we used electron microscopy, immunofluorescence and live video microscopy to show that IFT is absent or arrested in the mature flagellum of Trypanosoma brucei upon RNA interference (RNAi)-mediated knockdown of IFT88 and IFT140, respectively. Flagella assembled prior to RNAi did not shorten, showing that IFT is not essential for the maintenance of flagella length. Although the ultrastructure of the axoneme was not visibly affected, flagellar beating was strongly reduced and the distribution of several flagellar components was drastically modified. The R subunit of the protein kinase A was no longer concentrated in the flagellum but was largely found in the cell body whereas the kinesin 9B motor was accumulating at the distal tip of the flagellum. In contrast, the distal tip protein FLAM8 was dispersed along the flagellum. This reveals that IFT also functions in maintaining the distribution of some flagellar proteins after construction of the organelle is completed.